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sansio_multipart: A sansio parser for multipart/form-data

This lib provides a parser for the multipart/form-data format. You feed it bytes, and it will feed you events and data objects.

Requirements

Python 3.x

Installing

pip install sansio-multipart

Examples

Here's the setup for our examples.

Note: Our multipart body is split up in to many pieces, in order to make it as difficult to parse as possible. Only on the fourth chunk can we actually produce a Part object. This is just to illustrate a worst case scenario stream :D

from sansio_multipart import MultipartParser, NEED_DATA
from collections import deque

# boundary extracted from request's content-type header
boundary = '8banana133744910kmmr13a56!102!2405'.encode()

# chunks of data, as though they were read from a stream
chunks = deque(
    [
        b'--8banana133744910kmmr',
        b'13a56!102!2405\r\nContent-Disposition: form-da',
        b'ta; name="file_1"; filename="test_file1.tx',
        b't"\r\nContent-Type: application/octet-strea',
        b'm\r\ncontent-length: 9\r\n\r\nCompoo',
        b'per\r\n--8banana',
        b'133744910kmmr13a5',
        b'6!102!2405--\r\n'
    ]
)

There are a couple of ways to interact with the parser. Likely the most familiar way is to request events one by one. We'll pretend our deque is a socket, for illustrative purposes.

You'll be familiar with this pattern if you've used other sansio python libs, like h11.

with MultipartParser(boundary) as parser:
    while len(chunks):
        event = parser.next_event()
        if event is NEED_DATA:
            parser.recv(chunks.popleft())
            continue
        print(event)

# Outputs

# <sansio_multipart.parser.Part object at 0xb707d84c>
# PartData(raw=bytearray(b'Compooper'), size=9)

That isn't the only way to handle things. The following is probably the simplest way to interact with a similar stream. Enter the parser, throw data at it, and read events.

with MultipartParser(boundary) as parser:
    for chunk in chunks:
        events = parser.parse(chunk)
        print("Chunk events ->", events)

# Outputs:
# Chunk events: -> [<Events.NEED_DATA: 1>]
# Chunk events: -> [<Events.NEED_DATA: 1>]
# Chunk events: -> [<Events.NEED_DATA: 1>]
# Chunk events: -> [<Events.NEED_DATA: 1>]
# Chunk events: -> [<sansio_multipart.parser.Part object at 0xb7048a4c>, <Events.NEED_DATA: 1>]
# Chunk events: -> [PartData(raw=bytearray(b'Compooper'), size=9), <Events.NEED_DATA: 1>]
# Chunk events: -> [<Events.NEED_DATA: 1>]
# Chunk events: -> [<Events.FINISHED: 2>]
"""

Of course, you can just feed the entirity in. This time we'll have the full body data available, and two parts in our multipart (because it's multipart!).

full_data = b'--8banana133744910kmmr13a56!102!1823\r\nContent-Disposition: form-data; name="file_1"; filename="test_file1.txt"; Content-Type: application/octet-stream\r\n\r\nCompooper\r\n--8banana133744910kmmr13a56!102!1823\r\nContent-Disposition: form-data; name="data_1"\r\n\r\nwatwatwatwat=yesyesyes\r\n--8banana133744910kmmr13a56!102!1823--\r\n'

boundary = '8banana133744910kmmr13a56!102!1823'

with MultipartParser(boundary) as parser:
    print(parser.parse(full_data))

# Outputs
# [
#     <sansio_multipart.parser.Part object at 0xb707d7ac>,
#     PartData(raw=bytearray(b'Compooper'), size=9),
#     <sansio_multipart.parser.Part object at 0xb707d7ec>,
#     PartData(raw=bytearray(b'watwatwatwat=yesyesyes'), size=22),
#     <Events.FINISHED: 2>
# ]

You can buffer a PartData object to a Part object by passing it to the Part.buffer method, like part.buffer(part_data).

That's all there is to it!

Event reference:

  • NEED_DATA Given when there isn't enough data to continue giving other events or data objects.
  • FINISHED Given when the data has been successfully exhausted.

Data object reference:

  • Part The object representing the head of a multipart part.
  • PartData The object representing the body, or a segment of the body, of a multipart part. For any given part, you may have 1..n data objects.

Error reference:

  • UnexpectedExit Raised when you leave the context manager of the parser before a terminator line was parsed. Inherits from MultipartError, EOFError.
  • MalformedData Raised in cases where the data is out of spec for the multipart protocol, and cannot be parsed. Inherits from MultipartError.

Limitations

  • Only parses multipart/form-data as seen from actual browsers.
    • Not suitable as a general purpose multipart parser (e.g. for multipart emails).
    • No multipart/mixed support (RFC 2388, deprecated in RFC 7578)
    • No encoded-word encoding (RFC 2047).
    • No base64 or quoted-printable transfer encoding.
  • Part headers are expected to be encoded in the charset given to the Part/MultipartParser constructor. [For operability considerations, see RFC 7578, section 5.1.]

Changelog

  • 0.3 Complete api change. The parser is now a sansio parser, meaning no io happens internally. This makes it safe for use in projects that don't like uncontrolled io happening (like async).
  • 0.2 * Dropped support for Python versions below 3.6. Stay on 0.1 if you need Python 2.5+ support.
  • 0.1 (21.06.2010) * First release