                    HOW TO GET YOUR CODE ACCEPTED IN HAPROXY
                   READ THIS CAREFULLY BEFORE SUBMITTING CODE

THIS DOCUMENT PROVIDES SOME RULES TO FOLLOW WHEN SENDING CONTRIBUTIONS. PATCHES
NOT FOLLOWING THESE RULES WILL SIMPLY BE IGNORED IN ORDER TO PROTECT ALL OTHER
RESPECTFUL CONTRIBUTORS' VALUABLE TIME.


Abstract
--------

If you have never contributed to HAProxy before, or if you did so and noticed
that nobody seems to be interested in reviewing your submission, please do read
this long document carefully. HAProxy maintainers are particularly demanding on
respecting certain simple rules related to general code and documentation style
as well as splitting your patches and providing high quality commit messages.
The reason behind this is that your patch will be met multiple times in the
future, when doing some backporting work or when bisecting a bug, and it is
critical that anyone can quickly decide if the patch is right, wrong, if it
misses something, if it must be reverted or needs to be backported. Maintainers
are generally benevolent with newcomers and will help them provided their work
indicates they have at least read this document. Some have improved over time,
to the point of being totally trusted and gaining commit access so they don't
need to depend on anyone to pick their code. On the opposite, those who insist
not making minimal efforts however will simply be ignored.


Background
----------

HAProxy is a community-driven project. But like most highly technical projects
it takes a lot of time to develop the skills necessary to be autonomous in the
project, and there is a very small core team helped by a small set of very
active participants. While most of the core team members work on the code as
part of their day job, most participants do it on a voluntary basis during
their spare time. The ideal model for developers is to spend their time:
  1) developing new features
  2) fixing bugs
  3) doing maintenance backports
  4) reviewing other people's code

It turns out that on a project like HAProxy, like many other similarly complex
projects, the time spent is exactly the opposite:
  1) reviewing other people's code
  2) doing maintenance backports
  3) fixing bugs
  4) developing new features

A large part of the time spent reviewing code often consists in giving basic
recommendations that are already explained in this file. In addition to taking
time, it is not appealing for people willing to spend one hour helping others
to do the same thing over and over instead of discussing the code design, and
it tends to delay the start of code reviews.

Regarding backports, they are necessary to provide a set of stable branches
that are deployed in production at many places. Load balancers are complex and
new features often induce undesired side effects in other areas, which we will
call bugs. Thus it's common for users to stick to a branch featuring everything
they need and not to upgrade too often. This backporting job is critical to the
ecosystem's health and must be done regularly. Very often the person devoting
some time on backports has little to no information about the relevance (let
alone importance) of a patch and is unlikely to be an expert in the area
affected by the patch. It's the role of the commit message to explain WHAT
problem the patch tries to solve, WHY it is estimated that it is a problem, and
HOW it tries to address it. With these elements, the person in charge of the
backports can decide whether or not to pick the patch. And if the patch does
not apply (which is common for older versions) they have information in the
commit message about the principle and choices that the initial developer made
and will try to adapt the patch sticking to these principles. Thus, the time
spent backporting patches solely depends on the code quality and the commit
message details and accuracy.

When it turns to fixing bugs, before declaring a bug, there is an analysis
phase. It starts with "is this behaviour expected", "is it normal", "under what
circumstances does it happen", "when did it start to happen", "was it intended",
"was it just overlooked", and "how to fix it without breaking the initial
intent". A utility called "git bisect" is usually involved in determining when
the behaviour started to happen. It determines the first patch which introduced
the new behaviour. If the patch is huge, touches many areas, is really difficult
to read because it needlessly reindents code or adds/removes line breaks out of
context, it will be very difficult to figure what part of this patch broke the
behaviour. Then once the part is figured, if the commit message doesn't provide
a detailed description about the intent of the patch, i.e. the problem it was
trying to solve, why and how, the developer landing on that patch will really
feel powerless. And very often in this case, the fix for the problem will break
something else or something that depended on the original patch.

But contrary to what it could look like, providing great quality patches is not
difficult, and developers will always help contributors improve their patches
quality because it's in their interest as well. History has shown that first
time contributors can provide an excellent work when they have carefully read
this document, and that people coming from projects with different practices
can grow from first-time contributor to trusted committer in about 6 months.


Preparation
-----------

It is possible that you'll want to add a specific feature to satisfy your needs
or one of your customers'. Contributions are welcome, however maintainers are
often very picky about changes. Patches that change massive parts of the code,
or that touch the core parts without any good reason will generally be rejected
if those changes have not been discussed first.

The proper place to discuss your changes is the HAProxy Mailing List. There are
enough skilled readers to catch hazardous mistakes and to suggest improvements.
There is no other place where you'll find as many skilled people on the project,
and these people can help you get your code integrated quickly. You can
subscribe to it by sending an empty e-mail at the following address :

                        haproxy+subscribe@formilux.org

It is not even necessary to subscribe, you can post there and verify via the
public list archives that your message was properly delivered. In this case you
should indicate in your message that you'd like responders to keep you CCed.
Please visit http://haproxy.org/ to figure available options to join the list.

