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docs: Markdown and misc improvements [ci skip]

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Approved-by: Daniel Stenberg
Closes #3896
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Viktor Szakats 2019-05-16 22:11:27 +00:00
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docs/INTERNALS.md
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@ -34,7 +34,7 @@ curl internals
- [`curl_off_t`](#curl_off_t)
- [curlx](#curlx)
- [Content Encoding](#contentencoding)
- [hostip.c explained](#hostip)
- [`hostip.c` explained](#hostip)
- [Track Down Memory Leaks](#memoryleak)
- [`multi_socket`](#multi_socket)
- [Structs in libcurl](#structs)
@ -73,7 +73,7 @@ git
Portability
===========
We write curl and libcurl to compile with C89 compilers. On 32bit and up
We write curl and libcurl to compile with C89 compilers. On 32-bit and up
machines. Most of libcurl assumes more or less POSIX compliance but that's
not a requirement.
@ -125,7 +125,7 @@ Build tools
- GNU M4 1.4
- perl 5.004
- roffit 0.5
- groff ? (any version that supports "groff -Tps -man [in] [out]")
- groff ? (any version that supports `groff -Tps -man [in] [out]`)
- ps2pdf (gs) ?
<a name="winvsunix"></a>
@ -139,7 +139,7 @@ Windows vs Unix
In curl, this is solved with defines and macros, so that the source looks
the same in all places except for the header file that defines them. The
macros in use are sclose(), sread() and swrite().
macros in use are `sclose()`, `sread()` and `swrite()`.
2. Windows requires a couple of init calls for the socket stuff.
@ -178,14 +178,14 @@ Library
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
put in the lib/easy.c file.
put in the `lib/easy.c` file.
`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.
All printf()-style functions use the supplied clones in lib/mprintf.c. This
All printf()-style functions use the supplied clones in `lib/mprintf.c`. This
makes sure we stay absolutely platform independent.
[ `curl_easy_init()`][2] allocates an internal struct and makes some
@ -204,8 +204,8 @@ Library
`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.
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.
<a name="Curl_connect"></a>
Curl_connect()
@ -213,15 +213,15 @@ 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
(it does then use the proper underlying method, which may vary between
platforms and builds).
`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.
This function makes sure there's an allocated and initiated 'connectdata'
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 `Curl_easy` struct.
@ -230,15 +230,15 @@ Curl_connect()
multi_do()
---------
`multi_do()` makes sure the proper protocol-specific function is called. The
functions are named after the protocols they handle.
`multi_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
lib/sendf.c) function to send printf-style formatted data to the remote
`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_setup_transfer()` function (in lib/transfer.c) to setup the transfer
and returns.
`Curl_setup_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
then close this connection, setup a new connection and re-issue the DO
@ -252,9 +252,9 @@ Curl_readwrite()
Called during the transfer of the actual protocol payload.
During transfer, the progress functions in lib/progress.c are called at
During transfer, the progress functions in `lib/progress.c` are called at
frequent intervals (or at the user's choice, a specified callback might get
called). The speedcheck functions in lib/speedcheck.c are also used to
called). The speedcheck functions in `lib/speedcheck.c` are also used to
verify that the transfer is as fast as required.
<a name="multi_done"></a>
@ -286,11 +286,12 @@ 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
post functions.
code. There is a special file `lib/formdata.c` that offers all the
multipart post functions.
base64-functions for user+password stuff (and more) is in (lib/base64.c) and
all functions for parsing and sending cookies are found in (lib/cookie.c).
base64-functions for user+password stuff (and more) is in `lib/base64.c`
and all functions for parsing and sending cookies are found in
`lib/cookie.c`.
HTTPS uses in almost every case the same procedure as HTTP, with only two
exceptions: the connect procedure is different and the function used to read
@ -312,18 +313,18 @@ FTP
===
The `Curl_if2ip()` function can be used for getting the IP number of a
specified network interface, and it resides in lib/if2ip.c.
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.
they must be CRLF terminated. They must also be sent in one single `write()`
to make firewalls and similar happy.
