NSURLConnection - Is it possible to wait/block on a request? - macos

Question

I need to wait for a response from a SOAP webservice, I am calling via a NSURLConnection as I need to manipulate the data being returned and then return it from my class to the calling class..
Here is my code:
#import <Foundation/Foundation.h>
#interface UsersBLL : NSObject {
NSMutableData *webData;
NSMutableString *soapResults;
NSXMLParser *xmlParser;
BOOL *recordResults;
NSNumber *EmailCount;
}
#property(nonatomic, retain) NSMutableData *webData;
#property(nonatomic, retain) NSMutableString *soapResults;
#property(nonatomic, retain) NSXMLParser *xmlParser;
-(int)checkEmailAddress:(NSString*)emailAddress;
#end
#import "UsersBLL.h"
#implementation UsersBLL
#synthesize webData;
#synthesize soapResults;
#synthesize xmlParser;
-(id)init {
self = [super init];
return self;
}
-(int)checkEmailAddress:(NSString*)emailAddress {
// Build the SOAP envelope
NSString *soapMessage = [NSString stringWithFormat:
#"<?xml version=\"1.0\" encoding=\"utf-8\"?>\n"
"<soap:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\">\n"
"<soap:Body>\n"
"<CheckEmailAddress xmlns=\"http://tempuri.org/\">\n"
"<EmailAddress>%#</EmailAddress>\n"
"</CheckEmailAddress>\n"
"</soap:Body>\n"
"</soap:Envelope>\n", emailAddress];
NSLog(soapMessage);
NSURL *url = [NSURL URLWithString:#"http://photoswapper.mick-walker.co.uk/UsersService.asmx?op=CheckEmailAddress"];
NSMutableURLRequest *theRequest = [NSMutableURLRequest requestWithURL:url];
NSString *msgLength = [NSString stringWithFormat:#"%d", [soapMessage length]];
[theRequest addValue: #"text/xml; charset=utf-8" forHTTPHeaderField:#"Content-Type"];
[theRequest addValue: #"http://tempuri.org/CheckEmailAddress" forHTTPHeaderField:#"SOAPAction"];
[theRequest addValue: msgLength forHTTPHeaderField:#"Content-Length"];
[theRequest setHTTPMethod:#"POST"];
[theRequest setHTTPBody: [soapMessage dataUsingEncoding:NSUTF8StringEncoding]];
NSURLConnection *theConnection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
if( theConnection )
{
webData = [[NSMutableData data] retain];
}
else
{
NSLog(#"theConnection is NULL");
}
NSLog(#"%#", EmailCount);
}
-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
[webData setLength: 0];
}
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
[webData appendData:data];
}
-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
NSLog(#"ERROR with theConenction");
[connection release];
[webData release];
}
-(void)connectionDidFinishLoading:(NSURLConnection *)connection
{
NSLog(#"DONE. Received Bytes: %d", [webData length]);
NSString *theXML = [[NSString alloc] initWithBytes: [webData mutableBytes] length:[webData length] encoding:NSUTF8StringEncoding];
NSLog(theXML);
[theXML release];
if( xmlParser )
{
[xmlParser release];
}
xmlParser = [[NSXMLParser alloc] initWithData: webData];
[xmlParser setDelegate: self];
[xmlParser setShouldResolveExternalEntities: YES];
[xmlParser parse];
[connection release];
[webData release];
}
-(void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *) namespaceURI qualifiedName:(NSString *)qName
attributes: (NSDictionary *)attributeDict
{
if( [elementName isEqualToString:#"CheckEmailAddressResult"])
{
if(!soapResults)
{
soapResults = [[NSMutableString alloc] init];
}
recordResults = TRUE;
}
}
-(void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string
{
if( recordResults )
{
[soapResults appendString: string];
}
}
-(void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName
{
if( [elementName isEqualToString:#"CheckEmailAddressResult"])
{
recordResults = FALSE;
NSNumberFormatter *formatter = [[NSNumberFormatter alloc]init];
EmailCount = [formatter numberFromString:soapResults];
[formatter release];
[soapResults release];
soapResults = nil;
}
}
#end
CheckEmailAddress is declared as returning an integer value (I know it returns nothing in the sample above).
What I ideally want, is through the CheckEmailAddress method, return the value retrieved from the web service. However as the call NSURLConnection does not wait until the request has completed, I cannot do it.
I would be grateful if anyone could give me any potential ideas for workarounds.

Answer 1

The simplest solution would be using [NSURLConnection sendSynchronousRequest:returningResponse:error:].
It does not allow as much control as the approach you've taken, but is usually enough for most applications.

Answer 2

I have just posted a solution which wraps an asynchronous NSURLConnection to be able to block the calling thread. In case you need more control than the standard [NSURLConnection sendSynchronousRequest:returningResponse:error:] you can check out this link on StackOverflow:
NSURLConnection blocking wrapper implemented with semaphores

Answer 3

You have two choices:
Use +[NSURLConnection sendSynchronousRequest:returningResponse:error:]
Schedule the connection in a custom runloop mode, and run the loop in that mode until the data arrives or you have need to cancel the connection

Answer 4

It all depends on the level of asynchronism you need:
If it's OK to stay blocked during the whole request you may want to use
+[NSURLConnection sendSynchronousRequest:returningResponse:error:]
But, as suggested by Wade, be careful to add a timeout to your NSURLRequest, otherwise the connection might blocks and your application will hang.
If not, you can simply use the NSNotificationCenter. But you must be careful with race conditions over your data, specially if you are handling multiple requests