Req/Resp¶

Instances of the Request and Response classes are passed into responders as the second and third arguments, respectively.

import falcon


class Resource(object):

    def on_get(self, req, resp):
        resp.body = '{"message": "Hello world!"}'
        resp.status = falcon.HTTP_200

Request¶

class falcon.Request(env, options=None)[source]¶

Represents a client’s HTTP request.

Note

Request is not meant to be instantiated directly by responders.

Parameters:	env (dict) – A WSGI environment dict passed in from the server. See also PEP-3333. options (dict) – Set of global options passed from the API handler.

protocol¶: str – Either ‘http’ or ‘https’.

method¶: str – HTTP method requested (e.g., ‘GET’, ‘POST’, etc.)

host¶: str – Hostname requested by the client

subdomain¶: str – Leftmost (i.e., most specific) subdomain from the hostname. If only a single domain name is given, subdomain will be None.

Note

If the hostname in the request is an IP address, the value for subdomain is undefined.

user_agent¶: str – Value of the User-Agent header, or None if the header is missing.

app¶: str – Name of the WSGI app (if using WSGI’s notion of virtual hosting).

env¶: dict – Reference to the WSGI environ dict passed in from the server. See also PEP-3333.

context¶: dict – Dictionary to hold any data about the request which is specific to your app (e.g. session object). Falcon itself will not interact with this attribute after it has been initialized.

context_type¶: class – Class variable that determines the factory or type to use for initializing the context attribute. By default, the framework will instantiate standard dict objects. However, You may override this behavior by creating a custom child class of falcon.Request, and then passing that new class to falcon.API() by way of the latter’s request_type parameter.

uri¶: str – The fully-qualified URI for the request.

url¶: str – alias for uri.

relative_uri¶: str – The path + query string portion of the full URI.

path¶: str – Path portion of the request URL (not including query string).

query_string¶: str – Query string portion of the request URL, without the preceding ‘?’ character.

accept¶: str – Value of the Accept header, or ‘/‘ if the header is missing.

auth¶: str – Value of the Authorization header, or None if the header is missing.

client_accepts_json¶: bool – True if the Accept header indicates that the client is willing to receive JSON, otherwise False.

client_accepts_msgpack¶: bool – True if the Accept header indicates that the client is willing to receive MessagePack, otherwise False.

client_accepts_xml¶: bool – True if the Accept header indicates that the client is willing to receive XML, otherwise False.

content_type¶: str – Value of the Content-Type header, or None if the header is missing.

content_length¶: int – Value of the Content-Length header converted to an int, or None if the header is missing.

stream¶: File-like object for reading the body of the request, if any.

Note

If an HTML form is POSTed to the API using the application/x-www-form-urlencoded media type, Falcon will consume stream in order to parse the parameters and merge them into the query string parameters. In this case, the stream will be left at EOF.

Note also that the character encoding for fields, before percent-encoding non-ASCII bytes, is assumed to be UTF-8. The special _charset_ field is ignored if present.

Falcon expects form-encoded request bodies to be encoded according to the standard W3C algorithm (see also http://goo.gl/6rlcux).

date¶: datetime – Value of the Date header, converted to a datetime instance. The header value is assumed to conform to RFC 1123.

expect¶: str – Value of the Expect header, or None if the header is missing.

range¶

tuple of int – A 2-member tuple parsed from the value of the Range header.

The two members correspond to the first and last byte positions of the requested resource, inclusive. Negative indices indicate offset from the end of the resource, where -1 is the last byte, -2 is the second-to-last byte, and so forth.

Only continous ranges are supported (e.g., “bytes=0-0,-1” would result in an HTTPBadRequest exception when the attribute is accessed.)

if_match¶: str – Value of the If-Match header, or None if the header is missing.

if_none_match¶: str – Value of the If-None-Match header, or None if the header is missing.

if_modified_since¶: str – Value of the If-Modified-Since header, or None if the header is missing.

if_unmodified_since¶: str – Value of the If-Unmodified-Sinc header, or None if the header is missing.

if_range¶: str – Value of the If-Range header, or None if the header is missing.

headers¶: dict – Raw HTTP headers from the request with canonical dash-separated names. Parsing all the headers to create this dict is done the first time this attribute is accessed. This parsing can be costly, so unless you need all the headers in this format, you should use the get_header method or one of the convenience attributes instead, to get a value for a specific header.

params¶: dict – The mapping of request query parameter names to their values. Where the parameter appears multiple times in the query string, the value mapped to that parameter key will be a list of all the values in the order seen.

options¶: dict – Set of global options passed from the API handler.

client_accepts(media_type)[source]¶

Determines whether or not the client accepts a given media type.

Parameters:	media_type (str) – An Internet media type to check.
Returns:	`True` if the client has indicated in the Accept header that it accepts the specified media type. Otherwise, returns `False`.
Return type:	bool

client_prefers(media_types)[source]¶

Returns the client’s preferred media type, given several choices.

