AWS_REQUEST_ID_HEADER not always picked up in Display for RusotoError<E>

[Fuuzetsu]

There's a trait impl like

impl<E: Error + 'static> fmt::Display for RusotoError<E> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self {
// …
            RusotoError::Unknown(ref cause) => write!(
                f,
                "Request ID: {:?} Body: {}",
                cause.headers.get(AWS_REQUEST_ID_HEADER),
                cause.body_as_str()
            ),
// ...
        }
    }

and

/// Header used by AWS on responses to identify the request
pub const AWS_REQUEST_ID_HEADER: &str = "x-amzn-requestid";

but this isn't completely correct. For example, I sent a PutObjectRequest with md5 set to Some("fake") and in response I got:

Request ID: None Body: <?xml version="1.0" encoding="UTF-8"?>
<Error><Code>InvalidDigest</Code><Message>The Content-MD5 you specified was invalid.</Message><Content-MD5>fake</Content-MD5><RequestId>M99NXA1M3GDBERKX</RequestId><HostId>8eomc+jLMa4yGJk8BsYCCUdyd4mKVHhUA+/ILHFdcrVKMEcEbAKdnH8cAMXnDpeKkH99yqJkJis=</HostId></Error> (Unknown(BufferedHttpResponse {status: 400, body: "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<Error><Code>InvalidDigest</Code><Message>The Content-MD5 you specified was invalid.</Message><Content-MD5>fake</Content-MD5><RequestId>M99NXA1M3GDBERKX</RequestId><HostId>8eomc+jLMa4yGJk8BsYCCUdyd4mKVHhUA+/ILHFdcrVKMEcEbAKdnH8cAMXnDpeKkH99yqJkJis=</HostId></Error>", headers: {"x-amz-request-id": "M99NXA1M3GDBERKX", "x-amz-id-2": "8eomc+jLMa4yGJk8BsYCCUdyd4mKVHhUA+/ILHFdcrVKMEcEbAKdnH8cAMXnDpeKkH99yqJkJis=", "content-type": "application/xml", "transfer-encoding": "chunked", "date": "Tue, 08 Nov 2022 01:57:22 GMT", "server": "AmazonS3", "connection": "close"} })) (should_retry: false)

You'll notice how the header is x-amz-requestid so the Display instance fails to pick it up and shows None.

I noticed that some API docs such as https://docs.aws.amazon.com/apigateway/latest/developerguide/http-api-logging-variables.html specify that it can be either one:

The AWS endpoint's request ID from the x-amz-request-id or x-amzn-requestId header.