linting

.github/workflows/ci.yml

@@ -35,15 +35,6 @@ jobs:
       - name: Toolchain version
         run: go version
 
-      - name: Check gofmt
-        run: |
-          fmtout=$(gofmt -l .)
-          if [ -n "$fmtout" ]; then
-            echo "These files are not gofmt-clean:"
-            echo "$fmtout"
-            exit 1
-          fi
-
       # The Makefile defaults to gotip for local development; CI has a
       # real 1.27 toolchain on PATH as `go`.
       - name: Vet
@@ -64,3 +55,26 @@ jobs:
       # workflow's job.
       - name: Vet stress-tagged tests
         run: go vet -tags=stress ./integration/...
+
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Install Go
+        uses: actions/setup-go@v6
+        with:
+          go-version: ${{ env.GO_VERSION }}
+
+      # golangci-lint release binaries are built with the latest released
+      # Go and cannot type-check a `go 1.27` module, so build it from
+      # source with the toolchain installed above instead of using
+      # golangci/golangci-lint-action. setup-go's cache keeps this fast
+      # after the first run. Keep the pinned version in sync with the
+      # Makefile comment. Formatting (gofmt + goimports) is checked here
+      # too, via the formatters enabled in .golangci.yml.
+      - name: Install golangci-lint
+        run: go install github.com/golangci/golangci-lint/v2/cmd/golangci-lint@v2.12.2
+
+      - name: Lint
+        run: make GO=go lint

.golangci.yml

@@ -0,0 +1,85 @@
+version: "2"
+
+run:
+  # The stress tag only adds integration/stress_test.go; linting with it
+  # on covers the whole tree in one pass.
+  build-tags:
+    - stress
+
+linters:
+  # Standard set: errcheck, govet, ineffassign, staticcheck, unused.
+  default: standard
+  enable:
+    - gosec
+    - misspell
+    - unconvert
+  # golangci-lint vendors honnef.co/go/tools v0.7.0 (staticcheck
+  # 2026.1), whose IR builder panics on the Go 1.27 standard library.
+  # Re-enable staticcheck and unused once golangci-lint ships
+  # staticcheck 2026.2+.
+  disable:
+    - staticcheck
+    - unused
+  settings:
+    errcheck:
+      exclude-functions:
+        # Best-effort HTTP response writes; there is nothing useful to
+        # do with a client that hung up.
+        - (net/http.ResponseWriter).Write
+        # Close on a read-only body; errors there are meaningless.
+        - (io.ReadCloser).Close
+        # Fprint* is used on HTTP responses and hash.Hash writers, where
+        # the error is likewise not actionable.
+        - fmt.Fprint
+        - fmt.Fprintf
+        - fmt.Fprintln
+    gosec:
+      excludes:
+        # G104 (unhandled errors) duplicates errcheck, which is
+        # configured precisely above.
+        - G104
+        # G115 (integer overflow on conversion): tlog tile/index math
+        # converts between uint64, int64, and int pervasively and
+        # intentionally; the flagged sites are all bounded by tree size.
+        - G115
+        # G304 (file path from variable): key seeds, configs, and the
+        # storage root are operator-supplied paths by design.
+        - G304
+      config:
+        # Log data (tiles, checkpoints) is public and served over HTTP;
+        # world-readable directories and files are intentional.
+        G301: "0755"
+        G302: "0644"
+  exclusions:
+    rules:
+      # Tests build/run local binaries, hit local test servers with
+      # constructed URLs, and write world-readable fixtures; gosec's
+      # G107/G204/G306/G602 hits there are all noise.
+      - path: _test\.go
+        linters:
+          - gosec
+      # cactus-cli's purpose is fetching operator-supplied log URLs and
+      # reading operator-supplied cert files, so G703 (path traversal)
+      # and G704 (SSRF) flag the tool working as intended.
+      - path: cmd/cactus-cli/
+        text: "G70[34]"
+      # The tile handler serves stored binary tiles as
+      # application/octet-stream; G705's XSS taint trace (URL path ->
+      # storage key -> response body) is not script injection.
+      - path: tile/server\.go
+        text: "G705"
+
+issues:
+  # Report everything; the default per-linter and per-issue caps hide
+  # findings.
+  max-issues-per-linter: 0
+  max-same-issues: 0
+
+formatters:
+  enable:
+    - gofmt
+    - goimports
+  settings:
+    goimports:
+      local-prefixes:
+        - github.com/letsencrypt/cactus

