rpc: Upgrade WebSocketClient to support full client functionality

CHANGELOG.md

@@ -22,10 +22,15 @@
 
 - `[tendermint/proto-compiler]` Protobuf structs generator now also accepts commit IDs from the Tendermint Go repository ([#660])
 
+### IMPROVEMENTS:
+
+- `[rpc]` The `WebSocketClient` now adds support for all remaining RPC requests
+  by way of implementing the `Client` trait ([#646])
 
 [#650]: https://github.com/informalsystems/tendermint-rs/issues/650
 [#652]: https://github.com/informalsystems/tendermint-rs/pulls/652
 [#639]: https://github.com/informalsystems/tendermint-rs/pull/639
+[#646]: https://github.com/informalsystems/tendermint-rs/pull/646
 [#660]: https://github.com/informalsystems/tendermint-rs/issues/660
 [#665]: https://github.com/informalsystems/tendermint-rs/issues/665
 

docs/architecture/adr-008-event-subscription.md

@@ -218,7 +218,7 @@ WebSocket connection to provide subscription functionality (the
 #[async_trait]
 pub trait SubscriptionClient {
     /// `/subscribe`: subscribe to receive events produced by the given query.
-    async fn subscribe(&mut self, query: String) -> Result<Subscription>;
+    async fn subscribe(&mut self, query: Query) -> Result<Subscription>;
 }
 ```
 
@@ -323,19 +323,23 @@ pub enum EventType {
     ValidatorSetUpdates,
 }
 
-pub struct Condition {
-    key: String,
-    op: Operation,
-}
-
-pub enum Operation {
-    Eq(Operand),
-    Lt(Operand),
-    Lte(Operand),
-    Gt(Operand),
-    Gte(Operand),
-    Contains(Operand),
-    Exists,
+// A condition specifies a key (first parameter) and, depending on the
+// operation, an value which is an operand of some kind.
+pub enum Condition {
+    // Equals
+    Eq(String, Operand),
+    // Less than
+    Lt(String, Operand),
+    // Less than or equal to
+    Lte(String, Operand),
+    // Greater than
+    Gt(String, Operand),
+    // Greater than or equal to
+    Gte(String, Operand),
+    // Contains (to check if a key contains a certain sub-string)
+    Contains(String, String),
+    // Exists (to check if a key exists)
+    Exists(String),
 }
 
 // According to https://docs.tendermint.com/master/rpc/#/Websocket/subscribe,
@@ -346,7 +350,8 @@ pub enum Operation {
 // operand types to the `Operand` enum, as this would improve ergonomics.
 pub enum Operand {
     String(String),
-    Integer(i64),
+    Signed(i64),
+    Unsigned(u64),
     Float(f64),
     Date(chrono::Date),
     DateTime(chrono::DateTime),
@@ -361,7 +366,7 @@ track of all of the queries relating to a particular client.
 ```rust
 pub struct SubscriptionRouter {
     // A map of queries -> (map of subscription IDs -> result event tx channels)
-    subscriptions: HashMap<Query, HashMap<SubscriptionId, ChannelTx<Result<Event>>>>,
+    subscriptions: HashMap<String, HashMap<String, SubscriptionTx>>,
 }
 ```
 
@@ -372,21 +377,61 @@ server [drops subscription IDs from events][tendermint-2949], which is likely if
 we want to conform more strictly to the [JSON-RPC standard for
 notifications][jsonrpc-notifications].
 
-#### Two-Phase Subscribe/Unsubscribe
+### Handling Mixed Events and Responses
+
+Since a full client needs to implement both the `Client` and
+`SubscriptionClient` traits, for certain transports (like a WebSocket
+connection) we could end up receiving a mixture of events from subscriptions
+and responses to RPC requests. To disambiguate these different types of 
+incoming messages, a simple mechanism is proposed for the
+`WebSocketClientDriver` that keeps track of pending requests and only matures
+them once it receives its corresponding response.
 
-Due to the fact that a WebSocket connection lacks request/response semantics,
-when managing multiple subscriptions from a single client we need to implement a
-**two-phase subscription creation/removal process**:
+```rust
+pub struct WebSocketClientDriver {
+    // ...
 
-1. An outgoing, but unconfirmed, subscribe/unsubscribe request is tracked.
-2. The subscribe/unsubscribe request is confirmed or cancelled by a response
