tesseract caching: don't transcode tesseract's output, hash source file

For sanity's sake, deal with tesseract streams in binary without
transcoding (via universal_newlines, etc.). The only differences are
printing messages regarding spoofing.

Also hash the source file so that changes to the cache mechanism
invalidate old cache automatically. That is probably too aggressive,
but simple and safer than the previous approach.

tests/spoof/tesseract_cache.py

@@ -48,11 +48,17 @@ def main():
 
     m = hashlib.sha1()
 
-    version = subprocess.check_output(
+    tess_version = subprocess.check_output(
         ['tesseract', '--version'],
         stderr=subprocess.STDOUT)
 
-    m.update(version)
+    m.update(tess_version)
+
+    # Insert this source file into the hash function, to ensure that any
+    # changes to this file invalidate previous hashes
+    with open(__file__, 'rb') as f:
+        m.update(f.read())
+
     m.update(operation.encode())
 
     try:
@@ -93,10 +99,10 @@ def main():
             shutil.copy(cache_name, output_file)
 
         # Replicate output
-        with open(cache_name + '.stdout', 'r') as f:
-            print(f.read(), end='')
-        with open(cache_name + '.stderr', 'r') as f:
-            print(f.read(), end='', file=sys.stderr)
+        with open(cache_name + '.stdout', 'rb') as f:
+            sys.stdout.buffer.write(f.read())
+        with open(cache_name + '.stderr', 'rb') as f:
+            sys.stderr.buffer.write(f.read())
         sys.exit(0)
 
     # Cache miss
@@ -105,23 +111,22 @@ def main():
     # Call tesseract
     p = subprocess.Popen(
             ['tesseract'] + sys.argv[1:],
-            stdout=subprocess.PIPE, stderr=subprocess.PIPE,
-            universal_newlines=True)
+            stdout=subprocess.PIPE, stderr=subprocess.PIPE)
     stdout, stderr = p.communicate()
 
     if p.returncode != 0:
         # Do not cache errors or crashes
         print("Tesseract error", file=sys.stderr)
-        print(stdout, end='')
-        print(stderr, end='', file=sys.stderr)
+        sys.stdout.buffer.write(stdout)
+        sys.stderr.buffer.write(stderr)
         return p.returncode
 
-    with open(cache_name + '.stdout', 'w') as f:
+    with open(cache_name + '.stdout', 'wb') as f:
         f.write(stdout)
-    with open(cache_name + '.stderr', 'w') as f:
+    with open(cache_name + '.stderr', 'wb') as f:
         f.write(stderr)
-    print(stdout, end='')
-    print(stderr, end='', file=sys.stderr)
+    sys.stdout.buffer.write(stdout)
+    sys.stderr.buffer.write(stderr)
 
     # Insert file into cache
     if output_file != 'stdout':