SSL_CTX_set_tlsext_servername_callback, SSL_CTX_set_tlsext_servername_arg, SSL_get_servername_type, SSL_get_servername - handle server name indication (SNI)
#include <openssl/ssl.h> long SSL_CTX_set_tlsext_servername_callback(SSL_CTX *ctx, int (*cb)(SSL *, int *, void *)); long SSL_CTX_set_tlsext_servername_arg(SSL_CTX *ctx, void *arg); const char *SSL_get_servername(const SSL *s, const int type); int SSL_get_servername_type(const SSL *s);
SSL_CTX_set_tlsext_servername_callback() sets the application callback cb used by a server to perform any actions or configuration required based on the servername extension received in the incoming connection. When cb is NULL, SNI is not used. The arg value is a pointer which is passed to the application callback.
SSL_CTX_set_tlsext_servername_arg() sets a context-specific argument to be passed into the callback for this SSL_CTX.
SSL_get_servername() returns a servername extension value of the specified type if provided in the Client Hello or NULL.
SSL_get_servername_type() returns the servername type or -1 if no servername is present. Currently the only supported type (defined in RFC3546) is TLSEXT_NAMETYPE_host_name.
The ALPN and SNI callbacks are both executed during Client Hello processing. The servername callback is executed first, followed by the ALPN callback.
SSL_CTX_set_tlsext_servername_callback() and SSL_CTX_set_tlsext_servername_arg() both always return 1 indicating success.
ssl(7), SSL_CTX_set_alpn_select_cb(3), SSL_get0_alpn_selected(3)
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