*: refactoring to support streams

when creating a manifest from, or validating, a stream like a tar
archive, it requires thinking about some of the functions differently
than walking a directory tree.

This is the beginning of allowing for such features.

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

check.go

@@ -3,7 +3,6 @@ package mtree
 import (
 	"fmt"
 	"os"
-	"path/filepath"
 	"sort"
 )
 
@@ -51,7 +50,8 @@ func Check(root string, dh *DirectoryHierarchy, keywords []string) (*Result, err
 				creator.curSet = nil
 			}
 		case RelativeType, FullType:
-			info, err := os.Lstat(e.Path())
+			filename := e.Path()
+			info, err := os.Lstat(filename)
 			if err != nil {
 				return nil, err
 			}
@@ -71,10 +71,16 @@ func Check(root string, dh *DirectoryHierarchy, keywords []string) (*Result, err
 				if keywords != nil && !inSlice(kv.Keyword(), keywords) {
 					continue
 				}
-				curKeyVal, err := keywordFunc(filepath.Join(root, e.Path()), info)
+				fh, err := os.Open(filename)
 				if err != nil {
 					return nil, err
 				}
+				curKeyVal, err := keywordFunc(filename, info, fh)
+				if err != nil {
+					fh.Close()
+					return nil, err
+				}
+				fh.Close()
 				if string(kv) != curKeyVal {
 					failure := Failure{Path: e.Path(), Keyword: kv.Keyword(), Expected: kv.Value(), Got: KeyVal(curKeyVal).Value()}
 					result.Failures = append(result.Failures, failure)

creator.go

@@ -0,0 +1,9 @@
+package mtree
+
+// dhCreator is used in when building a DirectoryHierarchy
+type dhCreator struct {
+	DH     *DirectoryHierarchy
+	curSet *Entry
+	curDir *Entry
+	curEnt *Entry
+}

entry.go

@@ -0,0 +1,80 @@
+package mtree
+
+import (
+	"fmt"
+	"path/filepath"
+	"strings"
+)
+
+type byPos []Entry
+
+func (bp byPos) Len() int           { return len(bp) }
+func (bp byPos) Less(i, j int) bool { return bp[i].Pos < bp[j].Pos }
+func (bp byPos) Swap(i, j int)      { bp[i], bp[j] = bp[j], bp[i] }
+
+// Entry is each component of content in the mtree spec file
+type Entry struct {
+	Parent     *Entry   // up
+	Children   []*Entry // down
+	Prev, Next *Entry   // left, right
+	Set        *Entry   // current `/set` for additional keywords
+	Pos        int      // order in the spec
+	Raw        string   // file or directory name
+	Name       string   // file or directory name
+	Keywords   []string // TODO(vbatts) maybe a keyword typed set of values?
+	Type       EntryType
+}
+
+// Path provides the full path of the file, despite RelativeType or FullType
+func (e Entry) Path() string {
+	if e.Parent == nil || e.Type == FullType {
+		return filepath.Clean(e.Name)
+	}
+	return filepath.Clean(filepath.Join(e.Parent.Path(), e.Name))
+}
+
+func (e Entry) String() string {
+	if e.Raw != "" {
+		return e.Raw
+	}
+	if e.Type == BlankType {
+		return ""
+	}
+	if e.Type == DotDotType {
+		return e.Name
+	}
+	// TODO(vbatts) if type is RelativeType and a keyword of not type=dir
+	if e.Type == SpecialType || e.Type == FullType || inSlice("type=dir", e.Keywords) {
+		return fmt.Sprintf("%s %s", e.Name, strings.Join(e.Keywords, " "))
+	}
+	return fmt.Sprintf("    %s %s", e.Name, strings.Join(e.Keywords, " "))
+}
+
+// EntryType are the formats of lines in an mtree spec file
+type EntryType int
+
+// The types of lines to be found in an mtree spec file
+const (
+	SignatureType EntryType = iota // first line of the file, like `#mtree v2.0`
+	BlankType                      // blank lines are ignored
+	CommentType                    // Lines beginning with `#` are ignored
+	SpecialType                    // line that has `/` prefix issue a "special" command (currently only /set and /unset)
+	RelativeType                   // if the first white-space delimited word does not have a '/' in it. Options/keywords are applied.
+	DotDotType                     // .. - A relative path step. keywords/options are ignored
+	FullType                       // if the first word on the line has a `/` after the first character, it interpretted as a file pathname with options
+)
+
+// String returns the name of the EntryType
+func (et EntryType) String() string {
+	return typeNames[et]
+}
+
+var typeNames = map[EntryType]string{
+	SignatureType: "SignatureType",
+	BlankType:     "BlankType",
+	CommentType:   "CommentType",
+	SpecialType:   "SpecialType",
+	RelativeType:  "RelativeType",
+	DotDotType:    "DotDotType",
+	FullType:      "FullType",
+}

