[Bug] Web UI CSP blocks blob: URLs — dragging an image into chat fails with "NetworkError when attempting to fetch resource" #40814

Description

Environment

• opencode version: 1.18.12 (npm install -g opencode-ai, opencode-windows-x64)
• OS: Windows 10/11
• Browser: Firefox (error message "NetworkError when attempting to fetch resource" is Firefox-specific; Chrome shows "Failed to fetch")
• Setup: opencode web, accessed at http://localhost:4096

Description

Dragging an image into the web chat input and sending it always fails. The message never reaches the server (no message=process entry appears in the server log for the failed attempt), so the failure is entirely client-side.

Browser console shows the real cause — the server's own Content-Security-Policy blocks the blob: URLs the web client uses to read back the dropped image:

Content-Security-Policy: ... blocked loading ... blob:http://localhost:4096/<uuid> (connect-src)
Content-Security-Policy: ... blocked loading ... blob:http://localhost:4096/<uuid> (img-src)

The CSP header is served by the opencode server itself for the web UI (HEAD / response):

Content-Security-Policy: default-src 'self'; script-src 'self' 'wasm-unsafe-eval' 'sha256-...';
  style-src 'self' 'unsafe-inline'; img-src 'self' data: https:; font-src 'self' data:;
  media-src 'self' data:; connect-src * data:

Neither img-src nor connect-src includes blob:. Per the CSP spec, the * wildcard does not match the blob: scheme, so:

• fetch(blob.url) → blocked by connect-src → throws NetworkError
• <img src="blob:..."> previews → blocked by img-src

Steps to reproduce

1. Run opencode web and open http://localhost:4096 in Firefox.
2. Drag an image file into the chat input.
3. Send the message.
4. Toast shows "Failed to send prompt"; console shows the CSP violations above.

Expected behavior

Images dropped into the web chat are base64-encoded and sent to the server (or otherwise processed), as designed.

Root cause analysis

The web client (packages/app) stores dropped images in IndexedDB and references them via URL.createObjectURL(blob) (packages/app/src/utils/draft-store.ts). On send, blobDataUrl() first does fetch(blob.url) to read the blob back into a base64 data URL (draft-store.ts), then posts it inline in the JSON body of POST /session/{id}/prompt_async (packages/app/src/components/prompt-input/submit.ts).

That fetch(blob.url) on a blob: URL is blocked by the server's CSP connect-src * data: directive, producing the NetworkError. The failing request therefore never reaches the server. The same CSP also blocks inline <img> previews of blob: URLs via img-src.

There is no separate image-upload endpoint; images are embedded inline as base64, so the blob: fetch step is on the critical path for every image attachment in the web UI.

Suggested fix

Include blob: in the CSP directives, e.g.:

img-src 'self' data: blob: https:;
connect-src * data: blob:

(or the minimum required: img-src and connect-src must allow blob:).

Longer term, moving attachments to a dedicated upload endpoint (write blob server-side, reference by ID) would also avoid inlining multi-MB base64 into a single JSON POST, but the CSP fix alone resolves this specific failure.

Workarounds (current)

• Attach the image by its file path via @C:\path\image.png in the input (server reads the file directly; avoids blob: fetch).
• Use the TUI (opencode) which is not affected by the browser CSP.

Logs

• Server log (~/.local/share/opencode/log/opencode.log): no entries for the failed send — confirms the request never reached the server.

Plugins

No response

OpenCode version

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Steps to reproduce

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Screenshot and/or share link

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Operating System

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Terminal

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