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  • Subversion: Avoid proxy use on intranet

    - by l0b0
    I'm trying to exclude all intranet hosts from proxy use, but it looks like http-proxy-exceptions just looks at the command line string, not what the host name in the string resolves to. Because of this, it looks like the only way to avoid proxy use on the IP 123.456.789.012*, which also answers to vcs, vcs.example.org, svn, svn.example.org, subversion and subversion.example.org is to list all of them, not just the IP. Is there some trick to make Subversion either resolve IP addresses before checking for proxy exceptions, or exclude everything that is not a fully qualified DNS name (that is, doesn't contain a dot)? * Yes, I know that's not a valid IP

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  • Blocking IP's Nginx behind proxy

    - by FunkyChicken
    I'm running a Nginx 1.2.4 webserver here, and I'm behind a proxy of my hoster to prevent ddos attacks. The downside of being behind this proxy is that I need to get the REAL IP information from an extra header. In PHP it works great by doing $_SERVER[HTTP_X_REAL_IP] for example. Now before I was behind this proxy of my hoster I had a very effective way of blocking certain IP's by doing this: include /etc/nginx/block.conf and to allow/deny IP's there. But now due to the proxy, Nginx sees all traffic coming from 1 IP. Is there a way I can get Nginx to read the IP's like how PHP does, with the X-REAL-IP header?

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  • How to circumvent ISP Limiting "Unknown" traffic - (SSH)Proxy, VPN

    - by connery
    I am having issues with using a proxy/VPN, with my current ISP (Comenersol, Spain). From my point of view they limit traffic by protocol or by traffic they "know" and "dont know". I'll explain my findings so far below. Internet connection in Spain: ~400-420KByte/sec (speedtest.net) OpenVPN Server in Sweden(pfsense): 100/100Mbit. LZO Compression. TCP. Tun. Aes128 Squid Proxy server in Sweden (pfsense): 100/100 (same box as the vpn server). Plain, no encryption. Runs in stealth mode to hide the use of proxy. NOT running OpenVPN or Squid Proxy, this is my findings: When I download a file from my pfsense box in Sweden, I get maximum speed When I run speedtest.net and choose any european server (including Swedish), I get max speed When I download a torrent (with non default port above 10K), I get limited to ~100KByte/sec. Encryption is turned off If I download something through https, I get max speed Running either Squid Proxy or VPN, this is my findings When I download a file from my pfsense box in Sweden, I get ~100KByte/sec When I run speedtest.net and choose any european server (including Swedish and Spanish), I get ~100Kbyte/sec When I download a torrent, I get same limitation ~100KByte/sec When I download something through https, I get ~100KByte/sec I verify the speeds above with speedtest.net measure, firefox measure in addition to having bmon running in terminal in the background. This way I am certain that the speeds I get presented, are in fact correct. If I connect through a different ISP with VPN or Squid Proxy, I get better speeds (400KByte/sec ++) In short: Whenever I tunnel my traffic through Sweden, my SPanish ISP throttles the traffic. I thought tunneling it through Squid would solve the issue, since I then would no longer hide my traffic through encryption. This does not seem to be the case. Wget and fetch gives same result. I did not try 'nc', but I assume this would give the same result. Does anyone know how to circumvent this issue? I would very much like to be able to get full speed with Swedish ip, as this would make me able to stream TV at higher quality than today. 100KByte/sec just does not cut it quality wise. Thanks for reading. Looking forward for your help.

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  • Encrypt client connection with squid forward proxy using SSL

    - by Twisted Whisper
    I'm setting up a Squid forward proxy and I'm wondering if I could configure Squid in such a way that the connection from my web browser to squid is https regardless of whether the connection from squid to the destination website is http or https. In other words, I want my connection from my web browser to my forward proxy to be encrypted even though I'm just surfing normal http website through that proxy. Can it be done?

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  • Proxy - Some general questions

    - by user68802
    Is it possible to accomplish the following scenario with a proxy server? We are having one internet facing server that we want to put behind a proxy for some reasons. We want everything to work as before. When they do a request all connections will be forward to the internal server which will send back the information through the proxy. We want to be able to change to proxy to show an maintenance page whenever we are doing maintenance and change it back to forwarding traffic when we are done. We do also want to be able to keep forwarding all users that are using the sites but show an maintenance page for all new users for a time before showing the maintenance page for everyone in order to give the users some time to finish their work before kicking them out.

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  • Tomcat and HTTPS connect timeout (local Proxy resolves it)

    - by smas
    I have web application on the Tomcat with webservices. I've noticed that all web services connected to https get timeout. I run this app on my localhost in my company. When I redirect all my connections through Fiddler (local proxy) everything works correctly. I don't want to execute fiddler all the time. my computer -> [FIDDLER local proxy] -> [remote proxy] // WORKS my computer -> [remote proxy] // timeout How to increase tomcat logging to get more technical logs than only "timeout". Is there any other way to get more information what blocks the https URL?

