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logger.go
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logger.go
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// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
// Package logger defines a type for writing to logs. It's just a
// convenience type so that we don't have to pass verbose func(...)
// types around.
package logger
import (
"bufio"
"bytes"
"container/list"
"encoding/json"
"fmt"
"io"
"log"
"strings"
"sync"
"time"
"context"
"go4.org/mem"
"tailscale.com/envknob"
"tailscale.com/util/ctxkey"
)
// Logf is the basic Tailscale logger type: a printf-like func.
// Like log.Printf, the format need not end in a newline.
// Logf functions must be safe for concurrent use.
type Logf func(format string, args ...any)
// LogfKey stores and loads [Logf] values within a [context.Context].
var LogfKey = ctxkey.New("", Logf(log.Printf))
// A Context is a context.Context that should contain a custom log function, obtainable from FromContext.
// If no log function is present, FromContext will return log.Printf.
// To construct a Context, use Add
//
// Deprecated: Do not use.
type Context context.Context
// jenc is a json.Encode + bytes.Buffer pair wired up to be reused in a pool.
type jenc struct {
buf bytes.Buffer
enc *json.Encoder
}
var jencPool = &sync.Pool{New: func() any {
je := new(jenc)
je.enc = json.NewEncoder(&je.buf)
return je
}}
// JSON marshals v as JSON and writes it to logf formatted with the annotation to make logtail
// treat it as a structured log.
//
// The recType is the record type and becomes the key of the wrapper
// JSON object that is logged. That is, if recType is "foo" and v is
// 123, the value logged is {"foo":123}.
//
// Do not use recType "logtail", "v", "text", or "metrics", with any case.
// Those are reserved for the logging system.
//
// The level can be from 0 to 9. Levels from 1 to 9 are included in
// the logged JSON object, like {"foo":123,"v":2}.
func (logf Logf) JSON(level int, recType string, v any) {
je := jencPool.Get().(*jenc)
defer jencPool.Put(je)
je.buf.Reset()
je.buf.WriteByte('{')
je.enc.Encode(recType)
je.buf.Truncate(je.buf.Len() - 1) // remove newline from prior Encode
je.buf.WriteByte(':')
if err := je.enc.Encode(v); err != nil {
logf("[unexpected]: failed to encode structured JSON log record of type %q / %T: %v", recType, v, err)
return
}
je.buf.Truncate(je.buf.Len() - 1) // remove newline from prior Encode
je.buf.WriteByte('}')
// Magic prefix recognized by logtail:
logf("[v\x00JSON]%d%s", level%10, je.buf.Bytes())
}
// FromContext extracts a log function from ctx.
//
// Deprecated: Use [LogfKey.Value] instead.
func FromContext(ctx Context) Logf {
return LogfKey.Value(ctx)
}
// Ctx constructs a Context from ctx with fn as its custom log function.
//
// Deprecated: Use [LogfKey.WithValue] instead.
func Ctx(ctx context.Context, fn Logf) Context {
return LogfKey.WithValue(ctx, fn)
}
// WithPrefix wraps f, prefixing each format with the provided prefix.
func WithPrefix(f Logf, prefix string) Logf {
return func(format string, args ...any) {
f(prefix+format, args...)
}
}
// FuncWriter returns an io.Writer that writes to f.
func FuncWriter(f Logf) io.Writer {
return funcWriter{f}
}
// StdLogger returns a standard library logger from a Logf.
func StdLogger(f Logf) *log.Logger {
return log.New(FuncWriter(f), "", 0)
}
type funcWriter struct{ f Logf }
func (w funcWriter) Write(p []byte) (int, error) {
w.f("%s", p)
return len(p), nil
}
// Discard is a Logf that throws away the logs given to it.
func Discard(string, ...any) {}
// limitData is used to keep track of each format string's associated
// rate-limiting data.
type limitData struct {
bucket *tokenBucket // the token bucket associated with this string
nBlocked int // number of messages skipped
ele *list.Element // list element used to access this string in the cache
}
// rateFree are format string substrings that are exempt from rate limiting.
