typedef int (*SSL_client_hello_cb_fn)(SSL *s, int *al, void *arg); void SSL_CTX_set_client_hello_cb(SSL_CTX *c, SSL_client_hello_cb_fn *f, void *arg); int SSL_client_hello_isv2(SSL *s); unsigned int SSL_client_hello_get0_legacy_version(SSL *s); size_t SSL_client_hello_get0_random(SSL *s, const unsigned char **out); size_t SSL_client_hello_get0_session_id(SSL *s, const unsigned char **out); size_t SSL_client_hello_get0_ciphers(SSL *s, const unsigned char **out); size_t SSL_client_hello_get0_compression_methods(SSL *s, const unsigned char **out); int SSL_client_hello_get1_extensions_present(SSL *s, int **out, size_t *outlen); int SSL_client_hello_get0_ext(SSL *s, int type, const unsigned char **out, size_t *outlen);
SSL_client_hello_isv2() indicates whether the ClientHello was carried in a SSLv2 record and is in the SSLv2 format. The SSLv2 format has substantial differences from the normal SSLv3 format, including using three bytes per cipher suite, and not allowing extensions. Additionally, the SSLv2 format 'challenge' field is exposed via SSL_client_hello_get0_random(), padded to SSL3_RANDOM_SIZE bytes with zeros if needed. For SSLv2 format ClientHellos, SSL_client_hello_get0_compression_methods() returns a dummy list that only includes the null compression method, since the SSLv2 format does not include a mechanism by which to negotiate compression.
SSL_client_hello_get0_random(), SSL_client_hello_get0_session_id(), SSL_client_hello_get0_ciphers(), and SSL_client_hello_get0_compression_methods() provide access to the corresponding ClientHello fields, returning the field length and optionally setting an out pointer to the octets of that field.
Similarly, SSL_client_hello_get0_ext() provides access to individual extensions from the ClientHello on a per-extension basis. For the provided wire protocol extension type value, the extension value and length are returned in the output parameters (if present).
SSL_client_hello_get1_extensions_present() can be used prior to SSL_client_hello_get0_ext(), to determine which extensions are present in the ClientHello before querying for them. The out and outlen parameters are both required, and on success the caller must release the storage allocated for *out using OPENSSL_free(). The contents of *out is an array of integers holding the numerical value of the TLS extension types in the order they appear in the ClientHello. *outlen contains the number of elements in the array. In situations when the ClientHello has no extensions, the function will return success with *out set to NULL and *outlen set to 0.
It is also recommended that applications utilize a ClientHello callback and not use a servername callback, in order to avoid unexpected behavior that occurs due to the relative order of processing between things like session resumption and the historical servername callback.
The SSL_client_hello_* family of functions may only be called from code executing within a ClientHello callback.
SSL_client_hello_isv2() returns 1 for SSLv2-format ClientHellos and 0 otherwise.
SSL_client_hello_get0_random(), SSL_client_hello_get0_session_id(), SSL_client_hello_get0_ciphers(), and SSL_client_hello_get0_compression_methods() return the length of the corresponding ClientHello fields. If zero is returned, the output pointer should not be assumed to be valid.
SSL_client_hello_get0_ext() returns 1 if the extension of type 'type' is present, and 0 otherwise.
SSL_client_hello_get1_extensions_present() returns 1 on success and 0 on failure.
Licensed under the OpenSSL license (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at https://www.openssl.org/source/license.html.