How to Process file on S3 event through AWS lambda using C#

Question

I am looking for C# code blocks to read file from S3 on PUT event and upload the file to another bucket. I am fairly new to C# and see most of the blogs are either written for python and java. Any help will be highly appreciated.

Thanks,

Answer 1

I know it's too late but maybe this will help someone else. You need to add Amazon.Lambda.S3Events Nuget package. See code, this is how your Lambda Function should look like:

using System;
using System.Threading.Tasks;
using Amazon.Lambda.Core;
using Amazon.Lambda.S3Events;
using Amazon.S3;
using Amazon.S3.Model;

public async Task<string> FunctionHandler(S3Event evnt, ILambdaContext context)
{
    var s3Event = evnt.Records?[0].S3;
    if(s3Event == null)
    {
        return null;
    }

    try
    {
        var destinationBucketName = "your_bucket_to_upload";
        var destinationKey= "folder/subfolder/fileName.txt";

        var s3 = new AmazonS3Client();
        var request = new CopyObjectRequest
        {
            SourceBucket = s3Event.Bucket.Name,
            SourceKey = s3Event.Object.Key,
            DestinationBucket = destinationBucketName,
            DestinationKey = destinationKey
        };
        
        var response = await s3.CopyObjectAsync(request);
        return response.HttpStatusCode.ToString();
    }
    catch(Exception e)
    {
        context.Logger.LogLine($"Error getting object {s3Event.Object.Key} from bucket {s3Event.Bucket.Name}. Make sure they exist and your bucket is in the same region as this function.");
        context.Logger.LogLine(e.Message);
        context.Logger.LogLine(e.StackTrace);
        throw;
    }
}

You can find AWS Toolkit for Visual Studio here: https://docs.aws.amazon.com/lambda/latest/dg/csharp-package-toolkit.html