feign.core v13.2.1 Repeatedly writing "Content-Length"

[chiangzeon]

I have two applications, A and B. B invokes A through the interface exposed by A. However, an issue occurred where A failed to decode the HTTP message on the Tomcat side, resulting in an HTTP status code of 400. Through source code analysis, I found that in the feign.Client.Default#convertAndSend method, there is a section that adds request headers. When gzip or deflate compression of the request body is not enabled, "content-length" is written once, but it is written again later. See lines 179 to 198 of the feign.Client class.
The feign.RequestTemplate#body(feign.Request.Body) will calculate the length of the byte array and add it to the header. In tomcat-embed-core (v9.0.46), there is such a processing in org.apache.tomcat.util.http.MimeHeaders#getUniqueValue. If the existing header information is obtained, an exception will be thrown.

My current solutions are as follows:

1. Inject a feign.RequestInterceptor instance to remove duplicate header information.
2. Enable compression and manually calculate the request body length, but this involves modifications to other applications.