python-multipart 0.0.32: parse multipart form data and form fields using MultipartParser

# python-multipart MultipartParser API

This sample pins `python-multipart` 0.0.32 and verifies streaming multipart/form-data parsing using `multipart.MultipartParser`.

The contract verifies:
- `MultipartParser` processes streamed chunks of multipart payload and triggers lifecycle callbacks (`on_part_begin`, `on_header_field`, `on_header_value`, `on_headers_finished`, `on_part_data`, `on_part_end`, `on_end`).
- Reassembly of header fields and values (such as `Content-Disposition` and `Content-Type`) across multiple multipart parts.
- Correct extraction and reassembly of multipart body payload for form fields and file attachments.
- Enforcement of `max_header_count` limit, raising `MultipartParseError` when exceeded.
- Enforcement of `max_header_size` limit, raising `MultipartParseError` when exceeded.
- Rejection of malformed boundaries and invalid multipart stream data with `MultipartParseError`.

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: parse multipart form data and form fields using MultipartParser
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:pypi/python-multipart@0.0.32
Demonstrate these symbols/APIs:
  - multipart.MultipartParser

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:63c7db192c484ab54b33281d09f74bd0b633c2400bf98142a7358b9df4c256c1","contract":["MultipartParser parses streaming multipart/form-data payload chunk-by-chunk and dispatches lifecycle callbacks for parts, headers, and body segments.","MultipartParser accurately captures headers and extracts payload for multiple parts including standard form fields and file attachments.","MultipartParser raises MultipartParseError when max_header_count limit is exceeded.","MultipartParser raises MultipartParseError when max_header_size limit is exceeded.","MultipartParser raises MultipartParseError when given malformed multipart payloads or invalid boundary sequences."],"goal":"parse multipart form data and form fields using MultipartParser","kind":"HOW","packages":["pkg:pypi/python-multipart@0.0.32"],"schemaVersion":1,"symbols":["multipart.MultipartParser"]},"contractCommand":["python","test/contract.py"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"pypi","executionContext":"python","language":"python","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"pip","runtime":"python","schemaVersion":1},"license":"MIT-0","packages":["pkg:pypi/python-multipart@0.0.32"],"schemaVersion":1,"subject":"pkg:pypi/python-multipart@0.0.32","symbols":["multipart.MultipartParser"],"verifierAdapter":"python@1"}

python-multipart==0.0.32

{
  "schemaVersion": 1,
  "goal": "parse multipart form data and form fields using MultipartParser",
  "kind": "HOW",
  "packages": [
    "pkg:pypi/python-multipart@0.0.32"
  ],
  "symbols": [
    "multipart.MultipartParser"
  ]
}

import io
import multipart
from multipart.multipart import MultipartParser, MultipartParseError

# 1. Verify MultipartParser parses streaming multipart/form-data chunk-by-chunk and dispatches lifecycle callbacks
boundary = "----WebKitFormBoundaryXyZ123456"
field_payload = (
    f"--{boundary}\r\n"
    "Content-Disposition: form-data; name=\"username\"\r\n\r\n"
    "antigravity_user\r\n"
    f"--{boundary}--\r\n"
).encode("utf-8")

events = []
header_fields = []
header_values = []
part_datas = []

def on_header_field(data, start, end):
    header_fields.append(data[start:end].decode("latin-1"))

def on_header_value(data, start, end):
    header_values.append(data[start:end].decode("latin-1"))

def on_part_data(data, start, end):
    part_datas.append(data[start:end].decode("utf-8"))

parser1 = MultipartParser(
    boundary,
    {
        "on_part_begin": lambda: events.append("part_begin"),
        "on_header_field": on_header_field,
        "on_header_value": on_header_value,
        "on_header_end": lambda: events.append("header_end"),
        "on_headers_finished": lambda: events.append("headers_finished"),
        "on_part_data": on_part_data,
        "on_part_end": lambda: events.append("part_end"),
        "on_end": lambda: events.append("end"),
    },
)

chunk_size = 10
for i in range(0, len(field_payload), chunk_size):
    parser1.write(field_payload[i : i + chunk_size])
parser1.finalize()

assert "part_begin" in events
assert "".join(header_fields) == "Content-Disposition"
assert "".join(header_values) == "form-data; name=\"username\""
assert "headers_finished" in events
assert "".join(part_datas) == "antigravity_user"
assert "part_end" in events
assert "end" in events

