linters: add httpstatus linter

pkg/httpstatus/testdata/src/configured/configured.go

@@ -0,0 +1,29 @@
+package configured
+
+import "net/http"
+
+const created = http.StatusCreated // want `HTTP status code 201 should use its integer literal`
+const ok = http.StatusOK
+
+func response(w http.ResponseWriter, r *http.Request, code int) {
+	http.Error(w, "teapot", 418) // want `non-typical HTTP status code 418 is not allowed`
+	http.Error(w, "created", 201)
+	http.Error(w, "variable", code)
+
+	w.WriteHeader(200) // want `non-typical HTTP status code 200 is not allowed`
+	w.WriteHeader(code)
+	http.ResponseWriter.WriteHeader(w, 400) // want `non-typical HTTP status code 400 is not allowed`
+
+	http.NotFound(w, r)
+	_, _ = w.Write([]byte("response"))
+	http.Redirect(w, r, "/moved", 301)
+	http.Redirect(w, r, "/created", http.StatusCreated) // want `HTTP status code 201 should use its integer literal`
+}
+
+type unrelatedWriter struct{}
+
+func (unrelatedWriter) WriteHeader(int) {}
+
+func unrelated(writer unrelatedWriter) {
+	writer.WriteHeader(418)
+}

pkg/httpstatus/testdata/src/default/default.go

@@ -0,0 +1,22 @@
+package cases
+
+import "net/http"
+
+const ok = http.StatusOK // want `HTTP status code 200 should use its integer literal`
+const teapot = http.StatusTeapot
+
+func response(w http.ResponseWriter, r *http.Request, code int) {
+	_ = http.StatusNotFound // want `HTTP status code 404 should use its integer literal`
+
+	http.Error(w, "bad request", http.StatusBadRequest) // want `HTTP status code 400 should use its integer literal`
+	http.Error(w, "teapot", http.StatusTeapot)
+	http.Error(w, "created", 201)
+	w.WriteHeader(http.StatusGatewayTimeout) // want `HTTP status code 504 should use its integer literal`
+	w.WriteHeader(code)
+
+	http.NotFound(w, r)
+	_, _ = w.Write([]byte("response"))
+
+	http.Redirect(w, r, "/login", http.StatusFound) // want `HTTP status code 302 should use its integer literal`
+	http.Redirect(w, r, "/other", http.StatusMovedPermanently)
+}