Thursday, July 28, 2011

Adventures in Redirection III: The Revenge

Note: This blog is deprecated. @synthesize zach has moved to a new home, at zpasternack.org. This blog entry can be found on the new blog here. Please update your links.

After the last two entries on output redirection (here and here, if you missed them), a few folks said, “Zach, this is a Cocoa blog; what’s up with all the crazy C++ junk?” Fair enough. The main reason is that this was what I needed for the particular project I’m working on. Another reason is that C++ is what I did (a *lot*) in my previous life, so hopefully you’ll forgive me if I occasionally run home to mama. :)

In any case, the core code is plain ole C, so I thought, why not make a Cocoa version also? So here we go. The walkthrough is basically the same as the original C++ version, so I won't repeat it here.

@interface StandardOutputRedirector : NSObject
{
    int redirectionPipe[2];
    int oldStandardOutput;
    int oldStandardError;
    BOOL redirecting;
    NSMutableString* redirectedOutput;
}
- (void) startRedirecting;
- (void) stopRedirecting;
- (NSString*) output;
- (void) clearOutput;
@end

@implementation StandardOutputRedirector

enum { READ, WRITE };

#pragma mark - Memory Management

- (id) init
{
    if( (self = [super init]) ) {
        redirectedOutput = [[NSMutableString alloc] init];

        if( pipe( redirectionPipe ) != -1 ) {
            oldStandardOutput = dup( fileno(stdout) );
            oldStandardError = dup( fileno(stderr) );
        }
        setbuf( stdout, NULL );
        setbuf( stderr, NULL );
    }

    return self;
}

- (void) dealloc
{
    if( redirecting  ) {
        [self stopRedirecting];
    }

    if( oldStandardOutput > 0 ) {
        close( oldStandardOutput );
    }
    if( oldStandardError > 0 ) {
        close( oldStandardError );
    }
    if( redirectionPipe[READ] > 0 ) {
        close( redirectionPipe[READ] );
    }
    if( redirectionPipe[WRITE] > 0 ) {
        close( redirectionPipe[WRITE] );
    }

    [redirectedOutput release];

    [super dealloc];
}

#pragma mark - Public methods

- (void) startRedirecting
{
    if( redirecting ) return;

    dup2( redirectionPipe[WRITE], fileno(stdout) );
    dup2( redirectionPipe[WRITE], fileno(stderr) );
    redirecting = true;
}

- (void) stopRedirecting
{
    if( !redirecting ) return;

    dup2( oldStandardOutput, fileno(stdout) );
    dup2( oldStandardError, fileno(stderr) );
    redirecting = false;
}

- (NSString*) output
{
    const size_t bufferSize = 4096;
    char buffer[bufferSize];
    fcntl( redirectionPipe[READ], F_SETFL, O_NONBLOCK ); 
    ssize_t bytesRead = read( redirectionPipe[READ], buffer, bufferSize - 1 );
    while( bytesRead > 0 ) {
        buffer[bytesRead] = 0;
        NSString* tempString = [NSString stringWithCString:buffer encoding:NSUTF8StringEncoding];
        [redirectedOutput appendString:tempString];
        bytesRead = read( redirectionPipe[READ], buffer, bufferSize );
    }

    return [NSString stringWithFormat:@"%@", redirectedOutput];
}

- (void) clearOutput
{
    [redirectedOutput setString:@""];
}

@end


One thing I would note on the Cocoa version is that, this is intended for Mac OS X. I’ve not tried it on iOS, I’ve no idea if it would work, and I actually can’t think of a reason why you’d want to do it on iOS.

This Cocoa version (along with the original C++ implementation) is included with the sample project on github, here.

No comments:

Post a Comment

Post a Comment