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EDIT :: SSL_CTX_set_alpn_protos.3ssl

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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" SSL_CTX_set_alpn_protos, SSL_set_alpn_protos, SSL_CTX_set_alpn_select_cb, SSL_select_next_proto, SSL_get0_alpn_selected \- handle application layer protocol negotiation (ALPN) .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 1 \& #include <openssl/ssl.h> \& \& int SSL_CTX_set_alpn_protos(SSL_CTX *ctx, const unsigned char *protos, \& unsigned protos_len); \& int SSL_set_alpn_protos(SSL *ssl, const unsigned char *protos, \& unsigned protos_len); \& void SSL_CTX_set_alpn_select_cb(SSL_CTX *ctx, \& int (*cb) (SSL *ssl, \& const unsigned char **out, \& unsigned char *outlen, \& const unsigned char *in, \& unsigned int inlen, \& void *arg), void *arg); \& int SSL_select_next_proto(unsigned char **out, unsigned char *outlen, \& const unsigned char *server, \& unsigned int server_len, \& const unsigned char *client, \& unsigned int client_len) \& void SSL_get0_alpn_selected(const SSL *ssl, const unsigned char **data, \& unsigned int *len); .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" \&\fBSSL_CTX_set_alpn_protos()\fR and \fBSSL_set_alpn_protos()\fR are used by the client to set the list of protocols available to be negotiated. The \fBprotos\fR must be in protocol-list format, described below. The length of \fBprotos\fR is specified in \&\fBprotos_len\fR. .PP \&\fBSSL_CTX_set_alpn_select_cb()\fR sets the application callback \fBcb\fR used by a server to select which protocol to use for the incoming connection. When \fBcb\fR is \s-1NULL, ALPN\s0 is not used. The \fBarg\fR value is a pointer which is passed to the application callback. .PP \&\fBcb\fR is the application defined callback. The \fBin\fR, \fBinlen\fR parameters are a vector in protocol-list format. The value of the \fBout\fR, \fBoutlen\fR vector should be set to the value of a single protocol selected from the \fBin\fR, \&\fBinlen\fR vector. The \fBarg\fR parameter is the pointer set via \&\fBSSL_CTX_set_alpn_select_cb()\fR. .PP \&\fBSSL_select_next_proto()\fR is a helper function used to select protocols. It implements the standard protocol selection. It is expected that this function is called from the application callback \fBcb\fR. The protocol data in \fBserver\fR, \&\fBserver_len\fR and \fBclient\fR, \fBclient_len\fR must be in the protocol-list format described below. The first item in the \fBserver\fR, \fBserver_len\fR list that matches an item in the \fBclient\fR, \fBclient_len\fR list is selected, and returned in \fBout\fR, \fBoutlen\fR. The \fBout\fR value will point into either \fBserver\fR or \&\fBclient\fR, so it should be copied immediately. If no match is found, the first item in \fBclient\fR, \fBclient_len\fR is returned in \fBout\fR, \fBoutlen\fR. This function can also be used in the \s-1NPN\s0 callback. .PP \&\fBSSL_get0_alpn_selected()\fR returns a pointer to the selected protocol in \fBdata\fR with length \fBlen\fR. It is not NUL-terminated. \fBdata\fR is set to \s-1NULL\s0 and \fBlen\fR is set to 0 if no protocol has been selected. \fBdata\fR must not be freed. .SH "NOTES" .IX Header "NOTES" The protocol-lists must be in wire-format, which is defined as a vector of non-empty, 8\-bit length-prefixed, byte strings. The length-prefix byte is not included in the length. Each string is limited to 255 bytes. A byte-string length of 0 is invalid. A truncated byte-string is invalid. The length of the vector is not in the vector itself, but in a separate variable. .PP Example: .PP .Vb 5 \& unsigned char vector[] = { \& 6, \*(Aqs\*(Aq, \*(Aqp\*(Aq, \*(Aqd\*(Aq, \*(Aqy\*(Aq, \*(Aq/\*(Aq, \*(Aq1\*(Aq, \& 8, \*(Aqh\*(Aq, \*(Aqt\*(Aq, \*(Aqt\*(Aq, \*(Aqp\*(Aq, \*(Aq/\*(Aq, \*(Aq1\*(Aq, \*(Aq.\*(Aq, \*(Aq1\*(Aq \& }; \& unsigned int length = sizeof(vector); .Ve .PP The \s-1ALPN\s0 callback is executed after the servername callback; as that servername callback may update the \s-1SSL_CTX,\s0 and subsequently, the \s-1ALPN\s0 callback. .PP If there is no \s-1ALPN\s0 proposed in the ClientHello, the \s-1ALPN\s0 callback is not invoked. .SH "RETURN VALUES" .IX Header "RETURN VALUES" \&\fBSSL_CTX_set_alpn_protos()\fR and \fBSSL_set_alpn_protos()\fR return 0 on success, and non\-0 on failure. \s-1WARNING:\s0 these functions reverse the return value convention. .PP \&\fBSSL_select_next_proto()\fR returns one of the following: .IP "\s-1OPENSSL_NPN_NEGOTIATED\s0" 4 .IX Item "OPENSSL_NPN_NEGOTIATED" A match was found and is returned in \fBout\fR, \fBoutlen\fR. .IP "\s-1OPENSSL_NPN_NO_OVERLAP\s0" 4 .IX Item "OPENSSL_NPN_NO_OVERLAP" No match was found. The first item in \fBclient\fR, \fBclient_len\fR is returned in \&\fBout\fR, \fBoutlen\fR. .PP The \s-1ALPN\s0 select callback \fBcb\fR, must return one of the following: .IP "\s-1SSL_TLSEXT_ERR_OK\s0" 4 .IX Item "SSL_TLSEXT_ERR_OK" \&\s-1ALPN\s0 protocol selected. .IP "\s-1SSL_TLSEXT_ERR_NOACK\s0" 4 .IX Item "SSL_TLSEXT_ERR_NOACK" \&\s-1ALPN\s0 protocol not selected. .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fBssl\fR\|(3), \fBSSL_CTX_set_tlsext_servername_callback\fR\|(3), \&\fBSSL_CTX_set_tlsext_servername_arg\fR\|(3)

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