NAME
SSL_get_error – obtain result code for TLS/SSL I/O operation
SYNOPSIS
SSL Library (libssl, -lssl) libcrypto
#include <openssl/ssl.h>
int
SSL_get_error(const SSL *ssl, int ret);
DESCRIPTION
SSL_get_error() returns a result code (suitable for the C “switch” statement) for a preceding call to SSL_connect(3), SSL_accept(3), SSL_do_handshake(3), SSL_read(3), SSL_peek(3), or SSL_write(3) on ssl. The value returned by that TLS/SSL I/O function must be passed to SSL_get_error() in parameter ret.
In addition to ssl and ret, SSL_get_error() inspects the current thread's OpenSSL error queue. Thus, SSL_get_error() must be used in the same thread that performed the TLS/SSL I/O operation, and no other OpenSSL function calls should appear in between. The current thread's error queue must be empty before the TLS/SSL I/O operation is attempted, or SSL_get_error() will not work reliably.
RETURN VALUES
The following return values can currently occur:
- SSL_ERROR_NONE
-
The TLS/SSL I/O operation completed. This result code is returned if and only if ret > 0.
- SSL_ERROR_ZERO_RETURN
-
The TLS/SSL connection has been closed. If the protocol version is SSL 3.0 or TLS 1.0, this result code is returned only if a closure alert has occurred in the protocol, i.e., if the connection has been closed cleanly. Note that in this case SSL_ERROR_ZERO_RETURN does not necessarily indicate that the underlying transport has been closed.
- SSL_ERROR_WANT_READ, SSL_ERROR_WANT_WRITE
-
The operation did not complete; the same TLS/SSL I/O function should be called again later. If, by then, the underlying BIO has data available for reading (if the result code is SSL_ERROR_WANT_READ) or allows writing data (SSL_ERROR_WANT_WRITE), then some TLS/SSL protocol progress will take place, i.e., at least part of a TLS/SSL record will be read or written. Note that the retry may again lead to a SSL_ERROR_WANT_READ or SSL_ERROR_WANT_WRITE condition. There is no fixed upper limit for the number of iterations that may be necessary until progress becomes visible at application protocol level.
For socketBIO s (e.g., when SSL_set_fd() was used), select(2) or poll(2) on the underlying socket can be used to find out when the TLS/SSL I/O function should be retried.
Caveat: Any TLS/SSL I/O function can lead to either of SSL_ERROR_WANT_READ and SSL_ERROR_WANT_WRITE. In particular, SSL_read(3) or SSL_peek(3) may want to write data and SSL_write(3) may want to read data. This is mainly because TLS/SSL handshakes may occur at any time during the protocol (initiated by either the client or the server); SSL_read(3), SSL_peek(3), and SSL_write(3) will handle any pending handshakes.
- SSL_ERROR_WANT_CONNECT, SSL_ERROR_WANT_ACCEPT
-
The operation did not complete; the same TLS/SSL I/O function should be called again later. The underlying BIO was not connected yet to the peer and the call would block inconnect(2)/ accept(2). The SSL function should be called again when the connection is established. These messages can only appear with a BIO_s_connect(3) or BIO_s_accept(3) BIO, respectively. In order to find out when the connection has been successfully established, on many platforms select(2) or poll(2) for writing on the socket file descriptor can be used.
- SSL_ERROR_WANT_X509_LOOKUP
-
The operation did not complete because an application callback set by SSL_CTX_set_client_cert_cb(3) has asked to be called again. The TLS/SSL I/O function should be called again later. Details depend on the application.
- SSL_ERROR_SYSCALL
-
Some I/O error occurred. The OpenSSL error queue may contain more information on the error. If the error queue is empty (i.e., ERR_get_error() returns 0), ret can be used to find out more about the error: If ret == 0, an EOF was observed that violates the protocol. If ret == −1, the underlying BIO reported an I/O error (for socket I/O on Unix systems, consult errno for details).
- SSL_ERROR_SSL
-
A failure in the SSL library occurred, usually a protocol error. The OpenSSL error queue contains more information on the error.
SEE ALSO
HISTORY
SSL_get_error() first appeared in SSLeay 0.8.0 and have been available since OpenBSD 2.4.