ms/http_bufferln is a SAP Parameter attribute which is used to control Maximum buffer length for HTTP requests information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
Maximum buffer size of an HTTP or HTTPS request. The buffer is
dynamically allocated by the message server and released once the req
uest has been processed.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.