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  • HTTPS Proxy which answers CONNECT with own certificate

    - by user1109542
    I'm configuring a DMZ which has the following Scheme: Internet - Server A - Security Appliance - Server B - Intranet In this DMZ I need a Proxy server for http(s) connections from the Intranet to Internet. The Problem is, that all Traffic should be scanned by the Security Appliance. For this I have to terminate the SSL Connection at Server B, proxy it as plain http to Server A through the Security Appliance and then further as https into the Internet. An encryption is then persistent between the Client and Server B and the Target Server and Server A. The communication between Server A and Server B is unencrypted. I know about the security risks and that the client will see some warning about the unknown CA of Server B's certificate. As Software I want to use Apache Web Servers on Server A and Server B. As first step I tried to configure Server B that it serves as endpoint for the SSL Encryption. So it has to establish the encryption with the client (answering HTTP CONNECT). Listen 8443 <VirtualHost *:8443> ProxyRequests On ProxyPreserveHost On AllowCONNECT 443 # SSL ErrorLog logs/ssl_error_log TransferLog logs/ssl_access_log LogLevel debug SSLProxyEngine on SSLProxyMachineCertificateFile /etc/pki/tls/certs/localhost_private_public.crt <Proxy *> Order deny,allow Deny from all Allow from 192.168.0.0/22 </Proxy> </VirtualHost> With this Proxy only the CONNECT request is passed through and an encrypted Connection between the client and the target is established. Unfortunately there is no possibility to configure mod_proxy_connect to decrypt the SSL connection. Is there any possibility to accomplish that kind of proxying with Apache?

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  • mod_proxy failing as forward proxy in simple configuration

    - by Stabledog
    (On Mac OS X 10.6, Apache 2.2.11) Following the oft-repeated googled advice, I've set up mod_proxy on my Mac to act as a forward proxy for http requests. My httpd.conf contains this: <IfModule mod_proxy> ProxyRequests On ProxyVia On <Proxy *> Allow from all </Proxy> (Yes, I realize that's not ideal, but I'm behind a firewall trying to figure out why the thing doesn't work at all) So, when I point my browser's proxy settings to the local server (ip_address:80), here's what happens: I browse to http://www.cnn.com I see via sniffer that this is sent to Apache on the Mac Apache responds with its default home page ("It works!" is all this page says) So... Apache is not doing as expected -- it is not forwarding my browser's request out onto the Internet to cnn. Nothing in the logfile indicates an error or problem, and Apache returns a 200 header to the browser. Clearly there is some very basic configuration step I'm not understanding... but what?

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  • Proxy Server suggestions

    - by Jon Menefee
    Here is the question I have that hopefully is not too general of a question. I have a network with approximately 25 PC's, 3 servers and 25 IP cameras. I have a firewall already on the network and it works fine for what I need, but my client is asking me if there is a way to put a Proxy server on the network to monitor where his employees are going when they surf the Internet. He is not wanting to block them (at least not thru the Proxy server), but he wants to make sure that they arent going to sites that would compromise the networked PCs. I have looked at TMG and it is a little more than what I want. I hesitate adding another firewall to the system because of the security cameras that are presently on the network (IP Cameras). I just want to put a policy in AD that would make certain Users (or Computers) use a Proxy server. Any suggestions on a good proxy server are welcome. Thank you

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  • proxy server software for windows xp

    - by This is it
    Hi Is there a proxy software for Windows XP that can support HTTP, HTTPS, SMTP, IMAP, POP, FTP, etc. (the more the better)? We tried apache mod_proxy but FTP doesn't work through it (at least not all features). Maybe we don't need proxy server for following requirements (we are open for suggestions): - Centralized access point to internet for several users (proxy server?) - Users use Browser (firefox/IE - HTTP, HTTPS), Outlook (SMTP, POP, IMAP) - Logs to see where did users go on internet - Possiblity to connect to FTP server Windows xp, which is used as proxy server, is a virtual machine, and all other users/clients are virtual machines as well (Hyper-V)... Thanks for suggestions. Cheers

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  • Make my web-server traffic go through proxy?

    - by Eli
    I have a question that may or may not be possible. Basically Comcast isn't going to let me host a website on their ISP unless I have a business account. So, I spoke with my uncle who is big into networking and he told me to host my website through a proxy so Comcast cannot associate the website IP with my IP. I have purchases a proxy from proxy-hub.com, but I cannot seem to figure out what to do next. I may be approaching this totally wrong and I may need to create my own proxy server. Anybody have a clue? Thanks.

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  • C# Proposal: Compile Time Static Checking Of Dynamic Objects

    - by Paulo Morgado
    C# 4.0 introduces a new type: dynamic. dynamic is a static type that bypasses static type checking. This new type comes in very handy to work with: The new languages from the dynamic language runtime. HTML Document Object Model (DOM). COM objects. Duck typing … Because static type checking is bypassed, this: dynamic dynamicValue = GetValue(); dynamicValue.Method(); is equivalent to this: object objectValue = GetValue(); objectValue .GetType() .InvokeMember( "Method", BindingFlags.InvokeMethod, null, objectValue, null); Apart from caching the call site behind the scenes and some dynamic resolution, dynamic only looks better. Any typing error will only be caught at run time. In fact, if I’m writing the code, I know the contract of what I’m calling. Wouldn’t it be nice to have the compiler do some static type checking on the interactions with these dynamic objects? Imagine that the dynamic object that I’m retrieving from the GetValue method, besides the parameterless method Method also has a string read-only Property property. This means that, from the point of view of the code I’m writing, the contract that the dynamic object returned by GetValue implements is: string Property { get; } void Method(); Since it’s a well defined contract, I could write an interface to represent it: interface IValue { string Property { get; } void Method(); } If dynamic allowed to specify the contract in the form of dynamic(contract), I could write this: dynamic(IValue) dynamicValue = GetValue(); dynamicValue.Method(); This doesn’t mean that the value returned by GetValue has to implement the IValue interface. It just enables the compiler to verify that dynamicValue.Method() is a valid use of dynamicValue and dynamicValue.OtherMethod() isn’t. If the IValue interface already existed for any other reason, this would be fine. But having a type added to an assembly just for compile time usage doesn’t seem right. So, dynamic could be another type construct. Something like this: dynamic DValue { string Property { get; } void Method(); } The code could now be written like this; DValue dynamicValue = GetValue(); dynamicValue.Method(); The compiler would never generate any IL or metadata for this new type construct. It would only thee used for compile type static checking of dynamic objects. As a consequence, it makes no sense to have public accessibility, so it would not be allowed. Once again, if the IValue interface (or any other type definition) already exists, it can be used in the dynamic type definition: dynamic DValue : IValue, IEnumerable, SomeClass { string Property { get; } void Method(); } Another added benefit would be IntelliSense. I’ve been getting mixed reactions to this proposal. What do you think? Would this be useful?

