fix: allow well-known headers

See: #12

.github/workflows/diff.yaml

@@ -0,0 +1,32 @@
+name: check diff
+
+on:
+  push:
+    tags:
+      - '*'
+
+permissions:
+  contents: write
+
+jobs:
+  goreleaser:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: stable
+          check-latest: true
+
+      - name: Generate test
+        run: |
+          make generate
+
+      - name: Check diff
+        run: |
+          git diff --exit-code

analyzer.go

@@ -34,6 +34,8 @@ func run(pass *analysis.Pass) (any, error) {
 		return nil, fmt.Errorf("want %T, got %T", spctor, pass.ResultOf[inspect.Analyzer])
 	}
 
+	wellKnownHeaders := initialism()
+
 	nodeFilter := []ast.Node{
 		(*ast.CallExpr)(nil),
 	}
@@ -97,8 +99,8 @@ func run(pass *analysis.Pass) (any, error) {
 			return
 		}
 
-		headerKeyCanonical := http.CanonicalHeaderKey(headerKeyOriginal)
-		if headerKeyOriginal == headerKeyCanonical {
+		headerKeyCanonical, isWellKnown := canonicalHeaderKey(headerKeyOriginal, wellKnownHeaders)
+		if headerKeyOriginal == headerKeyCanonical || isWellKnown {
 			return
 		}
 
@@ -131,6 +133,17 @@ func run(pass *analysis.Pass) (any, error) {
 	return nil, outerErr
 }
 
+func canonicalHeaderKey(s string, m map[string]string) (string, bool) {
+	canonical := http.CanonicalHeaderKey(s)
+
+	wellKnown, ok := m[canonical]
+	if !ok {
+		return canonical, ok
+	}
+
+	return wellKnown, ok
+}
+
 func isHTTPHeader(named *types.Named) bool {
 	return named.Obj() != nil &&
 		named.Obj().Pkg() != nil &&

analyzer_test.go

@@ -22,6 +22,7 @@ func TestAnalyzer(t *testing.T) {
 		"common",
 		"embedded",
 		"global",
+		"initialism",
 		"struct",
 	}