Project

General

Profile

Hacking API server » History » Version 10

Tom Clegg, 05/11/2014 11:39 PM

1 1 Tom Clegg
h1. Hacking API server
2
3
{{toc}}
4
5
h2. Source tree layout
6
7
Everything is in @/services/api@.
8
9
Key pieces to know about before going much further:
10
11
|/|Usual Rails project layout|
12
|/app/controllers/application_controller.rb|Controller superclass with most of the generic API features like CRUD, authentication|
13
|/app/controllers/arvados/v1/|API methods other than generic CRUD (users#current, jobs#queue, ...)|
14
|/app/models/arvados_model.rb|Default Arvados model behavior: permissions, etag, uuid|
15
16
h2. Unlike a typical Rails project...
17
18
* Most responses are JSON. Very few HTML views. We don't normally talk to browsers, except during authentication.
19
* We assign UUID strings (see lib/assign_uuid.rb and app/models/arvados_model.rb)
20
* The @Links@ table emulates a graph database a la "RDF":http://www.rdfabout.com/quickintro.xpd. Much of the interesting information in Arvados is recorded as a Link between two other entities.
21
* For the most part, relations among objects are not expressed with the usual ActiveRelation features like belongs_to and has_many.
22
* Permissions: see below.
23
24
h2. Running in development mode
25
26
Save something like this at @~/bin/apiserver@, make it executable, make sure ~/bin is in your path:
27
28 7 Tom Clegg
<pre>
29
#!/bin/sh
30 1 Tom Clegg
set -e
31
cd ~/arvados/services/api
32 7 Tom Clegg
if ! [ -e self-signed.key ]
33
then
34 8 Tom Clegg
  # Generate a self-signed SSL key
35
  openssl req -new -x509 -nodes -out ./self-signed.pem -keyout ./self-signed.key -days 3650 -subj /CN=localhost
36 7 Tom Clegg
fi
37
if [ -e /usr/local/rvm/bin/rvm ]
38
then
39
  rvmexec="rvm-exec 2.1.1"
40
else
41
  rvmexec=""
42
fi
43
export ARVADOS_WEBSOCKETS=true
44 1 Tom Clegg
export RAILS_ENV=development
45 7 Tom Clegg
$rvmexec bundle install
46
exec $rvmexec bundle exec passenger start -d -p3030 --ssl --ssl-certificate self-signed.pem --ssl-certificate-key self-signed.key
47
</pre>
48 1 Tom Clegg
49 9 Tom Clegg
Notes:
50
* Here we use passenger instead of webrick (which is what we'd get with "@rails server@") in order to serve websockets from the same process as https. (You also have the option of serving https and wss from separate processes -- see @services/api/config/application.default.yml@ -- but the simplest way is to run both in the same process by setting @ARVADOS_WEBSOCKETS=true@.)
51
* Webrick can make its own self-signed SSL certificate, but passenger expects you to provide a certificate & key yourself. The above script generates a key/certificate pair the first time it runs, and leaves it in @services/api/self-signed.*@ to reuse next time.
52
* @bundle install@ ensures your installed gems satisfy the requirements in Gemfile and (if you have changed it locally) update Gemfile.lock appropriately. This should do the right thing after you change Gemfile yourself, or change Gemfile/Gemfile.lock by updating/merging master.
53
* If you're relying on rvm to provide a suitable version of Ruby, "@rvm-exec@" should do the right thing here. You can change the @2.1.1@ argument to the version you want to use (hopefully >= 2.1.1). If your system Ruby is >= 2.1.1, rvm is unnecessary.
54
55
56 1 Tom Clegg
h2. Headaches to avoid
57
58
If you make a change that affects the discovery document, you need to clear a few caches before your client will see the change.
59
* Restart API server or: @touch tmp/restart.txt@
60
* Clear API server disk cache: @rake tmp:cache:clear@
61
* Clear SDK discovery doc cache on client side: @rm -r ~/.cache/arvados/@
62 4 Tom Clegg
63
Do not store symbol keys (or values) in serialized attributes.
64
* Rails supplies @params@ as a HashWithIndifferentAccess so @params['foo']@ and @params[:foo]@ are equivalent. This is usually convenient. However, here we often copy arrays and hashes from @params@ to the database, and from there to API responses. JSON does not have HashWithIndifferentAccess (or symbols) and we want these serialized attributes to behave predictably everywhere.
65
* API server's policy is that serialized attributes (like @properties@ on a link) always have strings instead of symbols: these attributes look the same in the database, in the API server Rails application, in the JSON response sent to clients, and in the JSON objects received from clients.
66
* There is no validation (yet!) to check for this.
