INTERNALS: cat lib/README* >> INTERNALS

and a conversion to markdown. Removed the lib/README.* files. The idea
being to move toward having INTERNALS as the one and only "book" of
internals documentation.

Added a TOC to top of the document.

1 files changed, 528 insertions, 149 deletions

diff --git a/docs/INTERNALS b/docs/INTERNALS
index fe5c44995..b134260c3 100644
--- a/docs/INTERNALS
+++ b/docs/INTERNALS
@@ -1,18 +1,56 @@
-                                  _   _ ____  _
-                              ___| | | |  _ \| |
-                             / __| | | | |_) | |
-                            | (__| |_| |  _ <| |___
-                             \___|\___/|_| \_\_____|
-
-INTERNALS
+Table of Contents
+=================
 
- The project is split in two. The library and the client. The client part uses
- the library, but the library is designed to allow other applications to use
- it.
+ - [Intro](#intro)
+ - [git](#git)
+ - [Portability](#Portability)
+ - [Windows vs Unix](#winvsunix)
+ - [Library](#Library)
+   - [`Curl_connect`](#Curl_connect)
+   - [`Curl_do`](#Curl_do)
+   - [`Curl_readwrite`](#Curl_readwrite)
+   - [`Curl_done`](#Curl_done)
+   - [`Curl_disconnect`](#Curl_disconnect)
+ - [HTTP(S)](#http)
+ - [FTP](#ftp)
+   - [Kerberos](#kerberos)
+ - [TELNET](#telnet)
+ - [FILE](#file)
+ - [SMB](#smb)
+ - [LDAP](#ldap)
+ - [E-mail](#email)
+ - [General](#general)
+ - [Persistent Connections](#persistent)
+ - [multi interface/non-blocking](#multi)
+ - [SSL libraries](#ssl)
+ - [Library Symbols](#symbols)
+ - [Return Codes and Informationals](#returncodes)
+ - [AP/ABI](#abi)
+ - [Client](#client)
+ - [Memory Debugging](#memorydebug)
+ - [Test Suite](#test)
+ - [Asynchronous name resolves](#asyncdns)
+   - [c-ares](#cares)
+ - [`curl_off_t`](#curl_off_t)
+ - [curlx](#curlx)
+ - [Content Encoding](#contentencoding)
+ - [hostip.c explained](#hostip)
+ - [Track Down Memory Leaks](#memoryleak)
+ - [`multi_socket`](#multi_socket)
+
+<a name="intro"></a>
+curl internals
+==============
+
+ This project is split in two. The library and the client. The client part
+ uses the library, but the library is designed to allow other applications to
+ use it.
 
  The largest amount of code and complexity is in the library part.
 
-GIT
+
+<a name="git"></a>
+git
 ===
 
  All changes to the sources are committed to the git repository as soon as
@@ -23,6 +61,7 @@ GIT
  Tagging shall be used extensively, and by the time we release new archives we
  should tag the sources with a name similar to the released version number.
 
+<a name="Portability"></a>
 Portability
 ===========
 
@@ -34,45 +73,55 @@ Portability
  want it to remain functional and buildable with these and later versions
  (older versions may still work but is not what we work hard to maintain):
 
- OpenSSL      0.9.7
- GnuTLS       1.2
- zlib         1.1.4
- libssh2      0.16
- c-ares       1.6.0
- libidn       0.4.1
- cyassl       2.0.0
- openldap     2.0
- MIT Kerberos 1.2.4
- GSKit        V5R3M0
- NSS          3.14.x
- axTLS        1.2.7
- PolarSSL     1.3.0
- Heimdal      ?
- nghttp2      1.0.0
+Dependencies
+------------
+
+ - OpenSSL      0.9.7
+ - GnuTLS       1.2
+ - zlib         1.1.4
+ - libssh2      0.16
+ - c-ares       1.6.0
+ - libidn       0.4.1
+ - cyassl       2.0.0
+ - openldap     2.0
+ - MIT Kerberos 1.2.4
+ - GSKit        V5R3M0
+ - NSS          3.14.x
+ - axTLS        1.2.7
+ - PolarSSL     1.3.0
+ - Heimdal      ?
+ - nghttp2      1.0.0
+
+Operating Systems
+-----------------
 
  On systems where configure runs, we aim at working on them all - if they have
  a suitable C compiler. On systems that don't run configure, we strive to keep
  curl running fine on:
 