Parameters:	media_types (iterable of str) – One or more Internet media types from which to choose the client’s preferred type. This value must be an iterable collection of strings.
Returns:	The client’s preferred media type, based on the Accept header. Returns `None` if the client does not accept any of the given types.
Return type:	str

get_header(name, required=False)[source]¶

Return a raw header value as a string.

Parameters:	name (str) – Header name, case-insensitive (e.g., ‘Content-Type’) required (bool, optional) – Set to `True` to raise `HTTPBadRequest` instead of returning gracefully when the header is not found (default `False`).
Returns:	The value of the specified header if it exists, or `None` if the header is not found and is not required.
Return type:	str
Raises:	`HTTPBadRequest` – The header was not found in the request, but it was required.

get_param(name, required=False, store=None)[source]¶

Return the raw value of a query string parameter as a string.

Note

If an HTML form is POSTed to the API using the application/x-www-form-urlencoded media type, the parameters from the request body will be merged into the query string parameters.

If a key appears more than once in the form data, one of the values will be returned as a string, but it is undefined which one. Use req.get_param_as_list() to retrieve all the values.

Note

Similar to the way multiple keys in form data is handled, if a query parameter is assigned a comma-separated list of values (e.g., ‘foo=a,b,c’), only one of those values will be returned, and it is undefined which one. Use req.get_param_as_list() to retrieve all the values.

Parameters:	name (str) – Parameter name, case-sensitive (e.g., ‘sort’). required (bool, optional) – Set to `True` to raise `HTTPBadRequest` instead of returning `None` when the parameter is not found (default `False`). store (dict, optional) – A `dict`-like object in which to place the value of the param, but only if the param is present.
Returns:	The value of the param as a string, or `None` if param is not found and is not required.
Return type:	str
Raises:	`HTTPBadRequest` – A required param is missing from the request.

get_param_as_bool(name, required=False, store=None, blank_as_true=False)[source]¶

Return the value of a query string parameter as a boolean

The following boolean strings are supported:

TRUE_STRINGS = ('true', 'True', 'yes')
FALSE_STRINGS = ('false', 'False', 'no')

Parameters:	name (str) – Parameter name, case-sensitive (e.g., ‘detailed’). required (bool, optional) – Set to `True` to raise `HTTPBadRequest` instead of returning `None` when the parameter is not found or is not a recognized boolean string (default `False`). store (dict, optional) – A `dict`-like object in which to place the value of the param, but only if the param is found (default `None`). blank_as_true (bool) – If `True`, an empty string value will be treated as `True`. Normally empty strings are ignored; if you would like to recognize such parameters, you must set the keep_blank_qs_values request option to `True`. Request options are set globally for each instance of `falcon.API` through the req_options attribute.
Returns:	The value of the param if it is found and can be converted to a `bool`. If the param is not found, returns `None` unless required is `True`.
Return type:	bool
Raises:	`HTTPBadRequest` – A required param is missing from the request.

get_param_as_int(name, required=False, min=None, max=None, store=None)[source]¶

Return the value of a query string parameter as an int.

Parameters:

name (str) – Parameter name, case-sensitive (e.g., ‘limit’).
required (bool, optional) – Set to True to raise HTTPBadRequest instead of returning None when the parameter is not found or is not an integer (default False).
min (int, optional) – Set to the minimum value allowed for this param. If the param is found and it is less than min, an HTTPError is raised.
max (int, optional) – Set to the maximum value allowed for this param. If the param is found and its value is greater than max, an HTTPError is raised.
store (dict, optional) – A dict-like object in which to place the value of the param, but only if the param is found (default None).

Returns:

The value of the param if it is found and can be converted to: an integer. If the param is not found, returns None, unless required is True.

Return type:

int

Raises

HTTPBadRequest: The param was not found in the request, even though: it was required to be there. Also raised if the param’s value falls outside the given interval, i.e., the value must be in the interval: min <= value <= max to avoid triggering an error.

get_param_as_list(name, transform=None, required=False, store=None)[source]¶

Return the value of a query string parameter as a list.

List items must be comma-separated or must be provided as multiple instances of the same param in the query string ala application/x-www-form-urlencoded.

Parameters:	name (str) – Parameter name, case-sensitive (e.g., ‘ids’). transform (callable, optional) – An optional transform function that takes as input each element in the list as a `str` and outputs a transformed element for inclusion in the list that will be returned. For example, passing `int` will transform list items into numbers. required (bool, optional) – Set to `True` to raise `HTTPBadRequest` instead of returning `None` when the parameter is not found (default `False`). store (dict, optional) – A `dict`-like object in which to place the value of the param, but only if the param is found (default `None`).
Returns:	The value of the param if it is found. Otherwise, returns `None` unless required is True. Empty list elements will be discarded. For example a query string containing this: things=1,,3 or a query string containing this: things=1&things=&things=3 would both result in: ['1', '3']
Return type:	list
Raises:	`HTTPBadRequest` – A required param is missing from the request. `HTTPInvalidParam` – A tranform function raised an instance of `ValueError`.

log_error(message)[source]¶

Write an error message to the server’s log.

