From e146646665c6bbc97693eb815f684468784202ea Mon Sep 17 00:00:00 2001
From: Ben McClelland <ben.mcclelland@versity.com>
Date: Thu, 30 Jul 2026 08:37:51 -0700
Subject: [PATCH] fix: honor mpMaxParts across partNumber validation

Multipart partNumber validation was inconsistent because some handlers still
enforced the hardcoded S3 default while others used the instance-level
mpMaxParts setting. This created a split API contract where changing mpMaxParts
did not reliably affect all relevant endpoints. This change routes all
partNumber upper-bound checks through a shared effective limit helper so
deployments that customize mpMaxParts get consistent behavior across GetObject,
HeadObject, UploadPart, and UploadPartCopy, while preserving the default
S3-compatible maximum when mpMaxParts is unset.
---
 s3api/controllers/base.go        | 8 ++++++++
 s3api/controllers/object-get.go  | 2 +-
 s3api/controllers/object-head.go | 2 +-
 s3api/controllers/object-put.go  | 4 ++--
 4 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/s3api/controllers/base.go b/s3api/controllers/base.go
index 191cc4e2..03dda5b6 100644
--- a/s3api/controllers/base.go
+++ b/s3api/controllers/base.go
@@ -84,6 +84,14 @@ func (c S3ApiController) getAclHeaderValue(ctx fiber.Ctx, key string, defaultVal
 	return ctx.Get(key, defaultValues...)
 }
 
+func (c S3ApiController) effectiveMpMaxParts() int {
+	if c.mpMaxParts > 0 {
+		return c.mpMaxParts
+	}
+
+	return maxPartNumber
+}
+
 // Returns MethodNotAllowed for unmatched routes
 func (c S3ApiController) HandleErrorRoute(err error) Controller {
 	return func(ctx fiber.Ctx) (*Response, error) {
diff --git a/s3api/controllers/object-get.go b/s3api/controllers/object-get.go
index d418ad88..51f29bd8 100644
--- a/s3api/controllers/object-get.go
+++ b/s3api/controllers/object-get.go
@@ -451,7 +451,7 @@ func (c S3ApiController) GetObject(ctx fiber.Ctx) (*Response, error) {
 
 	var partNumber *int32
 	if ctx.Request().URI().QueryArgs().Has("partNumber") {
-		if partNumberQuery < minPartNumber || partNumberQuery > maxPartNumber {
+		if partNumberQuery < minPartNumber || partNumberQuery > int32(c.effectiveMpMaxParts()) {
 			debuglogger.Logf("invalid part number: %d", partNumberQuery)
 			return &Response{
 				MetaOpts: &MetaOptions{
diff --git a/s3api/controllers/object-head.go b/s3api/controllers/object-head.go
index 6e1acba7..5974e638 100644
--- a/s3api/controllers/object-head.go
+++ b/s3api/controllers/object-head.go
@@ -99,7 +99,7 @@ func (c S3ApiController) HeadObject(ctx fiber.Ctx) (*Response, error) {
 
 	var partNumber *int32
 	if ctx.Request().URI().QueryArgs().Has("partNumber") {
-		if partNumberQuery < minPartNumber || partNumberQuery > maxPartNumber {
+		if partNumberQuery < minPartNumber || partNumberQuery > int32(c.effectiveMpMaxParts()) {
 			debuglogger.Logf("invalid part number: %d", partNumberQuery)
 			return &Response{
 				MetaOpts: &MetaOptions{
diff --git a/s3api/controllers/object-put.go b/s3api/controllers/object-put.go
index fc381843..12331cd3 100644
--- a/s3api/controllers/object-put.go
+++ b/s3api/controllers/object-put.go
@@ -255,7 +255,7 @@ func (c S3ApiController) UploadPart(ctx fiber.Ctx) (*Response, error) {
 		}, err
 	}
 
-	if partNumber < minPartNumber || partNumber > int32(c.mpMaxParts) {
+	if partNumber < minPartNumber || partNumber > int32(c.effectiveMpMaxParts()) {
 		debuglogger.Logf("invalid part number: %d", partNumber)
 		return &Response{
 			MetaOpts: &MetaOptions{
@@ -390,7 +390,7 @@ func (c S3ApiController) UploadPartCopy(ctx fiber.Ctx) (*Response, error) {
 		}, s3err.GetAPIError(s3err.ErrNonEmptyRequestBody)
 	}
 
-	if partNumber < minPartNumber || partNumber > maxPartNumber {
+	if partNumber < minPartNumber || partNumber > int32(c.effectiveMpMaxParts()) {
 		debuglogger.Logf("invalid part number: %d", partNumber)
 		return &Response{
 			MetaOpts: &MetaOptions{