String manipulation

[Austin Einter <austin.einter@...>]

Hi All

I have a string as below.

INVITE\r\n
Content-Length:\r\n

\r\n

v=0\r\n

I want to change it to as below

INVITE\r\n
Content-Length: 3\r\n

\r\n

v=0\r\n

You can see in line starts with Content-Length, I have added 5 at the end because after empty line I have only 5 characters (that is v=0\r\n)

I am looking for what is the best way to do that.

The line Content-Length:\r\n can be of any form given below

a) Content-Length     :\r\n

b) Content-Length:    \r\n

c) Content-Length     :      \r\n

So you can any number of spaces can come anywhere around char : present in line

Can somebody kindly help what is the best way to do it in Lua 5.2

Many thanks

Austin