Added support to override built-in logger at runtime

GCDWebServer/Core/GCDWebServer.h

@@ -69,6 +69,12 @@ typedef GCDWebServerResponse* _Nullable (^GCDWebServerProcessBlock)(__kindof GCD
 typedef void (^GCDWebServerCompletionBlock)(GCDWebServerResponse* _Nullable response);
 typedef void (^GCDWebServerAsyncProcessBlock)(__kindof GCDWebServerRequest* request, GCDWebServerCompletionBlock completionBlock);
 
+/**
+ *  The GCDWebServerBuiltInLoggerBlock is used to override the built-in logger at runtime.
+ *  The message parameter is the formatted log message with the logging level.
+ */
+typedef void (^GCDWebServerBuiltInLoggerBlock)(NSString* _Nonnull message);
+
 /**
  *  The port used by the GCDWebServer (NSNumber / NSUInteger).
  *
@@ -573,6 +579,14 @@ extern NSString* const GCDWebServerAuthenticationMethod_DigestAccess;
  */
 + (void)setLogLevel:(int)level;
 
+/**
+ *  Set a logger to be used instead of the built-in logger which logs to stderr.
+ *
+ *  IMPORTANT: In order for this override to work, you should not be specifying
+ *  a custom logger at compile time with "__GCDWEBSERVER_LOGGING_HEADER__".
+ */
++ (void)setBuiltInLogger:(GCDWebServerBuiltInLoggerBlock)block;
+
 /**
  *  Logs a message to the logging facility at the VERBOSE level.
  */

GCDWebServer/Core/GCDWebServer.m

@@ -85,18 +85,24 @@ static BOOL _run;
 
 #ifdef __GCDWEBSERVER_LOGGING_FACILITY_BUILTIN__
 
+static GCDWebServerBuiltInLoggerBlock _builtInLoggerBlock;
+
 void GCDWebServerLogMessage(GCDWebServerLoggingLevel level, NSString* format, ...) {
   static const char* levelNames[] = {"DEBUG", "VERBOSE", "INFO", "WARNING", "ERROR"};
   static int enableLogging = -1;
   if (enableLogging < 0) {
     enableLogging = (isatty(STDERR_FILENO) ? 1 : 0);
   }
-  if (enableLogging) {
+  if (_builtInLoggerBlock || enableLogging) {
     va_list arguments;
     va_start(arguments, format);
     NSString* message = [[NSString alloc] initWithFormat:format arguments:arguments];
     va_end(arguments);
-    fprintf(stderr, "[%s] %s\n", levelNames[level], [message UTF8String]);
+    if (_builtInLoggerBlock) {
+      _builtInLoggerBlock([NSString stringWithFormat:@"[%s] %s", levelNames[level], [message UTF8String]]);
+    } else {
+      fprintf(stderr, "[%s] %s\n", levelNames[level], [message UTF8String]);
+    }
   }
 }
 
@@ -1091,6 +1097,14 @@ static inline NSString* _EncodeBase64(NSString* string) {
 #endif
 }
 
++ (void)setBuiltInLogger:(GCDWebServerBuiltInLoggerBlock)block {
+#if defined(__GCDWEBSERVER_LOGGING_FACILITY_BUILTIN__)
+  _builtInLoggerBlock = block;
+#else
+  GWS_DCHECK(false) // Built-in logger must be enabled in order to override
+#endif
+}
+
 - (void)logVerbose:(NSString*)format, ... {
   va_list arguments;
   va_start(arguments, format);