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  • BasicAuthProvider in ServiceStack

    - by Per
    I've got an issue with the BasicAuthProvider in ServiceStack. POST-ing to the CredentialsAuthProvider (/auth/credentials) is working fine. The problem is that when GET-ing (in Chrome): http://foo:pwd@localhost:81/tag/string/list the following is the result Handler for Request not found: Request.HttpMethod: GET Request.HttpMethod: GET Request.PathInfo: /login Request.QueryString: System.Collections.Specialized.NameValueCollection Request.RawUrl: /login?redirect=http%3a%2f%2flocalhost%3a81%2ftag%2fstring%2flist which tells me that it redirected me to /login instead of serving the /tag/... request. Here's the entire code for my AppHost: public class AppHost : AppHostHttpListenerBase, IMessageSubscriber { private ITagProvider myTagProvider; private IMessageSender mySender; private const string UserName = "foo"; private const string Password = "pwd"; public AppHost( TagConfig config, IMessageSender sender ) : base( "BM App Host", typeof( AppHost ).Assembly ) { myTagProvider = new TagProvider( config ); mySender = sender; } public class CustomUserSession : AuthUserSession { public override void OnAuthenticated( IServiceBase authService, IAuthSession session, IOAuthTokens tokens, System.Collections.Generic.Dictionary<string, string> authInfo ) { authService.RequestContext.Get<IHttpRequest>().SaveSession( session ); } } public override void Configure( Funq.Container container ) { Plugins.Add( new MetadataFeature() ); container.Register<BeyondMeasure.WebAPI.Services.Tags.ITagProvider>( myTagProvider ); container.Register<IMessageSender>( mySender ); Plugins.Add( new AuthFeature( () => new CustomUserSession(), new AuthProvider[] { new CredentialsAuthProvider(), //HTML Form post of UserName/Password credentials new BasicAuthProvider(), //Sign-in with Basic Auth } ) ); container.Register<ICacheClient>( new MemoryCacheClient() ); var userRep = new InMemoryAuthRepository(); container.Register<IUserAuthRepository>( userRep ); string hash; string salt; new SaltedHash().GetHashAndSaltString( Password, out hash, out salt ); // Create test user userRep.CreateUserAuth( new UserAuth { Id = 1, DisplayName = "DisplayName", Email = "[email protected]", UserName = UserName, FirstName = "FirstName", LastName = "LastName", PasswordHash = hash, Salt = salt, }, Password ); } } Could someone please tell me what I'm doing wrong with either the SS configuration or how I am calling the service, i.e. why does it not accept the supplied user/pwd? Update1: Request/Response captured in Fiddler2when only BasicAuthProvider is used. No Auth header sent in the request, but also no Auth header in the response. GET /tag/string/AAA HTTP/1.1 Host: localhost:81 Connection: keep-alive User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.11 (KHTML, like Gecko) Chrome/23.0.1271.64 Safari/537.11 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Encoding: gzip,deflate,sdch Accept-Language: en-US,en;q=0.8,sv;q=0.6 Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3 Cookie: ss-pid=Hu2zuD/T8USgvC8FinMC9Q==; X-UAId=1; ss-id=1HTqSQI9IUqRAGxM8vKlPA== HTTP/1.1 302 Found Location: /login?redirect=http%3a%2f%2flocalhost%3a81%2ftag%2fstring%2fAAA Server: Microsoft-HTTPAPI/2.0 X-Powered-By: ServiceStack/3,926 Win32NT/.NET Date: Sat, 10 Nov 2012 22:41:51 GMT Content-Length: 0 Update2 Request/Response with HtmlRedirect = null . SS now answers with the Auth header, which Chrome then issues a second request for and authentication succeeds GET http://localhost:81/tag/string/Abc HTTP/1.1 Host: localhost:81 Connection: keep-alive User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.11 (KHTML, like Gecko) Chrome/23.0.1271.64 Safari/537.11 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Encoding: gzip,deflate,sdch Accept-Language: en-US,en;q=0.8,sv;q=0.6 Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3 Cookie: ss-pid=Hu2zuD/T8USgvC8FinMC9Q==; X-UAId=1; ss-id=1HTqSQI9IUqRAGxM8vKlPA== HTTP/1.1 401 Unauthorized Transfer-Encoding: chunked Server: Microsoft-HTTPAPI/2.0 X-Powered-By: ServiceStack/3,926 Win32NT/.NET WWW-Authenticate: basic realm="/auth/basic" Date: Sat, 10 Nov 2012 22:49:19 GMT 0 GET http://localhost:81/tag/string/Abc HTTP/1.1 Host: localhost:81 Connection: keep-alive Authorization: Basic Zm9vOnB3ZA== User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.11 (KHTML, like Gecko) Chrome/23.0.1271.64 Safari/537.11 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Encoding: gzip,deflate,sdch Accept-Language: en-US,en;q=0.8,sv;q=0.6 Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3 Cookie: ss-pid=Hu2zuD/T8USgvC8FinMC9Q==; X-UAId=1; ss-id=1HTqSQI9IUqRAGxM8vKlPA==

