feat: add crc32 check

pkg/barrel/header.go

@@ -5,20 +5,18 @@ import (
 	"encoding/binary"
 )
 
-const (
-	HEADER_SIZE = 12
-)
-
 /*
 Record is a binary representation of how each record is persisted in the disk.
-The first three fields have a fixed size of 4 bytes (so 4+4+4=12 bytes fixed width "Header").
+The first three fields have a fixed size of 4 bytes (so 4+4+4+4=16 bytes fixed width "Header").
 Key size = 4 bytes which means tha max size of key can be (2^32)-1 = ~4.29GB.
-Key size = 4 bytes which means tha max size of value can be (2^32)-1 = ~4.29GB.
+Value size = 4 bytes which means tha max size of value can be (2^32)-1 = ~4.29GB.
 Each entry cannot exceed more than ~8.6GB as a theoretical limit.
+
 In a practical sense, this is also constrained by the memory of the underlying VM
 where this program would run.
+
 ------------------------------------------------------
-| time(4) | key_size(4) | val_size(4) | key | val    |
+| crc(4) | time(4) | key_size(4) | val_size(4) | key | val    |
 ------------------------------------------------------
 */
 type Record struct {
@@ -29,7 +27,7 @@ type Record struct {
 
 // Header represents the fixed width fields present at the start of every record.
 type Header struct {
-	// TODO: Add Expiry and CRC.
+	Checksum  uint32
 	Timestamp uint32
 	KeySize   uint32
 	ValSize   uint32

pkg/barrel/keydir.go

@@ -4,7 +4,7 @@ type Meta struct {
 	Timestamp  int
 	RecordSize int
 	RecordPos  int
-	FileID     string
+	FileID     int
 }
 
 type KeyDir map[string]Meta

pkg/barrel/ops.go

@@ -3,6 +3,7 @@ package barrel
 import (
 	"bytes"
 	"fmt"
+	"hash/crc32"
 	"time"
 )
 
@@ -30,12 +31,21 @@ func (b *Barrel) get(k string) ([]byte, error) {
 	// Get the offset position in record to start reading the value from.
 	valPos := meta.RecordSize - int(header.ValSize)
 
-	return record[valPos:], nil
+	// Read the value from the record.
+	val := record[valPos:]
+
+	// Validate the checksum.
+	if crc32.ChecksumIEEE(val) != header.Checksum {
+		return nil, fmt.Errorf("invalid data: checksum does not match")
+	}
+
+	return val, nil
 }
 
-func (b *Barrel) put(k string, val []byte) error {
+func (b *Barrel) put(k string, val []byte, expiry time.Time) error {
 	// Prepare header.
 	header := Header{
+		Checksum:  crc32.ChecksumIEEE(val),
 		Timestamp: uint32(time.Now().Unix()),
 		KeySize:   uint32(len(k)),
 		ValSize:   uint32(len(val)),
@@ -71,7 +81,7 @@ func (b *Barrel) put(k string, val []byte) error {
 		Timestamp:  int(record.Header.Timestamp),
 		RecordSize: len(buf.Bytes()),
 		RecordPos:  offset + len(buf.Bytes()),
-		FileID:     "TODO",
+		FileID:     b.df.ID(),
 	}
 
 	// Ensure filesystem's in memory buffer is flushed to disk.