Update build for OpenSSL-0.9.8j upgrade.
[dragonfly.git] / secure / lib / libssl / man / SSL_read.3
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132.\" ========================================================================
133.\"
134.IX Title "SSL_read 3"
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135.TH SSL_read 3 "2009-01-11" "0.9.8j" "OpenSSL"
136.\" For nroff, turn off justification. Always turn off hyphenation; it makes
137.\" way too many mistakes in technical documents.
138.if n .ad l
139.nh
984263bc 140.SH "NAME"
a7d27d5a 141SSL_read \- read bytes from a TLS/SSL connection.
984263bc 142.SH "SYNOPSIS"
e056f0e0 143.IX Header "SYNOPSIS"
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144.Vb 1
145\& #include <openssl/ssl.h>
e257b235 146\&
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147\& int SSL_read(SSL *ssl, void *buf, int num);
148.Ve
149.SH "DESCRIPTION"
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150.IX Header "DESCRIPTION"
151\&\fISSL_read()\fR tries to read \fBnum\fR bytes from the specified \fBssl\fR into the
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152buffer \fBbuf\fR.
153.SH "NOTES"
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154.IX Header "NOTES"
155If necessary, \fISSL_read()\fR will negotiate a \s-1TLS/SSL\s0 session, if
156not already explicitly performed by \fISSL_connect\fR\|(3) or
157\&\fISSL_accept\fR\|(3). If the
e257b235 158peer requests a re-negotiation, it will be performed transparently during
984263bc 159the \fISSL_read()\fR operation. The behaviour of \fISSL_read()\fR depends on the
e257b235 160underlying \s-1BIO\s0.
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161.PP
162For the transparent negotiation to succeed, the \fBssl\fR must have been
163initialized to client or server mode. This is being done by calling
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164\&\fISSL_set_connect_state\fR\|(3) or \fISSL_set_accept_state()\fR
165before the first call to an \fISSL_read()\fR or \fISSL_write\fR\|(3)
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166function.
167.PP
e056f0e0 168\&\fISSL_read()\fR works based on the \s-1SSL/TLS\s0 records. The data are received in
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169records (with a maximum record size of 16kB for SSLv3/TLSv1). Only when a
170record has been completely received, it can be processed (decryption and
171check of integrity). Therefore data that was not retrieved at the last
e056f0e0 172call of \fISSL_read()\fR can still be buffered inside the \s-1SSL\s0 layer and will be
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173retrieved on the next call to \fISSL_read()\fR. If \fBnum\fR is higher than the
174number of bytes buffered, \fISSL_read()\fR will return with the bytes buffered.
175If no more bytes are in the buffer, \fISSL_read()\fR will trigger the processing
176of the next record. Only when the record has been received and processed
177completely, \fISSL_read()\fR will return reporting success. At most the contents
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178of the record will be returned. As the size of an \s-1SSL/TLS\s0 record may exceed
179the maximum packet size of the underlying transport (e.g. \s-1TCP\s0), it may
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180be necessary to read several packets from the transport layer before the
181record is complete and \fISSL_read()\fR can succeed.
182.PP
e056f0e0 183If the underlying \s-1BIO\s0 is \fBblocking\fR, \fISSL_read()\fR will only return, once the
984263bc 184read operation has been finished or an error occurred, except when a
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185renegotiation take place, in which case a \s-1SSL_ERROR_WANT_READ\s0 may occur.
186This behaviour can be controlled with the \s-1SSL_MODE_AUTO_RETRY\s0 flag of the
187\&\fISSL_CTX_set_mode\fR\|(3) call.
984263bc 188.PP
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189If the underlying \s-1BIO\s0 is \fBnon-blocking\fR, \fISSL_read()\fR will also return
190when the underlying \s-1BIO\s0 could not satisfy the needs of \fISSL_read()\fR
984263bc 191to continue the operation. In this case a call to
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192\&\fISSL_get_error\fR\|(3) with the
193return value of \fISSL_read()\fR will yield \fB\s-1SSL_ERROR_WANT_READ\s0\fR or
194\&\fB\s-1SSL_ERROR_WANT_WRITE\s0\fR. As at any time a re-negotiation is possible, a
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195call to \fISSL_read()\fR can also cause write operations! The calling process
196then must repeat the call after taking appropriate action to satisfy the
e056f0e0 197needs of \fISSL_read()\fR. The action depends on the underlying \s-1BIO\s0. When using a
984263bc 198non-blocking socket, nothing is to be done, but \fIselect()\fR can be used to check
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199for the required condition. When using a buffering \s-1BIO\s0, like a \s-1BIO\s0 pair, data
200must be written into or retrieved out of the \s-1BIO\s0 before being able to continue.
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201.PP
202\&\fISSL_pending\fR\|(3) can be used to find out whether there
203are buffered bytes available for immediate retrieval. In this case
204\&\fISSL_read()\fR can be called without blocking or actually receiving new
205data from the underlying socket.
984263bc 206.SH "WARNING"
e056f0e0 207.IX Header "WARNING"
984263bc 208When an \fISSL_read()\fR operation has to be repeated because of
e056f0e0 209\&\fB\s-1SSL_ERROR_WANT_READ\s0\fR or \fB\s-1SSL_ERROR_WANT_WRITE\s0\fR, it must be repeated
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210with the same arguments.
211.SH "RETURN VALUES"
e056f0e0 212.IX Header "RETURN VALUES"
984263bc 213The following return values can occur:
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214.IP ">0" 4
215.IX Item ">0"
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216The read operation was successful; the return value is the number of
217bytes actually read from the \s-1TLS/SSL\s0 connection.
e056f0e0 218.IP "0" 4
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219The read operation was not successful. The reason may either be a clean
220shutdown due to a \*(L"close notify\*(R" alert sent by the peer (in which case
221the \s-1SSL_RECEIVED_SHUTDOWN\s0 flag in the ssl shutdown state is set
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222(see \fISSL_shutdown\fR\|(3),
223\&\fISSL_set_shutdown\fR\|(3)). It is also possible, that
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224the peer simply shut down the underlying transport and the shutdown is
225incomplete. Call \fISSL_get_error()\fR with the return value \fBret\fR to find out,
226whether an error occurred or the connection was shut down cleanly
227(\s-1SSL_ERROR_ZERO_RETURN\s0).
228.Sp
229SSLv2 (deprecated) does not support a shutdown alert protocol, so it can
230only be detected, whether the underlying connection was closed. It cannot
231be checked, whether the closure was initiated by the peer or by something
232else.
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233.IP "<0" 4
234.IX Item "<0"
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235The read operation was not successful, because either an error occurred
236or action must be taken by the calling process. Call \fISSL_get_error()\fR with the
237return value \fBret\fR to find out the reason.
238.SH "SEE ALSO"
a7d27d5a 239.IX Header "SEE ALSO"
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240\&\fISSL_get_error\fR\|(3), \fISSL_write\fR\|(3),
241\&\fISSL_CTX_set_mode\fR\|(3), \fISSL_CTX_new\fR\|(3),
242\&\fISSL_connect\fR\|(3), \fISSL_accept\fR\|(3)
243\&\fISSL_set_connect_state\fR\|(3),
18ed9402 244\&\fISSL_pending\fR\|(3),
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245\&\fISSL_shutdown\fR\|(3), \fISSL_set_shutdown\fR\|(3),
246\&\fIssl\fR\|(3), \fIbio\fR\|(3)