diff --git a/src/cli/ClientCLI/ClientCLI.c b/src/cli/ClientCLI/ClientCLI.c
index a2357c9..5f6bbcc 100644
--- a/src/cli/ClientCLI/ClientCLI.c
+++ b/src/cli/ClientCLI/ClientCLI.c
@@ -1,8 +1,8 @@
+#include "tlibc/filesystem.h"
+#include "tcp-chat/common_constants.h"
 #include "cli/ClientCLI/ClientCLI.h"
 #include "cli/term.h"
-#include "tcp-chat/common_constants.h"
-#include "tlibc/time.h"
-#include "tlibc/filesystem.h"
+#include "network/tcp-chat-protocol/v1.h"
 
 static const str greeting_art = STR(
     "   ^,,^                           ╱|\n"
@@ -108,11 +108,11 @@ static Result(void) ClientCLI_askUserNameAndPassword(str* username_out, str* pas
         try_void(term_readLine(username_buf.data, username_buf.size));
         username = str_from_cstr(username_buf.data);
         str_trim(&username, true);
-        if(username.size < USERNAME_SIZE_MIN || username.size > USERNAME_SIZE_MAX){
-            printf("ERROR: username length (in bytes) must be >= %i and <= %i\n", 
-                USERNAME_SIZE_MIN, USERNAME_SIZE_MAX);
+        str name_error_str = validateUsername_str(username);
+        if(name_error_str.data){
+            printf("ERROR: "FMT_str"\n", 
+                name_error_str.size, name_error_str.data);
         }
-        //TODO: validate username characters
         else break;
     }
 
diff --git a/src/cli/ClientCLI/ClientCLI.h b/src/cli/ClientCLI/ClientCLI.h
index 02b8f7d..e6b7570 100644
--- a/src/cli/ClientCLI/ClientCLI.h
+++ b/src/cli/ClientCLI/ClientCLI.h
@@ -4,7 +4,7 @@
 #include "tlibc/collections/List.h"
 #include "tcp-chat/client.h"
 #include "db/idb.h"
-#include "cli/ClientCLI/db_tables.h"
+#include "db/tables.h"
 
 typedef struct ClientCLI {
     Client* client;
diff --git a/src/cli/ClientCLI/db_tables.h b/src/cli/ClientCLI/db_tables.h
deleted file mode 100644
index 6f7ff61..0000000
--- a/src/cli/ClientCLI/db_tables.h
+++ /dev/null
@@ -1,14 +0,0 @@
-#pragma once
-#include "tcp-chat/common_constants.h"
-#include "tlibc/time.h"
-
-typedef struct ServerInfo {
-    u16 address_len;
-    char address[HOSTADDR_SIZE_MAX + 1];
-    u32 pk_base64_len;
-    char pk_base64[PUBLIC_KEY_BASE64_SIZE_MAX + 1];
-    u16 name_len;
-    char name[SERVER_NAME_SIZE_MAX + 1];
-    u16 desc_len;
-    char desc[SERVER_DESC_SIZE_MAX + 1];
-} ATTRIBUTE_ALIGNED(16*1024) ServerInfo;
diff --git a/src/db/tables.h b/src/db/tables.h
new file mode 100644
index 0000000..036f008
--- /dev/null
+++ b/src/db/tables.h
@@ -0,0 +1,44 @@
+#pragma once
+#include "tcp-chat/common_constants.h"
+#include "tlibc/time.h"
+
+
+typedef struct UserInfo {
+    u16 name_len;
+    char name[USERNAME_SIZE_MAX + 1];  // null-terminated
+    u8 token[PASSWORD_HASH_SIZE]; // token is hashed again on server side
+    DateTime registration_time_utc;
+} ATTRIBUTE_ALIGNED(256) UserInfo;
+
+
+typedef struct ServerInfo {
+    u16 address_len;
+    char address[HOSTADDR_SIZE_MAX + 1];
+    u32 pk_base64_len;
+    char pk_base64[PUBLIC_KEY_BASE64_SIZE_MAX + 1];
+    u16 name_len;
+    char name[SERVER_NAME_SIZE_MAX + 1];
+    u16 desc_len;
+    char desc[SERVER_DESC_SIZE_MAX + 1];
+} ATTRIBUTE_ALIGNED(16*1024) ServerInfo;
+
+
+typedef struct ChannelInfo {
+    u16 name_len;
+    char name[CHANNEL_NAME_SIZE_MAX + 1];
+    u16 desc_len;
+    char desc[CHANNEL_DESC_SIZE_MAX + 1];
+} ATTRIBUTE_ALIGNED(4*1024) ChannelInfo;
+
+
+typedef struct MessageMetadata {
+    DateTime receiving_time_utc;
+    u64 sender_id;
+    u16 data_size;
+} ATTRIBUTE_ALIGNED(64) MessageMetadata;
+
+
+typedef struct MessageBlock {
+    /* sequence of messages (MessageMetadata, byte[]) */
+    u8 data[16*1024];
+} MessageBlock;
diff --git a/src/network/tcp-chat-protocol/constant.h b/src/network/tcp-chat-protocol/constant.h
index f9ac1f6..8a58448 100644
--- a/src/network/tcp-chat-protocol/constant.h
+++ b/src/network/tcp-chat-protocol/constant.h
@@ -14,6 +14,7 @@ typedef struct PacketHeader {
     u8 _reserved1;
     u16 type;
     u32 _reserved4;
+    /* size of request/response struct */
     u64 content_size;
 } ATTRIBUTE_ALIGNED(64) PacketHeader;
 
