IO Channels — portable support for using files, pipes and sockets

The new functions g_io_channel_read_chars() , g_io_channel_read_line() , g_io_channel_read_line_string() , g_io_channel_read_to_end() , g_io_channel_write_chars() , g_io_channel_seek_position() , and g_io_channel_flush() should not be mixed with the deprecated functions g_io_channel_read() , g_io_channel_write() , and g_io_channel_seek() on the same channel.

GIOChannel instances are created with an initial reference count of 1. g_io_channel_ref() and g_io_channel_unref() can be used to increment or decrement the reference count respectively. When the reference count falls to 0, the GIOChannel is freed. (Though it isn't closed automatically, unless it was created using g_io_channel_new_file() .) Using g_io_add_watch() or g_io_add_watch_full() increments a channel's reference count.

To add a GIOChannel to the main event loop , use g_io_add_watch() or g_io_add_watch_full() . Here you specify which events you are interested in on the GIOChannel , and provide a function to be called whenever these events occur.

Once a GIOChannel has been created, it can be used in a generic manner with the functions g_io_channel_read_chars() , g_io_channel_write_chars() , g_io_channel_seek_position() , and g_io_channel_shutdown() .

To create a new GIOChannel on UNIX systems use g_io_channel_unix_new() . This works for plain file descriptors, pipes and sockets. Alternatively, a channel can be created for a file in a system independent manner using g_io_channel_new_file() .

The GIOChannel data type aims to provide a portable method for using file descriptors, pipes, and sockets, and integrating them into the main event loop . Currently, full support is available on UNIX platforms, support for Windows is only partially complete.

Functions

g_io_channel_unix_new () GIOChannel * g_io_channel_unix_new ( int fd ); Creates a new GIOChannel given a file descriptor. On UNIX systems this works for plain files, pipes, and sockets. The returned GIOChannel has a reference count of 1. The default encoding for GIOChannel is UTF-8. If your application is reading output from a command using via pipe, you may need to set the encoding to the encoding of the current locale (see g_get_charset() ) with the g_io_channel_set_encoding() function. By default, the fd passed will not be closed when the final reference to the GIOChannel data structure is dropped. If you want to read raw binary data without interpretation, then call the g_io_channel_set_encoding() function with NULL for the encoding argument. This function is available in GLib on Windows, too, but you should avoid using it on Windows. The domain of file descriptors and sockets overlap. There is no way for GLib to know which one you mean in case the argument you pass to this function happens to be both a valid file descriptor and socket. If that happens a warning is issued, and GLib assumes that it is the file descriptor you mean. Parameters fd a file descriptor. Returns a new GIOChannel.

g_io_channel_unix_get_fd () gint g_io_channel_unix_get_fd ( GIOChannel *channel ); Returns the file descriptor of the GIOChannel. On Windows this function returns the file descriptor or socket of the GIOChannel. Parameters channel a GIOChannel, created with g_io_channel_unix_new() . Returns the file descriptor of the GIOChannel.

g_io_channel_win32_new_fd () GIOChannel * g_io_channel_win32_new_fd ( gint fd ); Creates a new GIOChannel given a file descriptor on Windows. This works for file descriptors from the C runtime. This function works for file descriptors as returned by the open() , creat() , pipe() and fileno() calls in the Microsoft C runtime. In order to meaningfully use this function your code should use the same C runtime as GLib uses, which is msvcrt.dll. Note that in current Microsoft compilers it is near impossible to convince it to build code that would use msvcrt.dll. The last Microsoft compiler version that supported using msvcrt.dll as the C runtime was version 6. The GNU compiler and toolchain for Windows, also known as Mingw, fully supports msvcrt.dll. If you have created a GIOChannel for a file descriptor and started watching (polling) it, you shouldn't call read() on the file descriptor. This is because adding polling for a file descriptor is implemented in GLib on Windows by starting a thread that sits blocked in a read() from the file descriptor most of the time. All reads from the file descriptor should be done by this internal GLib thread. Your code should call only g_io_channel_read() . This function is available only in GLib on Windows. Parameters fd a C library file descriptor. Returns a new GIOChannel.

g_io_channel_win32_new_socket () GIOChannel * g_io_channel_win32_new_socket ( gint socket ); Creates a new GIOChannel given a socket on Windows. This function works for sockets created by Winsock. It's available only in GLib on Windows. Polling a GSource created to watch a channel for a socket puts the socket in non-blocking mode. This is a side-effect of the implementation and unavoidable. Parameters socket a Winsock socket Returns a new GIOChannel

g_io_channel_win32_new_messages () GIOChannel * g_io_channel_win32_new_messages ( gsize hwnd ); Creates a new GIOChannel given a window handle on Windows. This function creates a GIOChannel that can be used to poll for Windows messages for the window in question. Parameters hwnd a window handle. Returns a new GIOChannel.

