add ifd builder (for testing), and make sure unknown enums are handled..

when I switched to the included enum, the unknown enum exception switched
from KeyError to ValueError, this now fixes that..

ui/medashare/metadata/crw.py

@@ -619,6 +619,7 @@ class IFD(object):
 			if tag is None:
 				nextptr.append(res)
 				break
+
 			tag = self.getEnum(tag)
 			if tag in taghandlers:
 				res = taghandlers[tag](fh, endian, res, off)
@@ -639,7 +640,7 @@ class IFD(object):
 	def getEnum(self, key):
 		try:
 			return self.__enum(key)
-		except KeyError:
+		except ValueError:
 			return key
 
 	def __repr__(self):
@@ -919,6 +920,7 @@ def tiff_srational(endian, data):
 	return rational_dcomp(tiff_slong(endian, data))
 
 tifftypes = {
+	# function to decode, length of an element
 	1: (tiff_bytes, 1),
 	2: (tiff_ascii, 1),
 	3: (tiff_short, 2),
@@ -1083,7 +1085,7 @@ def idcrw(fh):
 
 	if hlen == 0x2a:
 		#TIFF/CR2
-		hoff, idstr, ver, hlen = readstruct(fh, endian + "I2sHI")
+		hoff, idstr, ver, rawifdoff = readstruct(fh, endian + "I2sHI")
 		if not isjpeg and (hoff != 0x10 or idstr != b'CR' or ver != 2):
 			raise ValueError('normal TIFF, not a CR2')
 		nextoff = [ hoff ]
@@ -1180,6 +1182,64 @@ class _TestCRW(unittest.TestCase):
 		l.sort()
 		set(l)
 
+	@staticmethod
+	def ifd_builder(endian, off, entries):
+		'''Build an IFD.  It is assumed to be rooted at off, but
+		will be returned as a bare string.  To locate it properly,
+		something like:
+		file = b'\x00' * off + ifd_builder('<', off)
+
+		needs to be used.  Obviously the prefix above is wrong and will
+		need to be a proper TIFF header and/or other IFDs.
+
+		The data will be added at the end.
+
+		entires is a list of tuples:
+			(tag, type, count, value)
+
+		Return value is a tuple of bytes, and offset of nextifd.
+		'''
+
+		entries = list(entries)
+		cnt = len(entries)
+
+		r = []
+
+		r.append(struct.pack(endian + 'H', cnt))
+
+		# offset + count + ifd entries + nextifd
+		extra = off + 2 + cnt * 12 + 4
+		sextra = extra
+		e = []	# extra values
+
+		for tag, _type, count, value in entries:
+			if len(value) <= 4:
+				r.append(struct.pack(endian + 'HHI', tag, _type, count) + value + b'\x00' * (4 - len(value)))
+			else:
+				r.append(struct.pack(endian + 'HHII', tag, _type, count, extra))
+				e.append(value)
+				extra += len(value)
+
+		r = b''.join(r)
+
+		nextoff = len(r) + off
+
+		assert len(r) + 4 == sextra - off
+
+		return r + b'\x00' * 4 + b''.join(e), len(r)
+
+	def test_unknown(self):
+		endian = '<'
+		off = 10
+
+		ifd, nextoff = self.ifd_builder(endian, off, [
+		    (65000, 1, 4, b'\x10' * 4),
+		    (65001, 1, 10, b'\x20' * 10)
+		    ])
+		fh = BytesIO(b'\x00' * 10 + ifd)
+
+		r = IFD(ExifTag, {}, fh, endian, off)
+
 	def test_bogus(self):
 		# make sure various bogus "files" raise an error