Fix brotlidump.py crashing when complex prefix code has exactly 1 non-zero code length (#635)
According to the format specification regarding complex prefix codes:
> If there are at least two non-zero code lengths, any trailing zero
> code lengths are omitted, i.e., the last code length in the
> sequence must be non-zero. In this case, the sum of (32 >> code
> length) over all the non-zero code lengths must equal to 32.
> If the lengths have been read for the entire code length alphabet
> and there was only one non-zero code length, then the prefix code
> has one symbol whose code has zero length.
The script does not handle a case where there is just 1 non-zero code
length where the sum rule doesn't apply, which causes a StopIteration
exception when it attempts to read past the list boundaries.
An example of such file is tests/testdata/mapsdatazrh.compressed. I made
sure this change doesn't break anything by processing all *.compressed
files from the testdata folder with no thrown exceptions.
diff --git a/research/brotlidump.py b/research/brotlidump.py
index a625368..7018934 100644
--- a/research/brotlidump.py
+++ b/research/brotlidump.py
@@ -1467,16 +1467,17 @@
#we use it for display until now; definition comes below
lengthCode = LengthAlphabet('#'+alphabet.name)
lengthIter = iter(lengths)
- while total<32:
+ lengthsLeft = len(lengths)
+ while total<32 and lengthsLeft>0:
+ lengthsLeft -= 1
newSymbol = next(lengthIter)
lol.description = str(lengthCode[newSymbol])
length = self.verboseRead(lol)
if length:
codeLengths[newSymbol] = length
total += 32>>length
- if total>=32:
- break
if total>32: raise ValueError("Stream format")
+ if len(codeLengths)==1: codeLengths[list(codeLengths.keys())[0]] = 0
#Now set the encoding of the lengthCode
lengthCode.setLength(codeLengths)
print("***** Lengths for {} will be coded as:".format(alphabet.name))
