You can do this in ErlyWeb by hacking the app controller's hook/1
function. You can match against the request string, e.g.
case yaws_arg:appmoddata(A) of
"/foo/bar" -> ...
"/baz" -> ...
end
or the parsed request, e.g.
case erlyweb:get_initial_ewc({ewc, A}) of
{ewc, foo_controller, foo_view, func, [A, "1", "2", "3"]} ->
...
{ewc, bar_controller, bar_view, func, [A, "1", "2", "3"]} ->
...
end.
The app controller gives you total control over how requests are
handled before they are processed by ErlyWeb.
Yariv
>
> Yariv,
>
> What we do with lift to support web services is to allow the developer
> to insert handler functions via pattern matching early in the HTTP
> cycle.
>
> For example (in Scala):
>
> LiftServlet.addHandler{
> case Request("POST", "rest" :: "foo" :: param1 :: _, body) =>
> handleFooPost(param1, body)
> case Request(method, "rest" :: "foo" :: param1 :: param2 :: _, _) =>
> handleFooCall(method, param1, param2)
> }
>
> Using pattern matching and guards to forward the meaningful parts of
> the requests to an appropriate handler is very successful (in terms of
> good resulting in implementation and low amount of features requests
> from the community.)
>
> Thanks,
>
> David
>
>
> >
> > Yariv
> >
> >
> >
> >
> > On Nov 13, 2007 2:59 AM, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote:
> > >
> > > Hello group,
> > >
> > > One of the weaknesses of ErlyWeb from my perspective is the lack of a
> > > Web services framework. With Erlang's focus on concurrency and
> > > Erlyweb's focus on making Erlang/Web development as easy as PHP etc.,
> > > this seems a surprising omission (at least, I *think* it's an
> > > omission; maybe it's there and I just haven't picked up on the fact).
> > >
> > > Probably the best point of comparison is Ruby on Rails (RoR). RoR has
> > > had a Web services framework (ActiveWebService) from the beginning;
> > > while it doesn't seem to have been that popular, it makes it
> > > incredibly easy to expose functionality as Web services.
> > >
> > > For the types of apps I generally work on, this is just golden; it
> > > makes RoR a strong contender as the toolset of choice where otherwise
> > > it wouldn't even be considered as an option.
> > >
> > > I'm aware that it's possible to use Yaws+erlsom, but it has a few
> > > weaknesses:
> > > - erlsom's install relies on sh; it doesn't install on Ubuntu without
> > > a bit of mucking around, and must be a challenge for Windows as well
> > > - setting up a Web service is a non-trivial exercise; just read
> > > through the relevant page (http://yaws.hyber.org/soap_intro.yaws) at
> > > the Yaws site
> > >
> > > Regards
> > >
> > > Dave M.
> > >
> > > On Nov 12, 6:04 am, "Yariv Sadan" <[EMAIL PROTECTED]> wrote:
> > > > Mojo,
> > > >
> > > > if you're building a simple CRUD app, you can build it in pretty much
> > > > any language with similar effort and results. ErlyWeb's goal is to
> > > > make building webapps in Erlang as easy as in Ruby/Python/PHP/etc and
> > > > I think it achieves it pretty well. AFAIK, Erlang will give you better
> > > > performance than the popular scripting languages, but you'll have to
> > > > benchmark it and decide how much it matters to you.
> > > >
> > > > If your app's backend is more complex than a few web servers that talk
> > > > to a single database server, Erlang can help you even more. If to
> > > > respond to a request, you need to do multiple things concurrently or
> > > > do some distributed computation, or fire off background processes for
> > > > asynchronous tasks, Erlang is the best choice by a long shot. Erlang
> > > > is much better than other languages for Comet apps that maintain
> > > > persistent connections to the clients (I'm sure you've seen the
> > > > apache-vs-yaws graph :) ).
> > > >
> > > > For more common needs, Erlang/ErlyWeb also has better support for
> > > > sharing session state (using Mnesia) and transaction-aware multi-db
> > > > connection pooling (using lightweight processes + messaging) than
> > > > other languages.
> > > >
> > > > Erlang/ErlyWeb is great for highly available applications (and for
> > > > interactive and highly productive development) due to its support for
> > > > hot code swapping. You can even change your database schema, recomplie
> > > > your app, and start using the new schema without taking your server
> > > > offline.
> > > >
> > > > And finally, Erlang is fun! :)
> > > >
> > > > Cheers,
> > > > Yariv
> > > >
> > >
> > > > On Nov 10, 2007 7:08 AM, mojo.talantikite <[EMAIL PROTECTED]> wrote:
> > > >
> > > >
> > > >
> > > > > Thanks for all the answers, I really appreciate them. Sometime later
> > > > > today or tomorrow I'd like to write up some questions that pertain to
> > > > > more of what I'm trying to do, but for now that gives me some pretty
> > > > > good ideas as to how I could use Erlang/ErlyWeb.
