httpx.ReadError happens for some websites without actual reason!

[AmericanY]

import trio
import httpx

proxies = {
    "all://": "http://127.0.0.1:8866"
}


async def main():
    async with httpx.AsyncClient(timeout=None, proxies=proxies, verify=False) as client:
        r = await client.get('https://cndt-certidao.tst.jus.br/inicio.faces')
        print(r)

if __name__ == "__main__":
    trio.run(main)

The proxy is being used is ref. to Fiddler

Traceback (most recent call last):
  File "C:\Users\AmericaN\Desktop\Lab\MyEnv\lib\site-packages\httpx\_transports\default.py", line 61, in map_httpcore_exceptions
    yield
  File "C:\Users\AmericaN\Desktop\Lab\MyEnv\lib\site-packages\httpx\_transports\default.py", line 203, in __aiter__
    async for part in self._httpcore_stream:
  File "C:\Users\AmericaN\Desktop\Lab\MyEnv\lib\site-packages\httpcore\_async\connection_pool.py", line 57, in __aiter__
    async for chunk in self.stream:
  File "C:\Users\AmericaN\Desktop\Lab\MyEnv\lib\site-packages\httpcore\_bytestreams.py", line 91, in __aiter__
    async for chunk in self._aiterator:
  File "C:\Users\AmericaN\Desktop\Lab\MyEnv\lib\site-packages\httpcore\_async\http11.py", line 208, in _receive_response_data
    event = await self._receive_event(timeout)
  File "C:\Users\AmericaN\Desktop\Lab\MyEnv\lib\site-packages\httpcore\_async\http11.py", line 225, in _receive_event
    data = await self.socket.read(self.READ_NUM_BYTES, timeout)
  File "C:\Users\AmericaN\Desktop\Lab\MyEnv\lib\site-packages\httpcore\_backends\trio.py", line 66, in read
    raise exc
  File "C:\Program Files\Python39\lib\contextlib.py", line 135, in __exit__    
    self.gen.throw(type, value, traceback)
  File "C:\Users\AmericaN\Desktop\Lab\MyEnv\lib\site-packages\httpcore\_exceptions.py", line 12, in map_exceptions
    raise to_exc(exc) from None
httpcore.ReadError

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "c:\Users\AmericaN\Desktop\Lab\ccap.py", line 16, in <module>
    trio.run(main)
  File "C:\Users\AmericaN\Desktop\Lab\MyEnv\lib\site-packages\trio\_core\_run.py", line 1932, in run
    raise runner.main_task_outcome.error
  File "c:\Users\AmericaN\Desktop\Lab\ccap.py", line 12, in main
    r = await client.get('https://cndt-certidao.tst.jus.br/inicio.faces')
  File "C:\Users\AmericaN\Desktop\Lab\MyEnv\lib\site-packages\httpx\_client.py", line 1722, in get
    return await self.request(
  File "C:\Users\AmericaN\Desktop\Lab\MyEnv\lib\site-packages\httpx\_client.py", line 1481, in request
    response = await self.send(
  File "C:\Users\AmericaN\Desktop\Lab\MyEnv\lib\site-packages\httpx\_client.py", line 1586, in send
    raise exc
  File "C:\Users\AmericaN\Desktop\Lab\MyEnv\lib\site-packages\httpx\_client.py", line 1577, in send
    await response.aread()
  File "C:\Users\AmericaN\Desktop\Lab\MyEnv\lib\site-packages\httpx\_models.py", line 1561, in aread
    self._content = b"".join([part async for part in self.aiter_bytes()])
  File "C:\Users\AmericaN\Desktop\Lab\MyEnv\lib\site-packages\httpx\_models.py", line 1561, in <listcomp>
    self._content = b"".join([part async for part in self.aiter_bytes()])
  File "C:\Users\AmericaN\Desktop\Lab\MyEnv\lib\site-packages\httpx\_models.py", line 1577, in aiter_bytes
    async for raw_bytes in self.aiter_raw():
  File "C:\Users\AmericaN\Desktop\Lab\MyEnv\lib\site-packages\httpx\_models.py", line 1631, in aiter_raw
    async for raw_stream_bytes in self.stream:
  File "C:\Users\AmericaN\Desktop\Lab\MyEnv\lib\site-packages\httpx\_client.py", line 150, in __aiter__
    async for chunk in self._stream:
  File "C:\Users\AmericaN\Desktop\Lab\MyEnv\lib\site-packages\httpx\_transports\default.py", line 204, in __aiter__
    yield part
  File "C:\Program Files\Python39\lib\contextlib.py", line 135, in __exit__
    self.gen.throw(type, value, traceback)
  File "C:\Users\AmericaN\Desktop\Lab\MyEnv\lib\site-packages\httpx\_transports\default.py", line 78, in map_httpcore_exceptions
    raise mapped_exc(message) from exc
httpx.ReadError

