[go-nuts] http Flush() causes "panic: runtime error: invalid memory address"

While implementing heartbeats for a long living HTTP connection on the
server,
I encountered a panic raised from the http package itself.
There isn't anything fancy in the implementation except for the fact that
the response writer
is passed to another goroutine. The code can be found
in http://play.golang.org/p/ElC4PpU-6S .
It doesn't run directly on the website, but I made sure it ran locally, and
the panic runtime
error is pretty reproducible and predictable.

These two threads suggested that writers not be passed to other goroutines,
but I'm not
convinced, since these panics don't occur if
* We don't write on line 14 `w.Write([]byte("hello"))`
* or if we don't provide the extra 100ms margin for the Sleep interval on
line 22 `time.Sleep(interval + 100 * time.Millisecond)`
https://groups.google.com/forum/#!searchin/golang-nuts/http$20flush/golang-nuts/vzVgBwJ1q2c/jCS_twDIScAJ
https://groups.google.com/forum/#!searchin/golang-nuts/http$20flush/golang-nuts/FLX9Ok5IepE/ePp3-nrcWFwJ

The output of `go version` is "go version go1.1.2 darwin/amd64", and I'm on
the latest
Mavericks OS.
Below is a copy of the reproducible code:
```
package main

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

func handler(w http.ResponseWriter, r *http.Request) {
   interval := 1 * time.Second
   ticker := time.NewTicker(interval)
   go func() {
     for _ = range ticker.C {
       w.Write([]byte("hello"))
       if f, ok := w.(http.Flusher); ok {
         fmt.Println("flush")
         f.Flush()
       }
     }
   }()

   time.Sleep(interval + 100 * time.Millisecond)
}

func startServer() {
   http.HandleFunc("/", handler)
   go func() {
     http.ListenAndServe(":8080", nil)
   }()
}

func main() {
   startServer()
   http.Get("http://localhost:8080/")
   time.Sleep(1 * time.Minute)
}
```

Here's the stack trace:
```

panic: runtime error: invalid memory address or nil pointer dereference

[signal 0xb code=0x1 addr=0x20 pc=0x5391c]


goroutine 10 [running]:

net/http.(*switchWriter).Write(0xc200078790, 0xc2000e9800, 0x5, 0x800, 0x0,
...)

/usr/local/go/src/pkg/net/http/chunked.go:0 +0x5c

bufio.(*Writer).Flush(0xc200095b80, 0xc20009c420, 0xc200000008)

/usr/local/go/src/pkg/bufio/bufio.go:465 +0x14a

net/http.(*response).Flush(0xc2000b3700)

/usr/local/go/src/pkg/net/http/server.go:952 +0x4a

main.func·001()

/tmp/ab.go:17 +0x1e2

created by main.handler

/tmp/ab.go:20 +0xac
```