Ochi Download Manager (ODM)

A segmented, resumable download manager for Windows, Linux and macOS, written in Go. ODM opens several connections per file, resumes at the exact byte where a transfer stopped, and organizes downloads into categories and scheduled queues. It runs as a desktop app, or headless with a JSON API.

Features

Downloading

• Up to 32 connections per file using Range requests (8 by default), with per-server overrides. Several connections use HTTP/1.1, one socket each. A single stream can still use HTTP/2.
• An idle connection takes half of the chunk that will take the longest to finish, when that chunk will take at least twice as long as the fastest one. Until a pace is known, it takes half of the largest remaining chunk.
• Resume after a pause, crash or restart from the exact byte offset. If a link expires, give the download a new address and it continues where it stopped, as long as the new address serves the same file.
• Range requests ask for the raw bytes (Accept-Encoding: identity, also over an Accept-Encoding set on the download), so a server that compresses unasked does not get its compressed bytes written into the file.
• A response that ends before its chunk is finished continues from the last byte written. One that brings no bytes at all is retried with a pause and gives up after the retry limit.
• Every range request carries the file's ETag (a strong one) or Last-Modified as If-Range, and a resume checks them first. If the file on the server has changed, the partial download is discarded and started again from the first byte. A 200 for a range that already covers the whole file is kept when that validator still matches.
• Servers that do not support ranges are fetched on a single stream.
• Global and per-download speed limits, plus an optional data cap per time window.
• HTTP and SOCKS5 proxies, or the system proxy (the default).

Organizing

• Files are sorted into category folders (Video/, Audio/, Documents/, …), and each category can have its own destination folder.
• Named queues with a run order. Each queue can download a set number of files at once.
• A scheduler per queue: start with ODM, start at a set time (once or on chosen weekdays), stop at a set time, retry failed files, and open a file, exit or shut down when the queue finishes.
• Site logins (HTTP Basic), import and export of the download list, and a site grabber that crawls a page and queues the files it links to.
• A new download never replaces an existing file: if the name is taken, it is saved as name (2).ext. Adding a link that is already in the list asks first, or follows a setting for the browser, clipboard and grabber.

Desktop

• A main window with a toolbar, category and queue tree, sortable list and multi-select.
• A progress window per download that shows each connection, and a dialog when a download completes.
• Runs from the system tray. ODM can launch at login, and starting it again brings the running window forward.
• Checks GitHub Releases for new versions. It only notifies; it never updates itself.

Integration

• A browser extension (Chrome, Edge, Firefox) hands downloads to ODM through native messaging, and opens them in a New Download window where you choose the folder and name, and for a stream the quality and audio track. ODM can register itself with each browser.
• A Download this video button appears over a video player when the extension sees the page load a video or audio file. It names the file after the page title. Streams split into many segments (HLS/DASH) are downloaded segment by segment in the quality you pick (the best by default); separate video and audio tracks are joined with ffmpeg if it is installed (next to ODM, on PATH, or chosen in Options > Downloads, which also shows the ffmpeg version ODM found). A live HLS stream is recorded until you stop the download (Pause or Stop), the broadcast ends, or nothing new arrives for a while; live DASH is not supported. With ffmpeg, streams made of MPEG-TS segments are saved as MP4 (remuxed, not re-encoded); without it they stay .ts. DRM-protected video is not supported and never will be.
• The extension's toolbar icon counts the media a page has loaded, and its popup lists them (from every frame) for players the button cannot find.
• A clipboard monitor queues downloadable URLs you copy. You can turn it on or off at any time.

Install

Once a version is tagged, prebuilt archives are attached to GitHub Releases:

Platform	Archive
Windows x64	odm-windows-amd64.zip
Linux x64	odm-linux-amd64.tar.gz
Linux ARM64	odm-linux-arm64.tar.gz
macOS (Apple silicon)	odm-darwin-arm64.tar.gz
macOS (Intel)	odm-darwin-amd64.tar.gz

Unpack the archive and run ODM.exe (Windows) or ./odm (Linux, macOS). Settings and download state are stored in <config>/odm/. <config> is %AppData% on Windows, ~/Library/Application Support on macOS and ~/.config on Linux.