hierarchy.go

@@ -1,11 +1,8 @@
 package mtree
 
 import (
-	"fmt"
 	"io"
-	"path/filepath"
 	"sort"
-	"strings"
 )
 
 // DirectoryHierarchy is the mapped structure for an mtree directory hierarchy
@@ -27,75 +24,3 @@ func (dh DirectoryHierarchy) WriteTo(w io.Writer) (n int64, err error) {
 	}
 	return sum, nil
 }
-
-type byPos []Entry
-
-func (bp byPos) Len() int           { return len(bp) }
-func (bp byPos) Less(i, j int) bool { return bp[i].Pos < bp[j].Pos }
-func (bp byPos) Swap(i, j int)      { bp[i], bp[j] = bp[j], bp[i] }
-
-// Entry is each component of content in the mtree spec file
-type Entry struct {
-	Parent, Child *Entry   // up, down
-	Prev, Next    *Entry   // left, right
-	Set           *Entry   // current `/set` for additional keywords
-	Pos           int      // order in the spec
-	Raw           string   // file or directory name
-	Name          string   // file or directory name
-	Keywords      []string // TODO(vbatts) maybe a keyword typed set of values?
-	Type          EntryType
-}
-
-// Path provides the full path of the file, despite RelativeType or FullType
-func (e Entry) Path() string {
-	if e.Parent == nil || e.Type == FullType {
-		return filepath.Clean(e.Name)
-	}
-	return filepath.Clean(filepath.Join(e.Parent.Path(), e.Name))
-}
-
-func (e Entry) String() string {
-	if e.Raw != "" {
-		return e.Raw
-	}
-	if e.Type == BlankType {
-		return ""
-	}
-	if e.Type == DotDotType {
-		return e.Name
-	}
-	// TODO(vbatts) if type is RelativeType and a keyword of not type=dir
-	if e.Type == SpecialType || e.Type == FullType || inSlice("type=dir", e.Keywords) {
-		return fmt.Sprintf("%s %s", e.Name, strings.Join(e.Keywords, " "))
-	}
-	return fmt.Sprintf("    %s %s", e.Name, strings.Join(e.Keywords, " "))
-}
-
-// EntryType are the formats of lines in an mtree spec file
-type EntryType int
-
-// The types of lines to be found in an mtree spec file
-const (
-	SignatureType EntryType = iota // first line of the file, like `#mtree v2.0`
-	BlankType                      // blank lines are ignored
-	CommentType                    // Lines beginning with `#` are ignored
-	SpecialType                    // line that has `/` prefix issue a "special" command (currently only /set and /unset)
-	RelativeType                   // if the first white-space delimited word does not have a '/' in it. Options/keywords are applied.
-	DotDotType                     // .. - A relative path step. keywords/options are ignored
-	FullType                       // if the first word on the line has a `/` after the first character, it interpretted as a file pathname with options
-)
-
-// String returns the name of the EntryType
-func (et EntryType) String() string {
-	return typeNames[et]
-}
-
-var typeNames = map[EntryType]string{
-	SignatureType: "SignatureType",
-	BlankType:     "BlankType",
-	CommentType:   "CommentType",
-	SpecialType:   "SpecialType",
-	RelativeType:  "RelativeType",
-	DotDotType:    "DotDotType",
-	FullType:      "FullType",
-}