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  • Design by Contract with Microsoft .Net Code Contract

    - by Fredrik N
    I have done some talks on different events and summits about Defensive Programming and Design by Contract, last time was at Cornerstone’s Developer Summit 2010. Next time will be at SweNug (Sweden .Net User Group). I decided to write a blog post about of some stuffs I was talking about. Users are a terrible thing! Protect your self from them ”Human users have a gift for doing the worst possible thing at the worst possible time.” – Michael T. Nygard, Release It! The kind of users Michael T. Nygard are talking about is the users of a system. We also have users that uses our code, the users I’m going to focus on is the users of our code. Me and you and another developers. “Any fool can write code that a computer can understand. Good programmers write code that humans can understand.” – Martin Fowler Good programmers also writes code that humans know how to use, good programmers also make sure software behave in a predictable manner despise inputs or user actions. Design by Contract   Design by Contract (DbC) is a way for us to make a contract between us (the code writer) and the users of our code. It’s about “If you give me this, I promise to give you this”. It’s not about business validations, that is something completely different that should be part of the domain model. DbC is to make sure the users of our code uses it in a correct way, and that we can rely on the contract and write code in a way where we know that the users will follow the contract. It will make it much easier for us to write code with a contract specified. Something like the following code is something we may see often: public void DoSomething(Object value) { value.DoIKnowThatICanDoThis(); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Where “value” can be uses directly or passed to other methods and later be used. What some of us can easily forget here is that the “value” can be “null”. We will probably not passing a null value, but someone else that uses our code maybe will do it. I think most of you (including me) have passed “null” into a method because you don’t know if the argument need to be specified to a valid value etc. I bet most of you also have got the “Null reference exception”. Sometimes this “Null reference exception” can be hard and take time to fix, because we need to search among our code to see where the “null” value was passed in etc. Wouldn’t it be much better if we can as early as possible specify that the value can’t not be null, so the users of our code also know it when the users starts to use our code, and before run time execution of the code? This is where DbC comes into the picture. We can use DbC to specify what we need, and by doing so we can rely on the contract when we write our code. So the code above can actually use the DoIKnowThatICanDoThis() method on the value object without being worried that the “value” can be null. The contract between the users of the code and us writing the code, says that the “value” can’t be null.   Pre- and Postconditions   When working with DbC we are specifying pre- and postconditions.  Precondition is a condition that should be met before a query or command is executed. An example of a precondition is: “The Value argument of the method can’t be null”, and we make sure the “value” isn’t null before the method is called. Postcondition is a condition that should be met when a command or query is completed, a postcondition will make sure the result is correct. An example of a postconditon is “The method will return a list with at least 1 item”. Commands an Quires When using DbC, we need to know what a Command and a Query is, because some principles that can be good to follow are based on commands and queries. A Command is something that will not return anything, like the SQL’s CREATE, UPDATE and DELETE. There are two kinds of Commands when using DbC, the Creation commands (for example a Constructor), and Others. Others can for example be a Command to add a value to a list, remove or update a value etc. //Creation commands public Stack(int size) //Other commands public void Push(object value); public void Remove(); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   A Query, is something that will return something, for example an Attribute, Property or a Function, like the SQL’s SELECT.   There are two kinds of Queries, the Basic Queries  (Quires that aren’t based on another queries), and the Derived Queries, queries that is based on another queries. Here is an example of queries of a Stack: //Basic Queries public int Count; public object this[int index] { get; } //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } To understand about some principles that are good to follow when using DbC, we need to know about the Commands and different Queries. The 6 Principles When working with DbC, it’s advisable to follow some principles to make it easier to define and use contracts. The following DbC principles are: Separate commands and queries. Separate basic queries from derived queries. For each derived query, write a postcondition that specifies what result will be returned, in terms of one or more basic queries. For each command, write a postcondition that specifies the value of every basic query. For every query and command, decide on a suitable precondition. Write invariants to define unchanging properties of objects. Before I will write about each of them I want you to now that I’m going to use .Net 4.0 Code Contract. I will in the rest of the post uses a simple Stack (Yes I know, .Net already have a Stack class) to give you the basic understanding about using DbC. A Stack is a data structure where the first item in, will be the first item