NSUrlRequest: where an app can find the default headers for HTTP request?

Question

Does anybody know where an iOS app can see the default headers that NSUrlRequest sets for an HTTP request?

Just creating NSUrlRequest with "http://.." NSURL and then asking: [request allHTTPHeaderFields] returns an empty dictionary. But I know that for example "Accept-Encoding" is set to "gzip". So I want to get all that fields and show them in a HTTP request demo.

I've also tried to swizzle [NSMutableURLRequest setValue:forHTTPHeaderField:], but it seems that it is not used by underlying API (NSURLRequest or NSURLConnection) to set those default fields I'm hunting for.

I'm making just a simple iOS demo which shows HTTP request and response information, so it doesn't really matters if it will be a public or private API used for that.

Answer 1

Your app cannot. It's done all down in CFNetwork - Communicating with HTTP Servers. I believe it just adds missing header values not supplied by NSURLRequest.

The defaults are:

• USER-AGENT "AppName - Eng/1.0 CFNetwork/485.13.9 Darwin/10.7.0"
• ACCEPT "*/*"
• ACCEPT-LANGUAGE "en-us"
• ACCEPT-ENCODING "gzip, deflate"
• CONNECTION "keep-alive"

Answer 2

hmm... maybe you might want to try within

- (NSURLRequest *)connection:(NSURLConnection *)connection willSendRequest:(NSURLRequest *)request redirectResponse:(NSURLResponse *)redirectResponse

method in your custom nsurlconnection class. although the documentation mentions something about redirects, this is certainly worth looking into.

Answer 3

That may be an overkill, but based on Matt Gallagher's blog post I've created even more simpler local HTTP listener and sent a separate [mutableCopy]ed request to it to be able to read and output all HTTP headers that this request has.

Better solution must be to setup a local HTTP request catcher, it must look nicer I think, but for the scope of simple demo just to show all sent/received headers this solution is OK.