1 .\" $OpenBSD: BIO_read.3,v 1.5 2016/12/06 14:45:08 schwarze Exp $
2 .\" OpenSSL 99d63d46 Oct 26 13:56:48 2016 -0400
4 .\" This file was written by Dr. Stephen Henson <steve@openssl.org>.
5 .\" Copyright (c) 2000, 2016 The OpenSSL Project. All rights reserved.
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21 .\" "This product includes software developed by the OpenSSL Project
22 .\" for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
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51 .Dd $Mdocdate: December 6 2016 $
91 and places the data in
95 performs the BIOs "gets" operation and places the data in
97 Usually this operation will attempt to read a line of data
98 from the BIO of maximum length
100 There are exceptions to this however, for example
102 on a digest BIO will calculate and return the digest
103 and other BIOs may not support
106 The returned string is always NUL-terminated.
117 attempts to write a null terminated string
122 One technique sometimes used with blocking sockets
123 is to use a system call (such as
126 or equivalent) to determine when data is available and then call
129 The equivalent with BIOs (that is call
131 on the underlying I/O structure and then call
133 to read the data) should
135 be used because a single call to
137 can cause several reads (and writes in the case of SSL BIOs)
138 on the underlying I/O structure and may block as a result.
141 (or equivalent) should be combined with non-blocking I/O
142 so successive reads will request a retry instead of blocking.
145 .Xr BIO_should_retry 3
146 for details of how to determine the cause of a retry and other I/O issues.
150 function is not supported by a BIO then it is possible to
151 work around this by adding a buffering BIO
155 All these functions return either the amount of data successfully
156 read or written (if the return value is positive) or that no data
157 was successfully read or written if the result is 0 or -1.
158 If the return value is -2, then the operation is not implemented
159 in the specific BIO type.
160 The trailing NUL is not included in the length returned by
163 A 0 or -1 return is not necessarily an indication of an error.
164 In particular when the source/sink is non-blocking or of a certain type
165 it may merely be an indication that no data is currently available and that
166 the application should retry the operation later.
169 .Xr BIO_should_retry 3