NSURLSessionUploadTask response content data is null

Question

Here's where I am so far with NSURLSessionUploadTask:

iOS application starts an NSURLSessionUploadTask using POST
server receives HTTP POST request
server reads content of the request so data is uploaded
server sends HTTP response to iOS consisting of the following:

HTTP/1.1 200 OK
Server: BaseHTTP/0.3 Python/2.7.10
Date: Fri, 30 Oct 2015 16:15:21 GMT
Content-Type: text/html
Content-Length: 96

<html><head><title>POST RESPONSE</title></head><body><p>The file was uploaded.</p></body></html>

iOS application receives response and NSLogs the response via NSURLSessionTaskDelegate -> URLSession:task:didCompleteWithError:

<NSHTTPURLResponse: 0x15d95110> { URL: http://10.157.239.129:42000/ } { status code: 200, headers {
    "Content-Length" = 96;
    "Content-Type" = "text/html";
    Date = "Fri, 30 Oct 2015 16:15:21 GMT";
    Server = "BaseHTTP/0.3 Python/2.7.10";
} }

however, when I try to NSLog the response content when the method NSURLSessionTaskDelegate: -> URLSession:dataTask:didReceiveData:

- (void)URLSession:(NSURLSession *)session
          dataTask:(NSURLSessionDataTask *)dataTask
    didReceiveData:(NSData *)data
{
    // Called when data task has received some data (not applicable for straight upload?)
    if (data != NULL)
    {
        NSLog(@"%s: %@", __PRETTY_FUNCTION__,[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding]);
    }
    else
    {
        NSLog(@"%s: but no actual data received.", __PRETTY_FUNCTION__);
    }

    // If we are not in the "active" or foreground then log some background information to the console
    if (UIApplication.sharedApplication.applicationState != UIApplicationStateActive)
    {
        [BackgroundTimeRemainingUtility NSLog];
    }
}

is called I get this for output:

2015-10-30 12:15:22.648 NSURLSessionUploadTaskExample[215:7286] -[ViewController URLSession:dataTask:didReceiveData:]: (null)

what is odd about this is that the response should not have triggered the if statement block if the data is null!
I also have evidence that the response data WAS sent to the iOS application via Wireshark. Here's a packet capture of the HTTP response from the server:

Can anyone tell me why iOS appears to be losing the content in the HTTP response?

Can you please look into this stackoverflow.com/q/38831704/5730180 ? — RajuBhai Rocker

drbobdugan drbobdugan · Accepted Answer · 2015-11-02T15:05:47

Because I was able to trace the HTTP 200 response from the server to the iOS application, I suspected the iOS application had a problem. I set a breakpoint at the line:

NSLog(@"%s: %@", __PRETTY_FUNCTION__,[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding]);

and examined the data object with the debugger:

Each of the 96 bytes in the response content was getting to NSURLSessionTaskDelegate: -> URLSession:dataTask:didReceiveData: So the NSString decoding in the NSLog was at fault. Now things were making sense. I was sending a 96 byte ASCII response, not a 96 byte UTF8 response!

I replaced the NSString decoder with the following:

NSLog(@"%s: %@", __PRETTY_FUNCTION__,[[NSString alloc]  initWithBytes:[data bytes] length:[data length] encoding: NSASCIIStringEncoding]);

Problem solved with the following output:

2015-11-02 10:04:47.086 NSURLSessionUploadTaskExample[561:363449] -[ViewController URLSession:dataTask:didReceiveData:]:<html><head><title>POST RESPONSE</title></head><body><p>The file was uploaded.</p></body></html>

I've also put a very basic NSURLSessionUploadTask example application and webserver on github here.

NSURLSessionUploadTask response content data is null

1 Answers