Make more fixes and improvements

tool/net/demo/unix-subprocess.lua

@@ -0,0 +1,44 @@
+-- example of how to run the ls command
+-- and pipe its output to the http user
+local unix = require "unix"
+function main()
+   syscall = 'commandv'
+   ls, errno = unix.commandv("ls")
+   if ls then
+      syscall = 'pipe'
+      reader, writer, errno = unix.pipe()
+      if reader then
+         syscall = 'fork'
+         child, errno = unix.fork()
+         if child then
+            if child == 0 then
+               unix.close(1)
+               unix.dup(writer)
+               unix.close(writer)
+               unix.close(reader)
+               unix.execve(ls, {ls, "-Shal"})
+               unix.exit(127)
+            else
+               unix.close(writer)
+               SetStatus(200)
+               SetHeader('Content-Type', 'text/plain')
+               while true do
+                  data = unix.read(reader)
+                  if data ~= "" then
+                     Write(data)
+                  else
+                     break
+                  end
+               end
+               unix.close(reader)
+               unix.wait(-1)
+               return
+            end
+         end
+      end
+   end
+   SetStatus(200)
+   SetHeader('Content-Type', 'text/plain')
+   Write(string.format('error %s calling %s()', unix.strerrno(errno), syscall))
+end
+main()