Using a custom NSURLProtocol with UIWebView and POST requests

Question

In my iOS app, I'm using a UIWebView and a custom protocol (with my own NSURLProtocol implementation). I've been fairly careful about making sure that whenever I load a url, I load something like this into my UIWebView:

myprotocol://myserver/mypath

and in my NSURLProtocol implementation, I take a mutable copy of the NSURLRequest, convert the URL to http: and send that to my server.

Everything works for HTTP GET requests. The problem I encounter is with POST requests. It seems like the UIWebView doesn't properly encode the form data in the HTTPBody if the request uses my custom protocol.

One work-around, since I'm using HTTPS for my server requests, is that I register my protocol handler to intercept http: instead of myprotocol: and I can convert all calls to https: This other question, here, pointed me toward that solution:

But I'm wondering if there's any alternative and/or better way of accomplishing what I want.

Answer 1

Instead of trying to use POST requests, one work around is to continue using GET requests for myprotocol:// URLs, but transform them in your NSURLProtocol implementation to an http:// and POST request to your server using the request query string as the body of the POST.

The worry with using GET requests to send large amounts of data is that somewhere along the request chain, the request line might get truncated. This appears to not be a problem, however, with locally-implemented protocols.

I wrote a short Cordova test app to experiment and I found that I was able to send through a little over 1 MiB of data without trouble to the HTTP request echoing service http://http-echo.jgate.de/

Here is my startLoading implementation:

- (void)startLoading {
    NSURL *url = [[self request] URL];
    NSString *query = [url query];
    // Create a copy of `url` without the query string.
    url = [[[NSURL alloc] initWithScheme:@"http" host:@"http-echo.jgate.de" path:[url path]] autorelease];
    NSMutableURLRequest *newRequest = [NSMutableURLRequest requestWithURL:url];
    [newRequest setHTTPMethod:@"POST"];
    [newRequest setAllHTTPHeaderFields:[[self request] allHTTPHeaderFields]];
    [newRequest addValue:@"close" forHTTPHeaderField:@"Connection"];
    [newRequest addValue:@"application/x-www-form-urlencoded;charset=UTF-8" forHTTPHeaderField:@"Content-Type"];
    [newRequest setHTTPBody:[query dataUsingEncoding:NSUTF8StringEncoding]];
    urlConnection = [[NSURLConnection alloc] initWithRequest:newRequest delegate:self];
    if (urlConnection) {
        receivedData = [[NSMutableData data] retain];
    }
}

I then implemented the NSURLConnection protocol methods to forward to the appropriate NSURLProtocolClient method, but building up the response data in the case of Transfer-Encoding:chunked (as is the case for responses from http://http-echo.jgate.de/).