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9a0b40af73
If it improves consistency across builds and sources, prefer 'greater' or newer/later/+, prefer no 'v'/'version` prefix. Closes #1866
89 lines
3.0 KiB
Markdown
89 lines
3.0 KiB
Markdown
---
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c: Copyright (C) The libssh2 project and its contributors.
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SPDX-License-Identifier: BSD-3-Clause
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Title: libssh2_sftp_write
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Section: 3
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Source: libssh2
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See-also:
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- libssh2_sftp_open_ex(3)
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---
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# NAME
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libssh2_sftp_write - write SFTP data
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# SYNOPSIS
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~~~c
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#include <libssh2.h>
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#include <libssh2_sftp.h>
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ssize_t 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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~~~
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# DESCRIPTION
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**libssh2_sftp_write(3)** 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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*handle* - SFTP file handle as returned by *libssh2_sftp_open_ex(3)*.
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*buffer* - points to the data to send off.
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*count* - 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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*libssh2_sftp_handle(3)* uses 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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# WRITE AHEAD
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Starting in libssh2 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 returns a positive number as soon as the first packet is acknowledged
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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 immediately figures 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 is 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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# 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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# ERRORS
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*LIBSSH2_ERROR_ALLOC* - An internal memory allocation call failed.
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*LIBSSH2_ERROR_SOCKET_SEND* - Unable to send data on socket.
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*LIBSSH2_ERROR_SOCKET_TIMEOUT* -
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*LIBSSH2_ERROR_SFTP_PROTOCOL* - 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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