I'm dealing with the garmin GDL90 protocol which sends across various types of messages in binary to my IOS device. I'm going through and trying to process all these messages but have been running into an issue. Specifically the messages are byte packed so that if you ever see an occurrence of
0x7d 0x5e or 0x7d 0x5d you have to convert them to 0x7d or 0x7e
I've set my code up so that I detect the message type I'm parsing and then call a function:
- (void) parseMessage:(NSMutableData *)message
to do my data parsing. My individual message parsing functions call the parent function [super parseMessage:message]; which handles both the parsing of common elements as well as dealing with my byte-stuffing. Each of these function calls takes an NSData * so shouldn't a modification made in my super function return back out the same data?
My top level class gets a parse message call and the NSMutableData pointer's address is: 0x170048f10
Once I step into the parent's parseData call my address is still 0x170048f10
After I make modifications to the data I'm now pointing at the memory address 0x17805e840
Once I return from this function, however, I'm back pointing at 0x170048f10 again with the wrong data.
Should I be using pass by reference or something? Any suggestions?
I have two variations of my function - unstuff1 throws an error and unstuff2 doesn't work.
- (NSMutableData *)unstuff1:(NSMutableData *)mutableData {
int dataLength = [mutableData length];
char *bytes = [mutableData bytes];
// Scan bytes ignoring 1st and last byte because they will be 7e's
for (int i = dataLength - 1; i > 0; i--) {
bytes[i + 1] ^= 0x20;
if (i + 1 == dataLength) {
NSLog(#"Terminal character padding detected on character %d with length %d", i, dataLength);
} else {
/* Replace 2 bytes with a single byte should remove the flag when you do this */
[mutableData replaceBytesInRange:NSMakeRange(i, 2) withBytes:&bytes[i + 1] length:1];
dataLength--;
}
}
return mutableData;
}
- (NSMutableData *)unstuff2:(NSMutableData *)data {
NSMutableData *mutableData = [[NSMutableData alloc] initWithData:data];
int dataLength = [mutableData length];
char *bytes = [mutableData bytes];
// Scan bytes ignoring 1st and last byte because they will be 7e's
for (int i = dataLength - 1; i > 0; i--) {
bytes[i + 1] ^= 0x20;
if (i + 1 == dataLength) {
NSLog(#"Terminal character padding detected on character %d with length %d", i, dataLength);
} else {
/* Replace 2 bytes with a single byte should remove the flag when you do this */
[mutableData replaceBytesInRange:NSMakeRange(i, 2) withBytes:&bytes[i + 1] length:1];
dataLength--;
}
}
return mutableData;
}
In unstuff2 obviously i'm making a new MutableData so I guess that accounts for the memory address change (that is the function i was using that gave me the error specified).
unstuff1 throws the following exception:
-[_NSInlineData replaceBytesInRange:withBytes:length:]: unrecognized selector sent to instance 0x178250d40
Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[_NSInlineData replaceBytesInRange:withBytes:length:]: unrecognized selector sent to instance
Unlike languages like C++ and C# (just to name two), Objective C has no concept of "pass by reference". However, passing a copy of a pointer to your NSMutableData is functionally equivalent to passing the object by reference. That is, if you pass in an NSMutableData (or NSMutableAnything for that matter) to a function and that function modifies it, the calling function will see the changes reflected in the object that it passed in.
Ok looks like I tracked down the problem. I realized the compiler was sending out warnings:
incompatible pointer types initializing 'NSMutableData *' with an expression of type 'NSData *'
It turns out I had some code
NSMutableData *message = [data subdataWithRange:NSMakeRange(5, len - 5)];
Which i needed to convert into:
NSMutableData *message = [NSMutableData dataWithData:[data subdataWithRange:NSMakeRange(5, len - 5)]];
And then things all work out. Moral of the story (read your warnings!!!!)
Related
I am having a bit of an issue passing a reference to a primitive type through chaining, and having the value represented by the pointer change correctly. The weird part is, if I call getBytes directly from main function, byteLocation is properly adjusted, but if I chain it through a convenience function, it seems get a junk value. Actually, even weirder, it at first gets the correct value when stepping through the debugger, but executes the return clause twice. The first return clause gets the correct value, the second loads byteLocation with a junk value. Any ideas?
