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

11
votes

I am new to golang and currently following this tutorial and source code here - http://golang.org/doc/articles/wiki/part2.go

After building this file, I am getting 

calvin$ ./mywebwiki2 
2012/07/23 17:12:59 http: panic serving [::1]:58820: runtime error: invalid memory address or nil pointer dereference
/usr/local/go/src/pkg/net/http/server.go:576 (0x3f202)
    _func_003: buf.Write(debug.Stack())
/private/tmp/bindist454984655/go/src/pkg/runtime/proc.c:1443 (0x10c79)
/private/tmp/bindist454984655/go/src/pkg/runtime/runtime.c:128 (0x11745)
/private/tmp/bindist454984655/go/src/pkg/runtime/thread_darwin.c:418 (0x148b5)
/Users/calvin/work/gowiki/mywebwiki2.go:33 (0x2248)
    viewHandler: fmt.Fprintf(w, "<h1>%s</h1><div>%s</div>", p.Title, p.Body)
/usr/local/go/src/pkg/net/http/server.go:690 (0x331ae)
    HandlerFunc.ServeHTTP: f(w, r)
/usr/local/go/src/pkg/net/http/server.go:926 (0x34030)
    (*ServeMux).ServeHTTP: mux.handler(r).ServeHTTP(w, r)
/usr/local/go/src/pkg/net/http/server.go:656 (0x32fc1)
    (*conn).serve: handler.ServeHTTP(w, w.req)
/private/tmp/bindist454984655/go/src/pkg/runtime/proc.c:271 (0xed7f)
2012/07/23 17:12:59 http: panic serving [::1]:58821: runtime error: invalid memory address or nil pointer dereference

Any idea what I did wrong to be causing this apparent memory corruption?

2
go
This error may also occur if the file requested isn't there (with no error handling). For me I forgot to create the test.txt file. – earth2jason

2 Answers

16
votes

There's an ignored err at line 36. The error probably says open .txt: no such file or directory if you tested in browser using URL http://localhost:8080/view/ or open foo.txt: no such file or directory if you tested in browser using URL http://localhost:8080/view/foo. In the later case there must be a file "foo.txt" in your working directory for this example code to work. After that the code seems to work for me locally.

Someone should probably fill an issue about the ignored error value.

1
votes

In the tutorial, you created the file TestPage previously. Which is the page you should be navigating to when you first build the server. In the tutorial, they have you navigate to view/test instead of view/TestPage as you should which is what creates the confusion.