This is a working version of multipart streaming.

- Fixed missing CRLF after header string.
 - Fixed not traversing through the buffer while reading.
 - Fixed content length of body stream are incorrect when attempts to finalize the multipart form data due to boundary settings not set yet.
 - Create a method named `setInitialAndFinalBoundaries` that attempts to reset all HTTP body parts boundary settings first before setting the initial and final boundaries.

Tested successfully on my own codes that does photo uploading to Flickr using `appendPartWithFileData:name:fileName:mimeType:`. I have not tried uploading from file URL but don't foresee any issue.

AFNetworking/AFHTTPClient.m

@@ -757,6 +757,7 @@ static inline NSString * AFContentTypeForPathExtension(NSString *extension) {
 @property (readonly, getter = isEmpty) BOOL empty;
 
 - (id)initWithStringEncoding:(NSStringEncoding)encoding;
+- (void)setInitialAndFinalBoundaries;
 
 @end
 
@@ -908,6 +909,9 @@ static inline NSString * AFContentTypeForPathExtension(NSString *extension) {
         return self.request;
     }
     
+    // We have to set the initial and final boundaries here so that the body stream returns the correct content length.
+    [self.bodyStream setInitialAndFinalBoundaries];
+    
     [self.request setValue:[NSString stringWithFormat:@"multipart/form-data; boundary=%@", kAFMultipartFormBoundary] forHTTPHeaderField:@"Content-Type"];
     [self.request setValue:[NSString stringWithFormat:@"%llu", [self.bodyStream contentLength]] forHTTPHeaderField:@"Content-Length"];
     [self.request setHTTPBodyStream:self.bodyStream];
@@ -946,12 +950,29 @@ static inline NSString * AFContentTypeForPathExtension(NSString *extension) {
     [super dealloc];
 }
 
+- (void)setInitialAndFinalBoundaries {
+    if ([self.HTTPBodyParts count] > 0) { // If there's any HTTP body parts...
+        // Reset all HTTP body parts boundary settings first.
+        for (AFHTTPBodyPart *theHTTPBodyPart in self.HTTPBodyParts) {
+            theHTTPBodyPart.hasInitialBoundary = NO;
+            theHTTPBodyPart.hasFinalBoundary = NO;
+        }
+        // Set the first and last object boundary settings.
+        [[self.HTTPBodyParts objectAtIndex:0] setHasInitialBoundary:YES];
+        [[self.HTTPBodyParts lastObject] setHasFinalBoundary:YES];
+    }
+}
+
 #pragma mark - NSStream subclass overrides
 
 - (void)open {
     if ([self.HTTPBodyParts count] > 0) {
-        [[self.HTTPBodyParts objectAtIndex:0] setHasInitialBoundary:YES];
+        // This call might be redundant but can be a good safety measure
-        [[self.HTTPBodyParts lastObject] setHasFinalBoundary:YES];
+        // to make sure that the boundary settings are correctly set.
+        // But even so, the length might be screw up if the user try to
+        // mess with the HTTP body part between finalizing the multipart
+        // form data request and here.
+        [self setInitialAndFinalBoundaries];
         
         self.HTTPBodyPartEnumerator = [self.HTTPBodyParts objectEnumerator];
     }
@@ -1015,7 +1036,7 @@ static inline NSString * AFContentTypeForPathExtension(NSString *extension) {
                 break;
             }
         } else {
-            bytesRead += [self.currentHTTPBodyPart read:buffer maxLength:length];
+            bytesRead += [self.currentHTTPBodyPart read:&buffer[bytesRead] maxLength:length - bytesRead];
         }
     }
     
@@ -1129,6 +1150,8 @@ typedef enum {
     for (NSString *field in [self.headers allKeys]) {
         [headerString appendString:[NSString stringWithFormat:@"%@: %@%@", field, [self.headers valueForKey:field], kAFMultipartFormCRLF]];
     }
+    // There's a CRLF after the header string.
+    [headerString appendString:kAFMultipartFormCRLF];
         
     return [NSString stringWithString:headerString];
 }
@@ -1172,17 +1195,17 @@ typedef enum {
         
     if (_phase == AFEncapsulationBoundaryPhase) {
         NSData *encapsulationBoundaryData = [([self hasInitialBoundary] ? AFMultipartFormInitialBoundary() : AFMultipartFormEncapsulationBoundary()) dataUsingEncoding:self.stringEncoding];
-        bytesRead += [self readData:encapsulationBoundaryData intoBuffer:buffer maxLength:(length - bytesRead)];
+        bytesRead += [self readData:encapsulationBoundaryData intoBuffer:&buffer[bytesRead] maxLength:(length - bytesRead)];
     }
     
     if (_phase == AFHeaderPhase) {
         NSData *headersData = [[self stringForHeaders] dataUsingEncoding:self.stringEncoding];
-        bytesRead += [self readData:headersData intoBuffer:buffer maxLength:(length - bytesRead)];
+        bytesRead += [self readData:headersData intoBuffer:&buffer[bytesRead] maxLength:(length - bytesRead)];
     }
     
     if (_phase == AFBodyPhase) {
         if ([self.inputStream hasBytesAvailable]) {
-            bytesRead += [self.inputStream read:buffer maxLength:(length - bytesRead)];
+            bytesRead += [self.inputStream read:&buffer[bytesRead] maxLength:(length - bytesRead)];
         }
         
         if (![self.inputStream hasBytesAvailable]) {
@@ -1192,7 +1215,7 @@ typedef enum {
     
     if (_phase == AFFinalBoundaryPhase) {
         NSData *closingBoundaryData = ([self hasFinalBoundary] ? [AFMultipartFormFinalBoundary() dataUsingEncoding:self.stringEncoding] : [NSData data]);
-        bytesRead += [self readData:closingBoundaryData intoBuffer:buffer maxLength:(length - bytesRead)];
+        bytesRead += [self readData:closingBoundaryData intoBuffer:&buffer[bytesRead] maxLength:(length - bytesRead)];
     }
 
     return bytesRead;