Idempotent UNSUB avoids sending multiple UNSUB messages when subscrip…

…tions are dropped or manually unsubscribed.

CHANGELOG.md

@@ -2,6 +2,13 @@
 
 ## Improvements
 
+- #180 idempotent unsubscription avoids sending
+  multiple UNSUB messages.
+
+# 0.9.16
+
+## Improvements
+
 - #178 client state has been reorganized to allow
   reading and writing to make progress independently,
   preventing issues that were sometimes encountered

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "nats"
-version = "0.9.16"
+version = "0.9.17"
 description = "A Rust NATS client"
 authors = ["Derek Collison <[email protected]>", "Tyler Neely <[email protected]>", "Stjepan Glavina <[email protected]>"]
 edition = "2018"

async-nats/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "async-nats"
-version = "0.9.16"
+version = "0.9.17"
 description = "An async Rust NATS client"
 authors = ["Derek Collison <[email protected]>", "Tyler Neely <[email protected]>", "Stjepan Glavina <[email protected]>"]
 edition = "2018"
@@ -17,7 +17,7 @@ maintenance = { status = "actively-developed" }
 
 [dependencies]
 blocking = "1.0.2"
-nats = { path = "..", version = "0.9.16" }
+nats = { path = "..", version = "0.9.17" }
 
 [dev-dependencies]
 smol = "1.2.5"

src/client.rs

@@ -348,7 +348,15 @@ impl Client {
         let mut read = self.state.read.lock();
 
         // Remove the subscription from the map.
-        read.subscriptions.remove(&sid);
+        if read.subscriptions.remove(&sid).is_none() {
+            // already unsubscribed
+
+            // NB see locking protocol for state.write and state.read
+            drop(read);
+            drop(write);
+
+            return Ok(());
+        }
 
         // Send an UNSUB message.
         if let Some(writer) = write.writer.as_mut() {