Disclaimer: I am an Xcode / iPhone SDK Noob.
I am trying to establish a client-side TCP/IP connection to an existing server. Upon connection, I expect to receive some data about the server (version, etc.).
When my connection is made, the NSStreamEventOpenCompleted event fires, so I know the connection is made. Next the NSStreamEventHasBytesAvailable event fires and I am executing the following code. The value 71 (int) is stored in len, which I believe is correct. However, the line
[data appendBytes:&buffer length:len];
is crashing (I think). There is no actual error thrown but I do see __TERMINATING_DUE_TO_UNCAUGHT_EXCEPTION__ even though I have clearly added error catching:
case NSStreamEventHasBytesAvailable:
{
NSMutableData *data=[[NSMutableData alloc] init];
uint8_t *buffer[1024];
unsigned int len=0;
len=[(NSInputStream *)stream read:buffer maxLength:1024];
if(len>0){
#try{
[data appendBytes:&buffer length:len];
}
#catch(NSException *ex){
NSLog(#"Fail: %#", ex);
}
[statusLabel setText:[data stringValue]];
//[bytesRead setIntValue:[bytesRead intValue]+len];
}else{
NSLog(#"No Buffer");
}
break ;
}
This is a problem down at the C level: you're confused about buffers and pointers.
This code:
uint8_t *buffer[1024];
gives you a stack buffer of 1024 pointers to uint8_ts, which is almost certainly not what you want. Instead:
uint8_t buffer[1024];
Later on, you're passing the address of your pointer on the stack to -[NSMutableData appendBytes:length:], which again is not what you want: as in the documentation, pass the first element:
[data appendBytes:buffer length:len];
There's a very thorough programming guide with complete code for what you're trying to do, you may want to reference it.
As for __TERMINATING_DUE_TO_UNCAUGHT_EXCEPTION__, memory corruption and bad pointer dereferencing isn't something you can catch with an Objective-C #try/#catch; it's much lower-level. On the other hand, you can still catch this in the debugger if you turn debugging on.
declare your buffer as:
uint8_t buffer[1024];
and do the append as:
[data appendBytes:buffer length:len];
For completeness read:maxLength: returns an NSInteger and will be negative if there was an error. Assigning it to an unsigned int discards this and can cause a crash.
Related
I'm trying to write a password encryption function into my app, following this article.
I wrote a function that runs the CCCalibratePBKDF function and outputs the number of rounds.
const uint32_t oneSecond = 1000;
uint rounds = CCCalibratePBKDF(kCCPBKDF2,
predictedPasswordLength,
predictedSaltLength,
kCCPRFHmacAlgSHA256,
kCCKeySizeAES128,
oneSecond);
This works perfectly, but when I try to implement the next part it all goes wrong.
I can start writing the CCKeyDerivationPBKDF function call and it auto-completes the function and all the parameters. As I go through filling it in all the parameters are also auto-completed.
- (NSData *)authenticationDataForPassword: (NSString *)password salt: (NSData *)salt rounds: (uint) rounds
{
const NSString *plainData = #"Fuzzy Aliens";
uint8_t key[kCCKeySizeAES128] = {0};
int keyDerivationResult = CCKeyDerivationPBKDF(kCCPBKDF2,
[password UTF8String],
[password lengthOfBytesUsingEncoding: NSUTF8StringEncoding],
[salt bytes],
[salt length],
kCCPRFHmacAlgSHA256,
rounds,
key,
kCCKeySizeAES128);
if (keyDerivationResult == kCCParamError) {
//you shouldn't get here with the parameters as above
return nil;
}
uint8_t hmac[CC_SHA256_DIGEST_LENGTH] = {0};
CCHmac(kCCHmacAlgSHA256,
key,
kCCKeySizeAES128,
[plainData UTF8String],
[plainData lengthOfBytesUsingEncoding: NSUTF8StringEncoding],
hmac);
NSData *hmacData = [NSData dataWithBytes: hmac length: CC_SHA256_DIGEST_LENGTH];
return hmacData;
}
But as soon as I hit ; it marks an error saying "No matching function for call to 'CCKeyDerivationPBKDF'" and it won't build or anything.
I've imported CommonCrypto/CommonKeyDerivation.h and CommonCrypto/CommonCryptor.h as both of these were necessary for the enum names.
First, make sure that you haven't done anything funny with your include path (in particular, I do not recommend #HachiEthan's solution, which just confuses things). In general, leave this alone, and specifically don't add things like /usr/include to it. Make sure you've added Security.framework to your link step. This is the usual cause of problems.
The biggest thing you want to be sure of is that you're getting the iOS 5 Security.framework (rather than some other version like the OS X 10.6 or iOS 4 versions). But my suspicion is that you have a problem with your build settings.
If you want to see a framework that does all of this for reference, take a look at RNCryptor.
