From c25391e9769270459c8256e91f43bbe1f6bba3f5 Mon Sep 17 00:00:00 2001
From: Erik van Velzen <erik@evanv.nl>
Date: Wed, 26 Oct 2022 09:02:13 +0200
Subject: [PATCH] satellite/metabase/rangedloop: uuid generation

Create helper function to generate ranges of UUIDs, for parallelizing
the segment loop.

Change-Id: I17dbc1d5effe27fc1a3491aa9ca56c692bd95df0
---
 satellite/metabase/rangedloop/uuid.go      | 44 ++++++++++
 satellite/metabase/rangedloop/uuid_test.go | 94 ++++++++++++++++++++++
 2 files changed, 138 insertions(+)
 create mode 100644 satellite/metabase/rangedloop/uuid.go
 create mode 100644 satellite/metabase/rangedloop/uuid_test.go

diff --git a/satellite/metabase/rangedloop/uuid.go b/satellite/metabase/rangedloop/uuid.go
new file mode 100644
index 000000000..7b553a1b4
--- /dev/null
+++ b/satellite/metabase/rangedloop/uuid.go
@@ -0,0 +1,44 @@
+// Copyright (C) 2022 Storj Labs, Inc.
+// See LICENSE for copying information.
+
+package rangedloop
+
+import (
+	"encoding/binary"
+
+	"storj.io/common/uuid"
+)
+
+// CreateUUIDBoundaries splits up the entire 128-bit UUID range into equal parts.
+func CreateUUIDBoundaries(nRanges uint32) ([]uuid.UUID, error) {
+	if nRanges == 0 {
+		// every time this line is executed a mathematician feels a disturbance in the force
+		nRanges = 1
+	}
+
+	increment := uint32(1 << 32 / uint64(nRanges))
+
+	result := []uuid.UUID{}
+
+	for i := uint32(1); i < nRanges; i++ {
+		topBits := i * increment
+
+		newUuid, err := MakeUUIDWithTopBits(topBits)
+		if err != nil {
+			return nil, err
+		}
+
+		result = append(result, newUuid)
+	}
+
+	return result, nil
+}
+
+// MakeUUIDWithTopBits creates a zeroed UUID with the top 32 bits set from the input.
+// Technically the result is not a UUID since it doesn't have the version and variant bits set.
+func MakeUUIDWithTopBits(topBits uint32) (uuid.UUID, error) {
+	bytes := make([]byte, 16)
+	binary.BigEndian.PutUint32(bytes, topBits)
+
+	return uuid.FromBytes(bytes)
+}
diff --git a/satellite/metabase/rangedloop/uuid_test.go b/satellite/metabase/rangedloop/uuid_test.go
new file mode 100644
index 000000000..fee6ca544
--- /dev/null
+++ b/satellite/metabase/rangedloop/uuid_test.go
@@ -0,0 +1,94 @@
+// Copyright (C) 2022 Storj Labs, Inc.
+// See LICENSE for copying information.
+
+package rangedloop_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"storj.io/common/uuid"
+	"storj.io/storj/satellite/metabase/rangedloop"
+)
+
+func TestMakeUuids(t *testing.T) {
+	inouts := []struct {
+		inTopBits uint32
+		outUuid   string
+	}{
+		{
+			0,
+			"00000000-0000-0000-0000-000000000000",
+		}, {
+			0xffffffff,
+			"ffffffff-0000-0000-0000-000000000000",
+		}, {
+			0x12345678,
+			"12345678-0000-0000-0000-000000000000",
+		},
+	}
+
+	for _, inout := range inouts {
+		createdUuid, err := rangedloop.MakeUUIDWithTopBits(inout.inTopBits)
+		require.NoError(t, err)
+		require.Equal(t, inout.outUuid, createdUuid.String())
+	}
+}
+
+func TestCreateUuidBoundaries(t *testing.T) {
+	inouts := []struct {
+		inNumRanges uint32
+		outUuids    []string
+	}{
+		{
+			0,
+			[]string{},
+		}, {
+			1,
+			[]string{},
+		}, {
+			2,
+			[]string{
+				"80000000-0000-0000-0000-000000000000",
+			},
+		}, {
+			4,
+			[]string{
+				"40000000-0000-0000-0000-000000000000",
+				"80000000-0000-0000-0000-000000000000",
+				"c0000000-0000-0000-0000-000000000000",
+			},
+		},
+	}
+
+	for _, inout := range inouts {
+		expectedUuids := []uuid.UUID{}
+		for _, outUuidString := range inout.outUuids {
+			outUuid, err := uuid.FromString(outUuidString)
+			require.NoError(t, err)
+			expectedUuids = append(expectedUuids, outUuid)
+		}
+
+		createdRange, err := rangedloop.CreateUUIDBoundaries(inout.inNumRanges)
+		require.NoError(t, err)
+		require.Equal(t, expectedUuids, createdRange)
+	}
+}
+
+func TestCreateUUIDBoundariesFor8191Ranges(t *testing.T) {
+	// 0x1fff = Mersenne prime 8191
+	boundaries, err := rangedloop.CreateUUIDBoundaries(0x1fff)
+	require.NoError(t, err)
+	require.Len(t, boundaries, 0x1ffe)
+
+	// floor(2 ^ 32 / 0x1fff) = 0x80040
+	secondUuid, err := uuid.FromString("00080040-0000-0000-0000-000000000000")
+	require.NoError(t, err)
+	require.Equal(t, secondUuid, boundaries[0])
+
+	// floor(2 ^ 32 / 0x1fff) * 0x1ffe = 0xfff7ff80
+	lastUuid, err := uuid.FromString("fff7ff80-0000-0000-0000-000000000000")
+	require.NoError(t, err)
+	require.Equal(t, lastUuid, boundaries[0x1ffd])
+}