g_io_channel_init () void g_io_channel_init ( GIOChannel *channel ); Initializes a GIOChannel struct. This is called by each of the above functions when creating a GIOChannel, and so is not often needed by the application programmer (unless you are creating a new type of GIOChannel). Parameters channel a GIOChannel

g_io_channel_new_file () GIOChannel * g_io_channel_new_file ( const gchar *filename , const gchar *mode , GError **error ); Open a file filename as a GIOChannel using mode mode . This channel will be closed when the last reference to it is dropped, so there is no need to call g_io_channel_close() (though doing so will not cause problems, as long as no attempt is made to access the channel after it is closed). Parameters filename A string containing the name of a file. [ type filename] mode One of "r", "w", "a", "r+", "w+", "a+". These have the same meaning as in fopen() error A location to return an error of type G_FILE_ERROR Returns A GIOChannel on success, NULL on failure.

g_io_channel_read_chars () GIOStatus g_io_channel_read_chars ( GIOChannel *channel , gchar *buf , gsize count , gsize *bytes_read , GError **error ); Replacement for g_io_channel_read() with the new API. Parameters channel a GIOChannel buf a buffer to read data into. [ out caller-allocates ][ array length=count][ element-type guint8] count the size of the buffer. Note that the buffer may not be completely filled even if there is data in the buffer if the remaining data is not a complete character. [ in ] bytes_read The number of bytes read. This may be zero even on success if count < 6 and the channel's encoding is non- NULL . This indicates that the next UTF-8 character is too wide for the buffer. [ out ][ optional ] error a location to return an error of type GConvertError or GIOChannelError. Returns the status of the operation.

g_io_channel_read_unichar () GIOStatus g_io_channel_read_unichar ( GIOChannel *channel , gunichar *thechar , GError **error ); Reads a Unicode character from channel . This function cannot be called on a channel with NULL encoding. Parameters channel a GIOChannel thechar a location to return a character. [ out ] error a location to return an error of type GConvertError or GIOChannelError Returns a GIOStatus

g_io_channel_read_line () GIOStatus g_io_channel_read_line ( GIOChannel *channel , gchar **str_return , gsize *length , gsize *terminator_pos , GError **error ); Reads a line, including the terminating character(s), from a GIOChannel into a newly-allocated string. str_return will contain allocated memory if the return is G_IO_STATUS_NORMAL . Parameters channel a GIOChannel str_return The line read from the GIOChannel, including the line terminator. This data should be freed with g_free() when no longer needed. This is a nul-terminated string. If a length of zero is returned, this will be NULL instead. [ out ] length location to store length of the read data, or NULL . [ out ][ optional ] terminator_pos location to store position of line terminator, or NULL . [ out ][ optional ] error A location to return an error of type GConvertError or GIOChannelError Returns the status of the operation.

g_io_channel_read_line_string () GIOStatus g_io_channel_read_line_string ( GIOChannel *channel , GString *buffer , gsize *terminator_pos , GError **error ); Reads a line from a GIOChannel, using a GString as a buffer. Parameters channel a GIOChannel buffer a GString into which the line will be written. If buffer already contains data, the old data will be overwritten. terminator_pos location to store position of line terminator, or NULL . [ nullable ] error a location to store an error of type GConvertError or GIOChannelError Returns the status of the operation.

g_io_channel_read_to_end () GIOStatus g_io_channel_read_to_end ( GIOChannel *channel , gchar **str_return , gsize *length , GError **error ); Reads all the remaining data from the file. Parameters channel a GIOChannel str_return Location to store a pointer to a string holding the remaining data in the GIOChannel. This data should be freed with g_free() when no longer needed. This data is terminated by an extra nul character, but there may be other nuls in the intervening data. [ out ][ array length=length][ element-type guint8] length location to store length of the data. [ out ] error location to return an error of type GConvertError or GIOChannelError Returns G_IO_STATUS_NORMAL on success. This function never returns G_IO_STATUS_EOF .

