Ok, so I've been using NSLog in objective-C for awhile now to debug and I know it's supposed to print to the terminal whatever I put in the parentheses. For some reason, it just stopped printing to the terminal and I'm not sure how to fix this error. I was wondering what other people would suggest doing to fix this problem. I've only included part of my code because I don't want to scare away someone from answering this simple (or at least I hope it's simple to fix) problem. When I run the code, the only two statements that print are "serverButton - Stage 1" and "serverButton - Stage 2 - Complete" but nothing else in between. FYI -(void)startServer is in another class called "Server" and I have made "server" a pointer to that said class.
-(IBAction)serverButton {
NSLog(#"serverButton - Stage 1");
[server startServer];
NSLog(#"serverButton - Stage 2 - Complete");
}
-(void)startServer {
NSLog(#"serverButton - Stage 1");
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC; // set to AF_INET to force IPv4
hints.ai_socktype = SOCK_DGRAM;
hints.ai_flags = AI_PASSIVE; // use my IP
if ((rv = getaddrinfo(NULL, MYPORT, &hints, &servinfo)) != 0) {
NSLog(#"ERROR: serverButton - Stage 1");
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
serverError = 1;
NSLog(#"Error");
}
Add a check to make sure server is not nil before you call startServer, if it was nil then nothing would get called and no error would be generated.
You say:
FYI -(void)startServer is in another class called "Server" and I have made "server" a pointer to that said class.
If I read that right, your server variable is actually pointing to a class, like so:
Class server = [Server class];
...
NSLog(#"begin");
[server startServer];
NSLog(#"end");
If that is the case, then your startServer method would have to be a class method:
+ (void)startServer {
NSLog(#"hello!");
}
If that is not the case, can you please post a little bit more code? Specifically, the part where you assign to that server variable would be helpful.
It looks like the problem isn't NSLog, but rather that startServer isn't actually getting sent to the receiver like you think it is.
If the NSLog doesn't print to the terminal (explain what is terminal). I assume terminal is the Xcode debugger console. Then, you need to check the Console.app, whether it's printed there.
The new version of Xcode doesn't have this problem.
Related
Before you decide its a tl:dr (too long, didnt read) post try to read at least some, since Its a question broken down in a lot of small pieces. Some of which you can probably answer and help me.
Please try to help me as much as you can. These types of problems are very common on the internet and I think you will help me and much more people after me.
I am currently researching HTTP services and the protocol itself so that I can discover if it is useful to me.
I have some basic questions as well as some code that needs to be discussed.
First I would like to know how does the communication start? I have discovered that the client sends a message in which it requests a resource (is this correct?). Then what happens? I (as a server) have to reply with what?
Do I need to append a carriage return and a line feed after every response? Somewhere it says there even need to be two (\r\n\r\n).
How can an asynchronous writing be established? (I hope this question is understandable) My primary goal is to achieve a connection between a client and a server and then a continuous data stream from server to the client. Does the client need to reply for every message it gets?
I hope I made my questions clear, since I'm not an expert in these things (yet, I am very interested in it).
And for the programming part of my problem.
I have managed to put together a simple program in Qt in C++ (server side) and a simple client in Objective C (iOS). The client connects and I can read the request header. It is like this:
Data available, incoming: "GET / HTTP/1.1
Host: localhost:9990
Connection: close
User-Agent: CFStream%20test/1.0 CFNetwork/609 Darwin/12.2.0
Should I reply to this header manually? And if so, what?
The client side code looks like this (i know its not pseudo but i think its pretty self-explanatory):
- (void)setupStream
{
NSURL *url = [NSURL URLWithString:#"http://localhost:9990"];
CFHTTPMessageRef message = CFHTTPMessageCreateRequest(NULL, (CFStringRef)#"GET", (CFURLRef)url, kCFHTTPVersion1_1);
stream = CFReadStreamCreateForHTTPRequest(NULL, message);
CFRelease(message);
if (!CFReadStreamSetProperty(stream, kCFStreamPropertyHTTPShouldAutoredirect, kCFBooleanTrue))
{
NSLog(#"Some error.");
}
CFDictionaryRef proxySettings = CFNetworkCopySystemProxySettings();
CFReadStreamSetProperty(stream, kCFStreamPropertyHTTPProxy, proxySettings);
CFRelease(proxySettings);
if (!CFReadStreamOpen(stream))
{
CFRelease(stream);
NSLog(#"Error opening stream.");
}
CFStreamClientContext context = {0, self, NULL, NULL, NULL};
CFReadStreamSetClient(stream, kCFStreamEventHasBytesAvailable | kCFStreamEventErrorOccurred, readStreamCallback, &context);
CFReadStreamScheduleWithRunLoop(stream, CFRunLoopGetCurrent(), kCFRunLoopCommonModes);
NSLog(#"Done");
}
This is the setup stream method. The stream variable is a class variable of type CFReadStreamRef.
