Do not invoke memcpy unless number of bytes to read greater than 0. Return more informative error message

Change-Id: I335736571e56af36f4de909e35f8d667693db7fe

cpp/src/arrow/io/memory.cc

@@ -257,9 +257,11 @@ Status BufferReader::Tell(int64_t* position) const {
 bool BufferReader::supports_zero_copy() const { return true; }
 
 Status BufferReader::Read(int64_t nbytes, int64_t* bytes_read, void* buffer) {
-  memcpy(buffer, data_ + position_, nbytes);
   *bytes_read = std::min(nbytes, size_ - position_);
-  position_ += *bytes_read;
+  if (*bytes_read) {
+    memcpy(buffer, data_ + position_, *bytes_read);
+    position_ += *bytes_read;
+  }
   return Status::OK();
 }
 

cpp/src/arrow/ipc/ipc-read-write-test.cc

@@ -756,8 +756,11 @@ TEST_F(TestTensorRoundTrip, NonContiguous) {
 }
 
 TEST(TestRecordBatchStreamReader, MalformedInput) {
-  auto empty = std::make_shared<Buffer>("");
-  auto garbage = std::make_shared<Buffer>("12345678");
+  const std::string empty_str = "";
+  const std::string garbage_str = "12345678";
+
+  auto empty = std::make_shared<Buffer>(empty_str);
+  auto garbage = std::make_shared<Buffer>(garbage_str);
 
   std::shared_ptr<RecordBatchReader> batch_reader;
 

cpp/src/arrow/ipc/message.cc

@@ -227,7 +227,10 @@ Status ReadMessage(io::InputStream* file, std::unique_ptr<Message>* message) {
   std::shared_ptr<Buffer> metadata;
   RETURN_NOT_OK(file->Read(message_length, &metadata));
   if (metadata->size() != message_length) {
-    return Status::IOError("Unexpected end of stream trying to read message");
+    std::stringstream ss;
+    ss << "Expected to read " << message_length << " metadata bytes, but "
+       << "only read " << metadata->size();
+    return Status::Invalid(ss.str());
   }
 
   return Message::ReadFrom(metadata, file, message);