openfut-bridge: handshake-independent ClientHello SNI capture

Peek the ClientHello with TcpStream::peek and parse SNI before the TLS
handshake, so we learn the hostname even when the client's ProtoSSL rejects
our self-signed cert (CertificateUnknown). tokio-rustls 0.24 lacks
LazyConfigAcceptor, so parse_sni() walks the record/handshake/extensions by
hand with full bounds checks. This is what revealed the redirected EA :443
dials as PIN/River telemetry rather than the Blaze redirector.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main.rs

@@ -94,6 +94,59 @@ fn build_router(state: ProxyState) -> Router {
         .with_state(state)
 }
 
+/// Extract the SNI host_name from a raw TLS ClientHello, if present.
+///
+/// This is handshake-independent: we parse the bytes the client sends first, so we
+/// learn the hostname even when the TLS handshake later fails (e.g. the client's
+/// ProtoSSL rejects our self-signed cert). All indexing is bounds-checked; on any
+/// malformed/short input we return None rather than panic.
+///
+/// ClientHello layout walked here: TLS record header (type=0x16, version, length) →
+/// handshake header (type=0x01, length) → client_version, 32-byte random,
+/// session_id, cipher_suites, compression_methods → extensions. The SNI extension
+/// (type 0x0000) holds a server_name_list whose first entry (name_type 0x00 =
+/// host_name) is the hostname.
+fn parse_sni(buf: &[u8]) -> Option<String> {
+    if buf.len() < 5 || buf[0] != 0x16 {
+        return None; // not a TLS handshake record
+    }
+    let mut p = 5;
+    if buf.len() < p + 4 || buf[p] != 0x01 {
+        return None; // not a ClientHello
+    }
+    p += 4; // handshake msg_type(1) + length(3)
+    p += 2 + 32; // client_version(2) + random(32)
+    let sid_len = *buf.get(p)? as usize;
+    p += 1 + sid_len;
+    let cs_len = u16::from_be_bytes([*buf.get(p)?, *buf.get(p + 1)?]) as usize;
+    p += 2 + cs_len;
+    let cm_len = *buf.get(p)? as usize;
+    p += 1 + cm_len;
+    let ext_total = u16::from_be_bytes([*buf.get(p)?, *buf.get(p + 1)?]) as usize;
+    p += 2;
+    let ext_end = (p + ext_total).min(buf.len());
+    while p + 4 <= ext_end {
+        let etype = u16::from_be_bytes([buf[p], buf[p + 1]]);
+        let elen = u16::from_be_bytes([buf[p + 2], buf[p + 3]]) as usize;
+        p += 4;
+        if p + elen > buf.len() {
+            break;
+        }
+        if etype == 0x0000 {
+            // SNI ext: server_name_list_len(2), name_type(1), name_len(2), name
+            let d = &buf[p..p + elen];
+            if d.len() >= 5 && d[2] == 0x00 {
+                let nlen = u16::from_be_bytes([d[3], d[4]]) as usize;
+                if 5 + nlen <= d.len() {
+                    return String::from_utf8(d[5..5 + nlen].to_vec()).ok();
+                }
+            }
+        }
+        p += elen;
+    }
+    None
+}
+
 async fn serve_tls(
     app: Router,
     cert_pem: Vec<u8>,
@@ -118,6 +171,23 @@ async fn serve_tls(
         let app = app.clone();
 
         tokio::spawn(async move {
+            // Peek the ClientHello (without consuming it) and log the SNI up front, so
+            // we capture the hostname even if the handshake below fails on cert pinning.
+            {
+                let mut peek = [0u8; 2048];
+                match tcp.peek(&mut peek).await {
+                    Ok(n) if n > 0 => match parse_sni(&peek[..n]) {
+                        Some(sni) => tracing::info!("ClientHello SNI (peek): {sni}"),
+                        None => tracing::info!(
+                            "ClientHello peek: no SNI ({n} bytes, first=0x{:02x})",
+                            peek[0]
+                        ),
+                    },
+                    Ok(_) => tracing::info!("ClientHello peek: 0 bytes"),
+                    Err(e) => tracing::warn!("ClientHello peek failed: {e}"),
+                }
+            }
+
             let tls_stream = match acceptor.accept(tcp).await {
                 Ok(s) => s,
                 Err(e) => {
@@ -126,7 +196,7 @@ async fn serve_tls(
                 }
             };
 
-            // Log SNI so we know which hostname the client is connecting for.
+            // Post-handshake SNI (only fires on success; the peek above is the reliable one).
             {
                 let (_, server_conn) = tls_stream.get_ref();
                 let sni = server_conn.server_name().unwrap_or("(none)");