GODRIVER-2906 Add container Env to Handshake.

[qingyang-hu]

GODRIVER-2906

Summary

• Update the metadata handshake client.env.name field to optional.
• Add client.env.container.

The values for client.env.container are sourced from the environment, see here.

Background & Motivation

client.env.container.runtime is untested since it requires "/.dockerenv", which exists in the root directory.

[github-actions]

API Change Report

No changes found!

[blink1073]

LGTM!

[prestonvasquez]

This line implies that we wouldn't append the client environment if the name and the container are unavailable. However, both name and container were made optional as part of DRIVERS-2570: https://github.com/mongodb/specifications/pull/1454/files#diff-0ecfac0976ff0bfe5b91b5bd52bc5a79dd1125434505ff22331c7cadf1b2f25eR170

I think we should completely remove this block.

If tests are failing, such as the handshake integration tests, it's because there is an expectation that they should contain a name which is now incorrect.

[qingyang-hu]

I'm afraid it's ambiguous. My understanding is that the entire client.env can be omitted because:

1. The spec states the env is optional.
2. Logically, we don't have to keep the env if it has nothing.

However, I will ask for clarification because we don't have a lot of reference implementations now.

Spec says:

If no fields of client.env would be populated, client.env MUST be entirely omitted. ref

[prestonvasquez]

Ah okay, so because the other fields in env depend on either name or container, if both are empty then implicitly the other fields will be empty. Could we add a comment to that effect?

[prestonvasquez]

Instead of nesting these conditions, suggest making them separate blocks for readability:

	var idx int32
	idx, dst = bsoncore.AppendDocumentElementStart(dst, "env")

	if name != "" {
		dst = bsoncore.AppendStringElement(dst, "name", name)
	}

	if !omitNonName {
		switch name {
		case envNameAWSLambda:
			dst = addMem(envVarAWSLambdaFunctionMemorySize)
			dst = addRegion(envVarAWSRegion)
		case envNameGCPFunc:
			dst = addMem(envVarFunctionMemoryMB)
			dst = addRegion(envVarFunctionRegion)
			dst = addTimeout(envVarFunctionTimeoutSec)
		case envNameVercel:
			dst = addRegion(envVarVercelRegion)
		}
	}

[prestonvasquez]

LGTM!