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Ports frontend/ (Jinja2/FastAPI, ~1180 LOC) to Go with html/template. No climate math, no DB, no auth here -- every route fetches from the backend's /content/* API, so this is I/O-bound glue with no hard-porting wall; the risk was always in reproducing the rendering exactly, not the language. Verified with a golden-HTML diff, not just unit tests: both the Python original and the Go rewrite were run against the same committed fixtures (frontend/tests/fixtures/) and every one of the 11 routes compared byte-for-byte. The only surviving differences after that process are insignificant inter-tag whitespace and one attribute where Go's stricter escaper HTML-encodes an apostrophe Jinja left literal (functionally identical in every browser) -- confirmed programmatically by normalizing whitespace and unescaping before diffing, not by eyeballing. That process caught defects unit tests alone would have missed, because map[string]any has no compile-time field check: - Render-context keys were snake_case throughout (content.py's Jinja convention, ported verbatim) while the templates -- written independently -- read PascalCase fields. A missing map key doesn't error in html/template, it silently renders empty, so this was invisible in every status code and every "it built" signal: title, meta description, canonical URL, OpenGraph tags, the homepage's entire ranked list, and the brand-tag/nav-active state were all blank across every page. Fixed by renaming every key to match each template's own header comment (the authoritative per-page field contract) and, where an API struct's exported fields already matched what a template needed (contentapi.CityInfo, Crumb, HomeRanked, HubCountry, ...), passing the struct straight through instead of hand-rewrapping it in a map -- removes a whole layer of future drift risk, not just this instance of it. - Three pages 500'd outright: `.ToolHref` needed a fully-composed href string, not the bare "lat,lon" fragment the handlers were building; the all-time-records table needed the raw contentapi.AllTimeRecords struct, not a re-wrapped map. - JSON-LD was being double-encoded: `<script type="application/ld+json">` is JAVASCRIPT context to html/template's contextual escaper regardless of the script's `type` attribute, so a template.HTML-typed value placed there gets re-escaped as a quoted JS string instead of emitted raw -- the entire structured-data payload shipped as a JSON string containing JSON, which no crawler would parse as the intended object. Needed template.JS instead, the type that actually means "trusted JS source." The glossary term page's JSON-LD was simply never built at all (the Jinja original assembled it inline in the template rather than through content.py's context dict, and that got lost in translation) -- added. - html/template silently strips literal HTML comments AND JavaScript comments from the parsed output (verified in isolation, zero template actions involved) -- confirmed as real engine behavior, not a bug in either port, so both need a FuncMap function returning template.HTML / template.JS respectively to survive parsing rather than a literal `<!-- -->` or `//` in the template source. Packaging: multi-stage Go build, final image alpine (not distroless -- the Swarm stack's env-entrypoint.sh shim needs bash), 187MB -> 22.6MB. Two defects caught before they reached a host: - The Swarm stack overrides `entrypoint:` with no `command:`, which drops the image's own CMD entirely (Docker/Swarm semantics, not merged) -- env-entrypoint.sh then fell through to its hardcoded `exec uvicorn app:app` fallback, which doesn't exist in this image. Every deploy would have exited 127. Fixed with an explicit `command:` on the stack's frontend service, and corrected the shim's stale comment claiming CMD passes through automatically. - `COPY --chown=thermograph` resolves the group by NAME at copy time; Alpine's `adduser -S` with no `-G` doesn't create a same-named group, so the classic (non-BuildKit) Docker builder -- which this CI runner falls back to, since it installs plain `docker.io` with no buildx plugin -- failed outright. Fixed with an explicit group and numeric --chown. Verification: go build/vet/test -race clean across all packages; the Docker image builds and passes its embedded go test step under both BuildKit and the classic builder; shellcheck 0 findings on the one script touched; rebased onto current main (the ERA5 lake stack landed on both main and dev during this work -- confirmed additive, no overlap with frontend/daemon).
59 lines
2.8 KiB
Markdown
59 lines
2.8 KiB
Markdown
# thermograph-frontend (Go)
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The SSR frontend service, ported from the Python implementation one directory
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up (`app.py` / `content.py` / `api_client.py` / `format.py`): server-rendered
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content pages, the interactive tool's SPA shells, and every static asset. It
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is I/O-bound glue over the backend's `/content/*` JSON API — no climate maths,
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no database, no auth.
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## Layout
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go.mod module thermograph/frontend (Go 1.26)
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main.go config + mux + static + graceful shutdown
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internal/config/ every env var the service reads (same names,
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defaults and required/optional split as the
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Python — see config.go's field docs)
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internal/contentapi/ backend /content/* client: TTL cache, bounded
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LRU, per-key single-flight, origin forwarding;
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typed payloads in types.go
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internal/render/ html/template engine over an embed.FS +
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response ETag helpers (W/"sha1[:20]",
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If-None-Match handling)
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internal/render/templates/ the page templates (embedded; *.tmpl)
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internal/contentdata/ glossary.yaml / pages.yaml loader (fail-loud
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validation, file order preserved)
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Dependencies: stdlib plus `gopkg.in/yaml.v3` — the committed SSR copy in
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`frontend/content/*.yaml` is shared with the rest of the repo and uses block/
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folded scalars, so a YAML parser is genuinely required.
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## Run locally
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cd frontend/server
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go build -o thermograph-frontend .
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cd .. # static/ and content/ resolve relative to the working dir
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THERMOGRAPH_API_BASE_INTERNAL=http://127.0.0.1:8137 \
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THERMOGRAPH_BASE=/thermograph \
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./server/thermograph-frontend
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`THERMOGRAPH_API_BASE_INTERNAL` is required — the boot fails loudly without it,
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same as the Python raised at import. Other env vars (all optional):
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`THERMOGRAPH_BASE` (default `/thermograph`; the image sets `/`),
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`THERMOGRAPH_API_VERSION` (default `v2` — bump only per the API-version pinning
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contract in `frontend/CLAUDE.md`), `THERMOGRAPH_API_BASE_PUBLIC`,
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`THERMOGRAPH_SSR_CACHE_TTL` (seconds, default 600),
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`THERMOGRAPH_GOOGLE_VERIFY` / `THERMOGRAPH_BING_VERIFY`, and `PORT`
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(default 8080).
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The process expects `static/` and `content/` in its working directory
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(`frontend/` locally, `/app` in the image). Templates are embedded in the
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binary; static assets and the YAML copy are read from disk.
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## Test / verify
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cd frontend/server
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go build ./... && go vet ./... && go test ./...
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The deployed binary is `/usr/local/bin/thermograph-frontend` inside the
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`emi/thermograph/frontend` image; the image name, `frontend-*` CI workflows and
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deploy path are unchanged from the Python service.
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