Add auto-port allocation

Resolves #30.

Ports are now dynamically allocated for each instance of `TWebMock`
allowing multiple instances to be created without manually managing the
port allocations. It is still possible to override the automatic
behaviour by specifying a port in the constructor e.g.
`TWebMock.Create(1234)`.

README.md

@@ -97,15 +97,15 @@ initialization
 end.
 ```
 
-By default `TWebMock` will bind to port `8080`. The port can be specified at
-creation.
+By default `TWebMock` will bind to a port dynamically assigned start at `8080`.
+This behaviour can be overriden by sepcifying a port at creation.
 ```Delphi
 WebMock := TWebMock.Create(8088);
 ```
 
 The use of `WebMock.URLFor` function within your tests is to simplify
-constructing a valid URL. The `BaseURL` property contains a valid URL for the
-server root.
+constructing a valid URL. The `Port` property containes the current bound port
+and `BaseURL` property contains a valid URL for the server root.
 
 ## Examples
 ### Stubbing

Source/Delphi.WebMock.pas

@@ -33,18 +33,24 @@ interface
   Delphi.WebMock.Dynamic.RequestStub, Delphi.WebMock.Response,
   Delphi.WebMock.ResponseBodySource, Delphi.WebMock.ResponseStatus,
   IdContext, IdCustomHTTPServer, IdGlobal, IdHTTPServer,
-  System.Classes, System.Generics.Collections, System.RegularExpressions;
+  System.Classes, System.Generics.Collections, System.RegularExpressions,
+  System.SysUtils;
 
 type
+  EWebMockError = class(Exception);
+  EWebMockExceededBindAttempts = class(EWebMockError);
+
   TWebWockPort = TIdPort;
 
   TWebMock = class(TObject)
+  class var NextPort: Integer;
   private
     FServer: TIdHTTPServer;
     FBaseURL: string;
     FStubRegistry: TList<IWebMockRequestStub>;
     FHistory: TList<IWebMockHTTPRequest>;
     procedure InitializeServer(const APort: TWebWockPort);
+    procedure StartServer(const APort: TWebWockPort);
     procedure OnServerRequest(AContext: TIdContext;
       ARequestInfo: TIdHTTPRequestInfo; AResponseInfo: TIdHTTPResponseInfo);
     function GetRequestStub(ARequestInfo: IWebMockHTTPRequest) : IWebMockRequestStub;
@@ -56,9 +62,11 @@   TWebMock = class(TObject)
       const AResponseHeaders: TStrings);
     procedure SetResponseStatus(AResponseInfo: TIdHTTPResponseInfo;
       const AResponseStatus: TWebMockResponseStatus);
+    function GetNextPort: Integer;
+    function GetPort: Integer;
     property Server: TIdHTTPServer read FServer write FServer;
   public
-    constructor Create(const APort: TWebWockPort = 8080);
+    constructor Create(const APort: TWebWockPort = 0);
     destructor Destroy; override;
     function Assert: TWebMockAssertion;
     procedure PrintStubRegistry;
@@ -75,16 +83,18 @@   TWebMock = class(TObject)
     property BaseURL: string read FBaseURL;
     property History: TList<IWebMockHTTPRequest> read FHistory;
     property StubRegistry: TList<IWebMockRequestStub> read FStubRegistry;
+    property Port: Integer read GetPort;
   end;
 
 implementation
 
 uses
   Delphi.WebMock.HTTP.Request,
   Delphi.WebMock.HTTP.RequestMatcher,
+  IdException,
   IdHTTP,
   IdSocketHandle,
-  System.SysUtils;
+  IdStack;
 
 { TWebMock }
 
@@ -93,7 +103,7 @@ function TWebMock.Assert: TWebMockAssertion;
   Result := TWebMockAssertion.Create(History);
 end;
 
-constructor TWebMock.Create(const APort: TWebWockPort = 8080);
+constructor TWebMock.Create(const APort: TWebWockPort = 0);
 begin
   inherited Create;
   FStubRegistry := TList<IWebMockRequestStub>.Create;
@@ -109,6 +119,22 @@ destructor TWebMock.Destroy;
   inherited;
 end;
 
+function TWebMock.GetNextPort: Integer;
+var
+  FIsInitial: Boolean;
+begin
+  AtomicCmpExchange(NextPort, 8080, 0, FIsInitial);
+  if FIsInitial then
+    Exit(NextPort);
+
+  Result := AtomicIncrement(NextPort);
+end;
+
+function TWebMock.GetPort: Integer;
+begin
+  Result := Server.Bindings.Items[0].Port;
+end;
+
 function TWebMock.GetRequestStub(ARequestInfo: IWebMockHTTPRequest) : IWebMockRequestStub;
 var
   LRequestStub: IWebMockRequestStub;
@@ -131,11 +157,9 @@ procedure TWebMock.InitializeServer(const APort: TWebWockPort);
 
   FServer := TIdHTTPServer.Create;
   Server.ServerSoftware := 'Delphi WebMocks';
-  Server.DefaultPort := APort;
   Server.OnCommandGet := OnServerRequest;
   Server.OnCommandOther := OnServerRequest;
-  Server.Active := True;
-  FBaseURL := Format('http://127.0.0.1:%d/', [Server.DefaultPort]);
+  StartServer(APort);
 end;
 
 procedure TWebMock.OnServerRequest(AContext: TIdContext;