If you have an idea about something to implement, *please* discuss it on the
list first. It has already happened several times that two persons did the same
thing simultaneously. This is a waste of time for both of them. It's also very
common to see some changes rejected because they're done in a way that will
conflict with future evolutions, or that does not leave a good feeling. It's
always unpleasant for the person who did the work, and it is unpleasant in
general because people's time and efforts are valuable and would be better
spent working on something else. That would not happen if these were discussed
first. There is no problem posting work in progress to the list, it happens
quite often in fact. Just prefix your mail subject with "RFC" (it stands for
"request for comments") and everyone will understand you'd like some opinion
on your work in progress. Also, don't waste your time with the doc when
submitting patches for review, only add the doc with the patch you consider
ready to merge (unless you need some help on the doc itself, of course).

Another important point concerns code portability. HAProxy requires gcc as the
C compiler, and may or may not work with other compilers. However it's known to
build using gcc 2.95 or any later version. As such, it is important to keep in
mind that certain facilities offered by recent versions must not be used in the
code:

  - declarations mixed in the code (requires gcc >= 3.x and is a bad practice)
  - GCC builtins without checking for their availability based on version and
    architecture ;
  - assembly code without any alternate portable form for other platforms
  - use of stdbool.h, "bool", "false", "true" : simply use "int", "0", "1"
  - in general, anything which requires C99 (such as declaring variables in
    "for" statements)

Since most of these restrictions are just a matter of coding style, it is
normally not a problem to comply. Please read doc/coding-style.txt for all the
details.

When modifying some optional subsystem (SSL, Lua, compression, device detection
engines), please make sure the code continues to build (and to work) when these
features are disabled. Similarly, when modifying the SSL stack, please always
ensure that supported OpenSSL versions continue to build and to work, especially
if you modify support for alternate libraries. Clean support for the legacy
OpenSSL libraries is mandatory, support for its derivatives is a bonus and may
occasionally break even though a great care is taken. In other words, if you
provide a patch for OpenSSL you don't need to test its derivatives, but if you
provide a patch for a derivative you also need to test with OpenSSL.

If your work is very confidential and you can't publicly discuss it, you can
also mail willy@haproxy.org directly about it, but your mail may be waiting
several days in the queue before you get a response, if you get a response at
all. Retransmit if you don't get a response by one week. Please note that
direct sent e-mails to this address for non-confidential subjects may simply
be forwarded to the list or be deleted without notification. An auto-responder
bot is in place to try to detect e-mails from people asking for help and to
redirect them to the mailing list. Do not be surprised if this happens to you.

If you'd like a feature to be added but you think you don't have the skills to
implement it yourself, you should follow these steps :

    1. discuss the feature on the mailing list. It is possible that someone
       else has already implemented it, or that someone will tell you how to
       proceed without it, or even why not to do it. It is also possible that
       in fact it's quite easy to implement and people will guide you through
       the process. That way you'll finally have YOUR patch merged, providing
       the feature YOU need.

    2. if you really can't code it yourself after discussing it, then you may
       consider contacting someone to do the job for you. Some people on the
       list might sometimes be OK with trying to do it.

The version control system used by the project (Git) keeps authorship
information in the form of the patch author's e-mail address. This way you will
be credited for your work in the project's history. If you contract with
someone to implement your idea you may have to discuss such modalities with
the person doing the work as by default this person will be mentioned as the
work's author.


Rules: the 12 laws of patch contribution
----------------------------------------

People contributing patches must apply the following rules. That may sound heavy
at the beginning but it's common sense more than anything else and contributors
do not think about them anymore after a few patches.

1) Comply with the license

   Before modifying some code, you have read the LICENSE file ("main license")
   coming with the sources, and all the files this file references. Certain
   files may be covered by different licenses, in which case it will be
   indicated in the files themselves. In any case, you agree to respect these
   licenses and to contribute your changes under the same licenses. If you want
   to create new files, they will be under the main license, or any license of
   your choice that you have verified to be compatible with the main license,
   and that will be explicitly mentioned in the affected files. The project's
   maintainers are free to reject contributions proposing license changes they
   feel are not appropriate or could cause future trouble.

2) Develop on development branch, not stable ones

   Your work may only be based on the latest development version. No development
   is made on a stable branch. If your work needs to be applied to a stable
   branch, it will first be applied to the development branch and only then will
   be backported to the stable branch. You are responsible for ensuring that
   your work correctly applies to the development version. If at any moment you
   are going to work on restructuring something important which may impact other
   contributors, the rule that applies is that the first sent is the first
   served. However it is considered good practice and politeness to warn others
   in advance if you know you're going to make changes that may force them to
   re-adapt their code, because they did probably not expect to have to spend
   more time discovering your changes and rebasing their work.

3) Read and respect the coding style

   You have read and understood "doc/coding-style.txt", and you're actively
   determined to respect it and to enforce it on your coworkers if you're going
   to submit a team's work. We don't care what text editor you use, whether it's
   an hex editor, cat, vi, emacs, Notepad, Word, or even Eclipse. The editor is
   only the interface between you and the text file. What matters is what is in
   the text file in the end. The editor is not an excuse for submitting poorly
   indented code, which only proves that the person has no consideration for
   quality and/or has done it in a hurry (probably worse). Please note that most
   bugs were found in low-quality code. Reviewers know this and tend to be much
   more reluctant to accept poorly formatted code because by experience they
   won't trust their author's ability to write correct code. It is also worth
   noting that poor quality code is painful to read and may result in nobody
   willing to waste their time even reviewing your work.

