---
c: Copyright (C) The libssh2 project and its contributors.
SPDX-License-Identifier: BSD-3-Clause
Title: libssh2_channel_write_ex
Section: 3
Source: libssh2
See-also:
  - libssh2_channel_open_ex(3)
  - libssh2_channel_read_ex(3)
---

# NAME

libssh2_channel_write_ex - write data to a channel stream blocking

# SYNOPSIS

~~~c
#include <libssh2.h>

ssize_t
libssh2_channel_write_ex(LIBSSH2_CHANNEL *channel,
                         int stream_id, char *buf,
                         size_t buflen);
~~~

# DESCRIPTION

Write data to a channel stream. All channel streams have one standard I/O
substream (stream_id == 0), and may have up to 2^32 extended data streams as
identified by the selected *stream_id*. The SSH2 protocol currently
defines a stream ID of 1 to be the stderr substream.

*channel* - active channel stream to write to.

*stream_id* - substream ID number (e.g. 0 or SSH_EXTENDED_DATA_STDERR)

*buf* - pointer to buffer to write

*buflen* - size of the data to write

*libssh2_channel_write(3)* and *libssh2_channel_write_stderr(3)* are
convenience macros for this function.

*libssh2_channel_write_ex(3)* will use as much as possible of the buffer
and put it into a single SSH protocol packet. This means that to get maximum
performance when sending larger files, you should try to always pass in at
least 32K of data to this function.

# RETURN VALUE

Actual number of bytes written or negative on failure.
LIBSSH2_ERROR_EAGAIN when it would otherwise block. While
LIBSSH2_ERROR_EAGAIN is a negative number, it is not really a failure per se.

# ERRORS

*LIBSSH2_ERROR_ALLOC* - An internal memory allocation call failed.

*LIBSSH2_ERROR_SOCKET_SEND* - Unable to send data on socket.

*LIBSSH2_ERROR_CHANNEL_CLOSED* - The channel has been closed.

*LIBSSH2_ERROR_CHANNEL_EOF_SENT* - The channel has been requested to be

*LIBSSH2_ERROR_BAD_USE* - This can be returned if you ignored a previous
return for LIBSSH2_ERROR_EAGAIN and rather than sending the original buffer with
the original size, you sent a new buffer with a different size.

closed.