- Windows      98
- AS/400       V5R3M0
- Symbian      9.1
- Windows CE   ?
- TPF          ?
+ - Windows      98
+ - AS/400       V5R3M0
+ - Symbian      9.1
+ - Windows CE   ?
+ - TPF          ?
+
+Build tools
+-----------
 
  When writing code (mostly for generating stuff included in release tarballs)
  we use a few "build tools" and we make sure that we remain functional with
  these versions:
 
- GNU Libtool  1.4.2
- GNU Autoconf 2.57
- GNU Automake 1.7 (we currently avoid 1.10 due to Solaris-related bugs)
- GNU M4       1.4
- perl         5.004
- roffit       0.5
- groff        ? (any version that supports "groff -Tps -man [in] [out]")
- ps2pdf (gs)  ?
+ - GNU Libtool  1.4.2
+ - GNU Autoconf 2.57
+ - GNU Automake 1.7
+ - GNU M4       1.4
+ - perl         5.004
+ - roffit       0.5
+ - groff        ? (any version that supports "groff -Tps -man [in] [out]")
+ - ps2pdf (gs)  ?
 
+<a name="winvsunix"></a>
 Windows vs Unix
 ===============
 
@@ -87,8 +136,9 @@ Windows vs Unix
 
  2. Windows requires a couple of init calls for the socket stuff.
 
-   That's taken care of by the curl_global_init() call, but if other libs also
-   do it etc there might be reasons for applications to alter that behaviour.
+   That's taken care of by the `curl_global_init()` call, but if other libs
+   also do it etc there might be reasons for applications to alter that
+   behaviour.
 
  3. The file descriptors for network communication and file operations are
     not easily interchangeable as in unix.
@@ -101,28 +151,29 @@ Windows vs Unix
 
    We set stdout to binary under windows
 
- Inside the source code, We make an effort to avoid '#ifdef [Your OS]'. All
+ Inside the source code, We make an effort to avoid `#ifdef [Your OS]`. All
  conditionals that deal with features *should* instead be in the format
- '#ifdef HAVE_THAT_WEIRD_FUNCTION'. Since Windows can't run configure scripts,
- we maintain a curl_config-win32.h file in lib directory that is supposed to
- look exactly as a curl_config.h file would have looked like on a Windows
+ `#ifdef HAVE_THAT_WEIRD_FUNCTION`. Since Windows can't run configure scripts,
+ we maintain a `curl_config-win32.h` file in lib directory that is supposed to
+ look exactly as a `curl_config.h` file would have looked like on a Windows
  machine!
 
  Generally speaking: always remember that this will be compiled on dozens of
  operating systems. Don't walk on the edge.
 
+<a name="Library"></a>
 Library
 =======
 
- (See LIBCURL-STRUCTS for a separate document describing all major internal
+ (See `LIBCURL-STRUCTS` for a separate document describing all major internal
  structs and their purposes.)
 
  There are plenty of entry points to the library, namely each publicly defined
  function that libcurl offers to applications. All of those functions are
- rather small and easy-to-follow. All the ones prefixed with 'curl_easy' are
+ rather small and easy-to-follow. All the ones prefixed with `curl_easy` are
  put in the lib/easy.c file.
 
- curl_global_init_() and curl_global_cleanup() should be called by the
+ `curl_global_init_()` and `curl_global_cleanup()` should be called by the
  application to initialize and clean up global stuff in the library. As of
  today, it can handle the global SSL initing if SSL is enabled and it can init
  the socket layer on windows machines. libcurl itself has no "global" scope.
@@ -130,51 +181,56 @@ Library
  All printf()-style functions use the supplied clones in lib/mprintf.c. This
  makes sure we stay absolutely platform independent.
 
- curl_easy_init() allocates an internal struct and makes some initializations.
- The returned handle does not reveal internals. This is the 'SessionHandle'
- struct which works as an "anchor" struct for all curl_easy functions. All
- connections performed will get connect-specific data allocated that should be
- used for things related to particular connections/requests.
+ [ `curl_easy_init()`][2] allocates an internal struct and makes some
+ initializations.  The returned handle does not reveal internals. This is the
+ 'SessionHandle' struct which works as an "anchor" struct for all `curl_easy`
+ functions. All connections performed will get connect-specific data allocated
+ that should be used for things related to particular connections/requests.
 
- curl_easy_setopt() takes three arguments, where the option stuff must be
- passed in pairs: the parameter-ID and the parameter-value. The list of
+ [`curl_easy_setopt()`][1] takes three arguments, where the option stuff must
+ be passed in pairs: the parameter-ID and the parameter-value. The list of
  options is documented in the man page. This function mainly sets things in
  the 'SessionHandle' struct.
 
