Turq, the mock HTTP server

Turq is a small HTTP server that is scriptable in a Python-based DSL. It is designed for mocking HTTP services quickly and interactively.

Starting Turq

First you need to install it, normally from PyPI, for example:

$ pip install turq

Now you have a Python module called turq, and you can run it with:

$ python -m turq

This will start Turq on port 13085 by default, or you can choose another one with the -p option:

$ sudo python -m turq -p 80

Assuming your hostname is machine.example, and the port is 13085, you can now open the Turq console at http://machine.example:13085/+turq/ or just http://localhost:13085/+turq/

The Turq console is where you post the rules that define your mock. Type in the code and hit “Commit”, and Turq will start serving that.

Rules structure

The code you post is pure Python code that is not sandboxed, which means you can import and use any modules if you wish so.

The code is interpreted right away. It should declare rules that will be applied to a matching request. Currently there is just one type of rule:

path(path='*', trailing_slash=True)

This rule will be applied to every request whose path matches the path parameter, with an asterisk * meaning “zero or more of any characters”. This is like routing in HTTP frameworks. The query string is not considered part of the path.

path('/foo') will match a request for /foo/, but path('/foo', trailing_slash=False) will not. A simple path() matches everything.

The path() function returns an object on which you then call methods to fill out your rule, i.e. how to respond to a matching request. Most methods can be daisy-chained. For example:

path('/index.html').html().gzip().expires('1 day')

You can also use a rule as a context manager:

with path('/index.html') as r:
    r.expires('1 day')

Matching rules are applied in the order they appear in your code. For example, given:


a request for /foo/bar/baz will result in status 500.

Simple rule elements


Set response status to code.

Rule.header(name, value, **params)

Set response header name to value.

If params are specified, they are appended as k=v pairs. For example:

header('Content-Type', 'text/html', charset='utf-8')


Content-Type: text/html; charset="utf-8"
Rule.add_header(name, value, **params)

Same as header(), but add the header, not replace it.

This can be used to send multiple headers with the same name, such as Via or Set-Cookie (but for the latter see cookie()).


Set response entity body to data.


Set response entity body to the contents of path.

The file at path is read when the rules are posted. path undergoes tilde expansion.


Set response entity body to the contents of url.

The resource at url is fetched once and cached until Turq exits. Note that this method only sets the entity body. HTTP status and headers are not copied from url.


Set response Content-Type to value.

Rule.text(text='Hello world!')

Set up a text/plain response.


Set up a text/plain response with lots of text.

Lines of dummy text will be generated so that the entity body is very roughly nbytes in length.

Rule.html(title='Hello world!', text='This is Turq!')

Set up a text/html response.

A basic HTML page with title and a paragraph of text is served.

Rule.lots_of_html(nbytes=20000, title='Hello world!')

Set up a text/html response with lots of text.

Like lots_of_text(), but wrapped in HTML paragraphs.

Rule.json(data={'result': 'turq'}, jsonp=True)

Set up a JSON or JSONP response.

data will be serialized into an application/json entity body. But if the request has a callback query parameter, data will be wrapped into a JSONP callback and served as application/javascript, unless you set jsonp to False.


Set up an application/javascript response.


Set up an application/xml response.

Rule.redirect(location, status=302)

Set up a redirection response.

Rule.cookie(name, value, max_age=None, expires=None, path=None, secure=False, http_only=False)

Add a cookie name with value.

The other arguments correspond to parameters of the Set-Cookie header. If specified, max_age and expires should be strings. Nothing is escaped.


Demand HTTP basic authentication (status code 401).

Rule.digest_auth(realm='Turq', nonce='twasbrillig')

Demand HTTP digest authentication (status code 401).


Check the request method to be one of methods (case-insensitive).

If it isn’t, send 405 Method Not Allowed with a plain-text error message.


Enable CORS on the response.

Currently this just sets Access-Control-Allow-Origin: *. Preflight requests are not yet handled.


Set the expiration time of the response.

when should be a specification of the number of minutes, hours or days, counted from the moment the rules are posted. Supported formats are: “10 min” or “10 minutes” or “5 h” or “5 hours” or “1 d” or “1 day”.


Apply Content-Encoding: gzip to the entity body.

Accept-Encoding of the request is ignored.

Alternating responses

Within any rule, Turq can switch between multiple sub-rules for successive requests. A group of sub-rules is initiated with the first() call, which begins the sub-rule for the first request. You will also have zero or more next() calls and zero or one then() call. If you have next() but no then(), the cycle will eventually return to first() and start over.

Easier to explain by example. Here we alternate between “foo” and “bar”:

with path('/') as r:

Here we arrive at “baz” and stay there:

with path('/') as r:

Rule elements declared outside of first(), next() and then() will be applied to every response. For example, here, we send a custom Server header with every response:

with path('/') as r:
    r.header('Server', 'WonkyHTTPd/1.4.2b')

Stochastic responses

Whereas first() et al. are deterministic, the maybe() call adds a stochastic dimension to the response.


Add a sub-rule that will be applied with probability.


Add a sub-rule that complements all maybe() rules.

This is just a shortcut that adds a maybe sub-rule with a probability equal to 1 minus all currently defined maybe. Thus, it must come after all maybe.

This can be used to imitate occasional errors:

with path() as r:
    r.maybe().status(502).text('Bad Gateway')

Probabilities don’t have to cover everything:

with path() as r:
    r.html(text='Welcome to our site!')
    r.maybe(0.01).cookie('evilTracking', '12345')

Parametrized responses

Sometimes you need the response to depend on the request. For example, suppose you have some crawler that fetches product info and expects the response to contain the requested product ID. You can do it easily with Turq:

path('/products').json(lambda req: {'id': req.query['id']})

Most rule elements that accept a simple value will also accept a function. The function is called with a Request object as the only argument.

class turq.Request(method, path, query, headers, body)

An HTTP request.


Request method.


The request path, excluding the query string.


A dictionary of parameters parsed from the query string. An empty dictionary if none can be parsed.


An rfc822.Message-like mapping of request headers.


Request entity body as a str if there is one, otherwise None.

If you need even more logic, you can provide a custom handler function, attaching it to the rule by using the rule as a decorator:

def process(req, r):
    if req.query['id'].startswith('SCR31-'):
        r.status(403).text('access to product info denied')
        r.json({'id': req.query['id']})


Turq does not provide full control over the HTTP exchange on the wire. For example:

  • it always closes the connection after handling one request (and for this reason does not send Content-Length by default);
  • the Server and Date response headers are always sent (but you can override them—in particular, set them to empty strings);
  • you cannot change the HTTP version that is sent in the response status line.

If you need to tweak such things, you might be better off using the good old netcat or writing some custom code.