[tomchristie]

Is there a public URL which replicates this behaviour?

[AIvashov]

Hello @tomchristie , I have same problem.

I couldn't reproduce this problem with a single use. But it consistently appears in the production. I'm making 4-5 requests in a lot of threads.

Code

import httpx

from typing import Optional
from httpx import Request, USE_CLIENT_DEFAULT


class HttpWrapper:
    client: httpx.AsyncClient
    session: Optional[httpx.AsyncClient] = None

    def __init__(self):
        self.session = httpx.AsyncClient(limits=httpx.Limits(
            max_keepalive_connections=None, max_connections=None, keepalive_expiry=None))

    async def connect(self):
        self.client = await self.session.__aenter__()

    async def disconnect(self):
        if self.session:
            await self.session.__aexit__(None, None, None)

async def main():
    http: HttpWrapper = HttpWrapper()
    await http.connect()
    some_data = {}
    request = Request(
        'POST',
        url='https://example.com',
        headers={
            'Authorization': f'Bearer bla-bla',
        },
        json=some_data,
    )

    response = await http.client.send(request, timeout=1.5, allow_redirects=USE_CLIENT_DEFAULT)
    print(response.status_code)
    print(response.json())

    await http.disconnect()


if __name__ == '__main__':
    import asyncio
    asyncio.run(main())

Logs

ConnectionResetError: [Errno 104] Connection reset by peer
  File "asyncio/selector_events.py", line 856, in _read_ready__data_received
    data = self._sock.recv(self.max_size)
BrokenResourceError: null
  File "httpcore/_backends/anyio.py", line 60, in read
    return await self.stream.receive(n)
  File "anyio/streams/tls.py", line 195, in receive
    data = await self._call_sslobject_method(self._ssl_object.read, max_bytes)
  File "anyio/streams/tls.py", line 137, in _call_sslobject_method
    data = await self.transport_stream.receive()
  File "anyio/_backends/_asyncio.py", line 1274, in receive
    raise self._protocol.exception
ReadError: null
  File "httpx/_transports/default.py", line 61, in map_httpcore_exceptions
    yield
  File "httpx/_transports/default.py", line 281, in handle_async_request
    ) = await self._pool.handle_async_request(
  File "httpcore/_async/connection_pool.py", line 234, in handle_async_request
    response = await connection.handle_async_request(
  File "httpcore/_async/connection.py", line 148, in handle_async_request
    return await self.connection.handle_async_request(
  File "httpcore/_async/http11.py", line 128, in handle_async_request
    ) = await self._receive_response(timeout)
  File "httpcore/_async/http11.py", line 189, in _receive_response
    event = await self._receive_event(timeout)
  File "httpcore/_async/http11.py", line 225, in _receive_event
    data = await self.socket.read(self.READ_NUM_BYTES, timeout)
  File "httpcore/_backends/anyio.py", line 65, in read
    raise ReadError from exc
ReadError: null
  File "ml_utils/base_requests.py", line 38, in handle_ml_request
    response: Response = await http.client.send(request, timeout=timeout, allow_redirects=allow_redirects)
  File "httpx/_client.py", line 1586, in send
    response = await self._send_handling_auth(
  File "httpx/_client.py", line 1616, in _send_handling_auth
    response = await self._send_handling_redirects(
  File "httpx/_client.py", line 1655, in _send_handling_redirects
    response = await self._send_single_request(request, timeout)
  File "httpx/_client.py", line 1699, in _send_single_request
    ) = await transport.handle_async_request(
  File "httpx/_transports/default.py", line 276, in handle_async_request
    (
  File "contextlib.py", line 137, in __exit__
    self.gen.throw(typ, value, traceback)
  File "httpx/_transports/default.py", line 78, in map_httpcore_exceptions
    raise mapped_exc(message) from exc

Env

Cpython 3.9.7

anyio | 3.6.2
httpx | 0.19.0
httpcore | 0.13.7

[T-256]

Can you paste the full error of latest version here?

