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• Web Services Primer for a WinForms Developer?

  - by Unicorns

  I've been writing client/server applications with Winforms for about six years now, but I have yet to venture into the web space (neither ASP.NET nor web services). Given the direction that the job market has been heading for some time and the fact that I have a basic curiosity, I'd like to get involved with writing web services, but I don't know where to start. I've read about various options (XML/SOAP vs. JSON, REST vs...well, actually I don't know what it's called, etc.), but I'm not sure what sort of criteria are in play when making the determination to use one or the other. Obviously, I'd like to leverage the tools that I have (Visual Studio, the .NET framework, etc.) without hamstringing myself into only targeting a particular audience (i.e. writing the service in such a way as to make it difficult to consume from a Windows Mobile/Android/iPhone client, for example). For the record, my plan--for now--is to use WCF for my web service development, but I'm open to using another .NET approach if that's advisable. I realize that this question is pretty open-ended so it may get closed, but here are some things I'm wondering: What are some things to consider when choosing the type of web service (REST, etc.) I intend to write? Is it possible (and, if so, feasible) to move from one approach to another? Can web services be written in an event-driven way? As I said I'm a Winforms developer, so I'm used to objects raising events for me to react to. For instance, if I have two clients connected to my service, is there a way for me to "push" information to one of them as a result of an action by the other? If this is possible, is this advisable or am I just not thinking about it correctly? What authentication mechanisms seem to work best for public-facing services? What about if I plan to have different types of OS'es and clients connecting to the service? Is there a generally accepted platform-agnostic approach? In the line of authentication, is this something that I should be doing myself (authenticating an managing sessions, etc.) or is this something should be handled at the framework level and I just define exactly how it should work? If that's the case, how do I tell who the requester has authenticated themselves as? I started writing an authentication mechanism (simple username/password combinations stored in the database and a corresponding session table with a GUID key) within my service and just requiring that key to be passed with every operation (other than logging in, of course), but I want to make sure that I'm not reinventing the wheel here. However, I also don't want to clutter up the server with a bunch of machine user accounts just to use Basic authentication. I'm also under the impression that Digest (and of course Windows) authentication requires a machine (or AD) user account.

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• Issues with LINQ (to Entity) [adding records]

  - by Mario

  I am using LINQ to Entity in a project, where I pull a bunch of data (from the database) and organize it into a bunch of objects and save those to the database. I have not had problems writing to the db before using LINQ to Entity, but I have run into a snag with this particular one. Here's the error I get (this is the "InnerException", the exception itself is useless!): New transaction is not allowed because there are other threads running in the session. I have seen that before, when I was trying to save my changes inside a loop. In this case, the loop finishes, and it tries to make that call, only to give me the exception. Here's the current code: try { //finalResult is a list of the keys to match on for the records being pulled foreach (int i in finalResult) { var queryEff = (from eff in dbMRI.MemberEligibility where eff.Member_Key == i && eff.EffDate >= DateTime.Now select eff.EffDate).Min(); if (queryEff != null) { //Add a record to the Process table Process prRecord = new Process(); prRecord.GroupData = qa; prRecord.Member_Key = i; prRecord.ProcessDate = DateTime.Now; prRecord.RecordType = "F"; prRecord.UsernameMarkedBy = "Autocard"; prRecord.GroupsId = qa.GroupsID; prRecord.Quantity = 2; prRecord.EffectiveDate = queryEff; dbMRI.AddObject("Process", prRecord); } } dbMRI.SaveChanges(); //<-- Crashes here foreach (int i in finalResult) { var queryProc = from pro in dbMRI.Process where pro.Member_Key == i && pro.UsernameMarkedBy == "Autocard" select pro; foreach (var qp in queryProc) { Audit aud = new Audit(); aud.Member_Key = i; aud.ProcessId = qp.ProcessId; aud.MarkDate = DateTime.Now; aud.MarkedByUsername = "Autocard"; aud.GroupData = qa; dbMRI.AddObject("Audit", aud); } } dbMRI.SaveChanges(); //<-- AND here (if the first one is commented out) } catch (Exception e) { //Do Something here } Basically, I need it to insert a record, get the identity for that inserted record and insert a record into another table with the identity from the first record. Given some other constraints, it is not possible to create a FK relationship between the two (I've tried, but some other parts of the app won't allow it, AND my DBA team for whatever reason hates FK's, but that's for a different topic :)) Any ideas what might be causing this? Thank!

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• mulformed Farsi characters on AWT

  - by jlover2010

  Hi As i started programming by jdk6, i had no problem in text components neither in awt nor in swing. But for labels or titles of awt components, yes : I couldn't have Farsi characters displayable on AWTs just as simple as Swing by typing them into the source code. lets check this SSCCE : import javax.swing.*; import java.awt.*; import java.io.*; import java.util.Properties; public class EmptyFarsiCharsOnAWT extends JFrame{ public EmptyFarsiCharsOnAWT() { super("????"); setDefaultCloseOperation(3); setVisible(rootPaneCheckingEnabled); } public static void main(String[] args) throws AWTException, IOException { JFrame jFrame = new EmptyFarsiCharsOnAWT(); MenuItem show ; // approach 1 = HardCoding : /* show = new MenuItem("\u0646\u0645\u0627\u06cc\u0634"); * */ // approach 2 = using simple utf-8 saved text file : /* BufferedReader in = new BufferedReader(new FileReader("farsiLabels.txt")); String showLabel = in.readLine(); in.close(); show = new MenuItem(showLabel); * */ // approach 3 = using properties file : FileReader in = new FileReader("farsiLabels.properties"); Properties farsiLabels = new Properties(); farsiLabels.load(in); show = new MenuItem(farsiLabels.getProperty("tray.show")); PopupMenu popUp = new PopupMenu(); popUp.add(show); // creating Tray object Image iconIamge = Toolkit.getDefaultToolkit().getImage("greenIcon.png"); TrayIcon trayIcon = new TrayIcon(iconIamge, null, popUp); SystemTray tray = SystemTray.getSystemTray(); tray.add(trayIcon); jFrame.setIconImage(iconIamge); } } Yes, i know each of three approaches in source code does right when you may test it from IDE , but if you make a JAR contains just this class (and its resources) by means of NetBeans project clean&build ,you won't see the expected characters and will just get EMPTY/BLANK SQUARES ! Unfortunately, opposed to other situations i encountered before, here there is no way to avoid using awt and make use of Swing in this case. And this was just an SSCCE i made to show the problem and my recent (also first) application suffers from this subject. And i think should have to let you know I posted this question a while ago in SDN and "the Java Ranch" forums and other native forums and still I'm watching... By the way i am using latest version of Netbeans IDE... I will be so grateful if anybody has a solution to this damn AWT components never rendered any Farsi character for me... Thanks in advance