out. Here is a basic implementation of a Stack where not contract is specified yet: public class Stack { private object[] _array; //Basic Queries public uint Count; public object this[uint index] { get { return _array[index]; } set { _array[index] = value; } } //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } //Is related to Count and this[] Query public object Top() { return this[Count]; } //Creation commands public Stack(uint size) { Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { this[++Count] = value; } public void Remove() { this[Count] = null; Count--; } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   Note: The Stack is implemented in a way to demonstrate the use of Code Contract in a simple way, the implementation may not look like how you would implement it, so don’t think this is the perfect Stack implementation, only used for demonstration.   Before I will go deeper into the principles I will simply mention how we can use the .Net Code Contract. I mention before about pre- and postcondition, is about “Require” something and to “Ensure” something. When using Code Contract, we will use a static class called “Contract” and is located in he “System.Diagnostics.Contracts” namespace. The contract must be specified at the top or our member statement block. To specify a precondition with Code Contract we uses the Contract.Requires method, and to specify a postcondition, we uses the Contract.Ensure method. Here is an example where both a pre- and postcondition are used: public object Top() { Contract.Requires(Count > 0, "Stack is empty"); Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   The contract above requires that the Count is greater than 0, if not we can’t get the item at the Top of a Stack. We also Ensures that the results (By using the Contract.Result method, we can specify a postcondition that will check if the value returned from a method is correct) of the Top query is equal to this[Count].   1. Separate Commands and Queries   When working with DbC, it’s important to separate Command and Quires. A method should either be a command that performs an Action, or returning information to the caller, not both. By asking a question the answer shouldn’t be changed. The following is an example of a Command and a Query of a Stack: public void Push(object value) public object Top() .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   The Push is a command and will not return anything, just add a value to the Stack, the Top is a query to get the item at the top of the stack.   2. Separate basic queries from derived queries There are two different kinds of queries,  the basic queries that doesn’t rely on another queries, and derived queries that uses a basic query. The “Separate basic queries from derived queries” principle is about about that derived queries can be specified in terms of basic queries. So this principles is more about recognizing that a query is a derived query or a basic query. It will then make is much easier to follow the other principles. The following code shows a basic query and a derived query: //Basic Queries public uint Count; //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   We can see that IsEmpty will use the Count query, and that makes the IsEmpty a Derived query.   3. For each derived query, write a postcondition that specifies what result will be returned, in terms of one or more basic queries.   When the derived query is recognize we can follow the 3ed principle. For each derived query, we can create a postcondition that specifies what result our derived query will return in terms of one or more basic queries. Remember that DbC is about contracts between the users of the code and us writing the code. So we can’t use demand that the users will pass in a valid value, we must also ensure that we will give the users what the users wants, when the user is following our contract. The IsEmpty query of the Stack will use a Count query and that will make the IsEmpty a Derived query, so we should now write a postcondition that specified what results will be returned, in terms of using a basic query and in this case the Count query, //Basic Queries public uint Count; //Derived Queries public bool IsEmpty() { Contract.Ensures(Contract.Result<bool>() == (Count == 0)); return Count == 0; } The Contract.Ensures is used to create a postcondition. The above code will make sure that the results of the IsEmpty (by using the Contract.Result to get the result of the IsEmpty method) is correct, that will say that the IsEmpty will be either true or false based on Count is equal to 0 or not. The postcondition are using a basic query, so the IsEmpty is now following the 3ed principle. We also have another Derived Query, the Top query, it will also need a postcondition and it uses all basic queries. The Result of the Top method must be the same value as the this[] query returns. //Basic Queries public uint Count; public object this[uint index] { get { return _array[index]; } set { _array[index] = value; } } //Derived Queries //Is related to Count and this[] Query public object Top() { Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   4. For each command, write a postcondition that specifies the value of every basic query.   