feat(openapi-fetch): only parse as JSON if content-type indicates JSON

packages/openapi-fetch/src/index.js

@@ -241,6 +241,14 @@ export default function createClient(clientOptions) {
       if (parseAs === "stream") {
         return { data: response.body, response };
       }
+      // only parse as JSON if content-type indicates JSON
+      if (parseAs === "json") {
+        const contentType = response.headers.get("content-type");
+        if (contentType?.includes("application/json")) {
+          return { data: await response.json(), response };
+        }
+        return { data: await response.text(), response };
+      }
       return { data: await response[parseAs](), response };
     }
 

packages/openapi-fetch/test/common/request.test.ts

@@ -340,8 +340,9 @@ describe("request", () => {
     function createCustomFetch(data: any) {
       const response = {
         clone: () => ({ ...response }),
-        headers: new Headers(),
+        headers: new Headers({ "content-type": "application/json" }),
         json: async () => data,
+        text: async () => JSON.stringify(data),
         status: 200,
         ok: true,
       } as Response;
@@ -353,7 +354,7 @@ describe("request", () => {
 
     const customFetch = createCustomFetch({});
     const client = createClient<paths>({ baseUrl: "https://fakeurl.example", fetch: customFetch });
-    client.GET("/resources", {
+    await client.GET("/resources", {
       customProperty: "value",
     });
   });

packages/openapi-fetch/test/common/response.test.ts

@@ -135,6 +135,71 @@ describe("response", () => {
     });
   });
 
+  describe("content-type handling", () => {
+    test("parses JSON when content-type is application/json", async () => {
+      const client = createObservedClient<paths>({}, async () =>
+        Response.json([{ id: "1", name: "Test" }], { status: 200 }),
+      );
+      const { data, error } = await client.GET("/resources");
+      expect(error).toBeUndefined();
+      expect(data).toEqual([{ id: "1", name: "Test" }]);
+    });
+
+    test("returns text when content-type is not application/json", async () => {
+      const client = createObservedClient<paths>({}, async () =>
+        new Response("plain text response", {
+          status: 200,
+          headers: { "Content-Type": "text/plain" },
+        }),
+      );
+      const { data, error } = await client.GET("/resources");
+      expect(error).toBeUndefined();
+      expect(data).toBe("plain text response");
+    });
+
+    test("returns text when content-type header is missing", async () => {
+      const client = createObservedClient<paths>({}, async () =>
+        new Response("no content type", { status: 200 }),
+      );
+      const { data, error } = await client.GET("/resources");
+      expect(error).toBeUndefined();
+      expect(data).toBe("no content type");
+    });
+
+    test("parses error as JSON when content-type is application/json", async () => {
+      const client = createObservedClient<paths>({}, async () =>
+        Response.json({ code: 404, message: "Not found" }, { status: 404 }),
+      );
+      const { data, error } = await client.GET("/resources");
+      expect(data).toBeUndefined();
+      expect(error).toEqual({ code: 404, message: "Not found" });
+    });
+
+    test("keeps error as text when content-type is not application/json", async () => {
+      const client = createObservedClient<paths>({}, async () =>
+        new Response("Error: something went wrong", {
+          status: 500,
+          headers: { "Content-Type": "text/plain" },
+        }),
+      );
+      const { data, error } = await client.GET("/resources");
+      expect(data).toBeUndefined();
+      expect(error).toBe("Error: something went wrong");
+    });
+
+    test("handles application/json with charset", async () => {
+      const client = createObservedClient<paths>({}, async () =>
+        new Response(JSON.stringify([{ id: "1", name: "Test" }]), {
+          status: 200,
+          headers: { "Content-Type": "application/json; charset=utf-8" },
+        }),
+      );
+      const { data, error } = await client.GET("/resources");
+      expect(error).toBeUndefined();
+      expect(data).toEqual([{ id: "1", name: "Test" }]);
+    });
+  });
+
   describe("parseAs", () => {
     const client = createObservedClient<paths>({}, async () => Response.json({}));