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1 .\" $OpenBSD: SSL_get_error.3,v 1.3 2018/03/21 05:07:04 schwarze Exp $
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51 .Dd $Mdocdate: March 21 2018 $
52 .Dt SSL_GET_ERROR 3
53 .Os
54 .Sh NAME
55 .Nm SSL_get_error
56 .Nd obtain result code for TLS/SSL I/O operation
57 .Sh SYNOPSIS
58 .In openssl/ssl.h
59 .Ft int
60 .Fn SSL_get_error "const SSL *ssl" "int ret"
61 .Sh DESCRIPTION
62 .Fn SSL_get_error
63 returns a result code (suitable for the C
64 .Dq switch
65 statement) for a preceding call to
66 .Xr SSL_connect 3 ,
67 .Xr SSL_accept 3 ,
68 .Xr SSL_do_handshake 3 ,
69 .Xr SSL_read 3 ,
70 .Xr SSL_peek 3 ,
71 or
72 .Xr SSL_write 3
73 on
74 .Fa ssl .
75 The value returned by that TLS/SSL I/O function must be passed to
76 .Fn SSL_get_error
77 in parameter
78 .Fa ret .
79 .Pp
80 In addition to
81 .Fa ssl
82 and
83 .Fa ret ,
84 .Fn SSL_get_error
85 inspects the current thread's OpenSSL error queue.
86 Thus,
87 .Fn SSL_get_error
88 must be used in the same thread that performed the TLS/SSL I/O operation,
89 and no other OpenSSL function calls should appear in between.
90 The current thread's error queue must be empty before the TLS/SSL I/O operation
91 is attempted, or
92 .Fn SSL_get_error
93 will not work reliably.
94 .Sh RETURN VALUES
95 The following return values can currently occur:
96 .Bl -tag -width Ds
97 .It Dv SSL_ERROR_NONE
98 The TLS/SSL I/O operation completed.
99 This result code is returned if and only if
100 .Fa ret
101 < 0.
102 .It Dv SSL_ERROR_ZERO_RETURN
103 The TLS/SSL connection has been closed.
104 If the protocol version is SSL 3.0 or TLS 1.0, this result code is returned
105 only if a closure alert has occurred in the protocol, i.e., if the connection
106 has been closed cleanly.
107 Note that in this case
108 .Dv SSL_ERROR_ZERO_RETURN
109 does not necessarily indicate that the underlying transport has been closed.
110 .It Dv SSL_ERROR_WANT_READ , Dv SSL_ERROR_WANT_WRITE
111 The operation did not complete;
112 the same TLS/SSL I/O function should be called again later.
113 If, by then, the underlying
114 .Vt BIO
115 has data available for reading (if the result code is
116 .Dv SSL_ERROR_WANT_READ )
117 or allows writing data
118 .Pq Dv SSL_ERROR_WANT_WRITE ,
119 then some TLS/SSL protocol progress will take place,
120 i.e., at least part of a TLS/SSL record will be read or written.
121 Note that the retry may again lead to a
122 .Dv SSL_ERROR_WANT_READ
123 or
124 .Dv SSL_ERROR_WANT_WRITE
125 condition.
126 There is no fixed upper limit for the number of iterations that may be
127 necessary until progress becomes visible at application protocol level.
128 .Pp
129 For socket
130 .Fa BIO Ns
131 s (e.g., when
132 .Fn SSL_set_fd
133 was used),
134 .Xr select 2
135 or
136 .Xr poll 2
137 on the underlying socket can be used to find out when the TLS/SSL I/O function
138 should be retried.
139 .Pp
140 Caveat: Any TLS/SSL I/O function can lead to either of
141 .Dv SSL_ERROR_WANT_READ
142 and
143 .Dv SSL_ERROR_WANT_WRITE .
144 In particular,
145 .Xr SSL_read 3
146 or
147 .Xr SSL_peek 3
148 may want to write data and
149 .Xr SSL_write 3
150 may want
151 to read data.
152 This is mainly because TLS/SSL handshakes may occur at any time during the
153 protocol (initiated by either the client or the server);
154 .Xr SSL_read 3 ,
155 .Xr SSL_peek 3 ,
156 and
157 .Xr SSL_write 3
158 will handle any pending handshakes.
159 .It Dv SSL_ERROR_WANT_CONNECT , Dv SSL_ERROR_WANT_ACCEPT
160 The operation did not complete; the same TLS/SSL I/O function should be
161 called again later.
162 The underlying BIO was not connected yet to the peer and the call would block
163 in
164 .Xr connect 2 Ns / Ns
165 .Xr accept 2 .
166 The SSL function should be
167 called again when the connection is established.
168 These messages can only appear with a
169 .Xr BIO_s_connect 3
170 or
171 .Xr BIO_s_accept 3
172 .Vt BIO ,
173 respectively.
174 In order to find out when the connection has been successfully established,
175 on many platforms
176 .Xr select 2
177 or
178 .Xr poll 2
179 for writing on the socket file descriptor can be used.
180 .It Dv SSL_ERROR_WANT_X509_LOOKUP
181 The operation did not complete because an application callback set by
182 .Xr SSL_CTX_set_client_cert_cb 3
183 has asked to be called again.
184 The TLS/SSL I/O function should be called again later.
185 Details depend on the application.
186 .It Dv SSL_ERROR_SYSCALL
187 Some I/O error occurred.
188 The OpenSSL error queue may contain more information on the error.
189 If the error queue is empty (i.e.,
190 .Fn ERR_get_error
191 returns 0),
192 .Fa ret
193 can be used to find out more about the error:
194 If
195 .Fa ret
196 == 0, an
197 .Dv EOF
198 was observed that violates the protocol.
199 If
200 .Fa ret
201 == \(mi1, the underlying
202 .Vt BIO
203 reported an
204 I/O error (for socket I/O on Unix systems, consult
205 .Dv errno
206 for details).
207 .It Dv SSL_ERROR_SSL
208 A failure in the SSL library occurred, usually a protocol error.
209 The OpenSSL error queue contains more information on the error.
210 .El
211 .Sh SEE ALSO
212 .Xr err 3 ,
213 .Xr ssl 3
214 .Sh HISTORY
215 .Fn SSL_get_error
216 first appeared in SSLeay 0.8 and have been available since
217 .Ox 2.4 .