Passenger::MessageChannel Class Reference
[Apache-independent support classes and function]

#include <MessageChannel.h>

List of all members.


Detailed Description

Convenience class for I/O operations on file descriptors.

This class provides convenience methods for:

There are two kinds of messages:

MessageChannel is to be wrapped around a file descriptor. For example:

    int p[2];
    pipe(p);
    MessageChannel channel1(p[0]);
    MessageChannel channel2(p[1]);
    
    // Send an array message.
    channel2.write("hello", "world !!", NULL);
    list<string> args;
    channel1.read(args);    // args now contains { "hello", "world !!" }

    // Send a scalar message.
    channel2.writeScalar("some long string which can contain arbitrary binary data");
    string str;
    channel1.readScalar(str);

The life time of a MessageChannel is independent from that of the wrapped file descriptor. If a MessageChannel object is destroyed, the file descriptor is not automatically closed. Call close() if you want to close the file descriptor.

Note:
I/O operations are not buffered.

Be careful with mixing the sending/receiving of array messages, scalar messages and file descriptors. If you send a collection of any of these in a specific order, then the receiving side must receive them in the exact some order. So suppose you first send a message, then a file descriptor, then a scalar, then the receiving side must first receive a message, then a file descriptor, then a scalar. If the receiving side does things in the wrong order then bad things will happen.

MessageChannel is not thread-safe, but is reentrant.


Public Member Functions

 MessageChannel ()
 Construct a new MessageChannel with no underlying file descriptor.
 MessageChannel (int fd)
 Construct a new MessageChannel with the given file descriptor.
void close ()
 Close the underlying file descriptor.
void write (const list< string > &args)
 Send an array message, which consists of the given elements, over the underlying file descriptor.
void write (const char *name,...)
 Send an array message, which consists of the given strings, over the underlying file descriptor.
void writeScalar (const string &str)
 Send a scalar message over the underlying file descriptor.
void writeScalar (const char *data, unsigned int size)
 Send a scalar message over the underlying file descriptor.
void writeRaw (const char *data, unsigned int size)
 Send a block of data over the underlying file descriptor.
void writeRaw (const string &data)
 Send a block of data over the underlying file descriptor.
void writeFileDescriptor (int fileDescriptor)
 Pass a file descriptor.
bool read (vector< string > &args)
 Read an array message from the underlying file descriptor.
bool readScalar (string &output)
 Read a scalar message from the underlying file descriptor.
bool readRaw (void *buf, unsigned int size)
 Read exactly size bytes of data from the underlying file descriptor, and put the result in buf.
int readFileDescriptor ()
 Receive a file descriptor, which had been passed over the underlying file descriptor.

Constructor & Destructor Documentation

Passenger::MessageChannel::MessageChannel (  )  [inline]

Construct a new MessageChannel with no underlying file descriptor.

Thus the resulting MessageChannel object will not be usable. This constructor exists to allow one to declare an "empty" MessageChannel variable which is to be initialized later.


Member Function Documentation

void Passenger::MessageChannel::close (  )  [inline]

Close the underlying file descriptor.

If this method is called multiple times, the file descriptor will only be closed the first time.

Exceptions:
SystemException 
boost::thread_interrupted 

void Passenger::MessageChannel::write ( const list< string > &  args  )  [inline]

Send an array message, which consists of the given elements, over the underlying file descriptor.

Parameters:
args The message elements.
Exceptions:
SystemException An error occured while writing the data to the file descriptor.
boost::thread_interrupted 
Precondition:
None of the message elements may contain a NUL character ('\0').
See also:
read(), write(const char *, ...)

void Passenger::MessageChannel::write ( const char *  name,
  ... 
) [inline]

Send an array message, which consists of the given strings, over the underlying file descriptor.

