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  • 4 Public Test (Beta)
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Modules, Objects and Interfaces

The code base of the Pythonic SnapSearch Client consists of four functional bundles of files, namely,

  1. main package: src/SnapSearch.
  2. test suite: tests/ and .travis.yml.
  3. documentation: docs/, examples/, LICENSE, and README.rst.
  4. distribution: MANIFEST.in and setup.py.

The main package exhibits three layers of abstraction, namely,

  1. backend service layer (SnapSearch.api): interfaces, parameters, and resource bundles for communication and data exchange with the backend service.
  2. core objects layer (SnapSearch.Client, SnapSearch.Detector, SnapSearch.Interceptor, and SnapSearch.error): framework agnostic objects and interfaces for advanced users of the client package.
  3. application bindings layer (i.e. SnapSearch.cgi and SnapSearch.wsgi): compositions and extensions of the core objects to simplify the integration of the client package with Python web applications.

The core objects are not unique to the Pythonic SnapSearch Client, the naming, functionality and interoperability of these objects are ubiquitious among all client packages of SnapSearch.

Coding Style Conventions

Design Choices

To enable the integration of SnapSearch into mainstream Python Web technologies, and to accommodate potential, future changes in SnapSearch’s backend service, we have made a number of design choices when implementating the Pythonic client package. This section explains the rationale behind these design choices.

Stateless Core Objects

The Pythonic client package decouples the three core objects, aka. Client, Detector, and Interceptor, from the incoming HTTP request. Specifically, the construction / instantiation of these three objects do NOT depend on information from a particular HTTP request. Moreover, instances of these three objects do NOT keep any internal states binding to an HTTP request.

Taking the Detector object for example, the only chance an instance of Detector ever sees an incoming HTTP request is through its __call__() method. The return value of this __call__() method is an encoded URL in case the request is eligible for interception with SnapSearch, or None otherwise.

class Detector(object):
    def __init__(self, ...):
        ...
    def __call__(self, request):
        """__call__(request) -> url or None"""

The benefit of having a stateless Detector is that, when serving multiple (and possibly concurrent) HTTP requests within a long-running server process – as is the case of WSGI web applications – all the detection tasks can be performed with a singleton Detector object. And the overhead of initializing the Detector object does not add to the response time serving each incoming HTTP request.

Backend Service Abstraction Layer

The Pythonic client package wraps the communication and data exchange with the backend service of SnapSearch in the SnapSearch.api subpackage, which forms an abstraction layer for the backend service.

This abstraction layer collects data conversion methods, protocols, parameters, and resource bundles, that are essential for invoking the backend service, yet do not need to be exposed to users of the client package.

Two pinciples were followed when designing this backend service abstraction layer.

  1. encapsulation of details: such that if the backend service ever changes, the change should be contained within the api subpackage. Namely, the core objects and the application bindings layers should be able to remain intact.
  2. preservation of information: such that if users of the client package ever need a piece of information available in the raw response from the backend service, they do not need to dig into the implimentation details of the api subpackage.

Message Extraction Decorator(s)

An intersting example practising the two design principles of the backend service abstraction layer (aka. SnapSearch.api) is the message extraction decorator defined in api.response.

The wsgi.InterceptorMiddleware and cgi.InterceptorController objects from the application bindings layer are for integrating SnapSearch with respective web applications. When the incoming HTTP request is eligible for interception (i.e. coming from a search engine robot), these two objects will send out search-engine-optimized responses from the backend service of SnapSearch.The customizable response_callback functions of respective objects are responsible for converting JSON-deserialized data structure from the backend service into valid HTTP messages (containing status code, headers, and html content).

