S3 Desktop

A fast, native desktop client for S3 and S3-compatible object storage.

UCloud US3 · AWS S3 · MinIO · anything that speaks the S3 API

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S3 Desktop is a Qt rewrite of an earlier MIT-licensed Go/Fyne client for S3-compatible storage. It is not a port: no line of the original Go/Fyne code was translated. The feature set was reimplemented from scratch on top of Qt 6 and a hand-written SigV4 signer, because the original's structure — a single 1150-line window that called into a vendor SDK from a background goroutine — is what made its bugs hard to fix in the first place.

Screenshot

Contents

• Screenshot
• What it does
• Differences from the original, and why
• Build
• Static build
• Tests
• Logs
• Layout
• Versioning
• License

What it does

Connections	Named profiles saved locally: endpoint, access key, secret key, bucket, region, prefix, TLS, addressing style. Test-connection button in the dialog.
Browse	Bucket list, then a folder-grouped object table with breadcrumb navigation and back/forward/up history (Alt+Left / Alt+Right / Alt+Up).
Bucket root	A connection that names no bucket opens on the account's bucket list — its own level, with its own breadcrumb, not a stand-in for a key prefix. Opening a bucket shows its objects and rewrites the path to Buckets › bucket › folder › …; the crumb and Alt+Up go back up to the list.
Search & sort	Client-side filter over the loaded objects; locale-aware, digit-aware sorting by name, size, or modified time. Folders always sort before files.
Paginate	Objects load 500 at a time, continuing from where the last page ended; Load more appends instead of replacing, so a 50 000-object bucket stays responsive.
Details	Key, size, modified time, ETag, and storage class for the selected row.
Transfers	Upload and download queue with per-item progress and cancel, run through QNetworkAccessManager so the UI thread is never blocked.
Sharing	Presigned GET URLs, valid for one hour, generated locally without a round trip.
Buckets	Create and delete buckets from a separate manager window, with client-side name validation.
CLI	--endpoint, --access-key, --secret-key, --bucket, --prefix, --region, --target, --ssl / --no-ssl. Each falls back to the ENDPOINT, ACCESS_KEY, SECRET_KEY, … environment variables the original used.

Differences from the original, and why

No vendor SDK. Signatures are computed with QCryptographicHash and QMessageAuthenticationCode against the published SigV4 specification. The signer is verified against AWS's own test vectors in the test suite, so a provider that rejects a request can be distinguished from a signer that is wrong.

No worker threads. Every request goes through the event loop; replies are delivered to the GUI thread by construction. The original called its UI toolkit from goroutines, which is the source of most of its stability problems.

Credentials in DPAPI. Secret keys are encrypted with CryptProtectData (Windows Data Protection API), so they are readable only by the user account that stored them. The original kept them in plaintext JSON. CredentialStore is a single interface, so another platform's keychain can be substituted without touching callers.

Provider differences are data, not branches. TargetProfile describes how a given provider lays out hostnames and derives a region — US3's s3-<region>.ufileos.com, AWS, MinIO, generic path-style — instead of scattering if provider == checks through the transport layer.

A virtualised table. ObjectModel keeps one index list over the loaded objects and never copies them; QTableView renders only visible rows. Fixed row height lets Qt compute visibility without querying the model per row, which is what keeps very large listings usable.

Build

Requirements: Qt 6 (Core, Gui, Widgets, Network — and Test for the suite), CMake 3.21+, and a C++17 compiler.

Verified with Qt 6.9.3 (mingw_64), GCC 13.1.0, CMake 4.0.1, and Ninja on Windows 11.

cmake -S . -B build -G Ninja -DCMAKE_BUILD_TYPE=Release \
      -DCMAKE_PREFIX_PATH=C:/Qt/6.9.3/mingw_64
cmake --build build

Note

The binary lands at build/s3desktop.exe. On Windows it is built as a GUI subsystem executable, so it will not attach a console window.