keywords.go

@@ -1,6 +1,7 @@
 package mtree
 
 import (
+	"archive/tar"
 	"crypto/md5"
 	"crypto/sha1"
 	"crypto/sha256"
@@ -17,7 +18,10 @@ import (
 // KeywordFunc is the type of a function called on each file to be included in
 // a DirectoryHierarchy, that will produce the string output of the keyword to
 // be included for the file entry. Otherwise, empty string.
-type KeywordFunc func(path string, info os.FileInfo) (string, error)
+// io.Reader `r` is to the file stream for the file payload. While this
+// function takes an io.Reader, the caller needs to reset it to the beginning
+// for each new KeywordFunc
+type KeywordFunc func(path string, info os.FileInfo, r io.Reader) (string, error)
 
 // KeyVal is a "keyword=value"
 type KeyVal string
@@ -165,7 +169,7 @@ var (
 )
 
 var (
-	modeKeywordFunc = func(path string, info os.FileInfo) (string, error) {
+	modeKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
 		permissions := info.Mode().Perm()
 		if os.ModeSetuid&info.Mode() > 0 {
 			permissions |= (1 << 11)
@@ -178,52 +182,43 @@ var (
 		}
 		return fmt.Sprintf("mode=%#o", permissions), nil
 	}
-	sizeKeywordFunc = func(path string, info os.FileInfo) (string, error) {
+	sizeKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
 		return fmt.Sprintf("size=%d", info.Size()), nil
 	}
-	cksumKeywordFunc = func(path string, info os.FileInfo) (string, error) {
+	cksumKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
 		if !info.Mode().IsRegular() {
 			return "", nil
 		}
-
-		fh, err := os.Open(path)
-		if err != nil {
-			return "", err
-		}
-		defer fh.Close()
-		sum, _, err := cksum(fh)
+		sum, _, err := cksum(r)
 		if err != nil {
 			return "", err
 		}
 		return fmt.Sprintf("cksum=%d", sum), nil
 	}
 	hasherKeywordFunc = func(name string, newHash func() hash.Hash) KeywordFunc {
-		return func(path string, info os.FileInfo) (string, error) {
+		return func(path string, info os.FileInfo, r io.Reader) (string, error) {
 			if !info.Mode().IsRegular() {
 				return "", nil
 			}
-
-			fh, err := os.Open(path)
-			if err != nil {
-				return "", err
-			}
-			defer fh.Close()
-
 			h := newHash()
-			if _, err := io.Copy(h, fh); err != nil {
+			if _, err := io.Copy(h, r); err != nil {
 				return "", err
 			}
 			return fmt.Sprintf("%s=%x", name, h.Sum(nil)), nil
 		}
 	}
-	timeKeywordFunc = func(path string, info os.FileInfo) (string, error) {
+	timeKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
 		t := info.ModTime().UnixNano()
 		if t == 0 {
 			return "time=0.000000000", nil
 		}
 		return fmt.Sprintf("time=%d.%9.9d", (t / 1e9), (t % (t / 1e9))), nil
 	}
-	linkKeywordFunc = func(path string, info os.FileInfo) (string, error) {
+	linkKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
+		if sys, ok := info.Sys().(*tar.Header); ok {
+			return sys.Linkname, nil
+		}
+
 		if info.Mode()&os.ModeSymlink != 0 {
 			str, err := os.Readlink(path)
 			if err != nil {
@@ -233,7 +228,7 @@ var (
 		}
 		return "", nil
 	}
-	typeKeywordFunc = func(path string, info os.FileInfo) (string, error) {
+	typeKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
 		if info.Mode().IsDir() {
 			return "type=dir", nil
 		}

keywords_linux.go

@@ -3,8 +3,10 @@
 package mtree
 
 import (
+	"archive/tar"
 	"crypto/sha1"
 	"fmt"
+	"io"
 	"os"
 	"os/user"
 	"strings"
@@ -14,7 +16,11 @@ import (
 )
 