<a name="kerberos"></a>
Kerberos
========
Kerberos support is mainly in lib/krb5.c and lib/security.c but also
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` and `socks_sspi.c` for SOCKS5 proxy specifics.
@ -331,55 +332,57 @@ Kerberos
TELNET
======
Telnet is implemented in lib/telnet.c.
Telnet is implemented in `lib/telnet.c`.
<a name="file"></a>
FILE
====
The file:// protocol is dealt with in lib/file.c.
The `file://` protocol is dealt with in `lib/file.c`.
<a name="smb"></a>
SMB
===
The smb:// protocol is dealt with in lib/smb.c.
The `smb://` protocol is dealt with in `lib/smb.c`.
<a name="ldap"></a>
LDAP
====
Everything LDAP is in lib/ldap.c and lib/openldap.c
Everything LDAP is in `lib/ldap.c` and `lib/openldap.c`.
<a name="email"></a>
E-mail
======
The e-mail related source code is in lib/imap.c, lib/pop3.c and lib/smtp.c.
The e-mail related source code is in `lib/imap.c`, `lib/pop3.c` and
`lib/smtp.c`.
<a name="general"></a>
General
=======
URL encoding and decoding, called escaping and unescaping in the source code,
is found in lib/escape.c.
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).
While transferring 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
`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.
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/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.
`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.
is found in `lib/version.c`.
<a name="persistent"></a>
Persistent Connections
@ -393,7 +396,7 @@ Persistent Connections
as well as all the options etc that the library-user may choose.
- The `Curl_easy` struct holds the "connection cache" (an array of
pointers to 'connectdata' structs).
pointers to `connectdata` structs).
- This enables the 'curl handle' to be reused on subsequent transfers.
@ -441,10 +444,10 @@ 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/vtls.[ch] system, and they are the only
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.
use. For example `vtls/openssl.[ch]` for the OpenSSL library.
<a name="symbols"></a>
Library Symbols
@ -463,7 +466,7 @@ 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
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.
@ -485,20 +488,20 @@ API/ABI
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
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.
`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 sets up its 'config' struct properly, then
The client mostly sets up 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.
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
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
session.
@ -509,30 +512,32 @@ Client
Memory Debugging
================
The file lib/memdebug.c contains debug-versions of a few functions. Functions
such as malloc, free, fopen, fclose, etc that somehow deal with resources
that might give us problems if we "leak" them. The functions in the memdebug
system do nothing fancy, they do their normal function and then log
information about what they just did. The logged data can then be analyzed
after a complete session,
The file `lib/memdebug.c` contains debug-versions of a few functions.
Functions such as `malloc()`, `free()`, `fopen()`, `fclose()`, etc that
somehow deal with resources that might give us problems if we "leak" them.
The functions in the memdebug system do nothing fancy, they do their normal
function and then log information about what they just did. The logged data
can then be analyzed after a complete session,
memanalyze.pl is the perl script present in tests/ that analyzes a log file
generated by the memory tracking system. It detects if resources are
`memanalyze.pl` is the perl script present in `tests/` that analyzes a log
file generated by the memory tracking system. It detects if resources are
allocated but never freed and other kinds of errors related to resource
management.
Internally, definition of preprocessor symbol DEBUGBUILD restricts code which
is only compiled for debug enabled builds. And symbol CURLDEBUG is used to
differentiate code which is _only_ used for memory tracking/debugging.
Internally, definition of preprocessor symbol `DEBUGBUILD` restricts code
which is only compiled for debug enabled builds. And symbol `CURLDEBUG` is
used to differentiate code which is _only_ used for memory
tracking/debugging.
Use -DCURLDEBUG when compiling to enable memory debugging, this is also
switched on by running configure with --enable-curldebug. Use -DDEBUGBUILD
when compiling to enable a debug build or run configure with --enable-debug.
Use `-DCURLDEBUG` when compiling to enable memory debugging, this is also
switched on by running configure with `--enable-curldebug`. Use
`-DDEBUGBUILD` when compiling to enable a debug build or run configure with
`--enable-debug`.
curl --version will list 'Debug' feature for debug enabled builds, and
`curl --version` will list 'Debug' feature for debug enabled builds, and
will list 'TrackMemory' feature for curl debug memory tracking capable
builds. These features are independent and can be controlled when running
the configure script. When --enable-debug is given both features will be
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>
@ -543,12 +548,12 @@ Test Suite
curl archive tree, and it contains a bunch of scripts and a lot of test case
data.
The main test script is runtests.pl that will invoke test servers like
httpserver.pl and ftpserver.pl before all the test cases are performed. The
test suite currently only runs on Unix-like platforms.
The main test script is `runtests.pl` that will invoke test servers like
`httpserver.pl` and `ftpserver.pl` before all the test cases are performed.
The test suite currently only runs on Unix-like platforms.
You'll find a description of the test suite in the tests/README file, and the
test case data files in the tests/FILEFORMAT file.
You'll find a description of the test suite in the `tests/README` file, and
the test case data files in the `tests/FILEFORMAT` file.
The test suite automatically detects if curl was built with the memory
debugging enabled, and if it was, it will detect memory leaks, too.
@ -576,7 +581,7 @@ Asynchronous name resolves
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:
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
@ -585,8 +590,8 @@ Asynchronous name resolves
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.)
didn't I got redefinition errors for several CRT functions (`malloc()`,
`stricmp()`, etc.)
<a name="curl_off_t"></a>
`curl_off_t`
@ -594,7 +599,7 @@ Asynchronous name resolves
`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
options that end with LARGE. The type is 64-bit large on most modern
platforms.
<a name="curlx"></a>
@ -607,15 +612,15 @@ curlx
additional functions.
We provide them through a single header file for easy access for apps:
"curlx.h"
`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().
`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()`.
Future
------
@ -649,27 +654,28 @@ Content Encoding
[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 (or more)
encodings from a set of commonly available compression techniques. These
schemes include 'deflate' (the zlib algorithm), 'gzip' 'br' (brotli) and
'compress'. A client requests that the server 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
schemes include `deflate` (the zlib algorithm), `gzip`, `br` (brotli) and
`compress`. A client requests that the server 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 encodings were used to encode the
includes a `Content-Encoding` header in the response. The value of the
`Content-Encoding` header indicates which encodings were used to encode the
data, in the order in which they were applied.
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. See sec [3.1.2.2 of RFC 7231][15]
for more information on the Content-Encoding header.
information on the `Accept-Encoding` header. See sec
[3.1.2.2 of RFC 7231][15] for more information on the `Content-Encoding`
header.
## Supported content encodings
The 'deflate', 'gzip' and 'br' content encodings are supported by libcurl.
The `deflate`, `gzip` and `br` content encodings are supported by libcurl.
Both regular and chunked transfers work fine. The zlib library is required
for the 'deflate' and 'gzip' encodings, while the brotli decoding library is
for the 'br' encoding.
for the `deflate` and `gzip` encodings, while the brotli decoding library is
for the `br` encoding.
## The libcurl interface
@ -677,45 +683,45 @@ Content Encoding
[`curl_easy_setopt`][1](curl, [`CURLOPT_ACCEPT_ENCODING`][5], string)
where string is the intended value of the Accept-Encoding header.
where string is the intended value of the `Accept-Encoding` header.
Currently, libcurl does support multiple encodings but only
understands how to process responses that use the "deflate", "gzip" and/or
"br" content encodings, so the only values for [`CURLOPT_ACCEPT_ENCODING`][5]
that will work (besides "identity," which does nothing) are "deflate",
"gzip" and "br". If a response is encoded using the "compress" or methods,
understands how to process responses that use the `deflate`, `gzip` and/or
`br` content encodings, so the only values for [`CURLOPT_ACCEPT_ENCODING`][5]
that will work (besides `identity`, which does nothing) are `deflate`,
`gzip` and `br`. 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.
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.
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
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
==================
`hostip.c` explained
====================
The main compile-time defines to keep in mind when reading the host*.c source
file are these:
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
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.
resolves. This can be Windows or \*nix.
