slightly less outdated

   ... analyzes the URL, it separates the different components and connects to

   the remote host. This may involve using a proxy and/or using SSL. The

   Curl_gethost() function in lib/hostip.c is used for looking up host names.

   Curl_resolv() function in lib/hostip.c is used for looking up host names

   (it does then use the proper underlying method, which may vary between

   platforms and builds).

   When Curl_connect is done, we are connected to the remote site. Then it is

   time to tell the server to get a document/file. Curl_do() arranges this.

   Curl_Transfer() function (in lib/transfer.c) to setup the transfer and

   returns.

   Starting in 7.9.1, if this DO function fails and the connection is being

   re-used, libcurl will then close this connection, setup a new connection

   and re-issue the DO request on that. This is because there is no way to be

   perfectly sure that we have discovered a dead connection before the DO

   function and thus we might wrongly be re-using a connection that was closed

   by the remote peer.

   If this DO function fails and the connection is being re-used, libcurl will

   then close this connection, setup a new connection and re-issue the DO

   request on that. This is because there is no way to be perfectly sure that

   we have discovered a dead connection before the DO function and thus we

   might wrongly be re-using a connection that was closed by the remote peer.

   Some time during the DO function, the Curl_setup_transfer() function must

   be called with some basic info about the upcoming transfer: what socket(s)

   to read/write and the expected file tranfer sizes (if known).

 o Transfer()

   Curl_perform() then calls Transfer() in lib/transfer.c that performs

   the entire file transfer.

   Curl_perform() then calls Transfer() in lib/transfer.c that performs the

   entire file transfer.

   During transfer, the progress functions in lib/progress.c are called at a

   frequent interval (or at the user's choice, a specified callback might get

 URL encoding and decoding, called escaping and unescaping in the source code,

 is found in lib/escape.c.

 While transfering data in Transfer() a few functions might get

 used. curl_getdate() in lib/getdate.c is for HTTP date comparisons (and

 more).

 While transfering data in Transfer() a few functions might get used.

 curl_getdate() in lib/parsedate.c is for HTTP date comparisons (and more).

 lib/getenv.c offers curl_getenv() which is for reading environment variables

 in a neat platform independent way. That's used in the client, but also in

 A function named curl_version() that returns the full curl version string is

 found in lib/version.c.

 If authentication is requested but no password is given, a getpass_r() clone

 exists in lib/getpass.c. libcurl offers a custom callback that can be used

 instead of this, but it doesn't change much to us.

Persistent Connections

======================

   all the options etc that the library-user may choose.

 o The 'SessionHandle' struct holds the "connection cache" (an array of

   pointers to 'connectdata' structs). There's one connectdata struct

   allocated for each connection that libcurl knows about.

 o This also enables the 'curl handle' to be reused on subsequent transfers,

   something that was illegal before libcurl 7.7.

   allocated for each connection that libcurl knows about. Note that when you

   use the multi interface, the multi handle will hold the connection cache

   and not the particular easy handle. This of course to allow all easy handles

   in a multi stack to be able to share and re-use connections.

 o This enables the 'curl handle' to be reused on subsequent transfers.

 o When we are about to perform a transfer with curl_easy_perform(), we first

   check for an already existing connection in the cache that we can use,

   otherwise we create a new one and add to the cache. If the cache is full

 o When the transfer operation is complete, we try to leave the connection

   open. Particular options may tell us not to, and protocols may signal

   closure on connections and then we don't keep it open of course.

 o When curl_easy_cleanup() is called, we close all still opened connections.

 o When curl_easy_cleanup() is called, we close all still opened connections,

   unless of course the multi interface "owns" the connections.

 You do realize that the curl handle must be re-used in order for the

 persistent connections to work.