fix: avoid Unexpected end of JSON input when response body is empty (#648)

Fixes #649 

Co-authored-by: Gregor Martynus <[email protected]>

Author: tsusdere

Diff for: src/fetch-wrapper.ts

@@ -153,7 +153,17 @@ export default function fetchWrapper(
 async function getResponseData(response: Response) {
   const contentType = response.headers.get("content-type");
   if (/application\/json/.test(contentType!)) {
-    return response.json();
+    return (
+      response
+        .json()
+        // In the event that we get an empty response body we fallback to
+        // using .text(), but this should be investigated since if this were
+        // to occur in the GitHub API it really should not return an empty body.
+        .catch(() => response.text())
+        // `node-fetch` is throwing a "body used already for" error if `.text()` is run
+        // after a failed .json(). To account for that we fallback to an empty string
+        .catch(() => "")
+    );
   }
 
   if (!contentType || /^text\/|charset=utf-8$/.test(contentType)) {

Diff for: test/request.test.ts

@@ -400,6 +400,32 @@ x//0u+zd/R/QRUzLOw4N72/Hu+UG6MNt5iDZFCtapRaKt6OvSBwy8w==
     );
   });
 
+  it("error response with no body (octokit/request.js#649)", () => {
+    const mock = fetchMock
+      .sandbox()
+      .get("path:/repos/octokit-fixture-org/hello-world/contents/README.md", {
+        status: 500,
+        body: undefined,
+        headers: {
+          "content-type": "application/json",
+        },
+      });
+
+    return request("GET /repos/{owner}/{repo}/contents/{path}", {
+      headers: {
+        accept: "content-type: application/json",
+      },
+      owner: "octokit-fixture-org",
+      repo: "hello-world",
+      path: "README.md",
+      request: {
+        fetch: mock,
+      },
+    }).catch((error) => {
+      expect(error.response.data).toEqual("");
+    });
+  });
+
   it("non-JSON response", () => {
     const mock = fetchMock
       .sandbox()