// Things should not be added to this unless they're already limited otherwise
// or are critical for generating important stats from the logs.
var rateFree = []string{
"magicsock: disco: ",
"magicsock: ParseEndpoint:",
// grinder stats lines
"SetPrefs: %v",
"peer keys: %s",
"v%v peers: %v",
// debug messages printed by 'tailscale bugreport'
"diag: ",
}
// RateLimitedFn is a wrapper for RateLimitedFnWithClock that includes the
// current time automatically. This is mainly for backward compatibility.
func RateLimitedFn(logf Logf, f time.Duration, burst int, maxCache int) Logf {
return RateLimitedFnWithClock(logf, f, burst, maxCache, time.Now)
}
// RateLimitedFnWithClock returns a rate-limiting Logf wrapping the given
// logf. Messages are allowed through at a maximum of one message every f
// (where f is a time.Duration), in bursts of up to burst messages at a
// time. Up to maxCache format strings will be tracked separately.
// timeNow is a function that returns the current time, used for calculating
// rate limits.
func RateLimitedFnWithClock(logf Logf, f time.Duration, burst int, maxCache int, timeNow func() time.Time) Logf {
if envknob.String("TS_DEBUG_LOG_RATE") == "all" {
return logf
}
var (
mu sync.Mutex
msgLim = make(map[string]*limitData) // keyed by logf format
msgCache = list.New() // a rudimentary LRU that limits the size of the map
)
return func(format string, args ...any) {
// Shortcut for formats with no rate limit
for _, sub := range rateFree {
if strings.Contains(format, sub) {
logf(format, args...)
return
}
}
mu.Lock()
rl, ok := msgLim[format]
if ok {
msgCache.MoveToFront(rl.ele)
} else {
rl = &limitData{
bucket: newTokenBucket(f, burst, timeNow()),
ele: msgCache.PushFront(format),
}
msgLim[format] = rl
if msgCache.Len() > maxCache {
delete(msgLim, msgCache.Back().Value.(string))
msgCache.Remove(msgCache.Back())
}
}
rl.bucket.AdvanceTo(timeNow())
// Make sure there's enough room for at least a few
// more logs before we unblock, so we don't alternate
// between blocking and unblocking.
if rl.nBlocked > 0 && rl.bucket.remaining >= 2 {
// Only print this if we dropped more than 1
// message. Otherwise we'd *increase* the total
// number of log lines printed.
if rl.nBlocked > 1 {
logf("[RATELIMIT] format(%q) (%d dropped)",
format, rl.nBlocked-1)
}
rl.nBlocked = 0
}
if rl.nBlocked == 0 && rl.bucket.Get() {
hitLimit := rl.bucket.remaining == 0
if hitLimit {
// Enter "blocked" mode immediately after
// reaching the burst limit. We want to
// always accompany the format() message
// with an example of the format, which is
// effectively the same as printing the
// message anyway. But this way they can
// be on two separate lines and we don't
// corrupt the original message.
rl.nBlocked = 1
}
mu.Unlock() // release before calling logf
logf(format, args...)
if hitLimit {
logf("[RATELIMIT] format(%q)", format)
}
} else {
rl.nBlocked++
mu.Unlock()
}
}
}
// SlowLoggerWithClock is a logger that applies rate limits similar to
// RateLimitedFnWithClock, but instead of dropping logs will sleep until they
// can be written. This should only be used for debug logs, and not in a hot path.
//
// The provided context, if canceled, will cause all logs to be dropped and
// prevent any sleeps.
func SlowLoggerWithClock(ctx context.Context, logf Logf, f time.Duration, burst int, timeNow func() time.Time) Logf {
var (
mu sync.Mutex
tb = newTokenBucket(f, burst, timeNow())
)
return func(format string, args ...any) {
if ctx.Err() != nil {
return
}
// Hold the mutex for the entire length of the check + log
// since our token bucket isn't concurrency-safe.
mu.Lock()
defer mu.Unlock()
tb.AdvanceTo(timeNow())
// If we can get a token, then do that and return.
if tb.Get() {
logf(format, args...)
return
}
// Otherwise, sleep for 2x the duration so that we don't
// immediately sleep again on the next call.
tmr := time.NewTimer(2 * f)
defer tmr.Stop()
select {
case curr := <-tmr.C:
tb.AdvanceTo(curr)
case <-ctx.Done():
return
}
if !tb.Get() {
log.Printf("[unexpected] error rate-limiting in SlowLoggerWithClock")
return
}
logf(format, args...)
