Added Feature: Example for Captive Portal system.

Feature note: Sets up a simple DNS server that answers all questions with the ESP softAP's IP as well as a HTTP server which redirects all requests to a captive portal welcoming page.
Triggers captive portal detection (log-in screen popup) for iOS, Android and Windows.
Includes example test for testing DNS redirect and HTTP redirect.

Closes https://github.com/espressif/esp-idf/issues/7099
Closes https://github.com/espressif/esp-idf/issues/4075

examples/protocols/http_server/captive_portal/example_test.py

@@ -0,0 +1,142 @@
+#!/usr/bin/env python
+#
+# Copyright 2021 Espressif Systems (Shanghai) PTE LTD
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import print_function
+
+import http.client
+import os
+import re
+import socket
+import sys
+
+import tiny_test_fw
+import ttfw_idf
+from tiny_test_fw import Utility
+
+try:
+    import wifi_tools
+except ImportError:
+    wifi_tools_path = str(os.getenv('IDF_PATH')) + '/examples/provisioning/softap_prov/utils'
+    if wifi_tools_path and wifi_tools_path not in sys.path:
+        sys.path.insert(0, wifi_tools_path)
+    import wifi_tools
+
+
+def test_redirect(ip, port):  # type: (str, str) -> str # pylint: disable=unused-argument
+    # Establish HTTP connection
+    sess = http.client.HTTPConnection(ip + ':' + port, timeout=15)
+
+    uri = '/test'
+    # GET response
+    sess.request('GET', url=uri)
+    resp = sess.getresponse()
+    resp_hdrs = resp.getheaders()
+
+    if resp.status != 302:
+        raise RuntimeError('Redirect failed, response status: {}'.format(resp.status))
+
+    for hdr in resp_hdrs:
+        if hdr[0] == 'location':
+            uri = hdr[1]
+
+    print('Redirected to uri: {}'.format(uri))
+
+    # Close HTTP connection
+    sess.close()
+
+    return uri
+
+
+def test_captive_page(ip, port, uri):  # type: (str, str, str) -> bool # pylint: disable=unused-argument
+    # Establish HTTP connection
+    sess = http.client.HTTPConnection(ip + ':' + port, timeout=15)
+
+    # GET response
+    sess.request('GET', url=uri)
+    resp = sess.getresponse()
+
+    resp_data = resp.read().decode()
+    search_str = 'Redirect to the captive portal'
+
+    if search_str not in resp_data:
+        raise RuntimeError('Failed to match {} with data from captive portal: {}'.format(search_str, resp_data))
+
+    # Close HTTP connection
+    sess.close()
+    return True
+
+
+@ttfw_idf.idf_example_test(env_tag='Example_WIFI_BT', ignore=True)
+def test_example_captive_portal(env, extra_data):  # type: (tiny_test_fw.Env.Env, None) -> None # pylint: disable=unused-argument
+    # Acquire DUT
+    dut1 = env.get_dut('captive_portal', 'examples/protocols/http_server/captive_portal', dut_class=ttfw_idf.ESP32DUT)
+
+    # Get binary file
+    binary_file = os.path.join(dut1.app.binary_path, 'captive_portal.bin')
+    bin_size = os.path.getsize(binary_file)
+    ttfw_idf.log_performance('captive_portal_bin_size', '{}KB'.format(bin_size // 1024))
+
+    # Upload binary and start testing
+    dut1.start_app()
+
+    # Parse IP address of STA
+    Utility.console_log('Waiting to connect with softAP')
+    ap_ip = dut1.expect(re.compile(r'Set up softAP with IP: (\d+.\d+.\d+.\d+)'), timeout=60)[0]
+
+    [ssid, password] = dut1.expect(re.compile(r"wifi_init_softap finished. SSID:'(\S+)' password:'(\S+)'"), timeout=30)
+    port = dut1.expect(re.compile(r"(?:[\s\S]*)Starting server on port: '(\d+)'"), timeout=30)[0]
+
+    iface = wifi_tools.get_wiface_name()
+    if iface is None:
+        raise RuntimeError('Failed to get Wi-Fi interface on host')
+    print('Interface name  : ' + iface)
+    print('SoftAP SSID     : ' + ssid)
+    print('SoftAP Password : ' + password)
+
+    try:
+        ctrl = wifi_tools.wpa_cli(iface, reset_on_exit=True)
+        print('Connecting to DUT SoftAP...')
+        try:
+            ip = ctrl.connect(ssid, password)
+        except RuntimeError as err:
+            Utility.console_log('error: {}'.format(err))
+        try:
+            got_ip = dut1.expect(re.compile(r'DHCP server assigned IP to a station, IP is: (\d+.\d+.\d+.\d+)'), timeout=60)
+            Utility.console_log('got_ip: {}'.format(got_ip))
+            got_ip = got_ip[0]
+            if ip != got_ip:
+                raise RuntimeError('SoftAP connected to another host! {} != {}'.format(ip, got_ip))
+        except tiny_test_fw.DUT.ExpectTimeout:
+            # print what is happening on DUT side
+            Utility.console_log('in exception tiny_test_fw.DUT.ExpectTimeout')
+            Utility.console_log(dut1.read())
+            raise
+        print('Connected to DUT SoftAP')
+
+        host_name = 'www.google.com'
+        host = socket.gethostbyname(host_name)
+        print('hostname: {} resolved to: {}'.format(host_name, host))
+        if host != ap_ip:
+            raise RuntimeError("DNS server failed to redirect question to the softAP's IP")
+
+        uri = test_redirect(ap_ip, port)
+        test_captive_page(ap_ip, port, uri)
+    finally:
+        ctrl.reset()
+
+
+if __name__ == '__main__':
+    test_example_captive_portal()  # pylint: disable=no-value-for-parameter