Reuse reqwest client on broadcasting

See https://users.rust-lang.org/t/reqwest-http-client-fails-when-too-much-concurrency/55644/2

plume-common/src/activity_pub/mod.rs

@@ -132,6 +132,14 @@ where
         .sign(sender)
         .expect("activity_pub::broadcast: signature error");
 
+    let client = if let Some(proxy) = proxy.clone() {
+        ClientBuilder::new().proxy(proxy)
+    } else {
+        ClientBuilder::new()
+    }
+    .connect_timeout(std::time::Duration::from_secs(5))
+    .build()
+    .expect("Can't build client");
     let mut rt = tokio::runtime::current_thread::Runtime::new()
         .expect("Error while initializing tokio runtime for federation");
     for inbox in boxes {
@@ -155,33 +163,26 @@ where
         headers.insert("Host", host_header_value.unwrap());
         headers.insert("Digest", request::Digest::digest(&body));
         rt.spawn(
-            if let Some(proxy) = proxy.clone() {
-                ClientBuilder::new().proxy(proxy)
-            } else {
-                ClientBuilder::new()
-            }
-            .connect_timeout(std::time::Duration::from_secs(5))
-            .build()
-            .expect("Can't build client")
-            .post(&inbox)
-            .headers(headers.clone())
-            .header(
-                "Signature",
-                request::signature(sender, &headers, ("post", url.path(), url.query()))
-                    .expect("activity_pub::broadcast: request signature error"),
-            )
-            .body(body)
-            .send()
-            .and_then(move |r| {
-                if r.status().is_success() {
-                    debug!("Successfully sent activity to inbox ({})", &inbox);
-                } else {
-                    warn!("Error while sending to inbox ({:?})", &r)
-                }
-                r.into_body().concat2()
-            })
-            .map(move |response| debug!("Response: \"{:?}\"\n", response))
-            .map_err(|e| warn!("Error while sending to inbox ({:?})", e)),
+            client
+                .post(&inbox)
+                .headers(headers.clone())
+                .header(
+                    "Signature",
+                    request::signature(sender, &headers, ("post", url.path(), url.query()))
+                        .expect("activity_pub::broadcast: request signature error"),
+                )
+                .body(body)
+                .send()
+                .and_then(move |r| {
+                    if r.status().is_success() {
+                        debug!("Successfully sent activity to inbox ({})", &inbox);
+                    } else {
+                        warn!("Error while sending to inbox ({:?})", &r)
+                    }
+                    r.into_body().concat2()
+                })
+                .map(move |response| debug!("Response: \"{:?}\"\n", response))
+                .map_err(|e| warn!("Error while sending to inbox ({:?})", e)),
         );
     }
     rt.run().unwrap();