}
}
// LogOnChange logs a given line only if line != lastLine, or if maxInterval has passed
// since the last time this identical line was logged.
func LogOnChange(logf Logf, maxInterval time.Duration, timeNow func() time.Time) Logf {
var (
mu sync.Mutex
sLastLogged string
tLastLogged = timeNow()
)
return func(format string, args ...any) {
s := fmt.Sprintf(format, args...)
mu.Lock()
if s == sLastLogged && timeNow().Sub(tLastLogged) < maxInterval {
mu.Unlock()
return
}
sLastLogged = s
tLastLogged = timeNow()
mu.Unlock()
// Re-stringify it (instead of using "%s", s) so something like "%s"
// doesn't end up getting rate-limited. (And can't use 's' as the pattern,
// as it might contain formatting directives.)
logf(format, args...)
}
}
// ArgWriter is a fmt.Formatter that can be passed to any Logf func to
// efficiently write to a %v argument without allocations.
type ArgWriter func(*bufio.Writer)
func (fn ArgWriter) Format(f fmt.State, _ rune) {
bw := argBufioPool.Get().(*bufio.Writer)
bw.Reset(f)
fn(bw)
bw.Flush()
argBufioPool.Put(bw)
}
var argBufioPool = &sync.Pool{New: func() any { return bufio.NewWriterSize(io.Discard, 1024) }}
// Filtered returns a Logf that silently swallows some log lines.
// Each inbound format and args is evaluated and printed to a string s.
// The original format and args are passed to logf if and only if allow(s) returns true.
func Filtered(logf Logf, allow func(s string) bool) Logf {
return func(format string, args ...any) {
msg := fmt.Sprintf(format, args...)
if !allow(msg) {
return
}
logf(format, args...)
}
}
// LogfCloser wraps logf to create a logger that can be closed.
// Calling close makes all future calls to newLogf into no-ops.
func LogfCloser(logf Logf) (newLogf Logf, close func()) {
var (
mu sync.Mutex
closed bool
)
close = func() {
mu.Lock()
defer mu.Unlock()
closed = true
}
newLogf = func(msg string, args ...any) {
mu.Lock()
if closed {
mu.Unlock()
return
}
mu.Unlock()
logf(msg, args...)
}
return newLogf, close
}
// AsJSON returns a formatter that formats v as JSON. The value is suitable to
// passing to a regular %v printf argument. (%s is not required)
//
// If json.Marshal returns an error, the output is "%%!JSON-ERROR:" followed by
// the error string.
func AsJSON(v any) fmt.Formatter {
return asJSONResult{v}
}
type asJSONResult struct{ v any }
func (a asJSONResult) Format(s fmt.State, verb rune) {
v, err := json.Marshal(a.v)
if err != nil {
fmt.Fprintf(s, "%%!JSON-ERROR:%v", err)
return
}
s.Write(v)
}
// TBLogger is the testing.TB subset needed by TestLogger.
type TBLogger interface {
Helper()
Logf(format string, args ...any)
}
// TestLogger returns a logger that logs to tb.Logf
// with a prefix to make it easier to distinguish spam
// from explicit test failures.
func TestLogger(tb TBLogger) Logf {
return func(format string, args ...any) {
tb.Helper()
tb.Logf(" ... "+format, args...)
}
}
// HTTPServerLogFilter is an io.Writer that can be used as the
// net/http.Server.ErrorLog logger, and will filter out noisy, low-signal
// messages that clutter up logs.
type HTTPServerLogFilter struct {
Inner Logf
}
func (lf HTTPServerLogFilter) Write(p []byte) (int, error) {
b := mem.B(p)
if mem.HasSuffix(b, mem.S(": EOF\n")) ||
mem.HasSuffix(b, mem.S(": i/o timeout\n")) ||
mem.HasSuffix(b, mem.S(": read: connection reset by peer\n")) ||
mem.HasSuffix(b, mem.S(": remote error: tls: bad certificate\n")) ||
mem.HasSuffix(b, mem.S(": tls: first record does not look like a TLS handshake\n")) {
// Skip this log message, but say that we processed it
return len(p), nil
}
lf.Inner("%s", p)
return len(p), nil
}