Rough first version of the moby tool

- terrible code
- lots needs changing
- can build a Moby from a config yaml that boots

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

vendor/github.com/surma/gocpio/writer.go

@@ -0,0 +1,118 @@
+package cpio
+
+import (
+	"io"
+	"fmt"
+)
+
+// A writer enables sequential writing of cpio archives.
+// A call to WriteHeader begins a new file. Every call to
+// write afterwards appends to that file, writing at most
+// hdr.Size bytes in total.
+type Writer struct {
+	w               io.Writer
+	inode           int64
+	length          int64
+	remaining_bytes int
+}
+
+func NewWriter(w io.Writer) *Writer {
+	return &Writer{
+		w:     w,
+		inode: 721,
+	}
+}
+
+func assemble(mode, typev int64) int64 {
+	return mode&0xFFF | ((typev & 0xF) << 12)
+}
+
+func (w *Writer) WriteHeader(hdr *Header) error {
+	// Bring last file to the defined length
+	e := w.zeros(int64(w.remaining_bytes))
+	if e != nil {
+		return e
+	}
+	e = w.pad(4)
+	if e != nil {
+		return e
+	}
+	bname := []byte(hdr.Name)
+	nlinks := 1
+	if hdr.Type == TYPE_DIR {
+		nlinks = 2
+	}
+	shdr := fmt.Sprintf("%s%08x%08x%08x%08x%08x%08x%08x%08x%08x%08x%08x%08x%08x",
+		"070701",
+		w.inode,
+		assemble(hdr.Mode, hdr.Type),
+		hdr.Uid,
+		hdr.Gid,
+		nlinks,
+		hdr.Mtime,
+		hdr.Size,
+		3, // major
+		1, // minor
+		hdr.Devmajor,
+		hdr.Devminor,
+		len(bname)+1, // +1 for terminating zero
+		0)            // check
+	_, e = w.countedWrite([]byte(shdr))
+	if e != nil {
+		return e
+	}
+
+	_, e = w.countedWrite(bname)
+	if e != nil {
+		return e
+	}
+
+	_, e = w.countedWrite([]byte{0})
+	if e != nil {
+		return e
+	}
+	w.inode++
+	w.remaining_bytes = int(hdr.Size)
+	return w.pad(4)
+}
+
+func (w *Writer) zeros(num int64) error {
+	for ; num > 0; num-- {
+		_, e := w.countedWrite([]byte{0})
+		if e != nil {
+			return e
+		}
+	}
+	return nil
+}
+
+// Brings the length of the file to a multiple of mod
+func (w *Writer) pad(mod int64) error {
+
+	return w.zeros((mod - (w.length % mod)) % mod)
+}
+
+func (w *Writer) Write(b []byte) (n int, e error) {
+	if len(b) > w.remaining_bytes {
+		b = b[0:w.remaining_bytes]
+	}
+	n, e = w.countedWrite(b)
+	w.remaining_bytes -= n
+	return
+}
+
+func (w *Writer) countedWrite(b []byte) (n int, e error) {
+	n, e = w.w.Write(b)
+	w.length += int64(n)
+	return n, e
+}
+
+// Writes trailer
+// Does not close underlying writer
+func (w *Writer) Close() error {
+	e := w.WriteHeader(&trailer)
+	if e != nil {
+		return e
+	}
+	return w.pad(512)
+}