SSL_GET_ERROR(3) | Library Functions Manual | SSL_GET_ERROR(3)

# NAME

`SSL_get_error` — obtain result code for TLS/SSL I/O operation

# SYNOPSIS

library “libssl” 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 socket BIOs (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 in connect(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

err(3), ssl(3)

# HISTORY

`SSL_get_error`() first appeared in SSLeay 0.8.0 and have been available since OpenBSD 2.4.

June 8, 2025 | Debian