Add os.FileInfo support in header

common.go

@@ -1,4 +1,4 @@
-/* 
+/*
 Copyright (c) 2013 Blake Smith <blakesmith0@gmail.com>
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
@@ -22,21 +22,25 @@ THE SOFTWARE.
 package ar
 
 import (
+	"errors"
+	"fmt"
+	"os"
+	"path"
 	"time"
 )
 
 const (
 	HEADER_BYTE_SIZE = 60
-	GLOBAL_HEADER = "!<arch>\n"
+	GLOBAL_HEADER    = "!<arch>\n"
 )
 
 type Header struct {
-	Name string
+	Name    string
 	ModTime time.Time
-	Uid int
-	Gid int
-	Mode int64
-	Size int64
+	Uid     int
+	Gid     int
+	Mode    int64
+	Size    int64
 }
 
 type slicer []byte
@@ -46,3 +50,133 @@ func (sp *slicer) next(n int) (b []byte) {
 	b, *sp = s[0:n], s[n:]
 	return
 }
+
+// FileInfo returns an os.FileInfo for the Header.
+func (h *Header) FileInfo() os.FileInfo {
+	return headerFileInfo{h}
+}
+
+// headerFileInfo implements os.FileInfo.
+type headerFileInfo struct {
+	h *Header
+}
+
+func (fi headerFileInfo) Size() int64        { return fi.h.Size }
+func (fi headerFileInfo) IsDir() bool        { return false }
+func (fi headerFileInfo) ModTime() time.Time { return fi.h.ModTime }
+func (fi headerFileInfo) Sys() interface{}   { return fi.h }
+func (fi headerFileInfo) Name() string       { return path.Base(fi.h.Name) }
+
+// Mode returns the permission and mode bits for the headerFileInfo.
+func (fi headerFileInfo) Mode() (mode os.FileMode) {
+	// Set file permission bits.
+	mode = os.FileMode(fi.h.Mode).Perm()
+
+	// Set setuid, setgid and sticky bits.
+	if fi.h.Mode&c_ISUID != 0 {
+		mode |= os.ModeSetuid
+	}
+	if fi.h.Mode&c_ISGID != 0 {
+		mode |= os.ModeSetgid
+	}
+	if fi.h.Mode&c_ISVTX != 0 {
+		mode |= os.ModeSticky
+	}
+
+	// Set file mode bits; clear perm, setuid, setgid, and sticky bits.
+	switch m := os.FileMode(fi.h.Mode) &^ 07777; m {
+	case c_ISDIR:
+		mode |= os.ModeDir
+	case c_ISFIFO:
+		mode |= os.ModeNamedPipe
+	case c_ISLNK:
+		mode |= os.ModeSymlink
+	case c_ISBLK:
+		mode |= os.ModeDevice
+	case c_ISCHR:
+		mode |= os.ModeDevice
+		mode |= os.ModeCharDevice
+	case c_ISSOCK:
+		mode |= os.ModeSocket
+	}
+
+	return mode
+}
+
+// sysStat, if non-nil, populates h from system-dependent fields of fi.
+var sysStat func(fi os.FileInfo, h *Header) error
+
+const (
+	// Mode constants from the USTAR spec:
+	// See http://pubs.opengroup.org/onlinepubs/9699919799/utilities/pax.html#tag_20_92_13_06
+	c_ISUID = 04000 // Set uid
+	c_ISGID = 02000 // Set gid
+	c_ISVTX = 01000 // Save text (sticky bit)
+
+	// Common Unix mode constants; these are not defined in any common tar standard.
+	// Header.FileInfo understands these, but FileInfoHeader will never produce these.
+	c_ISDIR  = 040000  // Directory
+	c_ISFIFO = 010000  // FIFO
+	c_ISREG  = 0100000 // Regular file
+	c_ISLNK  = 0120000 // Symbolic link
+	c_ISBLK  = 060000  // Block special file
+	c_ISCHR  = 020000  // Character special file
+	c_ISSOCK = 0140000 // Socket
+)
+
+// FileInfoHeader creates a partially-populated Header from fi.
+// If fi describes a symlink, FileInfoHeader records link as the link target.
+// If fi describes a directory, a slash is appended to the name.
+//
+// Since os.FileInfo's Name method only returns the base name of
+// the file it describes, it may be necessary to modify Header.Name
+// to provide the full path name of the file.
+func FileInfoHeader(fi os.FileInfo, link string) (*Header, error) {
+	if fi == nil {
+		return nil, errors.New("archive/tar: FileInfo is nil")
+	}
+	fm := fi.Mode()
+	h := &Header{
+		Name:    fi.Name(),
+		ModTime: fi.ModTime(),
+		Mode:    int64(fm.Perm()), // or'd with c_IS* constants later
+	}
+	switch {
+	case fm.IsRegular():
+		h.Size = fi.Size()
+	case fi.IsDir():
+		return nil, fmt.Errorf("archive/tar: directories not supported")
+	case fm&os.ModeSymlink != 0:
+		return nil, fmt.Errorf("archive/tar: symlinks not supported")
+	case fm&os.ModeDevice != 0:
+		return nil, fmt.Errorf("archive/tar: devices not supported")
+	case fm&os.ModeNamedPipe != 0:
+		return nil, fmt.Errorf("archive/tar: fifo not supported")
+	case fm&os.ModeSocket != 0:
+		return nil, fmt.Errorf("archive/tar: sockets not supported")
+	default:
+		return nil, fmt.Errorf("archive/tar: unknown file mode %v", fm)
+	}
+	if fm&os.ModeSetuid != 0 {
+		h.Mode |= c_ISUID
+	}
+	if fm&os.ModeSetgid != 0 {
+		h.Mode |= c_ISGID
+	}
+	if fm&os.ModeSticky != 0 {
+		h.Mode |= c_ISVTX
+	}
+	// If possible, populate additional fields from OS-specific
+	// FileInfo fields.
+	if sys, ok := fi.Sys().(*Header); ok {
+		// This FileInfo came from a Header (not the OS). Use the
+		// original Header to populate all remaining fields.
+		h.Uid = sys.Uid
+		h.Gid = sys.Gid
+		h.ModTime = sys.ModTime
+	}
+	if sysStat != nil {
+		return h, sysStat(fi, h)
+	}
+	return h, nil
+}