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• How to communicate between Client and Server in a Client-Server Application?

  - by Sanoj

  I would like to implement an Client-Server Application, where the business-logic, security validations and a database are at the server and the user interface are at the client. I would like to implement clients in different languages i.e. one in WPF/.NET, one Swing/Java , one in Android/Java and maybe one HTML/JavaScript client. The server will be on Internet, so I would like to be able to have encrypted communication. The client will send some lists of items to be added to the database, or update items, and do some transactions. The server will check if the items are already updated by another client, or update the item, add new items or delete items. How do I solve the communication between clients and the server in such a system? I have been thinking about: http/https webserver, and sending messages in JSON or XML and use Web Sockets for bi-directional communication. Use http in a RESTful way, except when WebSockets are needed. But I guess there are better solutions for native desktop applications than http? CORBA - I have just heard about it, and it's old and complex. Not much talk about it these days. XMPP/Jabber - I have just heard about it and I don't know if it fits me at all. EJabberd seams to be a popular implementation. AMQP - I have just heard about it and I don't know if it fits me at all. RabbitMQ seams to be a popular implementation. Windows Communication Foundation, Java RMI, Java Message Service - but are they language independent? I guess some of these alternatives are on different levels, maybe I can have i.e xmpp or amqp in web sockets over https? What technologys are used for this problem in companies today? and what is recommended to use? I have no experience of them other than webservers and http. Please give me some guidance in this jungle. What are the pros and cons of these technologies in my situation?

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• The best way to separate admin functionality from a public site?

  - by AndrewO

  I'm working on a site that's grown both in terms of user-base and functionality to the point where it's becoming evident that some of the admin tasks should be separate from the public website. I was wondering what the best way to do this would be. For example, the site has a large social component to it, and a public sales interface. But at the same time, there's back office tasks, bulk upload processing, dashboards (with long running queries), and customer relations tools in the admin section that I would like to not be effected by spikes in public traffic (or effect the public-facing response time). The site is running on a fairly standard Rails/MySQL/Linux stack, but I think this is more of an architecture problem than an implementation one: mainly, how does one keep the data and business logic in sync between these different applications? Some strategies that I'm evaluating: 1) Create a slave database of the public facing database on another machine. Extract out all of the model and library code so that it can be shared between the applications. Create new controllers and views for the admin interfaces. I have limited experience with replication and am not even sure that it's supposed to be used this way (most of the time I've seen it, it's been for scaling out the read capabilities of the same application, rather than having multiple different ones). I'm also worried about the potential for latency issues if the slave is not on the same network. 2) Create new more task/department-specific applications and use a message oriented middleware to integrate them. I read Enterprise Integration Patterns awhile back and they seemed to advocate this for distributed systems. (Alternatively, in some cases the basic Rails-style RESTful API functionality might suffice.) But, I have nightmares about data synchronization issues and the massive re-architecting that this would entail. 3) Some mixture of the two. For example, the only public information necessary for some of the back office tasks is a read-only completion time or status. Would it make sense to have that on a completely separate system and send the data to public? Meanwhile, the user/group admin functionality would be run on a separate system sharing the database? The downside is, this seems to keep many of the concerns I have with the first two, especially the re-architecting. I'm sure the answers are going to be highly dependent on a site's specific needs, but I'd love to hear success (or failure) stories.

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• Objective-c design advice for use of different data sources, swapping between test and live

  - by user200341

  I'm in the process of designing an application that is part of a larger piece of work, depending on other people to build an API that the app can make use of to retrieve data. While I was thinking about how to setup this project and design the architecture around it, something occurred to me, and I'm sure many people have been in similar situations. Since my work is depending on other people to complete their tasks, and a test server, this slows work down at my end. So the question is: What's the best practice for creating test repositories and classes, implementing them, and not having to depend on altering several places in the code to swap between the test classes and the actual repositories / proper api calls. Contemplate the following scenario: GetDataFromApiCommand *getDataCommand = [[GetDataFromApiCommand alloc]init]; getDataCommand.delegate = self; [getDataCommand getData]; Once the data is available via the API, "GetDataFromApiCommand" could use the actual API, but until then a set of mock data could be returned upon the call of [getDataCommand getData] There might be multiple instances of this, in various places in the code, so replacing all of them wherever they are, is a slow and painful process which inevitably leads to one or two being overlooked. In strongly typed languages we could use dependency injection and just alter one place. In objective-c a factory pattern could be implemented, but is that the best route to go for this? GetDataFromApiCommand *getDataCommand = [GetDataFromApiCommandFactory buildGetDataFromApiCommand]; getDataCommand.delegate = self; [getDataCommand getData]; What is the best practices to achieve this result? Since this would be most useful, even if you have the actual API available, to run tests, or work off-line, the ApiCommands would not necessarily have to be replaced permanently, but the option to select "Do I want to use TestApiCommand or ApiCommand". It is more interesting to have the option to switch between: All commands are test and All command use the live API, rather than selecting them one by one, however that would also be useful to do for testing one or two actual API commands, mixing them with test data. EDIT The way I have chosen to go with this is to use the factory pattern. I set up the factory as follows: @implementation ApiCommandFactory + (ApiCommand *)newApiCommand { // return [[ApiCommand alloc]init]; return [[ApiCommandMock alloc]init]; } @end And anywhere I want to use the ApiCommand class: GetDataFromApiCommand *getDataCommand = [ApiCommandFactory newApiCommand]; When the actual API call is required, the comments can be removed and the mock can be commented out. Using new in the message name implies that who ever uses the factory to get an object, is responsible for releasing it (since we want to avoid autorelease on the iPhone). If additional parameters are required, the factory needs to take these into consideration i.e: [ApiCommandFactory newSecondApiCommand:@"param1"]; This will work quite well with repositories as well.

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• json returned from a jsonresult in asp.net mvc .....

  - by Pandiya Chendur

  I am returning this from a json result from a controller, var genericResult = new { redirectUrl = Url.Action("Create", "Registration") , isRedirect = true }; return Json(genericResult); but when i inspect through firebug, {"redirectUrl":"/","isRedirect":true} if (data.isRedirect) { window.location.href = json.redirectUrl; } Any suggestion.... How to redirect?

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• How to read modelstate errors when returned by Json?

  - by user281180

  How can I display modelstate errors returned by Json ? I want to do somthing like that... if (!ValidateLogOn(Name, currentPassword)) { ModelState.AddModelError("_FORM", "Username or password is incorrect."); //Return a json object to the javascript return Json(new { ModelState }); } What must be my code in the view to read the modelstate errors and display them? My actual code in the view is as follows to read the Json values: function createCategoryComplete(e) { var obj = e.get_object(); alert(obj.Values); }

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• Pass object from JSON into MVC Controller - its always null ?

  - by SteveCl

  Hi I have seen a few questions on here related to the a similar issue, I have read them, followed them, but still i have the same problem. I am basically creating an object in javascript and trying to call a method on the controller that will return a string of html. Not JSON. I've been playing around with dataType and contentType but still no joy. So apologies if the code snippets are a bit messy. Build the object in JS. function GetCardModel() { var card = {}; card.CardTitle = $("#CardTitle").val(); card.TopicTitle = $("#TopicTitle").val(); card.TopicBody = $("#TopicBody").data("tEditor").value(); card.CardClose = $("#CardClose").val(); card.CardFromName = $("#CardFromName").val(); return card; } Take a look at the object - all looks good and as it should in JSON. var model = GetCardModel(); alert(JSON.stringify(GetCardModel())); Make the call... $.ajax({ type: "POST", url: "/Postcard/Create/Preview/", dataType: "json", //contentType: "application/json", date: GetCardModel(), processData: true, success: function (data) { alert("im back"); alert(data); }, error: function (xhr, ajaxOptions, error) { alert(xhr.status); alert("Error: " + xhr.responseText); //alert(error); } }); Always when I step into the controller, the object is ALWAYS there, but with null values for all the properties.

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• How to read modelstate errors when returned by Json?

