CFHTTPStream segmentation faul during NSRunLoop - objective-c

Question

I'm trying to assemble a toy application to interact with http servers via CoreFoundation. I'm not using NSURLConnection because I want to be able to specify a proxy different from the one set in the OSX System Preferences.
My problem is that I wasn't able to find any working example and the Apple documentation do not provide a working snippet of code.
Anyhow this is the code I pulled together:
#import <CoreFoundation/CoreFoundation.h>
#import <CoreServices/CoreServices.h>
#import <Foundation/Foundation.h>
void myCallBack (CFReadStreamRef stream, CFStreamEventType eventType, void *clientCallBackInfo){
NSLog(#"Something happened");
BOOL *done = ((BOOL *)clientCallBackInfo);
*done = TRUE;
}
int main(int argc, char *argv[]){
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
CFStringRef bodyString = CFSTR(""); // Usually used for POST data
CFStringRef url = CFSTR("http://www.apple.com");
CFURLRef myURL = CFURLCreateWithString(kCFAllocatorDefault, url, NULL);
CFStringRef requestMethod = CFSTR("GET");
CFHTTPMessageRef myRequest = CFHTTPMessageCreateRequest(kCFAllocatorDefault,
requestMethod,
myURL,
kCFHTTPVersion1_1);
if (myRequest){
NSLog(#"Request created: %# %#", CFHTTPMessageCopyRequestMethod(myRequest),
CFURLGetString(CFHTTPMessageCopyRequestURL(myRequest)));
}
CFDataRef bodyData = CFStringCreateExternalRepresentation(kCFAllocatorDefault, bodyString, kCFStringEncodingASCII, 0);
CFHTTPMessageSetBody(myRequest, bodyData);
NSLog(#"HTTPMessage body set");
CFDataRef mySerializedRequest = CFHTTPMessageCopySerializedMessage(myRequest);
NSLog(#"Serialized string generated");
CFStringRef mySerializedString = CFStringCreateFromExternalRepresentation(kCFAllocatorDefault,
mySerializedRequest,
kCFStringEncodingASCII);
NSLog(#"Serialized request: %#", mySerializedString);
CFReadStreamRef myReadStream = CFReadStreamCreateForHTTPRequest(kCFAllocatorDefault, myRequest);
BOOL done = FALSE;
CFReadStreamOpen(myReadStream);
CFOptionFlags registeredEvents = kCFStreamEventHasBytesAvailable | kCFStreamEventErrorOccurred | kCFStreamEventEndEncountered;
NSLog(#"Setting read stream client");
if (CFReadStreamSetClient(myReadStream, registeredEvents, myCallBack, (void *)&done)){
CFReadStreamScheduleWithRunLoop(myReadStream, CFRunLoopGetCurrent(),
kCFRunLoopCommonModes);
while (!done){
NSLog(#"Wait");
[[NSRunLoop currentRunLoop] run];
}
}else{
NSLog(#"Error setting readstream client");
}
CFRelease(myRequest);
CFRelease(myURL);
CFRelease(url);
CFRelease(mySerializedRequest);
myRequest = NULL;
mySerializedRequest = NULL;
[pool drain];
}
The code compiles but it throws a segfault:
Reading symbols for shared libraries .+++++...................... done
2010-09-06 21:36:34.470 a.out[27973:a0f] Request created: GET http://www.apple.com
2010-09-06 21:36:34.473 a.out[27973:a0f] HTTPMessage body set
2010-09-06 21:36:34.474 a.out[27973:a0f] Serialized string generated
2010-09-06 21:36:34.474 a.out[27973:a0f] Serialized request: GET / HTTP/1.1
2010-09-06 21:36:34.478 a.out[27973:a0f] Setting read stream client
2010-09-06 21:36:34.479 a.out[27973:a0f] Wait
Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: 13 at address: 0x0000000000000000
0x00007fff83b7b83d in _signalEventSync ()
(gdb) bt
#0 0x00007fff83b7b83d in _signalEventSync ()
#1 0x00007fff83b7b7f4 in _cfstream_solo_signalEventSync ()
#2 0x00007fff83b7b734 in _CFStreamSignalEvent ()
#3 0x00007fff8391c3a1 in HTTPReadStream::streamEvent ()
#4 0x00007fff83b7b883 in _signalEventSync ()
#5 0x00007fff83b7c5d9 in _cfstream_shared_signalEventSync ()
#6 0x00007fff83b1be91 in __CFRunLoopDoSources0 ()
#7 0x00007fff83b1a089 in __CFRunLoopRun ()
#8 0x00007fff83b1984f in CFRunLoopRunSpecific ()
#9 0x00007fff8300fa18 in -[NSRunLoop(NSRunLoop) runMode:beforeDate:] ()
#10 0x00007fff8300f8f7 in -[NSRunLoop(NSRunLoop) run] ()
#11 0x0000000100000c94 in main (argc=1, argv=0x7fff5fbff5b8) at test.m:56
I don't understand where the error is. Anyone can show me the light or point me to a clear example on how to manage CFHTTPStreams?
Thanks,
Andrea

Answer 1

The problem was that I didn't read carefully the documentation of CFReadStreamSetClient.
The third parameter has to be a reference to a CFStreamClientContext whereas I was passing a reference to an arbitrary pointer which instead has to be included into the context.
Fixing this resolved the segmentation fault and now the test ca is working as expected.