Don't panic decoding unknown header types on eventstream (#3355)

Author: Madrigal

aws/protocol/eventstream/debug.go

@@ -139,6 +139,6 @@ func valueFromType(typ valueType, val any) (Value, error) {
 		copy(tv[:], v)
 		return tv, err
 	default:
-		panic(fmt.Sprintf("unknown type, %s, %T", typ.String(), val))
+		return nil, fmt.Errorf("unable to decode unknown type, %s, %T", typ.String(), val)
 	}
 }

aws/protocol/eventstream/header.go

@@ -151,7 +151,7 @@ func decodeHeaderValue(r io.Reader) (Value, error) {
 		err = tv.decode(r)
 		v = tv
 	default:
-		panic(fmt.Sprintf("unknown value type %d", raw.Type))
+		return nil, fmt.Errorf("unable to decode header of unknown value type %d", raw.Type)
 	}
 
 	// Error could be EOF, let caller deal with it

aws/protocol/eventstream/header_test.go

@@ -1,6 +1,7 @@
 package eventstream
 
 import (
+	"bytes"
 	"reflect"
 	"testing"
 	"time"
@@ -64,3 +65,16 @@ func TestHeaders_Del(t *testing.T) {
 		t.Errorf("expect %v headers, got %v", e, a)
 	}
 }
+
+func TestHeaders_UnknownType(t *testing.T) {
+	buf := bytes.NewBuffer(nil)
+	buf.WriteByte(3)       // header name length
+	buf.WriteString("foo") // header name
+	buf.WriteByte(0xFF)    // unknown value type
+
+	_, err := decodeHeaders(buf)
+	// This shouldn't panic and should return an error
+	if err == nil {
+		t.Fatal("expect error for unknown header value type, got none")
+	}
+}