From 3619de6000b340dbd71eb12849410cc9ffbbaa64 Mon Sep 17 00:00:00 2001
From: Kim Alvefur <zash@zash.se>
Date: Sun, 15 Aug 2021 14:44:21 +0200
Subject: util.uuid: Add UUIDv7

Allows sorting by id as a substitute for sorting by timestamp since it
has the timestamp in the encoded in the first part, and only things that
happen extremely close together may get out of order by such a sort,
which might not matter.

From draft-ietf-uuidrev-rfc4122bis formerly draft-peabody-dispatch-new-uuid-format
---
 spec/util_uuid_spec.lua | 22 ++++++++++++++++++++++
 util/uuid.lua           | 17 +++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/spec/util_uuid_spec.lua b/spec/util_uuid_spec.lua
index 46400d00..7157d0ec 100644
--- a/spec/util_uuid_spec.lua
+++ b/spec/util_uuid_spec.lua
@@ -20,6 +20,28 @@ describe("util.uuid", function()
 			for _ = 1, 100 do
 				assert.is_string(uuid.generate():match(pattern));
 			end
+
+			assert.truthy(uuid.generate() ~= uuid.generate(), "does not generate the same UUIDv4 twice")
+		end);
+	end);
+	describe("#v7", function()
+		it("should also follow the UUID pattern", function()
+			local pattern = "^" .. table.concat({
+					string.rep("%x", 8),
+					string.rep("%x", 4),
+					"7" .. -- version
+					string.rep("%x", 3),
+					"[89ab]" .. -- reserved bits of 1 and 0
+					string.rep("%x", 3),
+					string.rep("%x", 12),
+				}, "%-") .. "$";
+
+			local one = uuid.v7(); -- one before the loop to ensure some time passes
+			for _ = 1, 100 do
+				assert.is_string(uuid.v7():match(pattern));
+			end
+			-- one after the loop when some time should have passed
+			assert.truthy(one < uuid.v7(), "should be ordererd")
 		end);
 	end);
 end);
diff --git a/util/uuid.lua b/util/uuid.lua
index 41c2e9cd..a70750bb 100644
--- a/util/uuid.lua
+++ b/util/uuid.lua
@@ -8,8 +8,10 @@
 
 local random = require "prosody.util.random";
 local random_bytes = random.bytes;
+local time = require "prosody.util.time";
 local hex = require "prosody.util.hex".encode;
 local m_ceil = math.ceil;
+local m_floor = math.floor;
 
 local function get_nibbles(n)
 	return hex(random_bytes(m_ceil(n/2))):sub(1, n);
@@ -24,7 +26,22 @@ local function generate()
 	return get_nibbles(8).."-"..get_nibbles(4).."-4"..get_nibbles(3).."-"..(get_twobits())..get_nibbles(3).."-"..get_nibbles(12);
 end
 
+local function generate_v7()
+	-- Sortable based on time and random
+	-- https://datatracker.ietf.org/doc/html/draft-peabody-dispatch-new-uuid-format-01#section-4.4
+	local t = time.now();
+	local unixts = m_floor(t);
+	local unixts_a = m_floor(unixts / 16);
+	local unixts_b = m_floor(unixts % 16);
+	local subsec = t % 1;
+	local subsec_a = m_floor(subsec * 0x1000);
+	local subsec_b = m_floor(subsec * 0x1000000) % 0x1000;
+	return ("%08x-%x%03x-7%03x-%4s-%12s"):format(unixts_a, unixts_b, subsec_a, subsec_b, get_twobits() .. get_nibbles(3), get_nibbles(12));
+end
+
 return {
+	v4 = generate;
+	v7 = generate_v7;
 	get_nibbles=get_nibbles;
 	generate = generate ;
 	-- COMPAT
-- 
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