ambrevar: Add network interface parsing functions.

.local/share/common-lisp/source/ambrevar/shell.lisp

@@ -263,3 +263,34 @@ different Btrfs subvolumes."
                           ;; character, like "\\[".
                           (uiop:native-namestring source)
                           (uiop:native-namestring destination))))
+
+(defun loopback? (interface)
+  (or (string= "link/loopback" (first (second interface)))
+      (string= "lo:" (second (first interface)))))
+
+(defun ipv4 (interface)
+  (when (string= "inet" (first (third interface)))
+    (ppcre:regex-replace "/.*" (second (third interface)) "")))
+
+;; TODO: Make class for interfaces?  Can iolib / usocket be helpful here?
+(defun interfaces (&optional interface)
+  "Return IP of current INTERFACE.
+INTERFACE is a string in the form of `wlp2s0'."
+  (let* ((raw-list (tokenize (run* "ip" "address" interface))))
+    (sera:collecting
+      (sera:do-splits ((l r) (raw-list (lambda (line)
+                                         (ppcre:scan "[0-9]+:" (first line)))))
+        (sera:and-let* ((split (subseq raw-list (max 0 (1- l)) r)))
+          (collect split))))))
+
+(defun interfaces-with-ipv4 ()
+  "Return list of interfaces with ipv4, excluding the loopback."
+  (remove-if (complement #'ipv4)
+             (remove-if #'loopback? (interfaces))))
+
+(defun current-interface ()
+  (first (interfaces-with-ipv4)))
+
+(export-always 'current-ip)
+(defun current-ip ()
+  (ipv4 (default-interface)))