Webmachine a practical executable model for HTTP Steve Vinoski - - PowerPoint PPT Presentation

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Webmachine a practical executable model for HTTP Steve Vinoski - - PowerPoint PPT Presentation

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Webmachine a practical executable model for HTTP Steve Vinoski Architect, Basho Technologies QCon SF 2011 16 Nov 2011 @stevevinoski http://steve.vinoski.net/ vinoski@ieee.org 1 Webmachine a practical executable model for HTTP a toolkit

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Webmachine

a practical executable model for HTTP

Steve Vinoski

Architect, Basho Technologies

QCon SF 2011 16 Nov 2011 @stevevinoski http://steve.vinoski.net/

vinoski@ieee.org

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Webmachine

a practical executable model for HTTP

HTTP-based systems a toolkit for

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Webmachine

HTTP-based systems a toolkit for

a practical executable model for HTTP

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Webmachine

HTTP-based systems well-behaved easily creating a toolkit for

a practical executable model for HTTP

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Webmachine

HTTP-based systems well-behaved easily creating? a toolkit for

a practical executable model for HTTP

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Webmachine

HTTP-based systems well-behaved? easily creating a toolkit for

a practical executable model for HTTP

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HTTP is complicated.

(see http://webmachine.basho.com/)

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Webmachine makes HTTP easier.

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  • module(twohundred_resource).
  • export([init/1, to_html/2]).
  • include_lib("webmachine/include/webmachine.hrl").

init([]) -> {ok, undefined}. to_html(ReqData, State) -> {"Hello, Webmachine world", ReqData, State}.

(that’s it!)

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Want to get more interesting?

Just add generate_etag or last_modified...

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...and now you have conditional requests.

generate_etag(RD, State) -> {mochihex:to_hex(erlang:phash2(State)), RD, State}. last_modified(RD, State) -> {filelib:last_modified(State#s.fpath), RD, State}.

Just add generate_etag or last_modified...

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A resource family is just a set of functions.

to_html(ReqData,State) -> {Body,ReqData,State}. generate_etag(ReqData,State) -> {ETag,ReqData,State}. last_modified(ReqData,State) -> {Time,ReqData,State}. resource_exists(ReqData,State) -> {bool,ReqData,State}. is_authorized(ReqData,State) -> {bool,ReqData,State}. ... f(ReqData,State) -> {RetV,ReqData,State}.

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A resource family is just a set of functions.

f(ReqData,State) -> {RetV,ReqData,State}.

Resource functions are referentially transparent and have a uniform interface.

function behavior request/ response data process state + +

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A resource family is just a set of functions.

f(ReqData,State) -> {RetV,ReqData,State}.

Resource functions are referentially transparent and have a uniform interface.

function behavior request/ response data process state + +

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A resource family is just a set of functions.

f(ReqData,State) -> {RetV,ReqData,State}.

Resource functions are referentially transparent and have a uniform interface.

function behavior request/ response data process state + +

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A resource family is just a set of functions.

f(ReqData,State) -> {RetV,ReqData,State}.

Resource functions are referentially transparent and have a uniform interface.

function behavior request/ response data process state + +

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A resource family is just a set of functions.

f(ReqData,State) -> {RetV,ReqData,State}.

Resource functions are referentially transparent and have a uniform interface.

function behavior request/ response data process state + +

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Manipulating Request/Response Data

f(ReqData,State) -> {RetV,ReqData,State}.

The wrq module accesses and (nondestructively) modifies ReqData.

wrq:get_req_header(HdrName,ReqData) -> 'undefined' | HdrVal wrq:get_qs_value(Key,Default,ReqData) -> Value wrq:set_resp_header(HdrName,HdrVal,ReqData) -> NewReqData

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URL Dispatching = Pattern Matching

{["a"],some_resource,[]} pattern resource family args

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URL Dispatching = Pattern Matching

{["a"],some_resource,[]} http://myhost/a match! any other URL no match If no patterns match, then 404 Not Found. /a

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URL Dispatching = Pattern Matching

{["a"],some_resource,[]} /a wrq:disp_path wrq:path wrq:path_info wrq:path_tokens [] "/a" [] []

