From a38257ab46e6898b77a6600ffc1508b29f87dc2a Mon Sep 17 00:00:00 2001
From: jbarba <jbarba@aidacanarias.com>
Date: Mon, 20 Oct 2025 01:03:46 +0100
Subject: [PATCH] fix(openapi-fetch): avoid errors parsing empty JSON bodies
 (200 with no content)

---
 .changeset/wet-waves-turn.md                  |  5 +++
 packages/openapi-fetch/src/index.js           | 23 +++++++---
 .../openapi-fetch/test/common/request.test.ts |  1 +
 .../test/common/response.test.ts              | 12 ++++++
 .../test/common/schemas/common.d.ts           | 42 +++++++++++++++++++
 .../test/common/schemas/common.yaml           | 11 +++++
 6 files changed, 88 insertions(+), 6 deletions(-)
 create mode 100644 .changeset/wet-waves-turn.md

diff --git a/.changeset/wet-waves-turn.md b/.changeset/wet-waves-turn.md
new file mode 100644
index 000000000..dd8f41d29
--- /dev/null
+++ b/.changeset/wet-waves-turn.md
@@ -0,0 +1,5 @@
+---
+"openapi-fetch": patch
+---
+
+Use text() when no content-length is provided to avoid errors parsing empty bodies (200 with no content)
diff --git a/packages/openapi-fetch/src/index.js b/packages/openapi-fetch/src/index.js
index be3b153a3..ab87033b3 100644
--- a/packages/openapi-fetch/src/index.js
+++ b/packages/openapi-fetch/src/index.js
@@ -230,18 +230,29 @@ export default function createClient(clientOptions) {
       }
     }
 
+    const contentLength = response.headers.get("Content-Length");
     // handle empty content
-    if (response.status === 204 || request.method === "HEAD" || response.headers.get("Content-Length") === "0") {
+    if (response.status === 204 || request.method === "HEAD" || contentLength === "0") {
       return response.ok ? { data: undefined, response } : { error: undefined, response };
     }
 
     // parse response (falling back to .text() when necessary)
     if (response.ok) {
-      // if "stream", skip parsing entirely
-      if (parseAs === "stream") {
-        return { data: response.body, response };
-      }
-      return { data: await response[parseAs](), response };
+      const getResponseData = async () => {
+        // if "stream", skip parsing entirely
+        if (parseAs === "stream") {
+          return response.body;
+        }
+
+        if (parseAs === "json" && !contentLength) {
+          // use text() when no content-length is provided to avoid errors parsing empty bodies (200 with no content)
+          const raw = await response.text();
+          return raw ? JSON.parse(raw) : undefined;
+        }
+
+        return await response[parseAs]();
+      };
+      return { data: await getResponseData(), response };
     }
 
     // handle errors
diff --git a/packages/openapi-fetch/test/common/request.test.ts b/packages/openapi-fetch/test/common/request.test.ts
index 7aa87e563..6a836520e 100644
--- a/packages/openapi-fetch/test/common/request.test.ts
+++ b/packages/openapi-fetch/test/common/request.test.ts
@@ -342,6 +342,7 @@ describe("request", () => {
         clone: () => ({ ...response }),
         headers: new Headers(),
         json: async () => data,
+        text: async () => JSON.stringify(data),
         status: 200,
         ok: true,
       } as Response;
diff --git a/packages/openapi-fetch/test/common/response.test.ts b/packages/openapi-fetch/test/common/response.test.ts
index ca7d21497..cdedabc4c 100644
--- a/packages/openapi-fetch/test/common/response.test.ts
+++ b/packages/openapi-fetch/test/common/response.test.ts
@@ -138,6 +138,18 @@ describe("response", () => {
   describe("parseAs", () => {
     const client = createObservedClient<paths>({}, async () => Response.json({}));
 
+    test("json with empty response", async () => {
+      const client = createObservedClient<paths>({}, async () => new Response());
+      const { data, error } = (await client.GET("/empty-json", {
+        parseAs: "json",
+      })) satisfies { data?: undefined };
+      if (error) {
+        throw new Error("parseAs json: error");
+      }
+
+      expect(data).toBe(undefined);
+    });
+
     test("text", async () => {
       const { data, error } = (await client.GET("/resources", {
         parseAs: "text",
diff --git a/packages/openapi-fetch/test/common/schemas/common.d.ts b/packages/openapi-fetch/test/common/schemas/common.d.ts
index b684c117e..2b81c4f28 100644
--- a/packages/openapi-fetch/test/common/schemas/common.d.ts
+++ b/packages/openapi-fetch/test/common/schemas/common.d.ts
@@ -727,6 +727,22 @@ export interface paths {
         patch?: never;
         trace?: never;
     };
+    "/empty-json": {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        get: operations["getEmptyJsonResponse"];
+        put?: never;
+        post?: never;
+        delete?: never;
+        options?: never;
+        head?: never;
+        patch?: never;
+        trace?: never;
+    };
 }
 export type webhooks = Record<string, never>;
 export interface components {
@@ -779,4 +795,30 @@ export interface operations {
             };
         };
     };
+    getEmptyJsonResponse: {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        requestBody?: never;
+        responses: {
+            /** @description Empty JSON Response */
+            200: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content?: never;
+            };
+            default: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": components["schemas"]["Error"];
+                };
+            };
+        };
+    };
 }
diff --git a/packages/openapi-fetch/test/common/schemas/common.yaml b/packages/openapi-fetch/test/common/schemas/common.yaml
index 72e1ea6e2..99bd4187d 100644
--- a/packages/openapi-fetch/test/common/schemas/common.yaml
+++ b/packages/openapi-fetch/test/common/schemas/common.yaml
@@ -421,6 +421,17 @@ paths:
             application/json:
               schema:
                 $ref: "#/components/schemas/Error"
+  /empty-json:
+    get:
+      operationId: getEmptyJsonResponse
+      responses:
+        200:
+          description: Empty JSON Response
+        default:
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/Error"
 components:
   schemas:
     Error: