Sample AWS API Gateway API to download Amazon S3 object with support to multi-part
curl https://<apigateway-invoke-url>/<stage>/<bucket>/<filename> --output <filename>
Downloading parts
curl https://<invoke-url>/<stage>/<bucket>/<filename>?partNumber=1 --output <filename_1>
curl https://<invoke-url>/<stage>/<bucket>/<filename>?partNumber=2 --output <filename_2>
curl https://<invoke-url>/<stage>/<bucket>/<filename>?partNumber=n --output <filename_n>
Joining the parts
cat <filename_*> > <filename>