From 56c3205aae19db3b2e78bc927603e050054cc740 Mon Sep 17 00:00:00 2001
From: 52funny <wwq9977@gmail.com>
Date: Tue, 22 Nov 2022 22:15:16 +0800
Subject: [PATCH] add more efficient way to calculate sha1 of file

---
 utils/file_hash.go | 150 +++++++++++++++++++++++++++++++++++++--------
 1 file changed, 125 insertions(+), 25 deletions(-)

diff --git a/utils/file_hash.go b/utils/file_hash.go
index 9cfa95c..2d21716 100644
--- a/utils/file_hash.go
+++ b/utils/file_hash.go
@@ -3,13 +3,17 @@ package utils
 import (
 	"crypto/sha1"
 	"fmt"
-	"hash"
 	"io"
+	"math"
 	"os"
+	"sort"
 )
 
 var BufSize = 1 << 16
 
+// number of the calculate routine
+var CalculateRoutine = 1 << 3
+
 func getChunkSize(size int64) int64 {
 	if size > 0 && size < 0x8000000 {
 		return 0x40000
@@ -22,6 +26,95 @@ func getChunkSize(size int64) int64 {
 	}
 	return 0x100000
 }
+
+// func FileSha1(path string) string {
+// 	file, err := os.Open(path)
+// 	if err != nil {
+// 		return ""
+// 	}
+// 	defer file.Close()
+
+// 	resHash := sha1.New()
+
+// 	state, _ := file.Stat()
+// 	chunk := getChunkSize(state.Size())
+
+// 	buf := make([]byte, BufSize)
+
+// 	var total int64 = 0
+// 	var partHash hash.Hash
+
+// LABEL:
+// 	for {
+// 		partHash = sha1.New()
+// 		total = 0
+// 		for {
+// 			n, err := file.Read(buf)
+// 			if err != nil {
+// 				if err == io.EOF {
+// 					break LABEL
+// 				}
+// 				return ""
+// 			}
+// 			partHash.Write(buf[:n])
+// 			total += int64(n)
+
+// 			if total >= chunk {
+// 				break
+// 			}
+// 		}
+// 		resHash.Write(partHash.Sum(nil))
+// 	}
+// 	if total > 0 {
+// 		resHash.Write(partHash.Sum(nil))
+// 	}
+// 	checksum := fmt.Sprintf("%x", resHash.Sum(nil))
+// 	return checksum
+// }
+
+type segmentInfo struct {
+	id     int64
+	offset int64
+}
+type segmentData struct {
+	id   int64
+	data []byte
+}
+
+func calculate(file *os.File, chunkSize int64, ch chan segmentInfo, outCh chan segmentData) {
+	buf := make([]byte, BufSize)
+	for {
+		info, ok := <-ch
+		// fmt.Println(info, ok)
+		if !ok {
+			break
+		}
+		partHash := sha1.New()
+		offset := info.offset
+		total := int64(0)
+		for {
+
+			// ReadAt not similar with Read
+			n, err := file.ReadAt(buf, offset)
+			offset += int64(n)
+			total += int64(n)
+
+			// write buf to hash to calculate the sha1
+			partHash.Write(buf[:n])
+
+			if total >= chunkSize {
+				break
+			}
+
+			if err != nil && err == io.EOF {
+				break
+			}
+
+		}
+		outCh <- segmentData{id: info.id, data: partHash.Sum(nil)}
+	}
+}
+
 func FileSha1(path string) string {
 	file, err := os.Open(path)
 	if err != nil {
@@ -34,34 +127,41 @@ func FileSha1(path string) string {
 	state, _ := file.Stat()
 	chunk := getChunkSize(state.Size())
 
-	buf := make([]byte, BufSize)
+	// segment length
+	segmentLen := int64(math.Ceil(float64(state.Size()) / float64(chunk)))
 
-	var total int64 = 0
-	var partHash hash.Hash
+	inCh := make(chan segmentInfo, segmentLen)
+	outCh := make(chan segmentData, CalculateRoutine)
 
-LABEL:
-	for {
-		partHash = sha1.New()
-		total = 0
-		for {
-			n, err := file.Read(buf)
-			if err != nil {
-				if err == io.EOF {
-					break LABEL
-				}
-				return ""
-			}
-			partHash.Write(buf[:n])
-			total += int64(n)
+	// start go routine
+	for i := 0; i < CalculateRoutine; i++ {
+		go calculate(file, chunk, inCh, outCh)
+	}
 
-			if total >= chunk {
-				break
-			}
-		}
-		resHash.Write(partHash.Sum(nil))
+	// send info data to go routine
+	for i := int64(0); i < segmentLen; i++ {
+		inCh <- segmentInfo{id: i, offset: chunk * i}
+	}
+	close(inCh)
+
+	// collect data
+	result := make([]segmentData, 0)
+	for i := int64(0); i < segmentLen; i++ {
+		result = append(result, <-outCh)
 	}
-	if total > 0 {
-		resHash.Write(partHash.Sum(nil))
+	// close the channel
+	close(outCh)
+
+	// sort by id asc
+	sort.Slice(result, func(i, j int) bool {
+		return result[i].id < result[j].id
+	})
+
+	// fmt.Printf("%d %x\n", result[1].id, result[1].data)
+	// fmt.Printf("%d %x\n", result[2].id, result[2].data)
+	// calculate file sha1
+	for i := 0; i < len(result); i++ {
+		resHash.Write(result[i].data)
 	}
 	checksum := fmt.Sprintf("%x", resHash.Sum(nil))
 	return checksum