- curl_easy_perform() is just a wrapper function that makes use of the multi
- API.  It basically curl_multi_init(), curl_multi_add_handle(),
- curl_multi_wait(), and curl_multi_perform() until the transfer is done and
- then returns.
+ `curl_easy_perform()` is just a wrapper function that makes use of the multi
+ API.  It basically calls `curl_multi_init()`, `curl_multi_add_handle()`,
+ `curl_multi_wait()`, and `curl_multi_perform()` until the transfer is done
+ and then returns.
 
  Some of the most important key functions in url.c are called from multi.c
  when certain key steps are to be made in the transfer operation.
 
- o Curl_connect()
+<a name="Curl_connect"></a>
+Curl_connect()
+--------------
 
    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_resolv() 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.
+   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.
 
    This function makes sure there's an allocated and initiated 'connectdata'
    struct that is used for this particular connection only (although there may
    be several requests performed on the same connect). A bunch of things are
    inited/inherited from the SessionHandle struct.
 
- o Curl_do()
+<a name="Curl_do"></a>
+Curl_do()
+---------
 
-   Curl_do() makes sure the proper protocol-specific function is called. The
+   `Curl_do()` makes sure the proper protocol-specific function is called. The
    functions are named after the protocols they handle.
 
    The protocol-specific functions of course deal with protocol-specific
-   negotiations and setup. They have access to the Curl_sendf() (from
+   negotiations and setup. They have access to the `Curl_sendf()` (from
    lib/sendf.c) function to send printf-style formatted data to the remote
    host and when they're ready to make the actual file transfer they call the
-   Curl_Transfer() function (in lib/transfer.c) to setup the transfer and
+   `Curl_Transfer()` function (in lib/transfer.c) to setup the transfer and
    returns.
 
    If this DO function fails and the connection is being re-used, libcurl will
@@ -183,11 +239,13 @@ Library
    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
+   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 transfer sizes (if known).
 
- o Curl_readwrite()
+<a name="Curl_readwrite"></a>
+Curl_readwrite()
+----------------
 
    Called during the transfer of the actual protocol payload.
 
@@ -196,18 +254,22 @@ Library
    called). The speedcheck functions in lib/speedcheck.c are also used to
    verify that the transfer is as fast as required.
 
- o Curl_done()
+<a name="Curl_done"></a>
+Curl_done()
+-----------
 
    Called after a transfer is done. This function takes care of everything
    that has to be done after a transfer. This function attempts to leave
-   matters in a state so that Curl_do() should be possible to call again on
+   matters in a state so that `Curl_do()` should be possible to call again on
    the same connection (in a persistent connection case). It might also soon
-   be closed with Curl_disconnect().
+   be closed with `Curl_disconnect()`.
 
- o Curl_disconnect()
+<a name="Curl_disconnect"></a>
+Curl_disconnect()
+-----------------
 
    When doing normal connections and transfers, no one ever tries to close any
-   connections so this is not normally called when curl_easy_perform() is
+   connections so this is not normally called when `curl_easy_perform()` is
    used. This function is only used when we are certain that no more transfers
    is going to be made on the connection. It can be also closed by force, or
    it can be called to make sure that libcurl doesn't keep too many
@@ -216,8 +278,9 @@ Library
    This function cleans up all resources that are associated with a single
    connection.
 
-
- HTTP(S)
+<a name="http"></a>
+HTTP(S)
+=======
 
  HTTP offers a lot and is the protocol in curl that uses the most lines of
  code. There is a special file (lib/formdata.c) that offers all the multipart
@@ -229,100 +292,123 @@ Library
  HTTPS uses in almost every means the same procedure as HTTP, with only two
  exceptions: the connect procedure is different and the function used to read
  or write from the socket is different, although the latter fact is hidden in
- the source by the use of Curl_read() for reading and Curl_write() for writing
- data to the remote server.
+ the source by the use of `Curl_read()` for reading and `Curl_write()` for
+ writing data to the remote server.
 
- http_chunks.c contains functions that understands HTTP 1.1 chunked transfer
+ `http_chunks.c` contains functions that understands HTTP 1.1 chunked transfer
  encoding.
 
- An interesting detail with the HTTP(S) request, is the Curl_add_buffer()
+ An interesting detail with the HTTP(S) request, is the `Curl_add_buffer()`
  series of functions we use. They append data to one single buffer, and when
  the building is done the entire request is sent off in one single write. This
  is done this way to overcome problems with flawed firewalls and lame servers.
 
