305 lines
13 KiB
Groff
305 lines
13 KiB
Groff
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.\" ========================================================================
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.\"
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.IX Title "SSL_GET_ERROR 3"
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.TH SSL_GET_ERROR 3 "2020-04-21" "1.1.1g" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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SSL_get_error \- obtain result code for TLS/SSL I/O operation
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/ssl.h>
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\&
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\& int SSL_get_error(const SSL *ssl, int ret);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\fBSSL_get_error()\fR returns a result code (suitable for the C \*(L"switch\*(R"
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statement) for a preceding call to \fBSSL_connect()\fR, \fBSSL_accept()\fR, \fBSSL_do_handshake()\fR,
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\&\fBSSL_read_ex()\fR, \fBSSL_read()\fR, \fBSSL_peek_ex()\fR, \fBSSL_peek()\fR, \fBSSL_shutdown()\fR,
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\&\fBSSL_write_ex()\fR or \fBSSL_write()\fR on \fBssl\fR. The value returned by that \s-1TLS/SSL I/O\s0
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function must be passed to \fBSSL_get_error()\fR in parameter \fBret\fR.
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.PP
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In addition to \fBssl\fR and \fBret\fR, \fBSSL_get_error()\fR inspects the
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current thread's OpenSSL error queue. Thus, \fBSSL_get_error()\fR must be
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used in the same thread that performed the \s-1TLS/SSL I/O\s0 operation, and no
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other OpenSSL function calls should appear in between. The current
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thread's error queue must be empty before the \s-1TLS/SSL I/O\s0 operation is
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attempted, or \fBSSL_get_error()\fR will not work reliably.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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The following return values can currently occur:
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.IP "\s-1SSL_ERROR_NONE\s0" 4
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.IX Item "SSL_ERROR_NONE"
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The \s-1TLS/SSL I/O\s0 operation completed. This result code is returned
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if and only if \fBret > 0\fR.
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.IP "\s-1SSL_ERROR_ZERO_RETURN\s0" 4
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.IX Item "SSL_ERROR_ZERO_RETURN"
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The \s-1TLS/SSL\s0 peer has closed the connection for writing by sending the
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close_notify alert.
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No more data can be read.
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Note that \fB\s-1SSL_ERROR_ZERO_RETURN\s0\fR does not necessarily
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indicate that the underlying transport has been closed.
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.IP "\s-1SSL_ERROR_WANT_READ, SSL_ERROR_WANT_WRITE\s0" 4
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.IX Item "SSL_ERROR_WANT_READ, SSL_ERROR_WANT_WRITE"
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The operation did not complete and can be retried later.
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.Sp
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\&\fB\s-1SSL_ERROR_WANT_READ\s0\fR is returned when the last operation was a read
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operation from a non-blocking \fB\s-1BIO\s0\fR.
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It means that not enough data was available at this time to complete the
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operation.
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If at a later time the underlying \fB\s-1BIO\s0\fR has data available for reading the same
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function can be called again.
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.Sp
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\&\fBSSL_read()\fR and \fBSSL_read_ex()\fR can also set \fB\s-1SSL_ERROR_WANT_READ\s0\fR when there is
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still unprocessed data available at either the \fB\s-1SSL\s0\fR or the \fB\s-1BIO\s0\fR layer, even
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for a blocking \fB\s-1BIO\s0\fR.
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See \fBSSL_read\fR\|(3) for more information.
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.Sp
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\&\fB\s-1SSL_ERROR_WANT_WRITE\s0\fR is returned when the last operation was a write
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to a non-blocking \fB\s-1BIO\s0\fR and it was unable to sent all data to the \fB\s-1BIO\s0\fR.
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When the \fB\s-1BIO\s0\fR is writeable again, the same function can be called again.
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.Sp
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Note that the retry may again lead to an \fB\s-1SSL_ERROR_WANT_READ\s0\fR or
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\&\fB\s-1SSL_ERROR_WANT_WRITE\s0\fR condition.
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There is no fixed upper limit for the number of iterations that
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may be necessary until progress becomes visible at application
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protocol level.
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.Sp
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It is safe to call \fBSSL_read()\fR or \fBSSL_read_ex()\fR when more data is available
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even when the call that set this error was an \fBSSL_write()\fR or \fBSSL_write_ex()\fR.
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However if the call was an \fBSSL_write()\fR or \fBSSL_write_ex()\fR, it should be called
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again to continue sending the application data.
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.Sp
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For socket \fB\s-1BIO\s0\fRs (e.g. when \fBSSL_set_fd()\fR was used), \fBselect()\fR or
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\&\fBpoll()\fR on the underlying socket can be used to find out when the
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\&\s-1TLS/SSL I/O\s0 function should be retried.
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.Sp
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Caveat: Any \s-1TLS/SSL I/O\s0 function can lead to either of
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\&\fB\s-1SSL_ERROR_WANT_READ\s0\fR and \fB\s-1SSL_ERROR_WANT_WRITE\s0\fR.
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In particular,
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\&\fBSSL_read_ex()\fR, \fBSSL_read()\fR, \fBSSL_peek_ex()\fR, or \fBSSL_peek()\fR may want to write data
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and \fBSSL_write()\fR or \fBSSL_write_ex()\fR may want to read data.
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This is mainly because
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\&\s-1TLS/SSL\s0 handshakes may occur at any time during the protocol (initiated by
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either the client or the server); \fBSSL_read_ex()\fR, \fBSSL_read()\fR, \fBSSL_peek_ex()\fR,
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\&\fBSSL_peek()\fR, \fBSSL_write_ex()\fR, and \fBSSL_write()\fR will handle any pending handshakes.