  - by learning

  How can I display modelstate errors returned by Json ? I want to do somthing like that... if (!ValidateLogOn(Name, currentPassword)) { ModelState.AddModelError("_FORM", "Username or password is incorrect."); //Return a json object to the javascript return Json(new { ModelState }); } What must be my code in the view to read the modelstate errors and display them? My actual code in the view is as follows to read the Json values: function createCategoryComplete(e) { var obj = e.get_object(); alert(obj.Values); }

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• jquery.ajax returns content-type "html" on iis while it returns content-type "json" on local host

  - by Sridhar

  Hi, I am using jQuery.ajax function to make an ajax call to a page method in asp.net. I specifically set the content-type to "application/json; charset=utf-8". When I looked at the response in the firebug it says the content-type is html. Following is the code to my ajax call $.ajax({ async: asyncVal, type: "POST", url: url + '/' + webMethod, data: dataPackage, contentType: "application/json; charset=UTF-8", dataType: "json", error: errorFunction, success: successFunction });

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• nginx: handling 404 with error_page

  - by ytw

  Originally, I have something like this in the nginx.conf file. location ^~ /test_api { types { application/json json; } root /usr/local/www/data; rewrite "/test_api/(.*)" /api_response/test_api_$1.json break; error_page 404 /api_response/unknown_request.json; } When a requested resource is not found locally, unknown_request.json (default response) is returned correctly. Then I had to change the rewrite to point to a remote server as follows: rewrite "/test_api/(.*)" $scheme://www.somedomain.com/test_api_$1 break; It doesn't return unknown_request.json (default response) anymore even though the remote server returns a 404. Is there a way to continue to return unknown_request.json to the client when the remote server returns a 404 assuming the remote server can't be changed to return unknown_request.json? Thanks very much.

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• Juju Openstack bundle: Can't launch an instance

