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coreHTTP Basic S3 Upload Demo


Single Threaded Vs Multi Threaded

There are two coreHTTP usage models, single threaded and multithreaded (multitasking). Although the demo on this page runs the HTTP library in a thread, it is actually demonstrating how to use coreHTTP in a single threaded environment (only one task uses the HTTP API in the demo). Whereas single threaded applications must repeatedly call the HTTP library, multithreaded applications instead can execute sending HTTP requests in the background within an agent (or daemon) task.


This example demonstrates sending a PUT request to the AWS S3 HTTP server and uploading a small file. It also performs a GET request to verify the size of the file after the upload. This example uses a network transport interface that uses mbedTLS to establish a mutually authenticated connection between an IoT device client running coreHTTP and AWS S3 HTTP server.

The core HTTP S3 upload demo project uses the FreeRTOS Windows port, so you can build and evaluate it with the free Community version of Visual Studios on Windows, without the need for any particular MCU hardware.

Source Code Organization

The demo project is called http_s3_upload_demo.sln and can be found in the FreeRTOS-Plus/Demo/coreHTTP_Windows_Simulator/HTTP_S3_Upload directory of the main FreeRTOS download (and in the coreHTTP_Windows_Simulator repository on Github)

Building the Demo Project

The demo project uses the free community edition of Visual Studio. To build the demo:

  1. Open the 'http_s3_upload_demo_demo.sln' Visual Studio solution file from within the Visual Studio IDE.
  2. Select 'Build Solution' from the IDE's 'Build' menu.

Note: If you are using Microsoft Visual Studio 2017 or earlier, then you must select a 'Platform Toolset' compatible with your version: 'Project -> RTOSDemos Properties -> Platform Toolset'.

Configuring the Demo Project

The demo uses the FreeRTOS-Plus-TCP TCP/IP stack, so follow the instructions provided for the TCP/IP starter project to ensure you:

  1. Have the pre-requisite components installed (such as WinPCap).
  2. Optionally set a static or dynamic IP address, gateway address and netmask.
  3. Optionally set a MAC address.
  4. Select an Ethernet network interface on your host machine.
  5. ...and importantly test your network connection before attempting to run the HTTP demo.

As delivered, the TCP/IP stack is configured to use a dynamic IP address.

Configuring the AWS S3 HTTP Server Connection

This demo uses a presigned URL to connect the AWS S3 HTTP server and authorize access to the object to download. The AWS S3 HTTP server's TLS connection uses server authentication only. At the application level, access to the object is authenticated with parameters in the presigned URL query. Follow the steps below for configuring your connection to AWS.

  1. Set up an Amazon Web Services (AWS) account:
    • If you have not already, create and activate an AWS account (which includes a free tier).
    • Accounts and permissions are set using AWS Identity and Access Management (IAM). IAM allows you to manage the permissions for each user. By default, no users have permissions until granted by the root owner.
      • To add an IAM user to your AWS account, see the IAM User Guide.
      • Set permissions for your AWS account to access FreeRTOS and AWS IoT by adding the policies below:
        • AmazonS3FullAccess
  2. Create a bucket in S3 by following the steps provided on AWS Docs
  3. Update a file to S3 by following the steps provided on AWS Docs
  4. Generate a presigned URL using the script located at FreeRTOS-Plus/Demo/coreHTTP_Windows_Simulator/Common/presigned_url_generator/ See FreeRTOS-Plus/Demo/coreHTTP_Windows_Simulator/Common/presigned_url_generato/ for usage instructions.


The demo first connects to the AWS S3 HTTP server with TLS server authentication. Then it creates an HTTP request to upload the data specified in democonfigDEMO_HTTP_UPLOAD_DATA. After uploading the file, it checks that file was successfully uploaded by requesting for the size of the file. The structure of the demo can be found in S3UploadHTTPExample.c on Github.

Connecting to the AWS S3 HTTP Server

The function connectToServerWithBackoffRetries() attempts to make a TCP connection to the HTTP server. If the connection fails, it retries after a timeout. The timeout value will exponentially increase until the maximum number of attempts are reached or the maximum timeout value is reached. connectToServerWithBackoffRetries() returns a failure status if the TCP connection cannot be established to the server after the configured number of attempts. The source code for connectToServerWithBackoffRetries() can be found in http_demo_utils.c on Github.

The function 'prvConnectToServer()' demonstrates how to establish a connection to the AWS S3 HTTP server using server authentication only. It uses the mbedTLS-based transport interface that is implemented in the file 'FreeRTOS-Plus/Source/Application-Protocols/network_transport/freertos_plus_tcp/using_mbedtls/using_mbedtls.c'. The definition of 'prvConnectToServer()' can be found in S3UploadHTTPExample.c on Github.

Upload data

The function 'prvUploadS3ObjectFile' demonstrates how to create a PUT request and specify the file to upload. The AWS S3 bucket to upload to and the name of file upon upload is specified in the presigned URL. To save memory, the same buffer is used for both the request headers and the for receiving the response. The response is received synchronously using API function 'HTTPClient_Send()'. A 200 OK response status-code is expected from the AWS S3 HTTP server; any other status-code received is an error.

The source code for 'prvUploadS3ObjectFile' can be found in S3UploadHTTPExample.c on Github.

Verifying upload

The function 'prvVerifyS3ObjectFileSize' calls 'prvGetS3ObjectFileSize' to retrieve the size of the object in the S3 bucket. The S3 HTTP server does not currently support HEAD requests using a presigned URL, so the 0th byte is requested. The size of the file is contained in the response's Content-Range header field. A 206 Partial Content response is expected from the server; any other response status-code received is an error.

The source code for 'prvGetS3ObjectFileSize' can be found in S3DownloadHTTPExample.c on Github.

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