🎉 完成

gif.go

@@ -0,0 +1,48 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package gif implements a GIF image gifdecoder and encoder.
+//
+// The GIF specification is at https://www.w3.org/Graphics/GIF/spec-gif89a.txt.
+
+package imgsz
+
+import (
+	"fmt"
+	"io"
+)
+
+func readFull(r io.Reader, b []byte) error {
+	_, err := io.ReadFull(r, b)
+	if err == io.EOF {
+		err = io.ErrUnexpectedEOF
+	}
+	return err
+}
+
+// gifdecoder is the type used to decode a GIF file.
+type gifdecoder struct {
+	// From header.
+	vers   string
+	width  int
+	height int
+
+	// Used when decoding.
+	tmp [1024]byte // must be at least 768 so we can read color table
+}
+
+func (d *gifdecoder) readHeaderAndScreenDescriptor(r io.Reader) error {
+	err := readFull(r, d.tmp[:13])
+	if err != nil {
+		return fmt.Errorf("gif: reading header: %v", err)
+	}
+	d.vers = string(d.tmp[:6])
+	if d.vers != "GIF87a" && d.vers != "GIF89a" {
+		return fmt.Errorf("gif: can't recognize format %q", d.vers)
+	}
+	d.width = int(d.tmp[6]) + int(d.tmp[7])<<8
+	d.height = int(d.tmp[8]) + int(d.tmp[9])<<8
+	// d.tmp[12] is the Pixel Aspect Ratio, which is ignored.
+	return nil
+}