Parse multipart/form-data in Azure Function

September 2, 2020

While working on an internal Azure Static Web Site project, I needed to upload CSV files to an Azure Function to import data to Cosmos DB.

When uploading a file to your API, the multipart/form-data content-type is used. The body’s format looks a bit “special” as it requires some parsing to get each file.

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-----WebKitFormBoundaryXvnFih9Jfw9ZdQNB
Content-Disposition: form-data; name': '"file"; filename="2020-9-2-localization.csv"
Content-Type: text/csv

id,name
test1,test1
test2,test2
------WebKitFormBoundaryXvnFih9Jfw9ZdQNB--

Similar like the previous article about parsing application/x-www-form-urlencoded in Azure Function, this content type is something you have to parse yourself as well.

To make it easier, you will have to install the following dependency to your project: npm i parse-multipart -S -E. The code looks like this:

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import { AzureFunction, Context, HttpRequest } from "@azure/functions";
import * as multipart from 'parse-multipart';

const httpTrigger: AzureFunction = async function (context: Context, req: HttpRequest): Promise<void> {
  const body = req.rawBody;
  // Retrieve the boundary id
  const boundary = multipart.getBoundary(req.headers["content-type"]);
  if (boundary) {
    const files: File[] = multipart.Parse(Buffer.from(body), boundary);

    if (files && files.length > 0) {
      // Do what you want to do with the file
    }

    context.res.status(200);
  } else {
    context.res.status(500).send("No file(s) found.");
  }
};

I hope this helps you get started processing your uploaded files.

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