Right, I've found the problem (and solution).
Because I was using ZXing I had to rename the .m file to .mm so it could run the C++ stuff in the ZXing library.
I don't know why but renaming the file this way broke the CCKeyDerivationPBKDF function.
I've now moved the crypto code into it's own class and left it as .m and all I need now is to include the two imports as I did in the original post.
I didn't have to include any frameworks or anything.
I am using the libical library to parse the iCalendar format and read the information I need out of it. It is working absolutely fine so far, but there is one odd thing concerning ical.
This is my code:
icalcomponent *root = icalparser_parse_string([iCalData cStringUsingEncoding:NSUTF8StringEncoding]);
if (root)
{
icalcomponent *currentEvent = icalcomponent_get_first_component(root, ICAL_VEVENT_COMPONENT);
while (currentEvent)
{
while(currentProperty)
{
icalvalue *value = icalproperty_get_value(currentProperty);
char *icalString = icalvalue_as_ical_string_r(value); //seems to leak
NSString *currentValueAsString = [NSString stringWithCString:icalString
encoding:NSUTF8StringEncoding];
icalvalue_free(value);
//...
//import data
//...
icalString = nil;
currentValueAsString = nil;
icalproperty_free(currentProperty);
currentProperty = icalcomponent_get_next_property(currentEvent, ICAL_ANY_PROPERTY);
} //end while
} //end while
icalcomponent_free(currentEvent);
}
icalcomponent_free(root);
//...
I did use instruments to check my memory usage and were able to find out, that this line seems to leak:
char *icalString = icalvalue_as_ical_string_r(value); //seems to leak
If I'd copy and paste this line 5 or six times my memory usage would grow about 400kb and never get released anymore.
There is no free method for the icalvalue_as_ical_string_r method because it's returning a char *..
Any suggestions how to solve this issue? I would appreciate any help!
EDIT
Taking a look at the apple doc says the following:
To get a C string from a string object, you are recommended to use UTF8String. This returns a const char * using UTF8 string encoding.
const char *cString = [#"Hello, world" UTF8String];
The C string you receive is owned by a temporary object, and will become invalid when automatic deallocation takes place. If you want to get a permanent C string, you must create a buffer and copy the contents of the const char * returned by the method.
But how to release a char * string properly now if using arc?
I tried to add #autorelease {...} in front of my while-loop but without any effort. Still increasing memory usage...
Careful with the statement "no free method...because it's returning a char*"; that is never something you can just assume.
In the absence of documentation you can look at the source code of the library to see what it does; for example:
http://libical.sourcearchive.com/documentation/0.44-2/icalvalue_8c-source.html
Unfortunately this function can do a lot of different things. There are certainly some cases where calling free() on the returned buffer would be right but maybe that hasn't been ensured in every case.
I think it would be best to request a proper deallocation method from the maintainers of the library. They need to clean up their own mess; the icalvalue_as_ical_string_r() function has at least a dozen cases in a switch that might have different deallocation requirements.
icalvalue_as_ical_string_r returns a char * because it has done a malloc() for your result string. If your pointer is non-NULL, you have to free() it after use.
I'm following the suggestion in the answer here for redirecting NSLog output on an iOS device to a file, which works great. The problem is that it no longer shows up in the console on the device. What I'd really like is a way to tee the stderr stream to both the console and the file. Does anyone have an idea how to do that?
I found an acceptable answer on another thread (NSLog() to both console and file).
The solution provided there is to only redirect to a file if a debugger is not detected, like this:
if (!isatty(STDERR_FILENO))
{
// Redirection code
}
Thanks to Sailesh for that answer.
Once you freopen() the file descriptor, you can read from it and do as you please with the data. Some ideas from this will be useful to you.
You could either write it back out to stdout, or try to write directly to /dev/console. I've never tried to open /dev/console on an iPhone, but I'm guessing it's possible despite being outside of the sandbox. I'm not sure how the app review process will treat it.
Or you can redirect to a TCP socket and view on a remote telnet client. No need for XCode this way!
Basically:
Create a standard C function which calls an Obj-C static method:
void tcpLogg_log(NSString* fmt, ...)
{
va_list args;
va_start(args, fmt);
[TCPLogger tcpLog:fmt :args];
va_end(args);
}
The static Obj-C method:
(void)tcpLog:(NSString*)fmt :(va_list)args
{
NSLogv(fmt, args);
if(sharedSingleton != nil && sharedSingleton.socket != nil)
{
NSString *time = [sharedSingleton.dateFormat stringFromDate:[NSDate date]];
NSString *msg = [[NSString alloc] initWithFormat:fmt arguments:args];
mach_port_t tid = pthread_mach_thread_np(pthread_self());
NSString *str = [NSString stringWithFormat:#"%#[%X]: %#\r\n", time, tid, msg];
NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding];
[sharedSingleton.socket writeData:data
withTimeout:NETWORK_CLIENT_TIMEOUT_PERIOD
tag:0];
}
}
Then in your .pch file, add the following lines to override NSLog()
define NSLog(...) tcpLogg_log(__VA_ARGS__);
void tcpLogg_log(NSString* fmt, ...);
Of course more details are required to handle the TCP Socket. Working source code is available here:
https://github.com/driedler/iOS-TCP-Logger/wiki/About
My app "streams" content (fixed sized files, hence quotation marks) from an HTTP server into a local file. Then there is another component of the app that opens that same file and displays it (plays it).
