commit 1ffa5846e8ada8b991fad61fb43b7cb2a411bd64
Author: kanade <kanade@kumo.work>
Date:   Thu Jun 30 17:25:24 2022 +0800

    init

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..f1c181e
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,12 @@
+# Binaries for programs and plugins
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+
+# Test binary, build with `go test -c`
+*.test
+
+# Output of the go coverage tool, specifically when used with LiteIDE
+*.out
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..6158730
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2019 golangkit
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..6a369f3
--- /dev/null
+++ b/README.md
@@ -0,0 +1 @@
+# filetag
\ No newline at end of file
diff --git a/etag.go b/etag.go
new file mode 100644
index 0000000..0b3ea5e
--- /dev/null
+++ b/etag.go
@@ -0,0 +1,102 @@
+package filetag
+
+import (
+	"bytes"
+	"crypto/sha1"
+	"encoding/base64"
+	"io"
+	"mime/multipart"
+	"os"
+)
+
+const (
+	_BlockBits = 22 // Indicate that the blockSize is 4M
+	_BlockSize = 1 << _BlockBits
+)
+
+func blockCount(fileSize int64) int {
+	return int((fileSize + (_BlockSize -1)) >> _BlockBits)
+}
+
+// 计算文件SHA1值
+func sha1Value(b []byte, r io.Reader) ([]byte, error) {
+
+	h := sha1.New()
+	_, err := io.Copy(h, r)
+	if err != nil {
+		return nil, err
+	}
+	return h.Sum(b), nil
+}
+
+// 依据文件大小将计算出etag值
+func Filename(fn string) (etag string, err error) {
+	f, err := os.Open(fn)
+	if err != nil {
+		return
+	}
+	defer f.Close()
+
+	fi, err := f.Stat()
+	if err != nil {
+		return
+	}
+
+	fileSize := fi.Size()
+	blockCnt := blockCount(fileSize)
+	sha1Buf := make([]byte, 0, 21)
+
+	if blockCnt <= 1 { // file size <= 4M
+		sha1Buf = append(sha1Buf, 0x16)
+		sha1Buf, err = sha1Value(sha1Buf, f)
+		if err != nil {
+			return
+		}
+	} else { // file size > 4M
+		sha1Buf = append(sha1Buf, 0x96)
+		sha1BlockBuf := make([]byte, 0, blockCnt * 20)
+		for i := 0; i < blockCnt; i ++ {
+			body := io.LimitReader(f, _BlockSize)
+			sha1BlockBuf, err = sha1Value(sha1BlockBuf, body)
+			if err != nil {
+				return
+			}
+		}
+		sha1Buf, _ = sha1Value(sha1Buf, bytes.NewReader(sha1BlockBuf))
+	}
+	etag = base64.URLEncoding.EncodeToString(sha1Buf)
+	return
+}
+
+// 依据文件大小将计算出etag值
+func Multipart(f *multipart.FileHeader) (etag string, err error) {
+	src, err := f.Open()
+	if err != nil {
+		return
+	}
+	defer src.Close()
+
+	blockCnt := blockCount(f.Size)
+	sha1Buf := make([]byte, 0, 21)
+
+	if blockCnt <= 1 { // file size <= 4M
+		sha1Buf = append(sha1Buf, 0x16)
+		sha1Buf, err = sha1Value(sha1Buf, src)
+		if err != nil {
+			return
+		}
+	} else { // file size > 4M
+		sha1Buf = append(sha1Buf, 0x96)
+		sha1BlockBuf := make([]byte, 0, blockCnt * 20)
+		for i := 0; i < blockCnt; i ++ {
+			body := io.LimitReader(src, _BlockSize)
+			sha1BlockBuf, err = sha1Value(sha1BlockBuf, body)
+			if err != nil {
+				return
+			}
+		}
+		sha1Buf, _ = sha1Value(sha1Buf, bytes.NewReader(sha1BlockBuf))
+	}
+	etag = base64.URLEncoding.EncodeToString(sha1Buf)
+	return
+}
\ No newline at end of file
diff --git a/etag_test.go b/etag_test.go
new file mode 100644
index 0000000..d4159f3
--- /dev/null
+++ b/etag_test.go
@@ -0,0 +1,15 @@
+package filetag
+
+import (
+	"fmt"
+	"testing"
+)
+
+func Test_etag(t *testing.T) {
+	etag, err := With("/Users/xorshine/Desktop/c.jpeg")
+	if err != nil {
+		t.Fatal(err)
+		return
+	}
+	fmt.Println(etag)
+}