Spaces:

ITookAPill
/

PyComp

Running on Zero

App Files Files Community

PyComp / python_doc_md /Intermediate /library /asyncio-stream.md

ITookAPill

PyComp First Commit

9273228 5 months ago

preview code

Raw

History Blame Contribute Delete

17.6 kB

A newer version of the Gradio SDK is available: 6.20.0

Upgrade

::: currentmodule asyncio :::

Streams {#asyncio-streams}

Source code: Lib/asyncio/streams.py{.interpreted-text role="source"}

Streams are high-level async/await-ready primitives to work with network connections. Streams allow sending and receiving data without using callbacks or low-level protocols and transports.

::: {#asyncio_example_stream} Here is an example of a TCP echo client written using asyncio streams:

import asyncio

async def tcp_echo_client(message):
    reader, writer = await asyncio.open_connection(
        '127.0.0.1', 8888)

    print(f'Send: {message!r}')
    writer.write(message.encode())
    await writer.drain()

    data = await reader.read(100)
    print(f'Received: {data.decode()!r}')

    print('Close the connection')
    writer.close()
    await writer.wait_closed()

asyncio.run(tcp_echo_client('Hello World!'))

:::

StreamReader

::::::::::: StreamReader Represents a reader object that provides APIs to read data from the IO stream. As an asynchronous iterable{.interpreted-text role="term"}, the object supports the async for{.interpreted-text role="keyword"} statement.

It is not recommended to instantiate StreamReader objects directly; use open_connection{.interpreted-text role="func"} and start_server{.interpreted-text role="func"} instead.

::: method feed_eof()

Acknowledge the EOF. :::

::: {.method async=""} read(n=-1)

Read up to n bytes from the stream.

If n is not provided or set to -1, read until EOF, then return all read bytes{.interpreted-text role="class"}. If EOF was received and the internal buffer is empty, return an empty bytes object.

If n is 0, return an empty bytes object immediately.

If n is positive, return at most n available bytes as soon as at least 1 byte is available in the internal buffer. If EOF is received before any byte is read, return an empty bytes object. :::

::: {.method async=""} readline()

Read one line, where "line" is a sequence of bytes ending with \n.

If EOF is received and \n was not found, the method returns partially read data.

If EOF is received and the internal buffer is empty, return an empty bytes object. :::

::: {.method async=""} readexactly(n)

Read exactly n bytes.

Raise an IncompleteReadError{.interpreted-text role="exc"} if EOF is reached before n can be read. Use the IncompleteReadError.partial{.interpreted-text role="attr"} attribute to get the partially read data. :::

::::: {.method async=""} readuntil(separator=b'n')

Read data from the stream until separator is found.

On success, the data and separator will be removed from the internal buffer (consumed). Returned data will include the separator at the end.

If the amount of data read exceeds the configured stream limit, a LimitOverrunError{.interpreted-text role="exc"} exception is raised, and the data is left in the internal buffer and can be read again.

If EOF is reached before the complete separator is found, an IncompleteReadError{.interpreted-text role="exc"} exception is raised, and the internal buffer is reset. The IncompleteReadError.partial{.interpreted-text role="attr"} attribute may contain a portion of the separator.

The separator may also be a tuple of separators. In this case the return value will be the shortest possible that has any separator as the suffix. For the purposes of LimitOverrunError{.interpreted-text role="exc"}, the shortest possible separator is considered to be the one that matched.

::: versionadded 3.5.2 :::

::: versionchanged 3.13

The separator parameter may now be a tuple{.interpreted-text role="class"} of separators. ::: :::::

::: method at_eof()

Return True if the buffer is empty and feed_eof{.interpreted-text role="meth"} was called. ::: :::::::::::

StreamWriter

:::::::::::::::::: StreamWriter Represents a writer object that provides APIs to write data to the IO stream.

It is not recommended to instantiate StreamWriter objects directly; use open_connection{.interpreted-text role="func"} and start_server{.interpreted-text role="func"} instead.

::: method write(data)

The method attempts to write the data to the underlying socket immediately. If that fails, the data is queued in an internal write buffer until it can be sent.

The data buffer should be a bytes, bytearray, or C-contiguous one-dimensional memoryview object.

The method should be used along with the drain() method:

stream.write(data)
await stream.drain()

:::

::: method writelines(data)

The method writes a list (or any iterable) of bytes to the underlying socket immediately. If that fails, the data is queued in an internal write buffer until it can be sent.

The method should be used along with the drain() method:

stream.writelines(lines)
await stream.drain()

:::

::: method close()

The method closes the stream and the underlying socket.

The method should be used, though not mandatory, along with the wait_closed() method:

stream.close()
await stream.wait_closed()

:::

::: method can_write_eof()

Return True if the underlying transport supports the write_eof{.interpreted-text role="meth"} method, False otherwise. :::

::: method write_eof()

Close the write end of the stream after the buffered write data is flushed. :::

::: attribute transport

Return the underlying asyncio transport. :::

::: method get_extra_info(name, default=None)

Access optional transport information; see BaseTransport.get_extra_info{.interpreted-text role="meth"} for details. :::

::: {.method async=""} drain()

Wait until it is appropriate to resume writing to the stream. Example:

writer.write(data)
await writer.drain()

This is a flow control method that interacts with the underlying IO write buffer. When the size of the buffer reaches the high watermark, drain() blocks until the size of the buffer is drained down to the low watermark and writing can be resumed. When there is nothing to wait for, the drain{.interpreted-text role="meth"} returns immediately. :::

::::: {.method async=""} start_tls(sslcontext, *, server_hostname=None, ssl_handshake_timeout=None, ssl_shutdown_timeout=None)

Upgrade an existing stream-based connection to TLS.

