bug.go

package main

import (
	"log"
	"net/http"
	"github.com/gorilla/mux"
	"database/sql"
	_ "github.com/mattn/go-sqlite3"
)

var db *sql.DB

func main() {
	var err error
	db, err := sql.Open("sqlite3", "./comments.db")
	if err != nil {
		panic(err)
	}
	defer db.Close()

	router := mux.NewRouter()
	router.HandleFunc("/comments/{domain}/{path}", createComment).Methods("POST")


	http.Handle("/", router)
	log.Println("Listening...")
	http.ListenAndServe(":7654", nil)
}

func createComment(writer http.ResponseWriter, request *http.Request) {
	query := `
		INSERT INTO comments(domain, path, body) VALUES ("foo.com", "/bar", "some text");
        `

	_, err := db.Exec(query)
	if err != nil {
		log.Printf("%q", err)
		return
	}
}

error.log

2014/02/28 19:01:07 http: panic serving [::1]:56399: runtime error: invalid memory address or nil pointer dereference
goroutine 5 [running]:
net/http.func·007()
	/usr/local/Cellar/go/1.1.2/src/pkg/net/http/server.go:1022 +0xac
sync/atomic.CompareAndSwapUint32()
	/usr/local/Cellar/go/1.1.2/src/pkg/sync/atomic/asm_amd64.s:14 +0xd
sync.(*Mutex).Lock(0x20)
	/usr/local/Cellar/go/1.1.2/src/pkg/sync/mutex.go:43 +0x35
database/sql.(*DB).conn(0x0, 0xc2000b8be0, 0xc2000b8b60, 0xc2000b8b41)
	/usr/local/Cellar/go/1.1.2/src/pkg/database/sql/sql.go:470 +0x35
database/sql.(*DB).exec(0x0, 0x4355f50, 0x5c, 0x0, 0x0, ...)
	/usr/local/Cellar/go/1.1.2/src/pkg/database/sql/sql.go:659 +0x68
database/sql.(*DB).Exec(0x0, 0x4355f50, 0x5c, 0x0, 0x0, ...)
	/usr/local/Cellar/go/1.1.2/src/pkg/database/sql/sql.go:650 +0x98
main.createComment(0xc2000a3cc0, 0xc2000c1230, 0xc2000ab5b0)
	/Users/sdqali/src/play/commentary/simple_bug.go:35 +0x52
net/http.HandlerFunc.ServeHTTP(0x43569c8, 0xc2000a3cc0, 0xc2000c1230, 0xc2000ab5b0)
	/usr/local/Cellar/go/1.1.2/src/pkg/net/http/server.go:1149 +0x3e
github.com/gorilla/mux.(*Router).ServeHTTP(0xc2000a7410, 0xc2000a3cc0, 0xc2000c1230, 0xc2000ab5b0)
	/usr/local/lib/golang/src/github.com/gorilla/mux/mux.go:98 +0x217
net/http.(*ServeMux).ServeHTTP(0xc2000aa4e0, 0xc2000a3cc0, 0xc2000c1230, 0xc2000ab5b0)
	/usr/local/Cellar/go/1.1.2/src/pkg/net/http/server.go:1416 +0x11d
net/http.serverHandler.ServeHTTP(0xc2000a7550, 0xc2000a3cc0, 0xc2000c1230, 0xc2000ab5b0)
	/usr/local/Cellar/go/1.1.2/src/pkg/net/http/server.go:1517 +0x16c
net/http.(*conn).serve(0xc2000c0120)
	/usr/local/Cellar/go/1.1.2/src/pkg/net/http/server.go:1096 +0x765
created by net/http.(*Server).Serve
	/usr/local/Cellar/go/1.1.2/src/pkg/net/http/server.go:1564 +0x266

looks like you closed your db connection, then you call exec on the closed connection