Give every JSON answer @meta, errors included (closes #201)

A panic in a JSON route's handler answered 500 with an empty body,
because the router's recoverer sits outside the middleware that adds
`@meta`. `JSONValidationMiddleware` now wraps the handler in the same
recoverer, and answers the panic with the JSON error body.

`/status.json` and the health check answered chi's empty 405 to any
method they do not take. They now answer with the same JSON 405 as the
routes under `/api/v1` and `/ip`.

The home page's IP lookup card showed only the answer's `data`. It now
shows the whole answer, `@meta` included.

A table test checks `@meta` on every JSON route, in its successes and
its errors.

Model: opus-5-5

internal/server/middleware_internal_test.go

@@ -2,6 +2,7 @@ package server
 
 import (
 	"bytes"
+	"context"
 	"encoding/json"
 	"io"
 	"log/slog"
@@ -119,7 +120,7 @@ func TestJSONAnswersPutNoUnitInAString(t *testing.T) {
 	paths := []string{
 		statusJSONPath,
 		statsPath,
-		"/.well-known/healthcheck.json",
+		healthCheckPath,
 		"/api/v1/ip/" + untrustedPeerAddr,
 		"/ip/" + untrustedPeerAddr,
 		asJSONPath,
@@ -156,6 +157,144 @@ func TestJSONAnswersPutNoUnitInAString(t *testing.T) {
 	}
 }
 