  - by user281985

  Deployed bundle:~makyo/openstack/2/openstack, on top of 7 physical boxes and 3 virtual ones. After changing vip_iface strings to point to right devices, e.g., br0 instead of eth0, and defining "/mnt/loopback|30G", in Cinder's block-device string, am able to navigate through openstack dashboard, error free. Following http://docs.openstack.org/grizzly/openstack-compute/install/apt/content/running-an-instance.html instructions, attempted to launch cirros 0.3.1 image; however, novalist shows the instance in error state. ubuntu@node7:~$ nova --debug boot --flavor 1 --image 28bed1bc-bc1c-4533-beee-8e0428ad40dd --key_name key2 --security_group default cirros REQ: curl -i http://keyStone.IP:5000/v2.0/tokens -X POST -H "Content-Type: application/json" -H "Accept: application/json" -H "User-Agent: python-novaclient" -d '{"auth": {"tenantName": "admin", "passwordCredentials": {"username": "admin", "password": "openstack"}}}' INFO (connectionpool:191) Starting new HTTP connection (1): keyStone.IP DEBUG (connectionpool:283) "POST /v2.0/tokens HTTP/1.1" 200 None RESP: [200] {'date': 'Tue, 10 Jun 2014 00:01:02 GMT', 'transfer-encoding': 'chunked', 'vary': 'X-Auth-Token', 'content-type': 'application/json'} RESP BODY: {"access": {"token": {"expires": "2014-06-11T00:01:02Z", "id": "3eefa1837d984426a633fe09259a1534", "tenant": {"description": "Created by Juju", "enabled": true, "id": "08cff06d13b74492b780d9ceed699239", "name": "admin"}}, "serviceCatalog": [{"endpoints": [{"adminURL": "http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239", "region": "RegionOne", "internalURL": "http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239", "publicURL": "http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239"}], "endpoints_links": [], "type": "compute", "name": "nova"}, {"endpoints": [{"adminURL": "http://nova.cloud.controller:9696", "region": "RegionOne", "internalURL": "http://nova.cloud.controller:9696", "publicURL": "http://nova.cloud.controller:9696"}], "endpoints_links": [], "type": "network", "name": "quantum"}, {"endpoints": [{"adminURL": "http://nova.cloud.controller:3333", "region": "RegionOne", "internalURL": "http://nova.cloud.controller:3333", "publicURL": "http://nova.cloud.controller:3333"}], "endpoints_links": [], "type": "s3", "name": "s3"}, {"endpoints": [{"adminURL": "http://i.p.s.36:9292", "region": "RegionOne", "internalURL": "http://i.p.s.36:9292", "publicURL": "http://i.p.s.36:9292"}], "endpoints_links": [], "type": "image", "name": "glance"}, {"endpoints": [{"adminURL": "http://i.p.s.39:8776/v1/08cff06d13b74492b780d9ceed699239", "region": "RegionOne", "internalURL": "http://i.p.s.39:8776/v1/08cff06d13b74492b780d9ceed699239", "publicURL": "http://i.p.s.39:8776/v1/08cff06d13b74492b780d9ceed699239"}], "endpoints_links": [], "type": "volume", "name": "cinder"}, {"endpoints": [{"adminURL": "http://nova.cloud.controller:8773/services/Cloud", "region": "RegionOne", "internalURL": "http://nova.cloud.controller:8773/services/Cloud", "publicURL": "http://nova.cloud.controller:8773/services/Cloud"}], "endpoints_links": [], "type": "ec2", "name": "ec2"}, {"endpoints": [{"adminURL": "http://keyStone.IP:35357/v2.0", "region": "RegionOne", "internalURL": "http://keyStone.IP:5000/v2.0", "publicURL": "http://i.p.s.44:5000/v2.0"}], "endpoints_links": [], "type": "identity", "name": "keystone"}], "user": {"username": "admin", "roles_links": [], "id": "b3730a52a32e40f0a9500440d1ef1c7d", "roles": [{"id": "e020001eb9a049f4a16540238ab158aa", "name": "Admin"}, {"id": "b84fbff4d5554d53bbbffdaad66b56cb", "name": "KeystoneServiceAdmin"}, {"id": "129c8b49d42b4f0796109aaef2069aa9", "name": "KeystoneAdmin"}], "name": "admin"}}} REQ: curl -i http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd -X GET -H "X-Auth-Project-Id: admin" -H "User-Agent: python-novaclient" -H "Accept: application/json" -H "X-Auth-Token: 3eefa1837d984426a633fe09259a1534" INFO (connectionpool:191) Starting new HTTP connection (1): nova.cloud.controller DEBUG (connectionpool:283) "GET /v1.1/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd HTTP/1.1" 200 719 RESP: [200] {'date': 'Tue, 10 Jun 2014 00:01:03 GMT', 'x-compute-request-id': 'req-7f3459f8-d3d5-47f1-97a3-8407a4419a69', 'content-type': 'application/json', 'content-length': '719'} RESP BODY: {"image": {"status": "ACTIVE", "updated": "2014-06-09T22:17:54Z", "links": [{"href": "http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd", "rel": "self"}, {"href": "http://nova.cloud.controller:8774/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd", "rel": "bookmark"}, {"href": "http://External.Public.Port:9292/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd", "type": "application/vnd.openstack.image", "rel": "alternate"}], "id": "28bed1bc-bc1c-4533-beee-8e0428ad40dd", "OS-EXT-IMG-SIZE:size": 13147648, "name": "Cirros 0.3.1", "created": "2014-06-09T22:17:54Z", "minDisk": 0, "progress": 100, "minRam": 0, "metadata": {}}} REQ: curl -i http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/flavors/1 -X GET -H "X-Auth-Project-Id: admin" -H "User-Agent: python-novaclient" -H "Accept: application/json" -H "X-Auth-Token: 3eefa1837d984426a633fe09259a1534" INFO (connectionpool:191) Starting new HTTP connection (1): nova.cloud.controller DEBUG (connectionpool:283) "GET /v1.1/08cff06d13b74492b780d9ceed699239/flavors/1 HTTP/1.1" 200 418 RESP: [200] {'date': 'Tue, 10 Jun 2014 00:01:04 GMT', 'x-compute-request-id': 'req-2c153110-6969-4f3a-b51c-8f1a6ce75bee', 'content-type': 'application/json', 'content-length': '418'} RESP BODY: {"flavor": {"name": "m1.tiny", "links": [{"href": "http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/flavors/1", "rel": "self"}, {"href": "http://nova.cloud.controller:8774/08cff06d13b74492b780d9ceed699239/flavors/1", "rel": "bookmark"}], "ram": 512, "OS-FLV-DISABLED:disabled": false, "vcpus": 1, "swap": "", "os-flavor-access:is_public": true, "rxtx_factor": 1.0, "OS-FLV-EXT-DATA:ephemeral": 0, "disk": 0, "id": "1"}} REQ: curl -i http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/servers -X POST -H "X-Auth-Project-Id: admin" -H "User-Agent: python-novaclient" -H "Content-Type: application/json" -H "Accept: application/json" -H "X-Auth-Token: 3eefa1837d984426a633fe09259a1534" -d '{"server": {"name": "cirros", "imageRef": "28bed1bc-bc1c-4533-beee-8e0428ad40dd", "key_name": "key2", "flavorRef": "1", "max_count": 1, "min_count": 1, "security_groups": [{"name": "default"}]}}' INFO (connectionpool:191) Starting new HTTP connection (1): nova.cloud.controller DEBUG (connectionpool:283) "POST /v1.1/08cff06d13b74492b780d9ceed699239/servers HTTP/1.1" 202 436 RESP: [202] {'date': 'Tue, 10 Jun 2014 00:01:05 GMT', 'x-compute-request-id': 'req-41e53086-6454-4efb-bb35-a30dc2c780be', 'content-type': 'application/json', 'location': 'http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/servers/2eb5e3ad-3044-41c1-bbb7-10f398f83e43', 'content-length': '436'} RESP BODY: {"server": {"security_groups": [{"name": "default"}], "OS-DCF:diskConfig": "MANUAL", "id": "2eb5e3ad-3044-41c1-bbb7-10f398f83e43", "links": [{"href": "http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/servers/2eb5e3ad-3044-41c1-bbb7-10f398f83e43", "rel": "self"}, {"href": "http://nova.cloud.controller:8774/08cff06d13b74492b780d9ceed699239/servers/2eb5e3ad-3044-41c1-bbb7-10f398f83e43", "rel": "bookmark"}], "adminPass": "oFRbvRqif2C8"}} REQ: curl -i http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/servers/2eb5e3ad-3044-41c1-bbb7-10f398f83e43 -X GET -H "X-Auth-Project-Id: admin" -H "User-Agent: python-novaclient" -H "Accept: application/json" -H "X-Auth-Token: 3eefa1837d984426a633fe09259a1534" INFO (connectionpool:191) Starting new HTTP connection (1): nova.cloud.controller DEBUG (connectionpool:283) "GET /v1.1/08cff06d13b74492b780d9ceed699239/servers/2eb5e3ad-3044-41c1-bbb7-10f398f83e43 HTTP/1.1" 200 1349 RESP: [200] {'date': 'Tue, 10 Jun 2014 00:01:05 GMT', 'x-compute-request-id': 'req-d91d0858-7030-469d-8e55-40e05e4d00fd', 'content-type': 'application/json', 'content-length': '1349'} RESP BODY: {"server": {"status": "BUILD", "updated": "2014-06-10T00:01:05Z", "hostId": "", "OS-EXT-SRV-ATTR:host": null, "addresses": {}, "links": [{"href": "http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/servers/2eb5e3ad-3044-41c1-bbb7-10f398f83e43", "rel": "self"}, {"href": "http://nova.cloud.controller:8774/08cff06d13b74492b780d9ceed699239/servers/2eb5e3ad-3044-41c1-bbb7-10f398f83e43", "rel": "bookmark"}], "key_name": "key2", "image": {"id": "28bed1bc-bc1c-4533-beee-8e0428ad40dd", "links": [{"href": "http://nova.cloud.controller:8774/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd", "rel": "bookmark"}]}, "OS-EXT-STS:task_state": "scheduling", "OS-EXT-STS:vm_state": "building", "OS-EXT-SRV-ATTR:instance_name": "instance-00000004", "OS-EXT-SRV-ATTR:hypervisor_hostname": null, "flavor": {"id": "1", "links": [{"href": "http://nova.cloud.controller:8774/08cff06d13b74492b780d9ceed699239/flavors/1", "rel": "bookmark"}]}, "id": "2eb5e3ad-3044-41c1-bbb7-10f398f83e43", "security_groups": [{"name": "default"}], "OS-EXT-AZ:availability_zone": "nova", "user_id": "b3730a52a32e40f0a9500440d1ef1c7d", "name": "cirros", "created": "2014-06-10T00:01:04Z", "tenant_id": "08cff06d13b74492b780d9ceed699239", "OS-DCF:diskConfig": "MANUAL", "accessIPv4": "", "accessIPv6": "", "progress": 0, "OS-EXT-STS:power_state": 0, "config_drive": "", "metadata": {}}} REQ: curl -i http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/flavors/1 -X GET -H "X-Auth-Project-Id: admin" -H "User-Agent: python-novaclient" -H "Accept: application/json" -H "X-Auth-Token: 3eefa1837d984426a633fe09259a1534" INFO (connectionpool:191) Starting new HTTP connection (1): nova.cloud.controller DEBUG (connectionpool:283) "GET /v1.1/08cff06d13b74492b780d9ceed699239/flavors/1 HTTP/1.1" 200 418 RESP: [200] {'date': 'Tue, 10 Jun 2014 00:01:05 GMT', 'x-compute-request-id': 'req-896c0120-1102-4408-9e09-cd628f2dd699', 'content-type': 'application/json', 'content-length': '418'} RESP BODY: {"flavor": {"name": "m1.tiny", "links": [{"href": "http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/flavors/1", "rel": "self"}, {"href": "http://nova.cloud.controller:8774/08cff06d13b74492b780d9ceed699239/flavors/1", "rel": "bookmark"}], "ram": 512, "OS-FLV-DISABLED:disabled": false, "vcpus": 1, "swap": "", "os-flavor-access:is_public": true, "rxtx_factor": 1.0, "OS-FLV-EXT-DATA:ephemeral": 0, "disk": 0, "id": "1"}} REQ: curl -i http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd -X GET -H "X-Auth-Project-Id: admin" -H "User-Agent: python-novaclient" -H "Accept: application/json" -H "X-Auth-Token: 3eefa1837d984426a633fe09259a1534" INFO (connectionpool:191) Starting new HTTP connection (1): nova.cloud.controller DEBUG (connectionpool:283) "GET /v1.1/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd HTTP/1.1" 200 719 RESP: [200] {'date': 'Tue, 10 Jun 2014 00:01:05 GMT', 'x-compute-request-id': 'req-454e9651-c247-4d31-8049-6b254de050ae', 'content-type': 'application/json', 'content-length': '719'} RESP BODY: {"image": {"status": "ACTIVE", "updated": "2014-06-09T22:17:54Z", "links": [{"href": "http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd", "rel": "self"}, {"href": "http://nova.cloud.controller:8774/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd", "rel": "bookmark"}, {"href": "http://External.Public.Port:9292/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd", "type": "application/vnd.openstack.image", "rel": "alternate"}], "id": "28bed1bc-bc1c-4533-beee-8e0428ad40dd", "OS-EXT-IMG-SIZE:size": 13147648, "name": "Cirros 0.3.1", "created": "2014-06-09T22:17:54Z", "minDisk": 0, "progress": 100, "minRam": 0, "metadata": {}}} +-------------------------------------+--------------------------------------+ | Property | Value | +-------------------------------------+--------------------------------------+ | OS-EXT-STS:task_state | scheduling | | image | Cirros 0.3.1 | | OS-EXT-STS:vm_state | building | | OS-EXT-SRV-ATTR:instance_name | instance-00000004 | | flavor | m1.tiny | | id | 2eb5e3ad-3044-41c1-bbb7-10f398f83e43 | | security_groups | [{u'name': u'default'}] | | user_id | b3730a52a32e40f0a9500440d1ef1c7d | | OS-DCF:diskConfig | MANUAL | | accessIPv4 | | | accessIPv6 | | | progress | 0 | | OS-EXT-STS:power_state | 0 | | OS-EXT-AZ:availability_zone | nova | | config_drive | | | status | BUILD | | updated | 2014-06-10T00:01:05Z | | hostId | | | OS-EXT-SRV-ATTR:host | None | | key_name | key2 | | OS-EXT-SRV-ATTR:hypervisor_hostname | None | | name | cirros | | adminPass | oFRbvRqif2C8 | | tenant_id | 08cff06d13b74492b780d9ceed699239 | | created | 2014-06-10T00:01:04Z | | metadata | {} | +-------------------------------------+--------------------------------------+ ubuntu@node7:~$ ubuntu@node7:~$ nova list +--------------------------------------+--------+--------+----------+ | ID | Name | Status | Networks | +--------------------------------------+--------+--------+----------+ | 2eb5e3ad-3044-41c1-bbb7-10f398f83e43 | cirros | ERROR | | +--------------------------------------+--------+--------+----------+ ubuntu@node7:~$ var/log/nova/nova-compute.log shows the following error: ... 2014-06-10 00:01:06.048 AUDIT nova.compute.claims [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Attempting claim: memory 512 MB, disk 0 GB, VCPUs 1 2014-06-10 00:01:06.049 AUDIT nova.compute.claims [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Total Memory: 3885 MB, used: 512 MB 2014-06-10 00:01:06.049 AUDIT nova.compute.claims [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Memory limit: 5827 MB, free: 5315 MB 2014-06-10 00:01:06.049 AUDIT nova.compute.claims [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Total Disk: 146 GB, used: 0 GB 2014-06-10 00:01:06.050 AUDIT nova.compute.claims [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Disk limit not specified, defaulting to unlimited 2014-06-10 00:01:06.050 AUDIT nova.compute.claims [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Total CPU: 2 VCPUs, used: 0 VCPUs 2014-06-10 00:01:06.050 AUDIT nova.compute.claims [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] CPU limit not specified, defaulting to unlimited 2014-06-10 00:01:06.051 AUDIT nova.compute.claims [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Claim successful 2014-06-10 00:01:06.963 WARNING nova.network.quantumv2.api [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] No network configured! 2014-06-10 00:01:08.347 ERROR nova.compute.manager [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Instance failed to spawn 2014-06-10 00:01:08.347 32223 TRACE nova.compute.manager [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Traceback (most recent call last): 2014-06-10 00:01:08.347 32223 TRACE nova.compute.manager [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 1118, in _spawn 2014-06-10 00:01:08.347 32223 TRACE nova.compute.manager [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] self._legacy_nw_info(network_info), 2014-06-10 00:01:08.347 32223 TRACE nova.compute.manager [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 703, in _legacy_nw_info 2014-06-10 00:01:08.347 32223 TRACE nova.compute.manager [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] network_info = network_info.legacy() 2014-06-10 00:01:08.347 32223 TRACE nova.compute.manager [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] AttributeError: 'list' object has no attribute 'legacy' 2014-06-10 00:01:08.347 32223 TRACE nova.compute.manager [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] 2014-06-10 00:01:08.919 AUDIT nova.compute.manager [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Terminating instance 2014-06-10 00:01:09.712 32223 ERROR nova.virt.libvirt.driver [-] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] During wait destroy, instance disappeared. 2014-06-10 00:01:09.718 INFO nova.virt.libvirt.firewall [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Attempted to unfilter instance which is not filtered 2014-06-10 00:01:09.719 INFO nova.virt.libvirt.driver [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Deleting instance files /var/lib/nova/instances/2eb5e3ad-3044-41c1-bbb7-10f398f83e43 2014-06-10 00:01:10.044 ERROR nova.compute.manager [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Error: ['Traceback (most recent call last):\n', ' File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 864, in _run_instance\n set_access_ip=set_access_ip)\n', ' File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 1123, in _spawn\n LOG.exception(_(\'Instance failed to spawn\'), instance=instance)\n', ' File "/usr/lib/python2.7/contextlib.py", line 24, in __exit__\n self.gen.next()\n', ' File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 1118, in _spawn\n self._legacy_nw_info(network_info),\n', ' File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 703, in _legacy_nw_info\n network_info = network_info.legacy()\n', "AttributeError: 'list' object has no attribute 'legacy'\n"] 2014-06-10 00:01:40.951 32223 AUDIT nova.compute.resource_tracker [-] Auditing locally available compute resources 2014-06-10 00:01:41.072 32223 AUDIT nova.compute.resource_tracker [-] Free ram (MB): 2861 2014-06-10 00:01:41.072 32223 AUDIT nova.compute.resource_tracker [-] Free disk (GB): 146 2014-06-10 00:01:41.073 32223 AUDIT nova.compute.resource_tracker [-] Free VCPUS: 1 2014-06-10 00:01:41.262 32223 INFO nova.compute.resource_tracker [-] Compute_service record updated for node5:node5.maas ... Can't seem to find any entries in quantum.conf related to "legacy". Any help would be appreciated. Cheers,

