thermograph/frontend/server/internal/config
Emi Griffith 9eecfc8eef
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frontend: rewrite the SSR content service in Go
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).
2026-07-23 17:51:31 -07:00
..
config.go frontend: rewrite the SSR content service in Go 2026-07-23 17:51:31 -07:00
config_test.go frontend: rewrite the SSR content service in Go 2026-07-23 17:51:31 -07:00