- FTP
+<a name="ftp"></a>
+FTP
+===
 
- The Curl_if2ip() function can be used for getting the IP number of a
+ The `Curl_if2ip()` function can be used for getting the IP number of a
  specified network interface, and it resides in lib/if2ip.c.
 
- Curl_ftpsendf() is used for sending FTP commands to the remote server. It was
- made a separate function to prevent us programmers from forgetting that they
- must be CRLF terminated. They must also be sent in one single write() to make
- firewalls and similar happy.
+ `Curl_ftpsendf()` is used for sending FTP commands to the remote server. It
+ was made a separate function to prevent us programmers from forgetting that
+ they must be CRLF terminated. They must also be sent in one single write() to
+ make firewalls and similar happy.
 
- Kerberos
+<a name="kerberos"></a>
+Kerberos
+--------
 
  Kerberos support is mainly in lib/krb5.c and lib/security.c but also
- curl_sasl_sspi.c and curl_sasl_gssapi.c for the email protocols and
- socks_gssapi.c & socks_sspi.c for SOCKS5 proxy specifics.
+ `curl_sasl_sspi.c` and `curl_sasl_gssapi.c` for the email protocols and
+ `socks_gssapi.c` and `socks_sspi.c` for SOCKS5 proxy specifics.
 
- TELNET
+<a name="telnet"></a>
+TELNET
+======
 
  Telnet is implemented in lib/telnet.c.
 
- FILE
+<a name="file"></a>
+FILE
+====
 
  The file:// protocol is dealt with in lib/file.c.
 
- SMB
+<a name="smb"></a>
+SMB
+===
 
  The smb:// protocol is dealt with in lib/smb.c.
 
- LDAP
+<a name="ldap"></a>
+LDAP
+====
 
  Everything LDAP is in lib/ldap.c and lib/openldap.c
 
- E-mail
+<a name="email"></a>
+E-mail
+======
 
  The e-mail related source code is in lib/imap.c, lib/pop3.c and lib/smtp.c.
 
- GENERAL
+<a name="general"></a>
+General
+=======
 
  URL encoding and decoding, called escaping and unescaping in the source code,
  is found in lib/escape.c.
 
  While transferring data in Transfer() a few functions might get used.
- curl_getdate() in lib/parsedate.c is for HTTP date comparisons (and more).
+ `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
- lib/url.c when checking the proxy environment variables. Note that contrary
- to the normal unix getenv(), this returns an allocated buffer that must be
- free()ed after use.
+ 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 lib/url.c when checking the proxy environment variables. Note that
+ contrary to the normal unix getenv(), this returns an allocated buffer that
+ must be free()ed after use.
 
  lib/netrc.c holds the .netrc parser
 
  lib/timeval.c features replacement functions for systems that don't have
  gettimeofday() and a few support functions for timeval conversions.
 
- A function named curl_version() that returns the full curl version string is
- found in lib/version.c.
+ A function named `curl_version()` that returns the full curl version string
+ is found in lib/version.c.
 
+<a name="persistent"></a>
 Persistent Connections
 ======================
 
  The persistent connection support in libcurl requires some considerations on
  how to do things inside of the library.
 
- o The 'SessionHandle' struct returned in the curl_easy_init() call must never
-   hold connection-oriented data. It is meant to hold the root data as well as
-   all the options etc that the library-user may choose.
- o The 'SessionHandle' struct holds the "connection cache" (an array of
+ - The 'SessionHandle' struct returned in the [`curl_easy_init()`][2] call
+   must never hold connection-oriented data. It is meant to hold the root data
+   as well as all the options etc that the library-user may choose.
+
+ - The 'SessionHandle' struct holds the "connection cache" (an array of
    pointers to 'connectdata' structs).
- o This enables the 'curl handle' to be reused on subsequent transfers.
- o When libcurl is told to perform a transfer, it first checks for an already
+
+ - This enables the 'curl handle' to be reused on subsequent transfers.
+
+ - When libcurl is told to perform a transfer, it first checks for an already
    existing connection in the cache that we can use. Otherwise it creates a
    new one and adds that the cache. If the cache is full already when a new
    connection is added added, it will first close the oldest unused one.
- o When the transfer operation is complete, the connection is left
+
+ - When the transfer operation is complete, the connection is left
    open. Particular options may tell libcurl not to, and protocols may signal
    closure on connections and then they won't be kept open of course.
- o When curl_easy_cleanup() is called, we close all still opened connections,
+
+ - When `curl_easy_cleanup()` is called, we close all still opened connections,
    unless of course the multi interface "owns" the connections.
 
  The curl handle must be re-used in order for the persistent connections to
  work.
 
+<a name="multi"></a>
 multi interface/non-blocking
 ============================
 
@@ -341,6 +427,7 @@ multi interface/non-blocking
  protocols are crappy examples and they are subject for rewrite in the future
  to better fit the libcurl protocol family.
 
+<a name="ssl"></a>
 SSL libraries
 =============
 
@@ -350,36 +437,39 @@ SSL libraries
  in future libcurl versions.
 
  To deal with this internally in the best way possible, we have a generic SSL
- function API as provided by the vtls.[ch] system, and they are the only SSL
- functions we must use from within libcurl. vtls is then crafted to use the
- appropriate lower-level function calls to whatever SSL library that is in
+ function API as provided by the vtls/vtls.[ch] system, and they are the only
+ SSL functions we must use from within libcurl. vtls is then crafted to use
+ the appropriate lower-level function calls to whatever SSL library that is in
  use. For example vtls/openssl.[ch] for the OpenSSL library.
 
+<a name="symbols"></a>
 Library Symbols
 ===============
 
- All symbols used internally in libcurl must use a 'Curl_' prefix if they're
+ All symbols used internally in libcurl must use a `Curl_` prefix if they're
  used in more than a single file. Single-file symbols must be made static.
- Public ("exported") symbols must use a 'curl_' prefix. (There are exceptions,
+ Public ("exported") symbols must use a `curl_` prefix. (There are exceptions,
  but they are to be changed to follow this pattern in future versions.) Public
- API functions are marked with CURL_EXTERN in the public header files so that
- all others can be hidden on platforms where this is possible.
+ API functions are marked with `CURL_EXTERN` in the public header files so
+ that all others can be hidden on platforms where this is possible.
 
+<a name="returncodes"></a>
 Return Codes and Informationals
 ===============================
 
  I've made things simple. Almost every function in libcurl returns a CURLcode,
- that must be CURLE_OK if everything is OK or otherwise a suitable error code
- as the curl/curl.h include file defines. The very spot that detects an error
- must use the Curl_failf() function to set the human-readable error
+ that must be `CURLE_OK` if everything is OK or otherwise a suitable error
+ code as the curl/curl.h include file defines. The very spot that detects an
+ error must use the `Curl_failf()` function to set the human-readable error
  description.
 
  In aiding the user to understand what's happening and to debug curl usage, we
- must supply a fair amount of informational messages by using the Curl_infof()
- function. Those messages are only displayed when the user explicitly asks for
- them. They are best used when revealing information that isn't otherwise
- obvious.
+ must supply a fair amount of informational messages by using the
+ `Curl_infof()` function. Those messages are only displayed when the user
+ explicitly asks for them. They are best used when revealing information that
+ isn't otherwise obvious.
 
+<a name="abi"></a>
 API/ABI
 =======
 
@@ -387,29 +477,31 @@ API/ABI
  that makes it easier to keep a solid API/ABI over time. See docs/libcurl/ABI
  for our promise to users.
 
+<a name="client"></a>
 Client
 ======
 
- main() resides in src/tool_main.c.
+ main() resides in `src/tool_main.c`.
 
- src/tool_hugehelp.c is automatically generated by the mkhelp.pl perl script
+ `src/tool_hugehelp.c` is automatically generated by the mkhelp.pl perl script
  to display the complete "manual" and the src/tool_urlglob.c file holds the
  functions used for the URL-"globbing" support. Globbing in the sense that the
  {} and [] expansion stuff is there.
 
  The client mostly messes around to setup its 'config' struct properly, then
- it calls the curl_easy_*() functions of the library and when it gets back
- control after the curl_easy_perform() it cleans up the library, checks status
- and exits.
+ it calls the `curl_easy_*()` functions of the library and when it gets back
+ control after the `curl_easy_perform()` it cleans up the library, checks
+ status and exits.
 
  When the operation is done, the ourWriteOut() function in src/writeout.c may
  be called to report about the operation. That function is using the
- curl_easy_getinfo() function to extract useful information from the curl
+ `curl_easy_getinfo()` function to extract useful information from the curl
  session.
 
  It may loop and do all this several times if many URLs were specified on the
  command line or config file.
 
+<a name="memorydebug"></a>
 Memory Debugging
 ================
 
@@ -439,6 +531,7 @@ Memory Debugging
  the configure script. When --enable-debug is given both features will be
  enabled, unless some restriction prevents memory tracking from being used.
 
+<a name="test"></a>
 Test Suite
 ==========
 
@@ -456,29 +549,315 @@ Test Suite
  The test suite automatically detects if curl was built with the memory
  debugging enabled, and if it was it will detect memory leaks, too.
 
-Building Releases
-=================
+<a name="asyncdns"></a>
+Asynchronous name resolves
+==========================
+
+ libcurl can be built to do name resolves asynchronously, using either the
+ normal resolver in a threaded manner or by using c-ares.
+
+<a name="cares"></a>
+[c-ares][3]
+------
+
+### Build libcurl to use a c-ares
+
+1. ./configure --enable-ares=/path/to/ares/install
+2. make
+
+### c-ares on win32
+
+ First I compiled c-ares. I changed the default C runtime library to be the
+ single-threaded rather than the multi-threaded (this seems to be required to
+ prevent linking errors later on). Then I simply build the areslib project
+ (the other projects adig/ahost seem to fail under MSVC).
+
+ Next was libcurl. I opened lib/config-win32.h and I added a:
+ `#define USE_ARES 1`
+
+ Next thing I did was I added the path for the ares includes to the include
+ path, and the libares.lib to the libraries.
+
+ Lastly, I also changed libcurl to be single-threaded rather than
+ multi-threaded, again this was to prevent some duplicate symbol errors. I'm
+ not sure why I needed to change everything to single-threaded, but when I
+ didn't I got redefinition errors for several CRT functions (malloc, stricmp,
+ etc.)
+
+<a name="curl_off_t"></a>
+`curl_off_t`
+==========
+
+ curl_off_t is a data type provided by the external libcurl include
+ headers. It is the type meant to be used for the [`curl_easy_setopt()`][1]
+ options that end with LARGE. The type is 64bit large on most modern
+ platforms.
+
+curlx
+=====
+
+ The libcurl source code offers a few functions by source only. They are not
+ part of the official libcurl API, but the source files might be useful for
+ others so apps can optionally compile/build with these sources to gain
+ additional functions.
+
+ We provide them through a single header file for easy access for apps:
+ "curlx.h"
+
+`curlx_strtoofft()`
+-------------------
+   A macro that converts a string containing a number to a curl_off_t number.
+   This might use the curlx_strtoll() function which is provided as source
+   code in strtoofft.c. Note that the function is only provided if no
+   strtoll() (or equivalent) function exist on your platform. If curl_off_t
+   is only a 32 bit number on your platform, this macro uses strtol().
+
+`curlx_tvnow()`
+---------------
+   returns a struct timeval for the current time.
+
+`curlx_tvdiff()`
+--------------
+   returns the difference between two timeval structs, in number of
+   milliseconds.
+
+`curlx_tvdiff_secs()`
+---------------------
+   returns the same as curlx_tvdiff but with full usec resolution (as a
+   double)
+
+Future
+------
+
+ Several functions will be removed from the public curl_ name space in a
+ future libcurl release. They will then only become available as curlx_
+ functions instead. To make the transition easier, we already today provide
+ these functions with the curlx_ prefix to allow sources to get built properly
+ with the new function names. The functions this concerns are:
+
+ - `curlx_getenv`
+ - `curlx_strequal`
+ - `curlx_strnequal`
+ - `curlx_mvsnprintf`
+ - `curlx_msnprintf`
+ - `curlx_maprintf`
+ - `curlx_mvaprintf`
+ - `curlx_msprintf`
+ - `curlx_mprintf`
+ - `curlx_mfprintf`
+ - `curlx_mvsprintf`
+ - `curlx_mvprintf`
+ - `curlx_mvfprintf`
+
+<a name="contentencoding"></a>
+Content Encoding
+================
+
+## About content encodings
+
+ [HTTP/1.1][4] specifies that a client may request that a server encode its
+ response. This is usually used to compress a response using one of a set of
+ commonly available compression techniques. These schemes are 'deflate' (the
+ zlib algorithm), 'gzip' and 'compress'. A client requests that the sever
+ perform an encoding by including an Accept-Encoding header in the request
+ document. The value of the header should be one of the recognized tokens
+ 'deflate', ... (there's a way to register new schemes/tokens, see sec 3.5 of
+ the spec). A server MAY honor the client's encoding request. When a response
+ is encoded, the server includes a Content-Encoding header in the
+ response. The value of the Content-Encoding header indicates which scheme was
+ used to encode the data.
+
+ A client may tell a server that it can understand several different encoding
+ schemes. In this case the server may choose any one of those and use it to
+ encode the response (indicating which one using the Content-Encoding header).
+ It's also possible for a client to attach priorities to different schemes so
+ that the server knows which it prefers. See sec 14.3 of RFC 2616 for more
+ information on the Accept-Encoding header.
+
+## Supported content encodings
+
+ The 'deflate' and 'gzip' content encoding are supported by libcurl. Both
+ regular and chunked transfers work fine.  The zlib library is required for
+ this feature.
+
+## The libcurl interface
+
+ To cause libcurl to request a content encoding use:
+
+  [`curl_easy_setopt`][1](curl, [`CURLOPT_ACCEPT_ENCODING`][5], string)
+
+ where string is the intended value of the Accept-Encoding header.
+
+ Currently, libcurl only understands how to process responses that use the
+ "deflate" or "gzip" Content-Encoding, so the only values for
+ [`CURLOPT_ACCEPT_ENCODING`][5] that will work (besides "identity," which does
+ nothing) are "deflate" and "gzip" If a response is encoded using the
+ "compress" or methods, libcurl will return an error indicating that the
+ response could not be decoded.  If <string> is NULL no Accept-Encoding header
+ is generated.  If <string> is a zero-length string, then an Accept-Encoding
+ header containing all supported encodings will be generated.
+
+ The [`CURLOPT_ACCEPT_ENCODING`][5] must be set to any non-NULL value for
+ content to be automatically decoded.  If it is not set and the server still
+ sends encoded content (despite not having been asked), the data is returned
+ in its raw form and the Content-Encoding type is not checked.
+
+## The curl interface
+
+ Use the [--compressed][6] option with curl to cause it to ask servers to
+ compress responses using any format supported by curl.
+
+<a name="hostip"></a>
+hostip.c explained
+==================
+
+ The main compile-time defines to keep in mind when reading the host*.c source
+ file are these:
+
+## `CURLRES_IPV6`
+
+ this host has getaddrinfo() and family, and thus we use that. The host may
+ not be able to resolve IPv6, but we don't really have to take that into
+ account. Hosts that aren't IPv6-enabled have CURLRES_IPV4 defined.
+
+## `CURLRES_ARES`
+
+ is defined if libcurl is built to use c-ares for asynchronous name
+ resolves. This can be Windows or *nix.
+
+## `CURLRES_THREADED`
+
+ is defined if libcurl is built to use threading for asynchronous name
+ resolves. The name resolve will be done in a new thread, and the supported
+ asynch API will be the same as for ares-builds. This is the default under
+ (native) Windows.
+
+ If any of the two previous are defined, `CURLRES_ASYNCH` is defined too. If
+ libcurl is not built to use an asynchronous resolver, `CURLRES_SYNCH` is
+ defined.
+
+## host*.c sources
+
+ The host*.c sources files are split up like this:
+
+ - hostip.c      - method-independent resolver functions and utility functions
+ - hostasyn.c    - functions for asynchronous name resolves
+ - hostsyn.c     - functions for synchronous name resolves
+ - asyn-ares.c   - functions for asynchronous name resolves using c-ares
+ - asyn-thread.c - functions for asynchronous name resolves using threads
+ - hostip4.c     - IPv4 specific functions
+ - hostip6.c     - IPv6 specific functions
+
+ The hostip.h is the single united header file for all this. It defines the
+ `CURLRES_*` defines based on the config*.h and curl_setup.h defines.
+
+<a name="memoryleak"></a>
+Track Down Memory Leaks
+=======================
+
+## Single-threaded
+
+  Please note that this memory leak system is not adjusted to work in more
+  than one thread. If you want/need to use it in a multi-threaded app. Please
+  adjust accordingly.
+
+
+## Build
+
+  Rebuild libcurl with -DCURLDEBUG (usually, rerunning configure with
+  --enable-debug fixes this). 'make clean' first, then 'make' so that all
+  files actually are rebuilt properly. It will also make sense to build
+  libcurl with the debug option (usually -g to the compiler) so that debugging
+  it will be easier if you actually do find a leak in the library.
+
+  This will create a library that has memory debugging enabled.
+
+## Modify Your Application
+
+  Add a line in your application code:
+
+       `curl_memdebug("dump");`
+
+  This will make the malloc debug system output a full trace of all resource
+  using functions to the given file name. Make sure you rebuild your program
+  and that you link with the same libcurl you built for this purpose as
+  described above.
+
+## Run Your Application
+
+  Run your program as usual. Watch the specified memory trace file grow.
+
+  Make your program exit and use the proper libcurl cleanup functions etc. So
+  that all non-leaks are returned/freed properly.
+
+## Analyze the Flow
+
+  Use the tests/memanalyze.pl perl script to analyze the dump file:
+
+    tests/memanalyze.pl dump
+
+  This now outputs a report on what resources that were allocated but never
+  freed etc. This report is very fine for posting to the list!
+
+  If this doesn't produce any output, no leak was detected in libcurl. Then
+  the leak is mostly likely to be in your code.
+
+<a name="multi_socket"></a>
+`multi_socket`
+==============
+
+ Implementation of the `curl_multi_socket` API
+
+  The main ideas of this API are simply:
 
