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1 | =pod |
2 | ||
3 | =head1 NAME | |
4 | ||
5a2443ae MC |
5 | SSL_read_ex, SSL_read, SSL_peek_ex, SSL_peek |
6 | - read bytes from a TLS/SSL connection | |
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7 | |
8 | =head1 SYNOPSIS | |
9 | ||
10 | #include <openssl/ssl.h> | |
11 | ||
beacb0f0 | 12 | int SSL_read_ex(SSL *ssl, void *buf, size_t num, size_t *readbytes); |
e34cfcf7 | 13 | int SSL_read(SSL *ssl, void *buf, int num); |
cc99526d | 14 | |
beacb0f0 | 15 | int SSL_peek_ex(SSL *ssl, void *buf, size_t num, size_t *readbytes); |
7714dc5e MC |
16 | int SSL_peek(SSL *ssl, void *buf, int num); |
17 | ||
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18 | =head1 DESCRIPTION |
19 | ||
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20 | SSL_read_ex() and SSL_read() try to read B<num> bytes from the specified B<ssl> |
21 | into the buffer B<buf>. On success SSL_read_ex() will store the number of bytes | |
beacb0f0 | 22 | actually read in B<*readbytes>. |
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23 | |
24 | SSL_peek_ex() and SSL_peek() are identical to SSL_read_ex() and SSL_read() | |
25 | respectively except no bytes are actually removed from the underlying BIO during | |
26 | the read, so that a subsequent call to SSL_read_ex() or SSL_read() will yield | |
6782e5fd | 27 | at least the same bytes. |
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28 | |
29 | =head1 NOTES | |
30 | ||
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31 | In the paragraphs below a "read function" is defined as one of SSL_read_ex(), |
32 | SSL_read(), SSL_peek_ex() or SSL_peek(). | |
7714dc5e | 33 | |
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34 | If necessary, a read function will negotiate a TLS/SSL session, if not already |
35 | explicitly performed by L<SSL_connect(3)> or L<SSL_accept(3)>. If the | |
cc99526d | 36 | peer requests a re-negotiation, it will be performed transparently during |
6782e5fd MC |
37 | the read function operation. The behaviour of the read functions depends on the |
38 | underlying BIO. | |
cc99526d | 39 | |
b72ff470 | 40 | For the transparent negotiation to succeed, the B<ssl> must have been |
7abe76e1 | 41 | initialized to client or server mode. This is being done by calling |
6782e5fd MC |
42 | L<SSL_set_connect_state(3)> or SSL_set_accept_state() before the first |
43 | invocation of a read function. | |
44 | ||
45 | The read functions work based on the SSL/TLS records. The data are received in | |
46 | records (with a maximum record size of 16kB). Only when a record has been | |
47 | completely received, can it be processed (decryption and check of integrity). | |
48 | Therefore data that was not retrieved at the last read call can still be | |
49 | buffered inside the SSL layer and will be retrieved on the next read | |
50 | call. If B<num> is higher than the number of bytes buffered then the read | |
51 | functions will return with the bytes buffered. If no more bytes are in the | |
52 | buffer, the read functions will trigger the processing of the next record. | |
53 | Only when the record has been received and processed completely will the read | |
57fd5170 | 54 | functions return reporting success. At most the contents of one record will |
6782e5fd MC |
55 | be returned. As the size of an SSL/TLS record may exceed the maximum packet size |
56 | of the underlying transport (e.g. TCP), it may be necessary to read several | |
57 | packets from the transport layer before the record is complete and the read call | |
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58 | can succeed. |
59 | ||
57fd5170 KR |
60 | If B<SSL_MODE_AUTO_RETRY> has been switched off and a non-application data |
61 | record has been processed, the read function can return and set the error to | |
62 | B<SSL_ERROR_WANT_READ>. | |
63 | In this case there might still be unprocessed data available in the B<BIO>. | |
64 | If read ahead was set using L<SSL_CTX_set_read_ahead(3)>, there might also still | |
65 | be unprocessed data available in the B<SSL>. | |
66 | This behaviour can be controlled using the L<SSL_CTX_set_mode(3)> call. | |
67 | ||
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68 | If the underlying BIO is B<blocking>, a read function will only return once the |
69 | read operation has been finished or an error occurred, except when a | |