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URL Dispatching = Pattern Matching

{["a"],some_resource,[]} /a wrq:disp_path wrq:path wrq:path_info wrq:path_tokens [] "/a" [] [] {["a" ,some_resource,[]}

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URL Dispatching = Pattern Matching

/a wrq:disp_path wrq:path wrq:path_info wrq:path_tokens [] "/a" [] [] ,some_resource,[]} {["a"

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URL Dispatching = Pattern Matching

{["a", '*'],some_resource,[]} /a wrq:disp_path wrq:path wrq:path_info wrq:path_tokens [] "/a" [] [] (binds the remaining path) ,some_resource,[]} {["a"

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URL Dispatching = Pattern Matching

{["a", '*'],some_resource,[]} /a wrq:disp_path wrq:path wrq:path_info wrq:path_tokens “b/c” "/a/b/c" [] [“b”, “c”] /a/b/c {["a", ],some_resource,[]}

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URL Dispatching = Pattern Matching

{["a", foo],some_resource,[]} /a wrq:disp_path wrq:path wrq:path_info wrq:path_tokens “b/c” "/a/b/c" [] [“b”, “c”] /a/b/c (name-binds a path segment) 404 {["a", ],some_resource,[]}

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URL Dispatching = Pattern Matching

{["a", foo],some_resource,[]} /a wrq:disp_path wrq:path wrq:path_info wrq:path_tokens [] "/a/b" [{foo, “b”}] [] /a/b {["a", foo some_resource,[]}

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URL Dispatching = Pattern Matching

wrq:disp_path wrq:path wrq:path_info wrq:path_tokens [] "/a/b" [{foo, “b”}] [] /a/b {["a", foo some_resource,[]}

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URL Dispatching = Pattern Matching

{["a", foo, '*'],some_resource,[]} wrq:disp_path wrq:path wrq:path_info wrq:path_tokens [] "/a/b" [{foo, “b”}] [] /a/b {["a", foo some_resource,[]}

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URL Dispatching = Pattern Matching

{["a", foo, '*'],some_resource,[]} wrq:disp_path wrq:path wrq:path_info wrq:path_tokens “c/d” "/a/b/c/d" [{foo, “b”}] [“c”,”d”] /a/b/c/d /a/b

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URL Dispatching = Pattern Matching

{["a", foo, '*'],some_resource,[]} wrq:disp_path wrq:path wrq:path_info wrq:path_tokens “c/d” "/a/b/c/d" [{foo, “b”}] [“c”,”d”] /a/b/c/d

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URL Dispatching = Pattern Matching

{["a", foo, '*'],some_resource,[]} wrq:disp_path wrq:path wrq:path_info wrq:path_tokens “c/d” "/a/b/c/d" [{foo, “b”}] [“c”,”d”] /a/b/c/d

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URL Dispatching = Pattern Matching

{["a", foo, '*'],some_resource,[]} wrq:disp_path wrq:path wrq:path_info wrq:path_tokens “c/d” "/a/b/c/d" [{foo, “b”}] [“c”,”d”] /a/b/c/d query strings are easy too /a/b/c/d?fee=ah&fie=ha wrq:get_qs_value("fie","",ReqData) -> "ha"

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An Example: Wriaki

  • A wiki built on Webmachine and Riak
  • Written by Bryan Fink of Basho as a sample

application for Riak

  • Wriaki is simple and elegant
  • https://github.com/basho/wriaki

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Wriaki Web Resources

  • User resources represent wiki users
  • Articles represent wiki pages
  • Archives represent individual page versions
  • History represents a page’s history
  • Sessions track user logins

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Wriaki Dispatch Map

{["wiki"], redirect_resource, "/wiki/Welcome"}. {["wiki",'*'], wiki_resource, []}. {[], redirect_resource, "/wiki/Welcome"}. {["user"], login_form_resource, []}. {["user",name], user_resource, []}. {["user",name,session], session_resource, []}. {["static",'*'], static_resource, "www"}.

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Wriaki Dispatch Map

{["wiki"], redirect_resource, "/wiki/Welcome"}.

