resolver: error from ResolveIPAddresses when no nameserver answered (closes #190)

ResolveIPAddresses now returns an error, not no addresses, when no
nameserver of the name's zone answered. A nameserver with status
timeout or error is not an answer; one answer, even NXDOMAIN, is
enough for an empty result without an error.

When every server of a zone fails, FindAuthoritativeNameservers moves
on to the parent name, whose servers only refer the query onward. Such
a referral now has status error, so it is no answer either, and a
hostname's saved records show it as error. The only caller, the
nameserver address lookup, already keeps the previous addresses on an
error; its comment no longer says the resolver hides this case.

Model: opus-5-5

README.md

@@ -491,8 +491,9 @@ tracks reachability:
 | `error`     | Query failed (timeout, SERVFAIL, REFUSED, network error)   |
 
 A nameserver that answers NXDOMAIN or with no records has status `ok` and
-empty `records`. A nameserver whose query failed has status `error`, empty
+empty `records`. A nameserver whose query failed, or that only referred it to
-`records`, and the reason in `error`.
+other nameservers, has status `error`, empty `records`, and the reason in
+`error`.
 
 `nameserverAddresses` lists, by nameserver, the sorted addresses its name
 resolves to. A state file without it loads, and the next check fills it in
@@ -508,9 +509,8 @@ standard: normalized scripts in `script/` are the entrypoints for the
 development workflow, and the Makefile targets are thin shims that call
 them. We provide:
 
-- `script/bootstrap` — install all dependencies (go, pinned goimports,
+- `script/bootstrap` — install all dependencies (go, `go mod download`).
-  `go mod download`). It does not install golangci-lint: see
+  It does not install golangci-lint: see `script/lint` below.
-  `script/lint` below.
 - `script/setup` — make a fresh clone ready for development: bootstrap
   plus the git pre-commit hook
 - `script/projectname` — print the project name (used for the Docker
@@ -527,8 +527,10 @@ them. We provide:
   host, and Docker is the only prerequisite. Caching is waived for
   linting: the lint stage is forced to execute on every run with
   `--no-cache-filter`, because a cached build lints nothing.
-- `script/fmt` — format all code (gofmt -s, goimports)
+- `script/fmt` — format all code (gofmt -s, goimports). goimports runs
-- `script/fmt-check` — check formatting (read-only)
+  with `go run` at a pinned commit, never from your `PATH`.
+- `script/fmt-check` — check formatting (read-only) with the same tools,
+  failing on any file `script/fmt` would change
 - `script/check` — run test, lint, and fmt-check
 - `script/docker` — build the Docker image tagged via `script/projectname`, with
   `--no-cache-filter=lint,builder` so the lint stage and the builder stage,

TODO.md

@@ -22,6 +22,8 @@ https://git.eeqj.de/sneak/dnswatcher/issues/149
 
 - 2026-10-01: `ResolveIPAddresses` returns an error, not no addresses, when no
   nameserver of the name's zone answered (closes #190).
+- 2026-10-01: `make fmt-check` fails on a file `goimports` would change; both
+  format scripts run `goimports` at its pinned commit, not from `PATH` (#119).
 - 2026-10-01: a hostname is queried at the servers of the zone it is in, found
   by following delegations for the name, not its last two labels (closes #189).
 - 2026-10-01: each nameserver's addresses are saved with its domain, and a
@@ -114,7 +116,7 @@ https://git.eeqj.de/sneak/dnswatcher/issues/149
 
 - 1.0 readiness: run it with a real config and read the logs:
   https://git.eeqj.de/sneak/dnswatcher/issues/66
-- `goimports` in `make fmt-check`, Markdown formatting:
+- Markdown formatting with prettier:
   https://git.eeqj.de/sneak/dnswatcher/issues/119
 - README accuracy sweep: https://git.eeqj.de/sneak/dnswatcher/issues/108
 - README sections required by policy:

internal/resolver/errors.go

@@ -11,8 +11,8 @@ var (
 	)
 
 	// ErrNoNameserverAnswered is returned when every nameserver
-	// asked about a name timed out or failed, so whether the name
+	// asked about a name timed out, failed or returned a referral,
-	// has addresses is unknown.
+	// so whether the name has addresses is unknown.
 	ErrNoNameserverAnswered = errors.New("no nameserver answered")
 
