Add ALPN support to TlsAcceptor

src/imp/openssl.rs

@@ -368,6 +368,29 @@ impl TlsAcceptor {
         let mut acceptor = SslAcceptor::mozilla_intermediate(SslMethod::tls())?;
         acceptor.set_private_key(&builder.identity.0.pkey)?;
         acceptor.set_certificate(&builder.identity.0.cert)?;
+        #[cfg(feature = "alpn")]
+        if !builder.alpn.is_empty() {
+            use self::openssl::ssl::SslRef;
+            // Wire format is each alpn preceded by its length as a byte.
+            let mut alpn_wire_format = Vec::with_capacity(
+                builder
+                    .alpn
+                    .iter()
+                    .map(|s| s.as_bytes().len())
+                    .sum::<usize>()
+                    + builder.alpn.len(),
+            );
+            for alpn in builder.alpn.iter().map(|s| s.as_bytes()) {
+                alpn_wire_format.push(alpn.len() as u8);
+                alpn_wire_format.extend(alpn);
+            }
+            acceptor.set_alpn_protos(&alpn_wire_format)?;
+            // set uo ALPN selection routine - as select_next_proto
+            acceptor.set_alpn_select_callback(move |_: &mut SslRef, list: &[u8]| {
+                    openssl::ssl::select_next_proto(&alpn_wire_format, list).ok_or(
+                            openssl::ssl::AlpnError::NOACK)
+            });
+        }
         for cert in builder.identity.0.chain.iter() {
             // https://www.openssl.org/docs/manmaster/man3/SSL_CTX_add_extra_chain_cert.html
             // specifies that "When sending a certificate chain, extra chain certificates are

src/lib.rs

@@ -522,6 +522,8 @@ pub struct TlsAcceptorBuilder {
     identity: Identity,
     min_protocol: Option<Protocol>,
     max_protocol: Option<Protocol>,
+    #[cfg(feature = "alpn")]
+    alpn: Vec<String>,
 }
 
 impl TlsAcceptorBuilder {
@@ -544,6 +546,16 @@ impl TlsAcceptorBuilder {
         self.max_protocol = protocol;
         self
     }
+
+    /// Accept specific protocols through ALPN (Application-Layer Protocol Negotiation).
+    ///
+    /// Defaults to empty.
+    #[cfg(feature = "alpn")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "alpn")))]
+    pub fn accept_alpn(&mut self, protocols: &[&str]) -> &mut TlsAcceptorBuilder {
+        self.alpn = protocols.iter().map(|s| (*s).to_owned()).collect();
+        self
+    }
 
     /// Creates a new `TlsAcceptor`.
     pub fn build(&self) -> Result<TlsAcceptor> {
@@ -609,6 +621,8 @@ impl TlsAcceptor {
             identity,
             min_protocol: Some(Protocol::Tlsv10),
             max_protocol: None,
+            #[cfg(feature = "alpn")]
+            alpn: vec![],
         }
     }