Support streaming of Bolt results

Summary:
Previously, our implementation of the Bolt protocol buffered all results in
memory before sending them out to the client. This implementation immediately
streams the results to the client to avoid any memory allocations. Also, this
implementation splits the interpretation and pulling logic into two.

Reviewers: teon.banek

Reviewed By: teon.banek

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D1495

src/communication/bolt/v1/encoder/client_encoder.hpp

@@ -44,6 +44,10 @@ class ClientEncoder : private BaseEncoder<Buffer> {
     WriteRAW(utils::UnderlyingCast(Signature::Init));
     WriteString(client_name);
     WriteMap(auth_token);
+    // Try to flush all remaining data in the buffer, but tell it that we will
+    // send more data (the end of message chunk).
+    if (!buffer_.Flush(true)) return false;
+    // Flush an empty chunk to indicate that the message is done.
     return buffer_.Flush();
   }
 
@@ -63,18 +67,18 @@ class ClientEncoder : private BaseEncoder<Buffer> {
    */
   bool MessageRun(const std::string &statement,
                   const std::map<std::string, DecodedValue> &parameters,
-                  bool flush = true) {
+                  bool have_more = true) {
     WriteRAW(utils::UnderlyingCast(Marker::TinyStruct2));
     WriteRAW(utils::UnderlyingCast(Signature::Run));
     WriteString(statement);
     WriteMap(parameters);
-    if (flush) {
-      return buffer_.Flush();
-    } else {
-      buffer_.Chunk();
-      // Chunk always succeeds, so return true
-      return true;
-    }
+    // Try to flush all remaining data in the buffer, but tell it that we will
+    // send more data (the end of message chunk).
+    if (!buffer_.Flush(true)) return false;
+    // Flush an empty chunk to indicate that the message is done. Here we
+    // forward the `have_more` flag to indicate if there is more data that will
+    // be sent.
+    return buffer_.Flush(have_more);
   }
 
   /**
@@ -90,6 +94,10 @@ class ClientEncoder : private BaseEncoder<Buffer> {
   bool MessageDiscardAll() {
     WriteRAW(utils::UnderlyingCast(Marker::TinyStruct));
     WriteRAW(utils::UnderlyingCast(Signature::DiscardAll));
+    // Try to flush all remaining data in the buffer, but tell it that we will
+    // send more data (the end of message chunk).
+    if (!buffer_.Flush(true)) return false;
+    // Flush an empty chunk to indicate that the message is done.
     return buffer_.Flush();
   }
 
@@ -106,6 +114,10 @@ class ClientEncoder : private BaseEncoder<Buffer> {
   bool MessagePullAll() {
     WriteRAW(utils::UnderlyingCast(Marker::TinyStruct));
     WriteRAW(utils::UnderlyingCast(Signature::PullAll));
+    // Try to flush all remaining data in the buffer, but tell it that we will
+    // send more data (the end of message chunk).
+    if (!buffer_.Flush(true)) return false;
+    // Flush an empty chunk to indicate that the message is done.
     return buffer_.Flush();
   }
 
@@ -122,6 +134,10 @@ class ClientEncoder : private BaseEncoder<Buffer> {
   bool MessageAckFailure() {
     WriteRAW(utils::UnderlyingCast(Marker::TinyStruct));
     WriteRAW(utils::UnderlyingCast(Signature::AckFailure));
+    // Try to flush all remaining data in the buffer, but tell it that we will
+    // send more data (the end of message chunk).
+    if (!buffer_.Flush(true)) return false;
+    // Flush an empty chunk to indicate that the message is done.
     return buffer_.Flush();
   }
 
@@ -138,7 +154,11 @@ class ClientEncoder : private BaseEncoder<Buffer> {
   bool MessageReset() {
     WriteRAW(utils::UnderlyingCast(Marker::TinyStruct));
     WriteRAW(utils::UnderlyingCast(Signature::Reset));
+    // Try to flush all remaining data in the buffer, but tell it that we will
+    // send more data (the end of message chunk).
+    if (!buffer_.Flush(true)) return false;
+    // Flush an empty chunk to indicate that the message is done.
     return buffer_.Flush();
   }
 };
-}
+}  // namespace communication::bolt