Context: I'm trying to download a binary file from a backend (that requires some data posted as json-body) and save it with file-saver using the filename specified by the backend in the content-disposition header. To access the headers I think I need the HttpResponse.
But I'm unable to use angular's HttpClient.post<T>(...): Observable<HttpResponse<T>>; method with a Blob.
When I call
this.httpclient.post<Blob>('MyBackendUrl',
params,
{observe: 'response', responseType: 'blob'});
the compiler complains about the 'blob' ('json' is accepted by the compiler):
error TS2345: Argument of type '{ observe: "response"; responseType: "blob"; }' is not assignable to parameter of type '{ headers?: HttpHeaders | { [header: string]: string | string[]; }; observe?: "body"; params?: Ht...'.
Types of property 'observe' are incompatible.
Type '"response"' is not assignable to type '"body"'.
When I put the options in an own object as seen in https://stackoverflow.com/a/48016652/2131459 (but without the "as" ...) the post(...):Observable is called and I cannot access the headers.
Btw, even the simple example return this.http.get<Blob>('backendUrl', {responseType: 'blob'}); as seen e.g. in https://stackoverflow.com/a/46882407/2131459 doesn't work for me.
Versions used
When using observe:response, don't type the call (post<Blob>(...)), as the returned Observable will be of HttpResponse. So this should work:
this.httpclient.post('MyBackendUrl',
params,
{observe: 'response', responseType: 'blob'}
);
Why this happens, is there's two versions of the post method, one with a generic type, one without:
/**
* Construct a POST request which interprets the body as JSON and returns the full event stream.
*
* @return an `Observable` of all `HttpEvent`s for the request, with a body type of `T`.
*/
post<T>(url: string, body: any | null, options: {
headers?: HttpHeaders | {
[header: string]: string | string[];
};
observe: 'events';
params?: HttpParams | {
[param: string]: string | string[];
};
reportProgress?: boolean;
responseType?: 'json';
withCredentials?: boolean;
}): Observable<HttpEvent<T>>;
/**
* Construct a POST request which interprets the body as an `ArrayBuffer` and returns the full response.
*
* @return an `Observable` of the `HttpResponse` for the request, with a body type of `ArrayBuffer`.
*/
post(url: string, body: any | null, options: {
headers?: HttpHeaders | {
[header: string]: string | string[];
};
observe: 'response';
params?: HttpParams | {
[param: string]: string | string[];
};
reportProgress?: boolean;
responseType: 'arraybuffer';
withCredentials?: boolean;
}): Observable<HttpResponse<ArrayBuffer>>;