Backend Development

In plain words: When you send data via an HTTP request, standard JSON usually works fine. However, if you need to upload a binary file (like a PDF or image) alongside text form fields in a single request, you must use a format called multipart/form-data . A boundary is a unique text divider placed between each piece of data so the receiving server knows where one file ends and the next form field begins. In Salesforce development, integrating with external REST APIs to upload files or documents is a frequent requirement. When the target API expects a file payload combined with metadata, simple JSON strings won't cut it. You need to construct a multipart HTTP request. Let's dive into how multipart data and boundary strings work under the hood, and look at a clean Apex implementation for handling file uploads.