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• JPA entity design / cannot delete entity

  - by timaschew

  I though its simple what I want, but I cannot find any solution for my problem. I'm using playframework 1.2.3 and it's using Hibernate as JPA. So I think playframework has nothing to do with the problem. I have some classes (I omit the nonrelevant fields) public class User { ... } public class Task { public DataContainer dataContainer; } public class DataContainer { public Session session; public User user; } public class Session { ... } So I have association from Task to DataContainer and from DataContainer to Sesssion and the DataContainer belongs to a User. The DataContainers can have always the same User, but the Session have to be different for each instance. And the DataContainer of a Task have also to be different in each instance. A DataContainer can have a Sesesion or not (it's optinal). I use only unidirectional assoc. It should be sufficient. In other words: Every Task must has one DataContainer. Every DataContainer must has one/the same User and can have one Session. To create a DB schema I use JPA annotations: @Entity public class User extends Model { ... } @Entity public class Task extends Model { @OneToOne(optional = false, cascade = CascadeType.ALL) public DataContainer dataContainer; } @Entity public class DataContainer extends Model { @OneToOne(optional = true, cascade = CascadeType.ALL) public Session session; @ManyToOne(optional = false, cascade = CascadeType.ALL) public User user; } @Entity public class Session extends Model { ... } BTW: Model is a play class and provides the primary id as long type. When I create some for each entity a object and 'connect them', I mean the associations, it works fine. But when I try to delete a Session, I get a constraint violation exception, because a DataContainer still refers to the Session I want to delete. I want that the Session (field) of the DataContainer will be set to null respectively the foreign key (session_id) should be unset in the database. This will be okay, because its optional. I don't know, I think I have multiple problems. Am I using the right annotation @OneToOne ? I found on the internet some additional annotation and attributes: @JoinColumn and a mappedBy attribute for the inverse relationship. But I don't have it, because its not bidirectional. Or is a bidirectional assoc. essentially? Another try was to use @OnDelete(action = OnDeleteAction.CASCADE) the the contraint changed from NO ACTIONs when update or delete to: ADD CONSTRAINT fk4745c17e6a46a56 FOREIGN KEY (session_id) REFERENCES annotation_session (id) MATCH SIMPLE ON UPDATE NO ACTION ON DELETE CASCADE; But in this case, when I delete a session, the DataContainer and User is deleted. That's wrong for me. EDIT: I'm using postgresql 9, the jdbc stuff is included in play, my only db config is db=postgres://app:app@localhost:5432/app

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• ASP.NET MVC 2 AJAX dilemma: Lose Models concept or create unmanageable JavaScript

  - by Slightly Frustrated

  Hi, Ok, let's assume we are working with ASP.NET MVC 2 (latest and greatest preview) and we want to create AJAX user interface with jQuery. So what are our real options here? Option 1 - Pass Json from the Controller to the view, and then the view submits Json back to the controller. This means (in the order given): User opens some View (let's say - /Invoices/January) which has to visualize a list of data (e.g. <IEnumerable<X.Y.Z.Models.Invoice>>) Controller retrieves the Model from the repository (assuming we are using repository pattern). Controller creates a new instance of a class which we will serialize to Json. The reasaon we do this, is because the model may not be serializable (circular reference ftl) Controller populates the soon-to-be-serialized class with data Controller serializes the class to Json and passes it the view. User does some change and submits the 'form' The View submits back Json to the controller The Controller now must 'manually' validate the input, because the Json passed does not bind to a Model See, if our View is communicating to the controller via Json, we lose the Model validation, which IMHO is incredible disadvantage. In this case, forget about data annotations and stuff. Option 2 - Ok, the alternative of the first approach is to pass the Models to the Views, which is the default behavior in the template when you start a new project. We pass a strong typed model to the view The view renders the appropriate html and javascript, sticking to the model property names. This is important! The user submits the form. If we stick to the model names, when we .serialize() the form and submit it to the controller it will map to a model. There is no Json mapping. The submitted form directly binds to a strongly typed model, hence, we can use the model validation. E.g. we keep the business logic where it should be. Problem with this approach is, if we refactor some of the Models (change property names, types, etc), the javascript we wrote would become invalid. We will have to manually refactor the scripting and hope we don't miss something. There is no way you can test it either. Ok, the question is - how to write an AJAX front end, which keeps the business logic validation in the model (e.g. controller passes and receives a Model type), but in the same time doesn't screw up the javascript and html when we refactor the model?

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• JSON or YAML encoding in GWT/Java on both client and server

  - by KennethJ

  I'm looking for a super simple JSON or YAML library (not particularly bothered which one) written in Java, and can be used in both GWT on the client, and in its original Java form on the server. What I'm trying to do is this: I have my models, which are shared between the client and the server, and these are the primary source of data interchange. I want to design the web service in between to be as simple as possible, and decided to take the RESTful approach. My problem is that I know our application will grow substantially in the future, and writing all the getters, setters, serialization, factories, etc. by hand fills me with absolute dread. So in order to avoid it, I decided to implement annotations to keep track of attributes on the models. The reason I can't just serialize everything directly, using GWT's own one, or one which works through reflection, is because we need a certain amount of logic going on in the serialization process. I.e. whether references to other models get serialized during the serialization of the original model, or whether an ID is just passed, and general simple things like that. I've then written an annotation processor to preprocess my shared models and generate an implementing class with all the getters, setters, serialization, lazy-loading, etc. To make a long story short, I need some type of simple YAML or JSON library, which allows me to encode and decode manually, so I can generate this code through my annotation processor. I have had a look around the interwebs, but every single one I ran into supported some reflection which, while all fine and dandy, make it pretty much useless for GWT. And in the case of GWT's own JSON library, it uses JSNI for speed purposes, making it useless server side. One solution I did think about involved writing writing two sets of serialization methods on the models, one for the client and one for the server, but I'd rather not do that. Also, I'm pretty new to GWT, and even though I have done a lot of Java, it was back in the 1.2 days, so it's a bit rusty. So if you think I'm going about this problem completely the wrong way, I'm open to suggestions.

