Not all SASL enabled POP3 servers support the AUTH command on its own
when trying to detect the supported mechanisms. As such changed the
mechanism detection to use the CAPA command instead.
Changed the order of the state machine to match the order of actual
events.
Reworked some comments and function parameter positioning that I missed
the other day.
Added support for detecting the supported SASL authentication mechanisms
via the AUTH command. There are two ways of detecting them, either by
using the AUTH command, that will return -ERR if not supported or by
using the CAPA command which will return SASL and the list of mechanisms
if supported, not include SASL if SASL authentication is not supported
or -ERR if the CAPA command is not supported. As such it seems simpler
to use the AUTH command and fallback to normal clear text authentication
if the the command is not supported.
Additionally updated the test cases to return -ERR when the AUTH command
is encountered. Additional test cases will be added when support for the
individual authentication mechanisms is added.
Moved EOB definition into header file.
Switched the logic around in pop3_endofresp() to allow for the
introduction of auth-mechanism detection.
Repositioned second and third function variables where they will fit
within the 78 character line limit.
Tidied up some comments.
Reworked the command sending from two specific LIST and RETR command
functions into a single command based function as well as the two
associated response handlers into a generic command handler.
This feature allows the user to specify and use additional POP3
commands such as UIDL and DELE via libcurl's CURLOPT_CUSTOMREQUEST or
curl's -X command line option.
Simplified the code to remove the need for a separate "LIST <msg id>"
command handler and state machine and instead use the LIST command
handler for both operations.
If you pass a URL to pop3 that does not contain a message ID as
part of the URL, it will currently ask for 'INBOX' which just
causes the pop3 server to return an error.
The change makes libcurl treat en empty message ID as a request
for LIST (list of pop3 message IDs). User's code could then
parse this and download individual messages as desired.
