Fetching Data from Response Headers in Angular 4.3.3 HttpClient

Question

Fetching Data from Response Headers in Angular 4.3.3 HttpClient

(Text Editor: Visual Studio Code; TypeScript Version: 2.2.1)

The main objective here is to fetch the headers of the response from a request

Let's consider a scenario where we make a POST request using HttpClient within a service:

import {
    Injectable
} from "@angular/core";

import {
    HttpClient,
    HttpHeaders,
} from "@angular/common/http";

@Injectable()
export class MyHttpClientService {
    const url = 'url';

    const body = {
        body: 'the body'
    };

    const headers = 'headers made with HttpHeaders';

    const options = {
        headers: headers,
        observe: "response", // to display the full response
        responseType: "json"
    };

    return this.http.post(sessionUrl, body, options)
        .subscribe(response => {
            console.log(response);
            return response;
        }, err => {
            throw err;
        });
}

Angular HttpClient Documentation

The issue begins with a Typescript error:

'Argument of type '{ 
    headers: HttpHeaders; 
    observe: string; 
    responseType: string;
}' is not assignable to parameter of type'{ 
    headers?: HttpHeaders;
    observe?: "body";
    params?: HttpParams; reportProgress?: boolean;
    respons...'.

Types of property 'observe' are incompatible.
Type 'string' is not assignable to type '"body"'.'
at: '51,49' source: 'ts'

It seems that I want to use an overloaded method for post() but encountering compatibility issues.

While attempting to fix the error by adjusting the structure like this:

const options = {
            headers: headers,
            "observe?": "response",
            "responseType?": "json",
        };

Although it compiles, I am only receiving the request body in JSON format.

Additionally, there is confusion around why some field names are followed by a '?' symbol. According to the Typescript documentation, this denotes optional fields.

I have also experimented with all the fields, both with and without '?', but had no success.

EDIT

Trying out solutions recommended on Stack Overflow regarding getting headers from API response in Angular 4. For the map solution:

this.http.post(url).map(resp => console.log(resp));

The Typescript compiler indicates that map does not exist as part of Observable.

Another attempt:

import { Response } from "@angular/http";

this.http.post(url).post((resp: Response) => resp)

This code compiles, but results in an unsupported Media Type response. These solutions should work for "Http" but not with "HttpClient".

EDIT 2

Even after trying the @Supamiu solution, I continue to face unsupported media type issue, suggesting an error in my headers. Therefore, the second solution mentioned earlier (using Response type) should ideally work. However, personally, mixing "Http" with "HttpClient" might not be the best approach, so I will stick to the Supamiu's solution.

javascript angular typescript request typescript2.0

Answer 1

Answer №1

If you want to see the complete response instead of just the content, you need to include observe: response in the options parameter when calling the function.

http
  .get<MyJsonData>('/data.json', {observe: 'response'})
  .subscribe(resp => {
    // In this case, resp is an instance of HttpResponse<MyJsonData>.
    // You can check its headers:
    console.log(resp.headers.get('X-Custom-Header'));
    // And access the body directly, which is typed as MyJsonData as specified.
    console.log(resp.body.someField);
  });

For more information, refer to HttpClient's documentation

Answer 2

If you want to see the complete response instead of just the content, you need to include observe: response in the options parameter when calling the function.

http
  .get<MyJsonData>('/data.json', {observe: 'response'})
  .subscribe(resp => {
    // In this case, resp is an instance of HttpResponse<MyJsonData>.
    // You can check its headers:
    console.log(resp.headers.get('X-Custom-Header'));
    // And access the body directly, which is typed as MyJsonData as specified.
    console.log(resp.body.someField);
  });

For more information, refer to HttpClient's documentation

Answer 3

Answer №2

The main issue here is with typecasting, so we need to use "response" as 'body'

One way to handle this is:

const options = {
    headers: headers,
    observe: "response" as 'body', // This will display the full response & it's used for type casting
    responseType: "json"
};

return this.http.post(sessionUrl, body, options)
    .subscribe(response => {
        console.log(response);
        return response;
    }, err => {
        throw err;
    });

Answer 4

The main issue here is with typecasting, so we need to use "response" as 'body'

One way to handle this is:

const options = {
    headers: headers,
    observe: "response" as 'body', // This will display the full response & it's used for type casting
    responseType: "json"
};

return this.http.post(sessionUrl, body, options)
    .subscribe(response => {
        console.log(response);
        return response;
    }, err => {
        throw err;
    });

Answer 5

Answer №3

Indeed, the issue stemmed from a Typescript complication.

Within the post() function code, 'options' was initially declared within the parameters as an "anonymous" interface.

