以官方文檔中的第7章為起點.
# 7.2 The Testing Skeleton.
import os
import flaskr
import unittest
import tempfile
class FlaskTestCase(unittest.TestCase):
def setUp(self):
self.db_fd, flaskr.app.config['DATABASE'] = tempfile.mkstemp()
flaskr.app.config['TESTING'] = True
self.app = flaskr.app.test_client()
with flaskr.app.app_context():
flaskr.init_db()
def tearDown(self):
os.close(self.db_fd)
os.unlink(flaskr.app.config['DATABASE'])
if __name__ == '__main__':
unittest.main()
下面我們看一下self.app = flaskr.app.test_client()這行代碼到底是干什么的.
# app.py
def test_client(self, use_cookies=True, **kwargs):
cls = self.test_client_class
if cls is None:
from flask.testing import FlaskClient as cls
return cls(self, self.response_class, use_cookies=use_cookies, **kwargs)
默認的test_client_class為None.所以看FlaskClient. FlaskClient繼承自Werkzeug.test中的Client，但是額外附帶了一些方法.
with flaskr.app.app_context(): flaskr.init_db() 中的app_context()方法已經(jīng)剖析過了：一個AppContext中含有app, url_adapter, g. 既然創(chuàng)建的AppContext含有g(shù)變量，那么flaskr.init_db()就可以順利的通過執(zhí)行了。
在7.8節(jié)的Keeping the Context Around有小段代碼：
app = flask.Flask(__name__)
with app.test_client() as c:
rv = c.get('/?tequila=42')
assert request.args['tequila'] == '42'
我們來看看flask是如何保持request可以正常工作而不是發(fā)出'Working outside of request context.'的錯誤.
在app.test_request_context():...中，很顯然的RequestContext被push了。但是app.test_client()卻繞了一下彎，不是那么明顯.
# testing.py
def __enter__(self):
if self.preserve_context:
raise RuntimeError('Cannot nest client invocations')
self.preserve_context = True
return self
在enter函數(shù)中, 將self.preserve_context設(shè)置為True. 并返回FlaskClient實例.FlaskClient繼承自Werkzeug中的Client.
# test.py in Werkzeug.
def get(self, *args, **kw):
"""Like open but method is enforced to GET."""
kw['method'] = 'GET'
return self.open(*args, **kw)
當(dāng)我們使用c.get('/?tequila=42')調(diào)用get方法時，實際上是return self.open(*args, **kw).
def open(self, *args, **kwargs):
kwargs.setdefault('environ_overrides', {}) \
['flask._preserve_context'] = self.preserve_context
as_tuple = kwargs.pop('as_tuple', False)
buffered = kwargs.pop('buffered', False)
follow_redirects = kwargs.pop('follow_redirects', False)
builder = make_test_environ_builder(self.application, *args, **kwargs)
return Client.open(self, builder,
as_tuple=as_tuple,
buffered=buffered,
follow_redirects=follow_redirects)
FlaskClient重寫了Client中的open方法.將kwargs中的flask._preserve_context參數(shù)設(shè)置為self.preserve_context，也就是True. 緊接著kwargs被傳入make_test_environ_builder函數(shù).
def make_test_environ_builder(app, path='/', base_url=None, *args, **kwargs):
http_host = app.config.get('SERVER_NAME')
app_root = app.config.get('APPLICATION_ROOT')
if base_url is None:
url = url_parse(path)
base_url = 'http://%s/' % (url.netloc or http_host or 'localhost')
if app_root:
base_url += app_root.lstrip('/')
if url.netloc:
path = url.path
if url.query:
path += '?' + url.query
return EnvironBuilder(path, base_url, *args, **kwargs)
下面我們看看傳入make_test_environ_builder的參數(shù)都有哪些：
- app = Flask實例.
- path = '/?tequila=42'
- base_url = None
- args = ()
- kwargs = {'method': 'GET', 'environ_overrides': {'flask._preserve_context': True}}
make_test_environ_builder返回EnvironBuilder. 傳入EnvironBuilder的參數(shù)除了base_url變?yōu)?http://localhost'， 其它都沒有變.返回一個EnvironBuilder.示例.
接下來調(diào)用Client.open(...)，在Clien.open()函數(shù)中，我們主要看builder中的kwargs中的'flask._preserve_context'是怎么傳入到wsgi_app中的。
# test.py in Werkzeug.
def open(self, *args, **kwargs):
as_tuple = kwargs.pop('as_tuple', False)
buffered = kwargs.pop('buffered', False)
follow_redirects = kwargs.pop('follow_redirects', False)
environ = None
if not kwargs and len(args) == 1:
if isinstance(args[0], EnvironBuilder):
# 在此處獲得builder中的environ.
environ = args[0].get_environ() #<---
elif isinstance(args[0], dict):
environ = args[0]
if environ is None:
builder = EnvironBuilder(*args, **kwargs)
try:
environ = builder.get_environ()
finally:
builder.close()
# 在此處開始run_wsgi_app 并獲得response.
response = self.run_wsgi_app(environ, buffered=buffered) # <---
# handle redirects
redirect_chain = []
while 1:
status_code = int(response[1].split(None, 1)[0])
if status_code not in (301, 302, 303, 305, 307) \
or not follow_redirects:
break
new_location = response[2]['location']
method = 'GET'
if status_code == 307:
method = environ['REQUEST_METHOD']
new_redirect_entry = (new_location, status_code)
if new_redirect_entry in redirect_chain:
raise ClientRedirectError('loop detected')
redirect_chain.append(new_redirect_entry)
environ, response = self.resolve_redirect(response, new_location,
environ,
buffered=buffered)
if self.response_wrapper is not None:
# 對response進行包裝.
response = self.response_wrapper(*response) # <---
if as_tuple:
return environ, response
return response # <---
在self.run_wsgi_app中, ’flask._preserve_context‘就包含在environ中.
def run_wsgi_app(app, environ, buffered=False):
environ = _get_environ(environ)
response = []
buffer = []
...
app_rv = app(environ, start_response) # <---
...
現(xiàn)在回過頭來，我們又進入了熟悉的Flask.wsgi_app(...)的處理流程中.
def wsgi_app(self, environ, start_response):
ctx = self.request_context(environ)
ctx.push()
...
finally:
if self.should_ignore_error(error):
error = None
ctx.auto_pop(error) # <---
wsgi_app最后會自動pop ctx.下面我們仔細分析一下相關(guān)代碼:
def auto_pop(self, exc):
if self.request.environ.get('flask._preserve_context') or \
(exc is not None and self.app.preserve_context_on_exception):
self.preserved = True
self._preserved_exc = exc
else:
self.pop(exc)
于是就真相大白了，原理auto_pop首行代碼就是判斷request.environ中是否有'flask._preserve_context'變量，另外兩個判斷條件可能與調(diào)試相關(guān)，暫時忽略.于是self.preserved = True. 當(dāng)然， 也就不會執(zhí)行self.pop(exc)了.不執(zhí)行的結(jié)果就是，RequestContext仍然保存在_request_ctx_stack上面， 當(dāng)然也就可以正常獲取request.args['tequila']的值，而不會出現(xiàn)working outside of context 的報錯了. 那什么時候pop ctx呢? 答案在此.
# testing.py
def __exit__(self, exc_type, exc_value, tb):
# 設(shè)置preserve-context變量為False.
self.preserve_context = False
# 獲得ctx, 測試兩個條件, 立即執(zhí)行top.pop().
top = _request_ctx_stack.top
if top is not None and top.preserved:
top.pop()
到此，我們也就搞清楚了官方文檔7.8節(jié)的那段代碼的背后原理.