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• Java program has errors, 80 lines of code

  - by user2961687

  I have a problem with a program. It contains a lot of errors in Eclipse. Sorry for my english and thank you in advance. Here is the task: I. Declare a class that contains private fields Jam: String taste, double weight Create constructors containing variables as parameters: (String taste, double weight), (double weight), (String taste). Parameters constructors should initialize class fields. In case the constructor does not provide the necessary parameter, it must be assumed that the field taste must have the value "No Name" and weight - 100.0. Introduce the use of all constructors creating objects that represent three kinds of jams. Note: it must be assumed that the only constructor with two parameters can be assigned to fields of the class. Declare a class Jar that contains the field Jam jam, a dedicated constructor initiating all declared fields and methods: open close isItOpen Next, create an object of class Jar and fill it with the selected type of jam, operations repeat for all the kinds of jams. This is my code this far: public class App { public static void main(String[] args) { Jam strawberry = new Jam("strawberry", 20.45); Jam raspberry = new Jam(40.50); Jam peach = new Jam("peach"); Jar jar_1 = new Jar(); Jar jar_2 = new Jar(); Jar jar_3 = new Jar(); jar_1.open(); jar_1.fillIn(strawberry); jar_2.fillIn(peach); jar_3.fillIn(raspberry); } } class Jam { String taste; double weight; public Jam(String taste, double weight) { this.taste = taste; this.weight = weight; } public Jam(double weight) { this.taste = "No name"; this.weight = weight; } public Jam(String taste) { this.taste = taste; this.weight = 100.0; } } class Jar { public Jam Jam = new Jam(); private String state_jar; public Jar() { Jam.weight = 0; Jam.taste = ""; state_jar = "closed"; } public static String open() { state_jar = open; return state_jar; } public static String close() { state_jar = "closed"; return state_jar; } public static boolean isItOpen() { return state_jar; } public void fillIn(Jam jam) { if (isItOpen == false) open(); this.Jam.weight = jam.weight; this.Jam.taste = jam.taste; this.Jam.close(); } }

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• many-to-many performance concerns with fluent nhibernate.

  - by Ciel

  I have a situation where I have several many-to-many associations. In the upwards of 12 to 15. Reading around I've seen that it's generally believed that many-to-many associations are not 'typical', yet they are the only way I have been able to create the associations appropriate for my case, so I'm not sure how to optimize any further. Here is my basic scenario. class Page { IList<Tag> Tags { get; set; } IList<Modification> Modifications { get; set; } IList<Aspect> Aspects { get; set; } } This is one of my 'core' classes, and coincidentally one of my core tables. Virtually half of the objects in my code can have an IList<Page>, and some of them have IList<T> where T has its own IList<Page>. As you can see, from an object oriented standpoint, this is not really a problem. But from a database standpoint this begins to introduce a lot of junction tables. So far it has worked fine for me, but I am wondering if anyone has any ideas on how I could improve on this structure. I've spent a long time thinking and in order to achieve the appropriate level of association required, I cannot think of any way to improve it. The only thing I have come up with is to make intermediate classes for each object that has an IList<Page>, but that doesn't really do anything that the HasManyToMany does not already do except introduce another class. It does not extend the functionality and, from what I can tell, it does not improve performance. Any thoughts? I am also concerned about Primary Key limits in this scenario. Most everything needs to be able to have these properties, but the Pages cannot be unique to each object, because they are going to be frequently shared and joined between multiple objects. All relationships are one-sided. (That is, a Page has no knowledge of what owns it). Because of this, I also have no Inverse() mapped HasManyToMany collections. Also, I have read the similar question : Usage of ORMs like NHibernate when there are many associations - performance concerns But it really did not answer my concerns.

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• dynamic button in jsp

  - by kawtousse

  hi everyone, in my jsp i have a table constructed dynamically like the following: retour.append("<tr>"); try { s= HibernateUtil.currentSession(); tx=s.beginTransaction(); Query query = s.createQuery(HQL_QUERY); for(Iterator it=query.iterate();it.hasNext();) { if(it.hasNext()){ Dailytimesheet object=(Dailytimesheet)it.next(); retour.append("<td>" +object.getActivity() +"</td>"); retour.append("<td>" +object.getProjectCode() + "</td>"); retour.append("<td>" +object.getWAName() + "</td>"); retour.append("<td>" +object.getTaskCode() +"</td>"); retour.append("<td>" +object.getTimeFrom() +"</td>"); retour.append("<td>" +object.getTimeSpent() + "</td>"); retour.append("<td>" +object.getPercentTaskComplete() + "</td>"); if (droitdaccess) { retour.append(""); retour.append(""); retour.append(""); retour.append("<td bordercolor=#FFFFFF>"); retour.append("<input type=\"hidden\" id=\"id_"+nomTab+"_"+compteur+"\" value=\""+object.getIdDailyTimeSheet()+"\"/>"); retour.append("<img src=\"icon_delete.gif\" onClick=\"deletearowById('id_"+nomTab+"_"+compteur+"')\" style=\"cursor:pointer\" name=\"action\" value=\"deleting\" />"); retour.append("</td>"); } } compteur++; retour.append("</tr>"); } //terminer la table. retour.append ("</table>"); next to the table i want to display a button named send in order to send the table content. I do not really want to dispaly this button where the table is empty. So at least if the table is populated by nly one record i want that button being displayed. How should i deal in this case. Thanks.

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• Flatten date range memberships retaining only the highest priority membership (TRANSACT-SQL)

  - by shadowranger

  Problem statement: A table contains an item_id, a category_id and a date range (begin_date and end_date). No item may be in more than one category on any given date (in general; during daily rebuilding it can be in an invalid state temporarily). By default, all items are added (and re-added if removed) to a category (derived from outside data) automatically on a daily basis, and their membership in that category matches the lifespan of the item (items have their own begin and end date, and usually spend their entire lives in the same category, which is why this matches). For items in category X, it is occasionally desirable to override the default category by adding them to category Y. Membership in category Y could entirely replace membership in category X (that is, the begin and end dates for membership in category Y would match the begin and end dates of the item itself), or it could override it for an arbitrary period of time (at the beginning, middle or end the item's lifespan, possibly overriding for short periods at multiple times). Membership in category Y is not renewed automatically and additions to that category is done by manual data entry. Every day, when category X is rebuilt, we get an overlap, where any item in category Y will now be in category X as well (which is forbidden, as noted previously). Goal: After each repopulation of category X (which is done in a rather complicated and fragile manner, and ideally would be left alone), I'm trying to find an efficient means of writing a stored procedure that: Identifies the overlaps Changes existing entries, adds new ones where necessary (such as in the case where an item starts in category X, switches to category Y, then eventually switches back to category X before ending), or removes entries (when an item is in category Y for its entire life) such that every item remains in category Y (and only Y) where specified, while category X membership is maintained when not overridden by category Y. Does not affect memberships of categories A, B, C, Z, etc., which do not have override categories and are built separately, by completely different rules. Note: It can be assumed that X membership covers the entire lifespan of the item before this procedure is called, so it is unnecessary to query any data outside this table. Bonus credit: If for some reason there are two adjacent or overlapping memberships in for the same item in category Y, stitching them together into a single entry is appreciated, but not necessary. Example: item_id category_id begin_date end_date 1 X 20080101 20090628 1 Y 20090101 20090131 1 Y 20090601 20090628 2 X 20080201 20080731 2 Y 20080201 20080731 Should become: item_id category_id begin_date end_date 1 X 20080101 20081231 1 Y 20090101 20090131 1 X 20090201 20090531 1 Y 20090601 20090628 2 Y 20080201 20080731 If it matters, this needs to work on SQL Server 2005 and SQL Server 2008

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• C++0x Overload on reference, versus sole pass-by-value + std::move?

