Refactor all examples:

fix #575, fix #604, fix #608, fix #634, fix #712

All examples are rewritten:

* Using Best Practices
* Mostly self-contained
* New examples to complete the feature matrix
* The server-framework example is removed

example/http/client/async/CMakeLists.txt

@@ -0,0 +1,17 @@
+#
+# Copyright (c) 2016-2017 Vinnie Falco (vinnie dot falco at gmail dot com)
+#
+# Distributed under the Boost Software License, Version 1.0. (See accompanying
+# file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+#
+# Official repository: https://github.com/boostorg/beast
+#
+
+GroupSources(include/boost/beast beast)
+GroupSources(example/http/client/async "/")
+
+add_executable (http-client-async
+    ${BOOST_BEAST_INCLUDES}
+    Jamfile
+    http_client_async.cpp
+)

example/http/client/async/Jamfile

@@ -0,0 +1,15 @@
+#
+# Copyright (c) 2016-2017 Vinnie Falco (vinnie dot falco at gmail dot com)
+#
+# Distributed under the Boost Software License, Version 1.0. (See accompanying
+# file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+#
+# Official repository: https://github.com/boostorg/beast
+#
+
+exe http-client-async :
+    http_client_async.cpp
+    :
+    <variant>coverage:<build>no
+    <variant>ubasan:<build>no
+    ;

example/http/client/async/http_client_async.cpp

@@ -0,0 +1,172 @@
+//
+// Copyright (c) 2016-2017 Vinnie Falco (vinnie dot falco at gmail dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+// Official repository: https://github.com/boostorg/beast
+//
+
+//------------------------------------------------------------------------------
+//
+// Example: HTTP client, asynchronous
+//
+//------------------------------------------------------------------------------
+
+#include <boost/beast/core.hpp>
+#include <boost/beast/http.hpp>
+#include <boost/beast/version.hpp>
+#include <boost/asio/connect.hpp>
+#include <boost/asio/ip/tcp.hpp>
+#include <cstdlib>
+#include <functional>
+#include <iostream>
+#include <memory>
+#include <string>
+
+using tcp = boost::asio::ip::tcp;       // from <boost/asio/ip/tcp.hpp>
+namespace http = boost::beast::http;    // from <boost/beast/http.hpp>
+
+//------------------------------------------------------------------------------
+
+// Report a failure
+void
+fail(boost::system::error_code ec, char const* what)
+{
+    std::cerr << what << ": " << ec.message() << "\n";
+}
+
+// Performs an HTTP GET and prints the response
+class session : public std::enable_shared_from_this<session>
+{
+    tcp::resolver resolver_;
+    tcp::socket socket_;
+    boost::beast::flat_buffer buffer_; // (Must persist between reads)
+    http::request<http::empty_body> req_;
+    http::response<http::string_body> res_;
+
+public:
+    // Resolver and socket require an io_service
+    explicit
+    session(boost::asio::io_service& ios)
+        : resolver_(ios)
+        , socket_(ios)
+    {
+    }
+
+    // Start the asynchronous operation
+    void
+    run(
+        char const* host,
+        char const* port,
+        char const* target)
+    {
+        // Set up an HTTP GET request message
+        req_.version = 11;
+        req_.method(http::verb::get);
+        req_.target(target);
+        req_.set(http::field::host, host);
+        req_.set(http::field::user_agent, BOOST_BEAST_VERSION_STRING);
+
+        // Look up the domain name
+        resolver_.async_resolve({host, port},
+            std::bind(
+                &session::on_resolve,
+                shared_from_this(),
+                std::placeholders::_1,
+                std::placeholders::_2));
+    }
+
+    void
+    on_resolve(
+        boost::system::error_code ec,
+        tcp::resolver::iterator result)
+    {
+        if(ec)
+            return fail(ec, "resolve");
+
+        // Make the connection on the IP address we get from a lookup
+        boost::asio::async_connect(socket_, result,
+            std::bind(
+                &session::on_connect,
+                shared_from_this(),
+                std::placeholders::_1));
+    }
+
+    void
+    on_connect(boost::system::error_code ec)
+    {
+        if(ec)
+            return fail(ec, "connect");
+
+        // Send the HTTP request to the remote host
+        http::async_write(socket_, req_,
+            std::bind(
+                &session::on_write,
+                shared_from_this(),
+                std::placeholders::_1));
+    }
+
+    void
+    on_write(boost::system::error_code ec)
+    {
+        if(ec)
+            return fail(ec, "write");
+        
+        // Receive the HTTP response
+        http::async_read(socket_, buffer_, res_,
+            std::bind(
+                &session::on_read,
+                shared_from_this(),
+                std::placeholders::_1));
+    }
+
+    void
+    on_read(boost::system::error_code ec)
+    {
+        if(ec)
+            return fail(ec, "read");
+
+        // Write the message to standard out
+        std::cout << res_ << std::endl;
+
+        // Gracefully close the socket
+        socket_.shutdown(tcp::socket::shutdown_both, ec);
+
+        // not_connected happens sometimes so don't bother reporting it.
+        if(ec && ec != boost::system::errc::not_connected)
+            return fail(ec, "shutdown");
+
+        // If we get here then the connection is closed gracefully
+    }
+};
+
+//------------------------------------------------------------------------------
+
+int main(int argc, char** argv)
+{
+    // Check command line arguments.
+    if(argc != 4)
+    {
+        std::cerr <<
+            "Usage: http-client-async <host> <port> <target>\n" <<
+            "Example:\n" <<
+            "    http-client-async www.example.com 80 /\n";
+        return EXIT_FAILURE;
+    }
+    auto const host = argv[1];
+    auto const port = argv[2];
+    auto const target = argv[3];
+
+    // The io_service is required for all I/O
+    boost::asio::io_service ios;
+
+    // Launch the asynchronous operation
+    std::make_shared<session>(ios)->run(host, port, target);
+
+    // Run the I/O service. The call will return when
+    // the get operation is complete.
+    ios.run();
+
+    return EXIT_SUCCESS;
+}