NSURLProtocol获取POST的body数据

- (NSData *)cachedRequestBody {
    if (!_cachedRequestBody) {
        if (self.request.HTTPBody != nil) {
            _cachedRequestBody = self.request.HTTPBody;
        } else if ([self.request.HTTPBodyStream conformsToProtocol:@protocol(NSCopying)]) {
            NSInputStream *bodyStream = [self.request.HTTPBodyStream copy];
            const NSUInteger bufferSize = 1024;
            uint8_t buffer[bufferSize];
            NSMutableData *data = [NSMutableData data];
            [bodyStream open];
            NSInteger readBytes = 0;
            do {
                readBytes = [bodyStream read:buffer maxLength:bufferSize];
                [data appendBytes:buffer length:readBytes];
            } while (readBytes > 0);
            [bodyStream close];
            _cachedRequestBody = data;
        }
    }
    return _cachedRequestBody;
}