From eb847a97cd49d8ec68819478c07b5f5bc6f5ac28 Mon Sep 17 00:00:00 2001
From: Elliot Nunn <elliotnunn@me.com>
Date: Mon, 8 Oct 2018 09:33:34 +0800
Subject: [PATCH] Read extents overflow file

---
 machfs/main.py | 23 +++++++++++------------
 test_all.py    | 11 ++++++++---
 2 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/machfs/main.py b/machfs/main.py
index 9bd87df..8b30443 100644
--- a/machfs/main.py
+++ b/machfs/main.py
@@ -125,8 +125,12 @@ class Volume(directory.AbstractFolder):
         extoflow = {}
         for rec in btree.dump_btree(extrec2bytes(drXTExtRec)):
             if rec[0] != 7: continue
-            # print(key, val)
-            pass
+            xkrFkType, xkrFNum, xkrFABN, extrec = struct.unpack_from('>xBLH12s', rec)
+            if xkrFkType == 0xFF:
+                fork = 'rsrc'
+            elif xkrFkType == 0:
+                fork = 'data'
+            extoflow[xkrFNum, fork, xkrFABN] = extrec
 
         cnids = {}
         childlist = [] # list of (parent_cnid, child_name, child_object) tuples
@@ -176,17 +180,12 @@ class Volume(directory.AbstractFolder):
                 f.type, f.creator, f.flags, f.x, f.y = struct.unpack_from('>4s4sHHH', filUsrWds)
 
                 for fork, length, extrec in [('data', filLgLen, filExtRec), ('rsrc', filRLgLen, filRExtRec)]:
-                    accum = bytearray()
-                    extrec = list(struct.unpack('>HHHHHH', extrec))
-                    extrec = list(zip(extrec[::2], extrec[1::2]))
-                    for extstart, extlength in extrec:
-                        if extlength == 0: continue
-                        astart = 512*drAlBlSt + drAlBlkSiz*extstart
-                        astop = astart + drAlBlkSiz*extlength
-                        accum.extend(from_volume[astart:astop])
+                    accum = bytearray(extrec2bytes(extrec))
+                    while len(accum) < length:
+                        next_blk = len(accum) // drAlBlkSiz
+                        next_extrec = extoflow[filFlNum, fork, next_blk]
+                        accum.extend(extrec2bytes(next_extrec))
                     del accum[length:] # logical length can be less than a number of blocks
-                    if len(accum) != length:
-                        raise ValueError('need to consult extents overflow file')
 
                     setattr(f, fork, accum)
 
diff --git a/test_all.py b/test_all.py
index 73f85c6..7bc3816 100644
--- a/test_all.py
+++ b/test_all.py
@@ -51,6 +51,11 @@ def test_macos_mount():
     os.system('umount /Volumes/ElmoTest')
     assert recovered == hf.data
 
-    # h2 = Volume()
-    # h2.read(ser)
-    # assert h2['testfile-000'].data == hf.data
+    h2 = Volume()
+    h2.read(ser)
+    assert h2['testfile-000'].data == hf.data
+
+def test_extents_overflow():
+    h = Volume()
+    h.read(open('SourceForEmulator.dmg','rb').read())
+    assert h['aa'].data == b'a' * 278528