For each command we will create a postconditon that specifies the value of basic queries. If we look at the Stack implementation we will have three Commands, one Creation command, the Constructor, and two others commands, Push and Remove. Those commands need a postcondition and they should include basic query to follow the 4th principle. //Creation commands public Stack(uint size) { Contract.Ensures(Count == 0); Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { Contract.Ensures(Count == Contract.OldValue<uint>(Count) + 1); Contract.Ensures(this[Count] == value); this[++Count] = value; } public void Remove() { Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   As you can see the Create command will Ensures that Count will be 0 when the Stack is created, when a Stack is created there shouldn’t be any items in the stack. The Push command will take a value and put it into the Stack, when an item is pushed into the Stack, the Count need to be increased to know the number of items added to the Stack, and we must also make sure the item is really added to the Stack. The postconditon of the Push method will make sure the that old value of the Count (by using the Contract.OldValue we can get the value a Query has before the method is called)  plus 1 will be equal to the Count query, this is the way we can ensure that the Push will increase the Count with one. We also make sure the this[] query will now contain the item we pushed into the Stack. The Remove method must make sure the Count is decreased by one when the top item is removed from the Stack. The Commands is now following the 4th principle, where each command now have a postcondition that used the value of basic queries. Note: The principle says every basic Query, the Remove only used one Query the Count, it’s because this command can’t use the this[] query because an item is removed, so the only way to make sure an item is removed is to just use the Count query, so the Remove will still follow the principle.   5. For every query and command, decide on a suitable precondition.   We have now focused only on postcondition, now time for some preconditons. The 5th principle is about deciding a suitable preconditon for every query and command. If we starts to look at one of our basic queries (will not go through all Queries and commands here, just some of them) the this[] query, we can’t pass an index that is lower then 1 (.Net arrays and list are zero based, but not the stack in this blog post ;)) and the index can’t be lesser than the number of items in the stack. So here we will need a preconditon. public object this[uint index] { get { Contract.Requires(index >= 1); Contract.Requires(index <= Count); return _array[index]; } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Think about the Contract as an documentation about how to use the code in a correct way, so if the contract could be specified elsewhere (not part of the method body), we could simply write “return _array[index]” and there is no need to check if index is greater or lesser than Count, because that is specified in a “contract”. The implementation of Code Contract, requires that the contract is specified in the code. As a developer I would rather have this contract elsewhere (Like Spec#) or implemented in a way Eiffel uses it as part of the language. Now when we have looked at one Query, we can also look at one command, the Remove command (You can see the whole implementation of the Stack at the end of this blog post, where precondition is added to more queries and commands then what I’m going to show in this section). We can only Remove an item if the Count is greater than 0. So we can write a precondition that will require that Count must be greater than 0. public void Remove() { Contract.Requires(Count > 0); Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   6. Write invariants to define unchanging properties of objects.   The last principle is about making sure the object are feeling great! This is done by using invariants. When using Code Contract we can specify invariants by adding a method with the attribute ContractInvariantMethod, the method must be private or public and can only contains calls to Contract.Invariant. To make sure the Stack feels great, the Stack must have 0 or more items, the Count can’t never be a negative value to make sure each command and queries can be used of the Stack. Here is our invariant for the Stack object: [ContractInvariantMethod] private void ObjectInvariant() { Contract.Invariant(Count >= 0); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   Note: The ObjectInvariant method will be called every time after a Query or Commands is called. Here is the full example using Code Contract:   public class Stack { private object[] _array; //Basic Queries public uint Count; public object this[uint index] { get { Contract.Requires(index >= 1); Contract.Requires(index <= Count); return _array[index]; } set { Contract.Requires(index >= 1); Contract.Requires(index <= Count); _array[index] = value; } } //Derived Queries //Is related to Count Query public bool IsEmpty() { Contract.Ensures(Contract.Result<bool>() == (Count == 0)); return Count == 0; } //Is related to Count and this[] Query public object Top() { Contract.Requires(Count > 0, "Stack is empty"); Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } //Creation commands public Stack(uint size) { Contract.Requires(size > 0); Contract.Ensures(Count == 0); Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { Contract.Requires(value != null); Contract.Ensures(Count == Contract.OldValue<uint>(Count) + 1); Contract.Ensures(this[Count] == value); this[++Count] = value; } public void Remove() { Contract.Requires(Count > 0); Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } [ContractInvariantMethod] private void ObjectInvariant() { Contract.Invariant(Count >= 0); } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Summary By using Design By Contract we can make sure the users are using our code in a correct way, and we must also make sure the users will get the expected results when they uses our code. This can be done by specifying contracts. To make it easy to use Design By Contract, some principles may be good to follow like the separation of commands an queries. With .Net 4.0 we can use the Code Contract feature to specify contracts.

