从NSInputStream读取垃圾

Question

Im using input streams to communicate with a POS device.

When i send the first request the response is normal. The problem comes when i send the second request because the second response is shorter than first one and that content is still in the stream. So i get the following:

First response:

<response>A really big response with much more things inside</response>

Second response;

<response>A not so big response</response>more things inside</response>

I do the following:

1) Open the streams

CFStreamCreatePairWithSocketToHost(NULL, (__bridge CFStringRef)host, [port intValue], &readStream, &writeStream);
iStream = (NSInputStream *)readStream;
oStream = (NSOutputStream *)writeStream;
[iStream setDelegate:self];
[oStream setDelegate:self];
[iStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
[oStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
[iStream open];
[oStream open];

2) then i write my request:

[oStream write:(uint8_t *)[request UTF8String] maxLength:[request length]];

3) when the response arrives i capture it and send it to the parser:

uint8_t buffer[MAX_BUFFER_SIZE];
[iStream read:buffer maxLength:MAX_BUFFER_SIZE - 1];
NSString *response = [NSString stringWithUTF8String:(char *)buffer];
free(buffer);

NSError *error;
NSDictionary *ret =[SimpleXMLConverter dictionaryForXMLString:response error:&error];

After this, i tried to close the streams and open them again before sending the second request

Thanks and regards

PS: its not a blocking issue because i can get the correct substring, but i dont understand why its happening

Answer 1

That's because your buffer string is not \\0 (NULL) terminated. Maybe uint8_t buffer[MAX_BUFFER_SIZE] = {0}; will solve your current problem.

However, you should consider one response could be longer than MAX_BUFFER_SIZE - 1 . Even if a response is shorter than it, read:maxLength: is not guaranteed to read all data at once. You must check the returned value and received data has entire response.

Moreover, DO NOT free(buffer) , because free() is only for malloc() ed memory, not for auto variables.