 var (
-	unameKeywordFunc = func(path string, info os.FileInfo) (string, error) {
+	unameKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
+		if hdr, ok := info.Sys().(*tar.Header); ok {
+			return fmt.Sprintf("uname=%s", hdr.Uname), nil
+		}
+
 		stat := info.Sys().(*syscall.Stat_t)
 		u, err := user.LookupId(fmt.Sprintf("%d", stat.Uid))
 		if err != nil {
@@ -22,19 +28,40 @@ var (
 		}
 		return fmt.Sprintf("uname=%s", u.Username), nil
 	}
-	uidKeywordFunc = func(path string, info os.FileInfo) (string, error) {
+	uidKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
+		if hdr, ok := info.Sys().(*tar.Header); ok {
+			return fmt.Sprintf("uid=%d", hdr.Uid), nil
+		}
 		stat := info.Sys().(*syscall.Stat_t)
 		return fmt.Sprintf("uid=%d", stat.Uid), nil
 	}
-	gidKeywordFunc = func(path string, info os.FileInfo) (string, error) {
-		stat := info.Sys().(*syscall.Stat_t)
+	gidKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
+		if hdr, ok := info.Sys().(*tar.Header); ok {
+			return fmt.Sprintf("gid=%d", hdr.Gid), nil
+		}
+		if stat, ok := info.Sys().(*syscall.Stat_t); ok {
 			return fmt.Sprintf("gid=%d", stat.Gid), nil
 		}
-	nlinkKeywordFunc = func(path string, info os.FileInfo) (string, error) {
-		stat := info.Sys().(*syscall.Stat_t)
+		return "", nil
+	}
+	nlinkKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
+		if stat, ok := info.Sys().(*syscall.Stat_t); ok {
 			return fmt.Sprintf("nlink=%d", stat.Nlink), nil
 		}
-	xattrKeywordFunc = func(path string, info os.FileInfo) (string, error) {
+		return "", nil
+	}
+	xattrKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
+		if hdr, ok := info.Sys().(*tar.Header); ok {
+			if len(hdr.Xattrs) == 0 {
+				return "", nil
+			}
+			klist := []string{}
+			for k, v := range hdr.Xattrs {
+				klist = append(klist, fmt.Sprintf("xattr.%s=%x", k, sha1.Sum([]byte(v))))
+			}
+			return strings.Join(klist, " "), nil
+		}
+
 		xlist, err := xattr.List(path)
 		if err != nil {
 			return "", err

keywords_unsupported.go

@@ -2,22 +2,36 @@
 
 package mtree
 
-import "os"
+import (
+	"archive/tar"
+	"fmt"
+	"io"
+	"os"
+)
 
 var (
-	unameKeywordFunc = func(path string, info os.FileInfo) (string, error) {
+	unameKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
+		if hdr, ok := info.Sys().(*tar.Header); ok {
+			return fmt.Sprintf("uname=%s", hdr.Uname), nil
+		}
 		return "", nil
 	}
-	uidKeywordFunc = func(path string, info os.FileInfo) (string, error) {
+	uidKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
+		if hdr, ok := info.Sys().(*tar.Header); ok {
+			return fmt.Sprintf("uid=%d", hdr.Uid), nil
+		}
 		return "", nil
 	}
-	gidKeywordFunc = func(path string, info os.FileInfo) (string, error) {
+	gidKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
+		if hdr, ok := info.Sys().(*tar.Header); ok {
+			return fmt.Sprintf("gid=%d", hdr.Gid), nil
+		}
 		return "", nil
 	}
-	nlinkKeywordFunc = func(path string, info os.FileInfo) (string, error) {
+	nlinkKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
 		return "", nil
 	}
-	xattrKeywordFunc = func(path string, info os.FileInfo) (string, error) {
+	xattrKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
 		return "", nil
 	}
 )

