gRPC client for q/kdb+.

q/kdb+ implements appropriate protocols to communicate between q processes using HTTP(1) protocol. There are some client libraries for q which implement the appropriate protocol but they are not suitable for integration in a large system. On the other hand it is now rare for HTTP to be a main protocol.

When your processes have a limited number of message types and furthermore you want to check the validity of contents, HTTP is unsuitable. Then gRPC comes into play, based on HTTP2 and allowing you to specify specific message types.

Users of q/kdb+ might have complained they could not use gRPC in q and used HTTP without any options, hacking erroneous messages leaning deeply against a chair-back. This library is a gRPC client implementation of q to pour water ("of life", if you will) to such a people.

As a protobuf message is strictly typed based on proto files, qrpc needs to compile source proto files at building a shared library. For this reason users have to put their proto files to use for gRPC under a directory specified by an environmental variable QRPC_PROTO_DIR.

And lo, and behold, qrpc automatically generates Rust code for gRPC client methods defined in service in the user input, and of course, q code to load the shared library. For example, services below;

// Service mocking a restaurant order system.
service Restaurant{
  // Customer submits an order and a kitchen returns a response.
  rpc Submit(Order) returns (Acceptance);
  // Customer finish a meal handing an expense and a restaurant displays a total due
  //  with an order history.
  rpc Finish(Expense) returns (Total);
  // Customer forcefully cancels an order.
  rpc Cancel(Order) returns (google.protobuf.Empty);
}

will be loaded into q as:

// Load gRPC client method submit.
.grpc.submit: `libqrpc 2: (`submit; 1);

// Load gRPC client method finish.
.grpc.finish: `libqrpc 2: (`finish; 1);

// Load gRPC client method cancel.
.grpc.cancel: `libqrpc 2: (`cancel; 1);

qrpc also supports enum message. For example, enum message

// Available menu.
enum Menu{
  smile = 0;
  pizza = 1; 
  spaghetti = 2;
  salad = 3;
  steak = 4;
  sushi = 5;
  hamburger = 6;
  chips = 7;
  coke = 8;
}

in a package restaurant will define enum variable .grpc.restaurant.Menu in the same file as the generated one for service:

// Source of enum message Menu.
.grpc.restaurant.Menu: `smile`pizza`spaghetti`salad`steak`sushi`hamburger`chips`coke;

Ordinary cargo command builds a library for you.

qrpc]$ cargo build --release
qrpc]$ cp target/release/libqrpc.so .
qrpc]$ q q/grpc.q
q)

And you are ready:)

1. Type Mapping
2. Message Examples
3. gRPC Example
4. Test