CLAUDE.md

@@ -23,6 +23,8 @@ make build              # builds bin/cactus, bin/cactus-cli, bin/cactus-keygen,
 make test               # gotip test ./...
 make test-race          # gotip test -race ./...
 make vet                # gotip vet ./...
+make lint               # golangci-lint run (config: .golangci.yml)
+make fmt                # golangci-lint fmt (gofmt + goimports)
 make integration        # gotip test -race -count=1 -tags=integration ./integration/...
 make stress             # bulk issuance stress test (800 certs, `stress` build tag)
 

Makefile

@@ -1,4 +1,4 @@
-.PHONY: build test test-race vet integration stress clean \
+.PHONY: build test test-race vet lint fmt integration stress clean \
 	docker-binaries docker-build docker-up docker-down docker-logs
 
 # cactus requires Go 1.27+ (built-in crypto/mldsa). Until 1.27 ships, the
@@ -22,6 +22,20 @@ test-race:
 vet:
 	$(GO) vet ./...
 
+# golangci-lint must itself be built with a Go 1.27+ toolchain to
+# type-check this module, and its release binaries are built with the
+# latest released Go, so install it from source:
+#   gotip install github.com/golangci/golangci-lint/v2/cmd/golangci-lint@v2.12.2
+# The PATH prefix makes golangci-lint's `go` invocations use $(GO)'s
+# toolchain.
+GOLANGCI_LINT ?= golangci-lint
+
+lint:
+	PATH="$$($(GO) env GOROOT)/bin:$$PATH" GOTOOLCHAIN=local $(GOLANGCI_LINT) run
+
+fmt:
+	PATH="$$($(GO) env GOROOT)/bin:$$PATH" GOTOOLCHAIN=local $(GOLANGCI_LINT) fmt
+
 integration:
 	$(GO) test -race -count=1 -tags=integration ./integration/...
 

acme/concurrent_test.go

@@ -35,7 +35,9 @@ func TestConcurrentFinalizeOnSameOrder(t *testing.T) {
 		mustMarshal(NewOrderReq{Identifiers: []Identifier{{Type: "dns", Value: "race.test"}}}))
 	resp, body := post(t, base, "/new-order", jws)
 	var ord OrderResp
-	json.Unmarshal(body, &ord)
+	if err := json.Unmarshal(body, &ord); err != nil {
+		t.Fatalf("unmarshal order: %v", err)
+	}
 
 	csrKey, _ := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
 	csrTmpl := &x509.CertificateRequest{

acme/enhancement_test.go

@@ -80,7 +80,9 @@ func TestEnhancementURLPending(t *testing.T) {
 		mustMarshal(NewOrderReq{Identifiers: []Identifier{{Type: "dns", Value: "enh.test"}}}))
 	resp, body := post(t, hsrv.URL, "/new-order", jws)
 	var ord OrderResp
-	json.Unmarshal(body, &ord)
+	if err := json.Unmarshal(body, &ord); err != nil {
+		t.Fatalf("unmarshal order: %v", err)
+	}
 	csrKey, _ := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
 	csr, _ := x509.CreateCertificateRequest(rand.Reader, &x509.CertificateRequest{
 		Subject: pkix.Name{CommonName: "enh.test"}, DNSNames: []string{"enh.test"},
@@ -90,7 +92,9 @@ func TestEnhancementURLPending(t *testing.T) {
 		mustMarshal(FinalizeReq{CSR: base64.RawURLEncoding.EncodeToString(csr)}))
 	resp, body = post(t, hsrv.URL, strings.TrimPrefix(ord.Finalize, hsrv.URL), jws)
 	var ord2 OrderResp
-	json.Unmarshal(body, &ord2)
+	if err := json.Unmarshal(body, &ord2); err != nil {
+		t.Fatalf("unmarshal order: %v", err)
+	}
 	if ord2.Certificate == "" {
 		t.Fatal("missing cert URL")
 	}

acme/handler.go

@@ -1081,7 +1081,7 @@ func (s *Server) handleCert(w http.ResponseWriter, r *http.Request) {
 		// If neither is configured, fall back to plain PEM rather than
 		// emitting an empty list (which BuildPropertyList rejects).
 		if len(taID) == 0 {
-			pem.Encode(w, &pem.Block{Type: "CERTIFICATE", Bytes: der})
+			_ = pem.Encode(w, &pem.Block{Type: "CERTIFICATE", Bytes: der})
 			return
 		}
 		pl, err := cert.BuildPropertyList(props)
@@ -1093,7 +1093,7 @@ func (s *Server) handleCert(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	w.Header().Set("Content-Type", "application/pem-certificate-chain")
-	pem.Encode(w, &pem.Block{Type: "CERTIFICATE", Bytes: der})
+	_ = pem.Encode(w, &pem.Block{Type: "CERTIFICATE", Bytes: der})
 }
 