  • The pathspec declares the path we want

to match

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Wriaki Dispatch Map

{["wiki"], redirect_resource, "/wiki/..."}.

  • The resource module declares which Erlang

module implements the resource

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Wriaki Dispatch Map

{[...], redirect_resource, "/wiki/Welcome"}.

  • Args is a list that Webmachine provides as the

argument to the resource module’s init function upon dispatching

  • (In Erlang, a string is a list)

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Redirect Resource

  • Dispatch target for paths / and /wiki
  • Aliases those paths to /wiki/Welcome

{["wiki"], redirect_resource, "/wiki/Welcome"}. {[], redirect_resource, "/wiki/Welcome"}.

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Redirect Init

  • Called whenever a request is dispatched to

the redirect resource

  • Returns its argument as state for the

request handling process

  • Argument comes from dispatch map

init(Target) -> {ok, Target}.

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Redirection

  • Effects redirection (HTTP status 301)
  • Returns true with redirected path
  • Redirect path is the process state returned

from init

  • Location K5 on Webmachine flow diagram

moved_permanently(RD, Target) -> {{true, Target}, RD, Target}.

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Wiki Pages

  • Implemented by wiki_resource module
  • Pages must be readable (of course)
  • Must also accept POSTs for editing

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Wiki Page Init

  • Called whenever a request is dispatched to

a wiki page

  • Returns a #ctx record as process state
  • Record holds connection to Riak database

where page data, user info, etc. are stored

init([]) -> {ok, Client} = wrc:connect(), {ok, #ctx{client = Client}}.

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Allowed Methods

  • Tells Webmachine what methods a wiki

page allows

  • POST and PUT allow writes
  • Webmachine default allows only HEAD and

GET allowed_methods(RD, Ctx) -> {['HEAD','GET','POST','PUT'], RD, Ctx}.

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Accepted Content

  • Tells Webmachine what content (MIME

types) a wiki page allows

  • Also what function to call to process each

MIME type

  • Call accept_form to handle URL-encoded

data

content_types_accepted(RD, Ctx) -> MT = "application/x-www-form-urlencoded", {[{MT, accept_form}], RD, Ctx}.

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Simplicity

  • Identify the resource functions specific to

each resource module

  • Webmachine provides reasonable defaults

for all resource functions

  • Take advantage of Erlang’s “let it crash”

philosophy

  • avoid reams of (buggy, incomplete) error-

handling code

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The Webmachine Visual Debugger

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Hooray!

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But sometimes things don’t go as well.

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But sometimes things don’t go as well.

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It’s nice to know where your errors are.

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It’s nice to know where your errors are.

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wrq:path(RD) -> "/d/test?q=1.5" {{error,{error,badarg, [{erlang,list_to_integer,["1.5"]}, {some_resource,resource_exists,2}...

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malformed_request(ReqData, State) -> {case catch list_to_integer(wrq:get_qs_value("q","0",ReqData)) of {'EXIT', _} -> true; _ -> false end, ReqData, State}.

  • export([malformed_request/2]).

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malformed_request(ReqData, State) -> {case catch list_to_integer(wrq:get_qs_value("q","0",ReqData)) of {'EXIT', _} -> true; _ -> false end, ReqData, State}.

  • export([malformed_request/2]).

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Visual debugging helps you put the fixes in the right place.

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Visual debugging helps you put the fixes in the right place.

400 Bad Request

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Webmachine is a higher-level abstraction for HTTP .

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Webmachine is a higher-level abstraction for HTTP .

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Webmachine is not a “framework.”

No built-in templating, no ORM or built-in storage. Webmachine is a good component in a framework.

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Webmachine is not an all-purpose network server.

No support for arbitrary sockets, etc. Webmachine is shaped like HTTP .

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Webmachine is

A toolkit for easily creating well-behaved HTTP systems.

a resource server for the Web.

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Webmachine is sincerely flattered.

dj-webmachine: clothesline: lemmachine: nodemachine: webmachine-ruby: Django/Python Clojure Agda JavaScript Ruby

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Webmachine

a practical executable model for HTTP http://webmachine.basho.com/

Steve Vinoski

vinoski@ieee.org

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