Prepends timestamp and request info to message, and writes the result out to the WSGI server’s error stream (wsgi.error).

Parameters:	message (str or unicode) – Description of the problem. On Python 2, instances of `unicode` will be converted to UTF-8.

Response¶

class falcon.Response[source]¶

Represents an HTTP response to a client request.

Note

Response is not meant to be instantiated directly by responders.

status¶

str – HTTP status line (e.g., ‘200 OK’). Falcon requires the full status line, not just the code (e.g., 200). This design makes the framework more efficient because it does not have to do any kind of conversion or lookup when composing the WSGI response.

If not set explicitly, the status defaults to ‘200 OK’.

Note

Falcon provides a number of constants for common status codes. They all start with the HTTP_ prefix, as in: falcon.HTTP_204.

body¶: str or unicode – String representing response content. If Unicode, Falcon will encode as UTF-8 in the response. If data is already a byte string, use the data attribute instead (it’s faster).

body_encoded¶: bytes – Returns a UTF-8 encoded version of body.

data¶

bytes – Byte string representing response content.

Use this attribute in lieu of body when your content is already a byte string (str or bytes in Python 2, or simply bytes in Python 3). See also the note below.

Note

Under Python 2.x, if your content is of type str, using the data attribute instead of body is the most efficient approach. However, if your text is of type unicode, you will need to use the body attribute instead.

Under Python 3.x, on the other hand, the 2.x str type can be thought of as having been replaced by what was once the unicode type, and so you will need to always use the body attribute for strings to ensure Unicode characters are properly encoded in the HTTP response.

stream¶: Either a file-like object with a read() method that takes an optional size argument and returns a block of bytes, or an iterable object, representing response content, and yielding blocks as byte strings. Falcon will use wsgi.file_wrapper, if provided by the WSGI server, in order to efficiently serve file-like objects.

stream_len¶: int – Expected length of stream (e.g., file size).

add_link(target, rel, title=None, title_star=None, anchor=None, hreflang=None, type_hint=None)[source]¶

Add a link header to the response.

Note

Calling this method repeatedly will cause each link to be appended to the Link header value, separated by commas.

Note

So-called “link-extension” elements, as defined by RFC 5988, are not yet supported. See also Issue #288.

Parameters:	target (str) – Target IRI for the resource identified by the link. Will be converted to a URI, if necessary, per RFC 3987, Section 3.1. rel (str) – Relation type of the link, such as “next” or “bookmark”. See also http://goo.gl/618GHr for a list of registered link relation types.

Kwargs:

title (str): Human-readable label for the destination of

the link (default None). If the title includes non-ASCII characters, you will need to use title_star instead, or provide both a US-ASCII version using title and a Unicode version using title_star.

title_star (tuple of str): Localized title describing the

destination of the link (default None). The value must be a two-member tuple in the form of (language-tag, text), where language-tag is a standard language identifier as defined in RFC 5646, Section 2.1, and text is a Unicode string.

Note:: language-tag may be an empty string, in which case the client will assume the language from the general context of the current request.
Note:: text will always be encoded as UTF-8. If the string contains non-ASCII characters, it should be passed as a unicode type string (requires the ‘u’ prefix in Python 2).

anchor (str): Override the context IRI with a different URI

(default None). By default, the context IRI for the link is simply the IRI of the requested resource. The value provided may be a relative URI.

hreflang (str or iterable): Either a single language-tag, or

a list or tuple of such tags to provide a hint to the client as to the language of the result of following the link. A list of tags may be given in order to indicate to the client that the target resource is available in multiple languages.

type_hint(str): Provides a hint as to the media type of the

result of dereferencing the link (default None). As noted in RFC 5988, this is only a hint and does not override the Content-Type header returned when the link is followed.

append_header(name, value)[source]¶

Set or append a header for this response.

Warning

If the header already exists, the new value will be appended to it, delimited by a comma. Most header specifications support this format, Cookie and Set-Cookie being the notable exceptions.

Parameters:	name (str) – Header name to set (case-insensitive). Must be of type `str` or `StringType`, and only character values 0x00 through 0xFF may be used on platforms that use wide characters. value (str) – Value for the header. Must be of type `str` or `StringType`, and only character values 0x00 through 0xFF may be used on platforms that use wide characters.

cache_control¶

Sets the Cache-Control header.

Used to set a list of cache directives to use as the value of the Cache-Control header. The list will be joined with ”, ” to produce the value for the header.

content_location¶: Sets the Content-Location header.

content_range¶

A tuple to use in constructing a value for the Content-Range header.

The tuple has the form (start, end, length), where start and end designate the byte range (inclusive), and length is the total number of bytes, or ‘*’ if unknown. You may pass int‘s for these numbers (no need to convert to str beforehand).

Note

You only need to use the alternate form, ‘bytes */1234’, for responses that use the status ‘416 Range Not Satisfiable’. In this case, raising falcon.HTTPRangeNotSatisfiable will do the right thing.