67
68 1 Tom Clegg
69
h2. Features
70
71
h3. Authentication
72
73
Involves
74
* UserSessionsController (in app/controllers/, not .../arvados/v1): this is an exceptional case where we actually talk to a browser.
75
76
h3. Permissions
77
78
Object-level permissions, aka ownership and sharing
79
* Models have their own idea of create/update permissions. Controllers don't worry about this.
80
* ArvadosModel updates/enforces modified_by_* and owner_uuid
81
* Lookups are not (yet) permission-restricted in the default scope, though. Controllers need to use Model.readable_by(user).
82
* ApplicationController uses an around_filter that verifies the supplied api_token and makes current_user available everywhere. If you need to override create/update permissions, use @act_as_system_user do ... end@.
83
* Unusual cases: KeepDisks and Collections can be looked up by inactive users (otherwise they wouldn't be able to read & clickthrough user agreements).
84
85
Controller-level permissions
86
* ApplicationController#require_auth_scope_all checks token scopes: currently, unless otherwise specified by a subclass controller, nothing is allowed unless scopes includes "all".
87
* ApplicationController has an admin_required filter available (not used by default)
88
89
h3. Error handling
90
91
* "Look up object by uuid, and send 404 if not found" is enabled by default, except for index/create actions.
92
93
h3. Routing
94
95
* API routes are in the @:arvados@ &rarr; @:v1@ namespace.
96
* Routes like @/jobs/queue@ have to come before @resources :jobs@ (otherwise @/jobs/queue@ will match @jobs#get(id=queue)@ first). (Better, we should rearrange these to use @resources :jobs do ...@ like in Workbench.)
97
* We use the standard Rails routes like @/jobs/:id@ but then we move params[:id] to params[:uuid] in our before_filters.
98
99
h3. Tests
100
101 10 Tom Clegg
* Run tests with @rvm-exec 2.1.1 bundle exec rake test@
102
* If prompted, migrate your test database by running @RAILS_ENV=test rvm-exec 2.1.1 bundle exec rake db:migrate@
103
* As above, you can leave out @rvm-exec 2.1.1@ if your system Ruby version is suitable. But don't leave out @bundle exec@.
104
* Run just the unit tests with @[...] rake test:units@ (or @test:functionals@ or @test:integration@).
105
* Run just a single test class (file) by specifying the file, like @[...] rake TEST=test/unit/owner_test.rb@ (save time in your "did that fix the failing test?" phase!)
106 1 Tom Clegg
* Functional tests need to authenticate themselves with @authorize_with :active@ (where @:active@ refers to an ApiClientAuthorization fixture)
107 10 Tom Clegg
* There is a deficit of tests, especially unit tests. This is a bug! It doesn't mean we don't want to test things.
108
109 1 Tom Clegg
110
h3. Discovery document
111
112
* Mostly, but not yet completely, generated by introspection (descendants of ArvadosModel are inspected at run time). But some controllers/actions are skipped, and some actions are renamed (e.g., Rails calls it "show" but everyone else calls it "get").
113
* Handled by Arvados::V1::SchemaController#index (used to be in #discovery_document before #1750). See @config/routes.rb@
114
* Must be available to anonymous clients.
115
* Has no tests! We test it by trying all of our SDKs against it.
116
117
h2. Development patterns
118
119
h3. Add a model
120
121
In shell:
122
* @rails g model FizzBuzz@
123
124
In @app/models/fizzbuzz.rb@:
125
* Change base class from @ActiveRecord::Base@ to @ArvadosModel@.
126
* Add some more standard behavior.
127
128
<pre><code class="ruby">
129
include AssignUuid
130
include KindAndEtag
131
include CommonApiTemplate
132
</code></pre>
133
134
In @db/migrate/{timestamp}_create_fizzbuzzes.rb@:
135
* Add the generic attribute columns.
136
* Run @t.timestamps@ and add (at least!) a @:uuid@ index.
137
138
<pre><code class="ruby">
139
class CreateFizzBuzz < ActiveRecord::Migration
140
  def change
141
    create_table :fizzbuzzes do |t|
142
      t.string :uuid, :null => false
143
      t.string :owner_uuid, :null => false
144
      t.string :modified_by_client_uuid
145
      t.string :modified_by_user_uuid
146
      t.datetime :modified_at
147
      t.text :properties
148
149
      t.timestamps
150
    end
151
    add_index :humans, :uuid, :unique => true
152
  end
153
end
154
</code></pre>
155
156
Apply the migration:
157
* @rake db:migrate@
158
* @RAILS_ENV=test rake db:migrate@ (to migrate your test database too)
159