  - by dean

  It seems the main advice concerning C++0x's rvalues is to add move constructors and move operators to your classes, until compilers default-implement them. But waiting is a losing strategy if you use VC10, because automatic generation probably won't be here until VC10 SP1, or in worst case, VC11. Likely, the wait for this will be measured in years. Here lies my problem. Writing all this duplicate code is not fun. And it's unpleasant to look at. But this is a burden well received, for those classes deemed slow. Not so for the hundreds, if not thousands, of smaller classes. ::sighs:: C++0x was supposed to let me write less code, not more! And then I had a thought. Shared by many, I would guess. Why not just pass everything by value? Won't std::move + copy elision make this nearly optimal? Example 1 - Typical Pre-0x constructor OurClass::OurClass(const SomeClass& obj) : obj(obj) {} SomeClass o; OurClass(o); // single copy OurClass(std::move(o)); // single copy OurClass(SomeClass()); // single copy Cons: A wasted copy for rvalues. Example 2 - Recommended C++0x? OurClass::OurClass(const SomeClass& obj) : obj(obj) {} OurClass::OurClass(SomeClass&& obj) : obj(std::move(obj)) {} SomeClass o; OurClass(o); // single copy OurClass(std::move(o)); // zero copies, one move OurClass(SomeClass()); // zero copies, one move Pros: Presumably the fastest. Cons: Lots of code! Example 3 - Pass-by-value + std::move OurClass::OurClass(SomeClass obj) : obj(std::move(obj)) {} SomeClass o; OurClass(o); // single copy, one move OurClass(std::move(o)); // zero copies, two moves OurClass(SomeClass()); // zero copies, one move Pros: No additional code. Cons: A wasted move in cases 1 & 2. Performance will suffer greatly if SomeClass has no move constructor. What do you think? Is this correct? Is the incurred move a generally acceptable loss when compared to the benefit of code reduction?

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• IP address numbers in MySQL subquery

  - by Iain Collins

  I have a problem with a subquery involving IPV4 addresses stored in MySQL (MySQL 5.0). The IP addresses are stored in two tables, both in network number format - e.g. the format output by MySQL's INET_ATON(). The first table ('events') contains lots of rows with IP addresses associated with them, the second table ('network_providers') contains a list of provider information for given netblocks. events table (~4,000,000 rows): event_id (int) event_name (varchar) ip_address (unsigned 4 byte int) network_providers table (~60,000 rows): ip_start (unsigned 4 byte int) ip_end (unsigned 4 byte int) provider_name (varchar) Simplified for the purposes of the problem I'm having, the goal is to create an export along the lines of: event_id,event_name,ip_address,provider_name If do a query along the lines of either of the following, I get the result I expect: SELECT provider_name FROM network_providers WHERE INET_ATON('192.168.0.1') >= network_providers.ip_start ORDER BY network_providers.ip_start DESC LIMIT 1 SELECT provider_name FROM network_providers WHERE 3232235521 >= network_providers.ip_start ORDER BY network_providers.ip_start DESC LIMIT 1 That is to say, it returns the correct provider_name for whatever IP I look up (of course I'm not really using 192.168.0.1 in my queries). However, when performing this same query as a subquery, in the following manner, it doesn't yield the result I would expect: SELECT event.id, event.event_name, (SELECT provider_name FROM network_providers WHERE event.ip_address >= network_providers.ip_start ORDER BY network_providers.ip_start DESC LIMIT 1) as provider FROM events Instead the a different (incorrect) value for network_provider is returned - over 90% (but curiously not all) values returned in the provider column contain the wrong provider information for that IP. Using event.ip_address in a subquery just to echo out the value confirms it contains the value I'd expect and that the subquery can parse it. Replacing event.ip_address with an actual network number also works, just using it dynamically in the subquery in this manner that doesn't work for me. I suspect the problem is there is something fundamental and important about subqueries in MySQL that I don't get. I've worked with IP addresses like this in MySQL quite a bit before, but haven't previously done lookups for them using a subquery. The question: I'd really appreciate an example of how I could get the output I want, and if someone here knows, some enlightenment as to why what I'm doing doesn't work so I can avoid making this mistake again. Notes: The actual real-world usage I'm trying to do is considerably more complicated (involving joining two or three tables). This is a simplified version, to avoid overly complicating the question. Additionally, I know I'm not using a between on ip_start & ip_end - that's intentional (the DB's can be out of date, and such cases the owner in the DB is almost always in the next specified range and 'best guess' is fine in this context) however I'm grateful for any suggestions for improvement that relate to the question. Efficiency is always nice, but in this case absolutely not essential - any help appreciated.

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• Interoperability between two AES algorithms