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  • InstallShield-2009: Basic MSI: How to run a custom action after user cancels uninstall (rollback)

    - by Samir
    InstallShield-2009 Premier: Basic msi project: What to do when I want a custom action to run when user clicks cancel button during uninstall? I put a custom action (a C# exe which would just show a message box) with Action Type: Type: Launch an executable Location: Stored in the Binary table Action Parameters: Source: exe path Target: a b c (doesn't matter, I don't need it) Additional Options: Return Processing: Synchronous (Check exit code) Run Only During Path Uninstall: unchecked Respond Options: In-Script Execution: Rollback Execution in System Context Executing Scheduling: disabled Insert into Sequence: Install UI-Sequence: <Absent from sequence> Install Execute Sequence: After InstallServices (what should I set here?) Install Execute Condition: (do I need to set? I left it blank) but it didn't fire the message box when I canceled the uninstall. How?

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  • Language Agnostic Basic Programming Question

    - by Rachel
    This is very basic question from programming point of view but as I am in learning phase, I thought I would better ask this question rather than having a misunderstanding or narrow knowledge about the topic. So do excuse me if somehow I mess it up. Question: Let's say I have class A,B,C and D now class A has some piece of code which I need to have in class B,C and D so I am extending class A in class B, class C, and class D Now how can I access the function of class A in other classes, do I need to create an object of class A and than access the function of class A or as am extending A in other classes than I can internally call the function using this parameter. If possible I would really appreciate if someone can explain this concept with code sample explaining how the logic flows. Note Example in Java, PHP and .Net would be appreciated.

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  • iPhone: How to Get Basic Authentication to HTTPS Web Service Using NSURLCredential

    - by ian1971
    I am trying to call an https web service (RESTful) using basic authentication. It works fine if I put the credentials in the url itself but I would rather add it to the request so that the password does not appear, for instance in an exception. I am using the following code: NSURLCredential *credential = [NSURLCredential credentialWithUser:@"myuser" password:@"mypassword" persistence:NSURLCredentialPersistenceForSession]; NSURLProtectionSpace *protectionSpace = [[NSURLProtectionSpace alloc] initWithHost:@"example.com" port:443 protocol:@"https" realm:nil authenticationMethod:NSURLAuthenticationMethodHTTPBasic]; [[NSURLCredentialStorage sharedCredentialStorage] setDefaultCredential:credential forProtectionSpace:protectionSpace]; NSURLConnection *theConnection = [NSURLConnection connectionWithRequest:theRequest delegate:self]; but it does not work. The didReceiveAuthenticationChallenge delegate method gets called and I can add a credential there but ideally I would send it with the request. Any ideas?