## `CURLRES_THREADED`
@ -728,20 +734,20 @@ hostip.c explained
libcurl is not built to use an asynchronous resolver, `CURLRES_SYNCH` is
defined.
## host*.c sources
## `host*.c` sources
The host*.c sources files are split up like this:
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
- `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.
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
@ -753,14 +759,13 @@ Track Down Memory Leaks
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
Rebuild libcurl with `-DCURLDEBUG` (usually, rerunning configure with
`--enable-debug` fixes this). `make clean` first, then `make` so that all
files are actually 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.
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.
@ -784,7 +789,7 @@ Track Down Memory Leaks
## Analyze the Flow
Use the tests/memanalyze.pl perl script to analyze the dump file:
Use the `tests/memanalyze.pl` perl script to analyze the dump file:
tests/memanalyze.pl dump
@ -800,45 +805,46 @@ Track Down Memory Leaks
Implementation of the `curl_multi_socket` API
The main ideas of this API are simply:
The main ideas of this API are simply:
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. 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).
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. 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.)
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.
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.
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 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 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].
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 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 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].
We created an internal "socket to easy handles" hash table that given
a socket (file descriptor) returns 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).
We created an internal "socket to easy handles" hash table that given
a socket (file descriptor) returns 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).
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.
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.
<a name="structs"></a>
Structs in libcurl
@ -851,31 +857,31 @@ for older and later versions as things don't change drastically that often.
## Curl_easy
The `Curl_easy` struct is the one returned to the outside in the external API
as a "CURL *". This is usually known as an easy handle in API documentations
as a `CURL *`. This is usually known as an easy handle in API documentations
and examples.
Information and state that is related to the actual connection is in the
'connectdata' struct. When a transfer is about to be made, libcurl will
`connectdata` struct. When a transfer is about to be made, libcurl will
either create a new connection or re-use an existing one. The particular
connectdata that is used by this handle is pointed out by
`Curl_easy->easy_conn`.
Data and information that regard this particular single transfer is put in
the SingleRequest sub-struct.
the `SingleRequest` sub-struct.
When the `Curl_easy` struct is added to a multi handle, as it must be in
order to do any transfer, the ->multi member will point to the `Curl_multi`
struct it belongs to. The ->prev and ->next members will then be used by the
multi code to keep a linked list of `Curl_easy` structs that are added to
that same multi handle. libcurl always uses multi so ->multi *will* point to
a `Curl_multi` when a transfer is in progress.
order to do any transfer, the `->multi` member will point to the `Curl_multi`
struct it belongs to. The `->prev` and `->next` members will then be used by
the multi code to keep a linked list of `Curl_easy` structs that are added to
that same multi handle. libcurl always uses multi so `->multi` *will* point
to a `Curl_multi` when a transfer is in progress.
->mstate is the multi state of this particular `Curl_easy`. When
`->mstate` is the multi state of this particular `Curl_easy`. When
`multi_runsingle()` is called, it will act on this handle according to which
state it is in. The mstate is also what tells which sockets to return for a
specific `Curl_easy` when [`curl_multi_fdset()`][12] is called etc.
The libcurl source code generally use the name 'data' for the variable that
The libcurl source code generally use the name `data` for the variable that
points to the `Curl_easy`.
When doing multiplexed HTTP/2 transfers, each `Curl_easy` is associated with
@ -890,16 +896,16 @@ for older and later versions as things don't change drastically that often.
re-use an existing one instead of creating a new as it creates a significant
performance boost.
Each 'connectdata' identifies a single physical connection to a server. If
Each `connectdata` identifies a single physical connection to a server. If
the connection can't be kept alive, the connection will be closed after use
and then this struct can be removed from the cache and freed.
Thus, the same `Curl_easy` can be used multiple times and each time select
another connectdata struct to use for the connection. Keep this in mind, as
it is then important to consider if options or choices are based on the
another `connectdata` struct to use for the connection. Keep this in mind,
as it is then important to consider if options or choices are based on the
connection or the `Curl_easy`.
