hpke-http for Python

hpke_http protects HTTP requests and replies with the Rust hpke-http/3 engine. Use the HTTPX or aiohttp client with an ASGI app.

Build this checkout

Build this checkout with the hpke-http/3 protocol:

make install-deps-python build-python

This installs the HTTPX, aiohttp, and FastAPI extras and builds the Rust binding from this checkout.

Protect an ASGI app

Wrap the app at one HTTPS path:

from hpke_http.middleware.fastapi import HPKEMiddleware

protected_app = HPKEMiddleware(
    app,
    recipient_private_key,
    key_id,
    resolve_psk,
    admit_replay,
    transport_path="/protected",
)

resolve_psk(psk_id, scope) returns the PSK for a public ID. It raises LookupError if the ID is unknown. admit_replay(replay_id, deadline, scope) atomically stores a new replay ID until the given exclusive Unix second. It returns True only for the first use. Both callbacks can be async.

The wrapper serves the public key at GET /protected. It accepts protected requests at POST /protected. The transport_path must match the full ASGI path. Set expected_authority if the logical host differs from the outer Host header. A lifespan shutdown closes the native server; call protected_app.close() at shutdown if the host sends no lifespan events.

The app receives its usual HTTP request fields and body. The wrapper checks START, every DATA part, END, and the outer body end before it starts the app. It keeps up to 256 KiB of checked body bytes in memory, then uses a temporary file. The app can send a finite reply or server-sent events (SSE). For SSE, send status 200 and Content-Type: text/event-stream. End each event with a blank line; the wrapper drops an incomplete last block.

For a browser page on another origin, put CORS outside the HPKE wrapper so it can answer the browser's OPTIONS request and add headers to fault replies:

from starlette.middleware.cors import CORSMiddleware

browser_app = CORSMiddleware(
    protected_app,
    allow_origins=["https://app.example.test"],
    allow_methods=["GET", "POST"],
    allow_headers=["cache-control", "content-type"],
)

Send requests with HTTPX

from hpke_http.middleware import Discover
from hpke_http.middleware.httpx import HPKEAsyncClient

async with HPKEAsyncClient(
    "https://api.example.test/protected",
    Discover(),
    psk,
    b"tenant-42",
) as client:
    response = await client.post(
        "https://api.example.test/items",
        json={"name": "Ada"},
    )
    response.raise_for_status()

    with open("large.bin", "rb") as source:
        response = await client.post(
            "https://api.example.test/upload",
            files={"upload": source},
        )

request() returns a fully checked httpx.Response. Normal HTTPX content, data, json, and files arguments work. The Rust writer reads source bytes as the HTTP library sends them. It groups bytes into request DATA parts of at most 64 KiB. You can also pass an async byte source as content.

For an SSE reply, use stream():

async with client.stream("GET", "https://api.example.test/events") as response:
    async for block in response.iter_sse():
        handle_sse_block(block)

iter_sse() yields each checked, LF-ended byte block. Decode and parse blocks with the SSE rules. For a finite reply in a stream context, call await response.read().

Send requests with aiohttp

import aiohttp
from hpke_http.middleware import Discover
from hpke_http.middleware.aiohttp import HPKEClientSession

form = aiohttp.FormData()
with open("large.bin", "rb") as source:
    form.add_field("upload", source, filename="large.bin")
    async with HPKEClientSession(endpoint, Discover(), psk, psk_id) as session:
        async with session.post(logical_url, data=form) as response:
            result = await response.read()

HPKEClientSession accepts bytes, text, form mappings, FormData, async byte sources, and JSON. It keeps the ordinary aiohttp request shape. The finite HPKEResponse has status, headers, read(), text(), json(), and raise_for_status(). Use session.stream() and iter_sse() for SSE.

Technical details

Keys and transport

Discover() gets the current public key before each call. Use PinnedKey(recipient_public_key, key_id) to use a fixed key without a GET. Both clients send the protected POST to their configured endpoint. Set target_origin="https://api.example.test" if a gateway serves a different logical host. The clients require HTTPS, check the logical target, and do not follow outer redirects. They do not retry a protected POST.

Generate a recipient key pair with generate_key_pair(). Recipient keys use X25519 and have 32 bytes. Key and PSK IDs are public opaque values of 1 to 255 bytes. A PSK needs at least 32 bytes of entropy. A Python bytes object cannot be erased in place; keep secret copies to a minimum.

Limits and payload coding

Set Limits(max_request_bytes=...) on both client and server for a service request cap. The HTTPX and aiohttp clients use this stream limit for every request. The low-level Client.protect(Request(...)) helper holds a full body in memory and uses max_body_len (8 MiB by default) as its cap. max_body_len also sets the finite reply and per-SSE-block cap. A host must also set limits for concurrent uploads, upload time, and temporary disk. An ASGI host can deliver one outer event larger than 64 KiB, so that event can use more memory.

Rust selects raw bytes or zstd for each request DATA part, finite reply body, and SSE block, then encrypts it. The recipient checks each tag before it decodes the part. This coding is part of the protected payload; it is not HTTP Content-Encoding.

The protocol does not hide payload size, record count, or timing, and it adds no random padding. HTTPS remains required. The request media type is message/hpke-http-request, and the reply media type is message/hpke-http-response.

Low-level streamed requests

The HTTPX and aiohttp clients send records on their own. For a custom HTTP transport, use the low-level writer. send_part writes one outer POST body part, end_outer_body closes that body, and source supplies byte chunks:

from hpke_http import Method, RequestHead

head = RequestHead(method=Method.POST, authority="api.example.test", path="/upload")
writer, start = client.begin_stream(head)
response_right = None
try:
    await send_part(start)
    async for chunk in source:
        offset = 0
        while offset < len(chunk):
            used, record = writer.push(chunk[offset:])
            if used == 0 and record is None:
                raise RuntimeError("request writer made no progress")
            offset += used
            if record is not None:
                await send_part(record)
    end, response_right = writer.finish()
    await send_part(end)
    await end_outer_body()
except BaseException:
    if response_right is not None:
        response_right.close()
    raise
finally:
    writer.close()

Use response_right to check the reply, then close it.

OpenedStreamRequest.feed() yields checked DATA parts. Store those parts until END and the outer body end pass. Then finish_eof() returns a StreamResponseRight, which can protect one reply. It has no request body; use the checked parts and OpenedStreamRequest.head to dispatch the request.

Runtime support

The package supports CPython 3.10 through 3.14. Wheels target Linux x86-64 and AArch64 and macOS universal2. Other Linux and macOS CPython targets need a Rust source build. Windows and PyPy are not supported.