Fix server crash when connection fails during TLS protocol detection

Wrap peek errors as temporary so http.Server retries instead of exiting.
This fixes crashes on Windows where security software or browsers may
connect and immediately disconnect during certificate pre-checks.

Also adds a 5-second read deadline during peek to prevent hanging on
slow or malicious clients.

Author: AlbertMN

internal/certs/mux.go

@@ -3,8 +3,20 @@ package certs
 import (
 	"crypto/tls"
 	"net"
+	"time"
 )
 
+// tempError wraps an error to be treated as temporary by http.Server.
+// This prevents the server from exiting when a connection fails during
+// protocol detection (e.g., client disconnects before sending data).
+type tempError struct {
+	err error
+}
+
+func (e *tempError) Error() string   { return e.err.Error() }
+func (e *tempError) Timeout() bool   { return false }
+func (e *tempError) Temporary() bool { return true }
+
 // MuxListener wraps a net.Listener and routes connections to either
 // TLS or plain HTTP based on the first byte of the connection.
 // TLS connections start with 0x16 (TLS handshake), HTTP starts with ASCII.
@@ -29,12 +41,20 @@ func (m *MuxListener) Accept() (net.Conn, error) {
 		return nil, err
 	}
 
+	// Set a deadline for the peek to avoid hanging on slow/malicious clients
+	conn.SetReadDeadline(time.Now().Add(5 * time.Second))
+
 	// Wrap connection to peek at first byte
 	pc := &peekConn{Conn: conn}
 	b, err := pc.peek()
+
+	// Clear the deadline for normal operation
+	conn.SetReadDeadline(time.Time{})
+
 	if err != nil {
 		conn.Close()
-		return nil, err
+		// Wrap as temporary error so http.Server retries instead of exiting
+		return nil, &tempError{err: err}
 	}
 
 	// TLS handshake starts with 0x16 (ContentType: Handshake)