NAME
SYNOPSIS
DESCRIPTION
NOTES
WARNINGS
RETURN VALUES
SEE ALSO
HISTORY
COPYRIGHT

NAME

SSL_write_ex, SSL_write, SSL_sendfile - write bytes to a TLS/SSL connection

SYNOPSIS

 #include <openssl/ssl.h>
 
 ossl_ssize_t SSL_sendfile(SSL *s, int fd, off_t offset, size_t size, int flags);
 int SSL_write_ex(SSL *s, const void *buf, size_t num, size_t *written);
 int SSL_write(SSL *ssl, const void *buf, int num);

DESCRIPTION

SSL_write_ex() and SSL_write() write num bytes from the buffer buf into the specified ssl connection. On success SSL_write_ex() will store the number of bytes written in *written.

SSL_sendfile() writes size bytes from offset offset in the file descriptor fd to the specified SSL connection s. This function provides efficient zero-copy semantics. SSL_sendfile() is available only when Kernel TLS is enabled, which can be checked by calling BIO_get_ktls_send(). It is provided here to allow users to maintain the same interface. The meaning of flags is platform dependent. Currently, under Linux it is ignored.

NOTES

In the paragraphs below a "write function" is defined as one of either SSL_write_ex(), or SSL_write().

If necessary, a write function will negotiate a TLS/SSL session, if not already explicitly performed by SSL_accept(3). If the peer requests a re-negotiation, it will be performed transparently during the write function operation. The behaviour of the write functions depends on the underlying BIO.

For the transparent negotiation to succeed, the ssl must have been initialized to client or server mode. This is being done by calling SSL_get_error(3) with the return value of the write function will yield SSL_ERROR_WANT_READ or SSL_ERROR_WANT_WRITE. As at any time a re-negotiation is possible, a call to a write function can also cause read operations! The calling process then must repeat the call after taking appropriate action to satisfy the needs of the write function. The action depends on the underlying BIO. When using a non-blocking socket, nothing is to be done, but select() can be used to check for the required condition. When using a buffering BIO, like a BIO pair, data must be written into or retrieved out of the BIO before being able to continue.

The write functions will only return with success when the complete contents of buf of length num has been written. This default behaviour can be changed with the SSL_MODE_ENABLE_PARTIAL_WRITE option of WARNINGS

When a write function call has to be repeated because SSL_CTX_set_mode(3) the pointer can be different, but the data and length should still be the same.

You should not call SSL_write() with num=0, it will return an error. SSL_write_ex() can be called with num=0, but will not send application data to the peer.

RETURN VALUES

SSL_write_ex() will return 1 for success or 0 for failure. Success means that all requested application data bytes have been written to the SSL connection or, if SSL_MODE_ENABLE_PARTIAL_WRITE is in use, at least 1 application data byte has been written to the SSL connection. Failure means that not all the requested bytes have been written yet (if SSL_MODE_ENABLE_PARTIAL_WRITE is not in use) or no bytes could be written to the SSL connection (if SSL_MODE_ENABLE_PARTIAL_WRITE is in use). Failures can be retryable (e.g. the network write buffer has temporarily filled up) or non-retryable (e.g. a fatal network error). In the event of a failure call > 0

The write operation was successful, the return value is the number of bytes actually written to the TLS/SSL connection.

<= 0

The write operation was not successful, because either the connection was closed, an error occurred or action must be taken by the calling process. Call SSL_get_error() with the return value ret to find out the reason.

Old documentation indicated a difference between 0 and -1, and that -1 was retryable. You should instead call SSL_get_error() to find out if it's retryable.

For SSL_sendfile(), the following return values can occur:

>= 0: The write operation was successful, the return value is the number of bytes of the file written to the TLS/SSL connection.
< 0: The write operation was not successful, because either the connection was closed, an error occurred or action must be taken by the calling process. Call SSL_get_error() with the return value to find out the reason.

COPYRIGHT

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at https://www.openssl.org/source/license.html.

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