/
listener.go
151 lines (122 loc) · 3.36 KB
/
listener.go
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package capture
import (
"errors"
"fmt"
"io"
"sync"
"github.com/google/gopacket"
"github.com/google/gopacket/pcap"
"github.com/rename-this/vhs/core"
// See https://pkg.go.dev/github.com/google/gopacket?tab=doc#hdr-A_Final_Note
_ "github.com/google/gopacket/layers"
)
// NewListener creates a new listener.
func NewListener(cap *Capture) Listener {
return &listener{
Capture: cap,
packets: make(chan gopacket.Packet),
}
}
// Listener listens for network traffic on a
// given address and port.
type Listener interface {
Packets() <-chan gopacket.Packet
Listen(core.Context)
Close()
}
type listener struct {
Capture *Capture
packets chan gopacket.Packet
handleMu sync.Mutex
handles []*pcap.Handle
}
// Packets retrieves a channel for all packets
// captured by this listener.
func (l *listener) Packets() <-chan gopacket.Packet {
return l.packets
}
// Listen starts listening.
func (l *listener) Listen(ctx core.Context) {
ctx.Logger = ctx.Logger.With().
Str(core.LoggerKeyComponent, "listener").
Logger()
for _, i := range l.Capture.Interfaces {
if h, err := l.newHandle(ctx, i, (*pcap.InactiveHandle).Activate); err != nil {
ctx.Errors <- err
} else {
go l.readPackets(ctx, h, h.LinkType())
}
}
}
type activateFn func(inactive *pcap.InactiveHandle) (*pcap.Handle, error)
func (l *listener) newHandle(ctx core.Context, i pcap.Interface, activate activateFn) (*pcap.Handle, error) {
ctx.Logger = ctx.Logger.With().
Interface("interface", i).
Logger()
ctx.Logger.Debug().Msg("creating new handle")
inactive, err := l.newInactiveHandler(i.Name)
if err != nil {
ctx.Logger.Debug().Err(err).Msgf("failed to create inactive handle for %s", i.Name)
return nil, nil
}
defer inactive.CleanUp()
handle, err := activate(inactive)
if err != nil {
return nil, fmt.Errorf("failed to activate %s: %w", i.Name, err)
}
ctx.Logger.Debug().Msg("handle activated")
filter := newBPFFilter(l.Capture, i)
ctx.Logger.Debug().Str("filter", filter).Msg("bpf filter created")
if err := handle.SetBPFFilter(filter); err != nil {
return nil, fmt.Errorf("failed to set filter: %w", err)
}
l.handleMu.Lock()
l.handles = append(l.handles, handle)
l.handleMu.Unlock()
return handle, nil
}
func (l *listener) readPackets(ctx core.Context, dataSource gopacket.PacketDataSource, decoder gopacket.Decoder) {
source := gopacket.NewPacketSource(dataSource, decoder)
source.Lazy = true
source.NoCopy = true
for {
select {
case <-ctx.StdContext.Done():
return
default:
p, err := source.NextPacket()
if errors.Is(err, io.EOF) {
continue
}
if err != nil {
if ctx.Config.DebugPackets {
ctx.Logger.Debug().Err(err).Msg("read packet failed")
}
continue
}
if ctx.Config.DebugPackets {
ctx.Logger.Debug().Str("p", p.String()).Msg("packet")
}
l.packets <- p
}
}
}
func (l *listener) newInactiveHandler(name string) (*pcap.InactiveHandle, error) {
inactive, err := pcap.NewInactiveHandle(name)
if err != nil {
return nil, fmt.Errorf("failed to create inactive handle: %w", err)
}
inactive.SetPromisc(true)
inactive.SetTimeout(pcap.BlockForever)
inactive.SetImmediateMode(true)
inactive.SetSnapLen(65536)
return inactive, nil
}
// Close closes the listener and all open handles.
func (l *listener) Close() {
l.handleMu.Lock()
defer l.handleMu.Unlock()
for _, handle := range l.handles {
handle.Close()
}
}