Function libnghttp2_sys::nghttp2_select_next_protocol

pub unsafe extern "C" fn nghttp2_select_next_protocol(
    out: *mut *mut c_uchar,
    outlen: *mut c_uchar,
    in_: *const c_uchar,
    inlen: c_uint
) -> c_int

@function

A helper function for dealing with NPN in client side or ALPN in server side. The |in| contains peer’s protocol list in preferable order. The format of |in| is length-prefixed and not null-terminated. For example, h2 and http/1.1 stored in |in| like this::

in[0] = 2
in[1..2] = "h2"
in[3] = 8
in[4..11] = "http/1.1"
inlen = 12

The selection algorithm is as follows:

1. If peer’s list contains HTTP/2 protocol the library supports, it is selected and returns 1. The following step is not taken.

2. If peer’s list contains http/1.1, this function selects http/1.1 and returns 0. The following step is not taken.

3. This function selects nothing and returns -1 (So called non-overlap case). In this case, |out| and |outlen| are left untouched.

Selecting h2 means that h2 is written into |*out| and its length (which is 2) is assigned to |*outlen|.

For ALPN, refer to https://tools.ietf.org/html/rfc7301

See http://technotes.googlecode.com/git/nextprotoneg.html for more details about NPN.

For NPN, to use this method you should do something like::

static int select_next_proto_cb(SSL* ssl,
                                unsigned char **out,
                                unsigned char *outlen,
                                const unsigned char *in,
                                unsigned int inlen,
                                void *arg)
{
    int rv;
    rv = nghttp2_select_next_protocol(out, outlen, in, inlen);
    if (rv == -1) {
        return SSL_TLSEXT_ERR_NOACK;
    }
    if (rv == 1) {
        ((MyType*)arg)->http2_selected = 1;
    }
    return SSL_TLSEXT_ERR_OK;
}
...
SSL_CTX_set_next_proto_select_cb(ssl_ctx, select_next_proto_cb, my_obj);