feat(fs): implement client-side multipart upload with File-Path header

[dnslin]

Description / 描述

Implement a new multipart upload API that supports client-side chunked uploads with concurrent upload capability.

实现新的分片上传接口，支持客户端分片并发上传。

API Endpoint: PUT /api/fs/multipart?action=upload|complete

Features / 功能:

• Uses File-Path header (consistent with /api/fs/put and /api/fs/form)
• Two-step workflow: upload chunks → complete
• Auto-initialize session on first chunk upload
• Support concurrent chunk uploads
• Idempotent chunk upload (re-uploading same chunk won't fail)
• Support Overwrite and As-Task headers
• Session auto-cleanup after expiration (2 hours)

Request Headers:

Header	Required	Description
File-Path	Yes	File path (URL encoded)
X-File-Size	First chunk	Total file size
X-Chunk-Size	First chunk	Chunk size
X-Chunk-Index	Yes	Chunk index (0-based)
X-Upload-Id	After first	Upload session ID
Overwrite	No	Overwrite existing file (default: true)
As-Task	No	Async upload on complete (default: false)

Motivation and Context / 背景

The existing upload APIs (/api/fs/put, /api/fs/form) don't support resumable uploads for large files. This new multipart upload API allows clients to:

• Split large files into chunks and upload them concurrently
• Resume interrupted uploads by re-uploading missing chunks
• Better handle unstable network conditions

现有的上传接口不支持大文件的断点续传。新的分片上传接口允许客户端：

• 将大文件分片并发上传
• 通过重新上传缺失的分片来恢复中断的上传
• 更好地处理不稳定的网络环境

Relates to #XXXX (如果有相关 issue 请填写)

How Has This Been Tested? / 测试

• Manual testing with Python async client
• Tested concurrent chunk uploads (4 parallel uploads)
• Tested idempotent chunk upload (re-upload same chunk)
• Tested session expiration cleanup
• Tested complete upload with As-Task=true
• Compiled successfully with go build

使用 Python 异步客户端进行手动测试，测试了并发上传、幂等性、会话过期清理等功能。

Checklist / 检查清单

• I have read the https://github.com/OpenListTeam/OpenList/blob/main/CONTRIBUTING.md document.
• I have formatted my code with go fmt or https://prettier.io/.
• I have added appropriate labels to this PR (or mentioned needed labels in the description if lacking permissions).
• I have requested review from relevant code authors using the "Request review" feature when applicable.
• I have updated the repository accordingly (If it's needed).
  • https://github.com/OpenListTeam/OpenList-Frontend #XXXX
  • https://github.com/OpenListTeam/OpenList-Docs - API documentation needed

[Copilot]

Pull request overview

This PR implements a new client-side multipart upload API that enables chunked file uploads with concurrent upload support and resumable capabilities. The implementation provides a two-step workflow (upload chunks → complete) with automatic session initialization and cleanup.

Key Changes:

• New PUT /api/fs/multipart endpoint supporting upload and complete actions
• Session-based chunk management with 2-hour expiration
• Idempotent chunk uploads allowing retry of failed chunks
• Support for concurrent chunk uploads via shared session state

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 11 comments.

File	Description
server/router.go	Adds the new /multipart endpoint with upload rate limiting and authentication middleware
server/handles/multipart.go	Implements HTTP handlers for chunk upload and completion actions with header-based API design
internal/fs/multipart.go	Core multipart session manager with chunk storage, merging, and cleanup logic
internal/model/multipart.go	Data structures for multipart sessions, chunk metadata, and API responses

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[dnslin]

@copilot open a new pull request to apply changes based on the comments in this thread

[KirCute]

能不能开始上传的时候就构建FileStream并调用驱动的上传，这样做至少有两个好处：

1. 可以在首个分片的上传请求里携带文件哈希，在驱动触发秒传，如果秒传成功，后续分片就都不用上传了
2. 可以同时进行用户终端->OpenList和OpenList->网盘两个上传过程，这两个过程分别吃服务器的下行和上行带宽，不冲突，可以很大程度上减少总的上传时间