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• Design for Vacation Tracking System

  - by Aaronaught

  I have been tasked with developing a system for tracking our company's paid time-off (vacation, sick days, etc.) At the moment we are using an Excel spreadsheet on a shared network drive, and it works pretty well, but we are concerned that we won't be able to "trust" employees forever and sometimes we run into locking issues when two people try to open the spreadsheet at once. So we are trying to build something a little more robust. I would like some input on this design in terms of maintainability, scalability, extensibility, etc. It's a pretty simple workflow we need to represent right now: I started with a basic MS Access schema like this: Employees (EmpID int, EmpName varchar(50), AllowedDays int) Vacations (VacationID int, EmpID int, BeginDate datetime, EndDate datetime) But we don't want to spend a lot of time building a schema and database like this and have to change it later, so I think I am going to go with something that will be easier to expand through configuration. Right now the vacation table has this schema: Vacations (VacationID int, PropName varchar(50), PropValue varchar(50)) And the table will be populated with data like this: VacationID | PropName | PropValue -----------+--------------+------------------ 1 | EmpID | 4 1 | EmpName | James Jones 1 | Reason | Vacation 1 | BeginDate | 2/24/2010 1 | EndDate | 2/30/2010 1 | Destination | Spectate Swamp 2 | ... | ... I think this is a pretty good, extensible design, we can easily add new properties to the vacation like the destination or maybe approval status, etc. I wasn't too sure how to go about managing the database of valid properties, I thought of putting them in a separate PropNames table but it gets complicated to manage all the different data types and people say that you shouldn't put CLR type names into a SQL database, so I decided to use XML instead, here is the schema: <VacationProperties> <PropertyNames>EmpID,EmpName,Reason,BeginDate,EndDate,Destination</PropertyNames> <PropertyTypes>System.Int32,System.String,System.String,System.DateTime,System.DateTime,System.String</PropertyTypes> <PropertiesRequired>true,true,false,true,true,false</PropertiesRequired> </VacationProperties> I might need more fields than that, I'm not completely sure. I'm parsing the XML like this (would like some feedback on the parsing code): string xml = File.ReadAllText("properties.xml"); Match m = Regex.Match(xml, "<(PropertyNames)>(.*?)</PropertyNames>"; string[] pn = m.Value.Split(','); // do the same for PropertyTypes, PropertiesRequired Then I use the following code to persist configuration changes to the database: string sql = "DROP TABLE VacationProperties"; sql = sql + " CREATE TABLE VacationProperties "; sql = sql + "(PropertyName varchar(100), PropertyType varchar(100) "; sql = sql + "IsRequired varchar(100))"; for (int i = 0; i < pn.Length; i++) { sql = sql + " INSERT VacationProperties VALUES (" + pn[i] + "," + pt[i] + "," + pv[i] + ")"; } // GlobalConnection is a singleton new SqlCommand(sql, GlobalConnection.Instance).ExecuteReader(); So far so good, but after a few days of this I then realized that a lot of this was just a more specific kind of a generic workflow which could be further abstracted, and instead of writing all of this boilerplate plumbing code I could just come up with a workflow and plug it into a workflow engine like Windows Workflow Foundation and have the users configure it: In order to support routing these configurations throw the workflow system, it seemed natural to implement generic XML Web Services for this instead of just using an XML file as above. I've used this code to implement the Web Services: public class VacationConfigurationService : WebService { [WebMethod] public void UpdateConfiguration(string xml) { // Above code goes here } } Which was pretty easy, although I'm still working on a way to validate that XML against some kind of schema as there's no error-checking yet. I also created a few different services for other operations like VacationSubmissionService, VacationReportService, VacationDataService, VacationAuthenticationService, etc. The whole Service Oriented Architecture looks like this: And because the workflow itself might change, I have been working on a way to integrate the WF workflow system with MS Visio, which everybody at the office already knows how to use so they could make changes pretty easily. We have a diagram that looks like the following (it's kind of hard to read but the main items are Activities, Authenticators, Validators, Transformers, Processors, and Data Connections, they're all analogous to the services in the SOA diagram above). The requirements for this system are: (Note - I don't control these, they were given to me by management) Main workflow must interface with Excel spreadsheet, probably through VBA macros (to ease the transition to the new system) Alerts should integrate with MS Outlook, Lotus Notes, and SMS (text messages). We also want to interface it with the company Voice Mail system but that is not a "hard" requirement. Performance requirements: Must handle 250,000 Transactions Per Second Should be able to handle up to 20,000 employees (right now we have 3) 99.99% uptime ("four nines") expected Must be secure against outside hacking, but users cannot be required to enter a username/password. Platforms: Must support Windows XP/Vista/7, Linux, iPhone, Blackberry, DOS 2.0, VAX, IRIX, PDP-11, Apple IIc. Time to complete: 6 to 8 weeks. My questions are: Is this a good design for the system so far? Am I using all of the recommended best practices for these technologies? How do I integrate the Visio diagram above with the Windows Workflow Foundation to call the ConfigurationService and persist workflow changes? Am I missing any important components? Will this be extensible enough to support any scenario via end-user configuration? Will the system scale to the above performance requirements? Will we need any expensive hardware to run it? Are there any "gotchas" I should know about with respect to cross-platform compatibility? For example would it be difficult to convert this to an iPhone app? How long would you expect this to take? (We've dedicated 1 week for testing so I'm thinking maybe 5 weeks?)