@@ -209,6 +233,44 @@ procedure TWebMock.SetResponseStatus(AResponseInfo: TIdHTTPResponseInfo;
     AResponseInfo.ResponseText := AResponseStatus.Text;
 end;
 
+procedure TWebMock.StartServer(const APort: TWebWockPort);
+var
+  LAttempt, LMaxAttempts: Integer;
+  LPort: Integer;
+  LSocketHandle: TIdSocketHandle;
+begin
+  LAttempt := 0;
+  LMaxAttempts := 3;
+  while not Server.Active do
+  begin
+    Inc(LAttempt);
+    if LAttempt >= LMaxAttempts then
+      raise EWebMockExceededBindAttempts.Create('Exceeded attempts to bind port.');
+    if APort > 0 then
+      LPort := APort
+    else
+      LPort := GetNextPort;
+    Server.Bindings.Clear;
+    LSocketHandle := Server.Bindings.Add;
+    LSocketHandle.Port := LPort;
+    try
+      Server.Active := True;
+      FBaseURL := Format('http://127.0.0.1:%d/', [LSocketHandle.Port]);
+    except
+      on E: EIdCouldNotBindSocket do
+      begin
+        Server.Active := False;
+        StartServer(APort);
+      end;
+      on E: EIdSocketError do
+      begin
+        Server.Active := False;
+        StartServer(APort);
+      end;
+    end;
+  end;
+end;
+
 function TWebMock.StubRequest(
   const AMatcher: TWebMockDynamicRequestMatcher): TWebMockDynamicRequestStub;
 var

Tests/Delphi.WebMock.Tests.pas

@@ -45,13 +45,15 @@   TWebMockTests = class(TObject)
     [TearDown]
     procedure TearDown;
     [Test]
-    procedure Create_WithNoArguments_StartsListeningOnPort8080;
+    procedure Create_WithNoArguments_StartsListeningOnPortGreaterThan8080;
+    [Test]
+    procedure Create_WithNoArgumentsWhenRepeated_StartsListeningOnDifferentPorts;
     [Test]
     procedure Create_WithPort_StartsListeningOnPortPort;
     [Test]
-    procedure BaseURL_ByDefault_ReturnsLocalHostURLWithDefaultPort;
+    procedure BaseURL_ByDefault_ReturnsLocalHostURLWithPort;
     [Test]
-    procedure BaseURL_WhenPortIsNotDefault_ReturnsLocalHostURLWithPort;
+    procedure Port_Always_ReturnsTheListeningPort;
     [Test]
     procedure Reset_Always_ClearsHistory;
     [Test]
@@ -96,34 +98,36 @@ procedure TWebMockTests.URLFor_GivenEmptyString_ReturnsBaseURL;
 
 procedure TWebMockTests.URLFor_GivenStringWithLeadingSlash_ReturnsCorrectlyJoinedURL;
 begin
-  Assert.AreEqual('http://127.0.0.1:8080/file', WebMock.URLFor('/file'));
+  Assert.AreEqual(Format('http://127.0.0.1:%d/file', [WebMock.Port]), WebMock.URLFor('/file'));
 end;
 
 procedure TWebMockTests.URLFor_GivenStringWithoutLeadingSlash_ReturnsCorrectlyJoinedURL;
 begin
-  Assert.AreEqual('http://127.0.0.1:8080/file', WebMock.URLFor('file'));
+  Assert.AreEqual(Format('http://127.0.0.1:%d/file', [WebMock.Port]), WebMock.URLFor('file'));
 end;
 
-procedure TWebMockTests.BaseURL_ByDefault_ReturnsLocalHostURLWithDefaultPort;
+procedure TWebMockTests.BaseURL_ByDefault_ReturnsLocalHostURLWithPort;
 begin
-  Assert.AreEqual('http://127.0.0.1:8080/', WebMock.BaseURL);
+  Assert.AreEqual(Format('http://127.0.0.1:%d/', [WebMock.Port]), WebMock.BaseURL);
 end;
 
-procedure TWebMockTests.BaseURL_WhenPortIsNotDefault_ReturnsLocalHostURLWithPort;
+procedure TWebMockTests.Create_WithNoArgumentsWhenRepeated_StartsListeningOnDifferentPorts;
+var
+  LWebMock1, LWebMock2: TWebMock;
 begin
-  WebMock.Free;
-  WebMock := TWebMock.Create(8088);
+  LWebMock1 := TWebMock.Create;
+  LWebMock2 := TWebMock.Create;
 
-  Assert.AreEqual('http://127.0.0.1:8088/', WebMock.BaseURL);
+  Assert.IsTrue(LWebMock2.Port > LWebMock1.Port);
 end;
 
-procedure TWebMockTests.Create_WithNoArguments_StartsListeningOnPort8080;
+procedure TWebMockTests.Create_WithNoArguments_StartsListeningOnPortGreaterThan8080;
 var
   LResponse: IHTTPResponse;
 begin
-  LResponse := WebClient.Get('http://localhost:8080/');
+  LResponse := WebClient.Get(WebMock.URLFor('/'));
 
-  Assert.AreEqual('Delphi WebMocks', LResponse.HeaderValue['Server']);
+  Assert.IsTrue(WebMock.Port > 8080);
 end;
 
 procedure TWebMockTests.Create_WithPort_StartsListeningOnPortPort;
@@ -132,12 +136,17 @@ procedure TWebMockTests.Create_WithPort_StartsListeningOnPortPort;
 begin
   WebMock.Free;
 
-  WebMock := TWebMock.Create(8088);
-  LResponse := WebClient.Get('http://localhost:8088/');
+  WebMock := TWebMock.Create(8079);
+  LResponse := WebClient.Get('http://localhost:8079/');
 
   Assert.AreEqual('Delphi WebMocks', LResponse.HeaderValue['Server']);
 end;
 
+procedure TWebMockTests.Port_Always_ReturnsTheListeningPort;
+begin
+  Assert.IsTrue(WebMock.Port > 0);
+end;
+
 procedure TWebMockTests.ResetHistory_Always_ClearsHistory;
 begin
   WebClient.Get(WebMock.URLFor('history'));