Parameters:

sslcontext: a configured instance of ~ssl.SSLContext{.interpreted-text role="class"}.
server_hostname: sets or overrides the host name that the target server's certificate will be matched against.
ssl_handshake_timeout is the time in seconds to wait for the TLS handshake to complete before aborting the connection. 60.0 seconds if None (default).
ssl_shutdown_timeout is the time in seconds to wait for the SSL shutdown to complete before aborting the connection. 30.0 seconds if None (default).

::: versionadded 3.11 :::

::: versionchanged 3.12 Added the ssl_shutdown_timeout parameter. ::: :::::

:::: method is_closing()

Return True if the stream is closed or in the process of being closed.

::: versionadded 3.7 ::: ::::

:::: {.method async=""} wait_closed()

Wait until the stream is closed.

Should be called after close{.interpreted-text role="meth"} to wait until the underlying connection is closed, ensuring that all data has been flushed before e.g. exiting the program.

::: versionadded 3.7 ::: :::: ::::::::::::::::::

Examples

TCP echo client using streams {#asyncio-tcp-echo-client-streams}

TCP echo client using the asyncio.open_connection{.interpreted-text role="func"} function:

import asyncio

async def tcp_echo_client(message):
    reader, writer = await asyncio.open_connection(
        '127.0.0.1', 8888)

    print(f'Send: {message!r}')
    writer.write(message.encode())
    await writer.drain()

    data = await reader.read(100)
    print(f'Received: {data.decode()!r}')

    print('Close the connection')
    writer.close()
    await writer.wait_closed()

asyncio.run(tcp_echo_client('Hello World!'))

::: seealso The TCP echo client protocol <asyncio_example_tcp_echo_client_protocol>{.interpreted-text role="ref"} example uses the low-level loop.create_connection{.interpreted-text role="meth"} method. :::

TCP echo server using streams {#asyncio-tcp-echo-server-streams}

TCP echo server using the asyncio.start_server{.interpreted-text role="func"} function:

import asyncio

async def handle_echo(reader, writer):
    data = await reader.read(100)
    message = data.decode()
    addr = writer.get_extra_info('peername')

    print(f"Received {message!r} from {addr!r}")

    print(f"Send: {message!r}")
    writer.write(data)
    await writer.drain()

    print("Close the connection")
    writer.close()
    await writer.wait_closed()

async def main():
    server = await asyncio.start_server(
        handle_echo, '127.0.0.1', 8888)

    addrs = ', '.join(str(sock.getsockname()) for sock in server.sockets)
    print(f'Serving on {addrs}')

    async with server:
        await server.serve_forever()

asyncio.run(main())

::: seealso The TCP echo server protocol <asyncio_example_tcp_echo_server_protocol>{.interpreted-text role="ref"} example uses the loop.create_server{.interpreted-text role="meth"} method. :::

Get HTTP headers

Simple example querying HTTP headers of the URL passed on the command line:

import asyncio
import urllib.parse
import sys

async def print_http_headers(url):
    url = urllib.parse.urlsplit(url)
    if url.scheme == 'https':
        reader, writer = await asyncio.open_connection(
            url.hostname, 443, ssl=True)
    else:
        reader, writer = await asyncio.open_connection(
            url.hostname, 80)

    query = (
        f"HEAD {url.path or '/'} HTTP/1.0\r\n"
        f"Host: {url.hostname}\r\n"
        f"\r\n"
    )

    writer.write(query.encode('latin-1'))
    while True:
        line = await reader.readline()
        if not line:
            break

        line = line.decode('latin1').rstrip()
        if line:
            print(f'HTTP header> {line}')

    # Ignore the body, close the socket
    writer.close()
    await writer.wait_closed()

url = sys.argv[1]
asyncio.run(print_http_headers(url))

Usage:

python example.py http://example.com/path/page.html

or with HTTPS:

python example.py https://example.com/path/page.html

Register an open socket to wait for data using streams {#asyncio_example_create_connection-streams}

Coroutine waiting until a socket receives data using the open_connection{.interpreted-text role="func"} function:

import asyncio
import socket

async def wait_for_data():
    # Get a reference to the current event loop because
    # we want to access low-level APIs.
    loop = asyncio.get_running_loop()

    # Create a pair of connected sockets.
    rsock, wsock = socket.socketpair()

    # Register the open socket to wait for data.
    reader, writer = await asyncio.open_connection(sock=rsock)

    # Simulate the reception of data from the network
    loop.call_soon(wsock.send, 'abc'.encode())

    # Wait for data
    data = await reader.read(100)

    # Got data, we are done: close the socket
    print("Received:", data.decode())
    writer.close()
    await writer.wait_closed()

    # Close the second socket
    wsock.close()

asyncio.run(wait_for_data())

::: seealso The register an open socket to wait for data using a protocol <asyncio_example_create_connection>{.interpreted-text role="ref"} example uses a low-level protocol and the loop.create_connection{.interpreted-text role="meth"} method.

The watch a file descriptor for read events <asyncio_example_watch_fd>{.interpreted-text role="ref"} example uses the low-level loop.add_reader{.interpreted-text role="meth"} method to watch a file descriptor. :::