Allow constructing Buffer from a std::string

include/cppkafka/buffer.h

@@ -40,6 +40,10 @@ namespace cppkafka {
  * 
  * This is only a view, hence you should convert the contents of a buffer into
  * some other container if you want to store it somewhere. 
+ *
+ * If you're using this to produce a message, you *need* to guarantee that the
+ * pointer that this buffer points to will still until the call to Producer::produce
+ * returns.
  */
 class Buffer {
 public:
@@ -62,6 +66,17 @@ public:
         static_assert(sizeof(T) == 1, "Buffer must point to elements of 1 byte");
     }
 
+    /**
+     * \brief Construct a buffer from a const string ref
+     *
+     * Note that you *can't use temporaries* here as they would be destructed after
+     * the constructor finishes.
+     */
+    Buffer(const std::string& data); 
+
+    // Don't allow construction from temporaries
+    Buffer(std::string&&) = delete;
+
     Buffer(const Buffer&) = delete;
     Buffer(Buffer&&) = default;
     Buffer& operator=(const Buffer&) = delete;

include/cppkafka/producer.h

@@ -70,11 +70,10 @@ class TopicConfiguration;
  * string payload = "some payload";
  *
  * // Write a message into an unassigned partition
- * producer.produce(topic, Partition(), Buffer(payload.data(), payload.size()));
+ * producer.produce(topic, Partition(), payload);
  *
- * // Write using a key
- * producer.produce(topic, Partition(), Buffer(payload.data(), payload.size()),
- *                  Buffer(key.data(), key.size()));
+ * // Write using a key on a fixed partition (42)
+ * producer.produce(topic, 42, payload, key);
  * 
  * \endcode
  */