From 525abb53fd8c40a0e0aea44cf62466c5a184c5cd Mon Sep 17 00:00:00 2001
From: AYM1607 <u.g.a.mariano@gmail.com>
Date: Tue, 3 Aug 2021 22:56:25 -0500
Subject: [PATCH] Finished index with its tests.

---
 internal/log/config.go     |   9 ++++
 internal/log/index.go      | 100 +++++++++++++++++++++++++++++++++++++
 internal/log/index_test.go |  57 +++++++++++++++++++++
 3 files changed, 166 insertions(+)
 create mode 100644 internal/log/config.go
 create mode 100644 internal/log/index.go
 create mode 100644 internal/log/index_test.go

diff --git a/internal/log/config.go b/internal/log/config.go
new file mode 100644
index 0000000..2df654d
--- /dev/null
+++ b/internal/log/config.go
@@ -0,0 +1,9 @@
+package log
+
+type Config struct {
+	Segment struct {
+		MaxStoreBytes uint64
+		MaxIndexBytes uint64
+		InitialOffset uint64
+	}
+}
diff --git a/internal/log/index.go b/internal/log/index.go
new file mode 100644
index 0000000..b88d1d8
--- /dev/null
+++ b/internal/log/index.go
@@ -0,0 +1,100 @@
+package log
+
+import (
+	"io"
+	"os"
+
+	"github.com/tysontate/gommap"
+)
+
+var (
+	offWidth uint64 = 4
+	posWidth uint64 = 8
+	entWidth        = offWidth + posWidth
+)
+
+type index struct {
+	file *os.File
+	mmap gommap.MMap
+	size uint64
+}
+
+func newIndex(f *os.File, c Config) (*index, error) {
+	idx := &index{
+		file: f,
+	}
+	fi, err := os.Stat(f.Name())
+	if err != nil {
+		return nil, err
+	}
+
+	// Get and store the file size.
+	idx.size = uint64(fi.Size())
+	// Grow the file to its max size so it can be memory mapped as a whole.
+	if err = os.Truncate(
+		f.Name(), int64(c.Segment.MaxIndexBytes),
+	); err != nil {
+		return nil, err
+	}
+	// Map the grown file to memory.
+	if idx.mmap, err = gommap.Map(
+		idx.file.Fd(),
+		gommap.PROT_READ|gommap.PROT_WRITE,
+		gommap.MAP_SHARED,
+	); err != nil {
+		return nil, err
+	}
+
+	return idx, nil
+}
+
+func (i *index) Read(in int64) (out uint32, pos uint64, err error) {
+	if i.size == 0 {
+		return 0, 0, io.EOF
+	}
+	if in == -1 {
+		// The last entity was requested
+		out = uint32((i.size / entWidth) - 1)
+	} else {
+		out = uint32(in)
+	}
+
+	pos = uint64(out) * entWidth
+
+	// Check that the index actually contains the record with the given offset.
+	if i.size < pos+entWidth {
+		return 0, 0, io.EOF
+	}
+
+	out = enc.Uint32(i.mmap[pos : pos+offWidth])
+	pos = enc.Uint64(i.mmap[pos+offWidth : pos+entWidth])
+	return out, pos, nil
+}
+
+func (i *index) Write(off uint32, pos uint64) error {
+	if uint64(len(i.mmap)) < i.size+entWidth {
+		return io.EOF
+	}
+	enc.PutUint32(i.mmap[i.size:i.size+offWidth], off)
+	enc.PutUint64(i.mmap[i.size+offWidth:i.size+entWidth], pos)
+	i.size += entWidth
+	return nil
+}
+
+func (i *index) Name() string {
+	return i.file.Name()
+}
+
+func (i *index) Close() error {
+	if err := i.mmap.Sync(gommap.MS_SYNC); err != nil {
+		return err
+	}
+	if err := i.file.Sync(); err != nil {
+		return err
+	}
+	if err := i.file.Truncate(int64(i.size)); err != nil {
+		return err
+	}
+
+	return i.file.Close()
+}
diff --git a/internal/log/index_test.go b/internal/log/index_test.go
new file mode 100644
index 0000000..ac24f5f
--- /dev/null
+++ b/internal/log/index_test.go
@@ -0,0 +1,57 @@
+package log
+
+import (
+	"io"
+	"io/ioutil"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestIndex(t *testing.T) {
+	// Create a temp file.
+	f, err := ioutil.TempFile(os.TempDir(), "index_tes")
+	require.NoError(t, err)
+	defer os.Remove(f.Name())
+
+	// Use a configuration that allows enough bytes for the test.
+	c := Config{}
+	c.Segment.MaxIndexBytes = 1024
+	idx, err := newIndex(f, c)
+	require.NoError(t, err)
+
+	_, _, err = idx.Read(-1)
+	require.Error(t, err, "Read should return an error on empty index.")
+
+	require.Equal(t, f.Name(), idx.Name(), "Name should return the same name as the underlying file.")
+
+	entries := []struct {
+		Off uint32
+		Pos uint64
+	}{
+		{Off: 0, Pos: 0},
+		{Off: 1, Pos: 10},
+	}
+
+	for _, want := range entries {
+		err = idx.Write(want.Off, want.Pos)
+		require.NoError(t, err, "No error when writing to an index with enough space.")
+
+		_, pos, err := idx.Read(int64(want.Off))
+		require.NoError(t, err, "No error when reading an existing record.")
+		require.Equal(t, want.Pos, pos, "Read pos should be the same as the read one.")
+	}
+
+	_, _, err = idx.Read(int64(len(entries)))
+	require.Equal(t, io.EOF, err, "Read should error with EOF when reading past the index records.")
+	_ = idx.Close()
+
+	f, _ = os.OpenFile(f.Name(), os.O_RDWR, 0600)
+	idx, err = newIndex(f, c)
+	require.NoError(t, err, "No error when creating index from an existing file.")
+	off, pos, err := idx.Read(-1)
+	require.NoError(t, err, "No error when reading the last record of a non empty index.")
+	require.Equal(t, uint32(1), off)
+	require.Equal(t, entries[1].Pos, pos)
+}