Build from source

ODM needs Go 1.23 or later. The engine uses only the standard library. The desktop UI is built with Fyne behind the fyne build tag, so it needs cgo.

Target	Command	Requirements
Windows	./scripts/build.sh windows	mingw-w64 (CC_WINDOWS, default x86_64-w64-mingw32-gcc)
Linux	./scripts/build.sh linux	libgl1-mesa-dev xorg-dev libxkbcommon-dev
macOS	./scripts/build.sh darwin (or darwin-intel)	Xcode command line tools
Headless	./scripts/build.sh cli	none

go test ./...                          # engine tests, no UI needed
go test -tags fyne ./internal/ui       # UI tests (cgo)
go build -tags fyne -o odm ./cmd/odm   # desktop build for the current OS

Usage

ODM.exe                                  # open the app
ODM.exe -hidden                          # start in the system tray
ODM.exe -add https://host/big.iso -no-ui # fetch one URL in the terminal, then exit

Flag	Meaning
-dir, -conns, -files	Override the download folder, connections per file, and simultaneous downloads
-add URL	Download one URL headless and exit
-no-ui, -open	Run without a window / control whether a window opens
-hidden	Start in the tray (used by launch-at-login)
-serve, -addr	Also serve the web UI and API on -addr (default 127.0.0.1:8721)
-register-browser, -unregister-browser	Register or remove the browser native host
-version	Print the version

Keyboard shortcuts (main list): Ctrl/Shift+click to select several downloads, Ctrl+A to select all, Del to remove, Enter to open the progress window, arrow keys to move, and Ctrl+N to add a URL. On macOS, use Cmd instead of Ctrl.

Tray and start-up. Closing the window hides ODM in the tray, and downloads keep running. Options → General controls close-to-tray and Launch ODM on startup. Launch-at-login is registered for the current user only: the Run key under HKCU on Windows, an XDG autostart entry on Linux, and a LaunchAgent on macOS. On Linux desktops without a tray (for example GNOME without an AppIndicator extension), the icon may not appear. Starting ODM again still shows the window.

Proxy. Options → Proxy / Socks offers three choices:

• No proxy.
• System settings (the default): the HTTP(S)_PROXY variables, and on Windows also the proxy set in Internet Options. Automatic configuration (PAC) scripts are not evaluated.
• A manual HTTP or SOCKS5 proxy.

Browser integration

1. In ODM, open Options → General → Register, or run ODM.exe -register-browser.
2. Install the extension from the release:
   • Chrome, Edge, Brave, Opera: unzip odm-extension-chromium.zip, then Developer mode → Load unpacked in chrome://extensions.
   • Firefox: open odm-extension-firefox.xpi (signed by Mozilla).
3. Restart the browser once.

extension/README.md has the details, including where the registration is written on each OS.

Security model

ODM opens no TCP port by default. A running instance listens on a Unix domain socket in the user's config directory (odm.sock). The browser relay uses this socket, and it also stops a second copy of ODM from starting. Web pages can send requests to 127.0.0.1 but cannot reach a socket file, so websites you visit cannot reach the API. The socket needs Windows 10 version 1803 or later. Without it, ODM still runs, but browser hand-off is disabled.

-serve exposes the web UI and API over TCP. That listener requires a random token generated at each start and printed at start-up. Opening /?token=… sets a SameSite=Strict cookie; scripts send the X-ODM-Token header. Requests from any other Origin are refused.

Headless mode and HTTP API

Builds without the desktop UI (./scripts/build.sh cli), or runs with -serve, serve a basic web UI and this JSON API. The web UI covers adding, pausing and removing downloads. Scheduler and most Options are desktop only.

