1SSL_WRITE(3ossl) OpenSSL SSL_WRITE(3ossl)
2
6 SSL_write_ex, SSL_write, SSL_sendfile - write bytes to a TLS/SSL
7 connection
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10 #include <openssl/ssl.h>
11 ossl_ssize_t SSL_sendfile(SSL *s, int fd, off_t offset, size_t size, int flags);
13 int SSL_write_ex(SSL *s, const void *buf, size_t num, size_t *written);
14 int SSL_write(SSL *ssl, const void *buf, int num);
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17 SSL_write_ex() and SSL_write() write num bytes from the buffer buf into
18 the specified ssl connection. On success SSL_write_ex() will store the
19 number of bytes written in *written.
20 SSL_sendfile() writes size bytes from offset offset in the file
22 descriptor fd to the specified SSL connection s. This function provides
23 efficient zero-copy semantics. SSL_sendfile() is available only when
24 Kernel TLS is enabled, which can be checked by calling
25 BIO_get_ktls_send(). It is provided here to allow users to maintain
26 the same interface. The meaning of flags is platform dependent.
27 Currently, under Linux it is ignored.
28
30 In the paragraphs below a "write function" is defined as one of either
31 SSL_write_ex(), or SSL_write().
32 If necessary, a write function will negotiate a TLS/SSL session, if not
34 already explicitly performed by SSL_connect(3) or SSL_accept(3). If the
35 peer requests a re-negotiation, it will be performed transparently
36 during the write function operation. The behaviour of the write
37 functions depends on the underlying BIO.
38 For the transparent negotiation to succeed, the ssl must have been
40 initialized to client or server mode. This is being done by calling
41 SSL_set_connect_state(3) or SSL_set_accept_state() before the first
42 call to a write function.
43 If the underlying BIO is blocking, the write functions will only
45 return, once the write operation has been finished or an error
46 occurred.
47 If the underlying BIO is nonblocking the write functions will also
49 return when the underlying BIO could not satisfy the needs of the
50 function to continue the operation. In this case a call to
51 SSL_get_error(3) with the return value of the write function will yield
52 SSL_ERROR_WANT_READ or SSL_ERROR_WANT_WRITE. As at any time a re-
53 negotiation is possible, a call to a write function can also cause read
54 operations! The calling process then must repeat the call after taking
55 appropriate action to satisfy the needs of the write function. The
56 action depends on the underlying BIO. When using a nonblocking socket,
57 nothing is to be done, but select() can be used to check for the
58 required condition. When using a buffering BIO, like a BIO pair, data
59 must be written into or retrieved out of the BIO before being able to
60 continue.
61 The write functions will only return with success when the complete
63 contents of buf of length num has been written. This default behaviour
64 can be changed with the SSL_MODE_ENABLE_PARTIAL_WRITE option of
65 SSL_CTX_set_mode(3). When this flag is set the write functions will
66 also return with success when a partial write has been successfully
67 completed. In this case the write function operation is considered
68 completed. The bytes are sent and a new write call with a new buffer
69 (with the already sent bytes removed) must be started. A partial write
70 is performed with the size of a message block, which is 16kB.
71
73 When a write function call has to be repeated because SSL_get_error(3)
74 returned SSL_ERROR_WANT_READ or SSL_ERROR_WANT_WRITE, it must be
75 repeated with the same arguments. The data that was passed might have
76 been partially processed. When SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER was
77 set using SSL_CTX_set_mode(3) the pointer can be different, but the
78 data and length should still be the same.
79 You should not call SSL_write() with num=0, it will return an error.
81 SSL_write_ex() can be called with num=0, but will not send application
82 data to the peer.
83
85 SSL_write_ex() will return 1 for success or 0 for failure. Success
86 means that all requested application data bytes have been written to
87 the SSL connection or, if SSL_MODE_ENABLE_PARTIAL_WRITE is in use, at
88 least 1 application data byte has been written to the SSL connection.
89 Failure means that not all the requested bytes have been written yet
90 (if SSL_MODE_ENABLE_PARTIAL_WRITE is not in use) or no bytes could be
91 written to the SSL connection (if SSL_MODE_ENABLE_PARTIAL_WRITE is in
92 use). Failures can be retryable (e.g. the network write buffer has
93 temporarily filled up) or non-retryable (e.g. a fatal network error).
94 In the event of a failure call SSL_get_error(3) to find out the reason
95 which indicates whether the call is retryable or not.
96 For SSL_write() the following return values can occur:
98 > 0 The write operation was successful, the return value is the number
100 of bytes actually written to the TLS/SSL connection.
101 <= 0
103 The write operation was not successful, because either the
104 connection was closed, an error occurred or action must be taken by
105 the calling process. Call SSL_get_error() with the return value
106 ret to find out the reason.
107 Old documentation indicated a difference between 0 and -1, and that
109 -1 was retryable. You should instead call SSL_get_error() to find
110 out if it's retryable.
111 For SSL_sendfile(), the following return values can occur:
113 >= 0
115 The write operation was successful, the return value is the number
116 of bytes of the file written to the TLS/SSL connection. The return
117 value can be less than size for a partial write.
118 < 0 The write operation was not successful, because either the
120 connection was closed, an error occurred or action must be taken by
121 the calling process. Call SSL_get_error() with the return value to
122 find out the reason.
123
125 SSL_get_error(3), SSL_read_ex(3), SSL_read(3) SSL_CTX_set_mode(3),
126 SSL_CTX_new(3), SSL_connect(3), SSL_accept(3) SSL_set_connect_state(3),
127 BIO_ctrl(3), ssl(7), bio(7)
128
130 The SSL_write_ex() function was added in OpenSSL 1.1.1. The
131 SSL_sendfile() function was added in OpenSSL 3.0.
132
134 Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
135 Licensed under the Apache License 2.0 (the "License"). You may not use
137 this file except in compliance with the License. You can obtain a copy
138 in the file LICENSE in the source distribution or at
139 <https://www.openssl.org/source/license.html>.
1403.0.5 2022-07-05 SSL_WRITE(3ossl)