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  • How to secure Firefox traffic (+DNS) through SOCKS proxy under Ubuntu 10.04?

    - by Maarx
    I'm using Ubuntu 10.04, and starting a SOCKS proxy with 'ssh -D', and setting Ubuntu to use it with "System - Preferences - Network Proxy". Firefox uses the proxy, and the proxy's IP appears when I visit a site like http://www.whatismyip.com/. My question is, is Firefox resolving DNS requests through this proxy? Is my web-browsing truly secure? (That is, until I exit the other end of the proxy. I know it's insecure after that.) (And I've verified the keys, I'm not being man-in-the-middled) (And--screw it. You know what I mean. Is it resolving DNS requests through the proxy?) I don't know how I would go about verifying such a thing for myself. Using additional hardware such as another debugging proxy is not an option. If Firefox isn't resolving my DNS requests through the SOCKS proxy, how do I go about fixing it?

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  • Programmatically Set Proxy Address, Port, User, Password throught Windows Registry

    - by Fábio Antunes
    I'm writing a small C# application that will use Internet Explorer to interact with a couple a websites, with help from WatiN. However, it will also require from time to time to use a proxy. I've came across Programmatically Set Browser Proxy Settings in C#, but this only enables me to enter a proxy address, and I also need to enter a Proxy username and password. How can I do that? Note: It doesn't matter if a solution changes the entire system Internet settings. However, I would prefer to change only IE proxy settings (for any connection). The solution has to work with IE8 and Windows XP SP3 or higher. I'd like to have the possibility to read the Proxy settings first, so that later I can undo my changes. EDIT With the help of the Windows Registry accessible through Microsoft.Win32.RegistryKey, i was able to apply a proxy something like this: RegistryKey registry = Registry.CurrentUser.OpenSubKey("Software\\Microsoft\\Windows\\CurrentVersion\\Internet Settings", true); registry.SetValue("ProxyEnable", 1); registry.SetValue("ProxyServer", "127.0.0.1:8080"); But how can i specify a username and a password to login at the proxy server? I also noticed that IE doesn't refresh the Proxy details for its connections once the registry was changed how can i order IE to refresh its connection settings from the registry? Thanks

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  • use proxy in python to fetch a webpage

    - by carmao
    I am trying to write a function in Python to use a public anonymous proxy and fetch a webpage, but I got a rather strange error. The code (I have Python 2.4): import urllib2 def get_source_html_proxy(url, pip, timeout): # timeout in seconds (maximum number of seconds willing for the code to wait in # case there is a proxy that is not working, then it gives up) proxy_handler = urllib2.ProxyHandler({'http': pip}) opener = urllib2.build_opener(proxy_handler) opener.addheaders = [('User-agent', 'Mozilla/5.0')] urllib2.install_opener(opener) req=urllib2.Request(url) sock=urllib2.urlopen(req) timp=0 # a counter that is going to measure the time until the result (webpage) is # returned while 1: data = sock.read(1024) timp=timp+1 if len(data) < 1024: break timpLimita=50000000 * timeout if timp==timpLimita: # 5 millions is about 1 second break if timp==timpLimita: print IPul + ": Connection is working, but the webpage is fetched in more than 50 seconds. This proxy returns the following IP: " + str(data) return str(data) else: print "This proxy " + IPul + "= good proxy. " + "It returns the following IP: " + str(data) return str(data) # Now, I call the function to test it for one single proxy (IP:port) that does not support user and password (a public high anonymity proxy) #(I put a proxy that I know is working - slow, but is working) rez=get_source_html_proxy("http://www.whatismyip.com/automation/n09230945.asp", "93.84.221.248:3128", 50) print rez The error: Traceback (most recent call last): File "./public_html/cgi-bin/teste5.py", line 43, in ? rez=get_source_html_proxy("http://www.whatismyip.com/automation/n09230945.asp", "93.84.221.248:3128", 50) File "./public_html/cgi-bin/teste5.py", line 18, in get_source_html_proxy sock=urllib2.urlopen(req) File "/usr/lib64/python2.4/urllib2.py", line 130, in urlopen return _opener.open(url, data) File "/usr/lib64/python2.4/urllib2.py", line 358, in open response = self._open(req, data) File "/usr/lib64/python2.4/urllib2.py", line 376, in _open '_open', req) File "/usr/lib64/python2.4/urllib2.py", line 337, in _call_chain result = func(*args) File "/usr/lib64/python2.4/urllib2.py", line 573, in lambda r, proxy=url, type=type, meth=self.proxy_open: \ File "/usr/lib64/python2.4/urllib2.py", line 580, in proxy_open if '@' in host: TypeError: iterable argument required I do not know why the character "@" is an issue (I have no such in my code. Should I have?) Thanks in advance for your valuable help.