tar.go

@@ -0,0 +1,185 @@
+package mtree
+
+import (
+	"archive/tar"
+	"io"
+	"io/ioutil"
+	"log"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// Streamer interface that wraps an io.ReadCloser with a function that will
+// return it's Hierarchy
+type Streamer interface {
+	io.ReadCloser
+	Hierarchy() (*DirectoryHierarchy, error)
+}
+
+// NewTarStreamer streams a tar archive and creates a file hierarchy based off
+// of the tar metadata headers
+func NewTarStreamer(r io.Reader, keywords []string) Streamer {
+	pR, pW := io.Pipe()
+	ts := &tarStream{
+		pipeReader: pR,
+		pipeWriter: pW,
+		creator:    dhCreator{DH: &DirectoryHierarchy{}},
+		teeReader:  io.TeeReader(r, pW),
+		tarReader:  tar.NewReader(pR),
+		keywords:   keywords,
+	}
+	go ts.readHeaders() // I don't like this
+	return ts
+}
+
+type tarStream struct {
+	creator    dhCreator
+	pipeReader *io.PipeReader
+	pipeWriter *io.PipeWriter
+	teeReader  io.Reader
+	tarReader  *tar.Reader
+	keywords   []string
+	err        error
+}
+
+func (ts *tarStream) readHeaders() {
+	// We have to start with the directory we're in, and anything beyond these
+	// items is determined at the time a tar is extracted.
+	e := Entry{
+		Name:     ".",
+		Keywords: []string{"size=0", "type=dir"},
+	}
+	ts.creator.curDir = &e
+	ts.creator.DH.Entries = append(ts.creator.DH.Entries, e)
+	for {
+		hdr, err := ts.tarReader.Next()
+		if err != nil {
+			ts.pipeReader.CloseWithError(err)
+			return
+		}
+
+		// Because the content of the file may need to be read by several
+		// KeywordFuncs, it needs to be an io.Seeker as well. So, just reading from
+		// ts.tarReader is not enough.
+		tmpFile, err := ioutil.TempFile("", "ts.payload.")
+		if err != nil {
+			ts.pipeReader.CloseWithError(err)
+			return
+		}
+		// for good measure
+		if err := tmpFile.Chmod(0600); err != nil {
+			tmpFile.Close()
+			os.Remove(tmpFile.Name())
+			ts.pipeReader.CloseWithError(err)
+			return
+		}
+		if _, err := io.Copy(tmpFile, ts.tarReader); err != nil {
+			tmpFile.Close()
+			os.Remove(tmpFile.Name())
+			ts.pipeReader.CloseWithError(err)
+			return
+		}
+
+		// Alright, it's either file or directory
+		e := Entry{
+			Name: filepath.Base(hdr.Name),
+			Pos:  len(ts.creator.DH.Entries),
+			Type: RelativeType,
+		}
+		// now collect keywords on the file
+		for _, keyword := range ts.keywords {
+			if keyFunc, ok := KeywordFuncs[keyword]; ok {
+				val, err := keyFunc(hdr.Name, hdr.FileInfo(), tmpFile)
+				if err != nil {
+					ts.setErr(err)
+				}
+				e.Keywords = append(e.Keywords, val)
+
+				// don't forget to reset the reader
+				if _, err := tmpFile.Seek(0, 0); err != nil {
+					tmpFile.Close()
+					os.Remove(tmpFile.Name())
+					ts.pipeReader.CloseWithError(err)
+					return
+				}
+			}
+		}
+		tmpFile.Close()
+		os.Remove(tmpFile.Name())
+
+		// compare directories, to determine parent of the current entry
+		cd := compareDir(filepath.Dir(hdr.Name), ts.creator.curDir.Path())
+		switch {
+		case cd == sameDir:
+			e.Parent = ts.creator.curDir
+			if e.Parent != nil {
+				e.Parent.Children = append(e.Parent.Children, &e)
+			}
+		case cd == parentDir:
+			e.Parent = ts.creator.curDir.Parent
+			if e.Parent != nil {
+				e.Parent.Children = append(e.Parent.Children, &e)
+			}
+		}
+
+		if hdr.FileInfo().IsDir() {
+			ts.creator.curDir = &e
+		}
+		// TODO getting the parent child relationship of these entries!
+		if hdr.FileInfo().IsDir() {
+			log.Println(strings.Split(hdr.Name, "/"), strings.Split(ts.creator.curDir.Path(), "/"))
+		}
+
+		ts.creator.DH.Entries = append(ts.creator.DH.Entries, e)
+
+		// Now is the wacky part of building out the entries. Since we can not
+		// control how the archive was assembled, can only take in the order given.
+		// Using `/set` will be tough. Hopefully i can do the directory stepping
+		// with relative paths, but even then I may get a new directory, and not
+		// the files first, but its directories first. :-\
+	}
+}
+
+type relationship int
+
+const (
+	unknownDir relationship = iota
+	sameDir
+	childDir
+	parentDir
+)
+
+func compareDir(curDir, prevDir string) relationship {
+	curDir = filepath.Clean(curDir)
+	prevDir = filepath.Clean(prevDir)
+	if curDir == prevDir {
+		return sameDir
+	}
+	if filepath.Dir(curDir) == prevDir {
+		return childDir
+	}
+	if curDir == filepath.Dir(prevDir) {
+		return parentDir
+	}
+	return unknownDir
+}
+
+func (ts *tarStream) setErr(err error) {
+	ts.err = err
+}
+
+func (ts *tarStream) Read(p []byte) (n int, err error) {
+	return ts.teeReader.Read(p)
+}
+
+func (ts *tarStream) Close() error {
+	return ts.pipeReader.Close()
+}
+
+func (ts *tarStream) Hierarchy() (*DirectoryHierarchy, error) {
+	if ts.err != nil && ts.err != io.EOF {
+		return nil, ts.err
+	}
+	return ts.creator.DH, nil
+}

