Merge pull request #1361 from moyogo/kerntable

Ignore the length of kern table sutable format 0

Lib/fontTools/ttLib/tables/_k_e_r_n.py

@@ -48,6 +48,19 @@ class table__k_e_r_n(DefaultTable.DefaultTable):
 				# This "version" is always 0 so we ignore it here
 				_, length, subtableFormat, coverage = struct.unpack(
 					">HHBB", data[:6])
+				if nTables == 1 and subtableFormat == 0:
+					# The "length" value is ignored since some fonts
+					# (like OpenSans and Calibri) have a subtable larger than
+					# its value.
+					nPairs, = struct.unpack(">H", data[6:8])
+					calculated_length = (nPairs * 6) + 14
+					if length != calculated_length:
+						log.warning(
+							"'kern' subtable longer than defined: "
+							"%d bytes instead of %d bytes" %
+							(calculated_length, length)
+						)
+					length = calculated_length
 			if subtableFormat not in kern_classes:
 				subtable = KernTable_format_unkown(subtableFormat)
 			else:
@@ -128,7 +141,6 @@ class KernTable_format_0(object):
 			">HHHH", data[:8])
 		data = data[8:]
 
-		nPairs = min(nPairs, len(data) // 6)
 		datas = array.array("H", data[:6 * nPairs])
 		if sys.byteorder != "big": datas.byteswap()
 		it = iter(datas)
@@ -153,6 +165,7 @@ class KernTable_format_0(object):
 	def compile(self, ttFont):
 		nPairs = len(self.kernTable)
 		searchRange, entrySelector, rangeShift = getSearchRange(nPairs, 6)
+		searchRange &= 0xFFFF
 		data = struct.pack(
 			">HHHH", nPairs, searchRange, entrySelector, rangeShift)
 
@@ -175,6 +188,10 @@ class KernTable_format_0(object):
 		if not self.apple:
 			version = 0
 			length = len(data) + 6
+			if length >= 0x10000:
+				log.warning('"kern" subtable overflow, '
+							'truncating length value while preserving pairs.')
+				length &= 0xFFFF
 			header = struct.pack(
 				">HHBB", version, length, self.format, self.coverage)
 		else:

Tests/ttLib/tables/_k_e_r_n_test.py

@@ -5,6 +5,7 @@ from fontTools.ttLib.tables._k_e_r_n import (
     KernTable_format_0, KernTable_format_unkown)
 from fontTools.misc.textTools import deHexStr
 from fontTools.misc.testTools import FakeFont, getXML, parseXML
+import itertools
 import pytest
 
 
@@ -120,12 +121,32 @@ KERN_VER_1_FMT_UNKNOWN_XML = [
     '</kernsubtable>',
 ]
 
+KERN_VER_0_FMT_0_OVERFLOWING_DATA = deHexStr(
+    '0000 '  #  0: version=0
+    '0001 '  #  2: nTables=1
+    '0000 '  #  4: version=0 (bogus field, unused)
+    '0274 '  #  6: length=628 (bogus value for 66164 % 0x10000)
+    '00 '    #  8: format=0
+    '01 '    #  9: coverage=1
+    '2B11 '  # 10: nPairs=11025
+    'C000 '  # 12: searchRange=49152
+    '000D '  # 14: entrySelector=13
+    '4266 '  # 16: rangeShift=16998
+) + deHexStr(' '.join(
+    '%04X %04X %04X' % (a, b, 0)
+    for (a, b) in itertools.product(range(105), repeat=2)
+))
+
 
 @pytest.fixture
 def font():
     return FakeFont(list("ABCDEFGHIJKLMNOPQRSTUVWXYZ"
                          "abcdefghijklmnopqrstuvwxyz"))
 
+@pytest.fixture
+def overflowing_font():
+    return FakeFont(["glyph%i" % i for i in range(105)])
+
 
 class KernTableTest(object):
 
@@ -364,6 +385,36 @@ class KernTable_format_0_Test(object):
         assert subtable[("B", "D")] == 1
         assert subtable[("B", "glyph65535")] == 2
 
+    def test_compileOverflowingSubtable(self, overflowing_font):
+        font = overflowing_font
+        kern = newTable("kern")
+        kern.version = 0
+        st = KernTable_format_0(0)
+        kern.kernTables = [st]
+        st.coverage = 1
+        st.tupleIndex = None
+        st.kernTable = {
+            (a, b): 0
+            for (a, b) in itertools.product(
+                font.getGlyphOrder(), repeat=2)
+        }
+        assert len(st.kernTable) == 11025
+        data = kern.compile(font)
+        assert data == KERN_VER_0_FMT_0_OVERFLOWING_DATA
+
+    def test_decompileOverflowingSubtable(self, overflowing_font):
+        font = overflowing_font
+        data = KERN_VER_0_FMT_0_OVERFLOWING_DATA
+        kern = newTable("kern")
+        kern.decompile(data, font)
+
+        st = kern.kernTables[0]
+        assert st.kernTable == {
+            (a, b): 0
+            for (a, b) in itertools.product(
+                font.getGlyphOrder(), repeat=2)
+        }
+
 
 if __name__ == "__main__":
     import sys