> > > >
> > > > > Overall, what do you feel are Erlang/ErlyWeb's particular strengths
> > > > > when it comes to web development? Of course you can pretty much get
> > > > > any language/framework to do what you need it to do, but how does this
> > > > > particular combination yield itself to solving (or simplifying)
> > > > > particular web development problems?
> > > >
> > > > > Thanks again, the answers were very helpful.
> > > >
> > > > > best,
> > > > > Mojo
> > > >
> > > > > On Nov 9, 6:25 am, Al <[EMAIL PROTECTED]> wrote:
> > > > > > On Nov 9, 9:08 am, "Yariv Sadan" <[EMAIL PROTECTED]> wrote:
> > > >
> > > > > > > On Nov 8, 2007 12:23 PM, mojo.talantikite <[EMAIL PROTECTED]>
> > > > > > > wrote:
> > > >
> > > > > > > > I'm in the very early stages of founding a startup, and
> > > > > > > > currently
> > > > > > > > we're in talks about what type of technology to be using. As
> > > > > > > > there
> > > > > > > > aren't too many people on board now, and none besides myself
> > > > > > > > that are
> > > > > > > > technical, there is a pretty blank slate for development as of
> > > > > > > > now.
> > > > > > > > After playing around with Erlang for the past couple of days I'm
> > > > > > > > starting to think about the pros/cons of using Erlang.
> > > >
> > > > > > > > Anyways, I have questions pertaining to how Erlang/ErlyWeb
> > > > > > > > addresses
> > > > > > > > certain needs and issues of scaling. I thought it might be more
> > > > > > > > useful
> > > > > > > > for a greater number of people if instead of speaking solely
> > > > > > > > about our
> > > > > > > > needs for our web app, we use an example people might be
> > > > > > > > familiar with
> > > > > > > > and get more from: YouTube. Here are some notes on a Google
> > > > > > > > Tech Talk
> > > > > > > > that was given, which also contains a link to the tech talk
> > > > > > > > video:
> > > > > > > >http://kylecordes.com/2007/07/12/youtube-scalability/
> > > >
> > > > > > > > Here are some questions that come to mind when thinking about
> > > > > > > > what
> > > > > > > > they faced:
> > > >
> > > > > > > > 1. Their main reason for choosing Python as their language is
> > > > > > > > because
> > > > > > > > development speed and productivity was (and is) very important
> > > > > > > > for
> > > > > > > > various reasons (one important one was probably showing
> > > > > > > > prototypes and
> > > > > > > > their progresses to potential investors). Erlang seems to be a
> > > > > > > > very
> > > > > > > > productive environment for some applications, but how does it
> > > > > > > > stand up
> > > > > > > > for web app development? Using Python, PHP, or Ruby has the
> > > > > > > > added
> > > > > > > > benefit of having lots of developers to draw from their
> > > > > > > > experiences --
> > > > > > > > how would Erlang compare?
> > > >
> > > > > > > Erlang definitely has fewer developers using it for webapps that
> > > > > > > PHP,
> > > > > > > Python or Ruby. My subjective take is that, having done PHP
> > > > > > > programming and played with RoR, ErlyWeb can be just as
> > > > > > > productive if
> > > > > > > not more and its code is very concise and expressive. I rarely
> > > > > > > feel
> > > > > > > that I'm writing repetitive code that doesn't directly solve the
> > > > > > > problem domain. Plus, I prefer Erlang's functional style to
> > > > > > > imperative
> > > > > > > one. I think FP makes your code more readable and debuggable.
> > > > > > > Erlang
> > > > > > > has fewer libraries than more popular languages, which may or may
> > > > > > > not
> > > > > > > affect you depending on your app's needs, but I think that the
> > > > > > > fewer
> > > > > > > libraries isn't as big an issue as some people say. Erlang has a
> > > > > > > variety of ways for talking to other lanugages and I'd rather
> > > > > > > write
> > > > > > > most of my code in Erlang in occasionally outsource some
> > > > > > > functionality
> > > > > > > to another language than lock my whole app to a language I don't
> > > > > > > like
> > > > > > > as much just because of the existence of a couple of libraries
> > > > > > > for it.
> > > > > > > Btw, Erlang also has some tools that other languages don't have --
> > > > > > > most notably, elegant concurrency and Mnesia.
> > > >
> > > > > > > > 2. Serving content was of course a big issue. They moved to
> > > > > > > > lighttpd
> > > > > > > > from Apache for their videos and got a lot of performance
> > > > > > > > increases
> > > > > > > > (they use CDNs for their most popular content). Yaws seems
> > > > > > > > great for
> > > > > > > > dynamic content, but is there anything better for the static
> > > > > > > > content?
> > > >
> > > > > > > Use lighttpd for static content and Yaws (or MochiWeb) for
> > > > > > > dynamic content.
