Classroom_Desktop/lib/classroom_network.py

"""Reading what ifupdown was told about this machine's network.

Only the parsing, so it can be tested against the file a real machine
actually has rather than against a running laptop.

WHY THIS EXISTS.

The Bible study laptop had working internet and a Plasma network applet
that said there was no connection. Both were true. Debian's installer had
been given the Wi-Fi during installation, so it wrote the network into
/etc/network/interfaces:

    auto wlp2s0
    iface wlp2s0 inet dhcp
        wpa-ssid  Something
        wpa-psk   a-secret

ifupdown brings that up with its own wpa_supplicant and dhcpcd, which is
why the internet works. NetworkManager ships with plugins=ifupdown and
[ifupdown] managed=false, so an interface named in that file is marked
UNMANAGED — which is why nmcli showed `wlp2s0  wifi  unmanaged`, why the
applet had nothing to report, and why scanning found nothing: an
unmanaged device is not a radio NetworkManager will scan with.

managed=false is deliberate and stays. It is what keeps a tower's static
Ethernet under ifupdown's control where an administrator put it. What has
to change is narrower: a WIRELESS interface should belong to
NetworkManager, so the room can see it, scan with it, and so its password
is stored the way this package stores passwords.

So this finds the wireless stanza and everything needed to recreate it as
a NetworkManager system connection.
"""

import re

# ifupdown's own spelling. Values may be quoted, and a psk may be a
# 64-character hex key rather than a passphrase.
SETTINGS = ("wpa-ssid", "wpa-psk", "wpa-key-mgmt", "wpa-conf", "wpa-proto")

_STANZA = re.compile(r"^\s*(iface|auto|allow-hotplug|source|source-directory)\s+(.*)$")


def _unquote(value):
    value = (value or "").strip()

    for quote in ('"', "'"):
        if len(value) >= 2 and value.startswith(quote) and value.endswith(quote):
            return value[1:-1]

    return value


def parse(text):
    """Every `iface` stanza in an interfaces file, with its options.

    Returns a list of dicts: name, family, method, options, and the line
    range the stanza occupies so a caller can comment exactly it out and
    nothing else.
    """
    lines = (text or "").splitlines()
    stanzas = []
    current = None

    for number, raw in enumerate(lines):
        line = raw.split("#", 1)[0].rstrip()
        match = _STANZA.match(line)

        if match:
            keyword, rest = match.group(1), match.group(2).split()

            if keyword == "iface":
                current = {
                    "name": rest[0] if rest else "",
                    "family": rest[1] if len(rest) > 1 else "",
                    "method": rest[2] if len(rest) > 2 else "",
                    "options": {},
                    "first": number,
                    "last": number,
                }
                stanzas.append(current)
            else:
                # auto/allow-hotplug end the previous stanza's body.
                current = None

            continue

        if current is None or not line.strip():
            continue

        parts = line.strip().split(None, 1)

        if not parts:
            continue

        current["options"][parts[0].lower()] = _unquote(
            parts[1] if len(parts) > 1 else "")
        current["last"] = number

    return stanzas


def wireless(stanzas, is_wireless):
    """The stanzas that describe a wireless interface.

    `is_wireless` answers for a device name, so the caller decides how to
    ask the machine — /sys/class/net/<name>/wireless in practice. A
    wpa-ssid is accepted as evidence on its own, for a machine whose
    device has since been renamed or removed.
    """
    found = []

    for stanza in stanzas:
        name = stanza.get("name") or ""

        if not name or name == "lo":
            continue

        if is_wireless(name) or "wpa-ssid" in stanza["options"]:
            found.append(stanza)

    return found


def credentials(stanza):
    """SSID and pre-shared key from a stanza, or (None, None).

    A stanza that points at a wpa_supplicant.conf instead of naming the
    network inline returns no SSID: that one is not ours to move, and the
    caller must leave it alone rather than guess.
    """
    options = stanza.get("options") or {}

    if "wpa-conf" in options and "wpa-ssid" not in options:
        return None, None

    return options.get("wpa-ssid") or None, options.get("wpa-psk") or None


def comment_out(text, stanza, marker="# ekklesia-classroom: "):
    """Comment out exactly one stanza, leaving every other byte alone."""
    lines = (text or "").splitlines(keepends=True)

    for number in range(stanza["first"], stanza["last"] + 1):
        if number < len(lines) and not lines[number].lstrip().startswith("#"):
            lines[number] = marker + lines[number]

    # The `auto`/`allow-hotplug` line above it would otherwise ask
    # ifupdown to bring up an interface it no longer has a stanza for.
    for number in range(stanza["first"] - 1, -1, -1):
        stripped = lines[number].strip() if number < len(lines) else ""

        if not stripped or stripped.startswith("#"):
            continue

        if re.match(r"^(auto|allow-hotplug)\s", stripped) and \
                stanza["name"] in stripped.split():
            lines[number] = marker + lines[number]

        break

    return "".join(lines)