Add read, async_read for message_headers:

fix #172, fix #173

This provides overloads of read and async_read to allow
reading message_headers objects.

include/beast/http/impl/read.ipp

@@ -9,6 +9,7 @@
 #define BEAST_HTTP_IMPL_READ_IPP_HPP
 
 #include <beast/http/concepts.hpp>
+#include <beast/http/headers_parser_v1.hpp>
 #include <beast/http/parse.hpp>
 #include <beast/http/parser_v1.hpp>
 #include <beast/core/bind_handler.hpp>
@@ -21,6 +22,185 @@ namespace http {
 
 namespace detail {
 
+template<class Stream, class DynamicBuffer,
+    bool isRequest, class Headers,
+        class Handler>
+class read_headers_op
+{
+    using alloc_type =
+        handler_alloc<char, Handler>;
+
+    using parser_type =
+        headers_parser_v1<isRequest, Headers>;
+
+    using message_type =
+        message_headers<isRequest, Headers>;
+
+    struct data
+    {
+        Stream& s;
+        DynamicBuffer& db;
+        message_type& m;
+        parser_type p;
+        Handler h;
+        bool started = false;
+        bool cont;
+        int state = 0;
+
+        template<class DeducedHandler>
+        data(DeducedHandler&& h_, Stream& s_,
+                DynamicBuffer& sb_, message_type& m_)
+            : s(s_)
+            , db(sb_)
+            , m(m_)
+            , h(std::forward<DeducedHandler>(h_))
+            , cont(boost_asio_handler_cont_helpers::
+                is_continuation(h))
+        {
+        }
+    };
+
+    std::shared_ptr<data> d_;
+
+public:
+    read_headers_op(read_headers_op&&) = default;
+    read_headers_op(read_headers_op const&) = default;
+
+    template<class DeducedHandler, class... Args>
+    read_headers_op(
+            DeducedHandler&& h, Stream& s, Args&&... args)
+        : d_(std::allocate_shared<data>(alloc_type{h},
+            std::forward<DeducedHandler>(h), s,
+                std::forward<Args>(args)...))
+    {
+        (*this)(error_code{}, false);
+    }
+
+    void
+    operator()(error_code ec, bool again = true);
+
+    friend
+    void* asio_handler_allocate(
+        std::size_t size, read_headers_op* op)
+    {
+        return boost_asio_handler_alloc_helpers::
+            allocate(size, op->d_->h);
+    }
+
+    friend
+    void asio_handler_deallocate(
+        void* p, std::size_t size, read_headers_op* op)
+    {
+        return boost_asio_handler_alloc_helpers::
+            deallocate(p, size, op->d_->h);
+    }
+
+    friend
+    bool asio_handler_is_continuation(read_headers_op* op)
+    {
+        return op->d_->cont;
+    }
+
+    template<class Function>
+    friend
+    void asio_handler_invoke(Function&& f, read_headers_op* op)
+    {
+        return boost_asio_handler_invoke_helpers::
+            invoke(f, op->d_->h);
+    }
+};
+
+template<class Stream, class DynamicBuffer,
+    bool isRequest, class Headers,
+        class Handler>
+void
+read_headers_op<Stream, DynamicBuffer, isRequest, Headers, Handler>::
+operator()(error_code ec, bool again)
+{
+    auto& d = *d_;
+    d.cont = d.cont || again;
+    while(! ec && d.state != 99)
+    {
+        switch(d.state)
+        {
+        case 0:
+            d.state = 1;
+            async_parse(d.s, d.db, d.p, std::move(*this));
+            return;
+
+        case 1:
+            // call handler
+            d.state = 99;
+            d.m = d.p.release();
+            break;
+        }
+    }
+    d.h(ec);
+}
+
+} // detail
+
+template<class SyncReadStream, class DynamicBuffer,
+    bool isRequest, class Headers>
+void
+read(SyncReadStream& stream, DynamicBuffer& dynabuf,
+    message_headers<isRequest, Headers>& msg)
+{
+    static_assert(is_SyncReadStream<SyncReadStream>::value,
+        "SyncReadStream requirements not met");
+    static_assert(is_DynamicBuffer<DynamicBuffer>::value,
+        "DynamicBuffer requirements not met");
+    error_code ec;
+    beast::http::read(stream, dynabuf, msg, ec);
+    if(ec)
+        throw system_error{ec};
+}
+
+template<class SyncReadStream, class DynamicBuffer,
+    bool isRequest, class Headers>
+void
+read(SyncReadStream& stream, DynamicBuffer& dynabuf,
+    message_headers<isRequest, Headers>& m,
+        error_code& ec)
+{
+    static_assert(is_SyncReadStream<SyncReadStream>::value,
+        "SyncReadStream requirements not met");
+    static_assert(is_DynamicBuffer<DynamicBuffer>::value,
+        "DynamicBuffer requirements not met");
+    headers_parser_v1<isRequest, Headers> p;
+    beast::http::parse(stream, dynabuf, p, ec);
+    if(ec)
+        return;
+    BOOST_ASSERT(p.complete());
+    m = p.release();
+}
+
+template<class AsyncReadStream, class DynamicBuffer,
+    bool isRequest, class Headers,
+        class ReadHandler>
+typename async_completion<
+    ReadHandler, void(error_code)>::result_type
+async_read(AsyncReadStream& stream, DynamicBuffer& dynabuf,
+    message_headers<isRequest, Headers>& m,
+        ReadHandler&& handler)
+{
+    static_assert(is_AsyncReadStream<AsyncReadStream>::value,
+        "AsyncReadStream requirements not met");
+    static_assert(is_DynamicBuffer<DynamicBuffer>::value,
+        "DynamicBuffer requirements not met");
+    beast::async_completion<ReadHandler,
+        void(error_code)> completion(handler);
+    detail::read_headers_op<AsyncReadStream, DynamicBuffer,
+        isRequest, Headers, decltype(
+            completion.handler)>{completion.handler,
+                stream, dynabuf, m};
+    return completion.result.get();
+}
+
+//------------------------------------------------------------------------------
+
+namespace detail {
+
 template<class Stream, class DynamicBuffer,
     bool isRequest, class Body, class Headers,
         class Handler>
@@ -138,8 +318,6 @@ operator()(error_code ec, bool again)
 
 } // detail
 
-//------------------------------------------------------------------------------
-
 template<class SyncReadStream, class DynamicBuffer,
     bool isRequest, class Body, class Headers>
 void