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• DSA signature verification input

  - by calccrypto

  What is the data inputted into DSA when PGP signs a message? From RFC4880, i found A Signature packet describes a binding between some public key and some data. The most common signatures are a signature of a file or a block of text, and a signature that is a certification of a User ID. im not sure if it is the entire public key, just the public key packet, or some other derivative of a pgp key packet. whatever it is, i cannot get the DSA signature to verify here is a sample im testing my program on: -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 abcd -----BEGIN PGP SIGNATURE----- Version: BCPG v1.39 iFkEARECABkFAk0z65ESHGFiYyAodGVzdCBrZXkpIDw+AAoJEC3Jkh8+bnkusO0A oKG+HPF2Qrsth2zS9pK+eSCBSypOAKDBgC2Z0vf2EgLiiNMk8Bxpq68NkQ== =gq0e -----END PGP SIGNATURE----- Dumped from pgpdump.net Old: Signature Packet(tag 2)(89 bytes) Ver 4 - new Sig type - Signature of a canonical text document(0x01). Pub alg - DSA Digital Signature Algorithm(pub 17) Hash alg - SHA1(hash 2) Hashed Sub: signature creation time(sub 2)(4 bytes) Time - Mon Jan 17 07:11:13 UTC 2011 Hashed Sub: signer's User ID(sub 28)(17 bytes) User ID - abc (test key) <> Sub: issuer key ID(sub 16)(8 bytes) Key ID - 0x2DC9921F3E6E792E Hash left 2 bytes - b0 ed DSA r(160 bits) - a1 be 1c f1 76 42 bb 2d 87 6c d2 f6 92 be 79 20 81 4b 2a 4e DSA s(160 bits) - c1 80 2d 99 d2 f7 f6 12 02 e2 88 d3 24 f0 1c 69 ab af 0d 91 -> hash(DSA q bits) and the public key for it is: -----BEGIN PGP PUBLIC KEY BLOCK----- Version: BCPG v1.39 mOIETTPqeBECALx+i9PIc4MB2DYXeqsWUav2cUtMU1N0inmFHSF/2x0d9IWEpVzE kRc30PvmEHI1faQit7NepnHkkphrXLAoZukAoNP3PB8NRQ6lRF6/6e8siUgJtmPL Af9IZOv4PI51gg6ICLKzNO9i3bcUx4yeG2vjMOUAvsLkhSTWob0RxWppo6Pn6MOg dMQHIM5sDH0xGN0dOezzt/imAf9St2B0HQXVfAAbveXBeRoO7jj/qcGx6hWmsKUr BVzdQhBk7Sku6C2KlMtkbtzd1fj8DtnrT8XOPKGp7/Y7ASzRtBFhYmMgKHRlc3Qg a2V5KSA8PohGBBMRAgAGBQJNM+p5AAoJEC3Jkh8+bnkuNEoAnj2QnqGtdlTgUXCQ Fyvwk5wiLGPfAJ4jTGTL62nWzsgrCDIMIfEG2shm8bjMBE0z6ngQAgCUlP7AlfO4 XuKGVCs4NvyBpd0KA0m0wjndOHRNSIz44x24vLfTO0GrueWjPMqRRLHO8zLJS/BX O/BHo6ypjN87Af0VPV1hcq20MEW2iujh3hBwthNwBWhtKdPXOndJGZaB7lshLJuW v9z6WyDNXj/SBEiV1gnPm0ELeg8Syhy5pCjMAgCFEc+NkCzcUOJkVpgLpk+VLwrJ /Wi9q+yCihaJ4EEFt/7vzqmrooXWz2vMugD1C+llN6HkCHTnuMH07/E/2dzciEYE GBECAAYFAk0z6nkACgkQLcmSHz5ueS7NTwCdED1P9NhgR2LqwyS+AEyqlQ0d5joA oK9xPUzjg4FlB+1QTHoOhuokxxyN =CTgL -----END PGP PUBLIC KEY BLOCK----- the public key packet of the key is mOIETTPqeBECALx+i9PIc4MB2DYXeqsWUav2cUtMU1N0inmFHSF/2x0d9IWEpVzEkRc30PvmEHI1faQi t7NepnHkkphrXLAoZukAoNP3PB8NRQ6lRF6/6e8siUgJtmPLAf9IZOv4PI51gg6ICLKzNO9i3bcUx4ye G2vjMOUAvsLkhSTWob0RxWppo6Pn6MOgdMQHIM5sDH0xGN0dOezzt/imAf9St2B0HQXVfAAbveXBeRoO 7jj/qcGx6hWmsKUrBVzdQhBk7Sku6C2KlMtkbtzd1fj8DtnrT8XOPKGp7/Y7ASzR in radix 64 i have tried many different combinations of sha1(< some data + 'abcd'),but the calculated value v never equals r, of the signature i know that the pgp implementation i used to create the key and signature is correct. i also know that my DSA implementation and PGP key data extraction program are correct. thus, the only thing left is the data to hash. what is the correct data to be hashed?

