1 files changed, 107 insertions, 0 deletions
diff --git a/morphlib/xfer-hole b/morphlib/xfer-hole
new file mode 100755
index 00000000..08222322
--- /dev/null
+++ b/morphlib/xfer-hole
@@ -0,0 +1,107 @@
+#!/usr/bin/env python
+
+
+import errno
+import os
+import sys
+
+
+SEEK_DATA = 3
+SEEK_HOLE = 4
+
+
+filename = sys.argv[1]
+fd = os.open(filename, os.O_RDONLY)
+pos = 0
+
+
+DATA = 'data'
+HOLE = 'hole'
+EOF = 'eof'
+
+
+def safe_lseek(fd, pos, whence):
+    try:
+        return os.lseek(fd, pos, whence)
+    except OSError as e:
+        if e.errno == errno.ENXIO:
+            return -1
+        raise
+
+
+def current_data_or_pos(fd, pos):
+    length = safe_lseek(fd, 0, os.SEEK_END)
+    next_data = safe_lseek(fd, pos, SEEK_DATA)
+    next_hole = safe_lseek(fd, pos, SEEK_HOLE)
+
+    if pos == length:
+        return EOF, pos
+    elif pos == next_data:
+        return DATA, pos
+    elif pos == next_hole:
+        return HOLE, pos
+    else:
+        assert False, \
+            ("Do not understand: pos=%d next_data=%d next_hole=%d" %
+             (pos, next_data, next_hole))
+
+
+def next_data_or_hole(fd, pos):
+    length = safe_lseek(fd, 0, os.SEEK_END)
+    next_data = safe_lseek(fd, pos, SEEK_DATA)
+    next_hole = safe_lseek(fd, pos, SEEK_HOLE)
+
+    if pos == length:
+        return EOF, pos
+    elif pos == next_data:
+        # We are at data.
+        if next_hole == -1 or next_hole == length:
+            return EOF, length
+        else:
+            return HOLE, next_hole
+    elif pos == next_hole:
+        # We are at a hole.
+        if next_data == -1 or next_data == length:
+            return EOF, length
+        else:
+            return DATA, next_data
+    else:
+        assert False, \
+            ("Do not understand: pos=%d next_data=%d next_hole=%d" %
+             (pos, next_data, next_hole))
+
+
+def find_data_and_holes(fd):
+    pos = safe_lseek(fd, 0, os.SEEK_CUR)
+
+    kind, pos = current_data_or_pos(fd, pos)
+    while kind != EOF:
+        yield kind, pos
+        kind, pos = next_data_or_hole(fd, pos)
+    yield kind, pos
+
+
+def make_xfer_instructions(fd):
+    prev_kind = None
+    prev_pos = None
+    for kind, pos in find_data_and_holes(fd):
+        if prev_kind == DATA:
+            yield (DATA, prev_pos, pos)
+        elif prev_kind == HOLE:
+            yield (HOLE, prev_pos, pos)
+        prev_kind = kind
+        prev_pos = pos
+
+
+def copy_slice_from_file(to, fd, start, end):
+    safe_lseek(fd, start, os.SEEK_SET)
+    data = os.read(fd, end - start)
+    to.write(data)
+    
+
+for kind, start, end in make_xfer_instructions(fd):
+    if kind == HOLE:
+        sys.stdout.write('HOLE\n%d\n' % (end - start))
+    elif kind == DATA:
+        sys.stdout.write('DATA\n%d\n' % (end - start))
+        copy_slice_from_file(sys.stdout, fd, start, end)