The resolution involved placing the options directly in raw format inside the parameters.

http.post("url", body, {headers: headers, observe: "response"}).subscribe...

Answer 6

Indeed, the issue stemmed from a Typescript complication.

Within the post() function code, 'options' was initially declared within the parameters as an "anonymous" interface.

The resolution involved placing the options directly in raw format inside the parameters.

http.post("url", body, {headers: headers, observe: "response"}).subscribe...

Answer 7

Answer №4

When utilizing the solution provided in the top answer and facing limitations such as lack of access to .keys() or .get() on response.headers, it is important to ensure that fetch is used instead of xhr.

Fetch requests are typically the default option, but Angular will resort to using xhr if xhr-only headers are detected (e.g. x-www-form-urlencoded).

To retrieve custom response headers, you must specify those headers along with another header known as Access-Control-Expose-Headers.

Answer 8

When utilizing the solution provided in the top answer and facing limitations such as lack of access to .keys() or .get() on response.headers, it is important to ensure that fetch is used instead of xhr.

Fetch requests are typically the default option, but Angular will resort to using xhr if xhr-only headers are detected (e.g. x-www-form-urlencoded).

To retrieve custom response headers, you must specify those headers along with another header known as Access-Control-Expose-Headers.

Answer 9

Answer №5

There are instances where, despite using the previous solution, custom headers cannot be retrieved in a CORS request. In such situations, it is necessary to whitelist the desired headers on the server side.

For instance: Access-Control-Expose-Headers: X-Total-Count

Answer 10

There are instances where, despite using the previous solution, custom headers cannot be retrieved in a CORS request. In such situations, it is necessary to whitelist the desired headers on the server side.

For instance: Access-Control-Expose-Headers: X-Total-Count

Answer 11

Answer №6

I recently implemented a method that worked flawlessly for me in Angular 10. This approach not only avoids assigning an arbitrary filename, but also retrieves the filename from the content-disposition header.

this._httpClient.get("api/FileDownload/GetFile", { responseType: 'blob' as 'json', observe: 'response' }).subscribe(response =>  { 
    /* Extract filename from Content-Disposition header */
    var filename = "";
    var disposition = response.headers.get('Content-Disposition');
    if (disposition && disposition.indexOf('attachment') !== -1) {
        var filenameRegex = /filename[^;=\n]*=((['"]).*?\2|[^;\n]*)/;
        var matches = filenameRegex.exec(disposition);
        if (matches != null && matches[1]) filename = matches[1].replace(/['"]/g, '');
    }
    // Download functionality
    var a = document.createElement('a');
    a.href = window.URL.createObjectURL(response.body);
    a.download = filename;
    a.dispatchEvent(new MouseEvent('click'));
})

Answer 12

I recently implemented a method that worked flawlessly for me in Angular 10. This approach not only avoids assigning an arbitrary filename, but also retrieves the filename from the content-disposition header.

this._httpClient.get("api/FileDownload/GetFile", { responseType: 'blob' as 'json', observe: 'response' }).subscribe(response =>  { 
    /* Extract filename from Content-Disposition header */
    var filename = "";
    var disposition = response.headers.get('Content-Disposition');
    if (disposition && disposition.indexOf('attachment') !== -1) {
        var filenameRegex = /filename[^;=\n]*=((['"]).*?\2|[^;\n]*)/;
        var matches = filenameRegex.exec(disposition);
        if (matches != null && matches[1]) filename = matches[1].replace(/['"]/g, '');
    }
    // Download functionality
    var a = document.createElement('a');
    a.href = window.URL.createObjectURL(response.body);
    a.download = filename;
    a.dispatchEvent(new MouseEvent('click'));
})

Answer 13

Answer №7

If you want to retrieve both headers and body in one call, you can specify the observer yield type like this:

http.post("url", body, {headers: headers, observe: "response" as "body"})

After that, you will be able to access the body and headers either in a pipe function or within a subscribe block:

http.post("url", body, {headers: headers, observe: "response" as "body"})
.pipe(
  tap(res => {
   // res.headers
   // res.body
  })
)
.subscribe(res => {
   // res.headers
   // res.body
})

Answer 14

If you want to retrieve both headers and body in one call, you can specify the observer yield type like this:

http.post("url", body, {headers: headers, observe: "response" as "body"})

After that, you will be able to access the body and headers either in a pipe function or within a subscribe block:

http.post("url", body, {headers: headers, observe: "response" as "body"})
.pipe(
  tap(res => {
   // res.headers
   // res.body
  })
)
.subscribe(res => {
   // res.headers
   // res.body
})

Fetching Data from Response Headers in Angular 4.3.3 HttpClient

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

Answer №7

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