luci-go: Tools for working with BSD style ar archives.

common/archive/ar/reader.go

+// Copyright 2016 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+/**
+ * Read an ar archive file.

[M-A Ruel, 2016/06/06 23:01:05]

Do not create 2 package comments

[mithro, 2016/06/07 12:28:52]

So this comment is somehow associated with the package?

+ */
+package ar
+
+import (
+        "bytes"
+        "errors"
+        "fmt"
+        "io"
+        "os"
+        "time"
+)
+
+type arFileInfo struct {
+        // os.FileInfo parts
+        name    string
+        size    int64
+        mode    uint32
+        modtime uint64
+        // Extra parts
+        uid int
+        gid int
+}
+
+// os.FileInfo interface
+func (fi arFileInfo) Name() string       { return fi.name }

[M-A Ruel, 2016/06/06 23:01:05]

use pointer methods otherwise this copies the struct each time.

[mithro, 2016/06/07 12:28:52]

Done.

+func (fi arFileInfo) Size() int64        { return fi.size }
+func (fi arFileInfo) Mode() os.FileMode  { return os.FileMode(fi.mode) }
+func (fi arFileInfo) ModTime() time.Time { return time.Unix(int64(fi.modtime), 0) }
+func (fi arFileInfo) IsDir() bool        { return fi.Mode().IsDir() }
+func (fi arFileInfo) Sys() interface{}   { return fi }
+
+// Extra
+func (fi arFileInfo) UserId() int  { return fi.uid }
+func (fi arFileInfo) GroupId() int { return fi.gid }
+
+var (
+        ErrHeader = errors.New("archive/ar: invalid ar header")
+)
+
+type ReaderStage uint
+
+const (
+        READ_HEADER ReaderStage = iota
+        READ_BODY               = iota

[M-A Ruel, 2016/06/06 23:01:05]

just iota for the first

[mithro, 2016/06/07 12:28:52]

Any idea why gofmt doesn't pick that one up?

[M-A Ruel, 2016/06/08 20:25:31]

I mean you can remove the complete "= iota". It's not gofmt's job to understand
that.