[AIvashov]

@T-256

ConnectionResetError: [Errno 104] Connection reset by peer
  File "asyncio/selector_events.py", line 856, in _read_ready__data_received
    data = self._sock.recv(self.max_size)
BrokenResourceError: null
  File "httpcore/_exceptions.py", line 8, in map_exceptions
    yield
  File "httpcore/backends/asyncio.py", line 33, in read
    return await self._stream.receive(max_bytes=max_bytes)
  File "anyio/streams/tls.py", line 195, in receive
    data = await self._call_sslobject_method(self._ssl_object.read, max_bytes)
  File "anyio/streams/tls.py", line 137, in _call_sslobject_method
    data = await self.transport_stream.receive()
  File "anyio/_backends/_asyncio.py", line 1274, in receive
    raise self._protocol.exception
ReadError: null
  File "httpx/_transports/default.py", line 60, in map_httpcore_exceptions
    yield
  File "httpx/_transports/default.py", line 353, in handle_async_request
    resp = await self._pool.handle_async_request(req)
  File "httpcore/_async/connection_pool.py", line 253, in handle_async_request
    raise exc
  File "httpcore/_async/connection_pool.py", line 237, in handle_async_request
    response = await connection.handle_async_request(request)
  File "httpcore/_async/connection.py", line 90, in handle_async_request
    return await self._connection.handle_async_request(request)
  File "httpcore/_async/http11.py", line 105, in handle_async_request
    raise exc
  File "httpcore/_async/http11.py", line 84, in handle_async_request
    ) = await self._receive_response_headers(**kwargs)
  File "httpcore/_async/http11.py", line 148, in _receive_response_headers
    event = await self._receive_event(timeout=timeout)
  File "httpcore/_async/http11.py", line 177, in _receive_event
    data = await self._network_stream.read(
  File "httpcore/backends/asyncio.py", line 35, in read
    return b""
  File "contextlib.py", line 137, in __exit__
    self.gen.throw(typ, value, traceback)
  File "httpcore/_exceptions.py", line 12, in map_exceptions
    raise to_exc(exc)
ReadError: null
  File "ml_utils/base_requests.py", line 39, in handle_ml_request
    response: Response = await http.client.send(request, follow_redirects=follow_redirects)
  File "httpx/_client.py", line 1617, in send
    response = await self._send_handling_auth(
  File "httpx/_client.py", line 1645, in _send_handling_auth
    response = await self._send_handling_redirects(
  File "httpx/_client.py", line 1682, in _send_handling_redirects
    response = await self._send_single_request(request)
  File "httpx/_client.py", line 1719, in _send_single_request
    response = await transport.handle_async_request(request)
  File "httpx/_transports/default.py", line 353, in handle_async_request
    resp = await self._pool.handle_async_request(req)
  File "contextlib.py", line 137, in __exit__
    self.gen.throw(typ, value, traceback)
  File "httpx/_transports/default.py", line 77, in map_httpcore_exceptions
    raise mapped_exc(message) from exc

[T-256]

Sorry I can't repro.
My Env:
Python 3.11.2 Win 11 22H2

Package           Version
----------------- --------
anyio             3.6.2
certifi           2023.5.7
h11               0.14.0
httpcore          0.17.1
httpx             0.24.0
idna              3.4
sniffio           1.3.0

How many concurrent task do you use when you get this error?
did you still get same error after updating all dependencies?

[AIvashov]

1. depending on the conditions, an average of 12-18
2. yes, i did

I then noticed that this error only appears when a request is made to a specific host. Is there a chance that this error is related to the server?

[T-256]

then I have no idea.

I then noticed that this error only appears when a request is made to a specific host.

Yes, the erros says TLS failed. I think server closes connection on client-hello packet.
is it possible for you to provide the code with that specific host?

[lee-cq]

It seems that I also encountered a similar error:
I want to download files from site A and upload them to site B, but I always encounter the above problem.