-   from the remote WebSocket server.
+    // Commands we've received but have not yet completed, indexed by their ID.
+    // A Terminate command is executed immediately.
+    pending_commands: HashMap<String, DriverCommand>,
+}
 
-The need for this two-phase subscribe/unsubscribe process is more clearly
-illustrated in the following sequence diagram:
+// The different types of requests that the WebSocketClient can send to its
+// driver.
+//
+// Each of SubscribeCommand, UnsubscribeCommand and SimpleRequestCommand keep
+// a response channel that allows for the driver to send a response later on
+// when it receives a relevant one.
+enum DriverCommand {
+    // Initiate a subscription request.
+    Subscribe(SubscribeCommand),
+    // Initiate an unsubscribe request.
+    Unsubscribe(UnsubscribeCommand),
+    // For non-subscription-related requests.
+    SimpleRequest(SimpleRequestCommand),
+    Terminate,
+}
+```
 
-![RPC client two-phase
-subscribe/unsubscribe](./assets/rpc-client-two-phase-subscribe.png)
+IDs of outgoing requests are randomly generated [UUIDv4] strings.
+
+The logic here is as follows:
+
+1. A call is made to `WebSocketClient::subscribe` or
+   `WebSocketClient::perform`.
+2. The client sends the relevant `DriverCommand` to its driver via its internal
+   communication channel.
+3. The driver receives the command, sends the relevant simple or subscription
+   request, and keeps track of the command in its `pending_commands` member
+   along with its ID. This allows the driver to continue handling outgoing 
+   requests and incoming responses in the meantime.
+4. If the driver receives a JSON-RPC message whose ID corresponds to an ID in
+   its `pending_commands` member, it assumes that response is relevant to that
+   command and sends back to the original caller by way of a channel stored in
+   one of the `SubscribeCommand`, `UnsubscribeCommand` or
+   `SimpleRequestCommand` structs. Failures are also communicated through this
+   same mechanism.
+5. The pending command is evicted from the `pending_commands` member.
 
 ## Status
 
@@ -433,4 +478,4 @@ None
 [futures-stream-mod]: https://docs.rs/futures/*/futures/stream/index.html
 [tendermint-2949]: https://github.com/tendermint/tendermint/issues/2949
 [jsonrpc-notifications]: https://www.jsonrpc.org/specification#notification
-
+[UUIDv4]: https://en.wikipedia.org/wiki/Universally_unique_identifier#Version_4_(random)

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light-client/src/components/io.rs

@@ -129,7 +129,7 @@ mod prod {
         }
 
         fn fetch_signed_header(&self, height: AtHeight) -> Result<TMSignedHeader, IoError> {
-            let client = self.rpc_client.clone();
+            let mut client = self.rpc_client.clone();
             let res = block_on(self.timeout, async move {
                 match height {
                     AtHeight::Highest => client.latest_commit().await,
@@ -151,7 +151,7 @@ mod prod {
                 AtHeight::At(height) => height,
             };
 
-            let client = self.rpc_client.clone();
+            let mut client = self.rpc_client.clone();
             let res = block_on(self.timeout, async move { client.validators(height).await })?;
 
             match res {

light-client/src/evidence.rs

@@ -42,7 +42,7 @@ mod prod {
     impl EvidenceReporter for ProdEvidenceReporter {
         #[pre(self.peer_map.contains_key(&peer))]
         fn report(&self, e: Evidence, peer: PeerId) -> Result<Hash, IoError> {
-            let client = self.rpc_client_for(peer)?;
+            let mut client = self.rpc_client_for(peer)?;
 
             let res = block_on(
                 self.timeout,

rpc/Cargo.toml

@@ -25,7 +25,15 @@ all-features = true
 
 [features]
 default = []
-http-client = [ "async-trait", "futures", "http", "hyper", "tokio/fs", "tokio/macros" ]
+http-client = [
+  "async-trait",
+  "futures",
+  "http",
+  "hyper",
+  "tokio/fs",
+  "tokio/macros",
+  "tracing"
+]
 secp256k1 = [ "tendermint/secp256k1" ]
 websocket-client = [
   "async-trait",