LFCGzipUtility.m

#import "LFCGzipUtility.h"
 
@implementation LFCGzipUtility
 
+ (NSData *)gzipData:(NSData*)pUncompressedData {
    if (!pUncompressedData || [pUncompressedData length] == 0) {
        NSLog(@"%s: Error: Can't compress an empty or null NSData object.", __func__);
        return nil;
    }
 
    z_stream zlibStreamStruct;
    zlibStreamStruct.zalloc    = Z_NULL;
    zlibStreamStruct.zfree     = Z_NULL;
    zlibStreamStruct.opaque    = Z_NULL;
    zlibStreamStruct.total_out = 0;
    zlibStreamStruct.next_in   = (Bytef*)[pUncompressedData bytes];
    zlibStreamStruct.avail_in  = [pUncompressedData length];
 
    int initError = deflateInit2(&zlibStreamStruct, Z_DEFAULT_COMPRESSION, Z_DEFLATED, (15+16), 8, Z_DEFAULT_STRATEGY);
    if (initError != Z_OK) {
        NSString *errorMsg = nil;
        switch (initError) {
            case Z_STREAM_ERROR:
                errorMsg = @"Invalid parameter passed in to function.";
                break;
            case Z_MEM_ERROR:
                errorMsg = @"Insufficient memory.";
                break;
            case Z_VERSION_ERROR:
                errorMsg = @"The version of zlib.h and the version of the library linked do not match.";
                break;
            default:
                errorMsg = @"Unknown error code.";
                break;
        }
        NSLog(@"%s: deflateInit2() Error: \"%@\" Message: \"%s\"", __func__, errorMsg, zlibStreamStruct.msg);
        return nil;
    }
 
    // Create output memory buffer for compressed data. The zlib documentation states that
    // destination buffer size must be at least 0.1% larger than avail_in plus 12 bytes.
    NSMutableData *compressedData = [NSMutableData dataWithLength:[pUncompressedData length] * 1.01 + 12];
 
    int deflateStatus;
    do {
        zlibStreamStruct.next_out = [compressedData mutableBytes] + zlibStreamStruct.total_out;
        zlibStreamStruct.avail_out = [compressedData length] - zlibStreamStruct.total_out;
        deflateStatus = deflate(&zlibStreamStruct, Z_FINISH);
 
    } while ( deflateStatus == Z_OK );
 
    // Check for zlib error and convert code to usable error message if appropriate
    if (deflateStatus != Z_STREAM_END) {
//        NSString *errorMsg = nil;
//        switch (deflateStatus) {
//            case Z_ERRNO:
//                errorMsg = @"Error occured while reading file.";
//                break;
//            case Z_STREAM_ERROR:
//                errorMsg = @"The stream state was inconsistent (e.g., next_in or next_out was NULL).";
//                break;
//            case Z_DATA_ERROR:
//                errorMsg = @"The deflate data was invalid or incomplete.";
//                break;
//            case Z_MEM_ERROR:
//                errorMsg = @"Memory could not be allocated for processing.";
//                break;
//            case Z_BUF_ERROR:
//                errorMsg = @"Ran out of output buffer for writing compressed bytes.";
//                break;
//            case Z_VERSION_ERROR:
//                errorMsg = @"The version of zlib.h and the version of the library linked do not match.";
//                break;
//            default:
//                errorMsg = @"Unknown error code.";
//                break;
//        }
        //NSLog(@"%s: zlib error while attempting compression: \"%@\" Message: \"%s\"", __func__, errorMsg, zlibStreamStruct.msg);
 
        deflateEnd(&zlibStreamStruct);
 
        return nil;
    }
 
    deflateEnd(&zlibStreamStruct);
 
    [compressedData setLength: zlibStreamStruct.total_out];
 
    NSLog(@"%s: Compressed file from %d KB to %d KB", __func__, [pUncompressedData length]/1024, [compressedData length]/1024);
    return compressedData;
}
 
+ (NSData *)ungzipData:(NSData *)compressedData {
    if ([compressedData length] == 0) {
        return compressedData;
    }
 
    unsigned full_length = [compressedData length];
    unsigned half_length = [compressedData length] / 2;
 
    NSMutableData *decompressed = [NSMutableData dataWithLength: full_length + half_length];
    BOOL done = NO;
    int status;
 
    z_stream strm;
    strm.next_in = (Bytef *)[compressedData bytes];
    strm.avail_in = [compressedData length];
    strm.total_out = 0;
    strm.zalloc = Z_NULL;
    strm.zfree = Z_NULL;
    if (inflateInit2(&strm, (15+32)) != Z_OK)
        return nil;
 
    while (!done) {
        if (strm.total_out >= [decompressed length]) {
            [decompressed increaseLengthBy: half_length];
        }
        strm.next_out = [decompressed mutableBytes] + strm.total_out;
        strm.avail_out = [decompressed length] - strm.total_out;
        // Inflate another chunk.
        status = inflate (&strm, Z_SYNC_FLUSH);
        if (status == Z_STREAM_END) {
            done = YES;
        } else if (status != Z_OK) {
            break;
        }
    }
 
    if (inflateEnd (&strm) != Z_OK) {
        return nil;
    }
    if (done) {
        [decompressed setLength:strm.total_out];
        return [NSData dataWithData: decompressed];
    }
    return nil;
}
 
@end