It is worth noting that it always appears after transmitting several chunks.

import asyncio
import time
import urllib.parse

from httpx import AsyncClient


async def main():
    async with AsyncClient() as source_client:
        async with source_client.stream(
            "GET", "URL", follow_redirects=True
        ) as stream_resp:

            async with AsyncClient(...) as target_client:
                await target_client.put(
                    "/api/fs/put",
                    headers={
                        "Content-Type": "application/octet-stream",
                        "Last-Modified": str(int(time.time() * 1000)),
                        "File-Path": urllib.parse.quote_plus("/path/to/file"),
                    },
                    content=stream_resp.aiter_bytes(),
                )


asyncio.run(main())

Traceback (most recent call last):
  File "/Users/lcq/PycharmProjects/alist-sync/venv/lib/python3.11/site-packages/httpx/_transports/default.py", line 66, in map_httpcore_exceptions
    yield
  File "/Users/lcq/PycharmProjects/alist-sync/venv/lib/python3.11/site-packages/httpx/_transports/default.py", line 366, in handle_async_request
    resp = await self._pool.handle_async_request(req)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/lcq/PycharmProjects/alist-sync/venv/lib/python3.11/site-packages/httpcore/_async/connection_pool.py", line 216, in handle_async_request
    raise exc from None
  File "/Users/lcq/PycharmProjects/alist-sync/venv/lib/python3.11/site-packages/httpcore/_async/connection_pool.py", line 196, in handle_async_request
    response = await connection.handle_async_request(
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/lcq/PycharmProjects/alist-sync/venv/lib/python3.11/site-packages/httpcore/_async/connection.py", line 101, in handle_async_request
    return await self._connection.handle_async_request(request)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/lcq/PycharmProjects/alist-sync/venv/lib/python3.11/site-packages/httpcore/_async/http11.py", line 143, in handle_async_request
    raise exc
  File "/Users/lcq/PycharmProjects/alist-sync/venv/lib/python3.11/site-packages/httpcore/_async/http11.py", line 113, in handle_async_request
    ) = await self._receive_response_headers(**kwargs)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/lcq/PycharmProjects/alist-sync/venv/lib/python3.11/site-packages/httpcore/_async/http11.py", line 186, in _receive_response_headers
    event = await self._receive_event(timeout=timeout)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/lcq/PycharmProjects/alist-sync/venv/lib/python3.11/site-packages/httpcore/_async/http11.py", line 224, in _receive_event
    data = await self._network_stream.read(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/lcq/PycharmProjects/alist-sync/venv/lib/python3.11/site-packages/httpcore/_backends/anyio.py", line 31, in read
    with map_exceptions(exc_map):
  File "/Users/lcq/.pyenv/versions/3.11.7/lib/python3.11/contextlib.py", line 158, in __exit__
    self.gen.throw(typ, value, traceback)
  File "/Users/lcq/PycharmProjects/alist-sync/venv/lib/python3.11/site-packages/httpcore/_exceptions.py", line 14, in map_exceptions
    raise to_exc(exc) from exc
httpcore.ReadError

