fix: add @fastify/compress to reduce bundle transfer size on mobile

[eusip]

Problem

The Happier server serves the web UI JS bundle (~19MB) without any compression. On mobile networks this causes the TCP connection to drop mid-transfer. The iOS app surfaces this as:

Server not supported — unexpected response

Fix

Register @fastify/compress globally in startApi() so all HTTP responses are compressed (gzip/zstd) before transmission. This reduces the ~19MB bundle to ~4–5MB on the wire.

app.register(import('@fastify/compress'), { global: true });

The plugin is registered alongside the existing @fastify/cors and @fastify/rate-limit plugins in apps/server/sources/app/api/api.ts, which is the single entry point for both full and light server flavors.

Impact

• Fixes the iOS "Server not supported" connection drop on mobile networks
• Benefits all self-hosted deployments — no proxy configuration required
• No behavioral change on fast connections; compression is transparent

Verification

curl -sI --compressed https://<your-happier-instance> | grep content-encoding
# content-encoding: gzip

Summary by CodeRabbit

• Improvements
  • API responses now benefit from automatic compression, delivering faster load times and reduced bandwidth consumption.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 8d01e266-cc6d-4113-9683-94b1436803d5

📥 Commits

Reviewing files that changed from the base of the PR and between 4ee9219 and 287541b.

⛔ Files ignored due to path filters (1)

• yarn.lock is excluded by !**/yarn.lock, !**/*.lock

📒 Files selected for processing (2)

• apps/server/package.json
• apps/server/sources/app/api/api.ts

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Walkthrough

The changes add HTTP compression support to the Fastify server by introducing the @fastify/compress dependency and registering the compression middleware globally during API startup.

Changes

Cohort / File(s)	Summary
Fastify Compression Setup apps/server/package.json, apps/server/sources/app/api/api.ts	Added @fastify/compress dependency (v8.3.1) and registered compression middleware in global mode for HTTP response compression.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely summarizes the main change: adding @fastify/compress to reduce bundle transfer size on mobile networks, which directly matches the primary objective of the PR.
Description check	✅ Passed	The PR description covers the problem statement, the fix implementation, impact analysis, and verification steps. While the template's 'How to test' section uses numbered steps, the description provides a verification command that accomplishes the same purpose. All critical information is present and well-structured.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[greptile-apps]

Greptile Summary

Registers @fastify/compress globally in startApi() to compress HTTP responses before transmission, reducing the ~19 MB JS bundle to ~4–5 MB on the wire and fixing the iOS "Server not supported" TCP drop on mobile. The plugin is correctly placed after cors / rate-limit and before route registration, so all Fastify-handled routes benefit without any per-route changes.

Confidence Score: 5/5

Safe to merge — the change is minimal, correct, and all remaining feedback is a non-blocking performance suggestion

Only a P2 observation about per-request re-compression overhead remains; no correctness, security, or reliability issues were found

No files require special attention

Important Files Changed

Filename	Overview
apps/server/sources/app/api/api.ts	Registers @fastify/compress globally after cors and rate-limit; plugin is correctly placed before route registration so all responses will be compressed
apps/server/package.json	Adds @fastify/compress@8.3.1 (exact-pinned, consistent with @fastify/swagger and @sentry/node); also reorders @sentry/node and @socket.io/redis-streams-adapter alphabetically
yarn.lock	Adds lock entries for @fastify/compress and its transitive deps (peek-stream, pumpify, duplexify, through2, stream-shift); lock changes look consistent with the declared dependency

Sequence Diagram

sequenceDiagram
    participant Client as iOS / Mobile Client
    participant Fastify as Fastify Server
    participant Compress as @fastify/compress
    participant StaticHandler as enableServeUi

    Client->>Fastify: GET / (Accept-Encoding: gzip)
    Fastify->>Compress: onSend hook (check Accept-Encoding)
    Fastify->>StaticHandler: route handler
    StaticHandler->>StaticHandler: readFile(index.html / bundle.js)
    StaticHandler-->>Fastify: reply.send(Buffer ~19MB)
    Fastify->>Compress: compress buffer (gzip)
    Compress-->>Fastify: compressed payload ~4-5MB
    Fastify-->>Client: 200 OK (Content-Encoding: gzip, ~4-5MB)

    Client->>Fastify: GET /v1/auth (Accept-Encoding: gzip)
    Fastify->>Compress: onSend hook
    Fastify-->>Client: 200 OK (Content-Encoding: gzip, small JSON)

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Comments Outside Diff (1)

1. apps/server/sources/app/api/utils/enableServeUi.ts, line 30-83 (link)

   Per-request re-compression of large static assets

   readFile loads the entire file into a Buffer and then @fastify/compress compresses it in-process on every request. For the ~19 MB JS bundle this means ~19 MB allocated for the raw content plus another pass to produce the compressed output on every cold fetch — with no caching of the compressed result.

   This works correctly and solves the mobile drop, but it adds CPU pressure proportional to concurrent downloads. A lower-cost alternative is to pre-compress the bundle at build time (emitting .gz / .br siblings) and serve the pre-compressed file directly, or to cache the compressed Buffer keyed by file path after the first compression. Not required to merge, but worth a follow-up ticket if the server serves the bundle to many concurrent mobile clients.

_{Reviews (1): Last reviewed commit: "fix: add @fastify/compress to reduce bun..." | Re-trigger Greptile}