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Example resources for Webmachine ( This project contains several sample webmachine resources that I've posted elsewhere at various times. This is a complete Webmachine app ready to be run and examined.

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Title: README for wmexamples
Author: Bryan Fink
Source URL:
Created: 2009.May.18

wmexamples is a demonstration Webmachine application.  It contains a
handful of Webmachine resources that I have posted elsewhere, but have
chosen to assembled here to show off.  To run this application, you'll

- Erlang -
- Git -


Checkout/unpack wmexamples.

cd wmexamples

If everything makes fine, run ./ or ./, then point
curl or a browser at http://localhost:8000.  You should get a "Hello,
new world" message back.

Example Resources

The best place to determine what resources are enabled is in
priv/dispatch.conf.  That file describes the dispatch table for this
Webmachine application, and also contains helpful comments.  Other
short descriptions of what examples are included are below.

CouchDB Proxy Resource

couchdb_proxy.erl describe a proxy resource for exposing raw CouchDB
through a webmachine app.  It does very minimal request processing -
only fixing Location headers such that clients of the webmachine
resource direct their requests properly.

To use couchdb_proxy.erl in your own application, copy the file to
your application's src tree, and also make sure the ibrowse is started
before any requests are made to the resource (wmexamples starts
ibrowse at startup in wmexamples.erl).

Environment Variable Resource

env_resource.erl was a sample resource for demonstrating
implementations of several Webmachine resource functions.  The goal of
this resource was to expose the ability to inspect and modify
OS-environment variables.

The story of env_resource's development is available in five blog
posts starting at

Sample Trace Resource

The Webmachine trace utility is available at
http://localhost:8000/wmtrace/ while this application is running.

Four example trace files have been included in the "traces" directory.
They are named example-trace-CODE.wmtrace, where CODE is the HTTP
status code the resource returned at the end of the request.

The sample trace files were generated with the sampletrace_resource,
which is included and exposed at http://localhost:8000/sampletrace
That resource isn't good for much other than generating those simple
examples, but I thought it best to include it for demonstration

POST Example (wwwform -> json)

formjson_resource.erl is mainly an example of how one might handle a
POST in a webmachine resource.  process_post/2 demonstrates how to
grab the request body out of the ReqData (wrq:req_body/1), and push a
response body into one (wrq:append_to_response_body/2).

Issuing a GET to formjson_resource will encode the query parameters of
the request as JSON, and return that encoding in the response body.

Issuing a POST to formjson_resource will assume that the body of the
request is application/x-www-form-urlencoded data, re-ecode it as
JSON, and return that JSON in the response body.

Dispatch Reloader

dispatch_watcher.erl defines a gen_server that can be started in the
background, and will watch dispatch.conf for changes, reloading it
when necessary.

By default, it checks "priv/dispatch.conf" for updates once a second.
This behavior can be changed by passing the configuration parameters:

  {dispatch, Path}: where Path is a string describing the path of an
                    alternate dispatch file
  {interval, Time}: where Time is an integer number of milliseconds
                    describing how long to wait between checks for
                    updates to the dispatch file

wmexamples starts dispatch_watcher by including a supervisor child
specification in the return value of wmexamples_sup:init/1.  It could
be started instead by appending "-s dispatch_watcher" to the final
command of, to get a dev-vs-production kind of


Example resources for Webmachine ( This project contains several sample webmachine resources that I've posted elsewhere at various times. This is a complete Webmachine app ready to be run and examined.



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