"Connection: close" header from target server is not honored

Created by: nicolayr

When the target server sends a Connection: close header, normal behavior as per the HTTP protocol is that both the client and server should close the connection when data transmission has completed.

Currently node-http-proxy doesn't honor this. Instead the connection is left open, which results in ECONNRESET errors being thrown on subsequent requests.

There are several related open issues, but I couldn't find any that directly address the same problem. For example: #446, #813, #859, #757, #966.