g_io_channel_write_chars () GIOStatus g_io_channel_write_chars ( GIOChannel *channel , const gchar *buf , gssize count , gsize *bytes_written , GError **error ); Replacement for g_io_channel_write() with the new API. On seekable channels with encodings other than NULL or UTF-8, generic mixing of reading and writing is not allowed. A call to g_io_channel_write_chars() may only be made on a channel from which data has been read in the cases described in the documentation for g_io_channel_set_encoding() . Parameters channel a GIOChannel buf a buffer to write data from. [ array ][ element-type guint8] count the size of the buffer. If -1, the buffer is taken to be a nul-terminated string. bytes_written The number of bytes written. This can be nonzero even if the return value is not G_IO_STATUS_NORMAL . If the return value is G_IO_STATUS_NORMAL and the channel is blocking, this will always be equal to count if count >= 0. [ out ] error a location to return an error of type GConvertError or GIOChannelError Returns the status of the operation.

g_io_channel_write_unichar () GIOStatus g_io_channel_write_unichar ( GIOChannel *channel , gunichar thechar , GError **error ); Writes a Unicode character to channel . This function cannot be called on a channel with NULL encoding. Parameters channel a GIOChannel thechar a character error location to return an error of type GConvertError or GIOChannelError Returns a GIOStatus

g_io_channel_flush () GIOStatus g_io_channel_flush ( GIOChannel *channel , GError **error ); Flushes the write buffer for the GIOChannel. Parameters channel a GIOChannel error location to store an error of type GIOChannelError Returns the status of the operation: One of G_IO_STATUS_NORMAL, G_IO_STATUS_AGAIN, or G_IO_STATUS_ERROR.

g_io_channel_seek_position () GIOStatus g_io_channel_seek_position ( GIOChannel *channel , gint64 offset , GSeekType type , GError **error ); Replacement for g_io_channel_seek() with the new API. Parameters channel a GIOChannel offset The offset in bytes from the position specified by type type a GSeekType. The type G_SEEK_CUR is only allowed in those cases where a call to g_io_channel_set_encoding() is allowed. See the documentation for g_io_channel_set_encoding() for details. error A location to return an error of type GIOChannelError Returns the status of the operation.

g_io_channel_shutdown () GIOStatus g_io_channel_shutdown ( GIOChannel *channel , gboolean flush , GError **err ); Close an IO channel. Any pending data to be written will be flushed if flush is TRUE . The channel will not be freed until the last reference is dropped using g_io_channel_unref() . Parameters channel a GIOChannel flush if TRUE , flush pending err location to store a GIOChannelError Returns the status of the operation.

g_io_channel_error_from_errno () GIOChannelError g_io_channel_error_from_errno ( gint en ); Converts an errno error number to a GIOChannelError. Parameters en an errno error number, e.g. EINVAL Returns a GIOChannelError error number, e.g. G_IO_CHANNEL_ERROR_INVAL .

g_io_channel_ref () GIOChannel * g_io_channel_ref ( GIOChannel *channel ); Increments the reference count of a GIOChannel. Parameters channel a GIOChannel Returns the channel that was passed in (since 2.6)

g_io_channel_unref () void g_io_channel_unref ( GIOChannel *channel ); Decrements the reference count of a GIOChannel. Parameters channel a GIOChannel

g_io_create_watch () GSource * g_io_create_watch ( GIOChannel *channel , GIOCondition condition ); Creates a GSource that's dispatched when condition is met for the given channel . For example, if condition is G_IO_IN, the source will be dispatched when there's data available for reading. The callback function invoked by the GSource should be added with g_source_set_callback() , but it has type GIOFunc (not GSourceFunc). g_io_add_watch() is a simpler interface to this same functionality, for the case where you want to add the source to the default main loop context at the default priority. On Windows, polling a GSource created to watch a channel for a socket puts the socket in non-blocking mode. This is a side-effect of the implementation and unavoidable. Parameters channel a GIOChannel to watch condition conditions to watch for Returns a new GSource

g_io_add_watch () guint g_io_add_watch ( GIOChannel *channel , GIOCondition condition , GIOFunc func , gpointer user_data ); Adds the GIOChannel into the default main loop context with the default priority. Parameters channel a GIOChannel condition the condition to watch for func the function to call when the condition is satisfied user_data user data to pass to func Returns the event source id

g_io_add_watch_full () guint g_io_add_watch_full ( GIOChannel *channel , gint priority , GIOCondition condition , GIOFunc func , gpointer user_data , GDestroyNotify notify ); Adds the GIOChannel into the default main loop context with the given priority. This internally creates a main loop source using g_io_create_watch() and attaches it to the main loop context with g_source_attach() . You can do these steps manually if you need greater control. [ rename-to g_io_add_watch] Parameters channel a GIOChannel priority the priority of the GIOChannel source condition the condition to watch for func the function to call when the condition is satisfied user_data user data to pass to func notify the function to call when the source is removed Returns the event source id

