Add async-ssl-system-executor http client example

This example HTTP client application uses the `system_executor` to show
how to use it with the I/O objects in ASIO and Beast.

Signed-off-by: Damian Jarek <damian.jarek93@gmail.com>

example/http/client/async-ssl-system-executor/CMakeLists.txt

@@ -0,0 +1,31 @@
+#
+# 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
+#
+
+if (OPENSSL_FOUND)
+    GroupSources(include/boost/beast beast)
+    GroupSources(example/common common)
+    GroupSources(example/http/client/async-ssl-system-executor "/")
+
+    add_executable (http-client-async-ssl-system-executor
+        ${BOOST_BEAST_FILES}
+        ${PROJECT_SOURCE_DIR}/example/common/root_certificates.hpp
+        Jamfile
+        http_client_async_ssl_system_executor.cpp
+    )
+
+    set_property(TARGET http-client-async-ssl-system-executor PROPERTY FOLDER "example-http-client")
+
+    target_link_libraries (http-client-async-ssl-system-executor
+        OpenSSL::SSL OpenSSL::Crypto
+        lib-asio
+        lib-asio-ssl
+        lib-beast
+        )
+
+endif()

example/http/client/async-ssl-system-executor/Jamfile

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+#
+# 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
+#
+
+import ac ;
+
+project
+    : requirements
+        [ ac.check-library /boost/beast//lib-asio-ssl : <library>/boost/beast//lib-asio-ssl/<link>static : <build>no ]
+    ;
+
+exe http-client-async-ssl-system-executor :
+    http_client_async_ssl_system_executor.cpp
+    :
+    <variant>coverage:<build>no
+    <variant>ubasan:<build>no
+    ;

example/http/client/async-ssl-system-executor/http_client_async_ssl_system_executor.cpp