The callback looks like this:
static void readStreamCallback(CFReadStreamRef aStream, CFStreamEventType event, void *client)
{
ViewController *controller = (ViewController*)client;
[controller handleEvent:event forStream:aStream];
}
And the handle event like this:
- (void)handleEvent:(CFStreamEventType)event forStream:(CFReadStreamRef)aStream
{
if (aStream != stream)
{
return;
}
NSLog(#"Handle event callback");
switch (event)
{
case kCFStreamEventHasBytesAvailable:
NSLog(#"Work log");
UInt8 bytes[11];
CFIndex length;
length = CFReadStreamRead(stream, bytes, 11); //I know 11 bytes is hard coded, its in testing stage now. Feel free to suggest me how to do it better.
if (length == -1)
{
NSLog(#"Error, data length = -1");
return;
}
NSLog(#"Len: %li, data: %s", length, bytes);
break;
default:
NSLog(#"Other event");
break;
}
}
And thats practically all the client code that is worth mentioning. The Qt Server part (I will only post the important parts) is done like this: (this is a subclassed QTcpServer class). First the startServer(); is called:
bool Server::startServer()
{
if (!this->listen(QHostAddress::Any, 9990))
return false;
return true;
}
When there is a connection incoming the incomingConnection is fired off with the socket descriptor as a parameter:
void Server::incomingConnection(int handle)
{
qDebug("New client connected");
ServerClient *client = new ServerClient(handle, this); //The constructor takes in the socket descriptor needed to set up the socket and the parent (this)
client->setVectorLocation(clients.count()); //This is a int from a Qvector in which i append the clients, its not important for understanding right now.
connect(client, SIGNAL(clientDisconnected(int)), this, SLOT(clientDisconnected(int)), Qt::QueuedConnection); //When the client socket emits a disconnected signal the ServerClient class emits a client disconnected signal which the server uses to delete that client from the vector (thats why I use "setVectorLocation(int)") - not important right now
clients.push_back(client); //And then I append the client to the QVector - not important right now
}
The ClientServer class constructor just creates a new socket and connects the required methods:
ServerClient::ServerClient(int handle, QObject *parent) :
QObject(parent)
{
socket = new QTcpSocket(this); //Socket is a class variable
connect(socket, SIGNAL(disconnected()), this, SLOT(disconnected()));
connect(socket, SIGNAL(readyRead()), this, SLOT(readyRead()));
socket->setSocketDescriptor(handle);
}
Ready read just writes me the data incoming (it wont be much user later i think):
void ServerClient::readyRead()
{
qDebug() << "Data available, incoming: " << socket->readAll();
}
And finally the write data:
void ServerClient::writeData(QByteArray *data)
{
data->append("\r\n\r\n"); //I have read this must be appended to all outgoing data from a HTTP server
socket->write(*data);
socket->flush();
qDebug() << "Written data to client: " << *data;
}
This code however does not always work. Sometimes when I write message like "Message" the client recieves all the data and some things that shouldnt be there (the new line and a wierd symbol - can NSLog cause this?). Sometimes when I send "Hellow" the client only gets "Hel" and some other funky stuff.
What are the problems? What should I pay more attention about? Anything that will help me will be MUCH appreciated. And please dont paste in some links that contain a book with a few hundred pages, Im sure this can be solved just by explaining things to me.
THANKS A LOT!
Jan.
You asked many questions ... and that's a perfectly legitimate thing to do :)
I confess - it was too long, I didn't read :(
BUT ...
1) Yes, the HTTP protocol does expect na "CRLF" ("\r\n"). Many servers and many clients are "forgiving", but strictly speaking - yes, you need them.
REFERENCE: RFC 2616
2) Wanting to understand HTTP "internals" is also perfectly legitimate - I applaud you.
One good way is to read the RFC(s).
Another is to use a "telnet" client: http://blog.tonycode.com/tech-stuff/http-notes/making-http-requests-via-telnet
Yet another is to study requests and responses in FF Firebug
3) Socket programming is another issue - which explains why sometimes you might read "hello world", and other times you might just get "hel".
Strong recommendation: Beej's Guide to Network Programming
4) Finally, no way would I actually write a server in Qt with C++ (except maybe as a toy "science experiment", or for some really off-the-wall requirement)
I would definitely write server code in C# (for Windows servers), Java (for everything else) or a scripting language I felt comfortable with (Perl, Ruby/RoR, Python and Lua all come to mind).
