Fix data corruption when output of snappy compression is more than 4GB

This fixes #201

snappy.cc

@@ -1499,7 +1499,7 @@ class SnappyDecompressor {
   // If ip < ip_limit_min_maxtaglen_ it's safe to read kMaxTagLength from
   // buffer.
   const char* ip_limit_min_maxtaglen_;
-  uint32_t peeked_;                  // Bytes peeked from reader (need to skip)
+  uint64_t peeked_;                  // Bytes peeked from reader (need to skip)
   bool eof_;                         // Hit end of input without an error?
   char scratch_[kMaximumTagLength];  // See RefillTag().
 
@@ -1726,7 +1726,7 @@ bool SnappyDecompressor::RefillTag() {
   assert(needed <= sizeof(scratch_));
 
   // Read more bytes from reader if needed
-  uint32_t nbuf = ip_limit_ - ip;
+  uint64_t nbuf = ip_limit_ - ip;
   if (nbuf < needed) {
     // Stitch together bytes from ip and reader to form the word
     // contents.  We store the needed bytes in "scratch_".  They
@@ -1739,7 +1739,7 @@ bool SnappyDecompressor::RefillTag() {
       size_t length;
       const char* src = reader_->Peek(&length);
       if (length == 0) return false;
-      uint32_t to_add = std::min<uint32_t>(needed - nbuf, length);
+      uint64_t to_add = std::min<uint64_t>(needed - nbuf, length);
       std::memcpy(scratch_ + nbuf, src, to_add);
       nbuf += to_add;
       reader_->Skip(to_add);
@@ -1802,6 +1802,7 @@ size_t Compress(Source* reader, Sink* writer, CompressionOptions options) {
   int token = 0;
   size_t written = 0;
   size_t N = reader->Available();
+  assert(N <= 0xFFFFFFFFu);
   const size_t uncompressed_size = N;
   char ulength[Varint::kMax32];
   char* p = Varint::Encode32(ulength, N);