- There's no magic to this. When you consider everything stable enough to be
- released, do this:
+   1 - The application can use whatever event system it likes as it gets info
+       from libcurl about what file descriptors libcurl waits for what action
+       on. (The previous API returns `fd_sets` which is very select()-centric).
 
-   1. Tag the source code accordingly.
+   2 - When the application discovers action on a single socket, it calls
+       libcurl and informs that there was action on this particular socket and
+       libcurl can then act on that socket/transfer only and not care about
+       any other transfers. (The previous API always had to scan through all
+       the existing transfers.)
 
-   2. run the 'maketgz' script (using 'make distcheck' will give you a pretty
-      good view on the status of the current sources). maketgz requires a
-      version number and creates the release archive. maketgz uses 'make dist'
-      for the actual archive building, why you need to fill in the Makefile.am
-      files properly for which files that should be included in the release
-      archives.
+  The idea is that [`curl_multi_socket_action()`][7] calls a given callback
+  with information about what socket to wait for what action on, and the
+  callback only gets called if the status of that socket has changed.
 
-   3. When that's complete, sign the output files.
+  We also added a timer callback that makes libcurl call the application when
+  the timeout value changes, and you set that with [`curl_multi_setopt()`][9]
+  and the [`CURLMOPT_TIMERFUNCTION`][10] option. To get this to work,
+  Internally, there's an added a struct to each easy handle in which we store
+  an "expire time" (if any). The structs are then "splay sorted" so that we
+  can add and remove times from the linked list and yet somewhat swiftly
+  figure out both how long time there is until the next nearest timer expires
+  and which timer (handle) we should take care of now. Of course, the upside
+  of all this is that we get a [`curl_multi_timeout()`][8] that should also
+  work with old-style applications that use [`curl_multi_perform()`][11].
 
-   4. Upload
+  We created an internal "socket to easy handles" hash table that given
+  a socket (file descriptor) return the easy handle that waits for action on
+  that socket.  This hash is made using the already existing hash code
+  (previously only used for the DNS cache).
 
-   5. Update web site and changelog on site
+  To make libcurl able to report plain sockets in the socket callback, we had
+  to re-organize the internals of the [`curl_multi_fdset()`][12] etc so that
+  the conversion from sockets to `fd_sets` for that function is only done in
+  the last step before the data is returned. I also had to extend c-ares to
+  get a function that can return plain sockets, as that library too returned
+  only `fd_sets` and that is no longer good enough. The changes done to c-ares
+  are available in c-ares 1.3.1 and later.
 
-   6. Send announcement to the mailing lists
 
- NOTE: you must have curl checked out from git to be able to do a proper
- release build. The release tarballs do not have everything setup in order to
- do releases properly.
+[1]: http://curl.haxx.se/libcurl/c/curl_easy_setopt.html
+[2]: http://curl.haxx.se/libcurl/c/curl_easy_init.html
+[3]: http://c-ares.haxx.se/
+[4]: https://tools.ietf.org/html/rfc7230 "RFC 7230"
+[5]: http://curl.haxx.se/libcurl/c/CURLOPT_ACCEPT_ENCODING.html
+[6]: http://curl.haxx.se/docs/manpage.html#--compressed
+[7]: http://curl.haxx.se/libcurl/c/curl_multi_socket_action.html
+[8]: http://curl.haxx.se/libcurl/c/curl_multi_timeout.html
+[9]: http://curl.haxx.se/libcurl/c/curl_multi_setopt.html
+[10]: http://curl.haxx.se/libcurl/c/CURLMOPT_TIMERFUNCTION.html
+[11]: http://curl.haxx.se/libcurl/c/curl_multi_perform.html
+[12]: http://curl.haxx.se/libcurl/c/curl_multi_fdset.html
\ No newline at end of file