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  • Rails' page caching vs. HTTP reverse proxy caches

    - by John Topley
    I've been catching up with the Scaling Rails screencasts. In episode 11 which covers advanced HTTP caching (using reverse proxy caches such as Varnish and Squid etc.), they recommend only considering using a reverse proxy cache once you've already exhausted the possibilities of page, action and fragment caching within your Rails application (as well as memcached etc. but that's not relevant to this question). What I can't quite understand is how using an HTTP reverse proxy cache can provide a performance boost for an application that already uses page caching. To simplify matters, let's assume that I'm talking about a single host here. This is my understanding of how both techniques work (maybe I'm wrong): With page caching the Rails process is hit initially and then generates a static HTML file that is served directly by the Web server for subsequent requests, for as long as the cache for that request is valid. If the cache has expired then Rails is hit again and the static file is regenerated with the updated content ready for the next request With an HTTP reverse proxy cache the Rails process is hit when the proxy needs to determine whether the content is stale or not. This is done using various HTTP headers such as ETag, Last-Modified etc. If the content is fresh then Rails responds to the proxy with an HTTP 304 Not Modified and the proxy serves its cached content to the browser, or even better, responds with its own HTTP 304. If the content is stale then Rails serves the updated content to the proxy which caches it and then serves it to the browser If my understanding is correct, then doesn't page caching result in less hits to the Rails process? There isn't all that back and forth to determine if the content is stale, meaning better performance than reverse proxy caching. Why might you use both techniques in conjunction?

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  • Firefox proxy dilemma

    - by Mike L.
    Any idea why when using system proxy settings in firefox, it can not accept a proxy such as: user:[email protected]:port ??? IE will allow and connect to a proxy in this format. Not only does firefox not work, but it does not prompt for the password, nor attempt to make a connection to the proxy. Basically get a "proxy server not found" error. Anybody know a way around this? I am working on a proxy switching program for IE & Firefox, and I would like to use system-wide proxy settings. If I just store the server:port combination, firefox prompts for the password, as well as IE. Then they can be cached and it will not ask again. Maybe my only option is to programmatically cache the user/pass? Anybody know a way to do this? I am pretty sure IE stores them at HTTP basic authentication passwords and I can add them with AddCredential. After saving a password for a proxy in firefox, it shows up in saved passwords in a format like "moz-proxy://server:port" anybody know how to programmatically add a saved password to firefox? Thanks

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  • Firefox proxy delima

    - by Mike L.
    Any idea why when using system proxy settings in firefox, it can not accept a proxy such as: user:[email protected]:port ??? IE will allow and connect to a proxy in this format. Not only does firefox not work, but it does not prompt for the password, nor attempt to make a connection to the proxy. Basically get a "proxy server not found" error. Anybody know a way around this? I am working on a proxy switching program for IE & Firefox, and I would like to use system-wide proxy settings. If I just store the server:port combination, firefox prompts for the password, as well as IE. Then they can be cached and it will not ask again. Maybe my only option is to programmatically cache the user/pass? Anybody know a way to do this? I am pretty sure IE stores them at HTTP basic authentication passwords and I can add them with AddCredential. After saving a password for a proxy in firefox, it shows up in saved passwords in a format like "moz-proxy://server:port" anybody know how to programmatically add a saved password to firefox? Thanks

