From: Mark Wooding <mdw@distorted.org.uk>
Date: Tue, 22 Apr 2014 13:12:48 +0000 (+0100)
Subject: addr-family-ipv6.lisp (ipaddr-string): Use IPv4 notation if appropriate.
X-Git-Url: https://git.distorted.org.uk/~mdw/zone/commitdiff_plain/1a339c77202274463e6150bea957ddf53b800815

addr-family-ipv6.lisp (ipaddr-string): Use IPv4 notation if appropriate.

This supports the v4-mapped range ::ffff:0.0.0.0/96, and the deprecated
v4-compatible range ::0.0.0.0/96 (with an exception for ::0/112 so that
the magic addresses ::1 and :: still comes out OK).  The output
behaviour here seems to match Linux's inet_ntop(3).
---

diff --git a/addr-family-ipv6.lisp b/addr-family-ipv6.lisp
index 4bec06c..e9dd1aa 100644
--- a/addr-family-ipv6.lisp
+++ b/addr-family-ipv6.lisp
@@ -157,7 +157,8 @@
 
     ;; Third step: output the two parts of the address either side of the
     ;; longest zero run.  If there are no zero words in the address, just
-    ;; write the whole thing.
+    ;; write the whole thing.  There's a special case here for the
+    ;; IPv6-mapped IPv4 address space ::ffff:0.0.0.0/96.
     (with-output-to-string (out)
       (flet ((chunk (start end)
 	       (when (< start end)
@@ -169,6 +170,17 @@
 		     (write-char #\: out))))))
 	(cond ((null best-start)
 	       (chunk 0 8))
+	      ((and (= best-start 0)
+		    (or (and (= best-length 5)
+			     (= (aref words 5) #xffff))
+			(= best-length 6)))
+	       (let ((v4addr (make-instance 'ip4addr
+					    :addr (ldb (byte 32 0) addr))))
+		 (write-string "::" out)
+		 (when (= best-length 5)
+		   (chunk 5 6)
+		   (write-char #\: out))
+		 (write-string (ipaddr-string v4addr) out)))
 	      (t
 	       (chunk 0 best-start)
 	       (write-string "::" out)