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• Show me your Linq to SQL architectures!

  - by Brad Heller

  I've been using Linq to SQL for a new implementation that I've been working on. I have about 5000 lines of code and am a little ways from a solid demo. I've been pretty satisfied with Linq to SQL so far -- the tools are excellent and pretty painless and it allows you to get a DAL up and running quickly. That said, there are some major draw backs that I just keep hitting over and over again. Namely how to handle separation of concerns between my DAL and my business layer and juggling that with different data contexts. Here is the architecture I've been using: My repositories do all my data access and they return Linq to SQL objects. Each of my Linq to SQL objects implements an IDetachable interface. A typical implementation looks like this: partial class PaymentDetail : IDetachable { #region IDetachable Members public bool IsAttached { get { return PropertyChanging != null; } } public void Detach() { if (IsAttached) { PropertyChanged = null; PropertyChanging = null; Transaction.Detach(); } } #endregion } Every time I do a DAL operation in my repository I "detach" when I'm done with the object (and it should theoretically detach from any child objects) to remove the DataContext's context. Like I said, this works pretty well, but there are some edge cases that seem to be a big pain in the ass. For instance, my Transaction object has many PaymentDetails. Even when there are no PaymentDetails in that collection it's still attached to the DataContext's context! Thus, if I try to update (I update by Attach()ing to the object and then SubmitChanges()) I get that dreaded "An attempt has been made to Attach or Add an entity that is not new, perhaps having been loaded from another DataContext. This is not supported." message. Anyway, I'm starting to doubt that this technology was a good gamble. Has anyone got a decent architecture that they're willing to share? I'd really love to use this technology but I feel like I spend 1/3 of my time just debugging is retarded quirks!

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• Catching a nested-in-template exception [C++]

  - by Karol

  Hello, I have a problem with writing a catch clause for an exception that is a class nested in a template. To be more specific, I have a following definition of the template and exception: /** Generic stack implementation. Accepts std::list, std::deque and std::vector as inner container. */ template < typename T, template < typename Element, typename = std::allocator<Element> > class Container = std::deque > class stack { public: class StackEmptyException { }; ... /** Returns value from the top of the stack. Throws StackEmptyException when the stack is empty. */ T top() const; ... } I have a following template method that I want exception to catch: template <typename Stack> void testTopThrowsStackEmptyExceptionOnEmptyStack() { Stack stack; std::cout << "Testing top throws StackEmptyException on empty stack..."; try { stack.top(); } catch (Stack::StackEmptyException) { // as expected. } std::cout << "success." << std::endl; } When I compile it (-Wall, -pedantic) I get the following error: In function ‘void testTopThrowsStackEmptyExceptionOnEmptyStack()’: error: expected type-specifier error: expected unqualified-id before ‘)’ token === Build finished: 2 errors, 0 warnings === Thanks in advance for any help! What is interesting, if the stack implementation was not a template, then the compiler would accept the code as it is.

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• Is this a good KVO-compliant way to model a mutable to-many relationship?

  - by andyvn22

  Say I'd like a mutable, unordered to-many relationship. For internal optimization reasons, it'd be best to store this in an NSMutableDictionary rather than an NSMutableSet. But I'd like to keep that implementation detail private. I'd also like to provide some KVO-compliant accessors, so: - (NSSet*)things; - (NSUInteger)countOfThings; - (void)addThings:(NSSet*)someThings; - (void)removeThings:(NSSet*)someThings; Now, it'd be convenient and less evil to provide accessors (private ones, of course, in my implementation file) for the dictionary as well, so: @interface MYClassWithThings () @property (retain) NSMutableDictionary* keyedThings; @end This seems good to me! I can use accessors to mess with my keyedThings within the class, but other objects think they're dealing with a mutable, unordered (, unkeyed!) to-many relationship. I'm concerned that several things I'm doing may be "evil" though, according to good style and Apple approval and whatnot. Have I done anything evil here? (For example, is it wrong not to provide setThings, since the things property is supposedly mutable?)

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• Access generic type parameter at runtime?

