[billythekidz]

Description

This PR removes the omitempty XML tag attribute from IsTruncated in ListMultipartUploadsResult and ListMultipartUploadPartsResult in messages.go.

Fixes #21 (following up on discussion in #21 (comment)).
Relates to upstream rclone issue: rclone/rclone#10078.

---

Root Cause

In messages.go, the multipart results structs previously defined IsTruncated as:

type ListMultipartUploadsResult struct {
    ...
    IsTruncated bool `xml:"IsTruncated,omitempty"`
}

type ListMultipartUploadPartsResult struct {
    ...
    IsTruncated bool `xml:"IsTruncated,omitempty"`
}

Because of omitempty, when the result was not truncated (IsTruncated == false), Go's encoding/xml encoder omitted the <IsTruncated> tag entirely from the XML response.

However, according to the Amazon S3 REST API specifications:

• Amazon S3 ListParts API specifies IsTruncated as a required boolean element.
• Amazon S3 ListMultipartUploads API specifies IsTruncated as a required boolean element.

When strict S3 clients (such as the official AWS Go SDK v1 used in Docker Distribution / OCI Registry distribution/distribution v2.8.x and v3.x) unmarshal the response, IsTruncated is modeled as a pointer: *bool.

Because <IsTruncated> was absent, resp.IsTruncated was left unpopulated (nil).

When Docker Distribution attempts to list parts during multipart chunked upload (distribution/registry/storage/driver/s3-aws/s3.go:593):

for *resp.IsTruncated { // <--- DEREFERENCES NIL POINTER
    ...
}

This resulted in an immediate crash:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x... ]

causing registry instances backed by rclone serve s3 / gofakes3 to enter a restart crash loop whenever an image blob upload occurred.

---

Changes Made

1. messages.go:

   • Changed xml:"IsTruncated,omitempty" to xml:"IsTruncated" in ListMultipartUploadsResult.
   • Changed xml:"IsTruncated,omitempty" to xml:"IsTruncated" in ListMultipartUploadPartsResult.
   • This matches the existing behavior in ListBucketResultBase and ListBucketVersionsResult, where IsTruncated is already defined without omitempty.

2. messages_test.go:

   • Added unit tests TestListMultipartUploadPartsResultIsTruncated and TestListMultipartUploadsResultIsTruncated to verify that <IsTruncated>false</IsTruncated> is explicitly emitted in serialized XML.

---

Verification & Testing

• Unit tests pass cleanly: go test -v ./....
• End-to-end verified with Docker Distribution (distribution:2.8.3) connected to rclone serve s3:
  • Before fix: Every multi-chunk docker push immediately panicked with nil pointer dereference at s3.go:593.
  • After fix: Multi-chunk image pushes (hello-world, alpine:latest) succeed with HTTP 202 Accepted and 201 Created; images can be pulled and cataloged without issues.

[ncw]

Can you fix the format error then I'll merge - thank you :-)

[billythekidz]

@ncw I have fixed the import ordering in messages_test.go using gofmt and force-pushed the updated commit (46b6bfd). Ready for review and merge. Thank you!

[ncw]

Perfect - thank you :-)

[ncw]

@billythekidz I tagged v0.0.11 if you want to make a PR pulling this back into rclone to fix rclone/rclone#10078.

Thank you

[billythekidz]

@ncw PR submitted to rclone/rclone: rclone/rclone#10089. Thank you for tagging the release!