daily-blood-pressure

Subscribable calendar feed of your daily Withings blood pressure measurements. A cron job fetches your readings once a day and publishes them as a .ics file you can subscribe to in Apple Calendar, Fantastical, Google Calendar, or any other calendar app.

Each reading appears as an all-day event titled 120/80 mmHg (7:04 AM) on the date you took the measurement.

Stack: Vercel (cron + blob storage) · Upstash Redis · Withings API

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What you need

• A Withings blood pressure monitor and account
• A Vercel account (free Hobby plan is fine)
• Node.js 18 or later
• The Vercel CLI: npm i -g vercel

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Setup

Clone the repo and install dependencies:

git clone https://github.com/omarmung/daily-blood-pressure.git
cd daily-blood-pressure
npm install

Log in to Vercel if you haven't already:

vercel login

Run the setup script:

npm run setup

The script walks you through everything in six steps:

1. Pick a project name — determines your Vercel URL (e.g. daily-bp-dustin → daily-bp-dustin.vercel.app)
2. Create a Withings developer app — the script gives you the exact callback URL to register; make sure to check "Public API integration" when creating the app
3. Configure your feed — name, start date, and timezone
4. Connect to Vercel — links the project and sets all environment variables automatically
5. Connect storage — Upstash Redis (for OAuth tokens) and Vercel Blob (for the .ics file), both from the Vercel dashboard
6. Deploy and authorize — deploys the project and walks you through the Withings OAuth flow

Total time: about 5 minutes.

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Subscribing to the feed

At the end of npm run setup, the script prints your .ics URL directly. Copy it and subscribe in your calendar app:

• Apple Calendar: File → New Calendar Subscription → paste the URL
• Fantastical: File → New Calendar Subscription → paste the URL
• Google Calendar: Other calendars → From URL → paste the URL

The calendar app will poll the feed periodically and new readings will appear within a few hours of the cron running. The cron schedule is set in vercel.json — adjust it to fit your timezone.

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How it works

Vercel Cron (daily)
  → refreshes Withings OAuth token (stored in Upstash Redis)
  → fetches all blood pressure measurements since FEED_START_DATE
  → generates a .ics file with one all-day event per reading
  → overwrites bp-{name}.ics in Vercel Blob

Each reading session produces one calendar event. Readings with only systolic or only diastolic present are skipped.

Multiple people

The codebase is designed for one Withings account per deployment. To run feeds for two people, deploy the repo twice with different FEED_NAME values and different Withings credentials. Both deployments can share the same Vercel Blob and Upstash Redis — the FEED_NAME namespaces all keys so there are no collisions.

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Environment variables

Variable	Description
WITHINGS_CLIENT_ID	From your Withings developer app
WITHINGS_CLIENT_SECRET	From your Withings developer app
FEED_NAME	Short identifier, e.g. dustin — used in filenames and the calendar title
FEED_START_DATE	Earliest date to include, e.g. 2024-01-01
FEED_TIMEZONE	IANA timezone name, e.g. America/Los_Angeles
UPSTASH_REDIS_REST_URL	Auto-provisioned when you connect Upstash Redis in Vercel
UPSTASH_REDIS_REST_TOKEN	Auto-provisioned when you connect Upstash Redis in Vercel
BLOB_READ_WRITE_TOKEN	Auto-provisioned when you connect Vercel Blob
CRON_SECRET	Auto-injected by Vercel to authenticate cron invocations

The setup script sets all the manual variables for you. The auto-provisioned ones appear automatically once you connect the storage services in the Vercel dashboard.

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Roadmap

• Append-only mode — on first run, fetch all history back to FEED_START_DATE; on subsequent runs, only fetch measurements since the last sync. Reduces Withings API calls as history grows.
• /api/status endpoint — returns the last successful sync timestamp from Redis, so you can verify the cron is running without checking Vercel logs.
• Input validation in setup script — validate FEED_START_DATE format and FEED_TIMEZONE against the IANA database before setting env vars.
• Custom domain support — the setup script currently assumes a .vercel.app URL; it should handle custom domains gracefully.
• Direct storage link in setup — step 5 currently links to the generic Vercel dashboard; should construct a direct link to the project's storage page.

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Re-authorizing

If your Withings token ever becomes invalid (e.g. after a long gap), visit:

https://your-project.vercel.app/api/auth

Before doing so, delete the bp:withings:refresh:{FEED_NAME} and bp:withings:userid:{FEED_NAME} keys from your Upstash Redis database, then complete the OAuth flow again.