Getting http address from text file by awk script

Today , I writed a awk script,it can get http address. The http address only contains number, alphabet,backslash and point. My awk script is following:

#! /bin/awk -f

{

　　httpIndex=index($0,"http://")

      if ( httpIndex > 0 )

     {

      　　match($0,/http://[[:alnum:].//)

         　httpstr=substr($0,RSTART,RSTART + RLENGTH -1 )

　　　  match(httpstr,/http:///[[:alnum:]./]/)　　　　　　　　// line 8

 　　　httpstr=substr(httpstr,RSTART,RSTRAT + RLENGTH -1 ) // line 9

            print httpstr

     }

}

I test this script by 1 000 line texts, I found I need add line 8 and line 9 code, otherwise some http address always behand by some special character ,such as space.