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gitea/contrib/render-plugins/example-wasm/README.md
Lunny Xiao 63fc35ea22
Add permissions for render plugin
2025-12-06 15:13:35 -08:00

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Go + WASM Render Plugin Example

This example shows how to build a frontend render plugin whose heavy lifting runs inside a WebAssembly module compiled from Go. The plugin loads the WASM binary in the browser, asks Go to post-process the fetched file content, and then renders the result inside the file viewer.

Files

  • manifest.json — plugin metadata consumed by the Gitea backend
  • render.js — the ES module entry point that initializes the Go runtime and renders files handled by the plugin
  • wasm/ — contains the Go source that compiles to plugin.wasm
  • wasm_exec.js — the Go runtime shim required by all Go-generated WASM binaries (copied verbatim from the Go distribution)
  • build.sh — helper script that builds plugin.wasm and produces a zip archive ready for upload

As with other plugins, declare any Gitea endpoints or external hosts the WASM module needs to call inside the permissions array in manifest.json. Without an explicit entry, the plugin may only download the file that is currently being rendered.

Build & Install

  1. Build the WASM binary and zip archive:

    cd contrib/render-plugins/example-wasm
./build.sh

    The script requires Go 1.21+ on your PATH. It stores the compiled WASM and an installable example-go-wasm.zip under dist/.

  2. In the Gitea web UI, visit Site Administration → Render Plugins, upload dist/example-go-wasm.zip, and enable the plugin.

  3. Open any file whose name ends with .wasmnote; the viewer will show the processed output from the Go code running inside WebAssembly.

How It Works

  • wasm/main.go exposes a single wasmProcessFile function to JavaScript. It uppercases each line, prefixes it with the line number, and runs entirely inside WebAssembly compiled from Go.
  • render.js injects the Go runtime (wasm_exec.js), instantiates the compiled module, and caches the exported wasmProcessFile function.
  • During initialization the frontend passes the sniffed MIME type and the first 1 KiB of file data to the plugin (options.mimeType/options.headChunk), allowing renderers to make decisions without issuing extra network requests.
  • During rendering the plugin downloads the target file, passes the contents to Go, and displays the transformed text with minimal styling.

Feel free to modify the Go source or the JS wrapper to experiment with richer interfaces between JavaScript and WebAssembly.