紧急服务[:: 1]：46738：运行时错误：无效的内存地址或nil指针取消引用

Question

Can someone explain what's happening? Is there something I might be missing? I am new to Go. I am making a simple CRUD application, it compiles ok, but when I start the server, it gives me an runtime error.

2017/10/08 11:11:59 http: multiple response.WriteHeader calls
2017/10/08 11:11:59 http: panic serving [::1]:46828: runtime error: invalid memory address or nil pointer dereference
goroutine 19 [running]:
net/http.(*conn).serve.func1(0xc42008ce60)
    /home/vikram/go/src/net/http/server.go:1697 +0xd0
panic(0x740160, 0x97cc10)
    /home/vikram/go/src/runtime/panic.go:491 +0x283
html/template.(*Template).escape(0x0, 0x0, 0x0)
    /home/vikram/go/src/html/template/template.go:95 +0x38
html/template.(*Template).Execute(0x0, 0x94d920, 0xc420186000, 0x719e00, 0x9ab500, 0xc4201820c0, 0x0)
    /home/vikram/go/src/html/template/template.go:119 +0x2f
main.indexHandler(0x9519e0, 0xc420186000, 0xc420160100)
    /home/vikram/Projects/golang/src/github.com/vikramdurai/blog-app-go/main.go:188 +0x185
net/http.HandlerFunc.ServeHTTP(0x7b8da8, 0x9519e0, 0xc420186000, 0xc420160100)
    /home/vikram/go/src/net/http/server.go:1918 +0x44
net/http.(*ServeMux).ServeHTTP(0x98ad20, 0x9519e0, 0xc420186000, 0xc420160100)
    /home/vikram/go/src/net/http/server.go:2254 +0x130
net/http.serverHandler.ServeHTTP(0xc420087110, 0x9519e0, 0xc420186000, 0xc420160100)
    /home/vikram/go/src/net/http/server.go:2619 +0xb4
net/http.(*conn).serve(0xc42008ce60, 0x9520a0, 0xc42007c280)
    /home/vikram/go/src/net/http/server.go:1801 +0x71d
created by net/http.(*Server).Serve
    /home/vikram/go/src/net/http/server.go:2720 +0x288

my main.go file is on github.

Answer 1

The call to ParseFiles returns nil and an error. The call to t.Execute panics because t is nil.

To avoid the panic, return from the handler after calling http.Error.

...
t, err := template.ParseFiles("index.html")

if err != nil {
    http.Error(w, err.Error(), http.StatusInternalServerError)
    return  
}
...

It's not a good idea to send error messages with possible implementation details to the client. I suggest the following:

...
t, err := template.ParseFiles("index.html")

if err != nil {
    log.Println(err)
    http.Error(w, "Internal server error", http.StatusInternalServerError)
    return  
}
...