Parameters:
name The first element of the message to send.
... Other elements of the message. These *must* be strings, i.e. of type char*. It is also required to terminate this list with a NULL.
Exceptions:
SystemException An error occured while writing the data to the file descriptor.
boost::thread_interrupted 
Precondition:
None of the message elements may contain a NUL character ('\0').
See also:
read(), write(const list<string> &)

void Passenger::MessageChannel::writeScalar ( const string &  str  )  [inline]

Send a scalar message over the underlying file descriptor.

Parameters:
str The scalar message's content.
Exceptions:
SystemException An error occured while writing the data to the file descriptor.
boost::thread_interrupted 
See also:
readScalar(), writeScalar(const char *, unsigned int)

void Passenger::MessageChannel::writeScalar ( const char *  data,
unsigned int  size 
) [inline]

Send a scalar message over the underlying file descriptor.

Parameters:
data The scalar message's content.
size The number of bytes in data.
Precondition:
data != NULL
Exceptions:
SystemException An error occured while writing the data to the file descriptor.
boost::thread_interrupted 
See also:
readScalar(), writeScalar(const string &)

void Passenger::MessageChannel::writeRaw ( const char *  data,
unsigned int  size 
) [inline]

Send a block of data over the underlying file descriptor.

This method blocks until everything is sent.

Parameters:
data The data to send.
size The number of bytes in data.
Precondition:
data != NULL
Exceptions:
SystemException An error occured while writing the data to the file descriptor.
boost::thread_interrupted 
See also:
readRaw()

void Passenger::MessageChannel::writeRaw ( const string &  data  )  [inline]

Send a block of data over the underlying file descriptor.

This method blocks until everything is sent.

Parameters:
data The data to send.
Precondition:
data != NULL
Exceptions:
SystemException An error occured while writing the data to the file descriptor.
boost::thread_interrupted 

void Passenger::MessageChannel::writeFileDescriptor ( int  fileDescriptor  )  [inline]

Pass a file descriptor.

This only works if the underlying file descriptor is a Unix socket.

Parameters:
fileDescriptor The file descriptor to pass.
Exceptions:
SystemException Something went wrong during file descriptor passing.
boost::thread_interrupted 
Precondition:
fileDescriptor >= 0
See also:
readFileDescriptor()

bool Passenger::MessageChannel::read ( vector< string > &  args  )  [inline]

Read an array message from the underlying file descriptor.

Parameters:
args The message will be put in this variable.
Returns:
Whether end-of-file has been reached. If so, then the contents of args will be undefined.
Exceptions:
SystemException If an error occured while receiving the message.
boost::thread_interrupted 
See also:
write()

bool Passenger::MessageChannel::readScalar ( string &  output  )  [inline]

Read a scalar message from the underlying file descriptor.

Parameters:
output The message will be put in here.
Returns:
Whether end-of-file was reached during reading.
Exceptions:
SystemException An error occured while writing the data to the file descriptor.
boost::thread_interrupted 
See also:
writeScalar()

bool Passenger::MessageChannel::readRaw ( void *  buf,
unsigned int  size 
) [inline]

Read exactly size bytes of data from the underlying file descriptor, and put the result in buf.

If end-of-file has been reached, or if end-of-file was encountered before size bytes have been read, then false will be returned. Otherwise (i.e. if the read was successful), true will be returned.

Parameters:
buf The buffer to place the read data in. This buffer must be at least size bytes long.
size The number of bytes to read.
Returns:
Whether reading was successful or whether EOF was reached.
Precondition:
buf != NULL
Exceptions:
SystemException Something went wrong during reading.
boost::thread_interrupted 
See also:
writeRaw()

int Passenger::MessageChannel::readFileDescriptor (  )  [inline]

Receive a file descriptor, which had been passed over the underlying file descriptor.

Returns:
The passed file descriptor.
Exceptions:
SystemException If something went wrong during the receiving of a file descriptor. Perhaps the underlying file descriptor isn't a Unix socket.
IOException Whatever was received doesn't seem to be a file descriptor.
boost::thread_interrupted 


The documentation for this class was generated from the following file:

Generated on Tue Jun 24 14:03:44 2008 for Passenger by  doxygen 1.5.5