`(*PacketSource).packetsToChannel()` error handling is incomplete

[Gaukas Wang]

TL;DR

The error handling in (*PacketSource).packetsToChannel() is incomplete and may lead to starvation. A catch-all rule is missing.

Minimal Example

Implementation

	f, _ := os.Open("../testdata/somepackets.pcap")
	defer f.Close()
	r, _ := pcapgo.NewReader(f)

	pktsrc := gopacket.NewPacketSource(r, r.LinkType())
	
	f.Close() // close the reader here

	for packet := range pktsrc.Packets() { // this will block after the last packets
		// do something
	}

Behavior

The program hangs instead of terminating.

Analysis

gopacket/packet.go

Lines 815 to 845 in 32ee382

 func (p *PacketSource) packetsToChannel() { 
 	defer close(p.c) 
 	for { 
 		packet, err := p.NextPacket() 
 		if err == nil { 
 			p.c <- packet 
 			continue 
 		} 
  
 		// Immediately retry for temporary network errors 
 		if nerr, ok := err.(net.Error); ok && nerr.Temporary() { 
 			continue 
 		} 
  
 		// Immediately retry for EAGAIN 
 		if err == syscall.EAGAIN { 
 			continue 
 		} 
  
 		// Immediately break for known unrecoverable errors 
 		if err == io.EOF || err == io.ErrUnexpectedEOF || 
 			err == io.ErrNoProgress || err == io.ErrClosedPipe || err == io.ErrShortBuffer || 
 			err == syscall.EBADF || 
 			strings.Contains(err.Error(), "use of closed file") { 
 			break 
 		} 
  
 		// Sleep briefly and try again 
 		time.Sleep(time.Millisecond * time.Duration(5)) 
 	} 
 } 

The function implementation missed the case where the returned error is not matched to any known cases.

In the current latest version of Go (1.21.4), (*os.File).Read() returns read /path/to/the/file: file already closed, which wraps os.ErrClosed and could be tested with errors.Is(err, os.ErrClosed), but is not equal to any existing error. Therefore it will not break out of the for loop and the channel will never be closed.

Proposed fix

• Testing against known errors should use errors.Is or its equivalent, not err == ErrToCompare.
• Should also add a catch-all case for unknown errors, since it is possible for the user to use a custom io.Reader.

I'd be happy to open a PR if the proposed fix sounds reasonable.

[Gaukas Wang]

Just realized errors.Is is added in Go 1.13. Since the go.mod of this package still specifies go 1.12, either we will create version-dependent packet.go file for Go 1.13 and above, or we shall bump up the minimum required version.