  - by lpfavreau

  Hello, I'm new to cryptography and I'm building some test applications to try and understand the basics of it. I'm not trying to build the algorithms from scratch but I'm trying to make two different AES-256 implementation talk to each other. I've got a database that was populated with this Javascript implementation stored in Base64. Now, I'm trying to get an Objective-C method to decrypt its content but I'm a little lost as to where the differences in the implementations are. I'm able to encrypt/decrypt in Javascript and I'm able to encrypt/decrypt in Cocoa but cannot make a string encrypted in Javascript decrypted in Cocoa or vice-versa. I'm guessing it's related to the initialization vector, nonce, counter mode of operation or all of these, which quite frankly, doesn't speak to me at the moment. Here's what I'm using in Objective-C, adapted mainly from this and this: @implementation NSString (Crypto) - (NSString *)encryptAES256:(NSString *)key { NSData *input = [self dataUsingEncoding: NSUTF8StringEncoding]; NSData *output = [NSString cryptoAES256:input key:key doEncrypt:TRUE]; return [Base64 encode:output]; } - (NSString *)decryptAES256:(NSString *)key { NSData *input = [Base64 decode:self]; NSData *output = [NSString cryptoAES256:input key:key doEncrypt:FALSE]; return [[[NSString alloc] initWithData:output encoding:NSUTF8StringEncoding] autorelease]; } + (NSData *)cryptoAES256:(NSData *)input key:(NSString *)key doEncrypt:(BOOL)doEncrypt { // 'key' should be 32 bytes for AES256, will be null-padded otherwise char keyPtr[kCCKeySizeAES256 + 1]; // room for terminator (unused) bzero(keyPtr, sizeof(keyPtr)); // fill with zeroes (for padding) // fetch key data [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding]; NSUInteger dataLength = [input length]; // See the doc: For block ciphers, the output size will always be less than or // equal to the input size plus the size of one block. // That's why we need to add the size of one block here size_t bufferSize = dataLength + kCCBlockSizeAES128; void* buffer = malloc(bufferSize); size_t numBytesCrypted = 0; CCCryptorStatus cryptStatus = CCCrypt(doEncrypt ? kCCEncrypt : kCCDecrypt, kCCAlgorithmAES128, kCCOptionECBMode | kCCOptionPKCS7Padding, keyPtr, kCCKeySizeAES256, nil, // initialization vector (optional) [input bytes], dataLength, // input buffer, bufferSize, // output &numBytesCrypted ); if (cryptStatus == kCCSuccess) { // the returned NSData takes ownership of the buffer and will free it on deallocation return [NSData dataWithBytesNoCopy:buffer length:numBytesCrypted]; } free(buffer); // free the buffer; return nil; } @end Of course, the input is Base64 decoded beforehand. I see that each encryption with the same key and same content in Javascript gives a different encrypted string, which is not the case with the Objective-C implementation that always give the same encrypted string. I've read the answers of this post and it makes me believe I'm right about something along the lines of vector initialization but I'd need your help to pinpoint what's going on exactly. Thank you!

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• Using empty row as default in a ComboBox with Style "DropDownList"?

  - by Pesche Helfer

  Hi board I am trying to write a method, that takes a ComboBox, a DataTable and a TextBox as arguments. The purpose of it is to filter the members displayed in the ComboBox according to the TextBox.Text. The DataTable contains the entire list of possible entries that will then be filtered. For filtering, I create a DataView of the DataTable, add a RowFilter and then bind this View to the ComboBox as DataSource. To prevent the user from typing into the ComboBox, I choose the DropDownStyle DropDownList. That’s working fine so far, except that the user should also be able to choose nothing / empty line. In fact, this should be the default member to be displayed (to prevent choosing a wrong member by accident, if the user clicks through the dialog too fast). I tried to solve this problem by adding a new Row to the view. While this works for some cases, the main issue here is that any DataTable can be passed to the method. If the DataTable contains columns that cannot be null and don’t contain a default value, I suppose I will raise an error by adding an empty row. A possibility would be to create a view that contains only the column that is defined as DisplayMember, and the one that is defined as ValueMember. Alas, this can’t be done with a view in C#. I would like to avoid creating a true copy of the DataTable at all cost, since who knows how big it will get with time. Do you have any suggestions how to get around this problem? Instead of a view, could I create an object containing two members and assign the DisplayMember and the ValueMember to these members? Would the members be passed as reference (what I hope) or would true copied be created (in which case it would not be a solution)? Thank you very much for your help! Best regards public static void ComboFilter(ComboBox cb, DataTable dtSource, TextBox filterTextBox) { cb.DropDownStyle = ComboBoxStyle.DropDownList; string displayMember = cb.DisplayMember; DataView filterView = new DataView(dtSource); filterView.AddNew(); filterView.RowFilter = displayMember + " LIKE '%" + filterTextBox.Text + "%'"; cb.DataSource = filterView; }

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• In Ruby, how does coerce() actually work?

  - by Jian Lin

  It is said that when we have a class Point and knows how to perform point * 3 like the following: class Point def initialize(x,y) @x, @y = x, y end def *(c) Point.new(@x * c, @y * c) end end point = Point.new(1,2) p point p point * 3 Output: #<Point:0x336094 @x=1, @y=2> #<Point:0x335fa4 @x=3, @y=6> but then, 3 * point is not understood: Point can't be coerced into Fixnum (TypeError) So we need to further define an instance method coerce: class Point def coerce(something) [self, something] end end p 3 * point Output: #<Point:0x3c45a88 @x=3, @y=6> So it is said that 3 * point is the same as 3.*(point) that is, the instance method * takes an argument point and invoke on the object 3. Now, since this method * doesn't know how to multiply a point, so point.coerce(3) will be called, and get back an array: [point, 3] and then * is once again applied to it, is that true? point * 3 which is the same as point.*(3) and now, this is understood and we now have a new Point object, as performed by the instance method * of the Point class. The question is: 1) who invokes point.coerce(3) ? Is it Ruby automatically, or is it some code inside of * method of Fixnum by catching an exception? Or is it by case statement that when it doesn't know one of the known types, then call coerce? 2) Does coerce always need to return an array of 2 elements? Can it be no array? Or can it be an array of 3 elements? 3) And is the rule that, the original operator (or method) * will then be invoked on element 0, with the argument of element 1? (element 0 and element 1 are the two elements in that array returned by coerce) Who does it? Is it done by Ruby or is it done by code in Fixnum? If it is done by code in Fixnum, then it is a "convention" that everybody follows when doing a coerce? So could it be the code in * of Fixnum do something like this: if (something.typeof? ...) else if ... # other type else if ... # other type else # if it is not a type I know array = something.coerce(self) return array[0].*(array[1]) end

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• How to change the extension of a processed xml file (using eXist & cocoon)

  - by Carsten C.

  Hi all, I'm really new to this whole web stuff, so please be nice if I missed something important to post. Short: Is there a possibility to change the name of a processed file (eXist-DB) after serialization? Here my case, the following request to my eXist-db: http://localhost:8080/exist/cocoon/db/caos/test.xml and I want after serialization the follwing (xslt is working fine): http://localhost:8080/exist/cocoon/db/caos/test.html I'm using the followong sitemap.xmap with cocoon (hoping this is responsible for it) <map:match pattern="db/caos/**"> <!-- if we have an xpath query --> <map:match pattern="xpath" type="request-parameter"> <map:generate src="xmldb:exist:///db/caos/{../1}/#{1}"/> <map:act type="request"> <map:parameter name="parameters" value="true"/> <map:parameter name="default.howmany" value="1000"/> <map:parameter name="default.start" value="1"/> <map:transform type="filter"> <map:parameter name="element-name" value="result"/> <map:parameter name="count" value="{howmany}"/> <map:parameter name="blocknr" value="{start}"/> </map:transform> <map:transform src=".snip./webapp/stylesheets/db2html.xsl"> <map:parameter name="block" value="{start}"/> <map:parameter name="collection" value="{../../1}"/> </map:transform> </map:act> <map:serialize type="html" encoding="UTF-8"/> </map:match> <!-- if the whole file will be displayed --> <map:generate src="xmldb:exist:/db/caos/{1}"/> <map:transform src="..snip../stylesheets/caos2soac.xsl"> <map:parameter name="collection" value="{1}"/> </map:transform> <map:transform type="encodeURL"/> <map:serialize type="html" encoding="UTF-8"/> </map:match> So my Question is: How do I change the extension of the test.xml to test.html after processing the xml file? Background: I'm generating some information out of some xml-dbs, this infos will be displayed in html (which is working), but i want to change some entrys later, after I generated the html site. To make this confortable, I want to use Jquery & Jeditable, but the code does not work on the xml files. Saving the generated html is not an option. tia for any suggestions [and|or] help CC Edit: After reading all over: could it be, that the extension is irrelevant and that this is only a problem of port 8080? I'm confused...