Method	Path	Purpose
GET / PUT	/api/settings	Read or update settings (applied immediately)
GET / POST	/api/downloads	List downloads, or add {"url","dir","connections","headers","speed_limit"}
GET / DELETE	/api/downloads/{id}	One download; DELETE ?file=true also deletes the file
POST	/api/downloads/{id}/pause | /resume | /retry | /open | /reveal	Control a download
POST	/api/downloads/{id}/limit | /options	Per-download speed limit / open-when-done
GET	/api/probe?url=	Size, type and file name of a URL without adding it
POST	/api/actions/pause-all | /resume-all | /clear-completed	Batch actions
GET	/api/events	Server-Sent Events stream of the list

How a download works

1. Probe. A ranged GET bytes=0-0 returns the file size, range support, file name, cookies and validators.
2. Plan. The file is split into up to N chunks of at least 64 KiB. A tiny last chunk is merged into the one before it.
3. Transfer. Workers write each chunk into the .odmpart file at its absolute offset. The first connection opens immediately. Another opens each time file bytes arrive on any connection after the last one opened, up to the configured limit, so one slow connection does not hold the rest back and a server that refuses every request is not asked again on more connections. Each range request asks for the raw bytes. With more than one connection the requests use HTTP/1.1, so each connection has its own socket. A worker that finishes early takes half of the chunk with the most time left, when that chunk will take at least twice as long as the fastest one; until a pace is known, that is the largest remaining chunk. A connection that receives no bytes for 30 seconds is closed and that chunk is retried from the last byte written; one still waiting for response headers gets 5 minutes, as a server may build the file before it answers. The other connections keep going. If the server answers a smaller range with the whole file, bytes already stored are kept and the remainder is fetched on one connection.
4. Finish. The .odmpart file is renamed to the final name.

Each chunk's progress ({id,start,end,done}) is saved as JSON, together with the ETag and Last-Modified from the probe, so a restart continues from the exact byte while the file on the server is unchanged. If If-Range fails (a 200 with another validator), or a later probe reports a different validator or size, ODM deletes the partial file and downloads the new one. A 200 with the same validator (or any 200 when there is no validator) is a server ignoring Range: the bytes already stored are kept and the rest is fetched on one connection, skipping the stored prefix of that body. A resume probe that finds ranges gone does the same. A weak ETag is never sent as If-Range. Segmented ranges, byte-offset resume and chunk splitting are standard download-manager techniques. ODM implements them in its own code.

Project layout

cmd/odm             entry point: desktop app, native-messaging relay, headless mode
internal/engine     probe, chunk planner, transfers, queues, scheduler, settings, state
internal/ui         desktop UI (Fyne): main window, progress, Scheduler, Options
internal/server     JSON + SSE API, token guard, embedded web UI
internal/ipc        Unix-socket control channel and single-instance lock
internal/native     native-messaging framing and browser-launch detection
internal/browserreg native-host registration for Chrome, Edge, Chromium, Firefox
internal/sysproxy   OS proxy lookup (environment, Windows Internet Options)
internal/autostart  launch at login (Run key, XDG autostart, LaunchAgent)
internal/update     GitHub Releases version check
internal/clipmon    clipboard watcher (native on Windows, via Fyne elsewhere) and URL detection
internal/osutil     open, reveal and shutdown helpers
cmd/extpack         builds the Chromium (.zip) and Firefox (.xpi) extension packages
internal/extpack    per-browser manifest derivation and packaging
extension/          MV3 browser extension source and native-host manifests

Roadmap

• A properties dialog for each download.
• A credentials prompt for HTTP 401 responses (Basic and Digest).
• ZIP preview, sounds, a virus-scan hook, grabber projects, and translations.
• Live DASH streams.
• Signed self-update, and code-signed Windows builds.

License

MIT © 2026 Ochi Download Manager contributors.

ODM is an independent implementation. It ships no code, binaries, assets or data from any other product, and it does not bypass copy protection or activation. Copyright protects expression, not ideas. This project claims rights only over its own source and asserts none over any idea, algorithm or behavior. See DISCLAIMER.md for the full statement.