Automatic decompresion of gzipped json response data not working - ios

Question

From all I have read gzipped response data should be automatically decompressed by the NS URL loading system. I am using AFNetworking and a AFJSONResponseSerializer to handle requests to a custom backend. I have experimented with adding "Accept-Encoding" = gzip to my request headers, but it has had no effect. My response headers include:
"Content-Encoding" = gzip;
"Content-Length" = 179837;
"Content-Type" = "application/json";
I am making the request like this:
[[AFHTTPRequestOperationManager sharedClient]
GET:#"some/endpoint"
parameters:#{#"foo":#"bar"}
success:^(AFHTTPRequestOperation *operation, id responseObject) {
NSLog(#"Response data size %u", operation.responseData.length);
NSURL *outputURL = [[APP_DELEGATE applicationDocumentsDirectory] URLByAppendingPathComponent:#"data.gzip"];
[operation.responseData writeToURL:outputURL atomically:NO];
}
failure:^(AFHTTPRequestOperation *operation, NSError *error) {
NSLog(#"ERROR [%d] [%#]", error.code, error.localizedDescription );
}];
When this runs the size of operation.responseData.length printed is what I expect. However, responseObject is nil when it should be an NSArray. I added the lines writing operation.responseData to test that the data received is what I expect. I can browse to data.gzip, uncompress it, and see my JSON.
It appears to me that the gzipped data received is not being automatically decompressed before my AFJSONResponseSerializer tries to handle it. Most of what I have found on Stackoverflow has either discussed how the decompression is automatic or suggested adding an "Accept-Encoding" = gzip header. Any suggestions would be appreciated.

Answer 1

Have you checked the output from the "custom backend" — use something like Charles Proxy which will let you see things like your response headers and raw content.
e.g. typical headers as shown in Charles:
HTTP/1.1 200 OK
Date Wed, 26 Nov 2014 22:25:33 GMT
Server Apache/2.2.24 (Unix) mod_hive/4.0 mod_ssl/2.2.24 OpenSSL/1.0.0-fips mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/5.0.2.2635 mod_fcgid/2.3.6
X-Powered-By PHP/5.3.29
P3P CP="NOI ADM DEV PSAi COM NAV OUR OTRo STP IND DEM"
Cache-Control no-cache
Pragma no-cache
Set-Cookie 4d3750fca133ae462ca26ca5a1cc0104=c7da991b30f53342846fff5ddaf3ea08; path=/
Cache-Control max-age=3600
Expires Wed, 26 Nov 2014 23:25:33 GMT
Host-Header 192fc2e7e50945beb8231a492d6a8024
Keep-Alive timeout=5, max=100
Connection Keep-Alive
Transfer-Encoding chunked
Content-Type text/html; charset=utf-8