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• Need help converting Ruby code to php code

  - by newprog

  Yesterday I posted this queston. Today I found the code which I need but written in Ruby. Some parts of code I have understood (I don't know Ruby) but there is one part that I can't. I think people who know ruby and php can help me understand this code. def do_create(image) # Clear any old info in case of a re-submit FIELDS_TO_CLEAR.each { |field| image.send(field+'=', nil) } image.save # Compose request vm_params = Hash.new # Submitting a file in ruby requires opening it and then reading the contents into the post body file = File.open(image.filename_in, "rb") # Populate the parameters and compute the signature # Normally you would do this in a subroutine - for maximum clarity all # parameters are explicitly spelled out here. vm_params["image"] = file # Contents will be read by the multipart object created below vm_params["image_checksum"] = image.image_checksum vm_params["start_job"] = 'vectorize' vm_params["image_type"] = image.image_type if image.image_type != 'none' vm_params["image_complexity"] = image.image_complexity if image.image_complexity != 'none' vm_params["image_num_colors"] = image.image_num_colors if image.image_num_colors != '' vm_params["image_colors"] = image.image_colors if image.image_colors != '' vm_params["expire_at"] = image.expire_at if image.expire_at != '' vm_params["licensee_id"] = DEVELOPER_ID #in php it's like this $vm_params["sequence_number"] = -rand(100000000);????? vm_params["sequence_number"] = Kernel.rand(1000000000) # Use a negative value to force an error when calling the test server vm_params["timestamp"] = Time.new.utc.httpdate string_to_sign = CREATE_URL + # Start out with the URL being called... #vm_params["image"].to_s + # ... don't include the file per se - use the checksum instead vm_params["image_checksum"].to_s + # ... then include all regular parameters vm_params["start_job"].to_s + vm_params["image_type"].to_s + vm_params["image_complexity"].to_s + # (nil.to_s => '', so this is fine for vm_params we don't use) vm_params["image_num_colors"].to_s + vm_params["image_colors"].to_s + vm_params["expire_at"].to_s + vm_params["licensee_id"].to_s + # ... then do all the security parameters vm_params["sequence_number"].to_s + vm_params["timestamp"].to_s vm_params["signature"] = sign(string_to_sign) #no problem # Workaround class for handling multipart posts mp = Multipart::MultipartPost.new query, headers = mp.prepare_query(vm_params) # Handles the file parameter in a special way (see /lib/multipart.rb) file.close # mp has read the contents, we can close the file now response = post_form(URI.parse(CREATE_URL), query, headers) logger.info(response.body) response_hash = ActiveSupport::JSON.decode(response.body) # Decode the JSON response string ##I have understood below def sign(string_to_sign) #logger.info("String to sign: '#{string_to_sign}'") Base64.encode64(HMAC::SHA1.digest(DEVELOPER_KEY, string_to_sign)) end # Within Multipart modul I have this: class MultipartPost BOUNDARY = 'tarsiers-rule0000' HEADER = {"Content-type" => "multipart/form-data, boundary=" + BOUNDARY + " "} def prepare_query (params) fp = [] params.each {|k,v| if v.respond_to?(:read) fp.push(FileParam.new(k, v.path, v.read)) else fp.push(Param.new(k,v)) end } query = fp.collect {|p| "--" + BOUNDARY + "\r\n" + p.to_multipart }.join("") + "--" + BOUNDARY + "--" return query, HEADER end end end Thanks for your help.

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• What Amazon S3 .NET Library is most useful and efficient?

  - by Geo

  There are two main open source .net Amazon S3 libraries. Three Sharp LitS3 I am currently using LitS3 in our MVC demo project, but there is some criticism about it. Has anyone here used both libraries so they can give an objective point of view. Below some sample calls using LitS3: On demo controller: private S3Service s3 = new S3Service() { AccessKeyID = "Thekey", SecretAccessKey = "testing" }; public ActionResult Index() { ViewData["Message"] = "Welcome to ASP.NET MVC!"; return View("Index",s3.GetAllBuckets()); } On demo view: <% foreach (var item in Model) { %> <p> <%= Html.Encode(item.Name) %> </p> <% } %> EDIT 1: Since I have to keep moving and there is no clear indication of what library is more effective and kept more up to date, I have implemented a repository pattern with an interface that will allow me to change library if I need to in the future. Below is a section of the S3Repository that I have created and will let me change libraries in case I need to: using LitS3; namespace S3Helper.Models { public class S3Repository : IS3Repository { private S3Service _repository; #region IS3Repository Members public IQueryable<Bucket> FindAllBuckets() { return _repository.GetAllBuckets().AsQueryable(); } public IQueryable<ListEntry> FindAllObjects(string BucketName) { return _repository.ListAllObjects(BucketName).AsQueryable(); } #endregion If you have any information about this question please let me know in a comment, and I will get back and edit the question. EDIT 2: Since this question is not getting attention, I integrated both libraries in my web app to see the differences in design, I know this is probably a waist of time, but I really want a good long run solution. Below you will see two samples of the same action with the two libraries, maybe this will motivate some of you to let me know your thoughts. WITH THREE SHARP LIBRARY: public IQueryable<T> FindAllBuckets<T>() { List<string> list = new List<string>(); using (BucketListRequest request = new BucketListRequest(null)) using (BucketListResponse response = service.BucketList(request)) { XmlDocument bucketXml = response.StreamResponseToXmlDocument(); XmlNodeList buckets = bucketXml.SelectNodes("//*[local-name()='Name']"); foreach (XmlNode bucket in buckets) { list.Add(bucket.InnerXml); } } return list.Cast<T>().AsQueryable(); } WITH LITS3 LIBRARY: public IQueryable<T> FindAllBuckets<T>() { return _repository.GetAllBuckets() .Cast<T>() .AsQueryable(); }

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• Should I add try/catch around when casting on an attribute of JSP implicit object?

