Add a subscription manager (#548)

* WIP: Add a subscription manager.

The idea is to use the `Subscriptions` struct from Substrate, which
is used to drive subscription futures to completion, and modify
it for "general" use.

* Allow IdProvider::Id and SubscriptionId to work together

Adds trait bounds that allow conversion between the two, removing
the need for generics in SubscriptionId.

* Update SubscriptionId tests

* Rustfmt

* Use `SubscriptionId` as the key for `active_subscriptions`

* Add subscription ID providers.

Adds two subscription ID providers which can be used
by the SubscriptionManager. One provides a simple numeric
ID, while the other provides a random string.

* Add some documentation

* Clean up comment and naming

* Change the NumericIdProvider to use `u64` IDs

Instead of providing a guarantee that we can convert between
`usize` and `u64` we make the assumptions that it's unlikely
that we're running on an architecture larger than 64-bits and
we use a `u64` directly.

* Add tests for IdProvider and SubscriptionManager

Note: There's one test that doesn't pass yet which has to do
with the `cancel()` function of the SubscriptionManager.

* Restore RandomStringIdProvider as the default provider

* Retain receiver.:

* Make test executor a lazy static

* Rustfmt

* Add a comment to test

* Remove `matches!` macro

Our Windows CI runner isn't up to date and thinks this
is still a nightly feature

Co-authored-by: Tomasz Drwięga <tomasz@parity.io>

pubsub/Cargo.toml

@@ -15,9 +15,12 @@ log = "0.4"
 parking_lot = "0.10.0"
 jsonrpc-core = { version = "14.1", path = "../core" }
 serde = "1.0"
+rand = "0.7"
 
 [dev-dependencies]
 jsonrpc-tcp-server = { version = "14.1", path = "../tcp" }
+futures = { version = "0.3", features = ["compat", "thread-pool"] }
+lazy_static = "1.4"
 
 [badges]
 travis-ci = { repository = "paritytech/jsonrpc", branch = "master"}

pubsub/src/lib.rs

@@ -9,6 +9,7 @@ extern crate log;
 
 mod delegates;
 mod handler;
+pub mod manager;
 pub mod oneshot;
 mod subscription;
 pub mod typed;