µWeb

h1. Request

{{>toc}}

The @Request@ object is an abstraction of the incoming HTTP request. This allows one simple interface that is independent of the underlying server that µWeb runs on (either [[Standalone]] using BaseHTTPServer, or [[Apache]] mode on @mod_python@).

From PageMaker methods, the request object is accessible as the @self.req@ member. The request object contains all the information about the incoming request: query arguments, post data, cookies and environment data. It is also the object where you define cookies that need to be provided to the client.

h1. Query arguments

All query arguments provided by the client are present on the request object. They are also accessible directly on the [[PageMaker]] object. The following code demonstrates both ways to access a query argument:

<pre><code class="html">

...

<form>

  <label for="name">Name: </label><input id="name" name="name" />

  <input type="submit" value="Tell us your name" />

</form>

...

</code></pre>

<pre><code class="python">

def NameFromQuery(self):

  # Retrieves the 'name' argument from the request object:

  name = self.req.vars['get'].getfirst('name')

  # Retrieves the 'name' argument directly from the PageMaker instance (linked to the request):

  name = self.get.getfirst('name')

  return name

</code></pre>

Using the @getfirst@ method, you get a single string returned from the query argument mapping, or a @None@ if no such value exists. Much like a dictionary's @get@ method, you can provide a second argument to the method, and have that returned instead as the default. 

Now, HTTP allows the client to provide the same query argument multiple times. Using @getfirst@ you would only get the very first defined argument. So a request that looks like @http://example.org/group?name=Bob&name=Mark&name=Jenny@ would only return 'Bob' in the previous example. To get all their names printed, you can use the following:

<pre><code class="html">

...

<form action="/group">

  <h2>Names in this group</h2>

  <!-- These would likely be generated with Javascript, but written here for demonstrative purposes -->

  <label for="name_1">Name: </label><input id="name_1" name="name" />

  <label for="name_2">Name: </label><input id="name_2" name="name" />

  <label for="name_3">Name: </label><input id="name_3" name="name" />

  <input type="submit" value="Send these names" />

</form>

...

</code></pre>

<pre><code class="python">

def MemberNames(self):

  names = self.get.getlist('name')

  return ', '.join(names)

</code></pre>

This returns a neat comma-separated string with all the provided names. The @getlist@ method does not take a default, but will instead return an empty list when there are no values for the requested argument name.

h1. Post data

Submitted form data is available on the request object as well. The interface is similar to that of the query arguments, and the @FieldStorage@ class already present in the @cgi@ module. If we take our initial example form handler, but now receive the data through HTTP POST, the code would look like this:

<pre><code class="html">

...

<form method="post">

  <label for="name">Name: </label><input id="name" name="name" />

  <input type="submit" value="Tell us your name" />

</form>

...

</code></pre>

<pre><code class="python">

def NameFromPost(self):

  # Retrieves the 'name' value from the request object:

  name = self.req.vars['post'].getfirst('name')

  # Retrieves the 'name' value directly from the PageMaker instance (linked to the request):

  name = self.post.getfirst('name')

  return name

</code></pre>

Like with the query arguments, @getfirst@ accepts a second argument that provides a default other than @None@.

Multiple values are again possible in the FieldStorage, and these work similar to how they do in query arguments:

<pre><code class="html">

...

<form action="/group" method="post">

  <h2>Names in this group</h2>

  <!-- These would likely be generated with Javascript, but written here for demonstrative purposes -->

  <label for="name_1">Name: </label><input id="name_1" name="name" />

  <label for="name_2">Name: </label><input id="name_2" name="name" />

  <label for="name_3">Name: </label><input id="name_3" name="name" />

  <input type="submit" value="Send these names" />

</form>

...

</code></pre>

<pre><code class="python">

def MemberNames(self):

  names = self.post.getlist('name')

  return ', '.join(names)

</code></pre>

h2. Uploading files

Processing an uploaded file is done using the the same @FieldStorage@ system as the rest of the POST data, and roughly looks like the following. When performing file uploads, be sure to define the @enctype@ of your form, or the uploaded file will have no contents.

<pre><code class="html">

...

<form method="post" enctype="multipart/form-data">

  <label for="avatar">Avatar: </label><input id="avatar" name="avatar" type="file" />

  <input type="submit" value="submit!" />

</form>

...

</code></pre>

<pre><code class="python">

def UpdateAvatar(self):

  # Retrieve the currently logged-in user

  user = self.GetCurrentUser()

  # This gets the name of the file that was uploaded

  avatar_name = self.post['avatar'].filename

  # This retrieves the content of the uploaded file, 

  avatar_data = self.post['avatar'].value

  self.SaveAvatar(user, avatar_data)

  return 'Your avatar has been replaced by %r' % avatar_name

</code></pre>

h2. Structured data using POST

One of the things that has been extended on the basic @FieldStorage@ in µWeb is the way it treats square backets ( [ and ] ) in POST data. A form field with the name @person[name]@ will result in a dictionary @person@ being created in the resulting @FieldStorage@:

<pre><code class="html">

...

