Fix error revealed by test x.compressed.03 which has a backward refer…

…ence for a symbol at the start of the data

CHANGELOG.md

@@ -8,6 +8,8 @@
 - Fixed issue with compressed input that contains data split across multiple metadata blocks
 - Some changes to unit/integration tests to better support testing issues in compression format
 - Renamed test module to conform to pattern expected by unittest
+- Unit tests can now test using multiple compressed versions of each uncompressed example file 
+- Fixed error revealed by one of the newly tested cases involving an edge case in compressed format
 
 ## [1.0.2] - 2021-02-02
 

README.md

@@ -10,7 +10,7 @@ which it is not practical to package or require platform-specific binaries. It i
 the decompression function, under the assumption that will be the most common use-case that
 might have that restriction. It is hundreds of times slower than the reference `brotli`.
 
-This is a hand port of the decompression portion of the Javascript project that is
+This code began as a hand port of the decompression portion of the Javascript project that is
 itself a hand port of the C code of the reference implementation.
 
 * JavaScript port of brotli [brotli.js](https://github.com/devongovett/brotli.js)

brotlidecpy/decode.py

@@ -465,8 +465,8 @@ def brotli_decompress_buffer(input_buffer):
                 kInsertLengthPrefixCode[insert_code].nbits)
             copy_length = kCopyLengthPrefixCode[copy_code].offset + br.read_bits(
                 kCopyLengthPrefixCode[copy_code].nbits)
-            prev_byte1 = output_buffer[pos - 1]
-            prev_byte2 = output_buffer[pos - 2]
+            prev_byte1 = output_buffer[pos - 1] if pos > 0 else 0
+            prev_byte2 = output_buffer[pos - 2] if pos > 1 else 0
             for j in range(0, insert_length):
                 if block_length[0] == 0:
                     decode_block_type(num_block_types[0], block_type_trees, 0, block_type, block_type_rb,