Firebase Cloud Function创建文档报错：返回不是有效JSON对象

在Flutter应用中使用Firestore数据库，需求是每个用户在UserFavourites集合下拥有一个以自身UID命名的专属文档。我编写了一个HTTPS可调用云函数，逻辑为检查目标文档是否存在，不存在则创建。但调用函数时触发错误：Error: internal Response is not valid JSON object，且测试用户的文档并未成功创建。

云函数代码 #

exports.createUserFavouritesDocument = functions
    .region("europe-west2")
    .https.onCall(async (data, context) => {
        const uid = data.uid;
        const favouritesRef = admin
            .firestore().collection("UserFavourites").doc(uid);
        return favouritesRef.get().then((doc) => {
            if (doc.exists) {
                return {
                    success: true
                };
            } else {
                return favouritesRef.set({
                        Stores: []
                    })
                    .then(() => {
                        return {
                            success: true
                        };
                    })
                    .catch((error) => {
                        // throw new functions
                        // .https
                        // .HttpsError("internal", "Error creating document.", error);
                        return {
                            error: "Error creating doc"
                        };
                    });
            }
        }).catch((error) => {
            if (error.code === "not-found") {
                return favouritesRef.set({
                        Stores: []
                    })
                    .then(() => {
                        return {
                            success: true
                        };
                    })
                    .catch((error) => {
                        // throw new functions
                        // .https
                        // .HttpsError("internal", "Error creating document.", error);
                        return {
                            error: "Error creating document"
                        };
                    });
            } else {
                // throw new functions
                // .https
                // .HttpsError("internal", "Error checking for document.", error);
                return {
                    error: "Error creating document"
                };
            }
        });
    });

Flutter调用代码 #

void _checkdoc() async {
    try {
        final result = await createUserFavouritesDocument.call(<String, dynamic>{
            'uid': FirebaseAuth.instance.currentUser!.uid,
        });
        print(result.data);
    } on FirebaseFunctionsException catch (e) {
        print("error");
        print('Error: ${e.code} ${e.message}');
    } catch (e) {
        print('Error: $e');
    }
}

问题根源 #

1. 错误处理不规范：Callable函数要求错误必须抛出functions.https.HttpsError类型，你注释掉了正确的错误抛出逻辑，返回普通对象会导致客户端解析JSON失败，触发Response is not valid JSON object错误。
2. 异步逻辑混乱：混合使用async/await和.then/.catch，容易导致返回值不符合预期。
3. UID获取不安全：从data.uid获取用户ID存在被篡改风险，应该从云函数的context.auth.uid获取（前提是客户端已通过Firebase Auth认证）。

修正后的云函数代码 #

exports.createUserFavouritesDocument = functions
    .region("europe-west2")
    .https.onCall(async (data, context) => {
        // 验证用户是否已认证
        if (!context.auth) {
            throw new functions.https.HttpsError(
                "unauthenticated",
                "用户未登录，无法执行此操作"
            );
        }

        const uid = context.auth.uid;
        const favouritesRef = admin.firestore().collection("UserFavourites").doc(uid);

        try {
            const doc = await favouritesRef.get();
            if (doc.exists) {
                return { success: true, message: "文档已存在" };
            } else {
                await favouritesRef.set({ Stores: [] });
                return { success: true, message: "文档创建成功" };
            }
        } catch (error) {
            throw new functions.https.HttpsError(
                "internal",
                "操作失败",
                error.message
            );
        }
    });

优化后的Flutter调用代码 #

void _checkUserFavouritesDoc() async {
    try {
        final user = FirebaseAuth.instance.currentUser;
        if (user == null) {
            print("用户未登录");
            return;
        }

        final result = await createUserFavouritesDocument.call({});
        print(result.data);
    } on FirebaseFunctionsException catch (e) {
        print('云函数错误: ${e.code} - ${e.message}');
    } catch (e) {
        print('未知错误: $e');
    }
}

额外检查 #

• 确保云函数服务账号拥有Firestore的读写权限，可在Firebase控制台的「规则」中配置UserFavourites集合的权限：

match /UserFavourites/{userId} {
  allow read, write: if request.auth != null && request.auth.uid == userId;
}

• 确认云函数已正确部署到europe-west2区域，Flutter端的Callable函数也需指定相同区域。

内容的提问来源于stack exchange，提问作者ReDue