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• Using jQuery to POST Form Data to an ASP.NET ASMX AJAX Web Service

  - by Rick Strahl

  The other day I got a question about how to call an ASP.NET ASMX Web Service or PageMethods with the POST data from a Web Form (or any HTML form for that matter). The idea is that you should be able to call an endpoint URL, send it regular urlencoded POST data and then use Request.Form[] to retrieve the posted data as needed. My first reaction was that you can’t do it, because ASP.NET ASMX AJAX services (as well as Page Methods and WCF REST AJAX Services) require that the content POSTed to the server is posted as JSON and sent with an application/json or application/x-javascript content type. IOW, you can’t directly call an ASP.NET AJAX service with regular urlencoded data. Note that there are other ways to accomplish this. You can use ASP.NET MVC and a custom route, an HTTP Handler or separate ASPX page, or even a WCF REST service that’s configured to use non-JSON inputs. However if you want to use an ASP.NET AJAX service (or Page Methods) with a little bit of setup work it’s actually quite easy to capture all the form variables on the client and ship them up to the server. The basic steps needed to make this happen are: Capture form variables into an array on the client with jQuery’s .serializeArray() function Use $.ajax() or my ServiceProxy class to make an AJAX call to the server to send this array On the server create a custom type that matches the .serializeArray() name/value structure Create extension methods on NameValue[] to easily extract form variables Create a [WebMethod] that accepts this name/value type as an array (NameValue[]) This seems like a lot of work but realize that steps 3 and 4 are a one time setup step that can be reused in your entire site or multiple applications. Let’s look at a short example that looks like this as a base form of fields to ship to the server: The HTML for this form looks something like this: <div id="divMessage" class="errordisplay" style="display: none"> </div> <div> <div class="label">Name:</div> <div><asp:TextBox runat="server" ID="txtName" /></div> </div> <div> <div class="label">Company:</div> <div><asp:TextBox runat="server" ID="txtCompany"/></div> </div> <div> <div class="label" ></div> <div> <asp:DropDownList runat="server" ID="lstAttending"> <asp:ListItem Text="Attending" Value="Attending"/> <asp:ListItem Text="Not Attending" Value="NotAttending" /> <asp:ListItem Text="Maybe Attending" Value="MaybeAttending" /> <asp:ListItem Text="Not Sure Yet" Value="NotSureYet" /> </asp:DropDownList> </div> </div> <div> <div class="label">Special Needs:<br /> <small>(check all that apply)</small></div> <div> <asp:ListBox runat="server" ID="lstSpecialNeeds" SelectionMode="Multiple"> <asp:ListItem Text="Vegitarian" Value="Vegitarian" /> <asp:ListItem Text="Vegan" Value="Vegan" /> <asp:ListItem Text="Kosher" Value="Kosher" /> <asp:ListItem Text="Special Access" Value="SpecialAccess" /> <asp:ListItem Text="No Binder" Value="NoBinder" /> </asp:ListBox> </div> </div> <div> <div class="label"></div> <div> <asp:CheckBox ID="chkAdditionalGuests" Text="Additional Guests" runat="server" /> </div> </div> <hr /> <input type="button" id="btnSubmit" value="Send Registration" /> The form includes a few different kinds of form fields including a multi-selection listbox to demonstrate retrieving multiple values. Setting up the Server Side [WebMethod] The [WebMethod] on the server we’re going to call is going to be very simple and just capture the content of these values and echo then back as a formatted HTML string. Obviously this is overly simplistic but it serves to demonstrate the simple point of capturing the POST data on the server in an AJAX callback. public class PageMethodsService : System.Web.Services.WebService { [WebMethod] public string SendRegistration(NameValue[] formVars) { StringBuilder sb = new StringBuilder(); sb.AppendFormat("Thank you {0}, <br/><br/>", HttpUtility.HtmlEncode(formVars.Form("txtName"))); sb.AppendLine("You've entered the following: <hr/>"); foreach (NameValue nv in formVars) { // strip out ASP.NET form vars like _ViewState/_EventValidation if (!nv.name.StartsWith("__")) { if (nv.name.StartsWith("txt") || nv.name.StartsWith("lst") || nv.name.StartsWith("chk")) sb.Append(nv.name.Substring(3)); else sb.Append(nv.name); sb.AppendLine(": " + HttpUtility.HtmlEncode(nv.value) + "<br/>"); } } sb.AppendLine("<hr/>"); string[] needs = formVars.FormMultiple("lstSpecialNeeds"); if (needs == null) sb.AppendLine("No Special Needs"); else { sb.AppendLine("Special Needs: <br/>"); foreach (string need in needs) { sb.AppendLine("&nbsp;&nbsp;" + need + "<br/>"); } } return sb.ToString(); } } The key feature of this method is that it receives a custom type called NameValue[] which is an array of NameValue objects that map the structure that the jQuery .serializeArray() function generates. There are two custom types involved in this: The actual NameValue type and a NameValueExtensions class that defines a couple of extension methods for the NameValue[] array type to allow for single (.Form()) and multiple (.FormMultiple()) value retrieval by name. The NameValue class is as simple as this and simply maps the structure of the array elements of .serializeArray(): public class NameValue { public string name { get; set; } public string value { get; set; } } The extension method class defines the .Form() and .FormMultiple() methods to allow easy retrieval of form variables from the returned array: /// <summary> /// Simple NameValue class that maps name and value /// properties that can be used with jQuery's /// $.serializeArray() function and JSON requests /// </summary> public static class NameValueExtensionMethods { /// <summary> /// Retrieves a single form variable from the list of /// form variables stored /// </summary> /// <param name="formVars"></param> /// <param name="name">formvar to retrieve</param> /// <returns>value or string.Empty if not found</returns> public static string Form(this NameValue[] formVars, string name) { var matches = formVars.Where(nv => nv.name.ToLower() == name.ToLower()).FirstOrDefault(); if (matches != null) return matches.value; return string.Empty; } /// <summary> /// Retrieves multiple selection form variables from the list of /// form variables stored. /// </summary> /// <param name="formVars"></param> /// <param name="name">The name of the form var to retrieve</param> /// <returns>values as string[] or null if no match is found</returns> public static string[] FormMultiple(this NameValue[] formVars, string name) { var matches = formVars.Where(nv => nv.name.ToLower() == name.ToLower()).Select(nv => nv.value).ToArray(); if (matches.Length == 0) return null; return matches; } } Using these extension methods it’s easy to retrieve individual values from the array: string name = formVars.Form("txtName"); or multiple values: string[] needs = formVars.FormMultiple("lstSpecialNeeds"); if (needs != null) { // do something with matches } Using these functions in the SendRegistration method it’s easy to retrieve a few form variables directly (txtName and the multiple selections of lstSpecialNeeds) or to iterate over the whole list of values. Of course this is an overly simple example – in typical app you’d probably want to validate the input data and save it to the database and then return some sort of confirmation or possibly an updated data list back to the client. Since this is a full AJAX service callback realize that you don’t have to return simple string values – you can return any of the supported result types (which are most serializable types) including complex hierarchical objects and arrays that make sense to your client code. POSTing Form Variables from the Client to the AJAX Service To call the AJAX service method on the client is straight forward and requires only use of little native jQuery plus JSON serialization functionality. To start add jQuery and the json2.js library to your page: <script src="Scripts/jquery.min.js" type="text/javascript"></script> <script src="Scripts/json2.js" type="text/javascript"></script> json2.js can be found here (be sure to remove the first line from the file): http://www.json.org/json2.js It’s required to handle JSON serialization for those browsers that don’t support it natively. With those script references in the document let’s hookup the button click handler and call the service: $(document).ready(function () { $("#btnSubmit").click(sendRegistration); }); function sendRegistration() { var arForm = $("#form1").serializeArray(); $.ajax({ url: "PageMethodsService.asmx/SendRegistration", type: "POST", contentType: "application/json", data: JSON.stringify({ formVars: arForm }), dataType: "json", success: function (result) { var jEl = $("#divMessage"); jEl.html(result.d).fadeIn(1000); setTimeout(function () { jEl.fadeOut(1000) }, 5000); }, error: function (xhr, status) { alert("An error occurred: " + status); } }); } The key feature in this code is the $("#form1").serializeArray();  call which serializes all the form fields of form1 into an array. Each form var is represented as an object with a name/value property. This array is then serialized into JSON with: JSON.stringify({ formVars: arForm }) The format for the parameter list in AJAX service calls is an object with one property for each parameter of the method. In this case its a single parameter called formVars and we’re assigning the array of form variables to it. The URL to call on the server is the name of the Service (or ASPX Page for Page Methods) plus the name of the method to call. On return the success callback receives the result from the AJAX callback which in this case is the formatted string which is simply assigned to an element in the form and displayed. Remember the result type is whatever the method returns – it doesn’t have to be a string. Note that ASP.NET AJAX and WCF REST return JSON data as a wrapped object so the result has a ‘d’ property that holds the actual response: jEl.html(result.d).fadeIn(1000); Slightly simpler: Using ServiceProxy.js If you want things slightly cleaner you can use the ServiceProxy.js class I’ve mentioned here before. The ServiceProxy class handles a few things for calling ASP.NET and WCF services more cleanly: Automatic JSON encoding Automatic fix up of ‘d’ wrapper property Automatic Date conversion on the client Simplified error handling Reusable and abstracted To add the service proxy add: <script src="Scripts/ServiceProxy.js" type="text/javascript"></script> and then change the code to this slightly simpler version: <script type="text/javascript"> proxy = new ServiceProxy("PageMethodsService.asmx/"); $(document).ready(function () { $("#btnSubmit").click(sendRegistration); }); function sendRegistration() { var arForm = $("#form1").serializeArray(); proxy.invoke("SendRegistration", { formVars: arForm }, function (result) { var jEl = $("#divMessage"); jEl.html(result).fadeIn(1000); setTimeout(function () { jEl.fadeOut(1000) }, 5000); }, function (error) { alert(error.message); } ); } The code is not very different but it makes the call as simple as specifying the method to call, the parameters to pass and the actions to take on success and error. No more remembering which content type and data types to use and manually serializing to JSON. This code also removes the “d” property processing in the response and provides more consistent error handling in that the call always returns an error object regardless of a server error or a communication error unlike the native $.ajax() call. Either approach works and both are pretty easy. The ServiceProxy really pays off if you use lots of service calls and especially if you need to deal with date values returned from the server  on the client. Summary Making Web Service calls and getting POST data to the server is not always the best option – ASP.NET and WCF AJAX services are meant to work with data in objects. However, in some situations it’s simply easier to POST all the captured form data to the server instead of mapping all properties from the input fields to some sort of message object first. For this approach the above POST mechanism is useful as it puts the parsing of the data on the server and leaves the client code lean and mean. It’s even easy to build a custom model binder on the server that can map the array values to properties on an object generically with some relatively simple Reflection code and without having to manually map form vars to properties and do string conversions. Keep in mind though that other approaches also abound. ASP.NET MVC makes it pretty easy to create custom routes to data and the built in model binder makes it very easy to deal with inbound form POST data in its original urlencoded format. The West Wind West Wind Web Toolkit also includes functionality for AJAX callbacks using plain POST values. All that’s needed is a Method parameter to query/form value to specify the method to be called on the server. After that the content type is completely optional and up to the consumer. It’d be nice if the ASP.NET AJAX Service and WCF AJAX Services weren’t so tightly bound to the content type so that you could more easily create open access service endpoints that can take advantage of urlencoded data that is everywhere in existing pages. It would make it much easier to create basic REST endpoints without complicated service configuration. Ah one can dream! In the meantime I hope this article has given you some ideas on how you can transfer POST data from the client to the server using JSON – it might be useful in other scenarios beyond ASP.NET AJAX services as well. Additional Resources ServiceProxy.js A small JavaScript library that wraps $.ajax() to call ASP.NET AJAX and WCF AJAX Services. Includes date parsing extensions to the JSON object, a global dataFilter for processing dates on all jQuery JSON requests, provides cleanup for the .NET wrapped message format and handles errors in a consistent fashion. Making jQuery Calls to WCF/ASMX with a ServiceProxy Client More information on calling ASMX and WCF AJAX services with jQuery and some more background on ServiceProxy.js. Note the implementation has slightly changed since the article was written. ww.jquery.js The West Wind West Wind Web Toolkit also includes ServiceProxy.js in the West Wind jQuery extension library. This version is slightly different and includes embedded json encoding/decoding based on json2.js.© Rick Strahl, West Wind Technologies, 2005-2010Posted in jQuery  ASP.NET  AJAX  

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• Is there any kind of established architecture for browser based games?

  - by black_puppydog

  I am beginning the development of a broser based game in which players take certain actions at any point in time. Big parts of gameplay will be happening in real life and just have to be entered into the system. I believe a good kind of comparison might be a platform for managing fantasy football, although I have virtually no experience playing that, so please correct me if I am mistaken here. The point is that some events happen in the program (i.e. on the server, out of reach for the players) like pulling new results from some datasource, starting of a new round by a game master and such. Other events happen in real life (two players closing a deal on the transfer of some team member or whatnot - again: have never played fantasy football) and have to be entered into the system. The first part is pretty easy since the game masters will be "staff" and thus can be trusted to a certain degree to not mess with the system. But the second part bothers me quite a lot, especially since the actions may involve multiple steps and interactions with different players, like registering a deal with the system that then has to be approved by the other party or denied and passed on to a game master to decide. I would of course like to separate the game logic as far as possible from the presentation and basic form validation but am unsure how to do this in a clean fashion. Of course I could (and will) put some effort into making my own architectural decisions and prototype different ideas. But I am bound to make some stupid mistakes at some point, so I would like to avoid some of that by getting a little "book smart" beforehand. So the question is: Is there any kind of architectural works that I can read up on? Papers, blogs, maybe design documents or even source code? Writing this down this seems more like a business application with business rules, workflows and such... Any good entry points for that? EDIT: After reading the first answers I am under the impression of having made a mistake when including the "MMO" part into the title. The game will not be all fancy (i.e. 3D or such) on the client side and the logic will completely exist on the server. That is, apart from basic form validation for the user which will also be mirrored on the server side. So the target toolset will be HTML5, JavaScript, probably JQuery(UI). My question is more related to the software architecture/design of a system that enforces certain rules. Separation of ruleset and presentation One problem I am having is that I want to separate the game rules from the presentation. The first step would be to make an own module for the game "engine" that only exposes an interface that allows all actions to be taken in a clean way. If an action fails with regard to some pre/post condition, the engine throws an exception which is then presented to the user like "you cannot sell something you do not own" or "after that you would end up in a situation which is not a valid game state." The problem here is that I would like to be able to not even present invalid action in the first place or grey out the corresponding UI elements. Changing and tweaking the ruleset Another big thing is the ruleset. It will probably evolve over time and most definitely must be tweaked. What's more, it should be possible (to a certain extent) to build a ruleset that fits a specific game round, i.e. choosing different kinds of behaviours in different aspects of the game. This would do something like "we play it with extension A today but we throw out extension B." For me, this screams "Architectural/Design pattern" but I have no idea on who might have published on something like this, not even what to google for.

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• How to build n-layered web architecture with PHP?

  - by Alex

  I have a description and design of a website and I need to redesign it to allow for new requirements. The website's purpose is the offering of government's contracts and bidding opportunities for different businesses.I'm dealing with the 3-tier architecture PHP website comprising of the user-interface tier(client's web browser),business logic layer(Apache web server with PHP engine in it and a couple of applications running within a web server as well) and a database layer(local mysql database). Now,i need to redesign it to su???rt distributed n-tier architecture and specify how I would go about it.After long hours of research i came to this solution: business logic should be separated into presentation and purely business logic tier to allow for n-layer architecture(user-interface,presentation tier,b.logic and data tier).I have decided to use ??? just for the presentation(since the original existing website is in PHP) and use it within apache web server.In the business logic i want to use J2?? implementation technology instead of implementing it in PHP(i.e using Zend app.server and smarty template) cz J2EE can provide much more essential container services which are essential for business logic,its robustness,maintainability and different critical business operations which will be carried out by the g?v?rnment's website.So,particularly,i want to use J??ss app.server with ?J? business objects in it which would provide all the b.logic in java and would interact with the database and so forth.In order to connect PHP on a web server with java on app.server i'm gonna use PHP/Java bridge API (or maybe Quercus or SOAP is better?).Finally,i have my data tier with mysql which will communicate with b.logic via JD??.Payment system application in ???.server is gonna use S??? to talk with credit card company. From your professional point of view,does it sound like a good way of redesigning the original website to allow for n-tier architecture considering the specifics of the website and the criticality of its operations?(payment system is included in it)or u would personally prefer to use PHP business objects for business logic as well instead of J2EE?If you have any wiser recommendation or some alternative,please let me know what is right or wrong in my current solution. H??? to hear your professional advice very s??n (I'm new to the area of web development) Thanks in advance

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• Why do I get "file is not of required architecture" when I try to build my app on an iphone?