  - by Bart van Heukelom

  Event dispatcher interface public interface EventDispatcher { <T> EventListener<T> addEventListener(EventListener<T> l); <T> void removeEventListener(EventListener<T> l); } Implementation public class DefaultEventDispatcher implements EventDispatcher { @SuppressWarnings("unchecked") private Map<Class, Set<EventListener>> listeners = new HashMap<Class, Set<EventListener>>(); public void addSupportedEvent(Class eventType) { listeners.put(eventType, new HashSet<EventListener>()); } @Override public <T> EventListener<T> addEventListener(EventListener<T> l) { Set<EventListener> lsts = listeners.get(T); // ****** error: cannot resolve T if (lsts == null) throw new RuntimeException("Unsupported event type"); if (!lsts.add(l)) throw new RuntimeException("Listener already added"); return l; } @Override public <T> void removeEventListener(EventListener<T> l) { Set<EventListener> lsts = listeners.get(T); // ************* same error if (lsts == null) throw new RuntimeException("Unsupported event type"); if (!lsts.remove(l)) throw new RuntimeException("Listener is not here"); } } Usage EventListener<ShapeAddEvent> l = addEventListener(new EventListener<ShapeAddEvent>() { @Override public void onEvent(ShapeAddEvent event) { // TODO Auto-generated method stub } }); removeEventListener(l); I've marked two errors with a comment above (in the implementation). Is there any way to get runtime access to this information?

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• Validation with State Pattern for Multi-Page Forms in ASP.NET

  - by philrabin

  I'm trying to implement the state pattern for a multi-page registration form. The data on each page will be accumulated and stored in a session object. Should validation (including service layer calls to the DB) occur on the page level or inside each state class? In other words, should the concrete implementation of IState be concerned with the validation or should it be given a fully populated and valid object? See "EmptyFormState" class below: namespace Example { public class Registrar { private readonly IState formEmptyState; private readonly IState baseInformationComplete; public RegistrarSessionData RegistrarSessionData { get; set;} public Registrar() { RegistrarSessionData = new RegistrarSessionData(); formEmptyState = new EmptyFormState(this); baseInformationComplete = new BasicInfoCompleteState(this); State = formEmptyState; } public IState State { get; set; } public void SubmitData(RegistrarSessionData data) { State.SubmitData(data); } public void ProceedToNextStep() { State.ProceedToNextStep(); } } //actual data stored in the session //to be populated by page public class RegistrarSessionData { public string FirstName { get; set; } public string LastName { get; set; } //will include values of all 4 forms } //State Interface public interface IState { void SubmitData(RegistrarSessionData data); void ProceedToNextStep(); } //Concrete implementation of IState //Beginning state - no data public class EmptyFormState : IState { private readonly Registrar registrar; public EmptyFormState(Registrar registrar) { this.registrar = registrar; } public void SubmitData(RegistrarSessionData data) { //Should Validation occur here? //Should each state object contain a validation class? (IValidator ?) //Should this throw an exception? } public void ProceedToNextStep() { registrar.State = new BasicInfoCompleteState(registrar); } } //Next step, will have 4 in total public class BasicInfoCompleteState : IState { private readonly Registrar registrar; public BasicInfoCompleteState(Registrar registrar) { this.registrar = registrar; } public void SubmitData(RegistrarSessionData data) { //etc } public void ProceedToNextStep() { //etc } } }

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• how to run XSL file using JavaScript / HTML file

  - by B. Kumar

  i want to run xsl file using javascript function. I wrote a javascrpt function which is working well with Firefox and Crom but it is not working on Internet Explorer function loadXMLDoc(dname) { if (window.XMLHttpRequest) { xhttp=new XMLHttpRequest(); } else { xhttp=new ActiveXObject("Microsoft.XMLHTTP"); } xhttp.open("GET",dname,false); xhttp.send(""); return xhttp.responseXML; } function displayResult() { xml=loadXMLDoc("NewXml.xml"); xsl=loadXMLDoc("NewFile.xsl"); // code for IE if (window.ActiveXObject) { ex=xml.transformNode(xsl); document.getElementById("example").innerHTML=ex; } // code for Mozilla, Firefox, Opera, etc. else if (document.implementation && document.implementation.createDocument) { xsltProcessor=new XSLTProcessor(); xsltProcessor.importStylesheet(xsl); resultDocument = xsltProcessor.transformToFragment(xml,document); document.getElementById("example").appendChild(resultDocument); } } Please help my by modifying this code or by another code so that i can work with Internet Explorer. Thanks

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• Adding custom methods to a subclassed NSManagedObject

  - by CJ

  I have a Core Data model where I have an entity A, which is an abstract. Entities B, C, and D inherit from entity A. There are several properties defined in entity A which are used by B, C, and D. I would like to leverage this inheritance in my model code. In addition to properties, I am wondering if I can add methods to entity A, which are implemented in it's sub-entities. For example: I add a method to the interface for entity A which returns a value and takes one argument I add implementations of this method to A, B, C, D Then, I call executeFetchRequest: to retrieve all instances of B I call the method on the objects retrieved, which should call the implementation of the method contained in B's implementation I have tried this, but when calling the method, I receive: [NSManagedObject methodName:]: unrecognized selector sent to instance I presume this is because the objects returned by executeFetchRequest: are proxy objects of some sort. Is there any way to leverage inheritance using subclassed NSManagedObjects? I would really like to be able to do this, otherwise my model code would be responsible for determining what type of NSManagedObject it's dealing with and perform special logic according to the type, which is undesirable. Any help is appreciated, thanks in advance.

