Oops! The type error is indicating that you tried to pass 'undefined' where a stream was required. Make sure to provide an Observable, Promise, Array, or Iterable when working with Angular Services

I've developed various services to interact with different APIs. The post services seem to be functioning, but an error keeps popping up:

ERROR TypeError: You provided 'undefined' where a stream was expected. Options include Observable, Promise, Array, or Iterable. at subscribeTo (subscribeTo.js:27)

The same type of error is encountered with the GET services, however, no data is retrieved in return. Below is one of the services:

GetClientData(): Observable<ClientDto> {
    let url_ = this.baseUrl + "https://xxxxxxxxxxxxxxxx/getClients";
    url_ = url_.replace(/[?&]$/, "");

    let options_ : any = {
        observe: "response",
        responseType: "blob",
        headers: new HttpHeaders({
            "Accept": "application/json"
        })
    };

    return this.http.request("get", url_, options_).pipe(_observableMergeMap((response_ : any) => {
        return this.processGetAllPermissions(response_);
    })).pipe(_observableCatch((response_: any) => {
        if (response_ instanceof HttpResponseBase) {
            try {
                return this.processGetAllPermissions(<any>response_);
            } catch (e) {
                return <Observable<ClientDto>><any>_observableThrow(e);
            }
        } else
            return <Observable<ClientDto>><any>_observableThrow(response_);
    }));
}
protected processGetAllPermissions(response: HttpResponseBase): Observable<ClientDto> {
    const status = response.status;
    const responseBlob = 
        response instanceof HttpResponse ? response.body : 
        (<any>response).error instanceof Blob ? (<any>response).error : undefined;

    let _headers: any = {}; if (response.headers) { for (let key of response.headers.keys()) { _headers[key] = response.headers.get(key); }};
    if (status === 200) {
        return blobToText(responseBlob).pipe(_observableMergeMap(_responseText => {
        let result200: any = null;
        let resultData200 = _responseText === "" ? null : JSON.parse(_responseText, this.jsonParseReviver);
        result200 = resultData200 ? ClientDto.fromJS(resultData200) : new ClientDto();
        return _observableOf(result200);
        }));
    } else if (status !== 200 && status !== 204) {
        return blobToText(responseBlob).pipe(_observableMergeMap(_responseText => {
        return throwException("An unexpected server error occurred.", status, _responseText, _headers);
        }));
    }
    return _observableOf<ClientDto>(<any>null);
}

Cloud Function

exports.getClients = functions.https.onRequest((req, res) => {

    res.set('Access-Control-Allow-Origin', 'http://localhost:4200');
    res.set('Access-Control-Allow-Methods', 'GET', 'POST');
    res.set('Access-Control-Allow-Headers', 'Content-Type');

    if (req.method === 'OPTIONS') {
        res.end();
    }

    else
    {

        let allClients = [];
        usersClients.get()
            .then(snapshot => {
                snapshot.forEach(doc => {
                    allClients.push(doc.data());
                });
                res.send(200, {
                    "data": allClients
                })
            })
            .catch(err => {
                console.log("Error getting data", err);
            });
    }
});

Answer №1

Here is a sample code snippet:

fetchData(url_, options_).then(
  response => {
    // Process response data
  },
  error => {
    // Handle any errors
  }
);

Answer №2

Encountered a similar issue within my Angular application. The problem stemmed from an interceptor responsible for managing errors during API requests, but failing to provide any response. Within the catchError function of the API call, this error was being returned. The solution involved implementing the following code snippet into the interceptor's error handling logic:

return throwError(...)

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