mv x/<tool> => xtool/<tool>

xtool/ar/reader.go

@@ -0,0 +1,140 @@
+/*
+ * 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"
+	"strings"
+	"unsafe"
+)
+
+// 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, error) {
+	buf := make([]byte, globalHeaderLen)
+	if _, err := io.ReadFull(r, buf); err != nil {
+		return nil, err
+	}
+	if string(buf) != globalHeader {
+		return nil, errInvalidHeader
+	}
+
+	return &Reader{r: r}, nil
+}
+
+func stringVal(b []byte) string {
+	return strings.TrimRight(string(b), " ")
+}
+
+func intVal(b []byte) (int64, error) {
+	return strconv.ParseInt(stringVal(b), 10, 64)
+}
+
+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 *Header, err error) {
+	var rec recHeader
+	var buf = (*[headerByteSize]byte)(unsafe.Pointer(&rec))[:]
+	if _, err = io.ReadFull(rd.r, buf); err != nil {
+		return
+	}
+
+	header = new(Header)
+	header.Name = stringVal(rec.name[:])
+	if header.Size, err = intVal(rec.size[:]); err != nil {
+		return
+	}
+
+	if header.Size%2 == 1 {
+		rd.pad = 1
+	} else {
+		rd.pad = 0
+	}
+
+	if rec.name[0] == '#' {
+		if n, e := strconv.ParseInt(strings.TrimPrefix(header.Name[3:], "#1/"), 10, 64); e == nil {
+			name := make([]byte, n)
+			if _, err = io.ReadFull(rd.r, name); err != nil {
+				return
+			}
+			header.Name = string(name)
+			header.Size -= n
+		}
+	}
+
+	rd.nb = int64(header.Size)
+	return
+}
+
+// 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
+}