From 1e58d792a57ee81c44e54ffe3cce7a132f55a389 Mon Sep 17 00:00:00 2001
From: Charles Korn <charleskorn@users.noreply.github.com>
Date: Mon, 7 Jul 2025 17:23:34 +1000
Subject: [PATCH] storage/remote: fix "http: read on closed response body"
 errors if chunkedSeriesSet.Next is called again after the series set is
 exhausted (#16838)

Signed-off-by: Charles Korn <charles.korn@grafana.com>
---
 storage/remote/codec.go      | 12 ++++++++++--
 storage/remote/codec_test.go | 35 +++++++++++++++++++++++++++++++++--
 2 files changed, 43 insertions(+), 4 deletions(-)

diff --git a/storage/remote/codec.go b/storage/remote/codec.go
index 80bb811500..3dbf432bcf 100644
--- a/storage/remote/codec.go
+++ b/storage/remote/codec.go
@@ -547,8 +547,9 @@ type chunkedSeriesSet struct {
 	mint, maxt    int64
 	cancel        func(error)
 
-	current storage.Series
-	err     error
+	current   storage.Series
+	err       error
+	exhausted bool
 }
 
 func NewChunkedSeriesSet(chunkedReader *ChunkedReader, respBody io.ReadCloser, mint, maxt int64, cancel func(error)) storage.SeriesSet {
@@ -564,6 +565,12 @@ func NewChunkedSeriesSet(chunkedReader *ChunkedReader, respBody io.ReadCloser, m
 // Next return true if there is a next series and false otherwise. It will
 // block until the next series is available.
 func (s *chunkedSeriesSet) Next() bool {
+	if s.exhausted {
+		// Don't try to read the next series again.
+		// This prevents errors like "http: read on closed response body" if Next() is called after it has already returned false.
+		return false
+	}
+
 	res := &prompb.ChunkedReadResponse{}
 
 	err := s.chunkedReader.NextProto(res)
@@ -575,6 +582,7 @@ func (s *chunkedSeriesSet) Next() bool {
 
 		_ = s.respBody.Close()
 		s.cancel(err)
+		s.exhausted = true
 
 		return false
 	}
diff --git a/storage/remote/codec_test.go b/storage/remote/codec_test.go
index c92f0f8cde..7aba1a133e 100644
--- a/storage/remote/codec_test.go
+++ b/storage/remote/codec_test.go
@@ -15,6 +15,7 @@ package remote
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"io"
 	"sync"
@@ -892,7 +893,8 @@ func TestChunkedSeriesSet(t *testing.T) {
 		flusher := &mockFlusher{}
 
 		w := NewChunkedWriter(buf, flusher)
-		r := NewChunkedReader(buf, config.DefaultChunkedReadLimit, nil)
+		wrappedReader := newOneShotCloser(buf)
+		r := NewChunkedReader(wrappedReader, config.DefaultChunkedReadLimit, nil)
 
 		chks := buildTestChunks(t)
 		l := []prompb.Label{
@@ -913,7 +915,7 @@ func TestChunkedSeriesSet(t *testing.T) {
 			require.NoError(t, err)
 		}
 
-		ss := NewChunkedSeriesSet(r, io.NopCloser(buf), 0, 14000, func(error) {})
+		ss := NewChunkedSeriesSet(r, wrappedReader, 0, 14000, func(error) {})
 		require.NoError(t, ss.Err())
 		require.Nil(t, ss.Warnings())
 
@@ -938,6 +940,9 @@ func TestChunkedSeriesSet(t *testing.T) {
 		}
 		require.Equal(t, numTestChunks, numResponses)
 		require.NoError(t, ss.Err())
+
+		require.False(t, ss.Next(), "Next() should still return false after it previously returned false")
+		require.NoError(t, ss.Err(), "Err() should not return an error if Next() is called again after it previously returned false")
 	})
 
 	t.Run("chunked reader error", func(t *testing.T) {
@@ -983,6 +988,32 @@ type mockFlusher struct{}
 
 func (f *mockFlusher) Flush() {}
 
+type oneShotCloser struct {
+	r      io.Reader
+	closed bool
+}
+
+func newOneShotCloser(r io.Reader) io.ReadCloser {
+	return &oneShotCloser{r, false}
+}
+
+func (c *oneShotCloser) Read(p []byte) (n int, err error) {
+	if c.closed {
+		return 0, errors.New("already closed")
+	}
+
+	return c.r.Read(p)
+}
+
+func (c *oneShotCloser) Close() error {
+	if c.closed {
+		return errors.New("already closed")
+	}
+
+	c.closed = true
+	return nil
+}
+
 const (
 	numTestChunks          = 3
 	numSamplesPerTestChunk = 5