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  • New features of C# 4.0

    This article covers New features of C# 4.0. Article has been divided into below sections. Introduction. Dynamic Lookup. Named and Optional Arguments. Features for COM interop. Variance. Relationship with Visual Basic. Resources. Other interested readings… 22 New Features of Visual Studio 2008 for .NET Professionals 50 New Features of SQL Server 2008 IIS 7.0 New features Introduction It is now close to a year since Microsoft Visual C# 3.0 shipped as part of Visual Studio 2008. In the VS Managed Languages team we are hard at work on creating the next version of the language (with the unsurprising working title of C# 4.0), and this document is a first public description of the planned language features as we currently see them. Please be advised that all this is in early stages of production and is subject to change. Part of the reason for sharing our plans in public so early is precisely to get the kind of feedback that will cause us to improve the final product before it rolls out. Simultaneously with the publication of this whitepaper, a first public CTP (community technology preview) of Visual Studio 2010 is going out as a Virtual PC image for everyone to try. Please use it to play and experiment with the features, and let us know of any thoughts you have. We ask for your understanding and patience working with very early bits, where especially new or newly implemented features do not have the quality or stability of a final product. The aim of the CTP is not to give you a productive work environment but to give you the best possible impression of what we are working on for the next release. The CTP contains a number of walkthroughs, some of which highlight the new language features of C# 4.0. Those are excellent for getting a hands-on guided tour through the details of some common scenarios for the features. You may consider this whitepaper a companion document to these walkthroughs, complementing them with a focus on the overall language features and how they work, as opposed to the specifics of the concrete scenarios. C# 4.0 The major theme for C# 4.0 is dynamic programming. Increasingly, objects are “dynamic” in the sense that their structure and behavior is not captured by a static type, or at least not one that the compiler knows about when compiling your program. Some examples include a. objects from dynamic programming languages, such as Python or Ruby b. COM objects accessed through IDispatch c. ordinary .NET types accessed through reflection d. objects with changing structure, such as HTML DOM objects While C# remains a statically typed language, we aim to vastly improve the interaction with such objects. A secondary theme is co-evolution with Visual Basic. Going forward we will aim to maintain the individual character of each language, but at the same time important new features should be introduced in both languages at the same time. They should be differentiated more by style and feel than by feature set. The new features in C# 4.0 fall into four groups: Dynamic lookup Dynamic lookup allows you to write method, operator and indexer calls, property and field accesses, and even object invocations which bypass the C# static type checking and instead gets resolved at runtime. Named and optional parameters Parameters in C# can now be specified as optional by providing a default value for them in a member declaration. When the member is invoked, optional arguments can be omitted. Furthermore, any argument can be passed by parameter name instead of position. COM specific interop features Dynamic lookup as well as named and optional parameters both help making programming against COM less painful than today. On top of that, however, we are adding a number of other small features that further improve the interop experience. Variance It used to be that an IEnumerable<string> wasn’t an IEnumerable<object>. Now it is – C# embraces type safe “co-and contravariance” and common BCL types are updated to take advantage of that. Dynamic Lookup Dynamic lookup allows you a unified approach to invoking things dynamically. With dynamic lookup, when you have an object in your hand you do not need to worry about whether it comes from COM, IronPython, the HTML DOM or reflection; you just apply operations to it and leave it to the runtime to figure out what exactly those operations mean for that particular object. This affords you enormous flexibility, and can greatly simplify your code, but it does come with a significant drawback: Static typing is not maintained for these operations. A dynamic object is assumed at compile time to support any operation, and only at runtime will you get an error if it wasn’t so. Oftentimes this will be no loss, because the object wouldn’t have a static type anyway, in other cases it is a tradeoff between brevity and safety. In order to facilitate this tradeoff, it is a design goal of C# to allow you to opt in or opt out of dynamic behavior on every single call. The dynamic type C# 4.0 introduces a new static type called dynamic. When you have an object of type dynamic you can “do things to it” that are resolved only at runtime: dynamic d = GetDynamicObject(…); d.M(7); The C# compiler allows you to call a method with any name and any arguments on d because it is of type dynamic. At runtime the actual object that d refers to will be examined to determine what it means to “call M with an int” on it. The type dynamic can be thought of as a special version of the type object, which signals that the object can be used dynamically. It is easy to opt in or out of dynamic behavior: any object can be implicitly converted to dynamic, “suspending belief” until runtime. Conversely, there is an “assignment conversion” from dynamic to any other type, which allows implicit conversion in assignment-like constructs: dynamic d = 7; // implicit conversion int i = d; // assignment conversion Dynamic operations Not only method calls, but also field and property accesses, indexer and operator calls and even delegate invocations can be dispatched dynamically: dynamic d = GetDynamicObject(…); d.M(7); // calling methods d.f = d.P; // getting and settings fields and properties d[“one”] = d[“two”]; // getting and setting thorugh indexers int i = d + 3; // calling operators string s = d(5,7); // invoking as a delegate The role of the C# compiler here is simply to package up the necessary information about “what is being done to d”, so that the runtime can pick it up and determine what the exact meaning of it is given an actual object d. Think of it as deferring part of the compiler’s job to runtime. The result of any dynamic operation is itself of type dynamic. Runtime lookup At runtime a dynamic operation is dispatched according to the nature of its target object d: COM objects If d is a COM object, the operation is dispatched dynamically through COM IDispatch. This allows calling to COM types that don’t have a Primary Interop Assembly (PIA), and relying on COM features that don’t have a counterpart in C#, such as indexed properties and default properties. Dynamic objects If d implements the interface IDynamicObject d itself is asked to perform the operation. Thus by implementing IDynamicObject a type can completely redefine the meaning of dynamic operations. This is used intensively by dynamic languages such as IronPython and IronRuby to implement their own dynamic object models. It will also be used by APIs, e.g. by the HTML DOM to allow direct access to the object’s properties using property syntax. Plain objects Otherwise d is a standard .NET object, and the operation will be dispatched using reflection on its type and a C# “runtime binder” which implements C#’s lookup and overload resolution semantics at runtime. This is essentially a part of the C# compiler running as a runtime component to “finish the work” on dynamic operations that was deferred by the static compiler. Example Assume the following code: dynamic d1 = new Foo(); dynamic d2 = new Bar(); string s; d1.M(s, d2, 3, null); Because the receiver of the call to M is dynamic, the C# compiler does not try to resolve the meaning of the call. Instead it stashes away information for the runtime about the call. This information (often referred to as the “payload”) is essentially equivalent to: “Perform an instance method call of M with the following arguments: 1. a string 2. a dynamic 3. a literal int 3 4. a literal object null” At runtime, assume that the actual type Foo of d1 is not a COM type and does not implement IDynamicObject. In this case the C# runtime binder picks up to finish the overload resolution job based on runtime type information, proceeding as follows: 1. Reflection is used to obtain the actual runtime types of the two objects, d1 and d2, that did not have a static type (or rather had the static type dynamic). The result is Foo for d1 and Bar for d2. 