From e91c130a1708a3b2dfb1c9c8ff29d6313320db01 Mon Sep 17 00:00:00 2001
From: Emmanuel T Odeke <emmanuel@orijtech.com>
Date: Sun, 25 Apr 2021 17:12:45 -0700
Subject: [PATCH] Gate use of the WAL behind a method check and return an error
 on attempted use

---
 .../prometheusremotewriteexporter/exporter.go    |  6 +++++-
 exporter/prometheusremotewriteexporter/wal.go    | 16 ++++++++++------
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/exporter/prometheusremotewriteexporter/exporter.go b/exporter/prometheusremotewriteexporter/exporter.go
index dc8d8d97c90..88f8a138967 100644
--- a/exporter/prometheusremotewriteexporter/exporter.go
+++ b/exporter/prometheusremotewriteexporter/exporter.go
@@ -283,7 +283,11 @@ func (prwe *PrwExporter) export(ctx context.Context, tsMap map[string]*prompb.Ti
 		return errs
 	}
 
-	// Now serialize the requests to the WAL.
+	if !prwe.walEnabled() {
+		return prwe.actualExport(ctx, requests)
+	}
+
+	// Otherwise, serialize the requests to the WAL.
 	if err := prwe.writeToWAL(ctx, requests); err != nil {
 		errs = append(errs, consumererror.Permanent(err))
 	}
diff --git a/exporter/prometheusremotewriteexporter/wal.go b/exporter/prometheusremotewriteexporter/wal.go
index 97d07458d3a..50073683fee 100644
--- a/exporter/prometheusremotewriteexporter/wal.go
+++ b/exporter/prometheusremotewriteexporter/wal.go
@@ -16,6 +16,7 @@ package prometheusremotewriteexporter
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"path/filepath"
 	"time"
@@ -63,9 +64,13 @@ func (wc *walConfig) refreshDuration() time.Duration {
 	return wc.RefreshDuration
 }
 
+func (prwe *PrwExporter) walEnabled() bool { return prwe.walConfig != nil }
+
+var errWALDisabled = errors.New("Write-Ahead-Log is disabled")
+
 func (prwe *PrwExporter) retrieveWALIndices(context.Context) (err error) {
-	if prwe.walConfig == nil {
-		return nil
+	if !prwe.walEnabled() {
+		return errWALDisabled
 	}
 
 	prwe.walMu.Lock()
@@ -117,7 +122,7 @@ func (prwe *PrwExporter) flushToWAL(ctx context.Context, reqL []*prompb.WriteReq
 }
 
 func (prwe *PrwExporter) turnOnWALIfEnabled() error {
-	if prwe.walConfig == nil {
+	if !prwe.walEnabled() {
 		return nil
 	}
 
@@ -154,9 +159,8 @@ func (prwe *PrwExporter) closeWAL() {
 }
 
 func (prwe *PrwExporter) writeToWAL(ctx context.Context, requests []*prompb.WriteRequest) error {
-	if prwe.walConfig == nil {
-		// The WAL isn't enabled.
-		return nil
+	if !prwe.walEnabled() {
+		return errWALDisabled
 	}
 
 	startTime := time.Now()