Pandoc Converter (pypandoc) + Wasmer

This demo shows how to use pypandoc (a Python wrapper around Pandoc) to convert text between markup formats. The program provides a small web UI, but the focus here is on how pypandoc.convert_text(...) is used.

Demo

https://pandoc-converter-example.wasmer.app/

How it Works (sections from app.py)

All logic lives in one file. Here are the relevant code sections related to pypandoc:

Supported formats

A list of markup formats is declared. These are passed directly to pypandoc:

SUPPORTED_FORMATS = [
    ("markdown", "Markdown"),
    ("rst", "reStructuredText"),
    ("html", "HTML"),
    ("latex", "LaTeX"),
    ("mediawiki", "MediaWiki"),
    ("docbook", "DocBook"),
    ("org", "Org Mode"),
]

Conversion call

The actual conversion happens in the POST request handler. The work is run in a background thread to avoid blocking the server:

converted = await asyncio.to_thread(
    pypandoc.convert_text,
    text,
    to=target_format,
    format=source_format,
)

Key details:

• format specifies the source format.
• to specifies the target format.
• The return value is the converted text, ready to display or save.

Error handling

If Pandoc raises an error, it is caught and safely escaped for display:

except (RuntimeError, OSError) as exc:
    escaped_error = html.escape(str(exc))
    return ERROR_TEMPLATE.replace("{escaped_error}", escaped_error)

This ensures that unsupported conversions or missing executables don’t crash the app.

---

Running Locally

1. Create a requirements.txt:

fastapi
uvicorn
pypandoc

2. Install dependencies:

pip install -r requirements.txt

3. Run the server:

uvicorn app:app --host 0.0.0.0 --port 8000

4. Convert via API (example without UI):

curl -X POST http://localhost:8000/api/hx/convert \
  -F 'source_format=markdown' \
  -F 'target_format=rst' \
  -F 'text=# Hello **world**'

The response will contain the converted text wrapped in HTML.

API endpoints:

• GET /api/pandoc-convert?from=markdown&to=html&text=... returns converted content as plain text.
• POST /api/pandoc-convert?from=markdown&to=html with form field text returns converted content as plain text.

On failure, endpoints return JSON { "error": "<msg>" } with status 400.

---

Deploying to Wasmer Edge (Overview)

1. Include app.py and requirements.txt.
2. Deploy to Wasmer Edge and point the web process to run Uvicorn (e.g., uvicorn app:app --host 0.0.0.0 --port $PORT).
3. Open https://<your-subdomain>.wasmer.app/ and try converting text between formats.

---

⚡ With this setup, the key takeaway is how to call pypandoc.convert_text with format and to arguments to transform text between markup languages.

Would you like me to also add a minimal example without FastAPI (just showing pypandoc.convert_text in a script) so the README highlights the conversion part even more directly?