4) Present clean work

   The time it takes for you to polish your code is always much smaller than the
   time it takes others to do it for you, because they always have to wonder if
   what they see is intended (meaning they didn't understand something) or if it
   is a mistake that needs to be fixed. And since there are less reviewers than
   submitters, it is vital to spread the effort closer to where the code is
   written and not closer to where it gets merged. For example if you have to
   write a report for a customer that your boss wants to review before you send
   it to the customer, will you throw on his desk a pile of paper with stains,
   typos and copy-pastes everywhere ? Will you say "come on, OK I made a mistake
   in the company's name but they will find it by themselves, it's obvious it
   comes from us" ? No. When in doubt, simply ask for help on the mailing list.

5) Documentation is very important

   There are four levels of importance of quality in the project :

   - The most important one, and by far, is the quality of the user-facing
     documentation. This is the first contact for most users and it immediately
     gives them an accurate idea of how the project is maintained. Dirty docs
     necessarily belong to a dirty project. Be careful to the way the text you
     add is presented and indented. Be very careful about typos, usual mistakes
     such as double consonants when only one is needed or "it's" instead of
     "its", don't mix US English and UK English in the same paragraph, etc.
     When in doubt, check in a dictionary. Fixes for existing typos in the doc
     are always welcome and chasing them is a good way to become familiar with
     the project and to get other participants' respect and consideration.

   - The second most important level is user-facing messages emitted by the
     code. You must try to see all the messages your code produces to ensure
     they are understandable outside of the context where you wrote them,
     because the user often doesn't expect them. That's true for warnings, and
     that's even more important for errors which prevent the program from
     working and which require an immediate and well understood fix in the
     configuration. It's much better to say "line 35: compression level must be
     an integer between 1 and 9" than "invalid argument at line 35". In HAProxy,
     error handling roughly represents half of the code, and that's about 3/4 of
     the configuration parser. Take the time to do something you're proud of. A
     good rule of thumb is to keep in mind that your code talks to a human and
     tries to teach them how to proceed. It must then speak like a human.

   - The third most important level is the code and its accompanying comments,
     including the commit message which is a complement to your code and
     comments. It's important for all other contributors that the code is
     readable, fluid, understandable and that the commit message describes what
     was done, the choices made, the possible alternatives you thought about,
     the reason for picking this one and its limits if any. Comments should be
     written where it's easy to have a doubt or after some error cases have been
     wiped out and you want to explain what possibilities remain. All functions
     must have a comment indicating what they take on input and what they
     provide on output. Please adjust the comments when you copy-paste a
     function or change its prototype, this type of lazy mistake is too common
     and very confusing when reading code later to debug an issue. Do not forget
     that others will feel really angry at you when they have to dig into your
     code for a bug that your code caused and they feel like this code is dirty
     or confusing, that the commit message doesn't explain anything useful and
     that the patch should never have been accepted in the first place. That
     will strongly impact your reputation and will definitely affect your
     chances to contribute again!

   - The fourth level of importance is in the technical documentation that you
     may want to add with your code. Technical documentation is always welcome
     as it helps others make the best use of your work and to go exactly in the
     direction you thought about during the design. This is also what reduces
     the risk that your design gets changed in the near future due to a misuse
     and/or a poor understanding. All such documentation is actually considered
     as a bonus. It is more important that this documentation exists than that
     it looks clean. Sometimes just copy-pasting your draft notes in a file to
     keep a record of design ideas is better than losing them. Please do your
     best so that other ones can read your doc. If these docs require a special
     tool such as a graphics utility, ensure that the file name makes it
     unambiguous how to process it. So there are no rules here for the contents,
     except one.  Please write the date in your file. Design docs tend to stay
     forever and to remain long after they become obsolete. At this point that
     can cause harm more than it can help. Writing the date in the document
     helps developers guess the degree of validity and/or compare them with the
     date of certain commits touching the same area.

6) US-ASCII only!

   All text files and commit messages are written using the US-ASCII charset.
   Please be careful that your contributions do not contain any character not
   printable using this charset, as they will render differently in different
   editors and/or terminals. Avoid latin1 and more importantly UTF-8 which some
   editors tend to abuse to replace some US-ASCII characters with their
   typographic equivalent which aren't readable anymore in other editors. The
   only place where alternative charsets are tolerated is in your name in the
   commit message, but it's at your own risk as it can be mangled during the
   merge. Anyway if you have an e-mail address, you probably have a valid
   US-ASCII representation for it as well.

7) Comments

   Be careful about comments when you move code around. It's not acceptable that
   a block of code is moved to another place leaving irrelevant comments at the
   old place, just like it's not acceptable that a function is duplicated without
   the comments being adjusted. The example below started to become quite common
   during the 1.6 cycle, it is not acceptable and wastes everyone's time :

      /* Parse switching <str> to build rule <rule>. Returns 0 on error. */
      int parse_switching_rule(const char *str, struct rule *rule)
      {
       ...
      }

      /* Parse switching <str> to build rule <rule>. Returns 0 on error. */
      void execute_switching_rule(struct rule *rule)
      {
       ...
      }

   This patch is not acceptable either (and it's unfortunately not that rare) :

    +   if (!session || !arg || list_is_empty(&session->rules->head))
    +         return 0;
    +
        /* Check if session->rules is valid before dereferencing it */
        if (!session->rules_allocated)
              return 0;

    -   if (!arg || list_is_empty(&session->rules->head))
    -         return 0;
    -

