libssh2

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.\" Copyright (C) The libssh2 project and its contributors.
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.\" SPDX-License-Identifier: BSD-3-Clause
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.TH libssh2_sftp_write 3 "1 Jun 2007" "libssh2 0.15" "libssh2"
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.SH NAME
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libssh2_sftp_write - write SFTP data
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.SH SYNOPSIS
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.nf
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#include <libssh2.h>
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#include <libssh2_sftp.h>
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ssize_t
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libssh2_sftp_write(LIBSSH2_SFTP_HANDLE *handle,
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                   const char *buffer,
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                   size_t count);
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.fi
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.SH DESCRIPTION
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\fBlibssh2_sftp_write(3)\fP writes a block of data to the SFTP server. This
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method is modeled after the POSIX write() function and uses the same calling
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semantics.
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\fIhandle\fP - SFTP file handle as returned by \fIlibssh2_sftp_open_ex(3)\fP.
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\fIbuffer\fP - points to the data to send off.
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\fIcount\fP - Number of bytes from 'buffer' to write. Note that it may not be
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possible to write all bytes as requested.
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\fIlibssh2_sftp_handle(3)\fP will use as much as possible of the buffer and
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put it into a single SFTP protocol packet. This means that to get maximum
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performance when sending larger files, you should try to always pass in at
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least 32K of data to this function.
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.SH WRITE AHEAD
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Starting in libssh2 version 1.2.8, the default behavior of libssh2 is to
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create several smaller outgoing packets for all data you pass to this function
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and it will return a positive number as soon as the first packet is
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acknowledged from the server.
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This has the effect that sometimes more data has been sent off but is not acked
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yet when this function returns, and when this function is subsequently called
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again to write more data, libssh2 will immediately figure out that the data is
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already received remotely.
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In most normal situation this should not cause any problems, but it should be
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noted that if you have once called libssh2_sftp_write() with data and it returns
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short, you MUST still assume that the rest of the data might have been cached so
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you need to make sure you do not alter that data and think that the version you
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have in your next function invoke will be detected or used.
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The reason for this funny behavior is that SFTP can only send 32K data in each
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packet and it gets all packets acked individually. This means we cannot use a
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simple serial approach if we want to reach high performance even on high
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latency connections. And we want that.
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.SH RETURN VALUE
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Actual number of bytes written or negative on failure.
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If used in non-blocking mode, it returns LIBSSH2_ERROR_EAGAIN when it would
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otherwise block. While LIBSSH2_ERROR_EAGAIN is a negative number, it is not
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really a failure per se.
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If this function returns 0 (zero) it should not be considered an error, but
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that there was no error but yet no payload data got sent to the other end.
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.SH ERRORS
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\fILIBSSH2_ERROR_ALLOC\fP - An internal memory allocation call failed.
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\fILIBSSH2_ERROR_SOCKET_SEND\fP - Unable to send data on socket.
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\fILIBSSH2_ERROR_SOCKET_TIMEOUT\fP -
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\fILIBSSH2_ERROR_SFTP_PROTOCOL\fP - An invalid SFTP protocol response was
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received on the socket, or an SFTP operation caused an errorcode to
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be returned by the server.
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.SH SEE ALSO
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.BR libssh2_sftp_open_ex(3)
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