2. Method lookup and overload resolution is performed on the type Foo with the call M(string,Bar,3,null) using ordinary C# semantics. 3. If the method is found it is invoked; otherwise a runtime exception is thrown. Overload resolution with dynamic arguments Even if the receiver of a method call is of a static type, overload resolution can still happen at runtime. This can happen if one or more of the arguments have the type dynamic: Foo foo = new Foo(); dynamic d = new Bar(); var result = foo.M(d); The C# runtime binder will choose between the statically known overloads of M on Foo, based on the runtime type of d, namely Bar. The result is again of type dynamic. The Dynamic Language Runtime An important component in the underlying implementation of dynamic lookup is the Dynamic Language Runtime (DLR), which is a new API in .NET 4.0. The DLR provides most of the infrastructure behind not only C# dynamic lookup but also the implementation of several dynamic programming languages on .NET, such as IronPython and IronRuby. Through this common infrastructure a high degree of interoperability is ensured, but just as importantly the DLR provides excellent caching mechanisms which serve to greatly enhance the efficiency of runtime dispatch. To the user of dynamic lookup in C#, the DLR is invisible except for the improved efficiency. However, if you want to implement your own dynamically dispatched objects, the IDynamicObject interface allows you to interoperate with the DLR and plug in your own behavior. This is a rather advanced task, which requires you to understand a good deal more about the inner workings of the DLR. For API writers, however, it can definitely be worth the trouble in order to vastly improve the usability of e.g. a library representing an inherently dynamic domain. Open issues There are a few limitations and things that might work differently than you would expect. · The DLR allows objects to be created from objects that represent classes. However, the current implementation of C# doesn’t have syntax to support this. · Dynamic lookup will not be able to find extension methods. Whether extension methods apply or not depends on the static context of the call (i.e. which using clauses occur), and this context information is not currently kept as part of the payload. · Anonymous functions (i.e. lambda expressions) cannot appear as arguments to a dynamic method call. The compiler cannot bind (i.e. “understand”) an anonymous function without knowing what type it is converted to. One consequence of these limitations is that you cannot easily use LINQ queries over dynamic objects: dynamic collection = …; var result = collection.Select(e => e + 5); If the Select method is an extension method, dynamic lookup will not find it. Even if it is an instance method, the above does not compile, because a lambda expression cannot be passed as an argument to a dynamic operation. There are no plans to address these limitations in C# 4.0. Named and Optional Arguments Named and optional parameters are really two distinct features, but are often useful together. Optional parameters allow you to omit arguments to member invocations, whereas named arguments is a way to provide an argument using the name of the corresponding parameter instead of relying on its position in the parameter list. Some APIs, most notably COM interfaces such as the Office automation APIs, are written specifically with named and optional parameters in mind. Up until now it has been very painful to call into these APIs from C#, with sometimes as many as thirty arguments having to be explicitly passed, most of which have reasonable default values and could be omitted. Even in APIs for .NET however you sometimes find yourself compelled to write many overloads of a method with different combinations of parameters, in order to provide maximum usability to the callers. Optional parameters are a useful alternative for these situations. Optional parameters A parameter is declared optional simply by providing a default value for it: public void M(int x, int y = 5, int z = 7); Here y and z are optional parameters and can be omitted in calls: M(1, 2, 3); // ordinary call of M M(1, 2); // omitting z – equivalent to M(1, 2, 7) M(1); // omitting both y and z – equivalent to M(1, 5, 7) Named and optional arguments C# 4.0 does not permit you to omit arguments between commas as in M(1,,3). This could lead to highly unreadable comma-counting code. Instead any argument can be passed by name. Thus if you want to omit only y from a call of M you can write: M(1, z: 3); // passing z by name or M(x: 1, z: 3); // passing both x and z by name or even M(z: 3, x: 1); // reversing the order of arguments All forms are equivalent, except that arguments are always evaluated in the order they appear, so in the last example the 3 is evaluated before the 1. Optional and named arguments can be used not only with methods but also with indexers and constructors. Overload resolution Named and optional arguments affect overload resolution, but the changes are relatively simple: A signature is applicable if all its parameters are either optional or have exactly one corresponding argument (by name or position) in the call which is convertible to the parameter type. Betterness rules on conversions are only applied for arguments that are explicitly given – omitted optional arguments are ignored for betterness purposes. If two signatures are equally good, one that does not omit optional parameters is preferred. M(string s, int i = 1); M(object o); M(int i, string s = “Hello”); M(int i); M(5); Given these overloads, we can see the working of the rules above. M(string,int) is not applicable because 5 doesn’t convert to string. M(int,string) is applicable because its second parameter is optional, and so, obviously are M(object) and M(int). M(int,string) and M(int) are both better than M(object) because the conversion from 5 to int is better than the conversion from 5 to object. Finally M(int) is better than M(int,string) because no optional arguments are omitted. Thus the method that gets called is M(int). Features for COM interop Dynamic lookup as well as named and optional parameters greatly improve the experience of interoperating with COM APIs such as the Office Automation APIs. In order to remove even more of the speed bumps, a couple of small COM-specific features are also added to C# 4.0. Dynamic import Many COM methods accept and return variant types, which are represented in the PIAs as object. In the vast majority of cases, a programmer calling these methods already knows the static type of a returned object from context, but explicitly has to perform a cast on the returned value to make use of that knowledge. These casts are so common that they constitute a major nuisance. In order to facilitate a smoother experience, you can now choose to import these COM APIs in such a way that variants are instead represented using the type dynamic. In other words, from your point of view, COM signatures now have occurrences of dynamic instead of object in them. This means that you can easily access members directly off a returned object, or you can assign it to a strongly typed local variable without having to cast. To illustrate, you can now say excel.Cells[1, 1].Value = "Hello"; instead of ((Excel.Range)excel.Cells[1, 1]).Value2 = "Hello"; and Excel.Range range = excel.Cells[1, 1]; instead of Excel.Range range = (Excel.Range)excel.Cells[1, 