From 3952d536397e550005e937068a20db60b1f69c92 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Giedrius=20Statkevi=C4=8Dius?=
 <giedrius.statkevicius@vinted.com>
Date: Fri, 9 Oct 2026 13:28:01 +0300
Subject: [PATCH] s3: respect partSize if size unknown
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If the size of the upload is unknown then with the current version
partSize is also ignored. This causes a problem where I am streaming
results (e.g. thanos-parquet-gateway) and know that the resulting file
will never be that huge to exceed the limit of part size * number of
parts. Now it allocates a lot of memory conservatively to get the
maximum possible object size. See
https://github.com/minio/minio-go/blob/master/docs/API.md#PutObject.md
and this
https://github.com/minio/minio-go/blob/master/api-put-object-common.go#L90-L92.

Cleanup one linter message while going through this function.

Signed-off-by: Giedrius Statkevičius <giedrius.statkevicius@vinted.com>
---
 providers/s3/s3.go      |  7 ++---
 providers/s3/s3_test.go | 64 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 67 insertions(+), 4 deletions(-)

diff --git a/providers/s3/s3.go b/providers/s3/s3.go
index b13eefa6d7..d616a296cc 100644
--- a/providers/s3/s3.go
+++ b/providers/s3/s3.go
@@ -8,6 +8,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"maps"
 	"net/http"
 	"os"
 	"runtime"
@@ -560,15 +561,13 @@ func (b *Bucket) Upload(ctx context.Context, name string, r io.Reader, opts ...o
 	}
 
 	partSize := b.partSize
-	if size < int64(partSize) {
+	if size >= 0 && size < int64(partSize) {
 		partSize = 0
 	}
 
 	// Cloning map since minio may modify it
 	userMetadata := make(map[string]string, len(b.putUserMetadata))
-	for k, v := range b.putUserMetadata {
-		userMetadata[k] = v
-	}
+	maps.Copy(userMetadata, b.putUserMetadata)
 
 	uploadOpts := objstore.ApplyObjectUploadOptions(opts...)
 
diff --git a/providers/s3/s3_test.go b/providers/s3/s3_test.go
index f12959d8ed..febd0342cc 100644
--- a/providers/s3/s3_test.go
+++ b/providers/s3/s3_test.go
@@ -15,6 +15,8 @@ import (
 	"testing/synctest"
 	"time"
 
+	"go.uber.org/atomic"
+
 	"github.com/efficientgo/core/testutil"
 	"github.com/go-kit/log"
 	"github.com/minio/minio-go/v7/pkg/encrypt"
@@ -418,6 +420,68 @@ func TestBucket_getServerSideEncryption(t *testing.T) {
 	testutil.Equals(t, encrypt.KMS, sse.Type())
 }
 
+type noSizerSpamReader struct {
+	n int
+}
+
+var _ io.Reader = &noSizerSpamReader{}
+
+func (n *noSizerSpamReader) ObjectSizer() (int64, error) {
+	return -1, nil
+}
+
+func (n *noSizerSpamReader) Read(p []byte) (int, error) {
+	if n.n <= 0 {
+		return 0, io.EOF
+	}
+	var i int
+	for i < len(p) && n.n > 0 {
+		p[i] = byte(42)
+		i++
+		n.n -= 1
+	}
+	return i, nil
+}
+
+func TestBucket_Put_PartSizeRespected(t *testing.T) {
+	var firstReqResponse, triggeredCondition atomic.Bool
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if !firstReqResponse.Load() {
+			_, err := w.Write([]byte(`<?xml version="1.0" encoding="UTF-8"?>
+<InitiateMultipartUploadResult xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
+    <Bucket>example-bucket</Bucket>
+    <Key>large-file.zip</Key>
+    <UploadId>7f8a9b0c1d2e3f4a5b6c7d8e9f0a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a</UploadId>
+</InitiateMultipartUploadResult>`))
+			testutil.Ok(t, err)
+			firstReqResponse.Store(true)
+			return
+		}
+
+		if r.Header.Get("X-Amz-Content-Sha256") == "STREAMING-AWS4-HMAC-SHA256-PAYLOAD" {
+			triggeredCondition.Store(true)
+			testutil.Equals(t, r.Header.Get("X-Amz-Decoded-Content-Length"), "5242880")
+		}
+	}))
+	defer srv.Close()
+
+	cfg := DefaultConfig
+	cfg.Bucket = "test-bucket"
+	cfg.Endpoint = srv.Listener.Addr().String()
+	cfg.Insecure = true
+	cfg.Region = "test123"
+	cfg.AccessKey = "test123"
+	cfg.SecretKey = "test123"
+	cfg.PartSize = 5 * 1024 * 1024
+
+	bkt, err := NewBucketWithConfig(log.NewNopLogger(), cfg, "test", nil)
+	testutil.Ok(t, err)
+
+	testutil.NotOk(t, bkt.Upload(t.Context(), "foo", &noSizerSpamReader{n: 10 * 1024 * 1024}))
+	testutil.Equals(t, true, triggeredCondition.Load())
+
+}
+
 func TestBucket_Get_ShouldReturnErrorIfServerTruncateResponse(t *testing.T) {
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Last-Modified", "Wed, 21 Oct 2015 07:28:00 GMT")