Golang File.ReadAt方法代碼示例

// NewReader returns a new table reader for the file. Closing the reader will
// close the file.
func NewReader(f db.File, o *db.Options) *Reader {
	r := &Reader{
		file:            f,
		comparer:        o.GetComparer(),
		verifyChecksums: o.GetVerifyChecksums(),
	}
	if f == nil {
		r.err = errors.New("leveldb/table: nil file")
		return r
	}
	stat, err := f.Stat()
	if err != nil {
		r.err = fmt.Errorf("leveldb/table: invalid table (could not stat file): %v", err)
		return r
	}
	var footer [footerLen]byte
	if stat.Size() < int64(len(footer)) {
		r.err = errors.New("leveldb/table: invalid table (file size is too small)")
		return r
	}
	_, err = f.ReadAt(footer[:], stat.Size()-int64(len(footer)))
	if err != nil && err != io.EOF {
		r.err = fmt.Errorf("leveldb/table: invalid table (could not read footer): %v", err)
		return r
	}
	if string(footer[footerLen-len(magic):footerLen]) != magic {
		r.err = errors.New("leveldb/table: invalid table (bad magic number)")
		return r
	}
	// Ignore the metaindex.
	_, n := decodeBlockHandle(footer[:])
	if n == 0 {
		r.err = errors.New("leveldb/table: invalid table (bad metaindex block handle)")
		return r
	}
	// Read the index into memory.
	indexBH, n := decodeBlockHandle(footer[n:])
	if n == 0 {
		r.err = errors.New("leveldb/table: invalid table (bad index block handle)")
		return r
	}
	r.index, r.err = r.readBlock(indexBH)
	return r
}

func TestBasics(t *testing.T) {
	fs := New()
	testCases := []string{
		// Create a top-level file.
		"1a: create /foo",
		// Create a child of that file. It should fail, since /foo is not a directory.
		"2a: create /foo/x fails",
		// Create a third-level file. It should fail, since /bar has not been created.
		// Similarly, opening that file should fail.
		"3a: create /bar/baz/y fails",
		"3b: open /bar/baz/y fails",
		// Make the /bar/baz directory; create a third-level file. Creation should now succeed.
		"4a: mkdirall /bar/baz",
		"4b: f = create /bar/baz/y",
		"4c: f.stat.name == y",
		// Write some data; read it back.
		"5a: f.write abcde",
		"5b: f.close",
		"5c: f = open /bar/baz/y",
		"5d: f.read 5 == abcde",
		"5e: f.readat 2 1 == bc",
		"5f: f.close",
		// Remove the file twice. The first should succeed, the second should fail.
		"6a: remove /bar/baz/y",
		"6b: remove /bar/baz/y fails",
		"6c: open /bar/baz/y fails",
		// Rename /foo to /goo. Trying to open /foo should succeed before the rename and
		// fail afterwards, and vice versa for /goo.
		"7a: open /foo",
		"7b: open /goo fails",
		"7c: rename /foo /goo",
		"7d: open /foo fails",
		"7e: open /goo",
		// Create /bar/baz/z and rename /bar/baz to /bar/caz.
		"8a: create /bar/baz/z",
		"8b: open /bar/baz/z",
		"8c: open /bar/caz/z fails",
		"8d: rename /bar/baz /bar/caz",
		"8e: open /bar/baz/z fails",
		"8f: open /bar/caz/z",
	}
	var f db.File
	for _, tc := range testCases {
		s := strings.Split(tc, " ")[1:]

		saveF := s[0] == "f" && s[1] == "="
		if saveF {
			s = s[2:]
		}

		fails := s[len(s)-1] == "fails"
		if fails {
			s = s[:len(s)-1]
		}

		var (
			fi  os.FileInfo
			g   db.File
			err error
		)
		switch s[0] {
		case "create":
			g, err = fs.Create(normalize(s[1]))
		case "open":
			g, err = fs.Open(normalize(s[1]))
		case "mkdirall":
			err = fs.MkdirAll(normalize(s[1]), 0755)
		case "remove":
			err = fs.Remove(normalize(s[1]))
		case "rename":
			err = fs.Rename(normalize(s[1]), normalize(s[2]))
		case "f.write":
			_, err = f.Write([]byte(s[1]))
		case "f.read":
			n, _ := strconv.Atoi(s[1])
			buf := make([]byte, n)
			_, err = io.ReadFull(f, buf)
			if err != nil {
				break
			}
			if got, want := string(buf), s[3]; got != want {
				t.Fatalf("%q: got %q, want %q", tc, got, want)
			}
		case "f.readat":
			n, _ := strconv.Atoi(s[1])
			off, _ := strconv.Atoi(s[2])
			buf := make([]byte, n)
			_, err = f.ReadAt(buf, int64(off))
			if err != nil {
				break
			}
			if got, want := string(buf), s[4]; got != want {
				t.Fatalf("%q: got %q, want %q", tc, got, want)
			}
		case "f.close":
			f, err = nil, f.Close()
		case "f.stat.name":
			fi, err = f.Stat()
			if err != nil {
				break
//.........這裏部分代碼省略.........