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POObjective C objects behaving strangely (using old references)
 

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  1. POObjective C objects behaving strangely (using old references)
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    <p>I'm getting so very strange behavior in my Objective C library (for iPhone). What I'm trying to do is take packets coming in (off of the accessory port), append them into a NSMutableData instance variable, and then check that to see if I have any complete packets. If I do, the [containsPacket] method will return the length of the packet, otherwise it will return -1. If it contains a packet, I make a new RASPPacket object with that data, and update my receivedData object with the rest of the data (subtracting the data I just created the RASPPacket with). I loop through this until length&lt;0 (meaning there are no more complete packets in receivedData).</p> <p>When I feed it one complete packet, it works as it should (containsPacket returns the right length, and receivedData becomes an empty NSMutableData). The weird thing is that the second time I call containsPacket, it still returns the same number (13), even though receivedData is empty. I put some NSLogs in there to see what was going on (since I am disconnected from the computer I can't step through using the debugger), the output of which is below.</p> <pre><code>- (void)receive:(NSData *)packet { [receivedData appendData:packet]; NSMutableString *dataString = [[NSMutableString alloc] init]; unsigned char *ptr = (unsigned char *)[receivedData bytes]; for(int i = 0; i &lt; [receivedData length]; i++) { [dataString appendFormat:@"%02X ", ptr[i]]; } NSLog(@"Received data: %@", dataString); int length = [RASPPacket containsPacket:receivedData]; NSLog(@"length is %i", length); while(length &gt; 0) { RASPPacket *receivedPacket = [[RASPPacket alloc] initWithIncomingPacket:[NSData dataWithBytes:[receivedData bytes] length:length]]; [receivedData setData:[NSMutableData dataWithBytes:([receivedData bytes]+length) length:([receivedData length] - length)]]; dataString = [[NSMutableString alloc] init]; ptr = (unsigned char *)[receivedData bytes]; for(int i = 0; i &lt; [receivedData length]; i++) { [dataString appendFormat:@"%02X ", ptr[i]]; } NSLog(@"new received data: %@", dataString); if([receivedPacket isValidPacket]) { [raspObject receive:receivedPacket]; NSLog(@"Complete packet is valid"); } [receivedPacket release]; length = [RASPPacket containsPacket:receivedData]; NSLog(@"length is %i", length); } } </code></pre> <p>And the containsPacket method:</p> <pre><code>+ (int)containsPacket:(NSData *)thePacket { //Return -1 by default (if it doesn't contain a complete packet) int returnValue = -1; unsigned char *data = (unsigned char *)[thePacket bytes]; NSMutableString *dataString = [[NSMutableString alloc] init]; unsigned char *ptr = (unsigned char *)[thePacket bytes]; for(int i = 0; i &lt; [thePacket length]; i++) { [dataString appendFormat:@"%02X ", ptr[i]]; } NSLog(@"containsPacket data: %@, len %i", dataString, [thePacket length]); NSLog(@"beginning return value %i", returnValue); //DLE counts the number of consecutive DLE bytes (0x10). An odd number means //we found the DLE we want, an even means it's just in a sequence in the message data int dleCount = 0; NSLog(@"a return value %i", returnValue); //Start i at 2 to skip 0x10 0x01 for(int i = 2; (i &lt; ([thePacket length] - 1)) &amp;&amp; returnValue &lt; 0; i++) { NSLog(@"b return value %i, i: %i, len: %i", returnValue, i, [thePacket length] - 1); //Check if we found 0x10 and 0x03 and there are at least three bytes extra (0x03 and checksum) if(data[i] == 0x10 &amp;&amp; data[i+1] == 0x03 &amp;&amp; [thePacket length] - 3 &gt; i) { int j = i - 1; dleCount = 1; while(data[j] == 0x10 &amp;&amp; j &gt;= 0) { dleCount++; j--; } if(dleCount % 2) { //Add 1 to convert to indices to length, 1 to go from 0x10 to 0x03, and 2 for checksum returnValue = i + 2 + 1 + 1; NSLog(@"c return value %i", returnValue); } } } NSLog(@"ending return value %i", returnValue); return returnValue; } </code></pre> <p>And finally, the NSLog output:</p> <pre><code>TestRaspLayer[922:6c03] Received data: 10 01 00 01 01 10 02 00 00 10 03 A1 07 TestRaspLayer[922:6c03] containsPacket data: 10 01 00 01 01 10 02 00 00 10 03 A1 07 , len 13 TestRaspLayer[922:6c03] beginning return value -1 TestRaspLayer[922:6c03] a return value -1 TestRaspLayer[922:6c03] b return value -1, i: 2, len: 12 TestRaspLayer[922:6c03] b return value -1, i: 3, len: 12 TestRaspLayer[922:6c03] b return value -1, i: 4, len: 12 TestRaspLayer[922:6c03] b return value -1, i: 5, len: 12 TestRaspLayer[922:6c03] b return value -1, i: 6, len: 12 TestRaspLayer[922:6c03] b return value -1, i: 7, len: 12 TestRaspLayer[922:6c03] b return value -1, i: 8, len: 12 TestRaspLayer[922:6c03] b return value -1, i: 9, len: 12 TestRaspLayer[922:6c03] c return value 13 TestRaspLayer[922:6c03] ending return value 13 TestRaspLayer[922:6c03] length is 13 TestRaspLayer[922:6c03] new received data: TestRaspLayer[922:6c03] RASP receive, interface: 1, command 1, looking for interface: 9, command 1 TestRaspLayer[922:6c03] Complete packet is valid TestRaspLayer[922:6c03] containsPacket data: , len 0 TestRaspLayer[922:6c03] beginning return value -1 TestRaspLayer[922:6c03] a return value -1 TestRaspLayer[922:6c03] b return value -1, i: 2, len: -1 TestRaspLayer[922:6c03] b return value -1, i: 3, len: -1 TestRaspLayer[922:6c03] b return value -1, i: 4, len: -1 TestRaspLayer[922:6c03] b return value -1, i: 5, len: -1 TestRaspLayer[922:6c03] b return value -1, i: 6, len: -1 TestRaspLayer[922:6c03] b return value -1, i: 7, len: -1 TestRaspLayer[922:6c03] b return value -1, i: 8, len: -1 TestRaspLayer[922:6c03] b return value -1, i: 9, len: -1 TestRaspLayer[922:6c03] c return value 13 TestRaspLayer[922:6c03] ending return value 13 TestRaspLayer[922:6c03] length is 13 </code></pre> <p>The first time it is going through the valid data, the second time it isn't, and shouldn't be continuing through the for loop (since i>[thePacket length]-1).</p>
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