fix(backend): rate-limit and cap report ingest, drop wildcard CORS (closes #20)

POST /api/v1/reports stays unauthenticated but is bounded. Each client
address, as the trusted-proxy logic resolves it, may send
REPORTS_PER_MINUTE reports a minute (default 60, counted by
go-chi/httprate over a sliding minute); past that it gets 429 with
Retry-After. reportbuf refuses a report that would take the report
files past DATA_DIR_MAX_BYTES (default 1 GiB), counting the files
already in DATA_DIR and unwritten reports at their uncompressed size;
the handler answers 507. CORS adds nothing unless CORS_ALLOWED_ORIGINS
lists origins. A limit that is not a positive number, or an origin
that is not a plain scheme://host[:port], stops the server from
starting.

Model: opus-5-5

backend/internal/config/config_test.go

@@ -0,0 +1,64 @@
+package config_test
+
+import (
+	"strings"
+	"testing"
+
+	"sneak.berlin/go/netwatch/internal/config"
+	"sneak.berlin/go/netwatch/internal/globals"
+	"sneak.berlin/go/netwatch/internal/logger"
+
+	"go.uber.org/fx"
+)
+
+// requireConfigError builds the config as main does and fails the
+// test unless that fails with an error naming setting. It uses
+// fx.New, because fxtest.New fails the test itself on an error.
+func requireConfigError(t *testing.T, setting string) {
+	t.Helper()
+
+	app := fx.New(
+		fx.NopLogger,
+		fx.Provide(globals.New, logger.New, config.New),
+		fx.Invoke(func(*config.Config) {}),
+	)
+
+	err := app.Err()
+	if err == nil || !strings.Contains(err.Error(), setting) {
+		t.Fatalf("config error = %v, want one naming %s", err, setting)
+	}
+}
+
+// TestReportsPerMinuteMustBePositive: unchecked, zero would panic
+// when the routes are built, and a negative rate would lift the
+// limit.
+func TestReportsPerMinuteMustBePositive(t *testing.T) {
+	t.Setenv("REPORTS_PER_MINUTE", "0")
+
+	requireConfigError(t, "REPORTS_PER_MINUTE")
+}
+
+// TestDataDirMaxBytesMustBeANumber: viper reads a value that is not
+// a number, such as "1GB", as 0, which would refuse every report.
+func TestDataDirMaxBytesMustBeANumber(t *testing.T) {
+	t.Setenv("DATA_DIR_MAX_BYTES", "1GB")
+
+	requireConfigError(t, "DATA_DIR_MAX_BYTES")
+}
+
+// TestCORSAllowedOriginsMustBeOrigins: "*" would let every origin in,
+// and an entry that is not a plain origin would match no page.
+func TestCORSAllowedOriginsMustBeOrigins(t *testing.T) {
+	for _, entry := range []string{
+		"*",
+		"https://*.netwatch.example",
+		"netwatch.example",
+		"https://netwatch.example/",
+	} {
+		t.Run(entry, func(t *testing.T) {
+			t.Setenv("CORS_ALLOWED_ORIGINS", entry)
+
+			requireConfigError(t, "CORS_ALLOWED_ORIGINS")
+		})
+	}
+}