[FR.] always send caller application name

[yjqg6666]

Which module is your feature request related to?
Plugin

Is your feature request related to a problem?
If the call path is A -> B -> C, B calls C in a different thread(without changing code). The C will have a new transaction trace and will never know who called. On the web side, the calling side is always a virtual node user. If we know which app made the call, we could change the application code to use pinpoint-sdk to wrap the existing code.

Describe the solution you'd like
In the http client plugins, insert a caller application name header to request.
Add a config to enable/disable this feature and a configure for header name.

A new PR would be made.
PR #8561 #8570 is made to resolve this issue.

[emeroad]

It seems that the data you are adding is the same type as Pinpoint-pAppName

public enum Header {
    // ~~
    HTTP_PARENT_APPLICATION_NAME("Pinpoint-pAppName"),
    HTTP_PARENT_APPLICATION_TYPE("Pinpoint-pAppType"),

What's the difference with Pinpoint-pAppName?
Works regardless of sampling?

[yjqg6666]

This header will always be sent regardless of sampling rate and async running in a different thread. The Pinpoint-pAppName header is only sent when the transaction is sampled and is hidden from application (profiler.tomcat/jetty.hidepinpointheader =true) to get.

In most of the use cases, the caller application name is the most valuable, esp. for API statistics (api upgrading/deprecation/ removal). The header name can be configured and the header can be fetched by callee app programmatically.

[emeroad]

This header will always be sent regardless of sampling rate and async running in a different thread. The Pinpoint-pAppName header is only sent when the transaction is sampled and is hidden from application (profiler.tomcat/jetty.hidepinpointheader =true) to get.

It is a bug that AsyncContext works in DisableTrace state.

• This feature has not been implemented yet.

The intended behavior is that AsyncContext should not work in DisableTrace.

In most of the use cases, the caller application name is the most valuable, esp. for API statistics (api upgrading/deprecation/ removal). The header name can be configured and the header can be fetched by callee app programmatically.

How about adding header api to Agent SDK?

Optional<Headers> headers = AgentContext.getHeaders();
if (headers.isPresent()) {
    Header header = headers.getParentApplicationName(); // getHeader("Pinpoint-pAppName"")
    header.getName();
    header.getValue();
}

[yjqg6666]

@emeroad if the transaction is not traced, you could not know who's calling?