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/Users/lcq/PycharmProjects/alist-sync/alist_sync/downloader.py", line 88, in <module>
    upload_stream(source, target)
  File "/Users/lcq/PycharmProjects/alist-sync/alist_sync/downloader.py", line 72, in upload_stream
    return asyncio.run(main())
           ^^^^^^^^^^^^^^^^^^^
  File "/Users/lcq/.pyenv/versions/3.11.7/lib/python3.11/asyncio/runners.py", line 190, in run
    return runner.run(main)
           ^^^^^^^^^^^^^^^^
  File "/Users/lcq/.pyenv/versions/3.11.7/lib/python3.11/asyncio/runners.py", line 118, in run
    return self._loop.run_until_complete(task)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/lcq/.pyenv/versions/3.11.7/lib/python3.11/asyncio/base_events.py", line 653, in run_until_complete
    return future.result()
           ^^^^^^^^^^^^^^^
  File "/Users/lcq/PycharmProjects/alist-sync/alist_sync/downloader.py", line 61, in main
    return await create_async_client(target_path.client).put(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/lcq/PycharmProjects/alist-sync/venv/lib/python3.11/site-packages/httpx/_client.py", line 1885, in put
    return await self.request(
           ^^^^^^^^^^^^^^^^^^^
  File "/Users/lcq/PycharmProjects/alist-sync/alist_sync/alist_client.py", line 65, in request
    return await super().request(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/lcq/PycharmProjects/alist-sync/venv/lib/python3.11/site-packages/httpx/_client.py", line 1530, in request
    return await self.send(request, auth=auth, follow_redirects=follow_redirects)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/lcq/PycharmProjects/alist-sync/venv/lib/python3.11/site-packages/httpx/_client.py", line 1617, in send
    response = await self._send_handling_auth(
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/lcq/PycharmProjects/alist-sync/venv/lib/python3.11/site-packages/httpx/_client.py", line 1645, in _send_handling_auth
    response = await self._send_handling_redirects(
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/lcq/PycharmProjects/alist-sync/venv/lib/python3.11/site-packages/httpx/_client.py", line 1682, in _send_handling_redirects
    response = await self._send_single_request(request)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/lcq/PycharmProjects/alist-sync/venv/lib/python3.11/site-packages/httpx/_client.py", line 1719, in _send_single_request
    response = await transport.handle_async_request(request)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/lcq/PycharmProjects/alist-sync/venv/lib/python3.11/site-packages/httpx/_transports/default.py", line 365, in handle_async_request
    with map_httpcore_exceptions():
  File "/Users/lcq/.pyenv/versions/3.11.7/lib/python3.11/contextlib.py", line 158, in __exit__
    self.gen.throw(typ, value, traceback)
  File "/Users/lcq/PycharmProjects/alist-sync/venv/lib/python3.11/site-packages/httpx/_transports/default.py", line 83, in map_httpcore_exceptions
    raise mapped_exc(message) from exc
httpx.ReadError

[dgegen]

Issue with Shared Instance of httpx.AsyncHTTPTransport()

I encountered a similar issue recently. In my case, the problem stemmed from the shared usage of an instance of httpx.AsyncHTTPTransport(), which resulted in httpx.ReadError being raised without a specific error message.

Code Illustrating the Problem:

# httpx_read_error_shared_transport._py
import asyncio
import logging

import httpx


class Downloader:
    def __init__(
        self,
        transport_retries=5,
        download_directory="./tmp",
        timeout=10,
    ) -> None:
        self.download_directory = download_directory
        self.timeout = timeout

        self.transport_retries = transport_retries
        self.transport = httpx.AsyncHTTPTransport(retries=transport_retries)

    async def download_url_list(
        self, url_list, max_concurrent_downloads=5, semaphore=None
    ):
        if semaphore is None:
            semaphore = asyncio.Semaphore(min(max_concurrent_downloads, len(url_list)))

        # --- ATTENTION ---
        # This line causes the error
        async_client = httpx.AsyncClient(transport=self.transport)
        # Instead of sharing `self.transport` , every client should have its own `transport`, e.g.:
        # async_client = httpx.AsyncClient(
        #     transport=httpx.AsyncHTTPTransport(retries=self.transport_retries)
        # )

        async with async_client as client:
            tasks = [
                self.download_and_save_file(
                    client=client,
                    url=url,
                    semaphore=semaphore,
                )
                for url in url_list
            ]

            results = await asyncio.gather(*tasks)
            logging.info(f"Result from download_url_list {results}")
        return results

    async def download_and_save_file(
        self, url, semaphore, client,
    ):
        try:
            async with semaphore:
                response = await client.get(url, timeout=self.timeout)
                response.raise_for_status()

        except httpx.HTTPStatusError as exc:
            logging.error(
                f"HTTP error {exc.response.status_code} - {exc.response.reason_phrase}",
            )
        except httpx.ReadError as exc:
            logging.error(f"Read error: {exc}", exc_info=True)
        except httpx.RequestError as exc:
            logging.error(f"Request error: {exc}", exc_info=True)
        except Exception as exc:
            logging.error(f"An unexpected error occurred: {exc}", exc_info=True)
        else:
            logging.info(f"Downloaded {url}.")
            return True
        return False


async def main_async(downloader):
    # A list of public urls
    url_list = [
        "https://upload.wikimedia.org/wikipedia/commons/a/a4/Ada_Lovelace_portrait.jpg",
        "https://upload.wikimedia.org/wikipedia/commons/8/87/Ada_Lovelace.jpg",
        "https://upload.wikimedia.org/wikipedia/commons/a/a4/Ada_Lovelace_portrait.jpg",
        "https://upload.wikimedia.org/wikipedia/commons/a/a4/Ada_Lovelace_portrait.jpg",
        "https://upload.wikimedia.org/wikipedia/commons/8/87/Ada_Lovelace.jpg",
        "https://upload.wikimedia.org/wikipedia/commons/a/a4/Ada_Lovelace_portrait.jpg",
    ]