 // certIndex extracts the issuance-log index from a standalone cert's
@@ -1243,7 +1243,7 @@ func (s *Server) handleCertLandmarkRelative(w http.ResponseWriter, r *http.Reque
 		return
 	}
 	w.Header().Set("Content-Type", "application/pem-certificate-chain")
-	pem.Encode(w, &pem.Block{Type: "CERTIFICATE", Bytes: der})
+	_ = pem.Encode(w, &pem.Block{Type: "CERTIFICATE", Bytes: der})
 }
 
 // serveEnhancementPending is the §9.1 "not yet available" response for a

acme/handler_test.go

@@ -160,7 +160,9 @@ func TestDirectoryEndpoint(t *testing.T) {
 	}
 	defer resp.Body.Close()
 	var d Directory
-	json.NewDecoder(resp.Body).Decode(&d)
+	if err := json.NewDecoder(resp.Body).Decode(&d); err != nil {
+		t.Fatalf("decode directory: %v", err)
+	}
 	if d.NewAccount == "" || d.NewOrder == "" || d.NewNonce == "" {
 		t.Errorf("directory missing fields: %+v", d)
 	}
@@ -213,7 +215,9 @@ func TestEndToEndIssuance(t *testing.T) {
 		t.Fatalf("new-order status=%d body=%s", resp.StatusCode, body)
 	}
 	var ord OrderResp
-	json.Unmarshal(body, &ord)
+	if err := json.Unmarshal(body, &ord); err != nil {
+		t.Fatalf("unmarshal order: %v", err)
+	}
 	orderURL := resp.Header.Get("Location")
 	if ord.Status != "ready" {
 		t.Errorf("order status = %q, want ready (auto-pass)", ord.Status)
@@ -242,7 +246,9 @@ func TestEndToEndIssuance(t *testing.T) {
 		t.Fatalf("finalize status=%d body=%s", resp.StatusCode, body)
 	}
 	var ord2 OrderResp
-	json.Unmarshal(body, &ord2)
+	if err := json.Unmarshal(body, &ord2); err != nil {
+		t.Fatalf("unmarshal body: %v", err)
+	}
 	if ord2.Status != "valid" {
 		t.Errorf("order status after finalize = %q", ord2.Status)
 	}
@@ -314,7 +320,9 @@ func newAccountAndOrder(t *testing.T, base, dnsName string) (*ecdsa.PrivateKey,
 		t.Fatalf("new-order: %d %s", resp.StatusCode, body)
 	}
 	var ord OrderResp
-	json.Unmarshal(body, &ord)
+	if err := json.Unmarshal(body, &ord); err != nil {
+		t.Fatalf("unmarshal body: %v", err)
+	}
 	return acctKey, kid, ord, resp.Header.Get("Location")
 }
 

acme/http01_test.go

@@ -101,7 +101,9 @@ func TestHTTP01ChallengeMode(t *testing.T) {
 		mustMarshal(NewOrderReq{Identifiers: []Identifier{{Type: "dns", Value: chHost}}}))
 	resp, body := post(t, hsrv.URL, "/new-order", jws)
 	var ord OrderResp
-	json.Unmarshal(body, &ord)
+	if err := json.Unmarshal(body, &ord); err != nil {
+		t.Fatalf("unmarshal body: %v", err)
+	}
 	if ord.Status != "pending" {
 		t.Errorf("order should be pending in http-01 mode, got %q", ord.Status)
 	}
@@ -115,7 +117,9 @@ func TestHTTP01ChallengeMode(t *testing.T) {
 	jws = jwsSign(t, acctKey, nil, kid, nonce, ord.Authorizations[0], []byte("{}"))
 	resp, body = post(t, hsrv.URL, authzPath, jws)
 	var az AuthzResp
-	json.Unmarshal(body, &az)
+	if err := json.Unmarshal(body, &az); err != nil {
+		t.Fatalf("unmarshal body: %v", err)
+	}
 	if len(az.Challenges) == 0 {
 		t.Fatalf("no challenges; body=%s", body)
 	}
@@ -139,14 +143,15 @@ func TestHTTP01ChallengeMode(t *testing.T) {
 		t.Fatalf("challenge POST status=%d body=%s", resp.StatusCode, body)
 	}
 	var got ChallengeMsg
-	json.Unmarshal(body, &got)
+	if err := json.Unmarshal(body, &got); err != nil {
+		t.Fatalf("unmarshal body: %v", err)
+	}
 	if got.Status != "valid" {
 		t.Errorf("challenge status = %q, want valid", got.Status)
 	}
 