diff --git a/src/network/tcp-chat-protocol/v1.c b/src/network/tcp-chat-protocol/v1.c
index ef7a2a2..663eccd 100644
--- a/src/network/tcp-chat-protocol/v1.c
+++ b/src/network/tcp-chat-protocol/v1.c
@@ -3,7 +3,7 @@
 str validateUsername_cstr(char username[USERNAME_SIZE_MAX+1], str* out_username_str){
     // must end with 0
     if(username[USERNAME_SIZE_MAX] != '\0'){
-        return STR("Username string doesn't end correctly");
+        return str_copy(STR("Username string doesn't end correctly"));
     }
 
     str u = str_from_cstr(username);
@@ -16,8 +16,13 @@ str validateUsername_cstr(char username[USERNAME_SIZE_MAX+1], str* out_username_
 }
 
 str validateUsername_str(str username){
-    if(username.size < USERNAME_SIZE_MIN){
-        return STR("Username length is too small");
+    if(username.size < USERNAME_SIZE_MIN || username.size > USERNAME_SIZE_MAX){
+        return str_from_cstr(
+            sprintf_malloc(
+                "username length (in bytes) must be >= %i and <= %i\n", 
+                USERNAME_SIZE_MIN, USERNAME_SIZE_MAX
+            )
+        );
     }
 
     for(u32 i = 0; i < username.size; i++){
@@ -28,8 +33,8 @@ str validateUsername_str(str username){
             c == '.' || c == '_' || c == '-')
             continue;
         
-        return STR("Username contains restricted characters. "
-            "Allowed characters: latin, digits, ._-");
+        return str_copy(STR("Username contains restricted characters. "
+            "Allowed characters: latin, digits, ._-"));
     }
 
     return str_null;
@@ -88,9 +93,9 @@ Result(void) LoginRequest_tryConstruct(LoginRequest *ptr, PacketHeader* header,
     _PacketHeader_construct(LoginRequest);
     memset(ptr, 0, sizeof(*ptr));
 
-    str username_check_error = validateUsername_str(username);
-    if(username_check_error.data){
-        Return RESULT_ERROR(username_check_error.data, false);
+    str name_error_str = validateUsername_str(username);
+    if(name_error_str.data){
+        Return RESULT_ERROR(name_error_str.data, true);
     }
     memcpy(ptr->username, username.data, username.size);
 
@@ -117,9 +122,9 @@ Result(void) RegisterRequest_tryConstruct(RegisterRequest *ptr, PacketHeader* he
     _PacketHeader_construct(RegisterRequest);
     memset(ptr, 0, sizeof(*ptr));
 
-    str username_check_error = validateUsername_str(username);
-    if(username_check_error.data){
-        Return RESULT_ERROR(username_check_error.data, false);
+    str name_error_str = validateUsername_str(username);
+    if(name_error_str.data){
+        Return RESULT_ERROR(name_error_str.data, true);
     }
     memcpy(ptr->username, username.data, username.size);
 
diff --git a/src/network/tcp-chat-protocol/v1.h b/src/network/tcp-chat-protocol/v1.h
index 19d9618..a403efe 100644
--- a/src/network/tcp-chat-protocol/v1.h
+++ b/src/network/tcp-chat-protocol/v1.h
@@ -1,6 +1,7 @@
 #pragma once
 #include "tlibc/errors.h"
 #include "tlibc/string/str.h"
+#include "tlibc/time.h"
 #include "network/tcp-chat-protocol/constant.h"
 