@@ -0,0 +1,245 @@
+//
+// Copyright (c) 2016-2019 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 SSL client, asynchronous, using system_executor
+//
+//------------------------------------------------------------------------------
+
+#include "example/common/root_certificates.hpp"
+
+#include <boost/beast/core.hpp>
+#include <boost/beast/http.hpp>
+#include <boost/beast/ssl.hpp>
+#include <boost/beast/version.hpp>
+#include <boost/asio/strand.hpp>
+#include <cstdlib>
+#include <functional>
+#include <iostream>
+#include <memory>
+#include <string>
+
+namespace beast = boost::beast;         // from <boost/beast.hpp>
+namespace http = beast::http;           // from <boost/beast/http.hpp>
+namespace net = boost::asio;            // from <boost/asio.hpp>
+namespace ssl = boost::asio::ssl;       // from <boost/asio/ssl.hpp>
+using tcp = boost::asio::ip::tcp;       // from <boost/asio/ip/tcp.hpp>
+
+//------------------------------------------------------------------------------
+
+// Report a failure
+void
+fail(beast::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_;
+    beast::ssl_stream<beast::tcp_stream> stream_;
+    beast::flat_buffer buffer_; // (Must persist between reads)
+    http::request<http::empty_body> req_;
+    http::response<http::string_body> res_;
+
+    // Objects are constructed with a strand to
+    // ensure that handlers do not execute concurrently.
+    session(net::strand<net::system_executor> strand, ssl::context& ctx)
+        : resolver_(strand)
+        , stream_(strand, ctx)
+    {
+    }
+
+public:
+    // Delegate construction to a prive constructor to be able to use
+    // the same strand for both I/O object.
+    explicit
+    session(ssl::context& ctx)
+        : session(net::make_strand(net::system_executor()), ctx)
+    {
+    }
+
+    // Start the asynchronous operation
+    void
+    run(
+        char const* host,
+        char const* port,
+        char const* target,
+        int version)
+    {
+        // Set SNI Hostname (many hosts need this to handshake successfully)
+        if(! SSL_set_tlsext_host_name(stream_.native_handle(), host))
+        {
+            beast::error_code ec{static_cast<int>(::ERR_get_error()), net::error::get_ssl_category()};
+            std::cerr << ec.message() << "\n";
+            return;
+        }
+
+        // Set up an HTTP GET request message
+        req_.version(version);
+        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,
+            beast::bind_front_handler(
+                &session::on_resolve,
+                shared_from_this()));
+    }
+
+    void
+    on_resolve(
+        beast::error_code ec,
+        tcp::resolver::results_type results)
+    {
+        if(ec)
+            return fail(ec, "resolve");
+
+        // Set a timeout on the operation
+        beast::get_lowest_layer(stream_).expires_after(std::chrono::seconds(30));
+
+        // Make the connection on the IP address we get from a lookup
+        beast::get_lowest_layer(stream_).async_connect(
+            results,
+            beast::bind_front_handler(
+                &session::on_connect,
+                shared_from_this()));
+    }
+
+    void
+    on_connect(beast::error_code ec, tcp::resolver::results_type::endpoint_type)
+    {
+        if(ec)
+            return fail(ec, "connect");
+
+        // Perform the SSL handshake
+        stream_.async_handshake(
+            ssl::stream_base::client,
+            beast::bind_front_handler(
+                &session::on_handshake,
+                shared_from_this()));
+    }
+
+    void
+    on_handshake(beast::error_code ec)
+    {
+        if(ec)
+            return fail(ec, "handshake");
+
+        // Set a timeout on the operation
+        beast::get_lowest_layer(stream_).expires_after(std::chrono::seconds(30));
+
+        // Send the HTTP request to the remote host
+        http::async_write(stream_, req_,
+            beast::bind_front_handler(
+                &session::on_write,
+                shared_from_this()));
+    }
+
+    void
+    on_write(
+        beast::error_code ec,
+        std::size_t bytes_transferred)
+    {
+        boost::ignore_unused(bytes_transferred);
+
+        if(ec)
+            return fail(ec, "write");
+
+        // Receive the HTTP response
+        http::async_read(stream_, buffer_, res_,
+            beast::bind_front_handler(
+                &session::on_read,
+                shared_from_this()));
+    }
+
+    void
+    on_read(
+        beast::error_code ec,
+        std::size_t bytes_transferred)
+    {
+        boost::ignore_unused(bytes_transferred);
+
+        if(ec)
+            return fail(ec, "read");
+
+        // Write the message to standard out
+        std::cout << res_ << std::endl;
+
+        // Set a timeout on the operation
+        beast::get_lowest_layer(stream_).expires_after(std::chrono::seconds(30));
+
+        // Gracefully close the stream
+        stream_.async_shutdown(
+            beast::bind_front_handler(
+                &session::on_shutdown,
+                shared_from_this()));
+    }
+
+    void
+    on_shutdown(beast::error_code ec)
+    {
+        if(ec == net::error::eof)
+        {
+            // Rationale:
+            // http://stackoverflow.com/questions/25587403/boost-asio-ssl-async-shutdown-always-finishes-with-an-error
+            ec = {};
+        }
+        if(ec)
+            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 && argc != 5)
+    {
+        std::cerr <<
+            "Usage: http-client-async-ssl-system-executor <host> <port> <target> [<HTTP version: 1.0 or 1.1(default)>]\n" <<
+            "Example:\n" <<
+            "    http-client-async-ssl-system-executor www.example.com 443 /\n" <<
+            "    http-client-async-ssl-system-executor www.example.com 443 / 1.0\n";
+        return EXIT_FAILURE;
+    }
+    auto const host = argv[1];
+    auto const port = argv[2];
+    auto const target = argv[3];
+    int version = argc == 5 && !std::strcmp("1.0", argv[4]) ? 10 : 11;
+
+    // The SSL context is required, and holds certificates
+    ssl::context ctx{ssl::context::tlsv12_client};
+
+    // This holds the root certificate used for verification
+    load_root_certificates(ctx);
+
+    // Verify the remote server's certificate
+    ctx.set_verify_mode(ssl::verify_peer);
+
+    // Launch the asynchronous operation
+    std::make_shared<session>(ctx)->run(host, port, target, version);
+
+
+    // The async operations will run on the system_executor.
+    // Because the main thread has nothing to do in this example, we just wait
+    // for the system_executor to run out of work.
+    net::system_executor().context().join();
+
+    return EXIT_SUCCESS;
+}