...

include/snipplib/network/snplib_netmsg.h

@@ -35,6 +35,7 @@ protected:
 
 public:
     using typename base_t::config_t;
+    using result_t = std::expected<keyval_netmsg_t, typename base_t::error_t>;
 
     keyval_netmsg_t(base_t::config_t config = {.keyval_delim = SNPLIB_DEFAULT_NETMSG_KEYVALUE_DELIM,
                                                .valseq_delim = SNPLIB_DEFAULT_NETMSG_VALUEVALUE_DELIM})
@@ -52,7 +53,7 @@ public:
     ~keyval_netmsg_t() = default;
 
     template <char_range_c R>
-    static keyval_netmsg_t fromBytes(R&& r,
+    static result_t fromBytes(R&& r,
                               base_t::config_t config = {.keyval_delim = SNPLIB_DEFAULT_NETMSG_KEYVALUE_DELIM,
                                                          .valseq_delim = SNPLIB_DEFAULT_NETMSG_VALUEVALUE_DELIM})
     {
@@ -61,16 +62,14 @@ public:
         // deep copy
         if constexpr (std::same_as<CharRangeT, std::remove_cvref_t<R>>) {
             std::ranges::copy(std::forward<R>(r), std::back_inserter(msg._ownByteSeq));
-            msg.fromCharRange(msg._ownByteSeq, std::move(config));
+            return msg.fromCharRange(msg._ownByteSeq, std::move(config));
         } else {
-            msg.fromCharRange(std::forward<R>(r), std::move(config));
+            return msg.fromCharRange(std::forward<R>(r), std::move(config));
         }
-
-        return msg;
     }
 
     // to satisfy net_message_c-concept
-    static keyval_netmsg_t fromBytes(std::span<const char> r,
+    static result_t fromBytes(std::span<const char> r,
                               base_t::config_t config = {.keyval_delim = SNPLIB_DEFAULT_NETMSG_KEYVALUE_DELIM,
                                                          .valseq_delim = SNPLIB_DEFAULT_NETMSG_VALUEVALUE_DELIM})
     {

include/snipplib/network/snplib_netproto.h

@@ -2,6 +2,7 @@
 
 #include "../concepts/snplib_concepts.h"
 #include "../utils/snplib_string.h"
+#include "snipplib/network/snplib_network.h"
 
 /*
 
@@ -119,23 +120,36 @@ struct netproto_stopseq_t {
         }
     }
 
+    // deduces a view-type from the input range-type
     template <typename IR>
     auto fromBytes(IR&& bytes)
         requires input_char_range_c<std::remove_cvref_t<IR>>
     {
-        using or_t = std::conditional_t<std::ranges::contiguous_range<IR>, std::span<const char>,
+        using or_t =
-                                        std::ranges::subrange<std::ranges::iterator_t<IR>>>;
+            std::conditional_t<std::ranges::contiguous_range<IR>, std::span<const char>,
+                               std::ranges::subrange<std::ranges::iterator_t<IR>, std::ranges::sentinel_t<IR>>>;
 
         return fromBytes<or_t>(std::forward<IR>(bytes));
     }
+
+    // to satisfy 'net_proto_c' concept
+    template <typename CharT = char>
+        requires(std::same_as<CharT, char> || std::same_as<CharT, const char>)
+    std::expected<std::span<CharT>, std::error_code> fromBytes(std::span<CharT> bytes)
+    {
+        return fromBytes<std::span<CharT>>(bytes);
+    }
 };
 
 
+static_assert(net_proto_c<netproto_stopseq_t<>>, "!!!");
+
+
 /*                          BINARY BLOB PROTOCOL                            */
 
 /*
  *       a sequence of bytes in format:
- *          <blob size field><bynary blob bytes>
+ *          <blob size field><binary blob bytes>
  *
         blob size field: a symbolic representation of a HEXIMAL UNSIGNED INTEGER (e.g. "000000FA", MUST BE IN
  UPPER-CASE!!!)