8) Short, readable identifiers

   Limit the length of your identifiers in the code. When your identifiers start
   to sound like sentences, it's very hard for the reader to keep on track with
   what operation they are observing. Also long names force expressions to fit
   on several lines which also cause some difficulties to the reader. See the
   example below :

       int file_name_len_including_global_path;
       int file_name_len_without_global_path;
       int global_path_len_or_zero_if_default;

       if (global_path)
               global_path_len_or_zero_if_default = strlen(global_path);
       else
               global_path_len_or_zero_if_default = 0;

       file_name_len_without_global_path = strlen(file_name);
       file_name_len_including_global_path =
               file_name_len_without_global_path + 1 + /* for '/' */
               global_path_len_or_zero_if_default ?
                       global_path_len_or_zero_if_default : default_path_len;

   Compare it to this one :

       int f, p;

       p = global_path ? strlen(global_path) : default_path_len;
       f = p + 1 + strlen(file_name);  /* 1 for '/' */

   A good rule of thumb is that if your identifiers start to contain more than
   3 words or more than 15 characters, they can become confusing. For function
   names it's less important especially if these functions are rarely used or
   are used in a complex context where it is important to differentiate between
   their multiple variants.

9) Unified diff only

   The best way to build your patches is to use "git format-patch". This means
   that you have committed your patch to a local branch, with an appropriate
   subject line and a useful commit message explaining what the patch attempts
   to do. It is not strictly required to use git, but what is strictly required
   is to have all these elements in the same mail, easily distinguishable, and
   a patch in "diff -up" format (which is also the format used by Git). This
   means the "unified" diff format must be used exclusively, and with the
   function name printed in the diff header of each block. That significantly
   helps during reviews. Keep in mind that most reviews are done on the patch
   and not on the code after applying the patch. Your diff must keep some
   context (3 lines above and 3 lines below) so that there's no doubt where the
   code has to be applied. Don't change code outside of the context of your
   patch (eg: take care of not adding/removing empty lines once you remove
   your debugging code). If you are using Git (which is strongly recommended),
   always use "git show" after doing a commit to ensure it looks good, and
   enable syntax coloring that will automatically report in red the trailing
   spaces or tabs that your patch added to the code and that must absolutely be
   removed. These ones cause a real pain to apply patches later because they
   mangle the context in an invisible way. Such patches with trailing spaces at
   end of lines will be rejected.

10) One patch per feature

   Please cut your work in series of patches that can be independently reviewed
   and merged. Each patch must do something on its own that you can explain to
   someone without being ashamed of what you did. For example, you must not say
   "This is the patch that implements SSL, it was tricky". There's clearly
   something wrong there, your patch will be huge, will definitely break things
   and nobody will be able to figure what exactly introduced the bug. However
   it's much better to say "I needed to add some fields in the session to store
   the SSL context so this patch does this and doesn't touch anything else, so
   it's safe". Also when dealing with series, you will sometimes fix a bug that
   one of your patches introduced. Please do merge these fixes (eg: using git
   rebase -i and squash or fixup), as it is not acceptable to see patches which
   introduce known bugs even if they're fixed later. Another benefit of cleanly
   splitting patches is that if some of your patches need to be reworked after
   a review, the other ones can still be merged so that you don't need to care
   about them anymore. When sending multiple patches for review, prefer to send
   one e-mail per patch than all patches in a single e-mail. The reason is that
   not everyone is skilled in all areas nor has the time to review everything
   at once. With one patch per e-mail, it's easy to comment on a single patch
   without giving an opinion on the other ones, especially if a long thread
   starts about one specific patch on the mailing list. "git send-email" does
   that for you though it requires a few trials before getting it right.

   If you can, please always put all the bug fixes at the beginning of the
   series. This often makes it easier to backport them because they will not
   depend on context that your other patches changed. As a hint, if you can't
   do this, there are little chances that your bug fix can be backported.

11) Real commit messages please!

   The commit message is how you're trying to convince a maintainer to adopt
   your work and maintain it as long as possible. A dirty commit message almost
   always comes with dirty code. Too short a commit message indicates that too
   short an analysis was done and that side effects are extremely likely to be
   encountered. It's the maintainer's job to decide to accept this work in its
   current form or not, with the known constraints. Some patches which rework
   architectural parts or fix sensitive bugs come with 20-30 lines of design
   explanations, limitations, hypothesis or even doubts, and despite this it
   happens when reading them 6 months later while trying to identify a bug that
   developers still miss some information about corner cases.

   So please properly format your commit messages. To get an idea, just run
   "git log" on the file you've just modified. Patches always have the format
   of an e-mail made of a subject, a description and the actual patch. If you
   are sending a patch as an e-mail formatted this way, it can quickly be
   applied with limited effort so that's acceptable :

     - A subject line (may wrap to the next line, but please read below)
     - an empty line (subject delimiter)
     - a non-empty description (the body of the e-mail)
     - the patch itself

   The subject describes the "What" of the change ; the description explains
   the "why", the "how" and sometimes "what next". For example a commit message
   looking like this will be rejected :

     | From: Mr Foobar <foobar@example.com>
     | Subject: BUG: fix typo in ssl_sock
     |

   This one as well (too long subject, not the right place for the details) :

     | From: Mr Foobar <foobar@example.com>
     | Subject: BUG/MEDIUM: ssl: use an error flag to prevent ssl_read() from
     |    returning 0 when dealing with large buffers because that can cause
     |    an infinite loop
     |

   This one ought to be used instead :

     | From: Mr Foobar <foobar@example.com>
     | Subject: BUG/MEDIUM: ssl: fix risk of infinite loop in ssl_sock
     |
     | ssl_read() must not return 0 on error or the caller may loop forever.
     | Instead we add a flag to the connection to notify about the error and
     | check it at all call places. This situation can only happen with large
     | buffers so a workaround is to limit buffer sizes. Another option would
     | have been to return -1 but it required to use signed ints everywhere
     | and would have made the patch larger and riskier. This fix should be
     | backported to versions 1.2 and upper.

