servername_cb
ctx->ext.servername_cb = (int (*)(SSL *, int *, void *))fp;
int (*servername_cb)(SSL *, int *, void *);
if (sctx->ext.servername_cb != NULL)
ret = sctx->ext.servername_cb(ussl, &altmp,
else if (s->session_ctx->ext.servername_cb != NULL)
ret = s->session_ctx->ext.servername_cb(ussl, &altmp,
if (sctx->ext.servername_cb != NULL
|| s->session_ctx->ext.servername_cb != NULL)
SSL_CTX_set_tlsext_servername_callback(s_ctx, servername_cb);