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• alignment and granularity of mmap

  - by OwnWaterloo

  I am confused by the specification of mmap. Let pa be the return address of mmap (the same as the specification) pa = mmap(addr, len, prot, flags, fildes, off); In my opinion after the function call succeed the following range is valid [ pa, pa+len ) My question is whether the range of the following is still valid? [ round_down(pa, pagesize) , round_up(pa+len, pagesize) ) [ base, base + size ] for short That is to say: is the base always aligned on the page boundary? is the size always a multiple of pagesize (the granularity is pagesize in other words) Thanks for your help. I think it is implied in this paragraph : The off argument is constrained to be aligned and sized according to the value returned by sysconf() when passed _SC_PAGESIZE or _SC_PAGE_SIZE. When MAP_FIXED is specified, the application shall ensure that the argument addr also meets these constraints. The implementation performs mapping operations over whole pages. Thus, while the argument len need not meet a size or alignment constraint, the implementation shall include, in any mapping operation, any partial page specified by the range [pa,pa+len). But I'm not sure and I do not have much experience on POSIX. Please show me some more explicit and more definitive evidence Or show me at least one system which supports POSIX and has different behavior Thanks agian.

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• Changing associativity

  - by Sorush Rabiee

  Hi... The associativity of stream insertion operator is rtl, forgetting this fact sometimes cause to runtime or logical errors. for example: 1st- int F() { static int internal_counter c=0; return ++c; } in the main function: //....here is main() cout<<”1st=”<<F()<<”,2nd=”<<F()<<”,3rd=”<<F(); and the output is: 1st=3,2nd=2,3rd=1 that is different from what we expect at first look. 2nd- suppose that we have an implementation of stack data structure like this: // //... a Stack<DataType> class …… // Stack<int> st(10); for(int i=1;i<11;i++) st.push(i); cout<<st.pop()<<endl<<st.pop()<<endl<<st.pop()<<endl<<st.pop()<<endl; expected output is something like: 10 9 8 7 but we have: 7 8 9 10 There is no internal bug of << implementation but it can be so confusing... and finally[:-)] my question: is there any way to change assocativity of an operator by overloading it?

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• A linked list with multiple heads in Java

  - by Emile

  Hi, I have a list in which I'd like to keep several head pointers. I've tried to create multiple ListIterators on the same list but this forbid me to add new elements in my list... (see Concurrent Modification exception). I could create my own class but I'd rather use a built-in implementation ;) To be more specific, here is an inefficient implementation of two basic operations and the one wich doesn't work : class MyList <E { private int[] _heads; private List<E _l; public MyList ( int nbHeads ) { _heads = new int[nbHeads]; _l = new LinkedList<E(); } public void add ( E e ) { _l.add(e); } public E next ( int head ) { return _l.get(_heads[head++]); // ugly } } class MyList <E { private Vector<ListIterator<E _iters; private List<E _l; public MyList ( int nbHeads ) { _iters = new Vector<ListIterator<E(nbHeads); _l = new LinkedList<E(); for( ListIterator<E iter : _iters ) iter = _l.listIterator(); } public void add ( E e ) { _l.add(e); } public E next ( int head ) { // ConcurrentModificationException because of the add() return _iters.get(head).next(); } } Emile

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• Web Grid, Client side Binding VS. Server side HTML generation

  - by Ron Harlev

  I'm working on replacing an existing web grid in an ASP.NET web application, with a new implementation. The existing grid is powerful, but not flexible enough. It also brings with it all kind of frameworks we don't like to have on our web pages. While looking into existing options I noticed I can break the available solutions into two main approaches. The older approach is represented best by the ASP.NET GridView. This is a classic ASP.NET control that generates the needed HTML on the server, based on a given set of data. The newer approach is depending on client side rendering, mainly with jQuery. A good example would be jqGrid. Only the data is sent to the client (Usually with JSON or XML) In the GridView case, if I want an AJAX behavior, I would have to implement it with something like an update panel. Is there a definitive choice I should make? Is there a good chance of achieving the same snappy behavior I get with jqGrid (even with many records), with server side rendered controls? Is there some hybrid implementation incorporating both approaches?

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• Scrollbar with Sprite and Rectangle won't move text, just the Rectangle it's painted on.