GIOFunc () gboolean ( *GIOFunc ) ( GIOChannel *source , GIOCondition condition , gpointer data ); Specifies the type of function passed to g_io_add_watch() or g_io_add_watch_full() , which is called when the requested condition on a GIOChannel is satisfied. Parameters source the GIOChannel event source condition the condition which has been satisfied data user data set in g_io_add_watch() or g_io_add_watch_full() Returns the function should return FALSE if the event source should be removed

g_io_channel_get_buffer_size () gsize g_io_channel_get_buffer_size ( GIOChannel *channel ); Gets the buffer size. Parameters channel a GIOChannel Returns the size of the buffer.

g_io_channel_set_buffer_size () void g_io_channel_set_buffer_size ( GIOChannel *channel , gsize size ); Sets the buffer size. Parameters channel a GIOChannel size the size of the buffer, or 0 to let GLib pick a good size

g_io_channel_get_buffer_condition () GIOCondition g_io_channel_get_buffer_condition ( GIOChannel *channel ); This function returns a GIOCondition depending on whether there is data to be read/space to write data in the internal buffers in the GIOChannel. Only the flags G_IO_IN and G_IO_OUT may be set. Parameters channel A GIOChannel Returns A GIOCondition

g_io_channel_get_flags () GIOFlags g_io_channel_get_flags ( GIOChannel *channel ); Gets the current flags for a GIOChannel, including read-only flags such as G_IO_FLAG_IS_READABLE . The values of the flags G_IO_FLAG_IS_READABLE and G_IO_FLAG_IS_WRITABLE are cached for internal use by the channel when it is created. If they should change at some later point (e.g. partial shutdown of a socket with the UNIX shutdown() function), the user should immediately call g_io_channel_get_flags() to update the internal values of these flags. Parameters channel a GIOChannel Returns the flags which are set on the channel

g_io_channel_set_flags () GIOStatus g_io_channel_set_flags ( GIOChannel *channel , GIOFlags flags , GError **error ); Sets the (writeable) flags in channel to ( flags & G_IO_FLAG_SET_MASK ). Parameters channel a GIOChannel flags the flags to set on the IO channel error A location to return an error of type GIOChannelError Returns the status of the operation.

g_io_channel_get_line_term () const gchar * g_io_channel_get_line_term ( GIOChannel *channel , gint *length ); This returns the string that GIOChannel uses to determine where in the file a line break occurs. A value of NULL indicates autodetection. Parameters channel a GIOChannel length a location to return the length of the line terminator Returns The line termination string. This value is owned by GLib and must not be freed.

g_io_channel_set_line_term () void g_io_channel_set_line_term ( GIOChannel *channel , const gchar *line_term , gint length ); This sets the string that GIOChannel uses to determine where in the file a line break occurs. Parameters channel a GIOChannel line_term The line termination string. Use NULL for autodetect. Autodetection breaks on "

", "\r

", "\r", "\0", and the Unicode paragraph separator. Autodetection should not be used for anything other than file-based channels. [ nullable ] length The length of the termination string. If -1 is passed, the string is assumed to be nul-terminated. This option allows termination strings with embedded nuls.

g_io_channel_get_buffered () gboolean g_io_channel_get_buffered ( GIOChannel *channel ); Returns whether channel is buffered. Parameters channel a GIOChannel Returns TRUE if the channel is buffered.

g_io_channel_set_buffered () void g_io_channel_set_buffered ( GIOChannel *channel , gboolean buffered ); The buffering state can only be set if the channel's encoding is NULL . For any other encoding, the channel must be buffered. A buffered channel can only be set unbuffered if the channel's internal buffers have been flushed. Newly created channels or channels which have returned G_IO_STATUS_EOF not require such a flush. For write-only channels, a call to g_io_channel_flush() is sufficient. For all other channels, the buffers may be flushed by a call to g_io_channel_seek_position() . This includes the possibility of seeking with seek type G_SEEK_CUR and an offset of zero. Note that this means that socket-based channels cannot be set unbuffered once they have had data read from them. On unbuffered channels, it is safe to mix read and write calls from the new and old APIs, if this is necessary for maintaining old code. The default state of the channel is buffered. Parameters channel a GIOChannel buffered whether to set the channel buffered or unbuffered

g_io_channel_get_encoding () const gchar * g_io_channel_get_encoding ( GIOChannel *channel ); Gets the encoding for the input/output of the channel. The internal encoding is always UTF-8. The encoding NULL makes the channel safe for binary data. Parameters channel a GIOChannel Returns A string containing the encoding, this string is owned by GLib and must not be freed.

