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SSL_CTX_set_mode

Section: OpenSSL (3)
Updated: 2017-05-25
Index Return to Main Contents

NAME

SSL_CTX_set_mode, SSL_set_mode, SSL_CTX_get_mode, SSL_get_mode - manipulate SSL engine mode

SYNOPSIS

 #include <openssl/ssl.h>

 long SSL_CTX_set_mode(SSL_CTX *ctx, long mode);
 long SSL_set_mode(SSL *ssl, long mode);

 long SSL_CTX_get_mode(SSL_CTX *ctx);
 long SSL_get_mode(SSL *ssl);

DESCRIPTION

SSL_CTX_set_mode() adds the mode set via bitmask in mode to ctx. Options already set before are not cleared.

SSL_set_mode() adds the mode set via bitmask in mode to ssl. Options already set before are not cleared.

SSL_CTX_get_mode() returns the mode set for ctx.

SSL_get_mode() returns the mode set for ssl.

NOTES

The following mode changes are available:

SSL_MODE_ENABLE_PARTIAL_WRITE: Allow SSL_write(..., n) to return r with 0 < r < n (i.e. report success when just a single record has been written). When not set (the default), SSL_write() will only report success once the complete chunk was written. Once SSL_write() returns with r, r bytes have been successfully written and the next call to SSL_write() must only send the n-r bytes left, imitating the behaviour of write().
SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER: Make it possible to retry SSL_write() with changed buffer location (the buffer contents must stay the same). This is not the default to avoid the misconception that non-blocking SSL_write() behaves like non-blocking write().
SSL_MODE_AUTO_RETRY: Never bother the application with retries if the transport is blocking. If a renegotiation take place during normal operation, a SSL_read(3) or SSL_write(3) would return with -1 and indicate the need to retry with SSL_ERROR_WANT_READ. In a non-blocking environment applications must be prepared to handle incomplete read/write operations. In a blocking environment, applications are not always prepared to deal with read/write operations returning without success report. The flag SSL_MODE_AUTO_RETRY will cause read/write operations to only return after the handshake and successful completion.
SSL_MODE_RELEASE_BUFFERS: When we no longer need a read buffer or a write buffer for a given SSL, then release the memory we were using to hold it. Released memory is either appended to a list of unused RAM chunks on the SSL_CTX, or simply freed if the list of unused chunks would become longer than SSL_CTX->freelist_max_len, which defaults to 32. Using this flag can save around 34k per idle SSL connection. This flag has no effect on SSL v2 connections, or on DTLS connections.
SSL_MODE_SEND_FALLBACK_SCSV: Send TLS_FALLBACK_SCSV in the ClientHello. To be set only by applications that reconnect with a downgraded protocol version; see draft-ietf-tls-downgrade-scsv-00 for details.
DO NOT ENABLE THIS if your application attempts a normal handshake. Only use this in explicit fallback retries, following the guidance in draft-ietf-tls-downgrade-scsv-00.