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  • Translate Basic Config.groovy log4j DSL to external log4j.properties

    - by Stephen Swensen
    The following is a basic log4j configuration inside Config.groovy using the log4j DSL with Grails 1.2, it works as expected (log all errors to the given file): log4j = { appenders { file name:'file', file:"c:/error.log" } error 'grails.app' root { error 'file' } } How would one translate this into a properties style log4j configuration file? The following does not work: log4j.rootLogger=ERROR, FA log4j.appender.FA=org.apache.log4j.FileAppender log4j.appender.FA.File=C:/error.log log4j.logger.grails.app=ERROR, FA I suspect it has something to do with the translation of error 'grails.app' but I really don't know. If it makes any difference, the properties file is configured externally: grails.config.locations = ["file:${basedir}/extconf/log4j.properties"] All I really want is an external log4j properties file which logs all application exceptions to a file.

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  • Best package for basic web-based file manager

    - by alchemical
    I'm looking for a basic web-based file management application. It must have an affordable price, and fairly easy installation would be a plus. ASP.Net / IIS based would be easiest for me to work with. Basically, I'd like it to create a secure web site where myself and a few people can exchange various types of files, etc. I'm looking for a package I can install on my own server rather than a web-based service, as I think I can get more space at a good price point this way. I could go custom coding, but I figure this is such a generic need, there must be something already mature out there at a decent price. What has worked best for you?

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  • Basic Ruby on Rails Question about routing

    - by Acidburn2k
    I have a controller without any related model. This controller is to span some informations from various models. I have lots of actions there, which define certain views on the page. What would be the best way to organize routes for this controller. What I would like is to have /dashboard/something point to any action in the dashboard controller. Not actions like new/edit but arbitrary (showstats, etc). With trail and error I made something like this: map.dashboard 'dashboard/:action', :controller => 'dashboard', :action => :action Now it is possible to access those url using helper: dashboard_url('actionname') This approch seems to be working ok, but is this the way to go? I am not quite sure understand, how are the helper method names generated. How to generate same helper names as in basic controllers "action_controller_url" ? That would be more generic and made the code more consistent. Thanks in advance.

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  • Visual C# GUI Designer basic tutorial

    - by cusack
    Hi, can you recommend a Visual C# Form Designer tutorial that is targeted at experienced programmers who have at least a basic knowledge of C# but are new to the VS C# Form Designer. At least it shouldn't be targeted at programming newbs, like Introduction to Visual C# 2008 Express Edition (it explains how a comment looks like in C#). So far I've found C# Programming Tutorial - Programming Winforms in C# on stackoverflow. Wishlist: ;-) I'm more interested in focus on the designer itself rather than an explanation of single gui-elements. In other words explaining separation between generated-code, what to not edit manually (visual-c#-designer-responsibility) and on the other hand the parts for which the programmer himself is responsible. So a little more abstract best-practice point of view pointing out some caveats would be great as well. I would prefer text over video as well, but that's minor. /Wishlist Perhaps even a Microsoft reference specific to the Visual c# forms designer (which I seem to have been unable to find) would be helpful.

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  • Installshield 2009 Premier Basic MSI: Not show a warning message window during uninstall

    - by Samir
    Installshield 2009 Premier Basic MSI: When I uninstall there is a Message Box saying that explorer has to be closed: [Title] My-Product-Name [List] Explorer [radio button 1, Selected by default] Automatically close applications and attempt to restart them after setup is complete [radio button 2] Do not close applications. (A Reboot will be required) [Ok Button] [Cancel Button] If I click OK [with radio button 1 selected] all opened folders are closed !!! How to get rid of this, I don't want any warning message box to show and not close explorer either? More info: I have a dll which is used to show explorer context menu with icons when we right click on any file/folder. This dll is registered during installation and unregistered during uninstall. When we uninstall WinRAR we don't see any such messages, do we?

