This is a preview version of the DisplayLink DL-7450 Software Development Kit Documentation. The functionality that is described and made available in this version is subject to addition, removal or change without warning.

http — functions for accessing external web services

This module provides functions for making HTTP requests to web endpoints. Requests can be made either synchronously or asynchronously.

A synchronous request blocks the Python application until a response is received or the request times out. An asynchronous request, on the other hand, is initiated in the background and immediately returns control to the application. Once the response is received, a callback function is invoked to handle it.

A running Python application can initiate up to 16 concurrent HTTP requests. Any attempt to create additional requests beyond this limit will fail immediately with status_code 89, corresponding to CURLE_NO_CONNECTION_AVAILABLE.

If a request is sent without any data, a Content-Length: 0 header will be automatically included.

It is the developer’s responsibility to ensure the validity of all arguments. For instance, although sending a GET request with a body is not standard practice and has undefined behavior, the http.get() function still accepts a data argument if needed for a specific use case.

Synchronous HTTP requests

These functions perform HTTP requests and return responses as instances of the http.Response class. The function will block until a response is received or the request fails.

http.get(url, headers=None, data=None, **kwargs)

Sends an HTTP GET request to the given url.

http.post(url, headers=None, data=None, **kwargs)

Sends an HTTP POST request to the given url.

Each function returns an http.Response object containing the status and response.

The request parameters are as follows:

  • url: A string representing a well-formed URL (Uniform Resource Locator).

  • headers: A dict of key-value pairs to be included in the request header as key: value. Both keys and values must be strings.

  • data: A bytes-like object representing the body of the request.

  • **kwargs: A set of optional keyword arguments passed to the request.

Currently supported optional arguments:

  • timeout: The number of seconds before the request times out. The default is 40. Setting this to 0 disables the timeout (use with caution, especially for synchronous requests).

  • cacert: A string containing one or more server certificates in X.509 format. If multiple certificates are provided, they should be concatenated in sequence within the string. By default, the system’s CA certificate store is used to verify server authenticity. If cacert is specified, it overrides the system store and only the provided certificates are used for verification

    import http
import json
from splashscreen import Splashscreen

URL = "https://6pantherpublicanonymous.blob.core.windows.net/dl-7450/content.json"
CERTIFICATE = """
-----BEGIN CERTIFICATE-----
MIIOkTCCDHmgAwIBAgITMwGFNsXF9GOnABFWcQAAAYU2xTANBgkqhkiG9w0BAQwF
ADBdMQswCQYDVQQGEwJVUzEeMBwGA1UEChMVTWljcm9zb2Z0IENvcnBvcmF0aW9u
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-----END CERTIFICATE-----
"""

screen = Splashscreen()

response = http.get(URL, cacert=CERTIFICATE)
if response.status_code() != 200:
    screen.add_text_box(f"error: {response.status_code()}")
else:
    content = json.loads(response.body())
    items = content["data"]["images"]
    screen.add_text_box(items)

The certificate can be stored as a string in the datastore.KvStore, such as:

import http
from splashscreen import Splashscreen
from datastore import KvStore

URL = "https://6pantherpublicanonymous.blob.core.windows.net/dl-7450/content.json"
CERTIFICATE = KvStore().get("cacert")

screen = Splashscreen()

def cb(response):
  if response.status_code() != 200:
    screen.add_text_box(
      f"error: {response.status_code()}")
  else:
    screen.add_text_box("Got content")

http.get_async(URL, cb, cacert=CERTIFICATE)

Asynchronous HTTP requests

These functions initiate HTTP requests asynchronously. The provided callback function handles the response.

http.get_async(url, on_response, headers=None, data=None, **kwargs)

Sends an HTTP GET request to the given url without blocking program flow.

http.post_async(url, on_response, headers=None, data=None, **kwargs)

Sends an HTTP POST request to the given url without blocking program flow.

The parameters are the same as their synchronous counterparts, with the addition of:

  • on_response: A Python callable that takes a single parameter. When the request is complete, the on_response function is called with the resulting http.Response as its argument.

Example::

import http
import json
from wakeup import wakeup
from splashscreen import Splashscreen

url = "https://6pantherpublicanonymous.blob.core.windows.net/dl-7450/content2.json"

splashscreen = Splashscreen()

def on_response(response):
    if response.status_code() != 200:
        raise Exception("Error getting content")
    content = json.loads(response.body())
    items = content["data"]["images"]
    splashscreen.add_text_box(items)

http.get_async(url, on_response, timeout=20)

Classes