tools: add lambda-promtail missing errchecks (#6541)

* tools: lambda-promtail missing errchecks

* undo undesired changes

tools/lambda-promtail/lambda-promtail/cw.go

@@ -31,19 +31,24 @@ func parseCWEvent(ctx context.Context, b *batch, ev *events.CloudwatchLogsEvent)
 	for _, event := range data.LogEvents {
 		timestamp := time.UnixMilli(event.Timestamp)
 
-		b.add(ctx, entry{labels, logproto.Entry{
+		if err := b.add(ctx, entry{labels, logproto.Entry{
 			Line:      event.Message,
 			Timestamp: timestamp,
-		}})
+		}}); err != nil {
+			return err
+		}
 	}
 
 	return nil
 }
 
 func processCWEvent(ctx context.Context, ev *events.CloudwatchLogsEvent) error {
-	batch, _ := newBatch(ctx)
+	batch, err := newBatch(ctx)
+	if err != nil {
+		return err
+	}
 
-	err := parseCWEvent(ctx, batch, ev)
+	err = parseCWEvent(ctx, batch, ev)
 	if err != nil {
 		return err
 	}
@@ -52,5 +57,6 @@ func processCWEvent(ctx context.Context, ev *events.CloudwatchLogsEvent) error {
 	if err != nil {
 		return err
 	}
+
 	return nil
 }

tools/lambda-promtail/lambda-promtail/main.go

@@ -5,12 +5,13 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"github.com/prometheus/common/model"
 	"net/url"
 	"os"
 	"strconv"
 	"strings"
 
+	"github.com/prometheus/common/model"
+
 	"github.com/aws/aws-lambda-go/events"
 	"github.com/aws/aws-lambda-go/lambda"
 	"github.com/aws/aws-sdk-go-v2/service/s3"
@@ -136,11 +137,11 @@ func handler(ctx context.Context, ev map[string]interface{}) error {
 		return err
 	}
 
-	switch event.(type) {
+	switch evt := event.(type) {
 	case *events.S3Event:
-		return processS3Event(ctx, event.(*events.S3Event))
+		return processS3Event(ctx, evt)
 	case *events.CloudwatchLogsEvent:
-		return processCWEvent(ctx, event.(*events.CloudwatchLogsEvent))
+		return processCWEvent(ctx, evt)
 	}
 
 	return err

tools/lambda-promtail/lambda-promtail/promtail.go

@@ -45,8 +45,9 @@ func newBatch(ctx context.Context, entries ...entry) (*batch, error) {
 	}
 
 	for _, entry := range entries {
-		err := b.add(ctx, entry)
-		return b, err
+		if err := b.add(ctx, entry); err != nil {
+			return nil, err
+		}
 	}
 
 	return b, nil

tools/lambda-promtail/lambda-promtail/s3.go

@@ -75,7 +75,6 @@ func parseS3Log(ctx context.Context, b *batch, labels map[string]string, obj io.
 	ls = applyExtraLabels(ls)
 
 	for scanner.Scan() {
-		i := 0
 		log_line := scanner.Text()
 		match := timestampRegex.FindStringSubmatch(log_line)
 
@@ -84,11 +83,12 @@ func parseS3Log(ctx context.Context, b *batch, labels map[string]string, obj io.
 			return err
 		}
 
-		b.add(ctx, entry{ls, logproto.Entry{
+		if err := b.add(ctx, entry{ls, logproto.Entry{
 			Line:      log_line,
 			Timestamp: timestamp,
-		}})
-		i++
+		}}); err != nil {
+			return err
+		}
 	}
 
 	return nil
@@ -114,8 +114,10 @@ func getLabels(record events.S3EventRecord) (map[string]string, error) {
 }
 
 func processS3Event(ctx context.Context, ev *events.S3Event) error {
-
-	batch, _ := newBatch(ctx)
+	batch, err := newBatch(ctx)
+	if err != nil {
+		return err
+	}
 
 	for _, record := range ev.Records {
 		labels, err := getLabels(record)
@@ -135,7 +137,7 @@ func processS3Event(ctx context.Context, ev *events.S3Event) error {
 
 	}
 
-	err := sendToPromtail(ctx, batch)
+	err = sendToPromtail(ctx, batch)
 	if err != nil {
 		return err
 	}