feat(rpc module): stream API for SubscriptionSink (#639)

* feat(rpc module): add_stream to subscription sink

* fix some nits

* unify parameters to rpc methods

* Update core/src/server/rpc_module.rs

* Update tests/tests/integration_tests.rs

Co-authored-by: David <dvdplm@gmail.com>

* address grumbles

* fix subscription tests

* new type for `SubscriptionCallback` and glue code

* remove unsed code

* remove todo

* add missing feature tokio/macros

* make `add_stream` cancel-safe

* rename add_stream and return status

* fix nits

* rename stream API -> streamify

* Update core/src/server/rpc_module.rs

* provide proper close reason

* spelling

* consume_and_streamify + docs

* fmt

* rename API pipe_from_stream

* improve logging; indicate which subscription method that failed

Co-authored-by: David <dvdplm@gmail.com>

core/Cargo.toml

@@ -11,6 +11,7 @@ anyhow = "1"
 arrayvec = "0.7.1"
 async-trait = "0.1"
 beef = { version = "0.5.1", features = ["impl_serde"] }
+async-channel = { version = "1.6", optional = true }
 thiserror = "1"
 futures-channel = { version = "0.3.14", default-features = false }
 futures-util = { version = "0.3.14", default-features = false, optional = true }
@@ -29,6 +30,7 @@ tokio = { version = "1.8", features = ["rt"], optional = true }
 default = []
 http-helpers = ["futures-util"]
 server = [
+	"async-channel",
 	"futures-util",
 	"rustc-hash",
 	"tracing",

core/src/server/helpers.rs

@@ -28,7 +28,7 @@ use std::io;
 
 use crate::{to_json_raw_value, Error};
 use futures_channel::mpsc;
-use futures_util::stream::StreamExt;
+use futures_util::StreamExt;
 use jsonrpsee_types::error::{
 	CallError, ErrorCode, ErrorObject, ErrorResponse, CALL_EXECUTION_FAILED_CODE, OVERSIZED_RESPONSE_CODE,
 	OVERSIZED_RESPONSE_MSG, UNKNOWN_ERROR_CODE,