 	// ErrCNAMEDepthExceeded is returned when a CNAME chain

internal/resolver/iterative.go

@@ -516,6 +516,7 @@ type queryState struct {
 	gotSERVFAIL bool
 	gotRefused  bool
 	gotTimeout  bool
+	gotReferral bool
 	netErr      error
 	hasRecords  bool
 }
@@ -578,6 +579,18 @@ func (r *Resolver) querySingleType(
 		return
 	}
 
+	// A reply with no answer that lists other nameservers, from a server
+	// that does not hold the name's zone, is a referral and says nothing
+	// about the name's records. A parent zone's servers send one when
+	// every server of the name's own zone failed and
+	// FindAuthoritativeNameservers moved on to the parent name.
+	if !msg.Authoritative && len(msg.Answer) == 0 &&
+		len(extractNSSet(msg.Ns)) > 0 {
+		state.gotReferral = true
+
+		return
+	}
+
 	collectAnswerRecords(msg, resp, state)
 }
 
@@ -626,6 +639,9 @@ func classifyResponse(resp *NameserverResponse, state queryState) {
 	case state.netErr != nil && !state.hasRecords:
 		resp.Status = StatusError
 		resp.Error = "network error: " + state.netErr.Error()
+	case state.gotReferral && !state.hasRecords:
+		resp.Status = StatusError
+		resp.Error = "server returned a referral"
 	case !state.hasRecords && !state.gotNXDomain:
 		resp.Status = StatusNoData
 	}
@@ -735,8 +751,8 @@ func (r *Resolver) LookupAllRecords(
 
 // ResolveIPAddresses resolves a hostname to all IPv4 and IPv6
 // addresses, following CNAME chains up to MaxCNAMEDepth. When no
-// nameserver of the name's zone answered, it returns an error wrapping
+// nameserver of the name's zone answered, it returns an error rather
-// ErrNoNameserverAnswered rather than no addresses.
+// than no addresses.
 func (r *Resolver) ResolveIPAddresses(
 	ctx context.Context,
 	hostname string,
@@ -778,8 +794,8 @@ func (r *Resolver) resolveIPWithCNAME(
 
 // collectIPs returns the addresses in the nameservers' answers and the
 // first CNAME target among them. It returns ErrNoNameserverAnswered when
-// every nameserver timed out or failed: that is not a name with no
+// every nameserver timed out, failed or returned a referral: that is not
-// addresses.
+// a name with no addresses.
 func collectIPs(
 	results map[string]*NameserverResponse,
 ) ([]string, string, error) {

internal/resolver/iterative_test.go

@@ -25,6 +25,22 @@ func TestCollectIPs_OneAnswerIsEnough(t *testing.T) {
 	assert.Empty(t, ips)
 }
 
+// TestCollectIPs_FailedIsNoAnswer checks that nameservers that all have
+// status error, from a refusal, a server failure, a network error or a
+// referral, are no answer rather than a name with no addresses.
+func TestCollectIPs_FailedIsNoAnswer(t *testing.T) {
+	t.Parallel()
+
+	ips, _, err := resolver.CollectIPs(
+		map[string]*resolver.NameserverResponse{
+			"ns1.example.": {Status: resolver.StatusError},
+			"ns2.example.": {Status: resolver.StatusError},
+		},
+	)
+	require.ErrorIs(t, err, resolver.ErrNoNameserverAnswered)
+	assert.Empty(t, ips)
+}
+
 func TestExtractRecordValue_LetterCase(t *testing.T) {
 	t.Parallel()
 

internal/resolver/resolver_test.go

@@ -662,6 +662,53 @@ func TestCollectIPs_NoNameserverAnswered(t *testing.T) {
 	assert.Empty(t, ips)
 }
 
