mitmproxy/doc-src/pathod.html

<div class="page-header">
   <h1>
        pathod
        <small>A pathological web daemon.</small>
    </h1>
</div>

At __pathod__'s heart is a small, terse language for crafting HTTP responses,
designed to be easy to specify in a request URL.  The simplest way to use
__pathod__ is to fire up the daemon, and specify the response behaviour you
want using this language in the request URL.  Here's a minimal example:

    http://localhost:9999/p/200

Everything after the "/p/" path component is a response specifier - in this
case just a vanilla 200 OK response. See the docs below to get (much) fancier.
You can also add anchors to the __pathod__ server that serve a fixed response
whenever a matching URL is requested:

    pathod -a "/foo=200"

Here, "/foo" a regex specifying the anchor path, and the part after the "=" is
a response specifier.

__pathod__ also has a nifty built-in web interface, which lets you play with
the language by previewing responses, exposes activity logs, online help and
various other goodies. Try it by visiting the server root:

    http://localhost:9999



<div class="page-header">
   <h1>Specifying Responses</h1>
</div>

The general form of a response is as follows:
    
    code[MESSAGE]:[colon-separated list of features]

Here's the simplest possible response specification, returning just an HTTP 200
OK message with no headers and no content:
    
    200

We can embellish this a bit by specifying an optional custom HTTP response
message (if we don't, __pathod__ automatically creates an appropriate one). By
default for a 200 response code the message is "OK", but we can change it like
this:

    200"YAY"

The quoted string here is an example of a <a href=#valuespec>Value
Specifier</a>, a syntax that is used throughout the __pathod__ response
specification language. In this case, the quotes mean we're specifying a
literal string, but there are many other fun things we can do. For example, we
can tell __pathod__ to generate 100k of random ASCII letters instead:

    200@100k,ascii_letters

Full documentation on the value specification syntax can be found in the next
section. 
   
Following the response code specifier is a colon-separated list of features.
For instance, this specifies a response with a body consisting of 1 megabyte of
random data:

    200:b@1m

And this is the same response with an ETag header added:

    200:b@1m:h"Etag"="foo"

Both the header name and the header value are full value specifiers. Here's the
same response again, but with a 1k randomly generated header name:

    200:b@1m:h@1k,ascii_letters="foo"

A few specific headers have shortcuts, because they're used so often. The
shortcut for the content-type header is "c":

    200:b@1m:c"text/json"

That's it for the basic response definition. Now we can start mucking with the
responses to break clients. One common hard-to-test circumstance is hangs or
slow responses. __pathod__ has a pause operator that you can use to define
precisely when and how long the server should hang. Here, for instance, we hang
for 120 seconds after sending 50 bytes (counted from the first byte of the HTTP
response):

    200:b@1m:p120,50

If that's not long enough, we can tell __pathod__ to hang forever:

    200:b@1m:p120,f

Or to send all data, and then hang without disconnecting:

    200:b@1m:p120,a

We can also ask __pathod__ to hang randomly:

    200:b@1m:pr,a

There is a similar mechanism for dropping connections mid-response. So, we can
tell __pathod__ to disconnect after sending 50 bytes:

    200:b@1m:d50

Or randomly:

    200:b@1m:dr

All of these features can be combined. Here's a response that pauses twice,
once at 10 bytes and once at 20, then disconnects at 5000:

    200:b@1m:p10,10:p20,10:d5000


## Response Features

<table class="table table-bordered table-condensed">
    <tbody >
        <tr>
            <td>
                hKEY=VALUE
            </td>
            <td>
                Set a header. Both KEY and VALUE are full <a href=#valuespec>Value Specifiers</a>. 
            </td>
        </tr>

        <tr>
            <td> 
                bVALUE
            </td>
            <td>
                Set the body. VALUE is a <a href=#valuespec>Value
                Specifier</a>. When the body is set, __pathod__ will
                automatically set the appropriate Content-Length header.
            </td>
        </tr>

        <tr>
            <td>
                cVALUE
            </td>
            <td>
                A shortcut for setting the Content-Type header. Equivalent to:

                <pre>h"Content-Type"=VALUE</pre>

            </td>
        </tr>

        <tr>
            <td>
                lVALUE
            </td>
            <td>
                A shortcut for setting the Location header. Equivalent to:

                    <pre>h"Content-Type"=VALUE</pre>

            </td>
        </tr>


        <tr>
            <td>
                dOFFSET
            </td>
            <td>
                Disconnect after OFFSET bytes. The offset can also be "r", in which case __pathod__
                will disconnect at a random point in the response.
            </td>
        </tr>

        <tr>
            <td>
                pSECONDS,OFFSET
            </td>
            <td>
                Pause for SECONDS seconds after OFFSET bytes. SECONDS can also be "f" to pause
                forever. OFFSET can also be "r" to generate a random offset, or "a" for an
                offset just after all data has been sent.
            </td>
        </tr>
    </tbody>
</table>

<a id="valuespec"></a>
## VALUE Specifiers

There are three different flavours of value specification. 

### Literal

Literal values are specified as a quoted strings: 

    "foo"

Either single or double quotes are accepted, and quotes can be escaped with
backslashes within the string:

    'fo\'o'


### Files

You can load a value from a specified file path. To do so, you have to specify
a _staticdir_ option to __pathod__ on the command-line, like so: 

    pathod -d ~/myassets

All paths are relative paths under this directory. File loads are indicated by
starting the value specifier with the left angle bracket:
    
    <my/path

The path value can also be a quoted string, with the same syntax as literals:

    <"my/path"


### Generated values

An @-symbol lead-in specifies that generated data should be used. There are two
components to a generator specification - a size, and a data type. By default
__pathod__ assumes a data type of "bytes". 

Here's a value specifier for generating 100 bytes:
    
    @100

You can use standard suffixes to indicate larger values. Here, for instance, is
a specifier for generating 100 megabytes:

    @100m

Data is generated and served efficiently - if you really want to send a
terabyte of data to a client, __pathod__ can do it. The supported suffixes are:


<table class="table table-bordered table-condensed">
    <tbody >
        <tr>
            <td>b</td> <td>1024**0 (bytes)</td>
        </tr>
        <tr>
            <td>k</td> <td>1024**1 (kilobytes)</td>
        </tr>
        <tr>
            <td>m</td> <td>1024**2 (megabytes)</td>
        </tr>
        <tr>
            <td>g</td> <td>1024**3 (gigabytes)</td>
        </tr>
        <tr>
            <td>t</td> <td>1024**4 (terabytes)</td>
        </tr>
    </tbody>
</table>

Data types are separated from the size specification by a comma. This
specification generates 100mb of ASCII:

    @100m,ascii

Supported data types are:

    
- ascii_letters
- ascii_lowercase
- ascii_uppercase
- digits
- hexdigits
- letters
- lowercase
- octdigits
- printable
- punctuation
- uppercase
- whitespace
- ascii
- bytes


<div class="page-header">
   <h1>API</h1>
</div>

__pathod__ exposes a simple API, intended to make it possible to drive and
inspect the daemon remotely for use in unit testing and the like. 


<table class="table table-bordered table-condensed">
    <tbody >
        <tr>
            <td>
                /api/clear_log
            </td>
            <td>
                A POST to this URL clears the log buffer.
            </td>
        </tr>
        <tr>
            <td>
                /api/info
            </td>
            <td>
                Basic version and configuration info.
            </td>
        </tr>
        <tr>
            <td>
                /api/log
            </td>
            <td>
                Returns the current log buffer. At the moment the buffer size is 500 entries -
                when the log grows larger than this, older entries are discarded. The returned
                data is a JSON dictionary, with the form:

                <pre>
                    {
                        'log': [ ENTRIES ]
                    }
                </pre>
                You can preview the JSON data returned for a log entry through the built-in web
                interface.
            </td>
        </tr>
    </tbody>
</table>

<div class="page-header">
   <h1>Error Responses</h1>
</div>

To let users distinguish crafted responses from internal pathod responses,
pathod uses the non-standard 800 response code to indicate errors. For example,
a request to:

    http://localhost:9999/p/foo

... will return an 800 response, because "foo" is not a valid page specifier.