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POReading a local file in Google App Engine with Go
 

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  1. POReading a local file in Google App Engine with Go
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    <p>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.</p> <pre><code>panic: runtime error: invalid memory address or nil pointer dereference </code></pre> <p>I'm pretty confused, however it will run without error if I comment out</p> <pre><code>channel &lt;- buffer[0:dat] </code></pre> <p>So I must be using channels incorrectly, Any help?</p> <p>Edit:</p> <p>This is the working code, many thanks to Kevin Ballard for helping me get this one.</p> <pre><code>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 &lt;- 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) } </code></pre>
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    1. USMike Samuel
    1. USseveibar
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    1. COThe panic should give you a backtrace. What line is it actually panic'ing on?
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      1. POReading a local file in Google App Engine with Go
      1. USKevin Ballard
    2. COI tried running your code locally and it didn't panic. Granted, it didn't actually work either, but that's because a) you're trying to write the response in a goroutine instead of synchronously within the handler (just get rid of the `go` before the `writeContent`) and b) you're writing individual bytes as numbers instead of writing the bytes as, well, bytes (change `writeContent` to just use `w.Write(bytes)`). Granted, even with that you'll have thread issues because you're reusing the buffer you're sending to the other channel.
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      1. POReading a local file in Google App Engine with Go
      1. USKevin Ballard
    3. CODid you mean change fmt.Fprint to w.Write(bytes)? (Thanks for the help btw)
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      1. USseveibar
 

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