IMHO .. and hope that helps!
Your questions pretty much amount to "how does HTTP work", and the full answer lies in the specification.
For debugging purposes, I'd like to access console printouts at runtime in a way similar to the Console app current on the App Store (that can be found here).
I did some searching of the docs and I can't find anything that's provided by Apple, but I feel like I'm missing something important. Any insight?
Thanks.
You can do so using <asl.h>. Here is an example that I threw together to create an array of console messages.
-(NSArray*)console
{
NSMutableArray *consoleLog = [NSMutableArray array];
aslclient client = asl_open(NULL, NULL, ASL_OPT_STDERR);
aslmsg query = asl_new(ASL_TYPE_QUERY);
asl_set_query(query, ASL_KEY_MSG, NULL, ASL_QUERY_OP_NOT_EQUAL);
aslresponse response = asl_search(client, query);
asl_free(query);
aslmsg message;
while((message = asl_next(response)) != NULL)
{
const char *msg = asl_get(message, ASL_KEY_MSG);
[consoleLog addObject:[NSString stringWithCString:msg encoding:NSUTF8StringEncoding]];
}
if (message != NULL) {
asl_free(message);
}
asl_free(response);
asl_close(client);
return consoleLog;
}
If your device is attached to Xcode, you can see console output (NSLogs and such) in the debug area:
If you're running the app and connecting to Xcode later, I believe you can get console logs in the Organizer.
Edit: to access the log file at runtime, you should try /var/log/system.log — but even better I recommend using a custom debug function, which would write to the system log and/or a text view in your app. (Check out NSLogv, which will be useful when writing a wrapper function.) This also has the advantage of letting you disable all debug logs from one place (just change your debug function).
I'm putting together a Mac OS X Application and I'm trying to register to receive Display Reconfiguration notices, but I'm very lost right now. I've been reading Apple's documentation and some forums posts, etc., but everything seems to assume a better knowledge of things than I apparently possess. I understand that I have to request the callback inside a run loop for it to work properly. I don't know how to set up a basic run loop for it, though. I also feel like the example Apple has in their documentation is missing stuff they are expecting me to already know. To display my ignorance here is what I feel like things should look like.
NSRunLoop *rLoop = [NSRunLoop currentRunLoop];
codeToStartRunLoop
void MyDisplayReconfigurationCallBack (
CGDirectDisplayID display,
CGDisplayChangeSummaryFlags flags,
void *userInfo);
{
if (flags & kCGDisplayAddFlag) {
NSLog (#"Display Added");
}
else if (kCGDisplayRemoveFlag) {
NSLog (#"Display Removed");
}
}
CGDisplayRegisterReconfigurationCallback(MyDisplayReconfigurationCallBack, NULL);
The actual code I got was from Apple's Example, but it tells me that flags is an undeclared identifier at this point and won't compile. Not that it would work right since I don't have it in a run loop. I was hoping to find a tutorial somewhere that explains registering for system callback in a run loop but have not been successful. If anyone could point me in the right direction I'd super appreciate it.
(I'm sure that you'll be able to tell from my question that I'm very green. I taught myself Objective-C out of a book as my first programming language. I skipped C, so every once in a while I hit a snag somewhere that I can't figure out.)
If you're writing a Mac OS X application, the AppKit has already set up a run loop for you, so you don't need to worry about that part. You really only need to create your own run loop in Cocoa when you are also creating your own thread.
For the "undeclared identifier" part, it looks like it's due to a typo/syntax mistake:
void MyDisplayReconfigurationCallBack (CGDirectDisplayID display,
CGDisplayChangeSummaryFlags flags,
void *userInfo);
// Semicolon makes this an invalid function definition^^
{
// This is an anonymous block,* and flags wasn't declared in it
if (flags & kCGDisplayAddFlag) {
// etc.
}
Also, unlike some other languages, you can't declare or define functions inside of other functions, methods, or blocks* -- they have to be at the top level of the file. You can't put this in the same place where you call CGDisplayRegisterReconfigurationCallback.