g_io_channel_set_encoding () GIOStatus g_io_channel_set_encoding ( GIOChannel *channel , const gchar *encoding , GError **error ); Sets the encoding for the input/output of the channel. The internal encoding is always UTF-8. The default encoding for the external file is UTF-8. The encoding NULL is safe to use with binary data. The encoding can only be set if one of the following conditions is true: The channel was just created, and has not been written to or read from yet.

The channel is write-only.

The channel is a file, and the file pointer was just repositioned by a call to g_io_channel_seek_position() . (This flushes all the internal buffers.)

The current encoding is NULL or UTF-8.

One of the (new API) read functions has just returned G_IO_STATUS_EOF (or, in the case of g_io_channel_read_to_end() , G_IO_STATUS_NORMAL ).

One of the functions g_io_channel_read_chars() or g_io_channel_read_unichar() has returned G_IO_STATUS_AGAIN or G_IO_STATUS_ERROR . This may be useful in the case of G_CONVERT_ERROR_ILLEGAL_SEQUENCE . Returning one of these statuses from g_io_channel_read_line() , g_io_channel_read_line_string() , or g_io_channel_read_to_end() does not guarantee that the encoding can be changed. Channels which do not meet one of the above conditions cannot call g_io_channel_seek_position() with an offset of G_SEEK_CUR , and, if they are "seekable", cannot call g_io_channel_write_chars() after calling one of the API "read" functions. Parameters channel a GIOChannel encoding the encoding type. [ nullable ] error location to store an error of type GConvertError Returns G_IO_STATUS_NORMAL if the encoding was successfully set

g_io_channel_get_close_on_unref () gboolean g_io_channel_get_close_on_unref ( GIOChannel *channel ); Returns whether the file/socket/whatever associated with channel will be closed when channel receives its final unref and is destroyed. The default value of this is TRUE for channels created by g_io_channel_new_file() , and FALSE for all other channels. Parameters channel a GIOChannel. Returns TRUE if the channel will be closed, FALSE otherwise.

g_io_channel_set_close_on_unref () void g_io_channel_set_close_on_unref ( GIOChannel *channel , gboolean do_close ); Whether to close the channel on the final unref of the GIOChannel data structure. The default value of this is TRUE for channels created by g_io_channel_new_file() , and FALSE for all other channels. Setting this flag to TRUE for a channel you have already closed can cause problems when the final reference to the GIOChannel is dropped. Parameters channel a GIOChannel do_close Whether to close the channel on the final unref of the GIOChannel data structure.

g_io_channel_read () GIOError g_io_channel_read ( GIOChannel *channel , gchar *buf , gsize count , gsize *bytes_read ); g_io_channel_read has been deprecated since version 2.2 and should not be used in newly-written code. Use g_io_channel_read_chars() instead. Reads data from a GIOChannel. Parameters channel a GIOChannel buf a buffer to read the data into (which should be at least count bytes long) count the number of bytes to read from the GIOChannel bytes_read returns the number of bytes actually read Returns G_IO_ERROR_NONE if the operation was successful.

g_io_channel_write () GIOError g_io_channel_write ( GIOChannel *channel , const gchar *buf , gsize count , gsize *bytes_written ); g_io_channel_write has been deprecated since version 2.2 and should not be used in newly-written code. Use g_io_channel_write_chars() instead. Writes data to a GIOChannel. Parameters channel a GIOChannel buf the buffer containing the data to write count the number of bytes to write bytes_written the number of bytes actually written Returns G_IO_ERROR_NONE if the operation was successful.

g_io_channel_seek () GIOError g_io_channel_seek ( GIOChannel *channel , gint64 offset , GSeekType type ); g_io_channel_seek has been deprecated since version 2.2 and should not be used in newly-written code. Use g_io_channel_seek_position() instead. Sets the current position in the GIOChannel, similar to the standard library function fseek() . Parameters channel a GIOChannel offset an offset, in bytes, which is added to the position specified by type type the position in the file, which can be G_SEEK_CUR (the current position), G_SEEK_SET (the start of the file), or G_SEEK_END (the end of the file) Returns G_IO_ERROR_NONE if the operation was successful.