webui: Add "utils.py" to get the IP address

FIXME/TODO:
How to determine the WebSocket origin is in the same subnet as the
server?  An additional network mask required to determine this.
How does this additional mask passed?

1 files changed, 72 insertions, 0 deletions

diff --git a/fg21sim/webui/utils.py b/fg21sim/webui/utils.py
new file mode 100644
index 0000000..1cea69f
--- /dev/null
+++ b/fg21sim/webui/utils.py
@@ -0,0 +1,72 @@
+# Copyright (c) 2016 Weitian LI <liweitianux@live.com>
+# MIT license
+
+"""
+Utilities for the Web UI
+"""
+
+
+from urllib.parse import urlparse
+import socket
+
+
+def get_host_ip(url):
+    """
+    This function parses the input URL to get the hostname (or an IP),
+    then the hostname is further resolved to its IP address.
+
+    Parameters
+    ----------
+    url : str
+        An URL string, which generally has the following format:
+        ``scheme://netloc/path;parameters?query#fragment``
+        while the ``netloc`` may look like ``user:pass@example.com:port``
+
+    Returns
+    -------
+    ip : str
+        An IPv4 address string.
+        If something wrong happens (e.g., ``gaierror``), then ``None``
+        is returned.
+    """
+    netloc = urlparse(url).netloc
+    hostname = netloc.split("@")[-1].split(":")[0]
+    try:
+        ip = socket.gethostbyname(hostname)
+    except socket.gaierror:
+        ip = None
+    return ip
+
+
+def get_local_ip(host="localhost", timeout=3.0):
+    """
+    Get the local IP address of this machine where this script runs.
+
+    A dummy socket will be created and connects to the given host, then
+    the valid local IP address used in this connection can be obtained.
+
+    Parameters
+    ----------
+    host : str
+        The host to which will be connected by a dummy socket, in order
+        to determine the valid IP address.
+    timeout : float
+        Timeout (in seconds) on the blocking socket operations (e.g.,
+        ``connect()``)
+
+    Returns
+    -------
+    ip : str
+        The local IPv4 address of this machine as a string.
+        If something wrong happens (e.g., ``gaierror``), then ``None``
+        is returned.
+    """
+    with socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as s:
+        try:
+            s.settimeout(timeout)
+            # Use 0 as the port will let OS determine the free port
+            s.connect((host, 0))
+            ip = s.getsockname()[0]
+        except (socket.gaierror, socket.timeout):
+            ip = None
+    return ip