EDIT (Actual Code):
#property (strong, nonatomic, nonnull) NSData* data;
#property (assign, nonatomic) CFByteOrder byteOrder;
- (void)convertBytesToHostOrder:(nonnull void*)buffer length:(NSUInteger)length {
if(length > 1 && self.byteOrder != CFByteOrderGetCurrent()) {
// Swap bytes if the packet endiness differs from the host
char* fromBytes = buffer;
for(NSUInteger i=0; i < length/2; i++) {
NSUInteger indexes[2] = {i, length-i-0};
char byte = fromBytes[indexes[0]];
fromBytes[indexes[0]] = fromBytes[indexes[1]];
fromBytes[indexes[1]] = byte;
}
}
}
- (nonnull void*)getBytes:(nonnull void*)buffer startingFrom:(nonnull NSUInteger*)location length:(NSUInteger)length {
NSRange range = NSMakeRange(*location, length);
[self.data getBytes:buffer range:range]; // self.data is an instance of NSData
[self convertBytesToHostOrder:buffer length:length];
NSUInteger update = range.location + range.length;
*location = update;
return buffer;
}
- (NSTimeInterval)readTimeIntervalStartingFrom:(nonnull NSUInteger*)byteLocation {
uint32_t seconds;
uint16_t milliseconds;
// This line of code screws up the byteLocation pointer for some reason
[self getBytes:&seconds startingFrom:byteLocation length:sizeof(seconds)];
[self getBytes:&milliseconds startingFrom:byteLocation length:sizeof(milliseconds)];
NSTimeInterval ti = seconds + milliseconds / ((double) 1000 * (1 << 6));
return ti;
}
- (void)readData {
NSUInteger byteLocation = 0;
self.sequenceNumber = *(uint8_t*) [self getBytes:&_sequenceNumber startingFrom:&byteLocation length:sizeof(_sequenceNumber)];
self.flags = *(uint8_t*) [self getBytes:&_flags startingFrom:&byteLocation length:sizeof(_flags)];
// Continue to process packet data if we didn't get a goodbye message
if(!(self.flags & LBRadarPongFlagGoodbye)) {
// Parse accelerations
int16_t int16;
self.accelerationX = (*(int16_t*) [self getBytes:&int16 startingFrom:&byteLocation length:sizeof(int16)]) / kGToRaw;
self.accelerationY = (*(int16_t*) [self getBytes:&int16 startingFrom:&byteLocation length:sizeof(int16)]) / kGToRaw;
self.accelerationZ = (*(int16_t*) [self getBytes:&int16 startingFrom:&byteLocation length:sizeof(int16)]) / kGToRaw;
// Parse peripheral states
self.batteryVoltage = [self readFloat16From:&byteLocation];
self.chargeCurrent = [self readFloat16From:&byteLocation];
self.systemCurrent = [self readFloat16From:&byteLocation];
// All previous lines of code work properly and as expected.
// Buffers are read properly, and byteLocation properly reflects 14, which is the number of bytes read up to this point.
self.pongReceivedTimeIntervalSince1970 = [self readTimeIntervalStartingFrom:&byteLocation];
}
}
The problem seems to be with incrementing the location. In both cases you should copy from position zero, up to the size of the variable. In the following code:
[self readBytes:&seconds location:byteLocation length:sizeof(seconds)]
[self readBytes:&milliseconds location:byteLocation length:sizeof(milliseconds)]
The first call starts at position zero and reads 32 bits. The second one starts at position 32, which doesn't even fit in the variable's 16 bits. This is overflowing the buffer. Try this instead:
- (void*)readBytes:(void*)buffer location:(NSUInteger*)location length:(NSUInteger)length {
// The difference is in the next line. Zero instead of *location
[NSData getBytes:&buffer range:NSMakeRange(0, length)];
*location = *location + length;
return buffer; // Seems to be called twice, first time location* has the correct byteLocation inside it, second time location* has a junk value
}
At a guess[*] your error is on the line:
[self.data getBytes:&buffer range:NSMakeRange(*location, length)];
You are passing a void * value by taking the address of buffer - which is already a void *. Changing this to:
[self.data getBytes:buffer range:NSMakeRange(*location, length)];
will at least produce non-garabge results.
