Reading a local file in Google App Engine with Go

I'm trying to use go instead of python for my website on google app engine. But I keep getting this error with my script when I test locally.

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

I'm pretty confused, however it will run without error if I comment out

channel <- buffer[0:dat]

So I must be using channels incorrectly, Any help?

Edit:

This is the working code, many thanks to Kevin Ballard for helping me get this one.

package defp

import (
    "fmt"
    "http"
    "os"
)

func getContent(filename string, channel chan []byte) {
    file, err := os.OpenFile(filename, os.O_RDONLY, 0666)
    defer file.Close()
    if err == nil {
        fmt.Printf("FILE FOUND : " + filename + " \n")
        buffer := make([]byte, 16)
        dat, err := file.Read(buffer)
        for err == nil {
            fmt.Printf("herp")
            channel <- buffer[0:dat]
            buffer = make([]byte, 16)
            dat, err = file.Read(buffer)
        }
        close(channel)
        fmt.Printf("DONE READING\n")
    } else {
        fmt.Printf("FILE NOT FOUND : " + filename + " \n")
    }
}
func writeContent(w http.ResponseWriter, channel chan []byte) {
    fmt.Printf("ATTEMPTING TO WRITE CONTENT\n")
    go func() {
        for bytes := range channel {
            w.Write(bytes)
            fmt.Printf("BYTES RECEIVED\n")
        }
    }()
    fmt.Printf("FINISHED WRITING\n")
}
func load(w http.ResponseWriter, path string) {
    fmt.Printf("ATTEMPTING LOAD " + path + "\n")
    channel := make(chan []byte, 50)
    writeContent(w, channel)
    getContent(path, channel)
}
func handle(w http.ResponseWriter, r *http.Request) {
    fmt.Printf("HANDLING REQUEST FOR " + r.URL.Path[1:] + "\n")
    load(w, r.URL.Path[1:])
}
func init() {
    http.HandleFunc("/", handle)
}

The reason why your program sometimes panics is that it is sometimes writing to <code>w http.ResponseWriter</code> after the program exits the <code>load</code> function. The <code>http</code> package automatically closes the <code>http.ResponseWriter</code> when the program exits the handler function. In function <code>writeContent</code>, the program will sometimes attempt to write to a closed <code>http.ResponseWriter</code>.

BTW: You can make the program source code much smaller if you use the <code>io.Copy</code> function.

To always get predictable behavior, make sure that all work that you want the program to perform in response to a HTTP request is done before you exit the handler function. For example:

func writeContent(w http.ResponseWriter, channel chan []byte) {
    fmt.Printf("ATTEMPTING TO WRITE CONTENT\n")
    for bytes := range channel {
            w.Write(bytes)
            fmt.Printf("BYTES RECEIVED\n")
    }
    fmt.Printf("FINISHED WRITING\n")
}

func load(w http.ResponseWriter, path string) {
    fmt.Printf("ATTEMPTING LOAD " + path + "\n")
    channel := make(chan []byte)
    workDone := make(chan byte)
    go func() {
            writeContent(w, channel)
            workDone <- 1 //Send an arbitrary value
    }()
    go func() {
            getContent(path, channel)
            workDone <- 2 //Send an arbitrary value
    }()
    <-workDone
    <-workDone
}

func handle(w http.ResponseWriter, r *http.Request) {
    fmt.Printf("HANDLING REQUEST FOR " + r.URL.Path[1:] + "\n")
    load(w, r.URL.Path[1:])
}