  - by WebDevHobo

  Warning: school assignment. For those of you still with me, I am tasked with making some scrollable content in Flash. Load in a TextFile using LoadURL(), then display it. To get the text, we've written our own class TextFieldExtended, which is basically just there to give the textfile location to the constructor and then have the class do the various steps of getting it and loading it for you. So I needed to get a Scrollbar, which I got here: http://kirupa.com/forum/showthread.php?t=245468 (all files in a zip linked at the end of this text) The thing is, it works with Sprites. After trying to get it to accept TextFieldExtended, I bumped into a block, since the scrollbar relied heavily on a Sprite property that TextFieldExtended didn't have or could have. So I tried adding the TextFieldExtended instance to a Sprite instance using addchild. A problem occurs here that I do not know how to handle. It seems that a Rectangle is drawn and the Text is drawn on that. I say this because the scrollbar moves the Rectangle up and down a bit, but the text doesn't scroll, just the Rectangle it is positioned in and the text then moves along with it. My question: can this be fixed, or is does this implementation of scrollbars need a lot of adaptations before this is possible? If so, any scrollbars you can recommend, because it's too extended for me at this point. All files: http://www.mediafire.com/?q2ium22gmox This was made in Flash CS4 using ActionScript3. The Example class is the final implementation

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• notify listener inside or outside inner synchronization

  - by Jary Zeels

  Hello all, I am struggling with a decision. I am writing a thread-safe library/API. Listeners can be registered, so the client is notified when something interesting happens. Which of the two implementations is most common? class MyModule { protected Listener listener; protected void somethingHappens() { synchronized(this) { ... do useful stuff ... listener.notify(); } } } or class MyModule { protected Listener listener; protected void somethingHappens() { Listener l = null; synchronized(this) { ... do useful stuff ... l = listener; } l.notify(); } } In the first implementation, the listener is notified inside the synchronization. In the second implementation, this is done outside the synchronization. I feel that the second one is advised, as it makes less room for potential deadlocks. But I am having trouble to convince myself. A downside of the second imlementation is that the client might receive 'incorrect' notifications, which happens if it accessed the module prior to the l.notify() statement. thanks a lot

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• Why should the "prime-based" hashcode implmentation be used instead of the "naive" one?

  - by Wilhelm

  I have seen that a prime number implmentation of the GetHashCode function is being recommend, for example here. However using the following code (in VB, sorry), it seems as if that implementation gives the same hash density as a "naive" xor implementation. If the density is the same, I would suppose there is the same probability of cllision in both implementations. Am I missing anything on why is the prime approach preferred? I am supossing that if the hash code is a byte I do not lose generality for the integer case. Sub Main() Dim XorHashes(255) As Integer Dim PrimeHashes(255) As Integer For i = 0 To 255 For j = 0 To 255 For k = 0 To 255 XorHashes(GetXorHash(i, j, k)) += 1 PrimeHashes(GetPrimeHash(i, j, k)) += 1 Next Next Next For i = 0 To 255 Console.WriteLine("{0}: {1}, {2}", i, XorHashes(i), PrimeHashes(i)) Next Console.ReadKey() End Sub Public Function GetXorHash(ByVal valueOne As Integer, ByVal valueTwo As Integer, ByVal valueThree As Integer) As Byte Return CByte((valueOne Xor valueTwo Xor valueThree) Mod 256) End Function Public Function GetPrimeHash(ByVal valueOne As Integer, ByVal valueTwo As Integer, ByVal valueThree As Integer) As Byte Dim TempHash = 17 TempHash = 31 * TempHash + valueOne TempHash = 31 * TempHash + valueTwo TempHash = 31 * TempHash + valueThree Return CByte(TempHash Mod 256) End Function

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• SOLVED: Lisp: macro calling a function works in interpreter, fails in compiler (SBCL + CMUCL)

  - by ttsiodras

  As suggested in a macro-related question I recently posted to SO, I coded a macro called "fast" via a call to a function (here is the standalone code in pastebin): (defun main () (progn (format t "~A~%" (+ 1 2 (* 3 4) (+ 5 (- 8 6)))) (format t "~A~%" (fast (+ 1 2 (* 3 4) (+ 5 (- 8 6))))))) This works in the REPL, under both SBCL and CMUCL: $ sbcl This is SBCL 1.0.52, an implementation of ANSI Common Lisp. ... * (load "bug.cl") 22 22 $ Unfortunately, however, the code no longer compiles: $ sbcl This is SBCL 1.0.52, an implementation of ANSI Common Lisp. ... * (compile-file "bug.cl") ... ; during macroexpansion of (FAST (+ 1 2 ...)). Use *BREAK-ON-SIGNALS* to ; intercept: ; ; The function COMMON-LISP-USER::CLONE is undefined. So it seems that by having my macro "fast" call functions ("clone","operation-p") at compile-time, I trigger issues in Lisp compilers (verified in both CMUCL and SBCL). Any ideas on what I am doing wrong and/or how to fix this?

