From d8a48f9eeaaa820a6e985e509d023cc05ae0702f Mon Sep 17 00:00:00 2001
From: James Mills <1290234+prologic@users.noreply.github.com>
Date: Wed, 20 Mar 2019 07:39:03 +1000
Subject: [PATCH] Use pre-defined errors as they are comparable and useful as
 exported symbols

---
 bitcask.go      | 20 ++++++++++++++------
 bitcask_test.go | 12 ++++++------
 2 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/bitcask.go b/bitcask.go
index 6d85889..72bd560 100644
--- a/bitcask.go
+++ b/bitcask.go
@@ -1,7 +1,7 @@
 package bitcask
 
 import (
-	"fmt"
+	"errors"
 	"hash/crc32"
 	"io"
 	"io/ioutil"
@@ -15,6 +15,14 @@ import (
 	"github.com/prologic/bitcask/internal"
 )
 
+var (
+	ErrKeyNotFound    = errors.New("error: key not found")
+	ErrKeyTooLarge    = errors.New("error: key too large")
+	ErrValueTooLarge  = errors.New("error: value too large")
+	ErrChecksumFailed = errors.New("error: checksum failed")
+	ErrDatabaseLocked = errors.New("error: database locked")
+)
+
 type Bitcask struct {
 	*flock.Flock
 
@@ -49,7 +57,7 @@ func (b *Bitcask) Get(key string) ([]byte, error) {
 
 	item, ok := b.keydir.Get(key)
 	if !ok {
-		return nil, fmt.Errorf("error: key not found %s", key)
+		return nil, ErrKeyNotFound
 	}
 
 	if item.FileID == b.curr.FileID() {
@@ -65,7 +73,7 @@ func (b *Bitcask) Get(key string) ([]byte, error) {
 
 	checksum := crc32.ChecksumIEEE(e.Value)
 	if checksum != e.Checksum {
-		return nil, fmt.Errorf("error: checksum falied %s %d != %d", key, e.Checksum, checksum)
+		return nil, ErrChecksumFailed
 	}
 
 	return e.Value, nil
@@ -73,10 +81,10 @@ func (b *Bitcask) Get(key string) ([]byte, error) {
 
 func (b *Bitcask) Put(key string, value []byte) error {
 	if len(key) > b.config.MaxKeySize {
-		return fmt.Errorf("error: key too large %d > %d", len(key), b.config.MaxKeySize)
+		return ErrKeyTooLarge
 	}
 	if len(value) > b.config.MaxValueSize {
-		return fmt.Errorf("error: value too large %d > %d", len(value), b.config.MaxValueSize)
+		return ErrValueTooLarge
 	}
 
 	offset, err := b.put(key, value)
@@ -369,7 +377,7 @@ func Open(path string, options ...option) (*Bitcask, error) {
 	}
 
 	if !locked {
-		return nil, fmt.Errorf("error: database locked %s", path)
+		return nil, ErrDatabaseLocked
 	}
 
 	return bitcask, nil
diff --git a/bitcask_test.go b/bitcask_test.go
index f3c584e..d8e8937 100644
--- a/bitcask_test.go
+++ b/bitcask_test.go
@@ -45,7 +45,7 @@ func TestAll(t *testing.T) {
 		assert.NoError(err)
 		_, err = db.Get("foo")
 		assert.Error(err)
-		assert.Equal("error: key not found foo", err.Error())
+		assert.Equal(ErrKeyNotFound, err)
 	})
 
 	t.Run("Sync", func(t *testing.T) {
@@ -92,7 +92,7 @@ func TestDeletedKeys(t *testing.T) {
 			assert.NoError(err)
 			_, err = db.Get("foo")
 			assert.Error(err)
-			assert.Equal("error: key not found foo", err.Error())
+			assert.Equal(ErrKeyNotFound, err)
 		})
 
 		t.Run("Sync", func(t *testing.T) {
@@ -120,7 +120,7 @@ func TestDeletedKeys(t *testing.T) {
 		t.Run("Get", func(t *testing.T) {
 			_, err = db.Get("foo")
 			assert.Error(err)
-			assert.Equal("error: key not found foo", err.Error())
+			assert.Equal(ErrKeyNotFound, err)
 		})
 
 		t.Run("Close", func(t *testing.T) {
@@ -148,7 +148,7 @@ func TestMaxKeySize(t *testing.T) {
 		value := []byte("foobar")
 		err = db.Put(key, value)
 		assert.Error(err)
-		assert.Equal("error: key too large 17 > 16", err.Error())
+		assert.Equal(ErrKeyTooLarge, err)
 	})
 }
 
@@ -170,7 +170,7 @@ func TestMaxValueSize(t *testing.T) {
 		value := []byte(strings.Repeat(" ", 17))
 		err = db.Put(key, value)
 		assert.Error(err)
-		assert.Equal("error: value too large 17 > 16", err.Error())
+		assert.Equal(ErrValueTooLarge, err)
 	})
 }
 
@@ -387,7 +387,7 @@ func TestLocking(t *testing.T) {
 
 	_, err = Open(testdir)
 	assert.Error(err)
-	assert.Equal(fmt.Sprintf("error: database locked %s", testdir), err.Error())
+	assert.Equal(ErrDatabaseLocked, err)
 }
 
 type benchmarkTestCase struct {