> > > >
> > > > > > > > 3. Another major issue YouTube ran into was serving their
> > > > > > > > thumbnails. Each video can have about 4 thumbnails and each
> > > > > > > > page,
> > > > > > > > while having only one video playing, could have 40-60
> > > > > > > > thumbnails per
> > > > > > > > page. Thumbnails, unlike video, aren't distributed across
> > > > > > > > hundreds of
> > > > > > > > machines (due to their size). So, you have lots of requests per
> > > > > > > > second and tons of disk seeks. Apache didn't really work out,
> > > > > > > > so they
> > > > > > > > then went to a modified version of lighttpd that put the disk
> > > > > > > > reads
> > > > > > > > into worker threads -- but they ran into issues with that as
> > > > > > > > well.
> > > > > > > > They finally went to Google's BTFE. How would Erlang look at
> > > > > > > > this
> > > > > > > > problem -- would Yaws help at all?
> > > >
> > > > > > > I'm not too familiar with this problem, but if it's static data,
> > > > > > > it's
> > > > > > > generally better to serve if from lighttpd than Yaws.
> > > >
> > > > > > Agreed LightHttpd or apache will outperform Yaws with static
> > > > > > content.
> > > > > > If its lots of small files/images look at using a cache like server
> > > > > > with lots and lots of RAM also consider using solid state disks
> > > > > > (SSDs)
> > > > > > in Raid 0 configs, these are much faster than traditional disks for
> > > > > > random small files, they blow away performance of even 15K scsi
> > > > > > arrays
> > > > > > for this job, as seeks on SSD flash are near zero in comparison. The
> > > > > > limit here is capacity. You can get 64GB SSDs with Sata interfaces
> > > > > > (Sata II soon from Samsung) raid these up with Sata Raid Boards on
> > > > > > fast PCIe interfaces + built in Sata ports in a mirror config You
> > > > > > will
> > > > > > be surprised at how kick ass fast these are for the job. You also
> > > > > > need
> > > > > > good server Gigabit ports that can be aggregated.
> > > >
> > > > > > > > 4. They use MySql to store metadata, but as the site got huge,
> > > > > > > > they
> > > > > > > > ran into some issues with it. They went from having one
> > > > > > > > database to
> > > > > > > > doing db replication. That caused issues eventually, one of
> > > > > > > > them
> > > > > > > > being that spreading read load (being asynchronous) caused the
> > > > > > > > database to serve outdated data from time to time. They then
> > > > > > > > went to
> > > > > > > > partitioning the database into shards. Overall, though, they're
> > > > > > > > running into issues due to the fact that they're trying to do
> > > > > > > > more and
> > > > > > > > more stuff with the data. For example, recommendation systems
> > > > > > > > and
> > > > > > > > data mining gets really hard on 100s of millions of views per
> > > > > > > > day, so
> > > > > > > > they are needing some solutions that can do parallel queries and
> > > > > > > > handle distributed computation. Would Mnesia be able to help
> > > > > > > > handle
> > > > > > > > these issues, or anything else from the Erlang world that could
> > > > > > > > deal
> > > > > > > > with these issues?
> > > >
> > > > > > > Mnesia is more suited for storing live session data than large
> > > > > > > amounts
> > > > > > > of persistent data. And Mnesia isn't really suited for data
> > > > > > > mining --
> > > > > > > just for simple queries. However, Erlang helps in that it allows
> > > > > > > you
> > > > > > > to connect to multiple databases using its great connection
> > > > > > > pooling
> > > > > > > capabilities (a process is spawned for each database connection,
> > > > > > > and a
> > > > > > > dispatcher process is responsible for routing queries to
> > > > > > > connection
> > > > > > > processes). If I were building YouTube in Erlang, I would consider
> > > > > > > doing all replication and partitioning work in the application
> > > > > > > code
> > > > > > > rather than relying on the database engine.
> > > >
> > > > > > Use flat files for the metadata and cache them where possible
> > > > > > across
> > > > > > machines, consider an appending meta file storage controller (write
> > > > > > it
> > > > > > yourself) and file formats that enable appending rather than
> > > > > > editing.
> > > > > > The trick heres is to only append to files where possible, editing
> > > > > > is
> > > > > > expense (Well percolating the changes is).Break the files up like
> > > > > > you
> > > > > > would database tables and crate summarized view files for common
> > > > > > queries.
> > > >
> > > > > > If there is a lot of data + analysis consider something like a map
> > > > > > reduce pattern to create views on the backend, erlang is excellent
> > > > > > for
> > > > > > this sort of stuff, blows the socks of most others.
> > > >
> > > > > > regards
> > > > > > Al
> > > >
> > > > > > Regards
> > > > > > Al
> > >
> > >
> > > >
> > >
> >
> > >
> >
>
>
>
> --
> lift, the secure, simple, powerful web framework
> http://liftweb.net
>
>
> >
>
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