feat(linux): Adapters and its Proxy row work on Linux

CHANGELOG.md

@@ -19,14 +19,12 @@ The format follows [Keep a Changelog](https://keepachangelog.com/); versions fol
   capture, and a refused START says what to do. The Statistics page and its CSV count
   packets that went around the tool and those the driver dropped, with a red line while
   either grows. Its files stay yours, and GitHub and Donate print the address instead of
-  starting a browser as root. On the Tools tab, TCP health and Adapters say they are
-  Windows-only for now, and the row menus grey out Show TCP health.
+  starting a browser as root. On the Tools tab, TCP health says it is Windows-only for now,
+  and the row menus grey out Show TCP health.
 
 - **Linux, experimental: Diagnostics speaks of Linux.** Its help explains what stops a
   session there - capture rights, the kernel, BTF and pydivert - and what to do, and
-  **Clean up the driver** says why there is nothing to clean up. **Add network adapters** and
-  **Add proxy settings** are greyed out and say why, because the Adapters tool works on
-  Windows only for now.
+  **Clean up the driver** says why there is nothing to clean up.
 
 - **Linux, experimental: Ping works.** It sends through the system's ping socket, which needs
   no sudo where the system lets your group send pings (`net.ipv4.ping_group_range`), and under
@@ -43,6 +41,13 @@ The format follows [Keep a Changelog](https://keepachangelog.com/); versions fol
   kernel cannot reset connections (WSL's), the entry is greyed out. A connection missing from
   the system's list has closed or belongs to another network namespace, such as a container's.
 
+- **Linux, experimental: Adapters and its Proxy row work, without sudo.** The adapters, their
+  addresses, gateways and the route to the internet are what `ip addr` and `ip route` show,
+  and each DNS server is listed at the adapter its questions leave through. The Proxy row
+  shows the desktop's proxy settings (GNOME) and the proxy variables in `/etc/environment`
+  and the `environment.d` folders, also under sudo as yours. **Add network adapters** and
+  **Add proxy settings** in Diagnostics work too.
+
 - **Ping on the Tools tab, to see the session's latency and loss arrive.** Type an address or a
   name and press **Start**: each ping is a row with its round trip and what came back, the last
   60 are charted, and the totals say what was lost. The ping goes on while another tab is in

README.md

@@ -212,16 +212,30 @@ exit code 1, as on Windows without administrator rights. Where Linux differs fro
   through a raw socket, which needs the capability CAP_NET_RAW: root has it unless the system
   takes it away, as some containers do. A ping Linux refuses shows its own word for it:
   `EPERM` usually means a firewall rule on this computer.
-  A zone of an IPv6 address can be the interface's name (`fe80::1%eth0`). TCP health and
-  Adapters say that they work on Windows only for now, and so do the row menu entries that open
-  them, and the Diagnostics boxes that add the adapters or the proxy to the report. The
+  A zone of an IPv6 address can be the interface's name (`fe80::1%eth0`). TCP health says that
+  it works on Windows only for now, and so do the row menu entries that open it. The
   Diagnostics help explains the Linux checks: capture rights, the kernel, BTF and pydivert.
 - **"Reset this connection"** on the Connections page works on Linux for TCP over IPv4 and IPv6,
   as root or with the capability CAP_NET_ADMIN. The program using the connection gets
   `ECONNABORTED`, and the other end gets a reset. It needs a kernel built with
   `CONFIG_INET_DIAG_DESTROY`: Ubuntu's is, WSL's is not, and there the entry is greyed out. A
   connection that is not in this system's list of connections has closed, or belongs to a
   container or another network namespace, and cannot be reset from here.
+- **Adapters** on the Tools tab works on Linux, without `sudo`. The adapters, their addresses,
+  the gateways and the route to the internet come from the kernel's own tables, as `ip addr`
+  and `ip route` show them, and the MAC address is written the way `ip` writes it. An adapter
+  whose driver reports no state, such as the loopback or a WireGuard tunnel, is Up when it has
+  a link (`ip` shows it as UNKNOWN). Each DNS server is listed at the adapter its questions
+  leave through: when systemd-resolved answers for this computer, `127.0.0.53` is at the
+  loopback and the servers it asks are at their own adapters. DHCP is Yes when an IPv4
+  address has a lease or the default route came from DHCP. The DHCP server and the DNS suffix
+  are not shown: only NetworkManager's own files hold them.
+- The **Proxy** row of Adapters shows the desktop's proxy settings (GNOME) and the proxy
+  variables in `/etc/environment`, the `environment.d` folders and your
+  `~/.config/environment.d`. Variables set in a shell's startup files, such as `~/.bashrc`, are
+  not read. The desktop's settings are read with `gsettings`, as you, also under `sudo`: this
+  is the one program the tool starts, and it sends nothing. There is no proxy for services as
+  on Windows (WinHTTP).
 
 ## The window
 
@@ -353,9 +367,9 @@ monitor is gone it returns to the centre of the current screen.
     field"** puts the expression into that field, replacing what is there. What you type
     stays until you close the program, even if you switch the language.
   - **Adapters** - every network adapter on this computer and the settings a test depends
-    on, the kind `ipconfig /all` prints (Windows only). The adapter your internet traffic
-    leaves through is at the top,
-    then the ones that are up. Choose one to see its addresses with their prefixes, the
+    on, the kind `ipconfig /all` prints (on Linux, `ip addr` and `ip route`). The adapter
+    your internet traffic leaves through is at the top, then the ones that are up. Choose
+    one to see its addresses with their prefixes, the
     gateway, the DNS servers, DHCP, the MAC address, the MTU and the link speed. A note
     warns when another device uses the same address. The list is read when you open the tab
     and when you press **Refresh**. Right-click a gateway or a DNS server to put its address
@@ -1603,9 +1617,11 @@ beantester/              the implementation package
   validators.py          number and range validation (shared by GUI, CLI and config file)
   portmap.py             socket table: local port -> PID (iphlpapi/ctypes; psutil fallback),
                          and every socket with its state for the Tools tab
-  adapters.py            network adapters and the route out (iphlpapi/ctypes), for the Tools tab
+  adapters.py            network adapters and the route out (iphlpapi/ctypes; on Linux the
+                         kernel's tables, sysfs and the resolver's files), for the Tools tab
   proxy.py               the proxy this account and this machine use (winhttp/ctypes and the
-                         registry), read only, for the Tools tab
+                         registry; on Linux gsettings and the environment files), read only,
+                         for the Tools tab
   tcpestats.py           what Windows' TCP stack measures for one connection (EStats,
                          iphlpapi/ctypes), for the Tools tab's TCP health
   tcpreset.py            reset one TCP connection (iphlpapi/ctypes; on Linux the kernel's
@@ -1614,6 +1630,10 @@ beantester/              the implementation package
                          finding it in the socket table, without calling Windows
   sockdiag.py            the kernel's own list of TCP sockets on Linux (sock_diag over
                          netlink), read only: where a reset finds the socket it destroys
+  rtnetlink.py           the kernel's tables of adapters, addresses and routes on Linux, and a
+                         route lookup (what ip route get asks), read only, for the adapters
+  netlink.py             the message socket to the Linux kernel under sockdiag and rtnetlink:
+                         one request out, its answer read to its end
   icmp.py                one ICMP echo request (iphlpapi/ctypes), for the Tools tab's Ping -
                          the only module that sends something of its own
   icmpsock.py            the same request on Linux, through the system's ping socket or a