在Go中检测失败的HTTP连接

Question

Let's suppose client uploads heavy image by http with slow internet connection, he opens connection to server, starts to write data and suddenly he loses this connection because of network problems. How can I detect this on server if handler function was not yet called. The solution I found is to check the connection state. But the problem is that it's not scalable, because a lot of goroutines will interact with global variable. Are there any more elegant solutions?

package main

import (
    "fmt"
    "log"
    "net"
    "net/http"
)

// current state of connections
var connStates = make(map[string]http.ConnState)

func main() {
    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        fmt.Println("got new request")
        fmt.Println(connStates)
    })

    srv := &http.Server{
        Addr: ":8080",
        ConnState: func(conn net.Conn, event http.ConnState) {
            if event != http.StateClosed {
                connStates[conn.RemoteAddr().String()] = event
            } else {
                if connStates[conn.RemoteAddr().String()] == http.StateActive {
                    fmt.Println("client cancelled request")
                }
                delete(connStates, conn.RemoteAddr().String())
            }
        },
    }
    log.Fatal(srv.ListenAndServe())
}

Answer 1

If you only need to have logs you can even simplify the code:

srv := &http.Server{
        Addr: ":8080",
        ConnState: func(conn net.Conn, event http.ConnState) {
            log.Printf("addr: %s, changed state to: %s", conn.RemoteAddr(), event.String())
        },
    }

That callback will be triggered on each change of the conn