DT headers added too late for Feign

[jodeev]

Feign (from Spring Cloud Finchley.SR1) appears to be altering the codepath a generated request takes and causes our auto-injection of DT headers to fail.

Description:

• The application uses Spring Boot (version 2.1.10.RELEASE) and Feign (from Spring Cloud Finchley.SR1).
• When using a rest client, generated by Feign, New Relic agent is adding headers too late: it comes to sun.net.www.protocol.http.HttpURLConnection#addRequestProperty and fails to add any headers with IllegalStateException("Already connected").
• With Spring's RestTemplate the headers are added correctly.

Test app showing this issue included here:
https://newrelic.zendesk.com/agent/tickets/442571

https://newrelic.aha.io/ideas/ideas/JAVA-I-1001

[gustavodaquino]

The problem persists using the following versions:

org.springframework.boot:2.6.10
com.newrelic.agent.java:newrelic-api:7.6.0
org.springframework.cloud:spring-cloud-starter-openfeign:3.1.3
io.github.openfeign:feign-httpclient:11.8

Regards.

[kford-newrelic]

@gustavodaquino any chance you have a sample app that reproduces the problem that you can share with us?

[kford-newrelic]

Unfortunately, we do not have the engineering bandwidth to further investigate this issue.

[jasonjkeller]

I believe this issue should actually be fixed in Java agent 8.0.1 by #1145