* Inspect the resulting @db/schema.rb@ and include it in your commit.
160
* Don't forget to @git add@ the new migration and model files.
161
162
h3. Add an attribute to a model
163
164
* Generate migration as usual
165
<pre>
166
rails g migration AddBazQuxToFooBar baz_qux:column_type_goes_here
167
</pre>
168
* Consider adding null constraints and a default value to the @add_column@ statement in the migration in @db/migrate/timestamp_add_baz_qux_to_foo_bar.rb@:
169
<pre><code class="ruby">, null: false, default: false</code></pre>
170
* Consider adding an index
171
* You probably want to add it to the API response template so clients can see it: @app/models/model_name.rb@ &rarr; @api_accessible :user ...@
172
* Sometimes it's only visible to privileged users; see @ping_secret@ in @app/models/keep_disk.rb@
173
* If it's a serialized attribute, add @serialize :the_attribute_name, Hash@ to the model. Always specify Hash or Array!
174 3 Tom Clegg
* Run @rake db:migrate@ and inspect your @db/schema.rb@ and include the new @schema.rb@ in the *same commit* as your @db/migrate/*.rb@ migration script.
175 1 Tom Clegg
* Run @rake tmp:cache:clear@ and @touch tmp/restart.txt@ in your dev apiserver, to force it to generate a new REST discovery document.
176
177
178
h3. Add a controller
179
180
* @rails g controller Arvados::V1::FizzBuzzesController@
181
* Avoid adding top-level controllers like @app/controllers/fizz_buzzes_controller.rb@.
182
* Avoid adding top-level routes. Everything should be in @namespace :arvados@ &rarr; @namespace :v1@ except oddballs like login/logout actions.
183
184
h3. Add a controller action
185
186
Add a route in @config/routes.rb@.
187
* Choose an appropriate HTTP method: GET has no side effects. POST creates something. PUT replaces/updates something.
188
* Use the block form:
189
<pre><code class="ruby">
190
resources :fizz_buzzes do
191
  # If the action operates on an object, i.e., a uuid is required,
192
  # this generates a route /arvados/v1/fizz_buzzes/{uuid}/blurfl
193
  post 'blurfl', on: :member
194
  # If not, this generates a route /arvados/v1/fizz_buzzes/flurbl
195
  get 'flurbl', on: :collection
196
end
197
</code></pre>
198
199
In @app/controllers/arvados/v1/fizz_buzzes_controller.rb@:
200
201
* Add a method to the controller class.
202
* Skip the "find_object" before_filters if it's a collection action.
203
* Specify required/optional parameters using a class method @_action_requires_parameters@.
204
<pre><code class="ruby">
205
skip_before_filter :find_object_by_uuid, only: [:flurbl]
206
skip_before_filter :render_404_if_no_object, only: [:flurbl]
207
208
def blurfl
209
  @object.do_whatever_blurfl_does!
210
  show
211
end
212
213
def self._flurbl_requires_parameters
214
  {
215
    qux: { type: 'integer', required: true, description: 'First flurbl qux must match this qux.' }
216
  }
217
end
218
def flurbl
219
  @object = model_class.where('qux = ?', params[:qux]).first
220
  show
221
end
222
</code></pre>
223
224
h3. Add a configuration parameter
225 6 Tom Clegg
226 1 Tom Clegg
* Add it to @config/application.default.yml@ with a sensible default value. (Don't fall back to default values at time of use, or define defaults in other places!)
227
* If there is no sensible default value, like @secret_token@: specify @~@ (i.e., nil) in @application.default.yml@ *and* put a default value in the @test@ section of @config/application.yml.example@ that will make tests pass.
228
* If there is a sensible default value for development/test but not for production, like return address for notification email messages, specify the test/dev default in the @common@ section @application.default.yml@ but specify @~@ (nil) in the @production@ section. This prevents someone from installing or *updating a production server* with defaults that don't make sense in production!
229 6 Tom Clegg
* Use @Rails.configuration.config_setting_name@ to retrieve the configured value. There is no need to check whether it is nil or missing: in those cases, "rake config:check" would have failed and the application would have refused to start.
230 2 Tom Clegg
231
232
h3. Add a test fixture
233
234
Generate last part of uuid from command line:
235
<pre><code class="ruby">ruby -e 'puts rand(2**512).to_s(36)[0..14]'
236
j0wqrlny07k1u12</code></pre>
237
Generate uuid from @rails console@:
238
<pre><code class="ruby">Group.generate_uuid
239
=> "xyzzy-j7d0g-8nw4r6gnnkixw1i"
240 1 Tom Clegg
</code></pre>