include/snipplib/network/snplib_network.h

@@ -29,15 +29,23 @@ concept net_proto_c = requires(T t) {
     // from session-level representation to transport-level one
     { t.toBytes(std::declval<CharRangeT>()) } -> char_range_or_range_of_char_ranges_c;
 
+    // from transport-level representation to session-level one
     requires(
         requires {
-            { t.fromBytes(std::declval<std::span<const char>>()) } -> char_range_c;
+            // { t.fromBytes(std::declval<std::span<const char>>()) } -> char_range_c;
+            { t.fromBytes(std::declval<std::span<const char>>()) } -> ret_expected_c;
+            requires char_range_c<std::remove_cvref_t<
+                decltype(std::declval<T>().fromBytes(std::declval<std::span<const char>>()).value())>>;
         } ||
         requires {
-            { t.fromBytes(std::declval<std::span<char>>()) } -> char_range_c;
+            // { t.fromBytes(std::declval<std::span<char>>()) } -> char_range_c;
+            { t.fromBytes(std::declval<std::span<char>>()) } -> ret_expected_c;
+            requires char_range_c<
+                std::remove_cvref_t<decltype(std::declval<T>().fromBytes(std::declval<std::span<char>>()).value())>>;
         });
 };
 
+
 template <typename T>
 concept net_message_c = requires(const T t_const) {
     // { t.toBytes() } -> char_range_or_range_of_char_ranges_c;
@@ -46,10 +54,12 @@ concept net_message_c = requires(const T t_const) {
     // can be constructed from contiguous byte range
     requires(
         requires {
-            { T::fromBytes(std::declval<std::span<const char>>()) } -> std::same_as<T>;
+            // { T::fromBytes(std::declval<std::span<const char>>()) } -> std::same_as<T>;
+            { T::fromBytes(std::declval<std::span<const char>>()) } -> ret_expected_type_c<T>;
         } ||
         requires {
-            { T::fromBytes(std::declval<std::span<char>>()) } -> std::same_as<T>;
+            // { T::fromBytes(std::declval<std::span<char>>()) } -> std::same_as<T>;
+            { T::fromBytes(std::declval<std::span<char>>()) } -> ret_expected_type_c<T>;
         });
 };
 
@@ -101,9 +111,9 @@ concept net_listener_c = requires(T t, const T t_const) {
 
     { t.accept() } -> async_retval_c<typename T::connection_t>;
 
-    { t.startListen() } -> ret_error_c;
+    { t.startListening() } -> ret_error_c;
 
-    t.stopListen();
+    t.stopListening();
 
     { t_const.endpoint() } -> net_endpoint_c;
 };
@@ -116,7 +126,7 @@ concept net_initiator_role_c = requires {
     []() {
         [[maybe_unused]] static constexpr std::array arr{// server role (listener of connections)
                                                          T::ROLE_SERVER,
-                                                         // cleant role (opener of connections)
+                                                         // client role (opener of connections)
                                                          T::ROLE_CLIENT};
     }();
 };
@@ -128,8 +138,10 @@ enum class net_initiator_role_e : int { ROLE_SERVER, ROLE_CLIENT };
 template <typename T>
 concept net_initiator_c =
     requires(T t, const T t_const) {
-        // common part
+        // common part:
+        //    must contain a static compile-time constant 'ROLE' of type satisfied to 'net_initiator_role_c' concept
         requires net_initiator_role_c<decltype(T::ROLE)>;
+        //    to be sure 'ROLE' is compile-time constant
         []() { [[maybe_unused]] static constexpr auto val = T::ROLE; }();
 
         net_connection_c<typename T::connection_t>;
@@ -139,9 +151,9 @@ concept net_initiator_c =
         // server-role
         { t.accept() } -> async_retval_c<typename T::connection_t>;
 
-        { t.startListen() } -> ret_error_c;
+        { t.startListening() } -> ret_error_c;
 
-        t.stopListen();
+        t.stopListening();
     }) && ((T::ROLE != decltype(T::ROLE)::ROLE_CLIENT) || requires(T t) {  // use of short-circuiting logic!!!
         // client-role
         { t.open() } -> async_retval_c<typename T::connection_t>;