Functions in libcurl will assume that connectdata->data points to the
Functions in libcurl will assume that `connectdata->data` points to the
`Curl_easy` that uses this connection (for the moment).
As a special complexity, some protocols supported by libcurl require a
@ -914,7 +920,7 @@ for older and later versions as things don't change drastically that often.
this single struct and thus can be considered a single connection for most
internal concerns.
The libcurl source code generally use the name 'conn' for the variable that
The libcurl source code generally use the name `conn` for the variable that
points to the connectdata.
<a name="Curl_multi"></a>
@ -923,7 +929,7 @@ for older and later versions as things don't change drastically that often.
Internally, the easy interface is implemented as a wrapper around multi
interface functions. This makes everything multi interface.
`Curl_multi` is the multi handle struct exposed as "CURLM *" in external
`Curl_multi` is the multi handle struct exposed as `CURLM *` in external
APIs.
This struct holds a list of `Curl_easy` structs that have been added to this
@ -950,9 +956,9 @@ for older and later versions as things don't change drastically that often.
`->conn_cache` points to the connection cache. It keeps track of all
connections that are kept after use. The cache has a maximum size.
`->closure_handle` is described in the 'connectdata' section.
`->closure_handle` is described in the `connectdata` section.
The libcurl source code generally use the name 'multi' for the variable that
The libcurl source code generally use the name `multi` for the variable that
points to the `Curl_multi` struct.
<a name="Curl_handler"></a>
@ -961,8 +967,8 @@ for older and later versions as things don't change drastically that often.
Each unique protocol that is supported by libcurl needs to provide at least
one `Curl_handler` struct. It defines what the protocol is called and what
functions the main code should call to deal with protocol specific issues.
In general, there's a source file named [protocol].c in which there's a
"struct `Curl_handler` `Curl_handler_[protocol]`" declared. In url.c there's
In general, there's a source file named `[protocol].c` in which there's a
`struct Curl_handler Curl_handler_[protocol]` declared. In `url.c` there's
then the main array with all individual `Curl_handler` structs pointed to
from a single array which is scanned through when a URL is given to libcurl
to work with.
@ -974,9 +980,9 @@ for older and later versions as things don't change drastically that often.
`->setup_connection` is called to allow the protocol code to allocate
protocol specific data that then gets associated with that `Curl_easy` for
the rest of this transfer. It gets freed again at the end of the transfer.
It will be called before the 'connectdata' for the transfer has been
It will be called before the `connectdata` for the transfer has been
selected/created. Most protocols will allocate its private
'struct [PROTOCOL]' here and assign `Curl_easy->req.protop` to point to it.
`struct [PROTOCOL]` here and assign `Curl_easy->req.protop` to point to it.
`->connect_it` allows a protocol to do some specific actions after the TCP
connect is done, that can still be considered part of the connection phase.
@ -1036,7 +1042,7 @@ for older and later versions as things don't change drastically that often.
limit which "direction" of socket actions that the main engine will
concern itself with.
- `PROTOPT_NONETWORK` - a protocol that doesn't use network (read file:)
- `PROTOPT_NONETWORK` - a protocol that doesn't use network (read `file:`)
- `PROTOPT_NEEDSPWD` - this protocol needs a password and will use a default
one unless one is provided
@ -1055,7 +1061,7 @@ for older and later versions as things don't change drastically that often.
## Curl_share
The libcurl share API allocates a `Curl_share` struct, exposed to the
external API as "CURLSH *".
external API as `CURLSH *`.
The idea is that the struct can have a set of its own versions of caches and
pools and then by providing this struct in the `CURLOPT_SHARE` option, those
@ -1072,7 +1078,7 @@ for older and later versions as things don't change drastically that often.
## CookieInfo
This is the main cookie struct. It holds all known cookies and related
information. Each `Curl_easy` has its own private CookieInfo even when
information. Each `Curl_easy` has its own private `CookieInfo` even when
they are added to a multi handle. They can be made to share cookies by using
the share API.