Some simplifications and a bugfix.

include/aedis/resp3/detail/read.hpp

@@ -206,10 +206,11 @@ struct consumer_op {
                yield self.complete(ec, m_type);
 
                if (m_type != type::push)
-                  requests.front().elements.pop();
+		  requests.front().elements.pop();
 
-            } while (!std::empty(requests.front().elements));
-            requests.pop();
+            } while (!std::empty(requests) && !std::empty(requests.front().elements));
+	    if (!std::empty(requests))
+	       requests.pop();
          } while (std::empty(requests));
       }
    }

include/aedis/resp3/detail/write.hpp

@@ -76,10 +76,8 @@ struct write_some_op {
 	    if (ec)
 	       break;
 
-	    requests.front().sent = true;
-
 	    if (std::empty(requests.front().elements)) {
-	       // We only pop when all commands in the pipeline has push
+	       // We only pop when all commands in the pipeline have push
 	       // responses like subscribe, otherwise, pop is done when the
 	       // response arrives.
 	       requests.pop();
@@ -93,12 +91,15 @@ struct write_some_op {
 
 template<
   class AsyncWriteStream,
-  class CompletionToken>
+  class CompletionToken =
+      net::default_completion_token_t<typename AsyncWriteStream::executor_type>
+  >
 auto
 async_write_some(
    AsyncWriteStream& stream,
    std::queue<request>& requests,
-   CompletionToken&& token)
+   CompletionToken&& token =
+      net::default_completion_token_t<typename AsyncWriteStream::executor_type>{})
 {
   return net::async_compose<
      CompletionToken,

include/aedis/resp3/impl/request.ipp

@@ -12,17 +12,11 @@ namespace resp3 {
 
 bool prepare_next(std::queue<request>& reqs)
 {
-   if (std::empty(reqs)) {
+   auto const cond = std::empty(reqs) || std::size(reqs) == 1;
+   if (cond)
       reqs.push({});
-      return true;
-   }
 
-   if (reqs.back().sent) {
-      reqs.push({});
-      return false;
-   }
-
-   return false;
+   return cond;
 }
 
 std::ostream& operator<<(std::ostream& os, request::element const& e)

include/aedis/resp3/request.hpp

@@ -37,7 +37,6 @@ public:
    };
    std::string payload;
    std::queue<element> elements;
-   bool sent = false;
 
 public:
    /// Return the size of the pipeline. i.e. how many commands it
@@ -138,13 +137,20 @@ public:
       elements.emplace(command::lpop, std::string{key});
    }
 
-   /// Adds ping to the request, see https://redis.io/commands/subscribe
-   void subscribe(std::string_view key)
+   /// Adds subscribe to the request, see https://redis.io/commands/subscribe
+   void subscribe(std::initializer_list<std::string_view> l)
    {
       // The response to this command is a push type.
-      detail::assemble(payload, "SUBSCRIBE", key);
+      std::initializer_list<std::string_view> dummy = {};
+      detail::assemble(payload, "SUBSCRIBE", l, std::cbegin(dummy), std::cend(dummy));
    }
 
+   void psubscribe(std::initializer_list<std::string_view> l)
+   {
+      std::initializer_list<std::string_view> dummy = {};
+      detail::assemble(payload, "PSUBSCRIBE", l, std::cbegin(dummy), std::cend(dummy));
+   }
+   
    /// Adds ping to the request, see https://redis.io/commands/unsubscribe
    void unsubscribe(std::string_view key)
    {
@@ -236,12 +242,6 @@ public:
       elements.emplace(command::lpush, std::string{key});
    }
    
-   void psubscribe( std::initializer_list<std::string_view> l)
-   {
-      std::initializer_list<std::string_view> dummy = {};
-      detail::assemble(payload, "PSUBSCRIBE", l, std::cbegin(dummy), std::cend(dummy));
-   }
-   
    /// Adds ping to the request, see https://redis.io/commands/publish
    void publish(std::string_view key, std::string_view msg)
    {