logpolicy: expose MaxBufferSize and MaxUploadSize options (#14903)

Updates tailscale/corp#26342

Signed-off-by: Joe Tsai <joetsai@digital-static.net>

logpolicy/logpolicy.go

@@ -503,6 +503,18 @@ type Options struct {
 	// If nil, [TransportOptions.New] is used to construct a new client
 	// with that particular transport sending logs to the default logs server.
 	HTTPC *http.Client
+
+	// MaxBufferSize is the maximum size of the log buffer.
+	// This controls the amount of logs that can be temporarily stored
+	// before the logs can be successfully upload.
+	// If zero, a default buffer size is chosen.
+	MaxBufferSize int
+
+	// MaxUploadSize is the maximum size per upload.
+	// This should only be set by clients that have been authenticated
+	// with the logging service as having a higher upload limit.
+	// If zero, a default upload size is chosen.
+	MaxUploadSize int
 }
 
 // New returns a new log policy (a logger and its instance ID).
@@ -603,10 +615,11 @@ func (opts Options) New() *Policy {
 	}
 
 	conf := logtail.Config{
-		Collection:   newc.Collection,
-		PrivateID:    newc.PrivateID,
-		Stderr:       logWriter{console},
-		CompressLogs: true,
+		Collection:    newc.Collection,
+		PrivateID:     newc.PrivateID,
+		Stderr:        logWriter{console},
+		CompressLogs:  true,
+		MaxUploadSize: opts.MaxUploadSize,
 	}
 	if opts.Collection == logtail.CollectionNode {
 		conf.MetricsDelta = clientmetric.EncodeLogTailMetricsDelta
@@ -620,7 +633,7 @@ func (opts Options) New() *Policy {
 	} else {
 		// Only attach an on-disk filch buffer if we are going to be sending logs.
 		// No reason to persist them locally just to drop them later.
-		attachFilchBuffer(&conf, opts.Dir, opts.CmdName, opts.Logf)
+		attachFilchBuffer(&conf, opts.Dir, opts.CmdName, opts.MaxBufferSize, opts.Logf)
 		conf.HTTPC = opts.HTTPC
 
 		if conf.HTTPC == nil {
@@ -676,9 +689,10 @@ func (opts Options) New() *Policy {
 // attachFilchBuffer creates an on-disk ring buffer using filch and attaches
 // it to the logtail config. Note that this is optional; if no buffer is set,
 // logtail will use an in-memory buffer.
-func attachFilchBuffer(conf *logtail.Config, dir, cmdName string, logf logger.Logf) {
+func attachFilchBuffer(conf *logtail.Config, dir, cmdName string, maxFileSize int, logf logger.Logf) {
 	filchOptions := filch.Options{
 		ReplaceStderr: redirectStderrToLogPanics(),
+		MaxFileSize:   maxFileSize,
 	}
 	filchPrefix := filepath.Join(dir, cmdName)
 

logtail/logtail.go

@@ -6,6 +6,7 @@ package logtail
 
 import (
 	"bytes"
+	"cmp"
 	"context"
 	"crypto/rand"
 	"encoding/binary"
@@ -78,6 +79,7 @@ type Config struct {
 	StderrLevel    int             // max verbosity level to write to stderr; 0 means the non-verbose messages only
 	Buffer         Buffer          // temp storage, if nil a MemoryBuffer
 	CompressLogs   bool            // whether to compress the log uploads
+	MaxUploadSize  int             // maximum upload size; 0 means using the default
 
 	// MetricsDelta, if non-nil, is a func that returns an encoding
 	// delta in clientmetrics to upload alongside existing logs.
@@ -157,6 +159,7 @@ func NewLogger(cfg Config, logf tslogger.Logf) *Logger {
 		url:            cfg.BaseURL + "/c/" + cfg.Collection + "/" + cfg.PrivateID.String() + urlSuffix,
 		lowMem:         cfg.LowMemory,
 		buffer:         cfg.Buffer,
+		maxUploadSize:  cfg.MaxUploadSize,
 		skipClientTime: cfg.SkipClientTime,
 		drainWake:      make(chan struct{}, 1),
 		sentinel:       make(chan int32, 16),
@@ -192,6 +195,7 @@ type Logger struct {
 	skipClientTime bool
 	netMonitor     *netmon.Monitor
 	buffer         Buffer
+	maxUploadSize  int
 	drainWake      chan struct{}        // signal to speed up drain
 	drainBuf       []byte               // owned by drainPending for reuse
 	flushDelayFn   func() time.Duration // negative or zero return value to upload aggressively, or >0 to batch at this delay
@@ -325,7 +329,7 @@ func (l *Logger) drainPending() (b []byte) {
 		}
 	}()
 
-	maxLen := maxSize
+	maxLen := cmp.Or(l.maxUploadSize, maxSize)
 	if l.lowMem {
 		// When operating in a low memory environment, it is better to upload
 		// in multiple operations than it is to allocate a large body and OOM.
@@ -775,9 +779,10 @@ func (l *Logger) appendTextOrJSONLocked(dst, src []byte, level int) []byte {
 	// That's okay as the Tailscale log service limit is actually 2*maxSize.
 	// However, so long as logging applications aim to target the maxSize limit,
 	// there should be no trouble eventually uploading logs.
-	if len(src) > maxSize {
+	maxLen := cmp.Or(l.maxUploadSize, maxSize)
+	if len(src) > maxLen {
 		errDetail := fmt.Sprintf("entry too large: %d bytes", len(src))
-		errData := appendTruncatedString(nil, src, maxSize/len(`\uffff`)) // escaping could increase size
+		errData := appendTruncatedString(nil, src, maxLen/len(`\uffff`)) // escaping could increase size
 
 		dst = append(dst, '{')
 		dst = l.appendMetadata(dst, l.skipClientTime, true, l.procID, l.procSequence, errDetail, errData, level)