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Language Selection

Auto-Detection​

When no --language flag is provided, wasmrun detects the project language by checking for marker files:

FileDetected LanguageRuntime
package.jsonnodejswasmhub nodejs runtime
Cargo.tomlrustwasmhub rust runtime; OS-kernel integration pending
go.modgowasmhub go runtime; OS-kernel integration pending
requirements.txtpythonwasmhub rustpython runtime
pyproject.tomlpythonwasmhub rustpython runtime

Detection is checked in this order. The first match wins.

Runtime availability

The OS kernel currently registers the Node.js runtime only. Python (rustpython) and Go runtimes are scaffolded in the codebase but not yet enabled, so Node.js projects are the fully supported path today.

# Has package.json → detected as nodejs
wasmrun os ./my-node-app
# 🔍 Detected: nodejs project

# Has requirements.txt → detected as python
wasmrun os ./my-python-app
# 🔍 Detected: python project

If no marker files are found:

Could not auto-detect language for project: ./my-project
Please specify --language

Manual Override​

Use -l or --language to force a specific language:

wasmrun os ./my-app --language nodejs
wasmrun os ./my-app -l python

Supported Values​

ValueAliasesRuntime
nodejsnode, js, javascriptwasmhub nodejs
pythonpywasmhub rustpython (integration in progress)

Any other value is rejected: Unsupported OS mode language: '<value>'. Supported languages: nodejs, python.

# All equivalent
wasmrun os ./app --language nodejs
wasmrun os ./app --language node
wasmrun os ./app --language js
wasmrun os ./app --language javascript

When to Override​

Override is useful when:

  • The project has multiple language markers (e.g., both package.json and requirements.txt)
  • Auto-detection picks the wrong language
  • You want to test the same project with a different runtime
# Project has both package.json and requirements.txt
# Force Python
wasmrun os ./hybrid-project --language python

Runtime Fetching​

Language runtimes are WASM binaries from wasmhub, pinned to a specific wasmhub release. They're fetched on first use and cached at ~/.wasmrun/runtimes/:

~/.wasmrun/runtimes/
├── nodejs.json       # Metadata: version, sha256, wasmhub release
├── nodejs-20.wasm    # Runtime binary (filename comes from the wasmhub manifest)
└── ...

Language Name Mapping​

wasmrun maps detected language names to wasmhub runtime names:

Detected Languagewasmhub Runtime
nodejs, javascript, jsnodejs
pythonrustpython

Other names pass through unchanged.

Cache Management​

Cached runtimes are keyed to the wasmhub release wasmrun is pinned to; when a new wasmrun version bumps the pin, stale runtimes are invalidated and re-fetched automatically. To force a re-download manually:

# Remove cached runtime and metadata
rm ~/.wasmrun/runtimes/nodejs*

# Next run will re-fetch
wasmrun os ./my-app

Integrity​

Every download is validated with a SHA-256 checksum. If a cached file is corrupted, wasmrun detects the mismatch and re-downloads automatically.

Runtime API​

Check runtime status via the REST API:

# Get detected language and cache status
curl http://localhost:8420/api/runtimes
{
  "detected_language": "nodejs",
  "wasmhub_runtime": "nodejs",
  "cached": true,
  "cached_version": "0.1.4",
  "wasmhub_version": "0.3.2",
  "available_languages": ["nodejs", "rustpython"]
}

wasmhub_version and available_languages come from the live wasmhub manifest and are omitted if it can't be fetched.

# Download the runtime binary directly
curl http://localhost:8420/api/runtime/nodejs -o runtime.wasm

See Also​