1]; Compiling without PIAs Primary Interop Assemblies are large .NET assemblies generated from COM interfaces to facilitate strongly typed interoperability. They provide great support at design time, where your experience of the interop is as good as if the types where really defined in .NET. However, at runtime these large assemblies can easily bloat your program, and also cause versioning issues because they are distributed independently of your application. The no-PIA feature allows you to continue to use PIAs at design time without having them around at runtime. Instead, the C# compiler will bake the small part of the PIA that a program actually uses directly into its assembly. At runtime the PIA does not have to be loaded. Omitting ref Because of a different programming model, many COM APIs contain a lot of reference parameters. Contrary to refs in C#, these are typically not meant to mutate a passed-in argument for the subsequent benefit of the caller, but are simply another way of passing value parameters. It therefore seems unreasonable that a C# programmer should have to create temporary variables for all such ref parameters and pass these by reference. Instead, specifically for COM methods, the C# compiler will allow you to pass arguments by value to such a method, and will automatically generate temporary variables to hold the passed-in values, subsequently discarding these when the call returns. In this way the caller sees value semantics, and will not experience any side effects, but the called method still gets a reference. Open issues A few COM interface features still are not surfaced in C#. Most notably these include indexed properties and default properties. As mentioned above these will be respected if you access COM dynamically, but statically typed C# code will still not recognize them. There are currently no plans to address these remaining speed bumps in C# 4.0. Variance An aspect of generics that often comes across as surprising is that the following is illegal: IList<string> strings = new List<string>(); IList<object> objects = strings; The second assignment is disallowed because strings does not have the same element type as objects. There is a perfectly good reason for this. If it were allowed you could write: objects[0] = 5; string s = strings[0]; Allowing an int to be inserted into a list of strings and subsequently extracted as a string. This would be a breach of type safety. However, there are certain interfaces where the above cannot occur, notably where there is no way to insert an object into the collection. Such an interface is IEnumerable<T>. If instead you say: IEnumerable<object> objects = strings; There is no way we can put the wrong kind of thing into strings through objects, because objects doesn’t have a method that takes an element in. Variance is about allowing assignments such as this in cases where it is safe. The result is that a lot of situations that were previously surprising now just work. Covariance In .NET 4.0 the IEnumerable<T> interface will be declared in the following way: public interface IEnumerable<out T> : IEnumerable { IEnumerator<T> GetEnumerator(); } public interface IEnumerator<out T> : IEnumerator { bool MoveNext(); T Current { get; } } The “out” in these declarations signifies that the T can only occur in output position in the interface – the compiler will complain otherwise. In return for this restriction, the interface becomes “covariant” in T, which means that an IEnumerable<A> is considered an IEnumerable<B> if A has a reference conversion to B. As a result, any sequence of strings is also e.g. a sequence of objects. This is useful e.g. in many LINQ methods. Using the declarations above: var result = strings.Union(objects); // succeeds with an IEnumerable<object> This would previously have been disallowed, and you would have had to to some cumbersome wrapping to get the two sequences to have the same element type. Contravariance Type parameters can also have an “in” modifier, restricting them to occur only in input positions. An example is IComparer<T>: public interface IComparer<in T> { public int Compare(T left, T right); } The somewhat baffling result is that an IComparer<object> can in fact be considered an IComparer<string>! It makes sense when you think about it: If a comparer can compare any two objects, it can certainly also compare two strings. This property is referred to as contravariance. A generic type can have both in and out modifiers on its type parameters, as is the case with the Func<…> delegate types: public delegate TResult Func<in TArg, out TResult>(TArg arg); Obviously the argument only ever comes in, and the result only ever comes out. Therefore a Func<object,string> can in fact be used as a Func<string,object>. Limitations Variant type parameters can only be declared on interfaces and delegate types, due to a restriction in the CLR. Variance only applies when there is a reference conversion between the type arguments. For instance, an IEnumerable<int> is not an IEnumerable<object> because the conversion from int to object is a boxing conversion, not a reference conversion. Also please note that the CTP does not contain the new versions of the .NET types mentioned above. In order to experiment with variance you have to declare your own variant interfaces and delegate types. COM Example Here is a larger Office automation example that shows many of the new C# features in action. using System; using System.Diagnostics; using System.Linq; using Excel = Microsoft.Office.Interop.Excel; using Word = Microsoft.Office.Interop.Word; class Program { static void Main(string[] args) { var excel = new Excel.Application(); excel.Visible = true; excel.Workbooks.Add(); // optional arguments omitted excel.Cells[1, 1].Value = "Process Name"; // no casts; Value dynamically excel.Cells[1, 2].Value = "Memory Usage"; // accessed var processes = Process.GetProcesses() .OrderByDescending(p =&gt; p.WorkingSet) .Take(10); int i = 2; foreach (var p in processes) { excel.Cells[i, 1].Value = p.ProcessName; // no casts excel.Cells[i, 2].Value = p.WorkingSet; // no casts i++; } Excel.Range range = excel.Cells[1, 1]; // no casts Excel.Chart chart = excel.ActiveWorkbook.Charts. Add(After: excel.ActiveSheet); // named and optional arguments chart.ChartWizard( Source: range.CurrentRegion, Title: "Memory Usage in " + Environment.MachineName); //named+optional chart.ChartStyle = 45; chart.CopyPicture(Excel.XlPictureAppearance.xlScreen, Excel.XlCopyPictureFormat.xlBitmap, Excel.XlPictureAppearance.xlScreen); var word = new Word.Application(); word.Visible = true; word.Documents.Add(); // optional arguments word.Selection.Paste(); } } The code is much more terse and readable than the C# 3.0 counterpart. Note especially how the Value property is accessed dynamically. This is actually an indexed property, i.e. a property that takes an argument; something which C# does not understand. However the argument is optional. Since the access is dynamic, it goes through the runtime COM binder which knows to substitute the default value and call the indexed property. Thus, dynamic COM allows you to avoid accesses to the puzzling Value2 property of Excel ranges. Relationship with Visual Basic A number of the features introduced to C# 4.0 already exist or will be introduced in some form or other in Visual Basic: · Late binding in VB is similar in many ways to dynamic lookup in C#, and can be expected to make more use of the DLR in the future, leading to further parity with C#. · Named and optional arguments have been part of Visual Basic for a long time, and the C# version of the feature is explicitly engineered with maximal VB interoperability in mind. · NoPIA and variance are both being introduced to VB and C# at the same time. VB in turn is adding a number of features that have hitherto been a mainstay of C#. As a result future versions of C# and VB will have much better feature parity, for the benefit of everyone. Resources All available resources concerning C# 4.0 can be accessed through the C# Dev Center. Specifically, this white paper and other resources can be found at the Code Gallery site. Enjoy! span.fullpost {display:none;}