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.IP "\s-1SSL_ERROR_WANT_CONNECT, SSL_ERROR_WANT_ACCEPT\s0" 4
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.IX Item "SSL_ERROR_WANT_CONNECT, SSL_ERROR_WANT_ACCEPT"
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The operation did not complete; the same \s-1TLS/SSL I/O\s0 function should be
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called again later. The underlying \s-1BIO\s0 was not connected yet to the peer
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and the call would block in \fBconnect()\fR/\fBaccept()\fR. The \s-1SSL\s0 function should be
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called again when the connection is established. These messages can only
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appear with a \fBBIO_s_connect()\fR or \fBBIO_s_accept()\fR \s-1BIO,\s0 respectively.
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In order to find out, when the connection has been successfully established,
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on many platforms \fBselect()\fR or \fBpoll()\fR for writing on the socket file descriptor
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can be used.
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.IP "\s-1SSL_ERROR_WANT_X509_LOOKUP\s0" 4
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.IX Item "SSL_ERROR_WANT_X509_LOOKUP"
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The operation did not complete because an application callback set by
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\&\fBSSL_CTX_set_client_cert_cb()\fR has asked to be called again.
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The \s-1TLS/SSL I/O\s0 function should be called again later.
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Details depend on the application.
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.IP "\s-1SSL_ERROR_WANT_ASYNC\s0" 4
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.IX Item "SSL_ERROR_WANT_ASYNC"
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The operation did not complete because an asynchronous engine is still
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processing data. This will only occur if the mode has been set to \s-1SSL_MODE_ASYNC\s0
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using \fBSSL_CTX_set_mode\fR\|(3) or \fBSSL_set_mode\fR\|(3) and an asynchronous capable
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engine is being used. An application can determine whether the engine has
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completed its processing using \fBselect()\fR or \fBpoll()\fR on the asynchronous wait file
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descriptor. This file descriptor is available by calling
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\&\fBSSL_get_all_async_fds\fR\|(3) or \fBSSL_get_changed_async_fds\fR\|(3). The \s-1TLS/SSL I/O\s0
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function should be called again later. The function \fBmust\fR be called from the
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same thread that the original call was made from.
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.IP "\s-1SSL_ERROR_WANT_ASYNC_JOB\s0" 4
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.IX Item "SSL_ERROR_WANT_ASYNC_JOB"
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The asynchronous job could not be started because there were no async jobs
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available in the pool (see \fBASYNC_init_thread\fR\|(3)). This will only occur if the
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mode has been set to \s-1SSL_MODE_ASYNC\s0 using \fBSSL_CTX_set_mode\fR\|(3) or
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\&\fBSSL_set_mode\fR\|(3) and a maximum limit has been set on the async job pool
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through a call to \fBASYNC_init_thread\fR\|(3). The application should retry the
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operation after a currently executing asynchronous operation for the current
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thread has completed.
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.IP "\s-1SSL_ERROR_WANT_CLIENT_HELLO_CB\s0" 4
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.IX Item "SSL_ERROR_WANT_CLIENT_HELLO_CB"
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The operation did not complete because an application callback set by
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\&\fBSSL_CTX_set_client_hello_cb()\fR has asked to be called again.
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The \s-1TLS/SSL I/O\s0 function should be called again later.
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Details depend on the application.
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.IP "\s-1SSL_ERROR_SYSCALL\s0" 4
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.IX Item "SSL_ERROR_SYSCALL"
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Some non-recoverable, fatal I/O error occurred. The OpenSSL error queue may
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contain more information on the error. For socket I/O on Unix systems, consult
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\&\fBerrno\fR for details. If this error occurs then no further I/O operations should
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be performed on the connection and \fBSSL_shutdown()\fR must not be called.
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.Sp
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This value can also be returned for other errors, check the error queue for
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details.
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.IP "\s-1SSL_ERROR_SSL\s0" 4
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.IX Item "SSL_ERROR_SSL"
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A non-recoverable, fatal error in the \s-1SSL\s0 library occurred, usually a protocol
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error. The OpenSSL error queue contains more information on the error. If this
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error occurs then no further I/O operations should be performed on the
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connection and \fBSSL_shutdown()\fR must not be called.
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.SH "BUGS"
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.IX Header "BUGS"
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The \fB\s-1SSL_ERROR_SYSCALL\s0\fR with \fBerrno\fR value of 0 indicates unexpected \s-1EOF\s0 from
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the peer. This will be properly reported as \fB\s-1SSL_ERROR_SSL\s0\fR with reason
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code \fB\s-1SSL_R_UNEXPECTED_EOF_WHILE_READING\s0\fR in the OpenSSL 3.0 release because
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it is truly a \s-1TLS\s0 protocol error to terminate the connection without
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a \fBSSL_shutdown()\fR.
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.PP
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The issue is kept unfixed in OpenSSL 1.1.1 releases because many applications
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which choose to ignore this protocol error depend on the existing way of
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reporting the error.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fBssl\fR\|(7)
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.SH "HISTORY"
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.IX Header "HISTORY"
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The \s-1SSL_ERROR_WANT_ASYNC\s0 error code was added in OpenSSL 1.1.0.
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The \s-1SSL_ERROR_WANT_CLIENT_HELLO_CB\s0 error code was added in OpenSSL 1.1.1.
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.SH "COPYRIGHT"
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.IX Header "COPYRIGHT"
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Copyright 2000\-2020 The OpenSSL Project Authors. All Rights Reserved.
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.PP
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Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file \s-1LICENSE\s0 in the source distribution or at
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<https://www.openssl.org/source/license.html>.
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