Re: The future of gitweb - part 2: JavaScript

From: Jakub Narebski <jnareb@gmail.com>
Date: Apr 17, 2011, 10:11 UTC
Message-ID: <201104171211.14118.jnareb@gmail.com>
In-Reply-To: <20110416225729.GB5739@external.screwed.box>

On Sun, 17 Apr 2011, Peter Vereshagin wrote:

> You're face to face with man who sold the world, Jakub!
> 2011/04/17 00:19:07 +0200 Jakub Narebski <jnareb@gmail.com> => To Peter Vereshagin :

> JN> > There are more disadvantages of such  an approach:
> JN> > - for CGI, the process is being executed on every request. On some systems, e.
> JN> >   g., Windows, launching a process is very expensive, sometimes more than

> JN> git-http-backend is written in C, not Perl.
> 
> Yes, it's about it.

Perl is much better for writing a web app such as gitweb (meant for
web browsers) than bare C.

Show 14 quoted lines

> JN> > - for development, some different parts of the code for the same purpose do
> JN> >   exist, e. g., client and storage i/o. The more it is being developed, the
> JN> >   more features it satisfies, the more such a code.
> JN> 
> JN> Gitweb is written in Perl.  This language is good for prototyping, for
> JN> fast development, and for easy writing of a web app.  Gitweb works on
> JN> porcelain level - it is an user interface (a web one).
> JN> 
> JN> C is good for performance.  git-http-backend is only an example
> JN> implementation.  The "smart" HTTP protocol works on porcelain level.
> 
> It doesn't mean that different parts of code do exist in them
> for the same purpose.  It doesn't mean that such a code can not
> be reused by both.  C code can be used by Perl.

C code can be used by Perl... but if you mean calling C code from Perl then first, there is no git library; libgit2 is work in progress yet. Second, there are no Perl bindings for libgit2. Third, doing Perl bindings to C in _portable_ way is major pain; XS is hard (this might change if/when Perl port of ctypes would be finished).

If you mean calling git commands from gitweb and parsing their output... that is what gitweb does.

But gitweb and git-http-backend doesn't have much common in functionality.

Show 11 quoted lines

> JN> >   For example, I suppose git-http-backend will have 'get a particular
> JN> >   commitdiff quickly without fetching all the repo' feature one day
> JN> >   to be used in web clients' scripts, e.g. will serve the same way
> JN> >   for git cli as a file system. This will make it have the same
> JN> >   feature like 'commitdiff' feature of a gitweb but implemented 
> JN> >   differently.
> JN> 
> JN> Unix philosophy which Git tries to follow is "do one thing and do it
> JN> well".
> 
> This is why the code must not be reused?

What is about code reuse? Gitweb calls git commands, and generates output in HTML for web browser. git-http-backend is responsible for communicating with git-upload-pack / git-receive-pack on behalf of git client.

> Does it mean "there is more than one way to do it and we will use
> all of them for the same purpose in the same project"?

No.

This means that it is gitweb job to tak to web browser, git-http-backend
to talk to "git fetch" or "git push", and web server to route to
correct script (backend).

> JN> I don't believe git-http-backend would ever talk to web browsers, and
> JN> it is quite unlikely for git to acquire non-distributed client-server
> JN> mode.

[...]

> JN> And if it does acquire such feature, then gitweb will be simply modified
> JN> to use it...
> 
> or git-http-backend? or both?

Gitweb, because it is porcelain. git-http-backend is plumbing. It is porcelain (high level, meant for end user) that uses plumbing (low level, meant for scripts and other commands).

> isn't it just better for them to reuse the same code?

There is nothing to reuse.

Show 15 quoted lines

> JN> > - the routing of the request, the deciding what to do with the particular
> JN> >   HTTP request, becomes more obfuscated. First, web server decides what CGI
> JN> >   should approve it. Plus two more decision makers are those 2 CGI, all different.
> JN> > 
> JN> > It's just why I never supposed git to have 2 different native web interfaces,
> JN> > especially in sight of plumbing vs porcelain contrast in cli, sorry for
> JN> > confusion.
> JN> 
> JN> Those are not two _web interfaces_.  Gitweb is one of web interfaces
> JN> to git repositories; more at
> JN>   https://git.wiki.kernel.org/index.php/Interfaces,_frontends,_and_tools#Web_Interfaces
> JN> 
> JN> Fetching and pushing via HTTP is not web interface, is HTTP _transport_.
> 
> But HTTP is an application protocol, not a transport protocol.

Fetching via "smart" HTTP protocol is actually git-over-http, with some extra work due to the fact that HTTP is stateless.

Show 5 quoted lines

> JN> For one [gitweb] you use web browser, for other [git-http-backend]
> JN> you use git itself. 
> 
> on the client side those are different projects.
> on the server side those are the same.

No, they are not the same. Besides minuscule part of being a CGI script they have nothing in common. Gitweb produces HTML output for consumption of web browser in response to given URL. git-http-backend proxies fetch and push request to git-upload-pack / git-receive-pack.

> 
> Different technologies, right. But not incompatible.

There is nothing to be compatible with.

> JN> But this discussion got very off-topic...
>
> Not about Javascript, right.

Well, except the fact that "git fetch" / "git push" is not a web browser, and that it would never use JavaScript... so git-http-backend wouldn't either.

But it is not about JavaScript use by gitweb.

-- 
Jakub Narebski
Poland