fix(middleware): apply PathRewrite to existing routing paths

middleware/path_rewrite.go

@@ -3,13 +3,22 @@ package middleware
 import (
 	"net/http"
 	"strings"
+
+	"github.com/go-chi/chi/v5"
 )
 
-// PathRewrite is a simple middleware which allows you to rewrite the request URL path.
+// PathRewrite replaces the first occurrence of old with new in the request URL path.
+// When the routing path has already been set, it is rewritten independently.
+// In a mounted router, the routing path is relative to the mount point, so old
+// and new should be relative to that point to affect routing. To rewrite a path
+// including the mount prefix, install PathRewrite on the parent router instead.
 func PathRewrite(old, new string) func(http.Handler) http.Handler {
 	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 			r.URL.Path = strings.Replace(r.URL.Path, old, new, 1)
+			if rctx := chi.RouteContext(r.Context()); rctx != nil && rctx.RoutePath != "" {
+				rctx.RoutePath = strings.Replace(rctx.RoutePath, old, new, 1)
+			}
 			next.ServeHTTP(w, r)
 		})
 	}

middleware/path_rewrite_absolute_probe_test.go

@@ -0,0 +1,89 @@
+package middleware_test
+
+import (
+	"fmt"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/go-chi/chi/v5"
+	"github.com/go-chi/chi/v5/middleware"
+)
+
+// Full-path rewrites belong before the router that consumes the mount prefix.
+func TestPathRewriteAbsoluteMountPlacement(t *testing.T) {
+	for _, placement := range []string{"parent", "mounted"} {
+		t.Run(placement, func(t *testing.T) {
+			root, sub := chi.NewRouter(), chi.NewRouter()
+			rewrite := middleware.PathRewrite("/api/old", "/api/new")
+			if placement == "parent" {
+				root.Use(rewrite)
+			} else {
+				sub.Use(rewrite)
+			}
+			sub.Get("/new/{id}", func(w http.ResponseWriter, r *http.Request) {
+				fmt.Fprintf(w, "%s|%s", r.URL.Path, chi.URLParam(r, "id"))
+			})
+			sub.NotFound(func(w http.ResponseWriter, r *http.Request) {
+				w.WriteHeader(http.StatusNotFound)
+				fmt.Fprintf(w, "%s|%s", r.URL.Path, chi.RouteContext(r.Context()).RoutePath)
+			})
+			root.Mount("/api", sub)
+			server := httptest.NewServer(root)
+			defer server.Close()
+			resp, err := server.Client().Get(server.URL + "/api/old/item")
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer resp.Body.Close()
+			body, err := io.ReadAll(resp.Body)
+			if err != nil {
+				t.Fatal(err)
+			}
+			wantCode, wantBody := http.StatusOK, "/api/new/item|item"
+			if placement == "mounted" {
+				wantCode, wantBody = http.StatusNotFound, "/api/new/item|/old/item"
+			}
+			if resp.StatusCode != wantCode || string(body) != wantBody {
+				t.Fatalf("got %d %q, want %d %q", resp.StatusCode, body, wantCode, wantBody)
+			}
+		})
+	}
+}
+
+// URLFormat changes only the routing path. Do not restore its removed suffix
+// by reconstructing RoutePath from URL.Path.
+func TestPathRewriteAfterURLFormat(t *testing.T) {
+	for _, prefix := range []string{"", "/api"} {
+		t.Run(prefix, func(t *testing.T) {
+			sub := chi.NewRouter()
+			sub.Use(middleware.URLFormat)
+			sub.Use(middleware.PathRewrite("/old", "/new"))
+			sub.Get("/new/{id}", func(w http.ResponseWriter, r *http.Request) {
+				fmt.Fprintf(w, "%s|%s|%s|%s", r.URL.Path, chi.URLParam(r, "id"), chi.RouteContext(r.Context()).RoutePath, r.Context().Value(middleware.URLFormatCtxKey))
+			})
+			var handler http.Handler = sub
+			if prefix != "" {
+				root := chi.NewRouter()
+				root.Mount(prefix, sub)
+				handler = root
+			}
+			server := httptest.NewServer(handler)
+			defer server.Close()
+			resp, err := server.Client().Get(server.URL + prefix + "/old/item.json")
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer resp.Body.Close()
+			body, err := io.ReadAll(resp.Body)
+			if err != nil {
+				t.Fatal(err)
+			}
+			want := prefix + "/new/item.json|item|/new/item|json"
+			if resp.StatusCode != http.StatusOK || string(body) != want {
+				t.Fatalf("got %d %q, want 200 %q", resp.StatusCode, body, want)
+			}
+		})
+	}
+}

