dsh-pdf-open

dsh-pdf-open

Adds one button to the DeepSeek Harness document preview: open the previewed PDF in your browser's own PDF viewer.

That is the whole feature. It exists because the shipped preview renders PDFs with PDF.js but exposes only fit-width and zoom — no rotation, no outline, no find — and its "Open" control launches an application on the host, which is useless when Harness runs on a headless server.

What you get

• Rotation, document outline, Ctrl+F find, print, two-page view — the browser viewer's own, mature controls.
• Nothing is uploaded or converted: the bytes come from the same server, over the same authenticated channel, and are rendered locally by your browser.
• Your PDF is never modified and never leaves the session's filesystem policy.

Requirements

• DeepSeek Harness with the Web UI (dsh web) and the right-side document preview. Developed against 0.2.1-rc.2; it uses only the connection, fs host services and the sidebar.right.tab.document.actions slot.
• No build step, no runtime dependencies, no changes to Harness source.

Install

From npm:

dsh plugin --profile web add dsh-pdf-open

Straight from this repository (no build step — the sources are the runtime files):

dsh plugin --profile web add github:wang2000star/dsh-pdf-open

From a local checkout:

dsh plugin --profile web add /absolute/path/to/dsh-pdf-open

Then restart dsh web once (the host half is an ES module, and Node's module cache means the route only appears after a restart), and refresh the page.

Uninstall:

dsh plugin --profile web remove dsh-pdf-open

Usage

Open a PDF in the workspace file preview. A new icon appears in the preview header, after the shipped controls. Click it; a new tab opens the same document in the browser's PDF viewer.

Why a separate route

/api/file (the shipped file route) reads the entire file into memory, returns one buffered response, and sends no Accept-Ranges. A browser PDF viewer wants range requests: it fetches the header, then only the pages you look at. Without them the whole file must arrive before the first page paints, which is painful on a remote server, and files above the route's byte cap fail with 413 instead of opening at all.

Measured on one deployment, for a 56 MB, 14-page PDF over the authenticated /api channel:

Request	Result
GET /api/file?path=… (shipped)	413 Payload Too Large, 12-byte body
GET /api/pdf-open/raw?path=…	200, 58,809,929 bytes, Accept-Ranges: bytes
Range: bytes=0-262143	206, 262,144 bytes in 8 ms
Range: bytes=50000000-	206, Content-Range: bytes 50000000-58809928/58809929
Range: bytes=99999999-	416, Content-Range: bytes */58809929

So the shipped route does not merely feel slow for files of this size: it refuses them. That is what this route fixes.

This plugin registers /api/pdf-open/raw, which:

• advertises Accept-Ranges: bytes and answers Range with 206;
• reads only the requested window through ctx.fs.readByteRange, so a bounded request never buffers the whole file;
• serves application/pdf with Content-Disposition: inline and no restrictive CSP, so the browser viewer takes over;
• caps one file at 512 MiB.

An open-ended request (Range: bytes=0-) still yields the whole remainder in one response, which is what a viewer asks for before it knows the page offsets. The win is that linearized PDFs then load page by page, the byte cap that made /api/file answer 413 is gone, and the file is read once instead of being buffered and copied.

Security

• The route lives on the authenticated /api channel: Harness authenticates the request before the handler runs, exactly like the shipped file route.
• Paths pass through ctx.fs.resolve, so the configured filesystem backend's sandbox and access policy still apply.
• Only regular .pdf files are served.
• URLs carry the absolute host path; treat them as sensitive and do not paste them into public places.

Limits

• Rotation and zoom are view state of the browser viewer: a reload returns to the document's own orientation. Use a PDF editor to rotate the file itself.
• One PDF per tab; no annotations, no OCR, no chat integration. If you want the model to read the document, use Harness's own tools or a full reader plugin.
• The previewed file must be previewable by the shipped renderer (the button only appears once the preview knows the file's host path).

Tests

node --test test/

The route handler is a pure fetch function over ctx.fs, so the tests run in plain Node against a fake filesystem: 200, HEAD, 206, suffix ranges, 416, malformed ranges, path validation, and filesystem error mapping.

Implementation notes

• GET/HEAD exact routes must use requestBody: 'buffered'. The carrier's streaming mode wraps the socket in a Request with a body; the WHATWG constructor rejects a body for GET/HEAD, the error escapes the handler, and the web server's fallback answers an empty 400 that the browser renders as its own error page. This is the difference from the shipped /api/file route.
• No Content-Security-Policy header. The shipped file route sends sandbox; default-src 'none'. Chromium happens to render PDFs behind that header, but it is a viewer-implementation detail; this route omits it so the viewer is not at the mercy of that behavior.
• Accept-Ranges is the whole point. Without it the browser downloads the complete file before the first page paints.

License

MIT