tar_test.go

@@ -0,0 +1,119 @@
+package mtree
+
+import (
+	"archive/tar"
+	"bytes"
+	"io"
+	"io/ioutil"
+	"os"
+	"testing"
+)
+
+func ExampleStreamer() {
+	fh, err := os.Open("./testdata/test.tar")
+	if err != nil {
+		// handle error ...
+	}
+	str := NewTarStreamer(fh, nil)
+	if err := extractTar("/tmp/dir", str); err != nil {
+		// handle error ...
+	}
+
+	dh, err := str.Hierarchy()
+	if err != nil {
+		// handle error ...
+	}
+
+	res, err := Check("/tmp/dir/", dh, nil)
+	if err != nil {
+		// handle error ...
+	}
+	if len(res.Failures) > 0 {
+		// handle validation issue ...
+	}
+}
+func extractTar(root string, tr io.Reader) error {
+	return nil
+}
+
+func TestTar(t *testing.T) {
+	/*
+		data, err := makeTarStream()
+		if err != nil {
+			t.Fatal(err)
+		}
+		buf := bytes.NewBuffer(data)
+		str := NewTarStreamer(buf, append(DefaultKeywords, "sha1"))
+	*/
+	fh, err := os.Open("./testdata/test.tar")
+	if err != nil {
+		t.Fatal(err)
+	}
+	str := NewTarStreamer(fh, append(DefaultKeywords, "sha1"))
+
+	if _, err := io.Copy(ioutil.Discard, str); err != nil && err != io.EOF {
+		t.Fatal(err)
+	}
+	if err := str.Close(); err != nil {
+		t.Fatal(err)
+	}
+	defer fh.Close()
+
+	/*
+		fi, err := fh.Stat()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if i != fi.Size() {
+			t.Errorf("expected length %d; got %d", fi.Size(), i)
+		}
+	*/
+	dh, err := str.Hierarchy()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if dh == nil {
+		t.Fatal("expected a DirectoryHierarchy struct, but got nil")
+	}
+	//dh.WriteTo(os.Stdout)
+}
+
+// minimal tar archive stream that mimics what is in ./testdata/test.tar
+func makeTarStream() ([]byte, error) {
+	buf := new(bytes.Buffer)
+
+	// Create a new tar archive.
+	tw := tar.NewWriter(buf)
+
+	// Add some files to the archive.
+	var files = []struct {
+		Name, Body string
+		Mode       int64
+		Type       byte
+		Xattrs     map[string]string
+	}{
+		{"x/", "", 0755, '5', nil},
+		{"x/files", "howdy\n", 0644, '0', nil},
+	}
+	for _, file := range files {
+		hdr := &tar.Header{
+			Name:   file.Name,
+			Mode:   file.Mode,
+			Size:   int64(len(file.Body)),
+			Xattrs: file.Xattrs,
+		}
+		if err := tw.WriteHeader(hdr); err != nil {
+			return nil, err
+		}
+		if len(file.Body) > 0 {
+			if _, err := tw.Write([]byte(file.Body)); err != nil {
+				return nil, err
+			}
+		}
+	}
+	// Make sure to check the error on Close.
+	if err := tw.Close(); err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}

walk.go

@@ -2,6 +2,7 @@ package mtree
 
 import (
 	"fmt"
+	"io"
 	"os"
 	"os/user"
 	"path/filepath"
@@ -14,13 +15,6 @@ import (
 // returns true, then the path is not included in the spec.
 type ExcludeFunc func(path string, info os.FileInfo) bool
 