   It is important to understand that for any reader to guess the text above
   when it's absent, it will take a huge amount of time. If you made the
   analysis leading to your patch, you must explain it, including the ideas
   you dropped if you had a good reason for this.

   While it's not strictly required to use Git, it is strongly recommended
   because it helps you do the cleanest job with the least effort. But if you
   are comfortable with writing clean e-mails and inserting your patches, you
   don't need to use Git.

   But in any case, it is important that there is a clean description of what
   the patch does, the motivation for what it does, why it's the best way to do
   it, its impacts, and what it does not yet cover. And this is particularly
   important for bugs. A patch tagged "BUG" must absolutely explain what the
   problem is, why it is considered as a bug. Anybody, even non-developers,
   should be able to tell whether or not a patch is likely to address an issue
   they are facing. Indicating what the code will do after the fix doesn't help
   if it does not say what problem is encountered without the patch. Note that
   in some cases the bug is purely theoretical and observed by reading the code.
   In this case it's perfectly fine to provide an estimate about possible
   effects. Also, in HAProxy, like many projects which take a great care of
   maintaining stable branches, patches are reviewed later so that some of them
   can be backported to stable releases.

   While reviewing hundreds of patches can seem cumbersome, with a proper
   formatting of the subject line it actually becomes very easy. For example,
   here's how one can find patches that need to be reviewed for backports (bugs
   and doc) between since commit ID 827752e :

       $ git log --oneline 827752e.. | grep 'BUG\|DOC'
       0d79cf6 DOC: fix function name
       bc96534 DOC: ssl: missing LF
       10ec214 BUG/MEDIUM: lua: the lua function Channel:close() causes a segf
       bdc97a8 BUG/MEDIUM: lua: outgoing connection was broken since 1.6-dev2
       ba56d9c DOC: mention support for RFC 5077 TLS Ticket extension in start
       f1650a8 DOC: clarify some points about SSL and the proxy protocol
       b157d73 BUG/MAJOR: peers: fix current table pointer not re-initialized
       e1ab808 BUG/MEDIUM: peers: fix wrong message id on stick table updates
       cc79b00 BUG/MINOR: ssl: TLS Ticket Key rotation broken via socket comma
       d8e42b6 DOC: add new file intro.txt
       c7d7607 BUG/MEDIUM: lua: bad error processing
       386a127 DOC: match several lua configuration option names to those impl
       0f4eadd BUG/MEDIUM: counters: ensure that src_{inc,clr}_gpc0 creates a

   It is made possible by the fact that subject lines are properly formatted and
   always respect the same principle : one part indicating the nature and
   severity of the patch, another one to indicate which subsystem is affected,
   and the last one is a succinct description of the change, with the important
   part at the beginning so that it's obvious what it does even when lines are
   truncated like above. The whole stable maintenance process relies on this.
   For this reason, it is mandatory to respect some easy rules regarding the
   way the subject is built. Please see the section below for more information
   regarding this formatting.

   As a rule of thumb, your patch MUST NEVER be made only of a subject line,
   it *must* contain a description. Even one or two lines, or indicating
   whether a backport is desired or not. It turns out that single-line commits
   are so rare in the Git world that they require special manual (hence
   painful) handling when they are backported, and at least for this reason
   it's important to keep this in mind.

   Maintainers who pick your patch may slightly adjust the description as they
   see fit. Do not see this as a failure to do a clean job, it just means they
   think it will help them do their daily job this way. The code may also be
   slightly adjusted before being merged (non-functional changes only, fix for
   typos, tabs vs spaces for example), unless your patch contains a
   Signed-off-By tag, in which case they will either modify it and mention the
   changes after your Signed-off-By line, or (more likely) ask you to perform
   these changes yourself. This ability to slightly adjust a patch before
   merging is is the main reason for not using pull requests which do not
   provide this facility and will require to iterate back and forth with the
   submitter and significantly delay the patch inclusion.

   Each patch fixing a bug MUST be tagged with "BUG", a severity level, an
   indication of the affected subsystem and a brief description of the nature
   of the issue in the subject line, and a detailed analysis in the message
   body. The explanation of the user-visible impact and the need for
   backporting to stable branches or not are MANDATORY. Bug fixes with no
   indication will simply be rejected as they are very likely to cause more
   harm when nobody is able to tell whether or not the patch needs to be
   backported or can be reverted in case of regression.

   When fixing a bug which is reproducible, if possible, the contributors are
   strongly encouraged to write a regression testing VTC file for varnishtest
   to add to reg-tests directory. More information about varnishtest may be
   found in README file of reg-tests directory and in doc/regression-testing.txt
   file.