This is done for caching purposes, so that when the same file is requested next time, it will no longer need to be downloaded from the server.
App's spec requires that all local content is encrypted (even with the most light weight encryption)
Question: has there been done any work, allowing one to simply redirect the stream to a library which will then save the stream encrypted into a file? And then, when I request the stream from the local file, the library returns an on the fly decrypted stream?
I've been searching for a solution with no results so far
Thanks
I ended up writing a custom solution that uses RC4 encryption from the built in Crypt library. It was surprisingly straight forward. Basically it involved creating a function that encrypts/decrypts chunks of NSData and then read/write those chunks to files... Here's the function that does the encryption in case someone else is interested:
- (NSData*)RC4EncryptDecryptWithKey:(NSString *)key operation:(CCOperation)operation
{
// convert to C string..
int keySize = [key length];
char keyPtr[keySize];
bzero(keyPtr, sizeof(keyPtr));
[key getCString:keyPtr
maxLength:sizeof(keyPtr)
encoding:NSUTF8StringEncoding];
// encode/decode
NSUInteger dataLength = [self length];
size_t bufferSize = dataLength;
void *buffer = malloc(bufferSize);
size_t numBytesOut = 0;
CCCryptorStatus cryptStatus = CCCrypt(operation,
kCCAlgorithmRC4,
kCCOptionECBMode,
keyPtr,
8,
NULL,
[self bytes],
dataLength,
buffer,
bufferSize,
&numBytesOut);
if (cryptStatus == kCCSuccess) {
return [NSData dataWithBytesNoCopy:buffer
length:numBytesOut
freeWhenDone:YES];
}
free(buffer);
return nil;
}
- (NSData*)RC4EncryptWithKey:(NSString*)key {
return [self RC4EncryptDecryptWithKey:key operation:kCCEncrypt];
}
- (NSData*)RC4DecryptWithKey:(NSString*)key {
return [self RC4EncryptDecryptWithKey:key operation:kCCDecrypt];
}
Obviously one could create something more secure (eg AES) or whatever (in fact I used examples of other encryption wrappers to write this one)
I wouldn't worry about encryption just because Apple says so.
Make this work how you want it (without encryption, it sounds like) and submit it for approval. If approved, you're good. If not, worry about it then. If your design requires you to make a decision now, your design might be flawed.
When converting a NSString to a char* using UTF8String, how to retain it?
According to the following link, when you use UTF8String the returned char* is pretty much autoreleased, so it won't last beyond the current function: http://developer.apple.com/mac/library/documentation/cocoa/reference/Foundation/Classes/NSString_Class/Reference/NSString.html#jumpTo_128
It says i have to copy it or something to keep it around. How can i do this?
The reason i ask is that if i do [myCharPointer retain] it doesn't retain it because it's not an obj-c object, it's a c pointer.
Thanks
You can use strdup()
const char* utf8Str = [#"an example string" UTF8String];
if (utf8Str != NULL)
{
stringIWantToKeep = strdup(utf8Str);
}
When you are done with stringIWantToKeep, you free it as though it was originally malloc'd.
Try using -getCString:maxLength:encoding:, e.g.:
NSUInteger bufferCount = sizeof(char) * ([string length] + 1);
const char *utf8Buffer = malloc(bufferCount);
if ([string getCString:utf8Buffer
maxLength:bufferCount
encoding:NSUTF8StringEncoding]) {
NSLog("Success! %s", utf8Buffer);
free(utf8Buffer); // Remember to do this, or you will get a memory leak!
}
If you need an object to retain/release as every other object you can do the following:
NSData* storage= [yourNSString dataUsingEncoding:NSUTF8StringEncoding];
char* yourCString= (char*)storage.bytes;
// your code flow here
Now you can pass both storage and yourCString to any function retaining/releasing storage as you like, when the retain count of storage will go to 0 the memory pointed by yourCString will be freed too.
I used this to keep a single copy of a very long string while having references created by strtok_r in beans and have the memory released only when all beans had been released.
A little note about (missing) BOM:
As stated here http://boredzo.org/blog/archives/2012-06-03/characters-in-nsstring dataUsingEncoding: should add BOM but i've checked with the debugger and there is no BOM in the returned bytes.