+// TestCollectIPs_ReferralIsNoAnswer asks a root server about
+// example.com, which the root zone does not hold, so it only refers the
+// query to the com servers. That reply is no answer, as is a parent
+// zone's when every server of the name's own zone failed.
+func TestCollectIPs_ReferralIsNoAnswer(t *testing.T) {
+	t.Parallel()
+
+	r := newTestResolver(t)
+
+	var resp *resolver.NameserverResponse
+
+	livednstest.Retry(
+		t,
+		"QueryNameserverIP(a.root-servers.net, example.com)",
+		func(ctx context.Context) error {
+			var err error
+
+			resp, err = r.QueryNameserverIP(
+				ctx, "a.root-servers.net.", "198.41.0.4",
+				"example.com",
+			)
+			if err != nil {
+				return err
+			}
+
+			// A timeout or a network error is no reply at all.
+			if resp.Status == resolver.StatusTimeout ||
+				strings.HasPrefix(resp.Error, "network error") {
+				return fmt.Errorf(
+					"%w: %s", livednstest.ErrNoAnswer, resp.Error,
+				)
+			}
+
+			return nil
+		},
+	)
+
+	assert.Equal(t, resolver.StatusError, resp.Status)
+	assert.Equal(t, "server returned a referral", resp.Error)
+
+	ips, _, err := resolver.CollectIPs(
+		map[string]*resolver.NameserverResponse{resp.Nameserver: resp},
+	)
+	require.ErrorIs(t, err, resolver.ErrNoNameserverAnswered)
+	assert.Empty(t, ips)
+}
+
 func TestResolveIPAddresses_ContextCanceled(t *testing.T) {
 	t.Parallel()
 

script/bootstrap

@@ -3,9 +3,8 @@
 # this repo. Idempotent: every install is guarded by a check so already
 # installed tools are skipped. Base tooling comes from nix, apt, brew,
 # or apk (detected in that order); assumes nothing is present.
-# goimports is installed via `go install` at a pinned commit (never
+# goimports is not installed here: script/fmt and script/fmt-check run
-# "latest") because script/fmt runs it on the host; script/fmt-check
+# it with `go run` at a pinned commit.
-# does not (it runs gofmt only).
 # The linter is NOT installed here: golangci-lint runs via docker only
 # (script/lint), pinned by image digest, so its only prerequisite is a
 # working docker.
@@ -13,10 +12,6 @@ set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
-# Pinned version, 2026-08-07 (same pin as the Dockerfile)
-# goimports v0.42.0
-GOIMPORTS_REF="golang.org/x/tools/cmd/goimports@009367f5c17a8d4c45a961a3a509277190a9a6f0"
-
 PKGMGR=""
 SUDO=""
 APT_UPDATED=""
@@ -71,10 +66,6 @@ main() {
     if missing make; then pkg_install gnumake make make make; fi
     if missing go; then pkg_install go golang go go; fi
 
-    # Format tools, pinned via go install (installs into
-    # "$(go env GOPATH)/bin"; ensure that is on your PATH).
-    if missing goimports; then go install "$GOIMPORTS_REF"; fi
-
     # Linting runs via docker only (script/lint). Warn, don't fail:
     # everything except `make lint` works without it.
     if missing docker; then

script/fmt

@@ -1,13 +1,19 @@
 #!/bin/sh
 # script/fmt: format all files (writes).
+#
+# goimports runs with `go run` at a pinned commit, never from PATH, so
+# every machine formats with the same version and nothing installs it.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
+# goimports v0.42.0, 2026-08-07. Must match script/fmt-check.
+GOIMPORTS_REF="golang.org/x/tools/cmd/goimports@009367f5c17a8d4c45a961a3a509277190a9a6f0"
+
 main() {
     cd "$ROOT"
     gofmt -s -w .
-    goimports -w .
+    go run "$GOIMPORTS_REF" -w .
 }
 
 main "$@"

script/fmt-check

@@ -1,18 +1,27 @@
 #!/bin/sh
-# script/fmt-check: check formatting (read-only). Same scope as
+# script/fmt-check: check formatting (read-only). Same tools and scope
-# script/fmt, but fails instead of writing.
+# as script/fmt, but fails instead of writing.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
+# goimports v0.42.0, 2026-08-07. Must match script/fmt.
+GOIMPORTS_REF="golang.org/x/tools/cmd/goimports@009367f5c17a8d4c45a961a3a509277190a9a6f0"
+
 main() {
     cd "$ROOT"
-    files="$(gofmt -l .)"
+    files="$(gofmt -s -l .)"
     if [ -n "$files" ]; then
         echo "gofmt: files not formatted:" >&2
         echo "$files" >&2
         exit 1
     fi
+    files="$(go run "$GOIMPORTS_REF" -l .)"
+    if [ -n "$files" ]; then
+        echo "goimports: files not formatted:" >&2
+        echo "$files" >&2
+        exit 1
+    fi
 }
 
 main "$@"