🐛 Fix .fetchError catching user errors

Should fix #318

Author: elbywan

src/resolver.ts

@@ -24,7 +24,7 @@ export const resolver = <T, Chain, R, E, CatcherResult>(wretch: T & Wretch<T, Ch
   const {
     _url: url,
     _options: opts,
-    _fetch: customFetch,
+    _fetch,
     _errorTransformer: errorTransformer,
     _catchers: _catchers,
     _resolvers: resolvers,
@@ -39,12 +39,17 @@ export const resolver = <T, Chain, R, E, CatcherResult>(wretch: T & Wretch<T, Ch
   let finalUrl = url
   const _fetchReq = middlewareHelper(middlewares)((url, options) => {
     finalUrl = url
-    const fetchImpl = customFetch || fetch
+    const fetchImpl = _fetch || fetch
     return fetchImpl(url, options)
   })(url, finalOptions)
   // Throws on an http error
   const referenceError = new Error()
   const throwingPromise: Promise<void | WretchResponse> = _fetchReq
+    .catch(error => {
+      // Interect fetch errors and mark them with a special symbol so that they can be caught by a matching catcher
+      error[FETCH_ERROR] = true
+      throw error
+    })
     .then(async response => {
       if (!response.ok) {
         const err = new WretchError()
@@ -75,7 +80,7 @@ export const resolver = <T, Chain, R, E, CatcherResult>(wretch: T & Wretch<T, Ch
       const catcher =
         catchers.get(error?.status) ||
         catchers.get(error?.name) ||
-        (!(error instanceof WretchError) && catchers.get(FETCH_ERROR)) ||
+        (error?.[FETCH_ERROR] && catchers.get(FETCH_ERROR)) ||
         catchers.get(CATCHER_FALLBACK)
 
       if (error.response && errorTransformer) {

test/mock.js

@@ -211,6 +211,10 @@ export function launch(port) {
     return "ok"
   })
 
+  server.get("/network-error", async request => {
+    request.socket.destroy()
+  })
+
   server.get("/*", async (request, reply) => {
     reply.status(404)
 

test/shared/wretch.spec.ts

@@ -431,6 +431,22 @@ export function createWretchTests(ctx: TestContext): void {
       expect(serverErrorCount).toBe(1)
     })
 
+    it("should catch fetch errors", async function () {
+      let fetchErrorCount = 0
+
+      // Trigger a fetch error by calling an endpoint destroying the socket
+      await wretch(_URL).url("/network-error").get().fetchError(() => { fetchErrorCount++ }).json()
+      // .fetchError should have caught that
+      expect(fetchErrorCount).toBe(1)
+
+      await wretch(_URL).url("/json").get()
+        .fetchError(() => { fetchErrorCount-- })
+        .json(() => { throw new Error() })
+        .catch(() => { /* ignore */ })
+      // .fetchError should not have been called, since the error was not a fetch error
+      expect(fetchErrorCount).toBe(1)
+    })
+
     it("should support mixing single and array error IDs", async function () {
       let count = 0