<form method="post">

  <label for="name">Name: </label><input id="name" name="person[name]" />

  <label for="age">Age: </label><input id="age" name="person[age]" />

  <label for="job">Job: </label><input id="job" name="person[job]" />

  <input type="submit" value="Update your profile" />

</form>

...

</code></pre>

<pre><code class="python">

def PersonalData(self):

  person = self.post.getfirst('person')

  return uweb.Response(json.dumps(person), content_type="application/json")

</code></pre>

In the above code here, the @person@ variable is a dictionary retrieved from the POST data, which is then presented to the client in JSON, by using a custom [[Response|repsonse]].

Note that the 'numeric' age value is a string. This is of course because everything submitted in forms is in the form of a string. Conversion to appropriate types will have to be handled by the [[PageMaker]]. The @person@ dictionary itself looks like this:

<pre><code class="python">

{'age': '28', 'job': 'Engineer', 'name': 'Elmer'}

</code></pre>

*N.B.:* When using structured form data, you still need to use the @getfirst@ method, because there might me separate (non-dictionary) values for the form name. There will never be more than one dictionary in the form values; if a single key is set more than once, the last-set value will be the one present in the dictionary.

h1. Cookies

h2. Reading cookies

Cookies provided by the client will also end up in the request object. They are both present on the request itself, as @self.req.vars['cookies']@, or through the @PageMaker@ instance itself as @self.cookies@ (both are from the scope of the PageMaker instance).

The cookie storage itself is a plain Python dictionary, which makes for particularly easy access. 

<pre><code class="python">

def CookieInfo(self):

  sample = self.cookies['sample']

  return 'The sample cookie is set to %r' % sample

</code></pre>

Cookies cannot be set by using this dictionary though, for that the @AddCookie@ method is required:

h2. Setting cookies

Response cookies are set using the request object. The method to use for this is @AddCookie@, the easiest use of which looks like this:

<pre><code class="python">

def SetCookie(self):

  self.req.AddCookie('example', 'this is an example cookie value set by µWeb')

  return 'A cookie named "example" was set.'

</code></pre>

This creates a cookie that does not expire, will be provided with every request to the originating domain, and can be read from Javascript. To change these default behaviors, there are a number of optional arguments that can be provided, as detailed below. Of course, while the examples show one argument used at a time, they can all be combined:

<pre><code class="python">

def ShortLivedCookie(self):

  """Sets an expiry time of the cookie, in this case 10 seconds."""

  self.req.AddCookie('quick', 'I will be gone soon', max_age=10)

def SecureCookie(self):

  """Sets a cookie with the 'secure' flag enabled.

  This means the cookie will only be provided with requests that the browser

  considers secure. This typically means they will only be present in requests

  that use SSL (https://).

  """

  self.req.AddCookie('secret', 'This server adores you', secure=True)

def HttpOnlyCookie(self):

  """Sets a cookie that is only transferred in HTTP requests.

  The cookie will not be readable from Javascript. This defaults to False.

  """

  self.req.AddCookie('secret', 'Please no Javascript', httponly=True)

def PathBoundCookie(self):

  """Sets a cookie that is is only valid for the path '/admin'.

  This means that the client (browser) will only provide it for requests

  that go to '/admin' or a deeper nested path (such as '/admin/users'

  but will not be provided for requests that go to '/blog'

  """

  self.req.AddCookie('user', 'bobbytables', path='/login')

def DomainBoundCookie(self):

  """Sets a cookie that is is only valid for the specified domain.

  By default, if a cookie is set for 'www.example.com' it will not be provided

  for requests that go to 'example.com' itself. If we set the cookie to be valid

  for '.domain.com', it will be valid for domain.com and all sub-domains.

  Explicitly specified domains MUST begin with a dot, or they will be rejected

  as per RFC2109. Additionally, cookies set by 'x.y.example.com' MAY NOT set

  their valid domain to be '.example.com' or they will be rejected.

  If the 'domain' is not specified, the cookie will be valid for the domain that

  set the cookie (as per HTTP_HOST from the environment)

  """

  self.req.AddCookie('session', 'SMqfUYLk3vCjkWL6', domain='.example.com')

</code></pre>

h1. Headers

h2. Incoming headers

Request headers are made available in the @headers@ member of the request object. This works like a regular dictionary (though writing to this dictionary is not guaranteed to be successful), where all the keys are in lower-case. The @get@ method works to retrieve the header, with an optional default if the header wasn't provided by the client.

