How to export CSV file with standard and custom API S/4HANA Cloud public edition

[QuyVu]

My customer request some requirements about processing CSV in S/4HANA Cloud. 

1. Can I enhance logic of a standard API( ex OData, SOAP) to return CSV file for client who call API. Can I enhance logic of a standard API to store a CSV file in server or local? (S/4HANA Cloud-standard APIs)
2. Can I create a custom API(ex OData, HTTP service) to return CSV file for client who call API. Can custome API store a CSV file in server or local?

About custom API, I created a simple HTTP service. But when I call FM GUI_DOWNLOAD to store a CSV file, I get an error that is using FM GUI_DOWNLOAD is not permitted.

I don't have technical knowledge to resolve this customer request. So, can hep me and give me knowledge related to my customer's request?

Best regards

[varunvenkat]

Hi,

1) The S/4HC standard APIs only support JSON/XML formats. One option to consider therefore would be to use the Integration Suite (a.k.a CPI) as a middleware where you can have a mapping logic to convert the XML structure to a CSV file (see an example here) 

2) The only possibility to create a "custom" APi would be a custom CDS View published as an external API. However this custom API only supports an XML format as well, so in this case, you would also need a middleware to carry out an XML to CSV mapping.

Best regards
Varun