# 2. Verify MultipartParser captures multiple parts including headers and file uploads
multipart_body = (
    f"--{boundary}\r\n"
    "Content-Disposition: form-data; name=\"title\"\r\n\r\n"
    "Sample Title\r\n"
    f"--{boundary}\r\n"
    "Content-Disposition: form-data; name=\"document\"; filename=\"test.txt\"\r\n"
    "Content-Type: text/plain; charset=utf-8\r\n\r\n"
    "File payload line 1\r\nFile payload line 2\r\n"
    f"--{boundary}--\r\n"
).encode("utf-8")

parsed_parts = []
current_part = {}
current_header_name = None

def on_part_begin():
    global current_part, current_header_name
    current_part = {"headers": {}, "data": bytearray()}
    current_header_name = None

def on_header_field(data, start, end):
    global current_header_name
    field_chunk = data[start:end].decode("latin-1")
    if current_header_name is None:
        current_header_name = field_chunk
    else:
        current_header_name += field_chunk

def on_header_value(data, start, end):
    global current_header_name
    val_chunk = data[start:end].decode("latin-1")
    if current_header_name in current_part["headers"]:
        current_part["headers"][current_header_name] += val_chunk
    else:
        current_part["headers"][current_header_name] = val_chunk

def on_header_end():
    global current_header_name
    current_header_name = None

def on_part_data(data, start, end):
    current_part["data"].extend(data[start:end])

def on_part_end():
    parsed_parts.append(current_part)

parser2 = MultipartParser(
    boundary,
    {
        "on_part_begin": on_part_begin,
        "on_header_field": on_header_field,
        "on_header_value": on_header_value,
        "on_header_end": on_header_end,
        "on_part_data": on_part_data,
        "on_part_end": on_part_end,
    },
)
parser2.write(multipart_body)
parser2.finalize()

assert len(parsed_parts) == 2, f"Expected 2 parts, got {len(parsed_parts)}"

part1 = parsed_parts[0]
assert "name=\"title\"" in part1["headers"].get("Content-Disposition", "")
assert bytes(part1["data"]).decode("utf-8") == "Sample Title"

part2 = parsed_parts[1]
assert "name=\"document\"" in part2["headers"].get("Content-Disposition", "")
assert "filename=\"test.txt\"" in part2["headers"].get("Content-Disposition", "")
assert part2["headers"].get("Content-Type") == "text/plain; charset=utf-8"
assert bytes(part2["data"]).decode("utf-8") == "File payload line 1\r\nFile payload line 2"

# 3. Verify max_header_count limit enforcement raises MultipartParseError
header_overflow_body = (
    f"--{boundary}\r\n"
    "H1: v1\r\n"
    "H2: v2\r\n"
    "H3: v3\r\n"
    "H4: v4\r\n\r\n"
    "data\r\n"
    f"--{boundary}--\r\n"
).encode("utf-8")

parser3 = MultipartParser(boundary, {}, max_header_count=3)
try:
    parser3.write(header_overflow_body)
    parser3.finalize()
    raise AssertionError("Expected MultipartParseError for header count overflow")
except MultipartParseError:
    pass

# 4. Verify max_header_size limit enforcement raises MultipartParseError
long_header_body = (
    f"--{boundary}\r\n"
    "X-Long-Header: " + ("B" * 200) + "\r\n\r\n"
    "data\r\n"
    f"--{boundary}--\r\n"
).encode("utf-8")

parser4 = MultipartParser(boundary, {}, max_header_size=64)
try:
    parser4.write(long_header_body)
    parser4.finalize()
    raise AssertionError("Expected MultipartParseError for header size overflow")
except MultipartParseError:
    pass

# 5. Verify malformed boundary or invalid multipart payload raises MultipartParseError
parser5 = MultipartParser("expected_boundary_1234", {})
try:
    parser5.write(b"completely invalid content without proper boundary\r\n")
    parser5.finalize()
    raise AssertionError("Expected MultipartParseError on malformed stream")
except MultipartParseError:
    pass

print("CONTRACT PASS: python-multipart MultipartParser verified offline")