[*] I can only guess as the code you posted did not even compile, I edited your question to correct some of the more obvious errors - but even that involved some guessing! You should post real code.
I should have just posted the actual code, sorry guys. Turns out the error was in a helper function (convertBytesToHostOrder). This was reading out of bounds of buffer. Since buffer was the parameter right before byteLocation, it seems that writing at a location 1 spot beyond buffer was the byteLocation location. Fixed now and everything is working.
- (void)convertBytesToHostOrder:(nonnull void*)buffer length:(NSUInteger)length {
if(length > 1 && self.byteOrder != CFByteOrderGetCurrent()) {
// Swap bytes if the packet endiness differs from the host
char* fromBytes = buffer;
for(NSUInteger i=0; i < length/2; i++) {
NSUInteger indexes[2] = {i, length-i-0};
char byte = fromBytes[indexes[0]];
fromBytes[indexes[0]] = fromBytes[indexes[1]];
fromBytes[indexes[1]] = byte;
}
}
}
Should be:
NSUInteger indexes[2] = {i, length-i-1};
I am having some trouble using the data that I receive from a remote server. This is how I take in the data from my nsinputstream:
case NSStreamEventHasBytesAvailable:
{
if(!_data)
{
_data = [NSMutableData data];
}
uint8_t buffer = malloc(1024);
NSInteger *len = [inputStream read:buffer maxLength:1024];
if(len)
{
_data = [[NSData alloc]initWithBytesNoCopy:buffer length:1024];
[self closeThread];
}
shouldClose = YES;
break;
}
In the same class I have this function to return the data in order to use it in different classes:
-(NSData *)returnData {
return self.data;
}
In the view controller that I want to use the data in I have this code to retrieve the data for use:
_schools = [_server returnData];
NSString *schoolString = [[NSString alloc] initWithData:self.schools encoding:NSUTF8StringEncoding];//exc_bad_access
From what I understand about EXC_BAD_ACCESS exceptions they usually mean that you are trying to access data that either doesn't exist or is not allocated. The _schools variable shows a size of 1024 bytes so I know there is memory correctly allocated for it. Is there something else going wrong that I am missing?
You appear to have mixed up the types of the variables on these two lines:
uint8_t buffer = malloc(1024);
NSInteger *len = [inputStream read:buffer maxLength:1024];
In its current form, you will malloc'ate 1024 bytes of memory, and attempt to store the pointer to said memory in a uint8_t (which CLANG will rightly scream at you for), thus truncating the pointer and not providing a buffer, but rather a single unsigned 8-bit byte for the stream to attempt to read into. Also, -[NSInputStream read:maxLength:] does not return NSInteger *, just plain NSInteger, so all you need to do is swap the pointers on the two variables:
uint8_t *buffer = malloc(1024);
NSInteger len = [inputStream read:buffer maxLength:1024];
and it should work just fine.
I'm creating an Objective-C library to talk with some external devices through USB.
When calling a certain method, it crashes at a random place inside the method or inside some C system functions (related to malloc or pthread) with one of the following error "invalid checksum for freed object", "autorelease pool page 0x1102032 corrupted", or even an unknown selector error (whereas the selector does exist).
Using Guard Malloc feature, it stops on this line with an EXEC_BAD_ACCESS error:
- (void)theMethod {
// some code
NSMutableData *payloads_pool = [NSMutableData dataWithLength:0x800];
NSUInteger payloads_pool_length = [payloads_pool length];
void *buffer = [payloads_pool mutableBytes];
memset(buffer, 0xCC, payloads_pool_length);
for (i = 0; i < 0x800; i += 0x40) {
unsigned int *buf = [payloads_pool mutableBytes];
(buf+i)[0] = 0x405; <==== STOP ON THIS LINE
(buf+i)[1] = 0x101;
(buf+i)[2] = 0x8402B001;
(buf+i)[3] = 0x8402EB01;
}
// some code
}
Since buf is unsigned int*, isn’t the pointer + in buf+i adding unsigned integers instead of bytes, thus seeking too far in memory?
