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).
2026-07-24 00:49:49 +00:00
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{{/* Ported from templates/glossary_term.html.j2. Extra data:
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.Breadcrumb; .Term string; .Others []{Slug, Term string};
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.JSONLDStr template.JS — the handler builds the WHOLE DefinedTerm object
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(the Jinja original interpolated `term|tojson` / `page_description|tojson`
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/ base_url inline; Go's JS-context escaping differs byte-wise from
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markupsafe's tojson, so the handler reproduces Python htmlsafe-tojson —
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ensure_ascii \uXXXX escapes plus <,>,&,' → <,>,&,' —
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and template.JS passes it through untouched);
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.Body template.HTML — glossary yaml `body` with {base} substituted. This
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is the Jinja `| safe` site: the content is trusted, committed copy from
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frontend/content/glossary.yaml, not user or API input. */}}{{template "base_head_start" .}}{{template "base_head_end" .}}<script type="application/ld+json">{{.JSONLDStr}}</script>{{template "base_body_start" .}}{{template "breadcrumb" .}}<article class="climate-page">
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<h1>{{.Term}}</h1>
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<p class="lede">{{.Body}}</p>
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<p><a class="cta" href="{{.Base}}/">See it live: grade any location's weather →</a></p>
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<div class="climate-foot">
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<h2>More terms</h2>
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<ul class="city-links">
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{{range .Others}}<li><a href="{{$.Base}}/glossary/{{.Slug}}">{{.Term}}</a></li>{{end}} </ul>
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</div>
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</article>
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{{template "base_body_end" .}}{{template "base_scripts_default" .}}{{template "base_tail" .}}
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