Azure http-trigger function to query HTTP POST request with multipart/form-data

Question

I am using Azure function apps with C# (or NodeJS). How to write a http post request to achieve below task?

Http triger function app should send an HTTP request to a different server to get some data.
Read the incoming response and send back by the http trigger source as a JSON file.

I am new to Azure function and your support would be greatly helpful.

For example

HTTP's headers:

Accept: */*
Accept-Encoding: gzip, deflate, br
Connection: Keep-Alive
Content-Length: 1330
Content-Type: multipart/form-data;boundary=XXXXabcXXXX
Keep-Alive: timeout=30000
Transfer-Encoding: chunked

HTTP Body:

--XXXXabcXXXX
Content-Disposition: form-data; name="RequestData"
Content-Type: application/JSON; charset=utf-8
Content-Transfer-Encoding: 8bit

{
    "cmdDict":
        {
        "application":"b",
        "application_session_id":"cd"
        },
    "appId": "123",
    "uId":"345645"
}
--XXXXabcXXXX
Content-Disposition : form-data; name="Parameter"; paramName="REQUEST_INFO"
Content-Type: application/json; charset=utf-8
Content-Transfer-Encoding: 8bit

{
"abc":
  {"x":"default",
   "y":[],
   "message":"HELLO WORLD"
  },
"D":1
}
--XXXXabcXXXX--

Max Ivanov · Accepted Answer · 2020-11-17 19:24:12Z

Here's how you can do the multipart/form-data request with Node.js in Azure Functions.

The only dependency you need to install is form-data from npm.

const https = require('https')
const FormData = require('form-data')

const host = 'postman-echo.com'
const path = '/post'
const method = 'POST'
const requestHeaders = {
  Accept: '*/*',
  // add headers here as necessary
}
const parts = [
  {
    name: 'RequestData',
    data: {
      cmdDict: {
        application: 'b',
        application_session_id: 'cd',
      },
      appId: '123',
      uId: '345645',
    },
    contentType: 'application/json; charset=utf-8',
  },
  {
    name: 'Parameter',
    data: {
      abc: { x: 'default', y: [], message: 'HELLO WORLD' },
      D: 1,
    },
    contentType: 'application/json; charset=utf-8',
  },
]

async function fetchFromOrigin() {
  return new Promise((resolve, reject) => {
    const form = new FormData()

    parts.forEach((part) =>
      form.append(part.name, JSON.stringify(part.data), {
        contentType: part.contentType,
      }),
    )

    const options = {
      host,
      path,
      method,
      headers: Object.assign({}, requestHeaders, form.getHeaders()),
    }

    const req = https.request(options, (res) => {
      if (res.statusCode < 200 || res.statusCode > 299) {
        return reject(new Error(`HTTP status code ${res.statusCode}`))
      }

      const body = []
      res.on('data', (chunk) => body.push(chunk))
      res.on('end', () => {
        const resString = Buffer.concat(body).toString()
        resolve(resString)
      })
    })

    req.on('error', (err) => reject(new Error(err.message)))
    form.pipe(req)
  })
}

module.exports = async function (context, req) {
  const res = await fetchFromOrigin()

  context.res = {
    body: res,
  }
}

Amazing! It worked like a charm. I just had to tweak name: name='Parameter; paramName=REQUEST_INFO' because there is no paramName in the library. Thank you so much!

Frank Borzage · Accepted Answer · 2020-11-17 09:36:58Z

Please refer to this code:

using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.Http;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
using Newtonsoft.Json;
using System.Net.Http;
using System.Net.Http.Headers;
using System;

namespace FunctionMultipart
{
    public static class Function1
    {
        [FunctionName("Function1")]
        public static async Task<IActionResult> Run(
            [HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)] HttpRequest req,
            ILogger log)
        {
            log.LogInformation("C# HTTP trigger function processed a request.");

            HttpClient _httpClient = new HttpClient();

            string URL = "https://postman-echo.com/post";
            using (var multiPartStream = new MultipartFormDataContent("XXXXabcXXXX"))
            {
                StringContent jsonPart1 = new StringContent("{\"cmdDict\": {\"application\":\"b\",\"application_session_id\":\"cd\"},\"appId\": \"123\",\"uId\":\"345645\"}");
                jsonPart1.Headers.ContentDisposition = new ContentDispositionHeaderValue("form-data");
                jsonPart1.Headers.ContentType = new MediaTypeHeaderValue("application/json");

                StringContent jsonPart2 = new StringContent("{\"abc\":{\"x\":\"default\",\"y\":[],\"message\":\"HELLO WORLD\"},\"D\":1}");
                jsonPart2.Headers.ContentDisposition = new ContentDispositionHeaderValue("form-data");
                jsonPart2.Headers.ContentType = new MediaTypeHeaderValue("application/json");

                multiPartStream.Add(jsonPart1, "RequestData");
                multiPartStream.Add(jsonPart2, "Parameter");
                HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Post, URL);
                request.Content = multiPartStream;
                //"application/json" - content type
                request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                request.Headers.AcceptEncoding.Add(new StringWithQualityHeaderValue("gzip"));
                request.Headers.AcceptEncoding.Add(new StringWithQualityHeaderValue("deflate"));
                request.Headers.AcceptEncoding.Add(new StringWithQualityHeaderValue("br"));
                request.Headers.Connection.Add("Keep-Alive");
                //request.Headers.Add("Content-Length", "1330");
                //request.Headers.Add("Content-Type", "multipart/form-data;boundary=XXXXabcXXXX");

                HttpCompletionOption option = HttpCompletionOption.ResponseContentRead;
                System.Net.ServicePointManager.ServerCertificateValidationCallback = ((sender, certificate, chain, sslPolicyErrors) => true);
                
                using (HttpResponseMessage response = _httpClient.SendAsync(request, option).Result)
                {
                    if (response.IsSuccessStatusCode)
                    {
                        String result = response.Content.ReadAsStringAsync().Result;
                        //var deserializedObject = JsonConvert.DeserializeObject<T>(response.Content.ReadAsStringAsync().Result);
                        //return deserializedObject.ToString();
                        log.LogInformation(result);
                    }
                }

            }

            return new OkObjectResult("ok");
        }
    }
}

Hey thank you so much for your reply. This is great! However, when I used webhook.site to listen to my request, I see that body of the message jsonPart1 and jsonPart2 is no in the message body. Do you know what may be missing?

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