rewrite uuidPrefix to not drop lines

helpers.go

@@ -1,36 +1,53 @@
 package main
 
 import (
-	"bufio"
+	"bytes"
 	"errors"
 	"fmt"
 	"io"
 	"strings"
 	"time"
 
 	"github.com/robfig/cron"
-	"golang.org/x/sync/errgroup"
+	"github.com/rs/xid"
 )
 
-func uuidPrefix(dest io.Writer, errGrp *errgroup.Group, uuid []byte) io.WriteCloser {
-	out, in := io.Pipe()
-	s := bufio.NewScanner(out)
-	errGrp.Go(func() (err error) {
-		for s.Scan() {
-			line := s.Bytes()
-			log := make([]byte, len(uuid)+len(line)+2)
-			pos := 0
-			for _, b := range [][]byte{uuid, []byte(" "), line, []byte("\n")} {
-				pos += copy(log[pos:], b)
-			}
-			_, err = dest.Write(log)
-			if err != nil {
-				return err
-			}
+// uuidPrefixer is a io.Writer that prefixes every line with UUID
+type uuidPrefixer struct {
+	uuid          []byte
+	writer        io.Writer
+	buf           *bytes.Buffer
+	lastIsNewline bool
+}
+
+// newUUIDPrefixer generates a new uuidPrefixer with an UUID
+func newUUIDPrefixer(dest io.Writer) *uuidPrefixer {
+	return &uuidPrefixer{
+		uuid:          []byte(xid.New().String() + " "),
+		writer:        dest,
+		buf:           bytes.NewBuffer(nil),
+		lastIsNewline: true,
+	}
+}
+
+// Write satisfies golang io.Writer
+func (prefixer *uuidPrefixer) Write(p []byte) (int, error) {
+	prefixer.buf.Reset()
+	for _, b := range p {
+		if prefixer.lastIsNewline {
+			prefixer.buf.Write(prefixer.uuid)
+			prefixer.lastIsNewline = false
+		}
+		prefixer.buf.WriteByte(b)
+		if b == '\n' {
+			prefixer.lastIsNewline = true
 		}
-		return
-	})
-	return in
+	}
+	n, err := prefixer.writer.Write(prefixer.buf.Bytes())
+	if n > len(p) {
+		n = len(p)
+	}
+	return n, err
 }
 
 func isQuiet(cr *CmdRequest) (bool, error) {

middlewares.go

@@ -19,7 +19,6 @@ import (
 	"time"
 
 	"github.com/getsentry/sentry-go"
-	"github.com/rs/xid"
 	"golang.org/x/sync/errgroup"
 )
 
@@ -67,25 +66,13 @@ func writeSyslog(g GuardFunc) GuardFunc {
 
 // insertUUID prefixes each line with a uuid unless errfile-no-uuid flag is set
 func insertUUID(g GuardFunc) GuardFunc {
-	errGrp := errgroup.Group{}
-	UUID := []byte(xid.New().String())
 	return func(ctx context.Context, cr *CmdRequest) (err error) {
 		if cr.ErrFileHideUUID {
 			return g(ctx, cr)
 		}
-		combined := uuidPrefix(cr.Status.Combined, &errGrp, UUID)
+	        combined := newUUIDPrefixer(cr.Status.Combined)
 		cr.Status.Combined = combined
-		if err = g(ctx, cr); err != nil {
-			_ = combined.Close()
-			return err
-		}
-		if err = combined.Close(); err != nil {
-			return err
-		}
-		if err = errGrp.Wait(); err != nil {
-			return err
-		}
-		return combined.Close()
+		return g(ctx, cr)
 	}
 }