12) Discuss on the mailing list

   Note, some first-time contributors might feel impressed or scared by posting
   to a list. This list is frequented only by nice people who are willing to
   help you polish your work so that it is perfect and can last long. What you
   think could be perceived as a proof of incompetence or lack of care will
   instead be a proof of your ability to work with a community. You will not be
   judged nor blamed for making mistakes. The project maintainers are the ones
   creating the most bugs and mistakes anyway, and nobody knows the project in
   its entirety anymore so you're just like anyone else. And people who have no
   consideration for other's work are quickly ejected from the list so the
   place is as safe and welcoming to new contributors as it is to long time
   ones.

   When submitting changes, please always CC the mailing list address so that
   everyone gets a chance to spot any issue in your code. It will also serve
   as an advertisement for your work, you'll get more testers quicker and
   you'll feel better knowing that people really use your work. It's often
   convenient to prepend "[PATCH]" in front of your mail's subject to mention
   that this e-mail contains a patch (or a series of patches), because it will
   easily catch reviewer's attention. It's automatically done by tools such as
   "git format-patch" and "git send-email". If you don't want your patch to be
   merged yet and prefer to show it for discussion, better tag it as "[RFC]"
   (stands for "Request For Comments") and it will be reviewed but not merged
   without your approval. It is also important to CC any author mentioned in
   the file you change, or a subsystem maintainers whose address is mentioned
   in a MAINTAINERS file. Not everyone reads the list on a daily basis so it's
   very easy to miss some changes. Don't consider it as a failure when a
   reviewer tells you you have to modify your patch, actually it's a success
   because now you know what is missing for your work to get accepted.  That's
   why you should not hesitate to CC enough people. Don't copy people who have
   no deal with your work area just because you found their address on the
   list. That's the best way to appear careless about their time and make them
   reject your changes in the future.


Patch classifying rules
-----------------------

There are 3 criteria of particular importance in any patch :
  - its nature (is it a fix for a bug, a new feature, an optimization, ...)
  - its importance, which generally reflects the risk of merging/not merging it
  - what area it applies to (eg: http, stats, startup, config, doc, ...)

It's important to make these 3 criteria easy to spot in the patch's subject,
because it's the first (and sometimes the only) thing which is read when
reviewing patches to find which ones need to be backported to older versions.
It also helps when trying to find which patch is the most likely to have caused
a regression.

Specifically, bugs must be clearly easy to spot so that they're never missed.
Any patch fixing a bug must have the "BUG" tag in its subject. Most common
patch types include :

  - BUG      fix for a bug. The severity of the bug should also be indicated
             when known. Similarly, if a backport is needed to older versions,
             it should be indicated on the last line of the commit message. The
             commit message MUST ABSOLUTELY describe the problem and its impact
             to non-developers. Any user must be able to guess if this patch is
             likely to fix a problem they are facing. Even if the bug was
             discovered by accident while reading the code or running an
             automated tool, it is mandatory to try to estimate what potential
             issue it might cause and under what circumstances. There may even
             be security implications sometimes so a minimum analysis is really
             required. Also please think about stable maintainers who have to
             build the release notes, they need to have enough input about the
             bug's impact to explain it. If the bug has been identified as a
             regression brought by a specific patch or version, this indication
             will be appreciated too. New maintenance releases are generally
             emitted when a few of these patches are merged. If the bug is a
             vulnerability for which a CVE identifier was assigned before you
             publish the fix, you can mention it in the commit message, it will
             help distro maintainers.

  - CLEANUP  code cleanup, silence of warnings, etc... theoretically no impact.
             These patches will rarely be seen in stable branches, though they
             may appear when they remove some annoyance or when they make
             backporting easier. By nature, a cleanup is always of minor
             importance and it's not needed to mention it.

  - DOC      updates to any of the documentation files, including README. Many
             documentation updates are backported since they don't impact the
             product's stability and may help users avoid bugs. So please
             indicate in the commit message if a backport is desired. When a
             feature gets documented, it's preferred that the doc patch appears
             in the same patch or after the feature patch, but not before, as it
             becomes confusing when someone working on a code base including
             only the doc patch won't understand why a documented feature does
             not work as documented.

  - REORG    code reorganization. Some blocks may be moved to other places,
             some important checks might be swapped, etc... These changes
             always present a risk of regression. For this reason, they should
             never be mixed with any bug fix nor functional change. Code is
             only moved as-is. Indicating the risk of breakage is highly
             recommended. Minor breakage is tolerated in such patches if trying
             to fix it at once makes the whole change even more confusing. That
             may happen for example when some #ifdefs need to be propagated in
             every file consecutive to the change.

  - BUILD    updates or fixes for build issues. Changes to makefiles also fall
             into this category. The risk of breakage should be indicated if
             known. It is also appreciated to indicate what platforms and/or
             configurations were tested after the change.

  - OPTIM    some code was optimised. Sometimes if the regression risk is very
             low and the gains significant, such patches may be merged in the
             stable branch. Depending on the amount of code changed or replaced
             and the level of trust the author has in the change, the risk of
             regression should be indicated. If the optimization depends on the
             architecture or on build options, it is important to verify that
             the code continues to work without it.

  - RELEASE  release of a new version (development or stable).

  - LICENSE  licensing updates (may impact distro packagers).

  - REGTEST  updates to any of the regression testing files found in reg-tests
             directory, including README or any documentation file.