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  • 24 Hours of PASS: 15 Powerful Dynamic Management Objects - Deck and Demos

    - by Adam Machanic
    Thank you to everyone who attended today's 24 Hours of PASS webcast on Dynamic Management Objects! I was shocked, awed, and somewhat scared when I saw the attendee number peak at over 800. I really appreciate your taking time out of your day to listen to me talk. It's always interesting presenting to people I can't see or hear, so I relied on Twitter for a form of nearly real-time feedback. I would like to especially thank everyone who left me tweets both during and after the presentation. Your feedback...(read more)

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  • 24 Hours of PASS: 15 Powerful Dynamic Management Objects - Deck and Demos

    - by Adam Machanic
    Thank you to everyone who attended today's 24 Hours of PASS webcast on Dynamic Management Objects! I was shocked, awed, and somewhat scared when I saw the attendee number peak at over 800. I really appreciate your taking time out of your day to listen to me talk. It's always interesting presenting to people I can't see or hear, so I relied on Twitter for a form of nearly real-time feedback. I would like to especially thank everyone who left me tweets both during and after the presentation. Your feedback...(read more)

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  • Dynamic vs Statically typed languages for websites

    - by Bradford
    Wanted to hear what others thought about this statement: I’ll contrast that with building a website. When rendering web pages, often you have very many components interacting on a web page. You have buttons over here and little widgets over there and there are dozens of them on a webpage, as well as possibly dozens or hundreds of web pages on your website that are all dynamic. With a system with a really large surface area like that, using a statically typed language is actually quite inflexible. I would find it painful probably to program in Scala and render a web page with it, when I want to interactively push around buttons and what-not. If the whole system has to be coherent, like the whole system has to type check just to be able to move a button around, I think that can be really inflexible. Source: http://www.infoq.com/interviews/kallen-scala-twitter

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  • Looking for a dynamic programming solution

    - by krammer
    Given a sequence of integers in range 1 to n. Each number can appear at most once. Let there be a symbol X in the sequence which means remove the minimum element from the list. There can be an arbitrarily number of X in the sequence. Example: 1,3,4,X,5,2,X The output is 1,2. We need to find the best way to perform this operation. The solution I have been thinking is: Scan the sequence from left to right and count number of X which takes O(n) time. Perform partial sorting and find the k smallest elements (k = number of X) which takes O(n+klogk) time using median of medians. Is there a better way to solve this problem using dynamic programming or any other way ?

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  • W2k8 RC1: Windows Media Servers (WMS) as proxy

    - by da_didi
    I will have one streaming-server (W2k8, unknown streaming protocol [rtsp, mss, http]) and half dozen streaming-servers as proxies to save bandwidth. I have read the documentation and installed the modules, but I am unsure how I have to configure the proxy's according to http://technet.microsoft.com/de-de/library/ee126142(en-us,WS.10).aspx - as a proxy or reverse proxy and how I minimize the bandwidth needs between origin server and proxy's. What is the best way to realize my setup? Any short how-tos? How can I announce all players to use the proxy? Route all rtsp/mms/http-requests through my proxy? Announce the proxy with DHCP-releases? Thanks!

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