1SSL_CTX_set_alpn_select_cb(3) OpenSSL SSL_CTX_set_alpn_select_cb(3)
2
6 SSL_CTX_set_alpn_protos, SSL_set_alpn_protos,
7 SSL_CTX_set_alpn_select_cb, SSL_select_next_proto,
8 SSL_get0_alpn_selected - handle application layer protocol negotiation
9 (ALPN)
10
12 #include <openssl/ssl.h>
13 int SSL_CTX_set_alpn_protos(SSL_CTX *ctx, const unsigned char *protos,
15 unsigned protos_len);
16 int SSL_set_alpn_protos(SSL *ssl, const unsigned char *protos,
17 unsigned protos_len);
18 void SSL_CTX_set_alpn_select_cb(SSL_CTX *ctx,
19 int (*cb) (SSL *ssl,
20 const unsigned char **out,
21 unsigned char *outlen,
22 const unsigned char *in,
23 unsigned int inlen,
24 void *arg), void *arg);
25 int SSL_select_next_proto(unsigned char **out, unsigned char *outlen,
26 const unsigned char *server,
27 unsigned int server_len,
28 const unsigned char *client,
29 unsigned int client_len)
30 void SSL_get0_alpn_selected(const SSL *ssl, const unsigned char **data,
31 unsigned int *len);
32
34 SSL_CTX_set_alpn_protos() and SSL_set_alpn_protos() are used by the
35 client to set the list of protocols available to be negotiated. The
36 protos must be in protocol-list format, described below. The length of
37 protos is specified in protos_len.
38 SSL_CTX_set_alpn_select_cb() sets the application callback cb used by a
40 server to select which protocol to use for the incoming connection.
41 When cb is NULL, ALPN is not used. The arg value is a pointer which is
42 passed to the application callback.
43 cb is the application defined callback. The in, inlen parameters are a
45 vector in protocol-list format. The value of the out, outlen vector
46 should be set to the value of a single protocol selected from the in,
47 inlen vector. The arg parameter is the pointer set via
48 SSL_CTX_set_alpn_select_cb().
49 SSL_select_next_proto() is a helper function used to select protocols.
51 It implements the standard protocol selection. It is expected that this
52 function is called from the application callback cb. The protocol data
53 in server, server_len and client, client_len must be in the protocol-
54 list format described below. The first item in the server, server_len
55 list that matches an item in the client, client_len list is selected,
56 and returned in out, outlen. The out value will point into either
57 server or client, so it should be copied immediately. If no match is
58 found, the first item in client, client_len is returned in out, outlen.
59 This function can also be used in the NPN callback.
60 SSL_get0_alpn_selected() returns a pointer to the selected protocol in
62 data with length len. It is not NUL-terminated. data is set to NULL and
63 len is set to 0 if no protocol has been selected. data must not be
64 freed.
65
67 The protocol-lists must be in wire-format, which is defined as a vector
68 of non-empty, 8-bit length-prefixed, byte strings. The length-prefix
69 byte is not included in the length. Each string is limited to 255
70 bytes. A byte-string length of 0 is invalid. A truncated byte-string is
71 invalid. The length of the vector is not in the vector itself, but in a
72 separate variable.
73 Example:
75 unsigned char vector[] = {
77 6, 's', 'p', 'd', 'y', '/', '1',
78 8, 'h', 't', 't', 'p', '/', '1', '.', '1'
79 };
80 unsigned int length = sizeof(vector);
81 The ALPN callback is executed after the servername callback; as that
83 servername callback may update the SSL_CTX, and subsequently, the ALPN
84 callback.
85 If there is no ALPN proposed in the ClientHello, the ALPN callback is
87 not invoked.
88
90 SSL_CTX_set_alpn_protos() and SSL_set_alpn_protos() return 0 on
91 success, and non-0 on failure. WARNING: these functions reverse the
92 return value convention.
93 SSL_select_next_proto() returns one of the following:
95 OPENSSL_NPN_NEGOTIATED
97 A match was found and is returned in out, outlen.
98 OPENSSL_NPN_NO_OVERLAP
100 No match was found. The first item in client, client_len is
101 returned in out, outlen.
102 The ALPN select callback cb, must return one of the following:
104 SSL_TLSEXT_ERR_OK
106 ALPN protocol selected.
107 SSL_TLSEXT_ERR_NOACK
109 ALPN protocol not selected.
110
112 ssl(3), SSL_CTX_set_tlsext_servername_callback(3),
113 SSL_CTX_set_tlsext_servername_arg(3)
1141.0.2o 2020-01-28 SSL_CTX_set_alpn_select_cb(3)