Issue #1288 - Part 2: Add a partial LZ4 decompression routine.

This function never writes beyond `aDest` + `aMaxOutputSize`, and is
therefore protexted against malicious datapackets.
It also ignores unconsumed input upon reaching `aMaxOutputSize` and can
therefore be used for parial decompression of LZ4 input up to a desired
resulting size of decompressed data.

1 files changed, 21 insertions, 0 deletions

diff --git a/mfbt/Compression.cpp b/mfbt/Compression.cpp
index 6be8020a9..5646b56b2 100644
--- a/mfbt/Compression.cpp
+++ b/mfbt/Compression.cpp
@@ -76,3 +76,24 @@ LZ4::decompress(const char* aSource, size_t aInputSize, char* aDest,
   return false;
 }
 
+bool
+LZ4::decompressPartial(const char* aSource, size_t aInputSize, char* aDest,
+                       size_t aMaxOutputSize, size_t* aOutputSize)
+{
+  CheckedInt<int> maxOutputSizeChecked = aMaxOutputSize;
+  MOZ_ASSERT(maxOutputSizeChecked.isValid());
+  CheckedInt<int> inputSizeChecked = aInputSize;
+  MOZ_ASSERT(inputSizeChecked.isValid());
+
+  int ret = LZ4_decompress_safe_partial(aSource, aDest,
+                                        inputSizeChecked.value(),
+                                        maxOutputSizeChecked.value(),
+                                        maxOutputSizeChecked.value());
+  if (ret >= 0) {
+    *aOutputSize = ret;
+    return true;
+  }
+
+  *aOutputSize = 0;
+  return false;
+}