    # Call download_url_list twice, such that `self.transport` is used by both of them.
    tasks = [
        downloader.download_url_list(url_list[:2]),
        downloader.download_url_list(url_list[2:]),
    ]
    results = await asyncio.gather(*tasks)
    logging.info(f"Result from main_async {results}")


if __name__ == "__main__":
    logging.basicConfig(level=logging.INFO)
    downloader = Downloader()
    asyncio.run(main_async(downloader))

Issue Reproduction

Executing the above python httpx_read_error_shared_transport.py may produce varying outputs similar to the ones described in this discussion. A part of an en example output is provided below:

Sample Output

ERROR:root:Read error:
Traceback (most recent call last):
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpx/_transports/default.py", line 69, in map_httpcore_exceptions
    yield
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpx/_transports/default.py", line 254, in __aiter__
    async for part in self._httpcore_stream:
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpcore/_async/connection_pool.py", line 367, in __aiter__
    raise exc from None
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpcore/_async/connection_pool.py", line 363, in __aiter__
    async for part in self._stream:
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpcore/_async/http11.py", line 349, in __aiter__
    raise exc
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpcore/_async/http11.py", line 341, in __aiter__
    async for chunk in self._connection._receive_response_body(**kwargs):
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpcore/_async/http11.py", line 210, in _receive_response_body
    event = await self._receive_event(timeout=timeout)
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpcore/_async/http11.py", line 224, in _receive_event
    data = await self._network_stream.read(
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpcore/_backends/anyio.py", line 31, in read
    with map_exceptions(exc_map):
  File "/Users/usr/.pyenv/versions/3.10.13/lib/python3.10/contextlib.py", line 153, in __exit__
    self.gen.throw(typ, value, traceback)
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpcore/_exceptions.py", line 14, in map_exceptions
    raise to_exc(exc) from exc
httpcore.ReadError

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/Users/usr/pydev/test.py", line 55, in download_and_save_file
    response = await client.get(url, timeout=self.timeout)
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpx/_client.py", line 1801, in get
    return await self.request(
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpx/_client.py", line 1574, in request
    return await self.send(request, auth=auth, follow_redirects=follow_redirects)
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpx/_client.py", line 1675, in send
    raise exc
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpx/_client.py", line 1669, in send
    await response.aread()
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpx/_models.py", line 911, in aread
    self._content = b"".join([part async for part in self.aiter_bytes()])
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpx/_models.py", line 911, in <listcomp>
    self._content = b"".join([part async for part in self.aiter_bytes()])
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpx/_models.py", line 929, in aiter_bytes
    async for raw_bytes in self.aiter_raw():
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpx/_models.py", line 987, in aiter_raw
    async for raw_stream_bytes in self.stream:
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpx/_client.py", line 149, in __aiter__
    async for chunk in self._stream:
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpx/_transports/default.py", line 253, in __aiter__
    with map_httpcore_exceptions():
  File "/Users/usr/.pyenv/versions/3.10.13/lib/python3.10/contextlib.py", line 153, in __exit__
    self.gen.throw(typ, value, traceback)
  File "/Users/usr/.pyenv/versions/venv/lib/python3.10/site-packages/httpx/_transports/default.py", line 86, in map_httpcore_exceptions
    raise mapped_exc(message) from exc
httpx.ReadError
INFO:root:Result from download_url_list [False, True]
INFO:root:Result from main_async [[False, True], [True, True, True, True]] 

Recommendation

As indicated in the script above, I was able to mitigate this problem by ensuring that each client instance has its own transport object
rather than sharing a single instance between multiple clients.

Perhaps this example of the inadvisable (and in hindsight naive) sharing of object instances between httpx.AsyncHTTPTransport() can help other users locate the source of the problem in their applications, or help improve the error message that users receive in a future version of this awesome package!