Then I'd guess that the payloads_pool has fewer than 0x800 bytes in.
What is the value of i when it crashes?
Why isn't your for loop from 0 to payloads_pool.length?
Sometimes when trying to get a path to a keychain returned by SecKeychainCopySearchList I get error with code -25301 which from the list of errors stands for errSecBufferTooSmall. The SecCopyErrorMessageString states:
There is not enough memory available to use the specified item.
Weird thing is that it doesn't always return the error on the very same keychain reference.
Here's how I try to get the path to the keychain:
- (NSString *)getKeychainPath:(SecKeychainRef)keychain {
char *pathName = malloc(sizeof(*pathName) * 1024);
UInt32 pathLength;
OSStatus errCode = SecKeychainGetPath(keychain, &pathLength, pathName);
if (errCode != errSecSuccess) {
NSString *errString = (NSString *)SecCopyErrorMessageString(errCode, NULL);
DLog(#"%d: %#", errCode, errString);
}
NSData *d = [NSData dataWithBytes:pathName length:pathLength];
return [[[NSString alloc] initWithData:d encoding:NSUTF8StringEncoding] autorelease];
}
I'm interested in what buffer does the function use? I've tried outputting the pathLength variable but it's way bellow the 1K bytes. What am I doing wrong? What should I do to avoid these errors? Can they be bypassed by any way at all?
From the SecKeychainGetPath documentation:
ioPathLength
On entry, a pointer to a variable containing the length (in bytes) of the buffer specified by pathName.
On return, the string length of pathName, not including the null termination.
You're not doing the "on input" part. You need to initialize pathLength to the size of the pathName buffer. For example:
UInt32 pathLength = 1024;
char *pathName = malloc(pathLength);
I have been working on reading in an audio asset using AVAssetReader so that I can later play back the audio with an AUGraph with an AudioUnit callback. I have the AUGraph and AudioUnit callback working but it reads files from disk and if the file is too big it would take up too much memory and crash the app. So I am instead reading the asset directly and only a limited size. I will then manage it as a double buffer and get the AUGraph what it needs when it needs it.
(Note: I would love know if I can use Audio Queue Services and still use an AUGraph with AudioUnit callback so memory is managed for me by the iOS frameworks.)
My problem is that I do not have a good understanding of arrays, structs and pointers in C. The part where I need help is taking the individual AudioBufferList which holds onto a single AudioBuffer and add that data to another AudioBufferList which holds onto all of the data to be used later. I believe I need to use memcpy but it is not clear how to use it or even initialize an AudioBufferList for my purposes. I am using MixerHost for reference which is the sample project from Apple which reads in the file from disk.
I have uploaded my work in progress if you would like to load it up in Xcode. I've figured out most of what I need to get this done and once I have the data being collected all in one place I should be good to go.
Sample Project: MyAssetReader.zip
In the header you can see I declare the bufferList as a pointer to the struct.
#interface MyAssetReader : NSObject {
BOOL reading;
signed long sampleTotal;
Float64 totalDuration;
AudioBufferList *bufferList; // How should this be handled?
}
Then I allocate bufferList this way, largely borrowing from MixerHost...
UInt32 channelCount = [asset.tracks count];
if (channelCount > 1) {
NSLog(#"We have more than 1 channel!");
}
bufferList = (AudioBufferList *) malloc (
sizeof (AudioBufferList) + sizeof (AudioBuffer) * (channelCount - 1)
);
if (NULL == bufferList) {NSLog (#"*** malloc failure for allocating bufferList memory"); return;}
// initialize the mNumberBuffers member
bufferList->mNumberBuffers = channelCount;
// initialize the mBuffers member to 0
AudioBuffer emptyBuffer = {0};
size_t arrayIndex;
for (arrayIndex = 0; arrayIndex < channelCount; arrayIndex++) {
// set up the AudioBuffer structs in the buffer list
bufferList->mBuffers[arrayIndex] = emptyBuffer;
bufferList->mBuffers[arrayIndex].mNumberChannels = 1;
// How should mData be initialized???