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• How can I get at the raw bytes of the request in WCF?

  - by Gregory Higley

  For logging purposes, I want to get at the raw request sent to my RESTful web service implemented in WCF. I have already implemented IDispatchMessageInspector. In my implementation of AfterReceiveRequest, I want to spit out the raw bytes of the message even (and especially) if the content of the message is invalid. This is for debugging purposes. My service works perfectly already, but it is often helpful when working through problems with clients who are trying to call the service to know what it was they sent, i.e., the raw bytes. For example, let's say that instead of sending a well-formed XML document, they post the string "your mama" to my service endpoint. I want to see that that's what they did. Unfortunately using MessageBuffer::CreateBufferedCopy() won't work unless the contents of the message are already well-formed XML. Here's (roughly) what I already have in my implementation of AfterReceiveRequest: // The immediately following line raises an exception if the message // does not contain valid XML. This is uncool because I want // the raw bytes regardless of whether they are valid or not. using (MessageBuffer buffer = request.CreateBufferedCopy(Int32.MaxValue)) { using (MemoryStream stream = new MemoryStream()) using (StreamReader reader = new StreamReader(stream)) { buffer.WriteMessage(stream); stream.Position = 0; Trace.TraceInformation(reader.ReadToEnd()); } request = buffer.CreateMessage(); } My guess here is that I need to get at the raw request before it becomes a Message. This will most likely have to be done at a lower level in the WCF stack than an IDispatchMessageInspector. Anyone know how to do this?

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• RegularExpression-esque search matching Objects in List

  - by Pindatjuh

  I'm currently working on an implementation of the following idea, and I was wondering if there is any literature on this subject. Working with Java, but the principle applies on any language with a decent type-system, I like to implement: matching Objects from a List using a RegularExpression-esque search: So let's say I have a List containing List<Object> x = new ArrayList<Object>(); x.add(new Object()); x.add("Hello World"); x.add("Second String"); x.add(5); // Integer (auto-boxing) x.add(6); // Integer Then I create a "Regular Expression" (not working with a stream of characters, but working with a stream of Objects), and instead of character-classes, I use type-system properties: [String][Integer] And this would match one sublist: {Match["Second String", 5]}. The expression: [String:length()<15] Will match two sublist (each of length 1) containing a String which instance is passing the expression instance.length() < 5: {Match["Hello World"],Match["Second String"]}. [Object][Object] Matches any pair in the List: {Match[Object,"Hello World"],Match["Second String", 5]}, in a streamed manner (no overlapping matches). Ofcourse, my implementation will have grouping, lookahead/lookbehinds and is hierarchical (i.e. matching n elements from Lists in Lists), etc. The above merely illustrates the concept. Is there a name for this principle, and is there literature available on it?

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• Calling a method on an unitialized object (null pointer)

  - by Florin

  What is the normal behavior in Objective-C if you call a method on an object (pointer) that is nil (maybe because someone forgot to initialize it)? Shouldn't it generate some kind of an error (segmentation fault, null pointer exception...)? If this is normal behavior, is there a way of changing this behavior (by configuring the compiler) so that the program raises some kind of error / exception at runtime? To make it more clear what I am talking about, here's an example. Having this class: @interface Person : NSObject { NSString *name; } @property (nonatomic, retain) NSString *name; - (void)sayHi; @end with this implementation: @implementation Person @synthesize name; - (void)dealloc { [name release]; [super dealloc]; } - (void)sayHi { NSLog(@"Hello"); NSLog(@"My name is %@.", name); } @end Somewhere in the program I do this: Person *person = nil; //person = [[Person alloc] init]; // let's say I comment this line person.name = @"Mike"; // shouldn't I get an error here? [person sayHi]; // and here [person release]; // and here

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• Table cell in a split-view controller - selected cell becomes deselected when called by reloadData

  - by bpapa

  I'm working on a universal app that uses a SplitViewController to present a master-detail view. In the iPad HIG on Split Views, Apple states: In general, indicate the current selection in the left pane in a persistent way. This behavior helps people understand the relationship between the item in the left pane and the contents of the right pane. This is important because the contents of the right pane can change, but they should always remain related to the item selected in the left pane. So I'm trying to maintain selection state on the left. Easy enough when the user taps, I just remove the deselectRowAtIndexPath:animated: message from tableView:didSelectRowAtIndexPath: implementation. But, I also want the selection state to show up by default (without a user tap). I wound up putting this in my tableView:cellForRowAtIndexPath: implementation: if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) { if (cellShouldBeSelected) cell.selected = YES; else cell.selected = NO; } The behavior I'm seeing, is that when the cells finall appear, for a fraction of a section the cell is indeed selected, but then the selection disappears without any user interaction. Any ideas? I set the new clearsSelectionOnViewWillAppear property to NO, but that doesn't seem to fix it, and it shouldn't really matter because I'm marking the cell as selected long after viewWillAppear is called - I'm actually doing it after some network activity and then sending the table view a reloadData message.

