[Serverless] Fix panic when running the extension without appsec enabled.

[purple4reina]

What does this PR do?

This pull request fixes a bug when running a java function in aws lambda without appsec enabled.

The problem stems from the fact that when a go interface can be implemented by a nil pointer, the interface itself is considered not nil. In the example below, the interface io.Reader is implemented in three ways, but only the first of which is considered nil. This is despite the second implementation be a nil pointer, as is the case which triggered the panic this PR addresses.

func main() {
	var r io.Reader
	fmt.Println(r == nil)    // true

	r = (*bytes.Buffer)(nil)
	fmt.Println(r == nil)    // false
	
	r = &bytes.Buffer{}
	fmt.Println(r == nil)    // false
}

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[Julio-Guerra]

I'd suggest you move this test into the lifecycle processor test suite as this is testing its nil-check is working as expected.

[purple4reina]

Good catch.

[purple4reina]

When I worked to move this test to the lifecycle processor suite, I hit the import cycle issue. Working around it created a pretty large diff. While I agree this isn't the perfect place for this test, I do think it is the best place for this test.

[purple4reina]

I've determined that the Serverless Integration Tests failures are also occurring on main and therefore are not caused by this pull request.

We are seeing the following log line for java and dotnet functions:

{
    "level": "ERROR",
    "message": "datadog: Malformed _X_AMZN_TRACE_ID value: Root=1-6414d1a3-4c0e6f6d4dce99ae7c78561a;Parent=69e50da0d91875c2;Sampled=1;Lineage=f1f89451:0"
}

[jcstorms1]

Are both appsecSubProcessor and appsecProxyProcessor supposed to be set? This else if will only get called if subProcessor is not equal to nil and it wasn't clear if that was intended. I'm guessing we use either a subprocessor or proxy, but not both?

[Julio-Guerra]

Yes, you got this right: appsec is either a "proxy subprocessor", or a "regular subprocessor".