  - by Dale

  My app seemingly runs fine in the simulator but the first time I hooked a phone up to my system and had it build for it I got a huge error log with things like: Build SCCUI of project SCCUI with configuration Debug CompileXIB HandleAlert.xib cd /Users/gdbriggs/Desktop/SCCUI setenv IBC_MINIMUM_COMPATIBILITY_VERSION 3.1 setenv PATH "/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin:/Developer/usr /bin:/usr/bin:/bin:/usr/sbin:/sbin" /Developer/usr/bin/ibtool --errors --warnings --notices --output-format human-readable-text --compile /Users/gdbriggs/Desktop/SCCUI/build/Debug-iphoneos/SCCUI.app/HandleAlert.nib /Users/gdbriggs/Desktop/SCCUI/HandleAlert.xib /* com.apple.ibtool.document.warnings */ /Users/gdbriggs/Desktop/SCCUI/HandleAlert.xib:13: warning: UITextView does not support data detectors when the text view is editable. Ld build/Debug-iphoneos/SCCUI.app/SCCUI normal armv6 cd /Users/gdbriggs/Desktop/SCCUI setenv IPHONEOS_DEPLOYMENT_TARGET 3.1 setenv MACOSX_DEPLOYMENT_TARGET 10.5 setenv PATH "/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin:/Developer/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin" /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/gcc-4.2 -arch armv6 -isysroot /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.1.sdk -L/Users/gdbriggs/Desktop/SCCUI/build/Debug-iphoneos -F/Users/gdbriggs/Desktop/SCCUI/build/Debug-iphoneos -F/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator3.1.sdk/System/Library/Frameworks -filelist /Users/gdbriggs/Desktop/SCCUI/build/SCCUI.build/Debug-iphoneos/SCCUI.build/Objects-normal/armv6/SCCUI.LinkFileList -mmacosx-version-min=10.5 -dead_strip -miphoneos-version-min=3.1 -framework Foundation -framework UIKit -framework CoreGraphics -framework MessageUI -o /Users/gdbriggs/Desktop/SCCUI/build/Debug-iphoneos/SCCUI.app/SCCUI ld: warning: in /Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator3.1.sdk/System/Library/Frameworks/Foundation.framework/Foundation, file is not of required architecture ld: warning: in /Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator3.1.sdk/System/Library/Frameworks/UIKit.framework/UIKit, file is not of required architecture ld: warning: in /Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator3.1.sdk/System/Library/Frameworks/CoreGraphics.framework/CoreGraphics, file is not of required architecture ld: warning: in /Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator3.1.sdk/System/Library/Frameworks/MessageUI.framework/MessageUI, file is not of required architecture Undefined symbols: "_OBJC_CLASS_$_UIDevice", referenced from: __objc_classrefs__DATA@0 in SCAuthenticationHandler.o "_OBJC_CLASS_$_NSString", referenced from: __objc_classrefs__DATA@0 in CCProxy.o __objc_classrefs__DATA@0 in AlertSummaryViewController.o __objc_classrefs__DATA@0 in HomeLevelController.o __objc_classrefs__DATA@0 in SCAuthenticationHandler.o __objc_classrefs__DATA@0 in SCRequestHandler.o "_UIApplicationMain", referenced from: _main in main.o "_objc_msgSend", referenced from: _main in main.o _main in main.o _main in main.o -[SCCUIAppDelegate applicationDidFinishLaunching:] in and it just keeps going. At / near the bottom it says: ld: symbol(s) not found collect2: ld returned 1 exit status What am I doing wrong?

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• How to start with entity framework and service oriented architecture?

  - by citronas

  At work I need to create a new web application, that will connection to an MySql Database. (So far I only have expercience with Linq-To-Sql classes and MSSQL Servers.) My superior tells me to use the entity framework (he probably refers to Linq-To-Entity) and provide everything as a service based architecture. Unfortunatly nobody at work has experience with that framework and with a real nice server oriented architecture. (till now no customer wanted to pay for architecture that he can't see. This speficic project I'm leading will be long-term, meaning multiple years, so it would be best to design it the way, that multiple targetting plattforms like asp.net, c# wpf, ... could use it) For now, the main target plattform is ASP.net So I do have the following questions: 1) Where can I read best what's really behind service oriented architecture (but for now beginner tutorials work fine as well) and how to do it in best practise? 2) So far I can't seem a real difference between Linq-To-Sql classes and the information I've google so far on the 'entity framework'. So, whats the difference? Where do I find nice tutorials for it. 3) Is there any difference in the entity framework regarding the database server (MSSQL or MySQL). If not, does that mean that code snipperts I will stumble across will word database independent? 4) I do you Visual Studio 2010. Do I have to regard something specific?

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• Showing Loading screen during REST service request in android app ?

  - by sat

  Currently here is what I am following, As soon as my app is launched, I have to send a request for REST service, It will take little time , so I thought of showing loading screen, In onCreate() of my Activity , first thing will be to show loading screen(progress dialog) , And I kick off the background Activity using AsyncTask , i.e. requesting for REST service and onPostexecute() I close the dialog and then I do setContentView(myxml); and update the UI . Can this approach be improved ? Problem which I faced was , Sometimes , Garbage collector may start(due to various reasons) and my app hangs at loading screen forever , because of Garbage collector , even request for REST service is not sent and because of it some wake up call comes and rest is disaster and Force close. But sometimes even ForceClose doesnot come fast , may be because of GC. so I cannot even go back and stuck in loading screen. Only thing which I can do at that point is to come back HOME. After that If I come back to my app its still loading , so definitely this approach seems to be a bad design. Whats the right approach ?

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• How to post to a request using node.js

  - by Mr JSON

  I am trying to post some json to a URL. I saw various other questions about this on stackoverflow but none of them seemed to be clear or work. This is how far I got, I modified the example on the api docs: var http = require('http'); var google = http.createClient(80, 'server'); var request = google.request('POST', '/get_stuff', {'host': 'sever', 'content-type': 'application/json'}); request.write(JSON.stringify(some_json),encoding='utf8'); //possibly need to escape as well? request.end(); request.on('response', function (response) { console.log('STATUS: ' + response.statusCode); console.log('HEADERS: ' + JSON.stringify(response.headers)); response.setEncoding('utf8'); response.on('data', function (chunk) { console.log('BODY: ' + chunk); }); }); When I post this to the server I get an error telling me that it's not of the json format or that it's not utf8, which they should be. I tried to pull the request url but it is null. I am just starting with nodejs so please be nice.

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• help understanding the concept of javascript callbacks with node.js, especially in loops

  - by Mr JSON

  hi I am just starting with node.js. I have done a little ajax stuff but nothing too complicated so callbacks are still kind of over my head. I looked at async but all I need is to run a few functions sequentially. I basically have something that pulls some json from an api, creates a new one and then does something with that. obviously i can't just run it because it runs everything at once and has an empty json. mostly they have to go sequentially but if while pulling a json from the api it can pull other json while it's waiting that is fine. I just got confused when putting the callback in a loop. what do I do with the index? i think i have seen some places that use callback inside the loop as kind of a recusive function and don't use for loops at all. simple examples would help alot thanks!

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• Redirect some URL requests to CloudFront and the rest direct to the normal server?

  - by indiehacker

  Say I have two types of URL requests that must be handled by my REST API: http://query.restapi.com/image.png?apikey=abc123 http://query.restapi.com/2.0/<apiKey>/resource.json?from=umi.us_census00.state_geometry Is it possible to redirect only some URL requests for static images (ie., regex: *.png?.*) to take advantage of CloudFront's caching and have the rest of the requests go directly to the normal EC2 server (or at least take a speedier indirect route to the normal EC2 server?). Perhaps the added request time for the misses to CloudFront is irrelevant to worry about? Or perhaps my situation is not best to use for CloudFront? I understand I will need to make DNS change where the current URL requests having http://query.restapi.com/some.png?apikey=0123 get redirected to http://d1234.cloudfront.net/some.png, but I am hoping there is some way for just redirecting static .png requests to take advantage of CloudFront?

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• How to configure Amazon Security Groups to achieve multi-tier architecture?

  - by ks78

  What is the preferred way to configure Amazon Security Groups to achieve a multi-tier architecture? Each of my instances has its own Security Group, which I only want to use for rules specific to an instance. I'd like to keep any rules which apply to multiple instances in a separate Security Group, which can then be assigned to instance Security Groups as necessary. As an example, I've setup a group called "admin", which allows administrative access from my IP. I added the "admin" group as the source to each of my instance security groups. However, I still can't access the instances from my IP without adding the rules directly to the instance's group. Am I missing something? Although it seems a multi-tier security architecture should be possible, it doesn't seem to be working.

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• How to configure Amazon Security Groups to achieve multi-tier architecture?

  - by ks78

  What is the preferred way to configure Amazon Security Groups to achieve a multi-tier architecture? Each of my instances has its own Security Group, which I only want to use for rules specific to an instance. I'd like to keep any rules which apply to multiple instances in a separate Security Group, which can then be assigned to instance Security Groups as necessary. As an example, I've setup a group called "admin", which allows administrative access from my IP. I added the "admin" group as the source to each of my instance security groups. However, I still can't access the instances from my IP without adding the rules directly to the instance's group. Am I missing something? Although it seems a multi-tier security architecture should be possible, it doesn't seem to be working.

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• Removing section in .sub file and renumber rest of lines?