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• Custom UILabel does not show text.

  - by Oscar

  Hi! I've made an custom UILabel class in which i draw a red line at the bottom of the frame. The red line is showing but i cant get the text to show. #import <UIKit/UIKit.h> @interface LetterLabel : UILabel { } @end #import "LetterLabel.h" @implementation LetterLabel - (id)initWithFrame:(CGRect)frame { if (self = [super initWithFrame:frame]) { // Initialization code } return self; } - (void)drawRect:(CGRect)rect { CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 2.0); CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 0.0, 0.0, 1.0); CGContextBeginPath(UIGraphicsGetCurrentContext()); CGContextMoveToPoint(UIGraphicsGetCurrentContext(), 0.0, self.frame.size.height); CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), self.frame.size.width, self.frame.size.height); CGContextStrokePath(UIGraphicsGetCurrentContext()); } - (void)dealloc { [super dealloc]; } @end #import <UIKit/UIKit.h> #import "Word.h" @interface WordView : UIView { Word *gameWord; } @property (nonatomic, retain) Word *gameWord; @end @implementation WordView @synthesize gameWord; - (id)initWithFrame:(CGRect)frame { if (self = [super initWithFrame:frame]) { self.backgroundColor = [UIColor whiteColor]; LetterLabel *label = [[LetterLabel alloc] initWithFrame:CGRectMake(0, 0, 20, 30)]; label.backgroundColor = [UIColor cyanColor]; label.textAlignment = UITextAlignmentCenter; label.textColor = [UIColor blackColor]; [label setText:@"t"]; [self addSubview:label]; } return self; } - (void)drawRect:(CGRect)rect { // Drawing code } - (void)dealloc { [gameWord release]; [super dealloc]; } @end

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• Ruby and duck typing: design by contract impossible?

  - by davetron5000

  Method signature in Java: public List<String> getFilesIn(List<File> directories) similar one in ruby def get_files_in(directories) In the case of Java, the type system gives me information about what the method expects and delivers. In Ruby's case, I have no clue what I'm supposed to pass in, or what I'll expect to receive. In Java, the object must formally implement the interface. In Ruby, the object being passed in must respond to whatever methods are called in the method defined here. This seems highly problematic: Even with 100% accurate, up-to-date documentation, the Ruby code has to essentially expose its implementation, breaking encapsulation. "OO purity" aside, this would seem to be a maintenance nightmare. The Ruby code gives me no clue what's being returned; I would have to essentially experiment, or read the code to find out what methods the returned object would respond to. Not looking to debate static typing vs duck typing, but looking to understand how you maintain a production system where you have almost no ability to design by contract. Update No one has really addressed the exposure of a method's internal implementation via documentation that this approach requires. Since there are no interfaces, if I'm not expecting a particular type, don't I have to itemize every method I might call so that the caller knows what can be passed in? Or is this just an edge case that doesn't really come up?

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• [Cocoa] Binding CoreData Managed Object to NSTextFieldCell subclass

  - by ndg

  I have an NSTableView which has its first column set to contain a custom NSTextFieldCell. My custom NSTextFieldCell needs to allow the user to edit a "desc" property within my Managed Object but to also display an "info" string that it contains (which is not editable). To achieve this, I followed this tutorial. In a nutshell, the tutorial suggests editing your Managed Objects generated subclass to create and pass a dictionary of its contents to your NSTableColumn via bindings. This works well for read-only NSCell implementations, but I'm looking to subclass NSTextFieldCell to allow the user to edit the "desc" property of my Managed Object. To do this, I followed one of the articles comments, which suggests subclassing NSFormatter to explicitly state which Managed Object property you would like the NSTextFieldCell to edit. Here's the suggested implementation: @implementation TRTableDescFormatter - (BOOL)getObjectValue:(id *)anObject forString:(NSString *)string errorDescription:(NSString **)error { if (anObject != nil){ *anObject = [NSDictionary dictionaryWithObject:string forKey:@"desc"]; return YES; } return NO; } - (NSString *)stringForObjectValue:(id)anObject { if (![anObject isKindOfClass:[NSDictionary class]]) return nil; return [anObject valueForKey:@"desc"]; } - (NSAttributedString*)attributedStringForObjectValue:(id)anObject withDefaultAttributes:(NSDictionary *)attrs { if (![anObject isKindOfClass:[NSDictionary class]]) return nil; NSAttributedString *anAttributedString = [[NSAttributedString alloc] initWithString: [anObject valueForKey:@"desc"]]; return anAttributedString; } @end I assign the NSFormatter subclass to my cell in my NSTextFieldCell subclass, like so: - (void)awakeFromNib { TRTableDescFormatter *formatter = [[[TRTableDescFormatter alloc] init] autorelease]; [self setFormatter:formatter]; } This seems to work, but is extremely patch. On occasion, clicking to edit a row will cause its value to nullify. On other occasions, the value you enter on one row will populate other rows within the table. I've been doing a lot of reading on this subject and would really like to get to the bottom of this. What's more frustrating is that my NSTextFieldCell is rendering exactly how I would like it to. This editing issue is my last obstacle! If anyone can help, that would be greatly appreciated.

