streaming

commit e6908ad17804237bb7f0669edc99e86339a18d84
parent 48bf5f705fadc940d6218ec5051f86d002541015
Author: Oliver Lowe <o@olowe.co>
Date:   Fri,  9 Aug 2024 20:33:55 +1000

pcap: support only current savefile version

Reduces the stuff our package exposes. As a bonus we actually return
an error if somehow we try to decode a file we may not be able to
safely such as older, newer or invalid versions.

Diffstat:
M
pcap/pcap.go
 | 
26
++++++++++++++++++--------
M
pcap/pcap_test.go
 | 
4
+---

2 files changed, 19 insertions(+), 11 deletions(-)
diff --git a/pcap/pcap.go b/pcap/pcap.go
@@ -17,13 +17,13 @@ const (
 	magicBigEndian    uint32 = 0xd4c3b2a1
 )
 
+var version = [2]uint16{2, 4}
+
 type GlobalHeader struct {
-	VersionMajor uint16
-	VersionMinor uint16
-	_            int32 // leftover from old pcap versions
-	_            int32 // leftover from old pcap versions
-	SnapLen      uint32
-	Network      uint32
+	_       int32 // leftover from old pcap versions
+	_       int32 // leftover from old pcap versions
+	SnapLen uint32
+	Network uint32
 }
 
 type Header struct {
@@ -57,9 +57,17 @@ func decode(reader io.Reader) (*File, error) {
 		return nil, fmt.Errorf("unknown magic number %#x", magic)
 	}
 
+	var v [2]uint16
+	if err := binary.Read(reader, binary.LittleEndian, &v); err != nil {
+		return nil, fmt.Errorf("read pcap version: %w", err)
+	}
+	if v != version {
+		return nil, fmt.Errorf("unsupported version %d.%d", v[0], v[1])
+	}
+
 	var gheader GlobalHeader
 	if err := binary.Read(reader, binary.LittleEndian, &gheader); err != nil {
-		return nil, fmt.Errorf("read global header: %w", err)
+		return nil, fmt.Errorf("read pcap version: %w", err)
 	}
 
 	var packets []Packet
@@ -94,8 +102,10 @@ func decode(reader io.Reader) (*File, error) {
 }
 
 func encode(file *File) ([]byte, error) {
-	b := make([]byte, 4)
+	b := make([]byte, 4+4) // magic + version
 	binary.NativeEndian.PutUint32(b, magicLittleEndian)
+	binary.NativeEndian.PutUint16(b[4:6], version[0])
+	binary.NativeEndian.PutUint16(b[6:8], version[1])
 	buf := bytes.NewBuffer(b)
 	if err := binary.Write(buf, binary.LittleEndian, &file.Header); err != nil {
 		return nil, fmt.Errorf("global header: %v", err)
diff --git a/pcap/pcap_test.go b/pcap/pcap_test.go
@@ -15,9 +15,7 @@ func TestDecode(t *testing.T) {
 	defer f.Close()
 
 	gheader := GlobalHeader{
-		VersionMajor: 2,
-		VersionMinor: 4,
-		SnapLen:      524288,
+		SnapLen: 524288,
 	}
 	header := Header{
 		// from tcpdump -tt -r testdata/text_udp.pcap