 	// The order should now be ready.
 	nonce = resp.Header.Get("Replay-Nonce")
-	jws = jwsSign(t, acctKey, nil, kid, nonce, hsrv.URL+"/order/"+lastSeg(ord.Finalize), []byte("{}"))
 	orderURL := strings.TrimSuffix(ord.Finalize, "/finalize/"+lastSeg(ord.Finalize)) + "/order/" + lastSeg(ord.Finalize)
 	_ = orderURL
 	// Skip the GET-as-POST order check; instead just finalize and
@@ -166,7 +171,9 @@ func TestHTTP01ChallengeMode(t *testing.T) {
 		t.Fatalf("finalize status=%d body=%s", resp.StatusCode, body)
 	}
 	var ord2 OrderResp
-	json.Unmarshal(body, &ord2)
+	if err := json.Unmarshal(body, &ord2); err != nil {
+		t.Fatalf("unmarshal body: %v", err)
+	}
 	if ord2.Status != "valid" {
 		t.Errorf("post-finalize order status = %q, want valid", ord2.Status)
 	}
@@ -228,13 +235,17 @@ func TestHTTP01ChallengeRejectsBadResponse(t *testing.T) {
 		mustMarshal(NewOrderReq{Identifiers: []Identifier{{Type: "dns", Value: chHost}}}))
 	resp, body := post(t, hsrv.URL, "/new-order", jws)
 	var ord OrderResp
-	json.Unmarshal(body, &ord)
+	if err := json.Unmarshal(body, &ord); err != nil {
+		t.Fatalf("unmarshal body: %v", err)
+	}
 	nonce = resp.Header.Get("Replay-Nonce")
 	authzURL := ord.Authorizations[0]
 	jws = jwsSign(t, acctKey, nil, kid, nonce, authzURL, []byte("{}"))
 	resp, body = post(t, hsrv.URL, strings.TrimPrefix(authzURL, hsrv.URL), jws)
 	var az AuthzResp
-	json.Unmarshal(body, &az)
+	if err := json.Unmarshal(body, &az); err != nil {
+		t.Fatalf("unmarshal body: %v", err)
+	}
 	if len(az.Challenges) == 0 {
 		t.Fatalf("no challenges; body=%s", body)
 	}

acme/persist_test.go

@@ -124,7 +124,9 @@ func finalizeOneCert(t *testing.T, base, dnsName string) (certURL, certID string
 		mustMarshal(NewOrderReq{Identifiers: []Identifier{{Type: "dns", Value: dnsName}}}))
 	resp, body := post(t, base, "/new-order", jws)
 	var ord OrderResp
-	json.Unmarshal(body, &ord)
+	if err := json.Unmarshal(body, &ord); err != nil {
+		t.Fatalf("unmarshal body: %v", err)
+	}
 
 	// CSR.
 	csrKey, _ := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
@@ -140,7 +142,9 @@ func finalizeOneCert(t *testing.T, base, dnsName string) (certURL, certID string
 		mustMarshal(FinalizeReq{CSR: base64.RawURLEncoding.EncodeToString(csrDER)}))
 	resp, body = post(t, base, strings.TrimPrefix(ord.Finalize, base), jws)
 	var ord2 OrderResp
-	json.Unmarshal(body, &ord2)
+	if err := json.Unmarshal(body, &ord2); err != nil {
+		t.Fatalf("unmarshal body: %v", err)
+	}
 	return ord2.Certificate, lastSegment(ord2.Certificate), acctKey, kid
 }
 

ca/issuer.go

@@ -10,10 +10,11 @@ import (
 	"math/big"
 	"time"
 
-	"github.com/letsencrypt/cactus/cert"
-	cactuslog "github.com/letsencrypt/cactus/log"
 	"golang.org/x/crypto/cryptobyte"
 	cryptobyte_asn1 "golang.org/x/crypto/cryptobyte/asn1"
+
+	"github.com/letsencrypt/cactus/cert"
+	cactuslog "github.com/letsencrypt/cactus/log"
 )
 
 // LogAPI is the subset of *log.Log the issuer needs. Defined as an

ca/validator.go

@@ -17,9 +17,10 @@ import (
 	"strings"
 	"time"
 
-	"github.com/letsencrypt/cactus/cert"
 	"golang.org/x/crypto/cryptobyte"
 	cryptobyte_asn1 "golang.org/x/crypto/cryptobyte/asn1"
+
+	"github.com/letsencrypt/cactus/cert"
 )
 
 // OrderInput carries the relevant ACME order state. It is the

cert/entry.go

@@ -8,8 +8,9 @@ import (
 	"hash"
 	"time"
 
-	"github.com/letsencrypt/cactus/tlogx"
 	"golang.org/x/crypto/cryptobyte"
+
+	"github.com/letsencrypt/cactus/tlogx"
 )
 
 // TBSCertificateLogEntry is the §5.2.1 ASN.1 SEQUENCE that the log