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• Is there a way to automaticly call all versions of an inherited method?

  - by Eric

  I'm writing a plug-in for a 3D modeling program. I have a custom class that wraps instances of elements in the 3D model, and in turn derives it's properties from the element it wraps. When the element in the model changes I want my class(es) to update their properties based on the new geometry. In the simplified example below. I have classes AbsCurveBasd, Extrusion, and Shell which are all derived from one another. Each of these classes implement a RefreshFromBaseShape() method which updates specific properties based on the current baseShape the class is wrapping. I can call base.RefreshFromBaseShape() in each implementation of RefreshFromBaseShape() to ensure that all the properties are updated. But I'm wondering if there is a better way where I don't have to remember to do this in every implementation of RefershFromBaseShape()? For example because AbsCurveBased does not have a parameterless constructor the code wont even compile unless the constructors call the base class constructors. public abstract class AbsCurveBased { internal Curve baseShape; double Area{get;set;} public AbsCurveBased(Curve baseShape) { this.baseShape = baseShape; RefreshFromBaseShape(); } public virtual void RefreshFromBaseShape() { //sets the Area property from the baseShape } } public class Extrusion : AbsCurveBased { double Volume{get;set;} double Height{get;set;} public Extrusion(Curve baseShape):base(baseShape) { this.baseShape = baseShape; RefreshFromBaseShape(); } public override void RefreshFromBaseShape() { base.RefreshFromBaseShape(); //sets the Volume property based on the area and the height } } public class Shell : Extrusion { double ShellVolume{get;set;} double ShellThickness{get;set;} public Shell(Curve baseShape): base(baseShape) { this.baseShape = baseShape; RefreshFromBaseShape(); } public void RefreshFromBaseShape() { base.RefreshFromBaseShape(); //sets this Shell Volume from the Extrusion properties and ShellThickness property } }

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• how to implement a really efficient bitvector sorting in python

  - by xiao

  Hello guys! Actually this is an interesting topic from programming pearls, sorting 10 digits telephone numbers in a limited memory with an efficient algorithm. You can find the whole story here What I am interested in is just how fast the implementation could be in python. I have done a naive implementation with the module bitvector. The code is as following: from BitVector import BitVector import timeit import random import time import sys def sort(input_li): return sorted(input_li) def vec_sort(input_li): bv = BitVector( size = len(input_li) ) for i in input_li: bv[i] = 1 res_li = [] for i in range(len(bv)): if bv[i]: res_li.append(i) return res_li if __name__ == "__main__": test_data = range(int(sys.argv[1])) print 'test_data size is:', sys.argv[1] random.shuffle(test_data) start = time.time() sort(test_data) elapsed = (time.time() - start) print "sort function takes " + str(elapsed) start = time.time() vec_sort(test_data) elapsed = (time.time() - start) print "sort function takes " + str(elapsed) start = time.time() vec_sort(test_data) elapsed = (time.time() - start) print "vec_sort function takes " + str(elapsed) I have tested from array size 100 to 10,000,000 in my macbook(2GHz Intel Core 2 Duo 2GB SDRAM), the result is as following: test_data size is: 1000 sort function takes 0.000274896621704 vec_sort function takes 0.00383687019348 test_data size is: 10000 sort function takes 0.00380706787109 vec_sort function takes 0.0371489524841 test_data size is: 100000 sort function takes 0.0520560741425 vec_sort function takes 0.374383926392 test_data size is: 1000000 sort function takes 0.867373943329 vec_sort function takes 3.80475401878 test_data size is: 10000000 sort function takes 12.9204008579 vec_sort function takes 38.8053860664 What disappoints me is that even when the test_data size is 100,000,000, the sort function is still faster than vec_sort. Is there any way to accelerate the vec_sort function?

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