RTF to HTML Cloud Function

RTF in, clean HTML out: a Java 21 Google Cloud Function that converts uploaded RTF documents into self-contained HTML, powered by the ScroogeXHTML RTF converter library.

Features

• Rich formatting — fonts, paragraph indents and borders, tables with cell borders, hyperlinks, bookmarks and footnotes.
• Self-contained output — JPG, PNG and BMP pictures up to 256 KB are embedded as Base64 data URIs.
• Safe by default — link targets are allow-list filtered by the converter, every response carries a restrictive Content-Security-Policy, and the demo pages show the result in a sandboxed iframe.
• Bounded resources — uploads are limited to 1 MB and read with a hard cap.
• Origin-restricted — only requests from https://www.scroogexhtml.com are accepted (CORS).

Requirements

• JDK 21+ and Maven 3.8+
• Google Cloud CLI (gcloud) for deployment
• ScroogeXHTML 11.4.0-SNAPSHOT and ScroogeXHTML-Pictures 11.4.0-SNAPSHOT in your Maven repository — see scroogexhtml.com

Quick start

Build the shaded JAR:

mvn clean package

Run the function locally on http://localhost:8080/:

mvn function:run

Convert a document:

curl -H "Origin: https://www.scroogexhtml.com" -F "file=@document.rtf" http://localhost:8080/

Note

Browsers send their own Origin header, which the function rejects unless it matches ALLOWED_ORIGIN in RtfToHtml.java. To try demo-local.html in a browser, serve it from a local web server and set ALLOWED_ORIGIN to that server's origin.

API

POST / with a multipart/form-data body. The first part whose file name ends in .rtf is converted; the form field name does not matter.

Status	Meaning
200	Converted document (text/html; charset=utf-8)
204	CORS preflight (OPTIONS) from the allowed origin
400	Not multipart/form-data, malformed multipart body, or no .rtf file
403	Missing or disallowed Origin
405	Method other than POST or OPTIONS
413	File larger than 1 MB

Errors are returned as text/plain messages.

Deployment

Deploy the contents of target/ as a 2nd gen function, or run deploy.cmd on Windows:

gcloud functions deploy rtf-to-html-demo-11 \
  --gen2 \
  --runtime=java21 \
  --region=europe-west10 \
  --entry-point=demo.RtfToHtml \
  --source=./target \
  --trigger-http \
  --allow-unauthenticated \
  --max-instances=3

demo-prod.html calls the deployed endpoint.

Files over 1 MB are rejected before conversion. A file close to that limit can still take longer to convert than the default 60 s request timeout (seen with 1 MB of unformatted text on the default instance size); increase --cpu or --timeout if you need more headroom.

Configuration

All settings are constants and converter options in RtfToHtml.java:

Setting	Default
ALLOWED_ORIGIN	https://www.scroogexhtml.com
MAX_SIZE_BYTES	1 MB
CONTENT_SECURITY_POLICY	default-src 'none', inline styles and data: images allowed
Embedded picture limit	256 KB (MemoryPictureAdapterDataURI)
Table cell borders	Taken from the RTF document (setConvertCellStyles, experimental)

The experimental cell-style option logs a warning for every conversion. The converter options (tables, footnotes, hyperlinks, CSS, font size unit, …) are documented at scroogexhtml.com.

Learn more

• ScroogeXHTML RTF converter — features, documentation and downloads
• RTF to HTML in the cloud — background article on this project
• Google Cloud Functions for Java

License

Mozilla Public License 2.0