net/http: Server.ConnContext accidentally modifies context for all connections #35750
Description
What version of Go are you using (go version)?
$ go version go version go1.13.4 linux/amd64
Does this issue reproduce with the latest release?
Yes.
What did you do?
Docs of ConnContext say that:
ConnContext optionally specifies a function that modifies the context used for a new connection c.
However, it assigns this new context to a variable shared between connections in the accept loop. Thus creating a growing chain of contexts.
Example code:
package main
import (
"context"
"fmt"
"net"
"net/http"
)
func main() {
server := &http.Server{
Addr: ":4444",
Handler: http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
rw.Header().Set("Connection", "close")
}),
ConnContext: func(ctx context.Context, c net.Conn) context.Context {
fmt.Printf("conn: %s\n", c.RemoteAddr())
if c2 := ctx.Value("conn"); c2 != nil {
fmt.Printf("existing: %s\n", c2.(net.Conn).RemoteAddr())
}
return context.WithValue(ctx, "conn", c)
},
}
go func() {
panic(server.ListenAndServe())
}()
var err error
fmt.Printf("\nrequest 1:\n")
_, err = http.Get("http://localhost:4444/")
if err != nil {
panic(err)
}
fmt.Printf("request 1 done\n")
fmt.Printf("\nrequest 2:\n")
_, err = http.Get("http://localhost:4444/")
if err != nil {
panic(err)
}
fmt.Printf("request 2 done\n")
}
What did you expect to see?
request 1: conn: [::1]:34022 request 1 done request 2: conn: [::1]:34024 request 2 done
What did you see instead?
request 1: conn: [::1]:34022 request 1 done request 2: conn: [::1]:34024 existing: [::1]:34022 request 2 done