+// TestJSONAnswersCarryMeta sends requests to every JSON route through the
+// server's router, and checks that each answer carries @meta with its three
+// fields. The answers include successes, and errors that the handlers, the
+// router and the middleware write. Before the fix a panic in a handler, and a
+// method /status.json or the health check does not take, answered with an
+// empty body (https://git.eeqj.de/sneak/routewatch/issues/201).
+func TestJSONAnswersCarryMeta(t *testing.T) {
+	t.Parallel()
+
+	// JSON routes whose handlers write nothing or panic, so that the JSON
+	// check on the route writes the error answer itself.
+	const (
+		writesNothingPath = "/writes-nothing.json"
+		panicsPath        = "/panics.json"
+	)
+
+	s := newServerWithTestRoutes(t)
+	s.resolver = &fakeResolver{}
+	s.streamer.GetMetricsTracker().SetConnected(true)
+	s.router.Get(writesNothingPath, JSONValidationMiddleware(http.HandlerFunc(
+		func(http.ResponseWriter, *http.Request) {})).ServeHTTP)
+	s.router.Get(panicsPath, JSONValidationMiddleware(http.HandlerFunc(
+		func(http.ResponseWriter, *http.Request) { panic(errDiskIO) })).ServeHTTP)
+
+	tests := []struct {
+		method   string
+		path     string
+		wantCode int
+	}{
+		// Answers that succeed
+		{http.MethodGet, statusJSONPath, http.StatusOK},
+		{http.MethodGet, healthCheckPath, http.StatusOK},
+		{http.MethodGet, "/ip", http.StatusOK},
+		{http.MethodGet, ownAddressPath, http.StatusOK},
+		{http.MethodGet, "/ip/" + addrInTestPrefixV4, http.StatusOK},
+		{http.MethodGet, statsPath, http.StatusOK},
+		{http.MethodGet, "/api/v1/ip/" + addrInTestPrefixV4, http.StatusOK},
+		{http.MethodGet, asJSONPath, http.StatusOK},
+		{http.MethodGet, "/api/v1/prefix/" + testPrefixV4, http.StatusOK},
+		{http.MethodGet, "/api/v1/search/as?q=google", http.StatusOK},
+		// Errors the handlers write
+		{http.MethodGet, "/ip/no-such-host.example", http.StatusBadRequest},
+		{http.MethodGet, "/api/v1/ip/no-such-host.example", http.StatusBadRequest},
+		{http.MethodGet, "/api/v1/as/foo", http.StatusBadRequest},
+		{http.MethodGet, "/api/v1/as/0", http.StatusNotFound},
+		{http.MethodGet, "/api/v1/prefix/192.0.2.0/33", http.StatusBadRequest},
+		{http.MethodGet, "/api/v1/prefix/198.51.100.0/24", http.StatusNotFound},
+		{http.MethodGet, "/api/v1/search/as", http.StatusBadRequest},
+		// Errors the router and the middleware write
+		{http.MethodGet, "/api/v1/no-such-route", http.StatusNotFound},
+		{http.MethodGet, "/ip/192.0.2.1/nothing", http.StatusNotFound},
+		{http.MethodPost, statsPath, http.StatusMethodNotAllowed},
+		{http.MethodPost, ownAddressPath, http.StatusMethodNotAllowed},
+		{http.MethodPost, statusJSONPath, http.StatusMethodNotAllowed},
+		{http.MethodPut, healthCheckPath, http.StatusMethodNotAllowed},
+		{http.MethodGet, writesNothingPath, http.StatusInternalServerError},
+		{http.MethodGet, panicsPath, http.StatusInternalServerError},
+	}
+
+	for _, tt := range tests {
+		checkAnswerCarriesMeta(t, s, httptest.NewRequestWithContext(
+			t.Context(), tt.method, tt.path, nil), tt.wantCode)
+	}
+
+	// A request whose time limit has already passed answers 504. The handlers
+	// write the answers of the first five routes, and the JSON check on the
+	// route writes the last.
+	pastTimeLimit, cancel := context.WithDeadline(t.Context(), time.Now())
+	defer cancel()
+
+	for _, path := range []string{
+		statusJSONPath, statsPath, "/ip/" + addrInTestPrefixV4,
+		"/api/v1/ip/" + addrInTestPrefixV4, asJSONPath, writesNothingPath,
+	} {
+		checkAnswerCarriesMeta(t, s, httptest.NewRequestWithContext(
+			pastTimeLimit, http.MethodGet, path, nil), http.StatusGatewayTimeout)
+	}
+
+	// With a store whose reads fail, the health check answers 503, and the
+	// handlers of the other routes 500.
+	failing := New(failingDB{}, newTestTable(),
+		streamer.New(logger.New(), metrics.New()), logger.New(), &config.Config{})
+	failing.resolver = &fakeResolver{}
+
+	checkAnswerCarriesMeta(t, failing, httptest.NewRequestWithContext(
+		t.Context(), http.MethodGet, healthCheckPath, nil),
+		http.StatusServiceUnavailable)
+
+	for _, path := range []string{
+		statusJSONPath, statsPath, asJSONPath,
+		"/api/v1/ip/" + addrInTestPrefixV4, "/ip/" + addrInTestPrefixV4,
+	} {
+		checkAnswerCarriesMeta(t, failing, httptest.NewRequestWithContext(
+			t.Context(), http.MethodGet, path, nil), http.StatusInternalServerError)
+	}
+}
+
+// checkAnswerCarriesMeta serves req through the server's router, and checks
+// that it answers wantCode with @meta and its three fields.
+func checkAnswerCarriesMeta(
+	t *testing.T, s *Server, req *http.Request, wantCode int,
+) {
+	t.Helper()
+
+	// The values README "API v1" gives the two fields that never change.
+	const (
+		wantTimeZone   = "UTC"
+		wantAPIVersion = 1
+	)
+
+	name := req.Method + " " + req.URL.String()
+
+	rec := httptest.NewRecorder()
+	s.router.ServeHTTP(rec, req)
+
+	if rec.Code != wantCode {
+		t.Errorf("%s: status %d, want %d; body %s", name, rec.Code, wantCode, rec.Body)
+	}
+
+	var answer map[string]any
+
+	err := json.Unmarshal(rec.Body.Bytes(), &answer)
+	if err != nil {
+		t.Errorf("%s: decoding the answer %q: %v", name, rec.Body, err)
+
+		return
+	}
+
+	meta, _ := answer[jsonKeyMeta].(map[string]any)
+	_, timeIsNumber := meta[metaKeyExecutionTimeMs].(float64)
+
+	if meta[metaKeyTimeZone] != wantTimeZone ||
+		meta[metaKeyAPIVersion] != float64(wantAPIVersion) || !timeIsNumber {
+		t.Errorf("%s: @meta %v, want time_zone %q, api_version %d and a "+
+			"number in execution_time_ms", name, meta, wantTimeZone, wantAPIVersion)
+	}
+}
+
 // stringsIn returns every string in a decoded JSON value, at any depth.
 func stringsIn(value any) []string {
 	var found []string