+        READ_CLOSED             = iota
+)
+
+type Reader struct {
+        stage         ReaderStage
+        r             io.Reader
+        bytesrequired int64
+        needspadding  bool
+}
+
+func NewReader(r io.Reader) (*Reader, error) {
+        reader := Reader{r: r, bytesrequired: 0, needspadding: false}
+        err := reader.checkBytes("header", []byte("!<arch>\n"))
+        if err != nil {
+                return nil, err
+        } else {
+                return &reader, nil
+        }
+}
+
+func (ar *Reader) checkBytes(name string, str []byte) error {
+        buffer := make([]byte, len(str))
+
+        count, err := io.ReadFull(ar.r, buffer)
+        if err != nil {
+                return err
+        }
+
+        if count != len(buffer) {
+                return errors.New(fmt.Sprintf("%s: Not enough data read (only %d, needed %d)", name, count, len(buffer)))
+        }
+
+        if bytes.Equal(str, buffer) {
+                return nil
+        } else {
+                return errors.New(fmt.Sprintf("%s: error in bytes (wanted: %v got: %v)", name, buffer, str))
+        }
+}
+
+func (ar *Reader) Close() error {
+        switch ar.stage {
+        case READ_HEADER:
+                // Good
+        case READ_BODY:
+                return errors.New("Usage error, reading a file.")
+        case READ_CLOSED:
+                return errors.New("Usage error, archive already closed.")
+        default:
+                panic(fmt.Sprintf("Unknown reader mode: %d", ar.stage))
+        }
+        //ar.r.Close()
+        ar.stage = READ_CLOSED
+        return nil
+}
+
+func (ar *Reader) readBytes(numbytes int64) error {
+        if numbytes > ar.bytesrequired {
+                return errors.New(fmt.Sprintf("To much data read! Needed %d, got %d", ar.bytesrequired, numbytes))
+        }
+
+        ar.bytesrequired -= numbytes
+        if ar.bytesrequired != 0 {
+                return nil
+        }
+
+        // Padding to 16bit boundary
+        if ar.needspadding {
+                err := ar.checkBytes("padding", []byte("\n"))
+                if err != nil {
+                        return err
+                }
+                ar.needspadding = false
+        }
+        ar.stage = READ_HEADER
+        return nil
+}
+
+// Check you can write bytes to the ar at this moment.
+func (ar *Reader) checkRead() error {
+        switch ar.stage {
+        case READ_HEADER:
+                return errors.New("Usage error, need to read header first.")
+                // Good
+        case READ_BODY:
+                return nil
+        case READ_CLOSED:
+                return errors.New("Usage error, archive closed.")
+        default:
+                panic(fmt.Sprintf("Unknown reader mode: %d", ar.stage))
+        }
+}
+
+// Check we have finished writing bytes
+func (ar *Reader) checkFinished() error {
+        if ar.bytesrequired != 0 {
+                return errors.New(fmt.Sprintf("Didn't read enough bytes %d still needed!", ar.bytesrequired))
+        }
+        return nil
+}
+
+func (ar *Reader) readPartial(name string, data []byte) error {
+        err := ar.checkRead()
+        if err != nil {
+                return err
+        }
+
+        datalen := int64(len(data))
+        if datalen > ar.bytesrequired {
+                return errors.New(fmt.Sprintf("To much data! Wanted %d, but had %d", ar.bytesrequired, datalen))
+        }
+
+        count, err := io.ReadFull(ar.r, data)
+        ar.readBytes(int64(count))
+        return nil
+}
+
+func (ar *Reader) readHeaderBytes(name string, bytes int, formatstr string) (int64, error) {
+        data := make([]byte, bytes)
+        _, err := io.ReadFull(ar.r, data)
+        if err != nil {
+                return -1, err
+        }
+
+        var output int64 = 0
+        _, err = fmt.Sscanf(string(data), formatstr, &output)
+        if err != nil {
+                return -1, err
+        }
+
+        if output <= 0 {
+                return -1, errors.New(fmt.Sprintf("%s: bad value %d", name, output))
+        }
+        return output, nil
+}
+
+func (ar *Reader) readHeader() (*arFileInfo, error) {
+        switch ar.stage {
+        case READ_HEADER:
+                // Good
+        case READ_BODY:
+                return nil, errors.New("Usage error, already writing a file.")
+        case READ_CLOSED:
+                return nil, errors.New("Usage error, archive closed.")
+        default:
+                panic(fmt.Sprintf("Unknown writer mode: %d", ar.stage))
+        }
+
+        var fi arFileInfo
+
+        // File name length prefixed with '#1/' (BSD variant), 16 bytes
+        namelen, err := ar.readHeaderBytes("filename length", 16, "#1/%13d")
+        if err != nil {
+                return nil, err
+        }
+
+        // Modtime, 12 bytes
+        modtime, err := ar.readHeaderBytes("modtime", 12, "%12d")
+        if err != nil {
+                return nil, err
+        }
+        fi.modtime = uint64(modtime)
+
+        // Owner ID, 6 bytes
+        ownerid, err := ar.readHeaderBytes("ownerid", 6, "%6d")
+        if err != nil {
+                return nil, err
+        }
+        fi.uid = int(ownerid)
+
+        // Group ID, 6 bytes
+        groupid, err := ar.readHeaderBytes("groupid", 6, "%6d")
+        if err != nil {
+                return nil, err
+        }
+        fi.gid = int(groupid)
+
+        // File mode, 8 bytes
+        filemod, err := ar.readHeaderBytes("groupid", 8, "%8o")
+        if err != nil {
+                return nil, err
+        }
+        fi.mode = uint32(filemod)
+
+        // File size, 10 bytes
+        size, err := ar.readHeaderBytes("datasize", 10, "%10d")
+        if err != nil {
+                return nil, err
+        }
+        fi.size = size - namelen
+
+        ar.stage = READ_BODY
+        ar.bytesrequired = size
+        ar.needspadding = (ar.bytesrequired%2 != 0)
+
+        // File magic, 2 bytes
+        err = ar.checkBytes("filemagic", []byte("\x60\n"))
+        if err != nil {
+                return nil, err
+        }
+
+        // Filename - BSD variant
+        filename := make([]byte, namelen)
+        err = ar.readPartial("filename", filename)
+        if err != nil {
+                return nil, err
+        }
+        fi.name = string(filename)
+
+        return &fi, nil
+}
+
+func (ar *Reader) Read(b []byte) (n int, err error) {
+        err = ar.readPartial("data", b)
+        if err != nil {
+                return -1, err
+        }
+        err = ar.checkFinished()
+        if err != nil {
+                return -1, err
+        }
+        return len(b), nil
+}
+func (ar *Reader) Next() (*arFileInfo, error) {
+        return ar.readHeader()
+}