Just as an sample (I have no idea what the rest of your code really looks like):
// MyClassThatIsInterestedInDisplayConfiguration.m
#import "MyClassThatIsInterestedInDisplayConfiguration.h"
// Define callback function at top level of file
void MyDisplayReconfigurationCallBack (
CGDirectDisplayID display,
CGDisplayChangeSummaryFlags flags,
void *userInfo)
{
if (flags & kCGDisplayAddFlag) {
NSLog (#"Display Added");
}
else if (kCGDisplayRemoveFlag) {
NSLog (#"Display Removed");
}
}
#implementation MyClassThatIsInterestedInDisplayConfiguration
- (void) comeOnBabyAndDoTheRegistrationWithMe {
// Register callback function inside a method
CGDisplayRegisterReconfigurationCallback(MyDisplayReconfigurationCallBack,
NULL);
}
#end
*The basic C curly-brace-delimited thing, not the new cool Obj-C ad hoc function thing.
I am finding the doc for CFStreamCreatePairWithSocketToCFHost confusing:
Specifically, its not clear to me how the function can set the readStream pointer to null on error.
as far as I understand, the pointer is passed by value - so the function can only change the objected pointed to by the pointer.
Right now I can't figure out how to detect connection errors.
Relevant doc snippet:
Creates readable and writable streams connected to a given CFHost object.
void CFStreamCreatePairWithSocketToCFHost (
CFAllocatorRef alloc,
CFHostRef host,
SInt32 port,
CFReadStreamRef *readStream,
CFWriteStreamRef *writeStream
);
readStream
Upon return, contains a CFReadStream object connected to the host host on port port, or NULL if there is a failure during creation. If you pass NULL, the function will not create a readable stream. Ownership follows the Create Rule.
This is my connecting code, it goes all the way to NSLog(#"Connected") even when the server is down.
NSLog(#"Attempting to (re)connect to %#:%d", m_host, m_port);
while(TRUE)
{
CFHostRef host = CFHostCreateWithName(kCFAllocatorDefault, (CFStringRef)m_host);
if (!host)
{
NSLog(#"Error resolving host %#", m_host);
[NSThread sleepForTimeInterval:5.0];
continue;
}
CFStreamCreatePairWithSocketToCFHost(kCFAllocatorDefault, host , m_port, &m_in, &m_out);
CFRelease(host);
if (!m_in)
{
NSLog(#"Error");
}
CFStreamClientContext context = {0, self,nil,nil,nil};
if (CFReadStreamSetClient(m_in, kCFStreamEventHasBytesAvailable | kCFStreamEventErrorOccurred | kCFStreamEventEndEncountered, networkReadEvent, &context))
{
CFReadStreamScheduleWithRunLoop(m_in, CFRunLoopGetCurrent(),kCFRunLoopCommonModes);
}
if (CFWriteStreamSetClient(m_out, kCFStreamEventErrorOccurred | kCFStreamEventEndEncountered, networkWriteEvent, &context))
{
CFWriteStreamScheduleWithRunLoop(m_out, CFRunLoopGetCurrent(),kCFRunLoopCommonModes);
}
BOOL success = CFReadStreamOpen(m_in);
CFErrorRef error = CFReadStreamCopyError(m_in);
if (!success || (error && CFErrorGetCode(error) != 0))
{
NSLog(#"Connect error %s : %d", CFErrorGetDomain(error), CFErrorGetCode(error));
[NSThread sleepForTimeInterval:5.0];
}
else
{
NSLog(#"Connected");
break;
}
}
From the "CFNetwork Programming Guide":
Opening a stream can be a lengthy process, so the CFReadStreamOpen and CFWriteStreamOpen functions avoid blocking by returning TRUE to
indicate that the process of opening the stream has begun. To check
the status of the open, call the functions CFReadStreamGetStatus and
CFWriteStreamGetStatus, which returnkCFStreamStatusOpening if the open
is still in progress, kCFStreamStatusOpen if the open is complete,
orkCFStreamStatusErrorOccurred if the open has completed but failed.
In most cases, it doesn’t matter whether the open is complete because
the CFStream functions that read and write will block until the stream
is open.
Also check out the kCFStreamEventOpenCompleted,
(http://developer.apple.com/library/ios/#documentation/CoreFoundation/Reference/CFStreamConstants/Reference/reference.html)
: a stream event that reports the successful completion of the opening
process. So to conclude, after calling CFReadStreamOpen (or Write),
which will probably succeed, register to listen to the "OpenCompleted"
event to identify a "real" success.
Surely after you call CFStreamCreatePairWithSocketToCFHost() just test readstream to see if it's NULL?
As you're passing in the memory location of the readstream pointer, the function can easily set that to whatever value it chooses (either a reference to a created object, or alternatively NULL).
Edit
I've tried your code, and I agree, it's very confusing. It appears that the CFReadStreamRef is readily created and opened, even for a nonsense host (I literally used "nonsense"). I don't believe this function will return NULL pointers for an unreachable host.