middleware/path_rewrite_mount_test.go

@@ -0,0 +1,75 @@
+package middleware_test
+
+import (
+	"fmt"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/go-chi/chi/v5"
+	"github.com/go-chi/chi/v5/middleware"
+)
+
+func TestPathRewritePlainHandler(t *testing.T) {
+	handler := middleware.PathRewrite("/old", "/new")(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, r.URL.Path)
+	}))
+	rec := httptest.NewRecorder()
+	handler.ServeHTTP(rec, httptest.NewRequest(http.MethodGet, "/old/item", nil))
+	if rec.Code != http.StatusOK || rec.Body.String() != "/new/item" {
+		t.Fatalf("got %d %q", rec.Code, rec.Body.String())
+	}
+}
+
+func TestPathRewriteMountedRouter(t *testing.T) {
+	for _, tc := range []struct {
+		name   string
+		prefix string
+		target string
+		want   string
+	}{
+		{"root", "", "/old/item?sort=asc", "/new/item|item|sort=asc"},
+		{"mount", "/api", "/api/old/item?sort=asc", "/api/new/item|item|sort=asc"},
+		{"nested mount", "/api/v1", "/api/v1/old/item?sort=asc", "/api/v1/new/item|item|sort=asc"},
+		{"no replacement", "/api", "/api/new/item?sort=asc", "/api/new/item|item|sort=asc"},
+		{"encoded parameter", "/api", "/api/old/a%2Fb?sort=asc", "/api/new/a/b|a%2Fb|sort=asc"},
+		{"replace once", "/api", "/api/old/old?sort=asc", "/api/new/old|old|sort=asc"},
+		{"mount prefix also matches", "/old", "/old/old/item?sort=asc", "/new/old/item|item|sort=asc"},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			sub := chi.NewRouter()
+			sub.Use(middleware.PathRewrite("/old", "/new"))
+			sub.Get("/new/{id}", func(w http.ResponseWriter, r *http.Request) {
+				fmt.Fprintf(w, "%s|%s|%s", r.URL.Path, chi.URLParam(r, "id"), r.URL.RawQuery)
+				if tc.prefix == "/old" && chi.RouteContext(r.Context()).RoutePath != "/new/item" {
+					t.Errorf("routing path = %q, want /new/item", chi.RouteContext(r.Context()).RoutePath)
+				}
+			})
+			var handler http.Handler = sub
+			if tc.prefix != "" {
+				root := chi.NewRouter()
+				if tc.prefix == "/api/v1" {
+					root.Route("/api", func(r chi.Router) { r.Mount("/v1", sub) })
+				} else {
+					root.Mount(tc.prefix, sub)
+				}
+				handler = root
+			}
+			server := httptest.NewServer(handler)
+			defer server.Close()
+			resp, err := server.Client().Get(server.URL + tc.target)
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer resp.Body.Close()
+			body, err := io.ReadAll(resp.Body)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if resp.StatusCode != http.StatusOK || string(body) != tc.want {
+				t.Fatalf("got %d %q, want 200 %q", resp.StatusCode, body, tc.want)
+			}
+		})
+	}
+}