raise ParserWarn instead of error on bad net-message decryption key (#342)

fixes #326

Author: markus-wa

examples/encrypted-net-messages/enc_net_msg.go

@@ -47,6 +47,10 @@ func main() {
 
 	p := dem.NewParserWithConfig(f, cfg)
 
+	p.RegisterEventHandler(func(warn events.ParserWarn) {
+		log.Println("WARNING:", warn.Message)
+	})
+
 	p.RegisterEventHandler(func(message events.ChatMessage) {
 		log.Println(message)
 	})

examples/encrypted-net-messages/enc_net_msg_test.go

@@ -15,3 +15,14 @@ func TestEncryptedNetMessages(t *testing.T) {
 
 	main()
 }
+
+// Make sure it doesn't error / crash
+func TestEncryptedNetMessages_BadKey(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test")
+	}
+
+	os.Args = []string{"cmd", "-demo", "../../test/cs-demos/match730_003528806449641685104_1453182610_271.dem", "-info", "../../test/cs-demos/match730_003449478367177343081_1946274414_112.dem.info"}
+
+	main()
+}

pkg/demoinfocs/demoinfocs_test.go

@@ -282,6 +282,51 @@ func TestUnexpectedEndOfDemo(t *testing.T) {
 	assert.Equal(t, demoinfocs.ErrUnexpectedEndOfDemo, err, "parsing cancelled but error was not ErrUnexpectedEndOfDemo")
 }
 
+func TestBadNetMessageDecryptionKey(t *testing.T) {
+	t.Parallel()
+
+	if testing.Short() {
+		t.Skip("skipping test due to -short flag")
+	}
+
+	const (
+		demPath  = csDemosPath + "/match730_003528806449641685104_1453182610_271.dem"
+		infoPath = csDemosPath + "/match730_003449478367177343081_1946274414_112.dem.info"
+	)
+
+	infoF, err := os.Open(infoPath)
+	assert.NoError(t, err)
+
+	b, err := ioutil.ReadAll(infoF)
+	assert.NoError(t, err)
+
+	k, err := demoinfocs.MatchInfoDecryptionKey(b)
+	assert.NoError(t, err)
+
+	f, err := os.Open(demPath)
+	assert.NoError(t, err)
+
+	defer f.Close()
+
+	cfg := demoinfocs.DefaultParserConfig
+	cfg.NetMessageDecryptionKey = k
+
+	p := demoinfocs.NewParserWithConfig(f, cfg)
+
+	var cantReadEncNetMsgWarns []events.ParserWarn
+
+	p.RegisterEventHandler(func(warn events.ParserWarn) {
+		if warn.Type == events.WarnTypeCantReadEncryptedNetMessage {
+			cantReadEncNetMsgWarns = append(cantReadEncNetMsgWarns, warn)
+		}
+	})
+
+	err = p.ParseToEnd()
+	assert.NoError(t, err)
+
+	assert.NotEmpty(t, cantReadEncNetMsgWarns)
+}
+
 func TestParseToEnd_Cancel(t *testing.T) {
 	t.Parallel()
 

pkg/demoinfocs/events/events.go

@@ -523,9 +523,14 @@ const (
 	WarnTypeTeamSwapPlayerNil          // TODO: figure out why this happens
 	WarnTypeGameEventBeforeDescriptors // may occur in POV demos
 
-	// WarnTypeMissingNetMessageDecryptionKey occurs when encrypted net-messages are encountered and the decryption key is missing
+	// WarnTypeMissingNetMessageDecryptionKey occurs when encrypted net-messages are encountered and the decryption key is missing.
 	// See ParserConfig.NetMessageDecryptionKey
 	WarnTypeMissingNetMessageDecryptionKey
+
+	// WarnTypeCantReadEncryptedNetMessage occurs when an encrypted net-messages can't be decrypted even though the decryption key is set.
+	// May occur because the decryption key used is incorrect.
+	// See ParserConfig.NetMessageDecryptionKey
+	WarnTypeCantReadEncryptedNetMessage
 )
 
 // ParserWarn signals that a non-fatal problem occurred during parsing.

pkg/demoinfocs/net_messages.go

@@ -5,7 +5,6 @@ import (
 	"encoding/binary"
 
 	"github.com/gogo/protobuf/proto"
-	"github.com/markus-wa/go-unassert"
 	"github.com/markus-wa/ice-cipher-go/pkg/ice"
 
 	bit "github.com/markus-wa/demoinfocs-golang/v2/internal/bitread"
@@ -97,13 +96,35 @@ func (p *parser) handleEncryptedData(msg *msg.CSVCMsg_EncryptedData) {
 	r := bytes.NewReader(b)
 	br := bit.NewSmallBitReader(r)
 
+	const (
+		byteLenPadding = 1
+		byteLenWritten = 4
+	)
+
 	paddingBytes := br.ReadSingleByte()
+
+	if int(paddingBytes) >= len(b)-byteLenPadding-byteLenWritten {
+		p.eventDispatcher.Dispatch(events.ParserWarn{
+			Message: "encrypted net-message has invalid number of padding bytes",
+			Type:    events.WarnTypeCantReadEncryptedNetMessage,
+		})
+
+		return
+	}
+
 	br.Skip(int(paddingBytes) << 3)
 
 	bBytesWritten := br.ReadBytes(4)
 	nBytesWritten := int(binary.BigEndian.Uint32(bBytesWritten))
 
-	unassert.Same(len(b), 5+int(paddingBytes)+nBytesWritten)
+	if len(b) != byteLenPadding+byteLenWritten+int(paddingBytes)+nBytesWritten {
+		p.eventDispatcher.Dispatch(events.ParserWarn{
+			Message: "encrypted net-message has invalid length",
+			Type:    events.WarnTypeCantReadEncryptedNetMessage,
+		})
+
+		return
+	}
 
 	cmd := br.ReadVarInt32()
 	size := br.ReadVarInt32()