Should the Prefer header be configurable to either "return-no-content" or "return-content", based on options, rather than hard-coded?

[ahsonkhan]

It looks like we hard-code (and always set) the Prefer: header to "return-no-content" everywhere in C++, rather than it be configured based on options:

azure-sdk-for-cpp/sdk/tables/azure-data-tables/src/table_clients.cpp

Lines 947 to 963 in 384552a

	std::string TableClient::PrepInsertEntity(
	std::string const& changesetId,
	Models::TableEntity entity)
	{
	std::string payload = Serializers::UpdateEntity(entity);
	std::string returnValue = "--" + changesetId + "\n";
	returnValue += "Content-Type: application/http\n";
	returnValue += "Content-Transfer-Encoding: binary\n\n";
	auto url = m_url;
	url.AppendPath(
	m_tableName + PartitionKeyFragment + entity.GetPartitionKey().Value + RowKeyFragment
	+ entity.GetRowKey().Value + ClosingFragment);
	returnValue += "PATCH " + url.GetAbsoluteUrl() + " HTTP/1.1\n";
	returnValue += "Content-Type: application/json\n";
	returnValue += "Content-Length: " + std::to_string(payload.length());
	returnValue += "Accept: application/json;odata=minimalmetadata\n";
	returnValue += "Prefer: return-no-content\n";

In .NET, that header is configurable to a ResponseFormat, which is documented to be one of two values:

<param name="responsePreference"> Specifies whether the response should include the inserted entity in the payload.
Possible values are return-no-content and return-content. </param>

https://github.com/Azure/azure-sdk-for-net/blob/f566cffd72d20403eb934e03e0e6fe4015a878e5/sdk/tables/Azure.Data.Tables/src/Generated/TableRestClient.cs#L1149-L1157

And only if a value is provided, does that header get set:
https://github.com/Azure/azure-sdk-for-net/blob/f566cffd72d20403eb934e03e0e6fe4015a878e5/sdk/tables/Azure.Data.Tables/src/Generated/TableRestClient.cs#L1123-L1126

GoLang also has these ResponseFormat constants:
https://github.com/Azure/azure-sdk-for-go/blob/e8ec092d8456cd6d0cb836f29a9759d3aac2687d/sdk/data/aztables/internal/zz_constants.go#L46-L59
And they get used to optionally set the request header:
https://github.com/Azure/azure-sdk-for-go/blob/e8ec092d8456cd6d0cb836f29a9759d3aac2687d/sdk/data/aztables/internal/zz_table_client.go#L385-L389

As an aside, PrepDeleteEntity has this line commented out, which we should either remove or fix if intended:

azure-sdk-for-cpp/sdk/tables/azure-data-tables/src/table_clients.cpp

Lines 884 to 887 in 384552a

	returnValue += "DELETE " + url.GetAbsoluteUrl() + " HTTP/1.1\n";
	returnValue += "Accept: application/json;odata=minimalmetadata\n";
	// returnValue += "Prefer: return-no-content\n";
	returnValue += "DataServiceVersion: 3.0;\n";

[gearama]

No custumer asked for it, the returned data contains the etag and all other useful info.

[ahsonkhan]

Looks like the option only exists in the generated "protocol" layer. It is hardcoded in .NET, within the public layer (and the option isn't exposed to the end user):
https://github.com/Azure/azure-sdk-for-net/blob/4e1173308d32f0413788359a87376e673f2ab15b/sdk/tables/Azure.Data.Tables/src/TableClient.cs#L495
https://github.com/Azure/azure-sdk-for-net/blob/4e1173308d32f0413788359a87376e673f2ab15b/sdk/tables/Azure.Data.Tables/src/TableClient.cs#L615

That said, the header is only optionally set in some cases.
For example, in SubmitTransaction, this header isn't set (since ResponseFormat is set to null):
https://github.com/Azure/azure-sdk-for-net/blob/4e1173308d32f0413788359a87376e673f2ab15b/sdk/tables/Azure.Data.Tables/src/TableClient.cs#L1625

Should we do the same? Is there any unintended consequence of us setting this header when it doesn't need to be set?

If we are fine with always setting this header in the request (even in the cases where other language SDKs don't), then the only actionable part of this issue is:

As an aside, PrepDeleteEntity has this line commented out, which we should either remove or fix if intended