What's a good HTTP library for (desktop Cocoa and) iPhone? Should just have a good interface to the basics like HTTP headers, get/post values (request string creation, URL encoding/decoding), sync and async requests... preferably pure Obj-C implementation. NSURL* is somewhat lacking.
I've had great success with the Three20 Project's TTURLRequest. It's a genericized version of the UI Elements used in the Facebook App.
How about what's already built into Cocoa in the forms of NSURLRequest and it's subclass NSMutableURLRequest? You'll probably also get to use NSURLConnection along with it...
Setting the post parameters in the HTTP body is pretty straight forward with NSMutableURLRequest, you can wrap it in a convenience method via a category if that's more desirable, similar to the OAuth library on google code:
http://oauth.googlecode.com/svn/code/obj-c1/OAuthConsumer/NSMutableURLRequest+Parameters.m
Checkout the setParameters override, specifically these lines:
NSData *postData = [encodedParameterPairs dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];
[self setHTTPBody:postData];
[self setValue:[NSString stringWithFormat:@"%d", [postData length]] forHTTPHeaderField:@"Content-Length"];
[self setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
Of course, you'll want to adjust the content-type header for the specific content of your post body (e.g. json, xml, etc).