When the patch cannot be categorized, it's best not to put any type tag, and to
only use a risk or complexity information only as below. This is commonly the
case for new features, which development versions are mostly made of.

The importance, complexity of the patch, or severity of the bug it fixes must
be indicated when relevant. A single upper-case word is preferred, among :

  - MINOR    minor change, very low risk of impact. It is often the case for
             code additions that don't touch live code. As a rule of thumb, a
             patch tagged "MINOR" is safe enough to be backported to stable
             branches. For a bug, it generally indicates an annoyance, nothing
             more.

  - MEDIUM   medium risk, may cause unexpected regressions of low importance or
             which may quickly be discovered. In short, the patch is safe but
             touches working areas and it is always possible that you missed
             something you didn't know existed (eg: adding a "case" entry or
             an error message after adding an error code to an enum). For a bug,
             it generally indicates something odd which requires changing the
             configuration in an undesired way to work around the issue.

  - MAJOR    major risk of hidden regression. This happens when large parts of
             the code are rearranged, when new timeouts are introduced, when
             sensitive parts of the session scheduling are touched, etc... We
             should only exceptionally find such patches in stable branches when
             there is no other option to fix a design issue. For a bug, it
             indicates severe reliability issues for which workarounds are
             identified with or without performance impacts.

  - CRITICAL medium-term reliability or security is at risk and workarounds,
             if they exist, might not always be acceptable. An upgrade is
             absolutely required. A maintenance release may be emitted even if
             only one of these bugs are fixed. Note that this tag is only used
             with bugs. Such patches must indicate what is the first version
             affected, and if known, the commit ID which introduced the issue.

The expected length of the commit message grows with the importance of the
change. While a MINOR patch may sometimes be described in 1 or 2 lines, MAJOR
or CRITICAL patches cannot have less than 10-15 lines to describe exactly the
impacts otherwise the submitter's work will be considered as rough sabotage.
If you are sending a new patch series after a review, it is generally good to
enumerate at the end of the commit description what changed from the previous
one as it helps reviewers quickly glance over such changes and not re-read the
rest.

For BUILD, DOC and CLEANUP types, this tag is not always relevant and may be
omitted.

The area the patch applies to is quite important, because some areas are known
to be similar in older versions, suggesting a backport might be desirable, and
conversely, some areas are known to be specific to one version. The area is a
single-word lowercase name the contributor find clear enough to describe what
part is being touched. The following list of tags is suggested but not
exhaustive:

  - examples  example files. Be careful, sometimes these files are packaged.

  - tests     regression test files. No code is affected, no need to upgrade.

  - reg-tests regression test files for varnishtest. No code is affected, no
              need to upgrade.

  - init      initialization code, arguments parsing, etc...

  - config    configuration parser, mostly used when adding new config keywords

  - http      the HTTP engine

  - stats     the stats reporting engine

  - cli       the stats socket CLI

  - checks    the health checks engine (eg: when adding new checks)

  - sample    the sample fetch system (new fetch or converter functions)

  - acl       the ACL processing core or some ACLs from other areas

  - filters   everything related to the filters core

  - peers     the peer synchronization engine

  - lua       the Lua scripting engine

  - listeners everything related to incoming connection settings

  - frontend  everything related to incoming connection processing

  - backend   everything related to LB algorithms and server farm

  - session   session processing and flags (very sensible, be careful)

  - server    server connection management, queueing

  - spoe      SPOE code

  - ssl       the SSL/TLS interface

  - proxy     proxy maintenance (start/stop)

  - log       log management

  - poll      any of the pollers

  - halog     the halog sub-component in the admin directory

  - htx       general HTX subsystem

  - mux-h1    HTTP/1.x multiplexer/demultiplexer

  - mux-h2    HTTP/2 multiplexer/demultiplexer

  - h1        general HTTP/1.x protocol parser

  - h2        general HTTP/2 protocol parser

Other names may be invented when more precise indications are meaningful, for
instance : "cookie" which indicates cookie processing in the HTTP core. Last,
indicating the name of the affected file is also a good way to quickly spot
changes. Many commits were already tagged with "stream_sock" or "cfgparse" for
instance.

It is required that the type of change and the severity when relevant are
indicated, as well as the touched area when relevant as well in the patch
subject. Normally, we would have the 3 most often. The two first criteria should
be present before a first colon (':'). If both are present, then they should be
delimited with a slash ('/'). The 3rd criterion (area) should appear next, also
followed by a colon. Thus, all of the following subject lines are valid :

Examples of subject lines :
  - DOC: document options forwardfor to logasap
  - DOC/MAJOR: reorganize the whole document and change indenting
  - BUG: stats: connection reset counters must be plain ascii, not HTML
  - BUG/MINOR: stats: connection reset counters must be plain ascii, not HTML
  - MEDIUM: checks: support multi-packet health check responses
  - RELEASE: Released version 1.4.2
  - BUILD: stats: stdint is not present on solaris
  - OPTIM/MINOR: halog: make fgets parse more bytes by blocks
  - REORG/MEDIUM: move syscall redefinition to specific places

Please do not use square brackets anymore around the tags, because they induce
more work when merging patches, which need to be hand-edited not to lose the
enclosed part.

In fact, one of the only square bracket tags that still makes sense is '[RFC]'
at the beginning of the subject, when you're asking for someone to review your
change before getting it merged. If the patch is OK to be merged, then it can
be merge as-is and the '[RFC]' tag will automatically be removed. If you don't
want it to be merged at all, you can simply state it in the message, or use an
alternate 'WIP/' prefix in front of your tag tag ("work in progress").

