From 24c9ea126b620f341ec95b9c779fddb55c144ab2 Mon Sep 17 00:00:00 2001
From: tv <tv@krebsco.de>
Date: Fri, 7 Dec 2018 13:17:16 +0100
Subject: lib.krebs.genipv6: init

---
 lib/krebs/genipv6.nix | 92 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 92 insertions(+)
 create mode 100644 lib/krebs/genipv6.nix

diff --git a/lib/krebs/genipv6.nix b/lib/krebs/genipv6.nix
new file mode 100644
index 00000000..8d5ca166
--- /dev/null
+++ b/lib/krebs/genipv6.nix
@@ -0,0 +1,92 @@
+lib:
+with lib;
+let {
+  body = netname: subnetname: suffix: rec {
+    address = let
+      suffix' =
+        if hasEmptyGroup (parseAddress suffix)
+          then suffix
+          else joinAddress "::" suffix;
+    in
+      checkAddress addressLength (joinAddress subnetPrefix suffix');
+    addressCIDR = "${address}/${toString addressLength}";
+    addressLength = 128;
+
+    inherit netname;
+    netCIDR = "${netAddress}/${toString netPrefixLength}";
+    netAddress = joinAddress netPrefix "::";
+    netHash = toString {
+      retiolum = 0;
+      wirelum = 1;
+    }.${netname};
+    netPrefix = "42:${netHash}";
+    netPrefixLength = {
+      retiolum = 32;
+      wirelum = 32;
+    }.${netname};
+
+    inherit subnetname;
+    subnetCIDR = "${subnetAddress}/${toString subnetPrefixLength}";
+    subnetAddress = joinAddress subnetPrefix "::";
+    subnetHash = hash subnetname;
+    subnetPrefix = joinAddress netPrefix subnetHash;
+    subnetPrefixLength = netPrefixLength + 16;
+
+    inherit suffix;
+    suffixLength = addressLength - subnetPrefixLength;
+  };
+
+  hash = s: head (match "0*(.*)" (substring 0 4 (hashString "sha256" s)));
+
+  dropLast = n: xs: reverseList (drop n (reverseList xs));
+  takeLast = n: xs: reverseList (take n (reverseList xs));
+
+  hasEmptyPrefix = xs: take 2 xs == ["" ""];
+  hasEmptySuffix = xs: takeLast 2 xs == ["" ""];
+  hasEmptyInfix = xs: any (x: x == "") (trimEmpty 2 xs);
+
+  hasEmptyGroup = xs:
+    any (p: p xs) [hasEmptyPrefix hasEmptyInfix hasEmptySuffix];
+
+  ltrimEmpty = n: xs: if hasEmptyPrefix xs then drop n xs else xs;
+  rtrimEmpty = n: xs: if hasEmptySuffix xs then dropLast n xs else xs;
+  trimEmpty = n: xs: rtrimEmpty n (ltrimEmpty n xs);
+
+  parseAddress = splitString ":";
+  formatAddress = concatStringsSep ":";
+
+  check = s: c: if !c then throw "${s}" else true;
+
+  checkAddress = maxaddrlen: addr: let
+    parsedaddr = parseAddress addr;
+    normalizedaddr = trimEmpty 1 parsedaddr;
+  in
+    assert (check "address malformed; lone leading colon: ${addr}" (
+      head parsedaddr == "" -> tail (take 2 parsedaddr) == ""
+    ));
+    assert (check "address malformed; lone trailing colon ${addr}" (
+      last parsedaddr == "" -> head (takeLast 2 parsedaddr) == ""
+    ));
+    assert (check "address malformed; too many successive colons: ${addr}" (
+      length (filter (x: x == "") normalizedaddr) > 1 -> addr == [""]
+    ));
+    assert (check "address malformed: ${addr}" (
+      all (test "[0-9a-f]{0,4}") parsedaddr
+    ));
+    assert (check "address is too long: ${addr}" (
+      length normalizedaddr * 16 <= maxaddrlen
+    ));
+    addr;
+
+  joinAddress = prefix: suffix: let
+    parsedPrefix = parseAddress prefix;
+    parsedSuffix = parseAddress suffix;
+    normalizePrefix = rtrimEmpty 2 parsedPrefix;
+    normalizeSuffix = ltrimEmpty 2 parsedSuffix;
+    delimiter =
+      optional (length (normalizePrefix ++ normalizeSuffix) < 8 &&
+                (hasEmptySuffix parsedPrefix || hasEmptyPrefix parsedSuffix))
+               "";
+  in
+    formatAddress (normalizePrefix ++ delimiter ++ normalizeSuffix);
+}
-- 
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