Pim van Pelt
589030cb00
No runtime change — the listener already uses net.ListenUDP + ReadFromUDP, which is the unconnected-socket pattern that accepts datagrams from any source. nginx reloads (new workers with fresh ephemeral source ports) are handled transparently. - udp.go: expanded comment on Run() explaining the design choice and contrasting with the `nc -k -u -l` latching quirk (which is an nc bug, not a kernel behaviour). - udp_test.go: new TestUDPListenerMultipleSources regresses against the multi-worker scenario by sending from three independent ListenPacket sockets (three different ephemeral source ports). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
95 lines
2.6 KiB
Go
95 lines
2.6 KiB
Go
package main
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import (
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"context"
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"log"
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"net"
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"strings"
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)
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// udpReadBufBytes is the SO_RCVBUF size requested. Bursts of ~10K lines/sec at
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// ~200B each comfortably fit; the kernel may cap below this.
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const udpReadBufBytes = 4 << 20
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// udpPacketBuf is the per-read buffer. A single nginx log line easily fits in
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// a few KB; 64K is the practical UDP datagram ceiling.
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const udpPacketBuf = 64 << 10
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// UDPListener receives nginx_ipng_stats_logtail datagrams on a local socket,
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// parses each packet as one log line, and forwards LogRecords to ch.
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type UDPListener struct {
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addr string
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v4bits int
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v6bits int
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ch chan<- LogRecord
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prom *PromStore // optional; bumps UDP ingest counters
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}
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func NewUDPListener(addr string, v4bits, v6bits int, ch chan<- LogRecord) *UDPListener {
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return &UDPListener{addr: addr, v4bits: v4bits, v6bits: v6bits, ch: ch}
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}
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// SetProm wires a PromStore so the listener can report received/success/consumed counts.
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func (u *UDPListener) SetProm(p *PromStore) { u.prom = p }
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// Run listens until ctx is cancelled.
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//
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// The socket is unconnected (ListenUDP + ReadFromUDP), so every datagram is
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// accepted regardless of its source address. This matters across nginx
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// reloads: the old worker processes hold their own ephemeral send sockets,
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// and the fresh worker set opens brand-new ones. The listener reads them
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// all. (Contrast with `nc -k -u -l`, which latches onto the first peer's
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// address and silently drops packets from anyone else — that is an `nc`
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// quirk, not a kernel behaviour, and does not apply here.)
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func (u *UDPListener) Run(ctx context.Context) {
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laddr, err := net.ResolveUDPAddr("udp", u.addr)
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if err != nil {
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log.Fatalf("udp: resolve %s: %v", u.addr, err)
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}
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conn, err := net.ListenUDP("udp", laddr)
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if err != nil {
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log.Fatalf("udp: listen %s: %v", u.addr, err)
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}
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defer conn.Close()
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if err := conn.SetReadBuffer(udpReadBufBytes); err != nil {
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log.Printf("udp: SetReadBuffer(%d): %v", udpReadBufBytes, err)
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}
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log.Printf("udp: listening on %s", conn.LocalAddr())
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go func() {
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<-ctx.Done()
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conn.Close()
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}()
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buf := make([]byte, udpPacketBuf)
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for {
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n, _, err := conn.ReadFromUDP(buf)
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if err != nil {
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if ctx.Err() != nil {
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return
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}
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log.Printf("udp: read: %v", err)
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continue
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}
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if u.prom != nil {
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u.prom.IncUDPPacket()
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}
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line := strings.TrimRight(string(buf[:n]), "\r\n")
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rec, ok := ParseUDPLine(line, u.v4bits, u.v6bits)
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if !ok {
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continue
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}
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if u.prom != nil {
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u.prom.IncUDPSuccess()
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}
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select {
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case u.ch <- rec:
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if u.prom != nil {
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u.prom.IncUDPConsumed()
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}
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default:
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// Channel full — drop rather than block the read loop.
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}
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}
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}
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