I am trying to understand more about HTTP Request Smuggling and I have been reading this article (https://portswigger.net/web-security/request-smuggling). Content-Length represents the length of the entity-body in bytes (https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Length) but where does the counting start?
Portswigger example (CL.TE)
POST / HTTP/1.1 Host: vulnerable-website.com Content-Length: 13 Transfer-Encoding: chunked 0 SMUGGLED
How was 13 derived? If I count the newlines before 0 and between 0 and "SMUGGLED", the total is 12? Do I count the newline after "Transfer-Encoding: chunked" as well?
Portswigger example (TE.CL)
POST / HTTP/1.1 Host: vulnerable-website.com Content-Length: 3 Transfer-Encoding: chunked 8 SMUGGLED 0
Similarly, where do I start the counting?
Any help is appreciated.