tar/asm: initial assmebly of tar stream

tar/asm/README.md

@@ -0,0 +1,18 @@
+asm
+===
+
+This library for assembly and disassembly of tar archives, facilitated by
+`github.com/vbatts/tar-split/tar/storage`.
+
+
+
+Thoughts
+--------
+
+While the initial implementation is based on a relative path, I'm thinking the
+next step is to have something like a FileGetter interface, of which a path
+based getter is just one type.
+
+Then you could pass a path based Getter and an Unpacker, and receive a
+io.Reader that is your tar stream.
+

tar/asm/assemble.go

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+package asm
+
+import (
+	"io"
+	"os"
+	"path"
+
+	"github.com/vbatts/tar-split/tar/storage"
+)
+
+func NewTarStream(relpath string, up storage.Unpacker) io.ReadCloser {
+	pr, pw := io.Pipe()
+	go func() {
+		for {
+			entry, err := up.Next()
+			if err != nil {
+				pw.CloseWithError(err)
+				break
+			}
+			switch entry.Type {
+			case storage.SegmentType:
+				if _, err := pw.Write(entry.Payload); err != nil {
+					pw.CloseWithError(err)
+					break
+				}
+			case storage.FileType:
+				if err := writeEntryFromRelPath(pw, relpath, entry); err != nil {
+					pw.CloseWithError(err)
+					break
+				}
+			}
+		}
+	}()
+	return pr
+}
+
+func writeEntryFromRelPath(w io.Writer, root string, entry *storage.Entry) error {
+	if entry.Size == 0 {
+		return nil
+	}
+
+	// FIXME might should have a check for '../../../../etc/passwd' attempts?
+	fh, err := os.Open(path.Join(root, entry.Name))
+	if err != nil {
+		return err
+	}
+	defer fh.Close()
+	if _, err := io.Copy(w, fh); err != nil {
+		return err
+	}
+
+	return nil
+}