Static build

A single self-contained .exe with no Qt DLLs beside it — nothing to install, nothing to put on PATH, nothing to break when a redistributable is missing.

Qt's own MinGW packages ship import libraries, not static ones: every member of their libQt6Core.a is named Qt6Core_dll_*.o, so -static can only resolve the references, never eliminate the DLL dependency. A genuinely static Qt has to be built from source:

# configure.bat in a qtbase source tree
configure.bat -static -static-runtime -release -opensource -confirm-license \
              -nomake examples -nomake tests -no-dbus -no-icu -platform win32-g++
# then, with Ninja
cmake --build . --parallel
cmake --install . --prefix C:/Qt/6.9.3/mingw1310_64_static

Then point the project at that prefix and turn the option on:

cmake -S . -B build-static -G Ninja -DCMAKE_BUILD_TYPE=Release \
      -DCMAKE_PREFIX_PATH=C:/Qt/6.9.3/mingw1310_64_static \
      -DS3DESKTOP_STATIC=ON
cmake --build build-static

S3DESKTOP_STATIC is off by default and deliberately not inferred from the Qt install: a static Qt is a separate prefix, and guessing from Qt6Core_LIBRARIES would make the build silently change character when CMAKE_PREFIX_PATH moves.

Important

A static Qt links no plugins by default. Without importing the Windows platform plugin the executable compiles and links cleanly, then dies at startup with "no Qt platform plugin could be initialized". The build imports QWindowsIntegrationPlugin, QModernWindowsStylePlugin, QSchannelBackendPlugin (TLS), and the ICO/JPEG/GIF image formats by type; under MinGW it also passes -static so libgcc, libstdc++ and libwinpthread are bound in rather than left as DLLs.

Result: s3desktop.exe at ~51 MB, importing only Windows system DLLs — no Qt6*.dll, no libgcc_s_seh-1.dll, no libstdc++-6.dll, no libwinpthread-1.dll.

Tests

ctest --test-dir build --output-on-failure

Important

The test binaries link Qt dynamically, so Qt's bin directory has to be on PATH (C:/Qt/6.9.3/mingw_64/bin); without it they exit with 0xc0000135 before running a single case. A -DS3DESKTOP_STATIC=ON build has no such requirement — the suite runs with nothing but C:\Windows\system32 on PATH.

Six suites, none of which need a display or a network:

Suite	Covers
test_sigv4	The signer, against AWS's worked examples and test-suite vectors
test_list_parser	XML listing responses, including provider quirks and error-code mapping
test_target_profile	Hostname layout and region derivation per provider
test_transfer_queue	The transfer state machine
test_object_model	Filtering, folder grouping, sorting, and bucket mode
test_object_browser	Back/forward/up, the breadcrumb at every level, and which rows the object commands are allowed to see

Logs

Every run writes s3desktop.log beside settings.json — on Windows that is %LOCALAPPDATA%\s3desktop\s3desktop\. The previous run is kept as s3desktop.log.1.

Each request records the URL that was actually built, the host that was actually signed, the port used, and the credential store's verdict on the secret. A failure adds the HTTP status, the server's <Code> and request id, and the response body, which for a signature problem is the only place the real reason appears. Secrets are redacted to four characters and two.

Set S3DESKTOP_LOG to override the path, or to off to turn logging off.

Layout

src/core/     transport, signing, config, credentials, transfers  (no GUI)
src/compat/   provider profiles
src/ui/       widgets, models, theme
tests/        Qt Test suites

core and compat link only against Qt Core/Network, so all of the logic that can be wrong without a user noticing is testable in isolation. ui is a separate static library so the model and theme can be exercised under a QApplication without opening the main window.

Versioning

VERSION holds the current release, one bare number per line. The Check for updates action fetches that file from this repository's default branch and compares it against the version compiled into the binary; if this build is older it offers to open the project page. Bumping a release means editing VERSION and kVersion in src/ui/MainWindow.cpp together.

License

MIT, as the original. See LICENSE.