  - by OverTheRainbow

  Here's the problem: An AVI file had a few seconds removed when it was ripped from a DVD, while its corresponding .sub subtitle file still contains the whole thing. So at around 2/3 into the movie, I need to remove the extra subtitles, and renumber the rest of the lines in the .sub files so that the remaining subtitles are displayed at the right time. I was hoping that SubTitle Workshop would be able to renumber the rest of the lines after I deleted the now-useless section, but it doesn't. What would be the easiest way to edit the sub file? Thank you.

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• How do I resolve "No JSON object could be decoded" on mythbuntu live CD?

  - by Neil

  I have been running a MythTV frontend on my laptop for some time against a MythTV backend installed in Linux Mint 12 on another computer, and everything works fine. Now, I'm trying out the Mythbuntu Live CD (12.04.1 32-bit) on the laptop, to turn it into a dedicated front end. It's connecting to the network just fine, and I can see my server. When I click on the frontend icon on the desktop, it asks me for the security code, which I've verified against mythtv-setup on the server. However, when I test that code, it shows the error message "No JSON object could be decoded". I've looked in the control center to see if there's something else I should be setting up. The message above implies to me that it can't find the server, but I can find no place in the control center to tell it where to find my myth backend, which I find a little odd. Does the live CD not work against a backend server on another machine?

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• Organizations &amp; Architecture UNISA Studies &ndash; Chap 7

  - by MarkPearl

  Learning Outcomes Name different device categories Discuss the functions and structure of I/.O modules Describe the principles of Programmed I/O Describe the principles of Interrupt-driven I/O Describe the principles of DMA Discuss the evolution characteristic of I/O channels Describe different types of I/O interface Explain the principles of point-to-point and multipoint configurations Discuss the way in which a FireWire serial bus functions Discuss the principles of InfiniBand architecture External Devices An external device attaches to the computer by a link to an I/O module. The link is used to exchange control, status, and data between the I/O module and the external device. External devices can be classified into 3 categories… Human readable – e.g. video display Machine readable – e.g. magnetic disk Communications – e.g. wifi card I/O Modules An I/O module has two major functions… Interface to the processor and memory via the system bus or central switch Interface to one or more peripheral devices by tailored data links Module Functions The major functions or requirements for an I/O module fall into the following categories… Control and timing Processor communication Device communication Data buffering Error detection I/O function includes a control and timing requirement, to coordinate the flow of traffic between internal resources and external devices. Processor communication involves the following… Command decoding Data Status reporting Address recognition The I/O device must be able to perform device communication. This communication involves commands, status information, and data. An essential task of an I/O module is data buffering due to the relative slow speeds of most external devices. An I/O module is often responsible for error detection and for subsequently reporting errors to the processor. I/O Module Structure An I/O module functions to allow the processor to view a wide range of devices in a simple minded way. The I/O module may hide the details of timing, formats, and the electro mechanics of an external device so that the processor can function in terms of simple reads and write commands. An I/O channel/processor is an I/O module that takes on most of the detailed processing burden, presenting a high-level interface to the processor. There are 3 techniques are possible for I/O operations Programmed I/O Interrupt[t I/O DMA Access Programmed I/O When a processor is executing a program and encounters an instruction relating to I/O it executes that instruction by issuing a command to the appropriate I/O module. With programmed I/O, the I/O module will perform the requested action and then set the appropriate bits in the I/O status register. The I/O module takes no further actions to alert the processor. I/O Commands To execute an I/O related instruction, the processor issues an address, specifying the particular I/O module and external device, and an I/O command. There are four types of I/O commands that an I/O module may receive when it is addressed by a processor… Control – used to activate a peripheral and tell it what to do Test – Used to test various status conditions associated with an I/O module and its peripherals Read – Causes the I/O module to obtain an item of data from the peripheral and place it in an internal buffer Write – Causes the I/O module to take an item of data form the data bus and subsequently transmit that data item to the peripheral The main disadvantage of this technique is it is a time consuming process that keeps the processor busy needlessly I/O Instructions With programmed I/O there is a close correspondence between the I/O related instructions that the processor fetches from memory and the I/O commands that the processor issues to an I/O module to execute the instructions. Typically there will be many I/O devices connected through I/O modules to the system – each device is given a unique identifier or address – when the processor issues an I/O command, the command contains the address of the address of the desired device, thus each I/O module must interpret the address lines to determine if the command is for itself. When the processor, main memory and I/O share a common bus, two modes of addressing are possible… Memory mapped I/O Isolated I/O (for a detailed explanation read page 245 of book) The advantage of memory mapped I/O over isolated I/O is that it has a large repertoire of instructions that can be used, allowing more efficient programming. The disadvantage of memory mapped I/O over isolated I/O is that valuable memory address space is sued up. Interrupts driven I/O Interrupt driven I/O works as follows… The processor issues an I/O command to a module and then goes on to do some other useful work The I/O module will then interrupts the processor to request service when is is ready to exchange data with the processor The processor then executes the data transfer and then resumes its former processing Interrupt Processing The occurrence of an interrupt triggers a number of events, both in the processor hardware and in software. When an I/O device completes an I/O operations the following sequence of hardware events occurs… The device issues an interrupt signal to the processor The processor finishes execution of the current instruction before responding to the interrupt The processor tests for an interrupt – determines that there is one – and sends an acknowledgement signal to the device that issues the interrupt. The acknowledgement allows the device to remove its interrupt signal The processor now needs to prepare to transfer control to the interrupt routine. To begin, it needs to save information needed to resume the current program at the point of interrupt. The minimum information required is the status of the processor and the location of the next instruction to be executed. The processor now loads the program counter with the entry location of the interrupt-handling program that will respond to this interrupt. It also saves the values of the process registers because the Interrupt operation may modify these The interrupt handler processes the interrupt – this includes examination of status information relating to the I/O operation or other event that caused an interrupt When interrupt processing is complete, the saved register values are retrieved from the stack and restored to the registers Finally, the PSW and program counter values from the stack are restored. Design Issues Two design issues arise in implementing interrupt I/O Because there will be multiple I/O modules, how does the processor determine which device issued the interrupt? If multiple interrupts have occurred, how does the processor decide which one to process? Addressing device recognition, 4 general categories of techniques are in common use… Multiple interrupt lines Software poll Daisy chain Bus arbitration For a detailed explanation of these approaches read page 250 of the textbook. Interrupt driven I/O while more efficient than simple programmed I/O still requires the active intervention of the processor to transfer data between memory and an I/O module, and any data transfer must traverse a path through the processor. Thus is suffers from two inherent drawbacks… The I/O transfer rate is limited by the speed with which the processor can test and service a device The processor is tied up in managing an I/O transfer; a number of instructions must be executed for each I/O transfer Direct Memory Access When large volumes of data are to be moved, an efficient technique is direct memory access (DMA) DMA Function DMA involves an additional module on the system bus. The DMA module is capable of mimicking the processor and taking over control of the system from the processor. It needs to do this to transfer data to and from memory over the system bus. DMA must the bus only when the processor does not need it, or it must force the processor to suspend operation temporarily (most common – referred to as cycle stealing). When the processor wishes to read or write a block of data, it issues a command to the DMA module by sending to the DMA module the following information… Whether a read or write is requested using the read or write control line between the processor and the DMA module The address of the I/O device involved, communicated on the data lines The starting location in memory to read from or write to, communicated on the data lines and stored by the DMA module in its address register The number of words to be read or written, communicated via the data lines and stored in the data count register The processor then continues with other work, it delegates the I/O operation to the DMA module which transfers the entire block of data, one word at a time, directly to or from memory without going through the processor. When the transfer is complete, the DMA module sends an interrupt signal to the processor, this the processor is involved only at the beginning and end of the transfer. I/O Channels and Processors Characteristics of I/O Channels As one proceeds along the evolutionary path, more and more of the I/O function is performed without CPU involvement. The I/O channel represents an extension of the DMA concept. An I/O channel ahs the ability to execute I/O instructions, which gives it complete control over I/O operations. In a computer system with such devices, the CPU does not execute I/O instructions – such instructions are stored in main memory to be executed by a special purpose processor in the I/O channel itself. Two types of I/O channels are common A selector channel controls multiple high-speed devices. A multiplexor channel can handle I/O with multiple characters as fast as possible to multiple devices. The external interface: FireWire and InfiniBand Types of Interfaces One major characteristic of the interface is whether it is serial or parallel parallel interface – there are multiple lines connecting the I/O module and the peripheral, and multiple bits are transferred simultaneously serial interface – there is only one line used to transmit data, and bits must be transmitted one at a time With new generation serial interfaces, parallel interfaces are becoming less common. In either case, the I/O module must engage in a dialogue with the peripheral. In general terms the dialog may look as follows… The I/O module sends a control signal requesting permission to send data The peripheral acknowledges the request The I/O module transfers data The peripheral acknowledges receipt of data For a detailed explanation of FireWire and InfiniBand technology read page 264 – 270 of the textbook

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