I suppose this makes sense, in as far as until one tries to open the stream, whether it will work or not is unknown.
So, the readStream param is a pointer to the CFReadStreamRef and, as such, can definitely be set to NULL by the function. &foo means "address of foo" and if you have the address you can set the value.
My reading of the documentation for CFStreamCreatePairWithSocketToCFHost is that they will be set to NULL on failure, but that failure is not about connection failure, but other kinds of failure (memory, etc). So not likely you'll get an error there.
Looks to me like the issue is that CFReadStreamOpen can return immediately with true when it can open the stream in the background and so this code is not really opening the stream or testing that it's been opened, merely queuing it for opening). From the documentation for CFReadStreamOpen:
" If the stream can open in the background without blocking, this function always returns true."
So I think you will need to follow the rest of the instructions for CFReadStreamOpen and schedule the stream on a run loop, or perhaps poll (though obviously polling in a tight loop isn't likely to work).
In the documentation for CFReadStreamOpen we see:
Opening a stream causes it to reserve all the system resources it requires. If the stream can open in the background without blocking, this function always returns true.
I suspect that the stream is opening in the background, and thus you are saying "Connected" before it actually opens. You've already scheduled the stream with a runloop, so if you let the run loop run, you'll probably get a callback with the event type set to kCFStreamEventErrorOccurred, and from there you can process the error appropriately.
everybody.
I want to understand, how i shoud procceed situations when an asynchronous method has "didFinish:#selector(SEL)" parameter.
My code example is:
//
// Authentication check
- ( void )authenticationSuccess: ( GDataServiceTicket* ) ticket
authenticatedWithError: ( NSError* ) error {
if ( error == nil )
{
NSLog( #"authentication success" );
}
else
{
NSLog( #"authentication error" );
}
}
//
- ( void ) fetchFeedOfSpreadsheets {
//create and authenticate to a google spreadsheet service
if ( !(mService) )
{
GDataServiceGoogleSpreadsheet *service = [self spreadsheetService];
[mService autorelease];
mService = [service retain];
}
// check autentication success ( invoke "authenticationSuccess" method for debug success & error )
[mService authenticateWithDelegate: self
didAuthenticateSelector:#selector(authenticationSuccess:
authenticatedWithError:) ];
// HERE I WANT TO MAKE A PAUSE AND WHAIT THE RESULT, EITHER I AUTHENTICATED OR NOT
// AND MAKE AN "IF" STATEMENT TO CONTINTUE WORKING ON SERVER, OR RETURN ERROR
//fetch retrieves the feed of spreadsheets entries
NSURL *feedURL = [ NSURL URLWithString: kGDataGoogleSpreadsheetsPrivateFullFeed ];
GDataServiceTicket *ticket;
ticket = [mService fetchFeedWithURL: feedURL
delegate: self
didFinishSelector: #selector(spreadsheetsTicket:finishedWithFeed:
error: ) ];
// HERE I WANT TO WAIT SECOND TIME. I WANT "spreadsheetsTicket:
// finishedWithFeed:error:" TO PROCCEED ERROR AND PUT A FEED IN SOME NSARRAY OBJECT
// AND AFTER THAT I WANT TO WORK WITH THAT NSARRAY RIGHT HERE
}
I's clear, that i can push the code i want into the end of "authenticationSuccess" method section, but it's also clear, that it's a wrong a way to solve the proble. There a number of situations like this, where i call an asynchronous method with a selector parameter, and i want to find a solution providing me a flexible code writing.
Thanks in advance.
It's a standard practice in Objective-C to put the code to be executed after the authentication in the authenticationSucess: method. You might not like it, but that is life.
Many people had the same complaint as you, so
on iOS 4 and later, there's something called blocks which allow you to write the code to be executed after the authentication in the method which initiates the authentication, as in
[mService authenticateAndExecute:^{
code to be executed when successfully authenticated ;
} whenError:^{
code to be executed when authentication failed;
} ];
But in this case you need to modify the API, which is possible by using categories. See this blog post by Mike Ash. He has many other posts on blocks on the same blog, which are also very instructive.
If you're going to use a library that works asynchronously (and therefore doesn't block your UI), you should have a good reason for trying to force it to work synchronously.
You should be checking for an authentication error at the end of your authenticationSuccess:authenticatedWithError: method, and calling the next request from there if there's a success. Similarly, in your spreadsheetsTicket:finishedWithFeed:error: check for an error, and continuing processing if there isn't one. It might be a better design to do that continued work in a separate method, but that's up to you.
Is there a specific reason you want to use the GData API in a synchronous fashion?