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  • Basic questions about SNMP

    - by David Hodgson
    Hi, I'm learning about SNMP, and writing some applications using it. I have some basic questions about the protocol: Do the agents store its state on the device itself? If there is a trap set on an agent, can you do a poll on the same OID to get the same information? Without using a mib file, is there a way to query a device for all of its information at once? If not, and you're writing your own customized manager, do you have to know the structure of what it reports up front? If you're setting up an agent to report, is there usually a way to control the frequency of how often it sends a trap? Or does it usually send a trap as often as some condition is satisfied?

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  • Scala type system : basic type mismatch

    - by SiM
    I have a basic type system type mismatch problem: I have a class with a method def Create(nodeItem : NodeItem) = {p_nodeStart.addEndNode(nodeItem)} where p_nodeStart is NodeCache class NodeCache[END_T<:BaseNode] private(node: Node) extends BaseNode { def addEndNode(endNode : END_T) = {this.CACHE_HAS_ENDNODES.Create(endNode)} and the error its giving me is: error: type mismatch; found : nodes.NodeItem required: Nothing def Create(nodeItem : NodeItem) = {p_nodeStart.addEndNode(nodeItem)} while the NodeCache is defined as object NodeTrigger { def Create() { val nodeTimeCache = NodeCache.Create[NodeItem](node) and in object NodeCache object NodeCache { def Create[END_T<:BaseNode]() { val nodeCache = new NodeCache[END_T](node); Any ideas, how to fix the error?

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  • Language Agnositc Basic Programming Question

    - by Rachel
    This is very basic question from programming point of view but as I am in learning phase, I thought I would better ask this question rather than having an misunderstanding or narrow knowledge about the topic. So do excuse me if somehow I mess it up. Question: Let say I have class A,B,C and D now class A has some piece of code which I need to have in class B,C and D so I am extending class A in class B, class C, and class D Now how can I access the function of class A in other classes, do I need to create an object of class A and than access the function of class A or as am extending A in other classes than I can internally call the function using this parameter. If possible I would really appreciate if someone can explain this concept with code sample explaining how the logic flows.

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  • C/C++ Allegro program causes Windows 7 to switch to Aero Basic

    - by Matt H
    Hi SO, I'm just trying out the allegro library, and here is the code which I've got so far: #include <allegro.h> int main(int argc, char *argv[]) { allegro_init(); // initialize the allegro libraries install_keyboard(); // initialize keyboard functions set_color_depth(16); // set the color depth set_gfx_mode(GFX_AUTODETECT_WINDOWED, 640, 480, 0, 0); // set up 640*480px window BITMAP *pic = NULL; pic = load_bitmap("C:/picture.bmp", NULL); // load the picture blit(pic, screen, 0, 0, 0, 0, 1000, 1000); readkey(); destroy_bitmap(pic); return 0; } END_OF_MAIN() It works fine, but when I run it, while the program's window is open, Windows 7 changes the theme from Aero to Aero basic. If you aren't sure what I mean, this pops up (I got this from Google, which is why it says Vista rather than Windows 7): 1) Why? 2) How can I ensure that this doesn't happen?

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  • Not Seeing Ajax Requests In Firebug If Header Has Been Modified

    - by FluidFoundation
    Hey braintrust, I'm making an ajax call using jQuery's library to an api, which requires a username and password encoded to base64 be added to the header. here's a basic example: $.ajax({ type: "GET", contentType: 'application/json', beforeSend:function(xhr){ xhr.setRequestHeader("Authentication", "Basic " + base64EncodedValue); } url: 'https://api.company.com/uri/', complete: function(result) { alert(result); } }); But when this fires off, I get a black alert box, so it doesn't appear as if something is coming back. There is no log in the Firebug console that a get ajax request was done. However, if I remove the beforeSend option, I do see the ajax request get logged, but the request gets back a 'not authorized', so it definitely hit the right place. Any ideas on why it's not showing up in Firebug so I can verify the headers are being sent out correctly?

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  • http_post_data basic authentication?