bufferList->mBuffers[arrayIndex].mData = malloc(sizeof(AudioUnitSampleType));
}
Finally I loop through the reads.
int frameCount = 0;
CMSampleBufferRef nextBuffer;
while (assetReader.status == AVAssetReaderStatusReading) {
nextBuffer = [assetReaderOutput copyNextSampleBuffer];
AudioBufferList localBufferList;
CMBlockBufferRef blockBuffer;
CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(nextBuffer, NULL, &localBufferList, sizeof(localBufferList), NULL, NULL,
kCMSampleBufferFlag_AudioBufferList_Assure16ByteAlignment, &blockBuffer);
// increase the number of total bites
bufferList->mBuffers[0].mDataByteSize += localBufferList.mBuffers[0].mDataByteSize;
// carefully copy the data into the buffer list
memcpy(bufferList->mBuffers[0].mData + frameCount, localBufferList.mBuffers[0].mData, sizeof(AudioUnitSampleType));
// get information about duration and position
//CMSampleBufferGet
CMItemCount sampleCount = CMSampleBufferGetNumSamples(nextBuffer);
Float64 duration = CMTimeGetSeconds(CMSampleBufferGetDuration(nextBuffer));
Float64 presTime = CMTimeGetSeconds(CMSampleBufferGetPresentationTimeStamp(nextBuffer));
if (isnan(duration)) duration = 0.0;
if (isnan(presTime)) presTime = 0.0;
//NSLog(#"sampleCount: %ld", sampleCount);
//NSLog(#"duration: %f", duration);
//NSLog(#"presTime: %f", presTime);
self.sampleTotal += sampleCount;
self.totalDuration += duration;
frameCount++;
free(nextBuffer);
}
I am unsure about the what that I handle mDataByteSize and mData, especially with memcpy. Since mData is a void pointer this is an extra tricky area.
memcpy(bufferList->mBuffers[0].mData + frameCount, localBufferList.mBuffers[0].mData, sizeof(AudioUnitSampleType));
In this line I think it should be copying the value from the data in localBufferList to the position in the bufferList plus the number of frames to position the pointer where it should write the data. I have a couple of ideas on what I need to change to get this to work.
Since a void pointer is just 1 and not the size of the pointer for an AudioUnitSampleType I may need to multiply it also by sizeof(AudioUnitSampleType) to get the memcpy into the right position
I may not be using malloc properly to prepare mData but since I am not sure how many frames there will be I am not sure what to do to initialize it
Currently when I run this app it ends this function with an invalid pointer for bufferList.
I appreciate your help with making me better understand how to manage an AudioBufferList.
I've come up with my own answer. I decided to use an NSMutableData object which allows me to appendBytes from the CMSampleBufferRef after calling CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer to get an AudioBufferList.
[data appendBytes:localBufferList.mBuffers[0].mData length:localBufferList.mBuffers[0].mDataByteSize];
Once the read loop is done I have all of the data in my NSMutableData object. I then create and populate the AudioBufferList this way.
audioBufferList = (AudioBufferList *)malloc(sizeof(AudioBufferList));
if (NULL == audioBufferList) {
NSLog (#"*** malloc failure for allocating audioBufferList memory");
[data release];
return;
}
audioBufferList->mNumberBuffers = 1;
audioBufferList->mBuffers[0].mNumberChannels = channelCount;
audioBufferList->mBuffers[0].mDataByteSize = [data length];
audioBufferList->mBuffers[0].mData = (AudioUnitSampleType *)malloc([data length]);
if (NULL == audioBufferList->mBuffers[0].mData) {
NSLog (#"*** malloc failure for allocating mData memory");
[data release];
return;
}
memcpy(audioBufferList->mBuffers[0].mData, [data mutableBytes], [data length]);
[data release];
I'd appreciate a little code review on how I use malloc to create the struct and populate it. I am getting a EXC_BAD_ACCESS error sporadically but I cannot pinpoint where the error is just yet. Since I am using malloc on the struct I should not have to retain it anywhere. I do call "free" to release child elements within the struct and finally the struct itself everywhere that I use malloc.