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70 | non-application data record has been processed and B<SSL_MODE_AUTO_RETRY> is |
71 | not set. | |
72 | Note that if B<SSL_MODE_AUTO_RETRY> is set and only non-application data is | |
73 | available the call will hang. | |
cc99526d | 74 | |
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75 | If the underlying BIO is B<non-blocking>, a read function will also return when |
76 | the underlying BIO could not satisfy the needs of the function to continue the | |
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77 | operation. |
78 | In this case a call to L<SSL_get_error(3)> with the | |
6782e5fd | 79 | return value of the read function will yield B<SSL_ERROR_WANT_READ> or |
57fd5170 KR |
80 | B<SSL_ERROR_WANT_WRITE>. |
81 | As at any time it's possible that non-application data needs to be sent, | |
82 | a read function can also cause write operations. | |
83 | The calling process then must repeat the call after taking appropriate action | |
84 | to satisfy the needs of the read function. | |
85 | The action depends on the underlying BIO. | |
86 | When using a non-blocking socket, nothing is to be done, but select() can be | |
87 | used to check for the required condition. | |
88 | When using a buffering BIO, like a BIO pair, data must be written into or | |
89 | retrieved out of the BIO before being able to continue. | |
cc99526d | 90 | |
9b86974e | 91 | L<SSL_pending(3)> can be used to find out whether there |
57fd5170 KR |
92 | are buffered bytes available for immediate retrieval. |
93 | In this case the read function can be called without blocking or actually | |
94 | receiving new data from the underlying socket. | |
c19b6c92 | 95 | |
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96 | =head1 RETURN VALUES |
97 | ||
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98 | SSL_read_ex() and SSL_peek_ex() will return 1 for success or 0 for failure. |
99 | Success means that 1 or more application data bytes have been read from the SSL | |
beacb0f0 KR |
100 | connection. |
101 | Failure means that no bytes could be read from the SSL connection. | |
740bfeba | 102 | Failures can be retryable (e.g. we are waiting for more bytes to |
beacb0f0 KR |
103 | be delivered by the network) or non-retryable (e.g. a fatal network error). |
104 | In the event of a failure call L<SSL_get_error(3)> to find out the reason which | |
ed9fa2c7 | 105 | indicates whether the call is retryable or not. |
7714dc5e | 106 | |
3cdc2f8f | 107 | For SSL_read() and SSL_peek() the following return values can occur: |
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108 | |
109 | =over 4 | |
110 | ||
beacb0f0 | 111 | =item E<gt> 0 |
cc99526d | 112 | |
beacb0f0 KR |
113 | The read operation was successful. |
114 | The return value is the number of bytes actually read from the TLS/SSL | |
115 | connection. | |
cc99526d | 116 | |
beacb0f0 | 117 | =item Z<><= 0 |
cc99526d | 118 | |
beacb0f0 KR |
119 | The read operation was not successful, because either the connection was closed, |
120 | an error occurred or action must be taken by the calling process. | |
121 | Call L<SSL_get_error(3)> with the return value B<ret> to find out the reason. | |
d93eb21c | 122 | |
beacb0f0 KR |
123 | Old documentation indicated a difference between 0 and -1, and that -1 was |
124 | retryable. | |
125 | You should instead call SSL_get_error() to find out if it's retryable. | |
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126 | |
127 | =back | |
128 | ||
129 | =head1 SEE ALSO | |
130 | ||
7714dc5e | 131 | L<SSL_get_error(3)>, L<SSL_write_ex(3)>, |
9b86974e RS |
132 | L<SSL_CTX_set_mode(3)>, L<SSL_CTX_new(3)>, |
133 | L<SSL_connect(3)>, L<SSL_accept(3)> | |
134 | L<SSL_set_connect_state(3)>, | |
135 | L<SSL_pending(3)>, | |
136 | L<SSL_shutdown(3)>, L<SSL_set_shutdown(3)>, | |
b97fdb57 | 137 | L<ssl(7)>, L<bio(7)> |
cc99526d | 138 | |
b5c4bbbe JL |
139 | =head1 HISTORY |
140 | ||
141 | The SSL_read_ex() and SSL_peek_ex() functions were added in OpenSSL 1.1.1. | |
142 | ||
e2f92610 RS |
143 | =head1 COPYRIGHT |
144 | ||
b5c4bbbe | 145 | Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved. |
e2f92610 | 146 | |
4746f25a | 147 | Licensed under the Apache License 2.0 (the "License"). You may not use |
e2f92610 RS |
148 | this file except in compliance with the License. You can obtain a copy |
149 | in the file LICENSE in the source distribution or at | |
150 | L<https://www.openssl.org/source/license.html>. | |
151 | ||
152 | =cut |