ardump: todo

x/ar/reader.go

@@ -0,0 +1,148 @@
+/*
+ * Copyright (c) 2024 The GoPlus Authors (goplus.org). All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package ar
+
+import (
+	"io"
+	"strconv"
+	"time"
+)
+
+// Provides read access to an ar archive.
+// Call next to skip files
+//
+// Example:
+//	reader := NewReader(f)
+//	var buf bytes.Buffer
+//	for {
+//		_, err := reader.Next()
+//		if err == io.EOF {
+//			break
+//		}
+//		if err != nil {
+//			t.Errorf(err.Error())
+//		}
+//		io.Copy(&buf, reader)
+//	}
+
+type Reader struct {
+	r   io.Reader
+	nb  int64
+	pad int64
+}
+
+// Copies read data to r. Strips the global ar header.
+func NewReader(r io.Reader) *Reader {
+	io.CopyN(io.Discard, r, 8) // Discard global header
+
+	return &Reader{r: r}
+}
+
+func (rd *Reader) string(b []byte) string {
+	i := len(b) - 1
+	for i > 0 && b[i] == 32 {
+		i--
+	}
+
+	return string(b[0 : i+1])
+}
+
+func (rd *Reader) numeric(b []byte) int64 {
+	i := len(b) - 1
+	for i > 0 && b[i] == 32 {
+		i--
+	}
+
+	n, _ := strconv.ParseInt(string(b[0:i+1]), 10, 64)
+
+	return n
+}
+
+func (rd *Reader) octal(b []byte) int64 {
+	i := len(b) - 1
+	for i > 0 && b[i] == 32 {
+		i--
+	}
+
+	n, _ := strconv.ParseInt(string(b[3:i+1]), 8, 64)
+
+	return n
+}
+
+func (rd *Reader) skipUnread() error {
+	skip := rd.nb + rd.pad
+	rd.nb, rd.pad = 0, 0
+	if seeker, ok := rd.r.(io.Seeker); ok {
+		_, err := seeker.Seek(skip, io.SeekCurrent)
+		return err
+	}
+
+	_, err := io.CopyN(io.Discard, rd.r, skip)
+	return err
+}
+
+func (rd *Reader) readHeader() (*Header, error) {
+	headerBuf := make([]byte, headerByteSize)
+	if _, err := io.ReadFull(rd.r, headerBuf); err != nil {
+		return nil, err
+	}
+
+	header := new(Header)
+	s := slicer(headerBuf)
+
+	header.Name = rd.string(s.next(16))
+	header.ModTime = time.Unix(rd.numeric(s.next(12)), 0)
+	header.Uid = int(rd.numeric(s.next(6)))
+	header.Gid = int(rd.numeric(s.next(6)))
+	header.Mode = rd.octal(s.next(8))
+	header.Size = rd.numeric(s.next(10))
+
+	rd.nb = int64(header.Size)
+	if header.Size%2 == 1 {
+		rd.pad = 1
+	} else {
+		rd.pad = 0
+	}
+
+	return header, nil
+}
+
+// Call Next() to skip to the next file in the archive file.
+// Returns a Header which contains the metadata about the
+// file in the archive.
+func (rd *Reader) Next() (*Header, error) {
+	err := rd.skipUnread()
+	if err != nil {
+		return nil, err
+	}
+
+	return rd.readHeader()
+}
+
+// Read data from the current entry in the archive.
+func (rd *Reader) Read(b []byte) (n int, err error) {
+	if rd.nb == 0 {
+		return 0, io.EOF
+	}
+	if int64(len(b)) > rd.nb {
+		b = b[0:rd.nb]
+	}
+	n, err = rd.r.Read(b)
+	rd.nb -= int64(n)
+
+	return
+}