  - by Michael Mao

  Hi all: Basically what I mean is like this: List<String[]> routes = (List<String[]>)application.getAttribute("routes"); For the above code, it tries to get an attribute named "routes" from the JSP implicit object - application. But as everyone knows, after this line of code, routes may very well contains a null - which means this application hasn't got an attribute named "routes". Is this "casting on null" good programming practice in Java or not? Basically I try to avoid exceptions such as java.io.InvalidCastException I reckon things like this are more as "heritage" of Java 1.4 when generic types were not introduced to this language. So I guess everything stored in application attributes as Objects (Similar to traditional ArrayList). And when you do "downcast", there might be invalid casts. What would you do in this case? Update: Just found that although in the implicit object application I did store a List of String arrays, when I do this : List<double[]> routes = (List<double[]>)application.getAttribute("routes"); It doesn't produce any error... And I felt not comfortable already... And even with this code: out.print(routes.get(0)); It does print out something strange : [Ljava.lang.String;@18b352f Am I printing a "pointer to String"? I can finally get an exception like this: out.print(routes.get(0)[1]); with error : java.lang.ClassCastException: [Ljava.lang.String; Because it was me to add the application attribute, I know which type should it be cast to. I feel this is not "good enough", what if I forget the exact type? I know there are still some cases where this sort of thing would happen, such as in JSP/Servlet when you do casting on session attributes. Is there a better way to do this? Before you say:"OMG, why you don't use Servlets???", I should justify my reason as this: - because my uni sucks, its server can only work with Servlets generated by JSP, and I don't really want to learn how to fix issues like that. look at my previous question on this , and this is uni homework, so I've got no other choice, forget all about war, WEB-INF,etc, but "code everything directly into JSP" - because the professors do that too. :)

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• Question about Architecture for Viewing Images in ASP.NET MVC App

  - by Charlie Flowers

  I have an approach in mind for an image viewer in a web app, and want to get a sanity check and any thoughts you stackoverflowers might have. Here's the whirlwind nutshell summary: I'm working on an ASP.NET MVC application that will run in my company's retail stores. Even though it is a web application, we own the store machines and have control over them. We have a "windows agent" running on the store machine which we can talk to from the browser via javascript (it is a WCF service, and our web app has permission to talk to it from the browser). One of the web pages needs to be an "image viewer" page with some common things like Rotate & Zoom. Now, there are some WebForms controls that offer Rotate and Zoom. However, they take up server resources and generate a good bit of traffic between the server and the browser. For example, the Rotate function would cause an ajax call to the server, which would then generate a new image written to a .NET Canvas object, which would then be written to a file on the server, which would then be returned from the ajax call and refreshed inside the browser. Normally, that's a pretty good way of doing things. But in our case, we have code running on the store machine that we can communicate with. This leads me to consider the following approach: When the user asks to view an image, we tell our "windows agent" to download it from our image server to the store machine. We then redirect our browser to our image viewer page, which will pull the image from the local file we just wrote to the store machine. When the user clicks "Rotate", we cause JavaScript code in the browser to call our "windows agent" software, asking it to perform the "Rotate" function. The "windows agent" does the rotation using the same kind of imaging control that would formerly have been used on the server, but it does so now on the store machine. Javascript in the browser then refreshes the image on the page to show the newly rotated image. Zoom and similar features would be implemented the same way. This seems to be much more efficient, scalable, and responsive for the end-users. However, I've never heard of anything like it being done, mostly because it's rare to have this combination of a web app plus a "windows agent" on the client machine. What do you think? Feasible? Reasonable? Any pitfalls I overlooked or improvements / suggestions you can see? Has anyone done anything like this who would like to offer the wisdom of experience? Thanks!

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• How to pass parameters to Apache Pivot's wtkx:include tag?

  - by Andrew Swan

  I need to create a reusable UI component that accepts a number of parameters (e.g. an image URL and some label text), similar to how JSP tags can accept parameters. The Pivot docs for the "wtkx:include" tag say: The tag allows a WTKX file to embed content defined in an external WTKX file as if it was defined in the source file itself. This is useful for ... defining reusable content templates I was hoping that I could define my component in a WTKX file using standard Pivot components (e.g. a TextInput) and pass it one or more parameters; for example my reusable template called "row.wtkx" might contain a row with an image and a text field, like this (where the ${xxx} bits are the parameters): <TablePane.Row xmlns="org.apache.pivot.wtk"> <ImageView image="@images/${image_url}" /> <TextInput text="${title}" /> </TablePane.Row> I could then reuse this component within a TablePane as follows: <rows> <TablePane.Row> <Label text="Painting"/> <Label text="Title"/> </TablePane.Row> <wtkx:include src="row.wtkx" image_url="mona_lisa.jpg" title="Mona Lisa"/> <wtkx:include src="row.wtkx" image_url="pearl_earring.jpg" title="Girl with a Pearl Earring"/> <wtkx:include src="row.wtkx" image_url="melting_clocks.jpg" title="Melting Clocks"/> </rows> I've made up the ${...} syntax myself just to show what I'm trying to do. Also, there could be other ways to pass the parameter values other than using attributes of the "wtkx:include" tag itself, e.g. pass a JSON-style map called say "args". The ability to pass parameters like this would make the include tag much more powerful, e.g. in my case allow me to eliminate a lot of duplication between the table row declarations. Or is "wtkx:include" not the right way to be doing this?

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• JSF 2.0: Preserving component state across multiple views

  - by tlind

  The web application I am developing using MyFaces 2.0.3 / PrimeFaces 2.2RC2 is divided into a content and a navigation area. In the navigation area, which is included into multiple pages using templating (i.e. <ui:define>), there are some widgets (e.g. a navigation tree, collapsible panels etc.) of which I want to preserve the component state across views. For example, let's say I am on the home page. When I navigate to a product details page by clicking on a product in the navigation tree, my Java code triggers a redirect using navigationHandler.handleNavigation(context, null, "/detailspage.jsf?faces-redirect=true") Another way of getting to that details page would be by directly clicking on a product teaser that is shown on the home page. The corresponding <h:link> would lead us to the details page. In both cases, the expansion state of my navigation tree (a PrimeFaces tree component) and my collapsible panels is lost. I understand this is because the redirect / h:link results in the creation of a new view. What is the best way of dealing with this? I am already using MyFaces Orchestra in my project along with its conversation scope, but I am not sure if this is of any help here (since I'd have to bind the expansion/collapsed state of the widgets to a backing bean... but as far as I know, this is not possible). Is there a way of telling JSF which component states to propagate to the next view, assuming that the same component exists in that view? I guess I could need a pointer into the right direction here. Thanks! Update 1: I just tried binding the panels and the tree to a session-scoped bean, but this seems to have no effect. Also, I guess I would have to bind all child components (if any) manually, so this doesn't seem like the way to go. Update 2: Binding UI components to non-request scoped beans is not a good idea (see link I posted in a comment below). If there is no easier approach, I might have to proceed as follows: When a panel is collapsed or the tree is expanded, save the current state in a session-scoped backing bean (!= the UI component itself) The components' states are stored in a map. The map key is the component's (hopefully) unique, relative ID. I cannot use the whole absolute component path here, since the IDs of the parent naming containers might change if the view changes, assuming these IDs are generated programmatically. As soon as a new view gets constructed, retrieve the components' states from the map and apply them to the components. For example, in case of the panels, I can set the collapsed attribute to a value retrieved from my session-scoped backing bean.