-type dhCreator struct {
-	DH     *DirectoryHierarchy
-	curSet *Entry
-	curDir *Entry
-	curEnt *Entry
-}
-
 var defaultSetKeywords = []string{"type=file", "nlink=1", "flags=none", "mode=0664"}
 
 // Walk from root directory and assemble the DirectoryHierarchy. excludes
@@ -76,11 +70,26 @@ func Walk(root string, exlcudes []ExcludeFunc, keywords []string) (*DirectoryHie
 					Keywords: keywordSelector(defaultSetKeywords, keywords),
 				}
 				for _, keyword := range SetKeywords {
-					if str, err := KeywordFuncs[keyword](path, info); err == nil && str != "" {
+					err := func() error {
+						var r io.Reader
+						if info.Mode().IsRegular() {
+							fh, err := os.Open(path)
+							if err != nil {
+								return err
+							}
+							defer fh.Close()
+							r = fh
+						}
+						if str, err := KeywordFuncs[keyword](path, info, r); err == nil && str != "" {
 							e.Keywords = append(e.Keywords, str)
 						} else if err != nil {
 							return err
 						}
+						return nil
+					}()
+					if err != nil {
+						return err
+					}
 				}
 				creator.curSet = &e
 				creator.DH.Entries = append(creator.DH.Entries, e)
@@ -88,9 +97,26 @@ func Walk(root string, exlcudes []ExcludeFunc, keywords []string) (*DirectoryHie
 				// check the attributes of the /set keywords and re-set if changed
 				klist := []string{}
 				for _, keyword := range SetKeywords {
-					if str, err := KeywordFuncs[keyword](path, info); err == nil && str != "" {
+					err := func() error {
+						var r io.Reader
+						if info.Mode().IsRegular() {
+							fh, err := os.Open(path)
+							if err != nil {
+								return err
+							}
+							defer fh.Close()
+							r = fh
+						}
+						str, err := KeywordFuncs[keyword](path, info, r)
+						if err != nil {
+							return err
+						}
+						if str != "" {
 							klist = append(klist, str)
-					} else if err != nil {
+						}
+						return nil
+					}()
+					if err != nil {
 						return err
 					}
 				}
@@ -122,11 +148,26 @@ func Walk(root string, exlcudes []ExcludeFunc, keywords []string) (*DirectoryHie
 			Parent: creator.curDir,
 		}
 		for _, keyword := range keywords {
-			if str, err := KeywordFuncs[keyword](path, info); err == nil && str != "" {
-				if !inSlice(str, creator.curSet.Keywords) {
+			err := func() error {
+				var r io.Reader
+				if info.Mode().IsRegular() {
+					fh, err := os.Open(path)
+					if err != nil {
+						return err
+					}
+					defer fh.Close()
+					r = fh
+				}
+				str, err := KeywordFuncs[keyword](path, info, r)
+				if err != nil {
+					return err
+				}
+				if str != "" && !inSlice(str, creator.curSet.Keywords) {
 					e.Keywords = append(e.Keywords, str)
 				}
-			} else if err != nil {
+				return nil
+			}()
+			if err != nil {
 				return err
 			}
 		}
@@ -245,7 +286,7 @@ func readOrderedDirNames(dirname string) ([]string, error) {
 	return append(names, dirnames...), nil
 }
 
-// signatureEntries is helper function that returns a slice of Entry's
+// signatureEntries is a simple helper function that returns a slice of Entry's
 // that describe the metadata signature about the host. Items like date, user,
 // machine, and tree (which is specified by argument `root`), are considered.
 // These Entry's construct comments in the mtree specification, so if there is