    - by kristian nissen
    I have a remote service that I need to access, according to the documentation it's restricted using basic authentication and all requests have to be posted (HTTP POST). The documentation contains this code example - VB script: Private Function SendRequest(ByVal Url, ByVal Username, ByVal Password, ByVal Request) Dim XmlHttp Set XmlHttp = CreateObject("MSXML2.XmlHttp") XmlHttp.Open "POST", Url, False, Username, Password XmlHttp.SetRequestHeader "Content-Type", "text/xml" XmlHttp.Send Request Set SendRequest = XmlHttp End Function how can I accomplish this in PHP? When I post data to the remote server it replies: 401 Unauthorized Access which is fine because I'm not posting my user/pass just the data. Bu when I add my user/pass as it's describe here: http://dk.php.net/manual/en/http.request.options.php like this: $res = http_post_data('https://example.com', $data, array( 'Content-Type: "text/xml"', 'httpauth' => base64_encode('user:pass'), 'httpauthtype' => HTTP_AUTH_BASIC ) ); the protocol is https - I get a runtime error in return (it's a .Net service). I have tried it without the base64_encode but with the same result.

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  • Eclipse Basic Web Development?

    - by Sean Ochoa
    I want to start doing web development with Eclipse. Not Java, tomcat, axis2, or anything else anymore complicated than basic XHTML / JS / CSS development, at this time. Problem 1: I realize that it can edit those files, but its trying to manage my HTML docs as part of "my workspace", and all I want it to do is manage the files as part of my local www server HTdocs directory. Problem 2: I would like to edit WYSIWYG-style, if possible. I tried installing a plug-in for that, but I wasn't able to get w4 toolkit to function properly. This would really help me to speed up development, I think. Follow-up: I've installed WTP and its dependencies (except for the tests portion, which had install problems due to dependencies that were seemingly irreconcilable).

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  • SQLITE basic syntax

    - by Doori Bar
    I seem to misunderstand a basic syntax, why this sample works: sqlite3_prepare_v2(db, "insert into test values('boo','boo',0);", strlen(querystring)+1 , &stmt, NULL); if ((rc = sqlite3_step(stmt)) != SQLITE_DONE) fprintf(stderr, "Error: sqlite3_step() %d. Error Message %s;\n",rc,sqlite3_errmsg(db)); But when I try this query: "insert into test(strtest) values('boo');" I get an error: Error: sqlite3_step() 19. Error Message constraint failed; What am I missing? table test is: "create table test (blobtest BLOB(4) NOT NULL, strtest VARCHAR NOT NULL, inttest INTEGER NOT NULL );" Thanks, Doori Bar

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  • Extremely basic PHP and Mysql

    - by fighella
    Background: I am more of a designer than a programmer, but have hacked templates for many open source CMS's (Drupal, Joomla, Wordpress) I want to start from scratch in regards to the relations of php and a mysql database. Lets assume I have a working database and php engine locally. What would be my first step to connecting to my database and creating a table... (im happy to be led to an appropriate tutorial...) Many of the tutorials I have seen start with basic php, but I would rather explore the connection between the db and the php.

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  • Basic date/time manipulation in NHiberate query

    - by Yann Trevin
    I'm trying to restrict my NHibernate query with some basic date/time manipulation. More specifically, I want to execute the following statement (pseudo-SQL): select * from article where created_on + lifespan >= sysdate with: created_on is mapped to a property of type DateTime. lifespan is mapped to a property of type TimeSpan. sysdate is the current date/time (of the database server or ofthe application host, I don't care) Is there any built-in way to do that by using the Criteria-API or HQL? return session .CreateCriteria<Article>() .Add( ? ) .List<Article>();

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  • Basic PHP question for Drupal Views theming

    - by oalo
    My PHP and programming knowledge is extremely basic, so this is probably a dumb question: I am theming a View in Drupal 6, and I want to add an id with a consecutive number to each item in the view (first item would have the id #item1, the second #item2, etc). I am customizing the style output (views-view-unformatted--MYVIEWNAME.tpl.php) and the row style output (views-view-fields--MYVIEWNAME.tpl.php), and I want to add a counter variable in the foreach loop in the style output tpl, and then use that variable in the row style output tpl, but the last one is not recognizing the variable. It does not give me any errors, but doesnt print the number. I understand this has probably something to do with variables visibility, how can I declare the counter variable in the style .tpl so I can the use it in the row style .tpl? Thank you

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