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• Using a Button to navigate to another Page in a NavigationWindow

  - by Will

  I'm trying to use the navigation command framework in WPF to navigate between Pages within a WPF application (desktop; not XBAP or Silverlight). I believe I have everything configured correctly, yet its not working. I build and run without errors, I'm not getting any binding errors in the Output window, but my navigation button is disabled. Here's the app.xaml for a sample app: <Application x:Class="Navigation.App" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" StartupUri="First.xaml"> </Application> Note the StartupUri points to First.xaml. First.xaml is a Page. WPF automatically hosts my page in a NavigationWindow. Here's First.xaml: <Page x:Class="Navigation.First" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="First"> <Grid> <Button CommandParameter="/Second.xaml" CommandTarget="{Binding RelativeSource= {RelativeSource FindAncestor, AncestorType={x:Type NavigationWindow}}}" Command="NavigationCommands.GoToPage" Content="Go!"/> </Grid> </Page> The button's CommandTarget is set to the NavigationWindow. The command is GoToPage, and the page is /Second.xaml. I've tried setting the CommandTarget to the containing Page, the CommandParameter to "Second.xaml" (First.xaml and Second.xaml are both in the root of the solution), and I've tried leaving the CommandTarget empty. I've also tried setting the Path to the Binding to various navigational-related public properties on the NavigationWindow. Nothing has worked so far. What am I missing here? I really don't want to do my navigation in code. Clarification. If, instead of using a button, I use a Hyperlink: <Grid> <TextBlock> <Hyperlink NavigateUri="Second.xaml">Go! </Hyperlink> </TextBlock> </Grid> everything works as expected. However, my UI requirements means that using a Hyperlink is right out. I need a big fatty button for people to press. That's why I want to use the button to navigate. I just want to know how I can get the Button to provide the same ability that the Hyperlink does in this case.

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• C# - calling ext. DLL function containing Delphi "variant record" parameter

  - by CaldonCZE

  Hello, In external (Delphi-created) DLL I've got the following function that I need to call from C# application. function ReadMsg(handle: longword; var Msg: TRxMsg): longword; stdcall; external 'MyDll.dll' name 'ReadMsg'; The "TRxMsg" type is variant record, defined as follows: TRxMsg = record case TypeMsg: byte of 1: (accept, mask: longword); 2: (SN: string[6]); 3: (rx_rate, tx_rate: word); 4: (rx_status, tx_status, ctl0, ctl1, rflg: byte); end; In order to call the function from C#, I declared auxiliary structure "my9Bytes" containing array of bytes and defined that it should be marshalled as 9 bytes long array (which is exactly the size of the Delphi record). private struct my9Bytes { [MarshalAs(UnmanagedType.ByValArray, ArraySubType = UnmanagedType.U1, SizeConst = 9)] public byte[] data; } Then I declared the imported "ReadMsg" function, using the "my9bytes" struct. [DllImport("MyDll.dll")] private static extern uint ReadMsg(uint handle, ref my9Bytes myMsg); I can call the function with no problem... Then I need to create structure corresponding to the original "TRxMsg" variant record and convert my auxiliary "myMsg" array into this structure. I don't know any C# equivalent of Delphi variant array, so I used inheritance and created the following classes. public abstract class TRxMsg { public byte typeMsg; } public class TRxMsgAcceptMask:TRxMsg { public uint accept, mask; //... } public class TRxMsgSN:TRxMsg { public string SN; //... } public class TRxMsgMRate:TRxMsg { public ushort rx_rate, tx_rate; //... } public class TRxMsgStatus:TRxMsg { public byte rx_status, tx_status, ctl0, ctl1, rflg; //... } Finally I create the appropriate object and initialize it with values manually converted from "myMsg" array (I used BitConverter for this). This does work fine, this solution seems to me a little too complicated, and that it should be possible to do this somehow more directly, without the auxiliary "my9bytes" structures or the inheritance and manual converting of individual values. So I'd like to ask you for a suggestions for the best way to do this. Thanks a lot!

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• Precise explanation of JavaScript <-> DOM circular reference issue

  - by Joey Adams

  One of the touted advantages of jQuery.data versus raw expando properties (arbitrary attributes you can assign to DOM nodes) is that jQuery.data is "safe from circular references and therefore free from memory leaks". An article from Google titled "Optimizing JavaScript code" goes into more detail: The most common memory leaks for web applications involve circular references between the JavaScript script engine and the browsers' C++ objects' implementing the DOM (e.g. between the JavaScript script engine and Internet Explorer's COM infrastructure, or between the JavaScript engine and Firefox XPCOM infrastructure). It lists two examples of circular reference patterns: DOM element → event handler → closure scope → DOM DOM element → via expando → intermediary object → DOM element However, if a reference cycle between a DOM node and a JavaScript object produces a memory leak, doesn't this mean that any non-trivial event handler (e.g. onclick) will produce such a leak? I don't see how it's even possible for an event handler to avoid a reference cycle, because the way I see it: The DOM element references the event handler. The event handler references the DOM (either directly or indirectly). In any case, it's almost impossible to avoid referencing window in any interesting event handler, short of writing a setInterval loop that reads actions from a global queue. Can someone provide a precise explanation of the JavaScript ↔ DOM circular reference problem? Things I'd like clarified: What browsers are effected? A comment in the jQuery source specifically mentions IE6-7, but the Google article suggests Firefox is also affected. Are expando properties and event handlers somehow different concerning memory leaks? Or are both of these code snippets susceptible to the same kind of memory leak? // Create an expando that references to its own element. var elem = document.getElementById('foo'); elem.myself = elem; // Create an event handler that references its own element. var elem = document.getElementById('foo'); elem.onclick = function() { elem.style.display = 'none'; }; If a page leaks memory due to a circular reference, does the leak persist until the entire browser application is closed, or is the memory freed when the window/tab is closed?

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