The tags are not rigid, follow your intuition first, and they may be readjusted
when your patch is merged. It may happen that a same patch has a different tag
in two distinct branches. The reason is that a bug in one branch may just be a
cleanup or safety measure in the other one because the code cannot be triggered.


Working with Git
----------------

For a more efficient interaction between the mainline code and your code, you
are strongly encouraged to try the Git version control system :

                        http://git-scm.com/

It's very fast, lightweight and lets you undo/redo your work as often as you
want, without making your mistakes visible to the rest of the world. It will
definitely help you contribute quality code and take other people's feedback
in consideration. In order to clone the HAProxy Git repository :

   $ git clone http://git.haproxy.org/git/haproxy.git/       (development)

If you decide to use Git for your developments, then your commit messages will
have the subject line in the format described above, then the whole description
of your work (mainly why you did it) will be in the body. You can directly send
your commits to the mailing list, the format is convenient to read and process.

It is recommended to create a branch for your work that is based on the master
branch :

   $ git checkout -b 20150920-fix-stats master

You can then do your work and even experiment with multiple alternatives if you
are not completely sure that your solution is the best one :

   $ git checkout -b 20150920-fix-stats-v2

Then reorder/merge/edit your patches :

   $ git rebase -i master

When you think you're ready, reread your whole patchset to ensure there is no
formatting or style issue :

   $ git show master..

And once you're satisfied, you should update your master branch to be sure that
nothing changed during your work (only needed if you left it unattended for days
or weeks) :

   $ git checkout -b 20150920-fix-stats-rebased
   $ git fetch origin master:master
   $ git rebase master

You can build a list of patches ready for submission like this :

   $ git format-patch master

The output files are the patches ready to be sent over e-mail, either via a
regular e-mail or via git send-email (carefully check the man page). Don't
destroy your other work branches until your patches get merged, it may happen
that earlier designs will be preferred for various reasons. Patches should be
sent to the mailing list : haproxy@formilux.org and CCed to relevant subsystem
maintainers or authors of the modified files if their address appears at the
top of the file.

Please don't send pull requests, they are really inconvenient as they make it
much more complicate to perform minor adjustments, and nobody benefits from
any comment on the code while on a list all subscribers learn a little bit on
each review of anyone else's code.


What to do if your patch is ignored
-----------------------------------

All patches merged are acknowledged by the maintainer who picked it. If you
didn't get an acknowledgement, check the mailing list archives to see if your
mail was properly delivered there and possibly if anyone responded and you did
not get their response (please look at http://haproxy.org/ for the mailing list
archive's address).

If you see that your mail is there but nobody responded, please recheck:
  - was the subject clearly indicating that it was a patch and/or that you were
    seeking some review?

  - was your email mangled by your mail agent? If so it's possible that
    nobody had the willingness yet to mention it.

  - was your email sent as HTML? If so it definitely ended in spam boxes
    regardless of the archives.

  - did the patch violate some of the principles explained in this document?

If none of these cases matches, it might simply be that everyone was busy when
your patch was sent and that it was overlooked. In this case it's fine to
either resubmit it or respond to your own email asking if anything's wrong
about it. In general don't expect a response after one week of silence, just
because your email will not appear in anyone else's current window. So after
one week it's time to resubmit.

Among the mistakes that tend to make reviewers not respond are those who send
multiple versions of a patch in a row. It's natural for others then to wait for
the series to stabilize. And once it doesn't move anymore everyone forgot about
it. As a rule of thumb, if you have to update your original email more than
twice, first double-check that your series is really ready for submission, and
second, start a new thread and stop responding to the previous one. In this
case it is well appreciated to mention a version of your patch set in the
subject such as "[PATCH v2]", so that reviewers can immediately spot the new
version and not waste their time on the old one.

If you still do not receive any response, it is possible that you've already
played your last card by not respecting the basic principles multiple times
despite being told about it several times, and that nobody is willing to spend
more of their time than normally needed with your work anymore. Your best
option at this point probably is to ask "did I do something wrong" than to
resend the same patches.


How to be sure to irritate everyone
-----------------------------------

Among the best ways to quickly lose everyone's respect, there is this small
selection, which should help you improve the way you work with others, if
you notice you're already practising some of them:
  - repeatedly send improperly formatted commit messages, with no type or
    severity, or with no commit message body. These ones require manual
    edition, maintainers will quickly learn to recognize your name.

  - repeatedly send patches which break something, and disappear or take a long
    time to provide a fix.

  - fail to respond to questions related to features you have contributed in
    the past, which can further lead to the feature being declared unmaintained
    and removed in a future version.

  - send a new patch iteration without taking *all* comments from previous
    review into consideration, so that the reviewer discovers they have to do
    the exact same work again.

  - "hijack" an existing thread to discuss something different or promote your
    work. This will generally make you look like a fool so that everyone wants
    to stay away from your e-mails.

  - continue to send pull requests after having been explained why they are not
    welcome.

  - give wrong advices to people asking for help, or sending them patches to
    try which make no sense, waste their time, and give them a bad impression
    of the people working on the project.

  - be disrespectful to anyone asking for help or contributing some work. This
    may actually even get you kicked out of the list and banned from it.

-- end