<pre><code class="python">

def Headers(self):

  # Hostname that the client (browser) requested:

  host = self.req.headers['host']

  # Retrieves the user-agent from the request

  user_agent = self.req.headers.get('user-agent', 'unknown')

  return 'The host %r was visited by the user-agent identified as %r.' % (host, user_agent)

</code></pre>

h2. Outgoing headers

*While it is possible to provide response headers via the @Request@ object, it is strongly advised to provide them using the [[Response]] object. This generally leads to clearer code, and has less caveats than using the methods laid out below.*

Adding headers to outgoing responses can be done using the @AddHeader@ method of the request object. Please note that cookies can be set more easily (as described [[Request#Setting cookies|above]]), as well as creating [[Response#Redirect|redirects]]. Responding with a custom content-type and HTTP status code will be explained below. Setting your own headers, for example to provide ETags, is done like this:

<pre><code class="python">

def TaggedResponse(self, content):

  self.req.AddHeader('ETag', hashlib.sha1(conten).hexdigest())

  return content

</code></pre>

The above example returns a simple ETag based on the "SHA-1 hash":http://en.wikipedia.org/wiki/SHA-1 of the content returned. 

h3. Content-type

The content-type of the reply would usually be configured by returning a custom [[Response]] object. When it is not desirable to use this, the content-type can be set using the @SetContentType@ method of the request object:

<pre><code class="python">

def CustomContent(self):

  with file('lolcat.jpg') as image:

    self.req.SetContentType('image/jpeg')

    return image.read()

</code></pre>

*N.B.:* Note that returning a @Response@ object will override the content-type set on the @request@ object. That is, _returning the image in the example above using @Response@ (without the @content-type@ defined there) will create a response with the default @text/html@ content-type._

h3. HTTP Response code

The HTTP response code on the webserver reply can also be set directly on the @request@ object when a full @Response@ object is for any reason not desirable:

<pre><code class="python">

def FourOhFour(self, path):

  self.req.SetHttpCode(404)

  return "Sorry, we don't have a page that looks like %r" % path

</code></pre>

*N.B.:* Note that returning a @Response@ object will override the HTTP status code set on the @request@ object. That is, _using a Response object in the example above (without providing the @httpcode@ argument) will return a HTTP 200 OK response._

h1. Environment

The request object also has available a number of environment variables. This is a dictionary that exists as the @env@ member of the request object. By default a number of commonly used (or useful) variables will be available, as well as all the HTTP request headers. These latter ones will be prefixed 'HTTP_', and all dashes will be converted to underscores, such that @Content-type@ becomes @HTTP_CONTENT_TYPE@. The other variables are explained below:

|_.Header |_.Meaning |

| CONTENT_LENGTH | The length of the HTTP POST data. Value default to 0 if no POST has been performed. |

| CONTENT_TYPE | The content-type of the HTTP POST data, or empty string. |

| HTTP_HOST | The host that the client is requesting (e.g. _underdark.nl_). |

| HTTP_REFERER | The URL from where people were linked to this page, where provided by the client. |

| HTTP_USER_AGENT | Browser identification string of the client. |

| PATH_INFO | Path portion of the request URL (e.g. _/admin/login_). |

| QUERY_STRING | The raw string of query arguments as received by the server (before parsing, refer to [[Request#Query arguments|query arguments]] for an easier interface). |

| REMOTE_ADDR | The client's network address (IPv4 or IPv6, whichever is provided by the underlying system). |

| REQUEST_METHOD | The request method. Typically one of @GET@, @HEAD@ or @POST@. |

| UWEB_MODE | This is the operational method of µWeb, which is either @STANDALONE@ or @MOD_PYTHON@. |

h2. Extended environment

If more information is required, the environment dictionary can be extended with a number of additional points of information. This can be done by calling the @ExtendedEnvironment@ method. This will expand the environment dictionary, and for the benefit of the caller, return it as well. Note that calling this routinely might significantly reduce performance, as extending the environment will among things, perform reverse-DNS lookups.

The additional values are the following:

|_.Header |_.Meaning |

| DOCUMENT_ROOT | Working directory of the web server (for the given @VirtualHost@ if running on Apache). |

| RAW_REQUEST | Raw HTTP request as received by the server, before any parsing. |

| REMOTE_HOST | Fully Qualified Domain Name of the client, checked using DNS. |

| SERVER_NAME | Local machine name of the computer running the web server. |

| SERVER_PORT | Listening port of the web server. |

| SERVER_LOCAL_NAME | The FQDN name of the server as known to the web server (Apache @VirtualHost@ affects this). |

| SERVER_LOCAL_IP | The local IP that the server runs on. If the server has multiple IPs configured, the one used to connect to the client will be present here. |

| SERVER_PROTOCOL | The protocol used for the current connection. Typically @HTTP/1.0@ or @HTTP/1.1@. |

h3. Apache-only extended environment

Requesting @ExtendedEnvironment@ on Apache will also add the following keys to the @env@ dictionary:

|_.Header |_.Meaning |

| AUTH_TYPE | Authentication that was used. Typically one of @basic@ or @digest@. |

| CONNECTION_ID | Connection ID as provided by Apache. |

| MODPYTHON_HANDLER | Module name of the [[Request Router]] used for the site. |

| MODPYTHON_INTERPRETER | Name of the @VirtualHost@ of the requested site. |

| MODPYTHON_PHASE | Phase that @mod_python@ was in when @ExtendedEnvironment@ was called. This typically is @PythonHandler@ |

| REMOTE_USER | Username of the authenticated user (available only when using HTTP Authentication). |