For users not knowing the details structure of the backend’s response body, the api subpackage provides a pre-processing decorator that extracts and converts the response body into a simple dict of the form,

{
    "code": 200,
    "headers":
    [
        ["Content-Type", "html"],
        ["Date", "Thu, 13 Mar 2014 14:20:18 GMT"]
    ],
    "html": "<html><head> ... </html>"
}

And the implementation of a response_callback becomes straightforward,

import SnapSearch.api as api
@api.response.message_extractor
def response_callback(response_body):
    """Removes all HTTP headers except Location"""
    response_body['headers'] = [
        (key, val) for key, val in response_body['headers']
        if key.lower() in (b"location", )]
    return response_body

For advanced users that do need to manipulate the raw response body. They can simply remove the decorator and receive the full response body as defined in https://snapsearch.io/documentation#parameters

Test Suite

Style Checking

The preliminary form of testing is to run the pep8 tool over the source code to enforce style conformance to PEP 8.

$ pip install pep8
$ pep8 . --verbose

Unit Test

The test suite of the Pythonic SnapSearch-Client is composed of unittest (unittest2 in Python 2.6) test cases. They can be executed either directly as runnable python modules, i.e.,

$ pip install unittest2  # only if you are using python 2.6
$ python -m tests.test_detector -v

Or, invoked by third-party testing tools, such as coverage.

$ pip install coverage
$ coverage run -m tests.test_detector -v

API Credentials

Some test cases require API credentials (i.e. api_email and api_key) to access the backend service of SnapSearch. When running these test cases, there will be a prompt asking for the credentials in the form of <email>:<key>,

$ coverage run -m tests.test_client -v
test_client_init (__main__.TestClientInit) ... ok
test_client_init_external_api_url (__main__.TestClientInit) ... ok
test_client_init_external_ca_path (__main__.TestClientInit) ... ok
test_client_call_bad_api_url (__main__.TestClientMethods) ... ok
API credentials: <email>:<key>
...

The API credentials can also be specified as an environment variable, i.e.,

$ env SNAPSEARCH_API_CREDENTIALS=<email>:<key> \
> coverage run -m tests -v

Integration Test

Besides running test cases locally, the source code repository also enforces unsupervised integration test through Travis-CI. The setup script for integration test is .travis.yml.

To make API credentials available to unsupervised integration test, the environment variable SNAPSEARCH_API_CREDENTIALS is kept in .travis.yml as encrypted data.

env:
  global:
    secure: "... encrypted data ..."

For detailed instructions on how to update this encrypted data, see http://docs.travis-ci.com/user/encryption-keys/

Test Coverage

When revisions have been committed to the code base, it is important to ensure those new changes are covered by test cases. It would help to review the test coverage statistics after each coverage run, i.e.,

$ env SNAPSEARCH_API_CREDENTIALS=<email>:<key> \
> coverage run --omit ""*test*,*requests*,*curl*,*pkg*"" -m tests -v
$ coverage report -m
Name                          Stmts   Miss  Cover   Missing
-----------------------------------------------------------
src/SnapSearch/__init__          11      0   100%
src/SnapSearch/_compat           30     10    67%   37-43, 52-53, 69, 79
src/SnapSearch/api/__init__      22      0   100%
src/SnapSearch/api/backend       83     20    76%   46-73, 144-145, 153, 166-168, 175-176, 186
src/SnapSearch/api/environ       59      0   100%
src/SnapSearch/api/response      49      0   100%
src/SnapSearch/cgi               57      0   100%
src/SnapSearch/client            36      0   100%
src/SnapSearch/detector          77      0   100%
src/SnapSearch/error             15      0   100%
src/SnapSearch/interceptor       34      0   100%
src/SnapSearch/wsgi              35      0   100%
-----------------------------------------------------------
TOTAL                           508     30    94%

In case there are missing lines for modules other than _compat and api.backend (these two modules handle compatibility issues across different platforms, so the low test coverage is expected), there should be a new test case to improve the coverage.

Release

Release the source tarball to PyPI – the official Python packages index. Remember to bump the version number (or delete any previous release having the same version number).

$ python setup.py sdist upload

For further information about distributing Python modules, see http://docs.python.org/distutils/

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