mitmproxy/README.mkd

Pathod

Pathod is a pathological HTTP/S daemon, useful for testing and torturing client software. At Pathod's core is a small, terse language for crafting HTTP responses. The simplest way to use Pathod is to fire up the daemon, and specify the respnse behaviour you want using this language in the request URL. Here's a minimal example:

http://localhost:9999/p/200

Everything below the magic "/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 --anchor "/foo=200"

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

Pathod also has a nifty built-in web interface, which exposes activity logs, online help and various other goodies. Try it by visiting the server root:

http://localhost:9999

Specifying Responses

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 Value Specifier, 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-separateed 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 shorcut 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

Features

hKEY=VALUE

Set a header. Both KEY and VALUE are full Value Specifiers.

bVALUE

Set the body. VALUE is a Value Specifier. When the body is set, Pathod will automatically set the appropriate Content-Length header.

cVALUE

A shortcut for setting the Content-Type header. Equivalent to:

h"Content-Type"=VALUE

lVALUE

A shortcut for setting the Location header. Equivalent to:

h"Content-Type"=VALUE

dOFFSET

Disconnect after OFFSET bytes. The offset can also be "r", in which case Pathod will disconnect at a random point in the response.

pSECONDS,OFFSET

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.

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

The supported suffixes are:

b = 1024**0 (bytes)
k = 1024**1 (kilobytes)
m = 1024**2 (megabytes)
g = 1024**3 (gigabytes)
t = 1024**4 (terabytes)

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