 #define PROTOCOL_VERSION 1 /* 1.0.0 */
@@ -15,7 +16,7 @@ Valid username:
 - allowed characters: latin, digits, ._-
 */
 /// validates username char[] and constructs str from it
-/// @return str_null on success, stack-allocated error message on fail
+/// @return str_null on success, heap-allocated error message on fail
 str validateUsername_cstr(char username[USERNAME_SIZE_MAX+1], str* out_username_str) ATTRIBUTE_WARN_UNUSED_RESULT;
 
 str validateUsername_str(str username) ATTRIBUTE_WARN_UNUSED_RESULT;
@@ -119,3 +120,38 @@ void RegisterResponse_construct(RegisterResponse* ptr, PacketHeader* header,
     u64 user_id);
 
 
+typedef struct SendMessageRequest {
+    u64 channel_id;
+    u16 data_size;
+    /* stream of size data_size */
+} ALIGN_PACKET_STRUCT SendMessageRequest;
+
+void SendMessageRequest_construct(SendMessageRequest* ptr, PacketHeader* header,
+    u64 channel_id, u16 data_size);
+
+
+typedef struct SendMessageResponse {
+    u64 message_id;
+    DateTime receiving_time_utc;
+} ALIGN_PACKET_STRUCT SendMessageResponse;
+
+void SendMessageResponse_construct(SendMessageResponse* ptr, PacketHeader* header,
+    u64 message_id, DateTime receiving_time_utc);
+
+
+typedef struct GetMessageBlockRequest {
+    u64 message_block_id;
+} ALIGN_PACKET_STRUCT GetMessageBlockRequest;
+
+void GetMessageBlockRequest_construct(GetMessageBlockRequest* ptr, PacketHeader* header,
+    u64 message_block_id);
+
+
+typedef struct GetMessageBlockResponse {
+    u32 data_size;
+    /* stream of size data_size */
+} ALIGN_PACKET_STRUCT GetMessageBlockResponse;
+
+void GetMessageBlockResponse_construct(GetMessageBlockResponse* ptr, PacketHeader* header,
+    u32 data_size);
+
diff --git a/src/server/db_tables.h b/src/server/db_tables.h
deleted file mode 100644
index a3ec148..0000000
--- a/src/server/db_tables.h
+++ /dev/null
@@ -1,17 +0,0 @@
-#pragma once
-#include "tcp-chat/common_constants.h"
-#include "tlibc/time.h"
-
-typedef struct UserInfo {
-    u16 name_len;
-    char name[USERNAME_SIZE_MAX + 1];  // null-terminated
-    u8 token[PASSWORD_HASH_SIZE]; // token is hashed again on server side
-    DateTime registration_time;
-} ATTRIBUTE_ALIGNED(256) UserInfo;
-
-typedef struct ChannelInfo {
-    u16 name_len;
-    char name[CHANNEL_NAME_SIZE_MAX + 1];
-    u16 desc_len;
-    char desc[CHANNEL_DESC_SIZE_MAX + 1];
-} ATTRIBUTE_ALIGNED(4*1024) ChannelInfo;
diff --git a/src/server/responses/GetMessageBlock.c b/src/server/responses/GetMessageBlock.c
new file mode 100644
index 0000000..1c9f5de
--- /dev/null
+++ b/src/server/responses/GetMessageBlock.c
@@ -0,0 +1,23 @@
+#include "responses.h"
+
+#define LOGGER conn->server->logger
+#define LOG_FUNC conn->server->log_func
+
+declare_RequestHandler(GetMessageBlock)
+{
+    Deferral(4);
+    logInfo(log_ctx, "requested %s", req_type_name);
+    
+    // receive request
+    GetMessageBlockRequest req;
+    try_void(PacketHeader_validateContentSize(req_head, sizeof(req)));
+    try_void(EncryptedSocketTCP_recvStruct(&conn->sock, &req));
+
+    // send response
+    GetMessageBlockResponse res;
+    GetMessageBlockResponse_construct(&res, res_head, );
+    try_void(EncryptedSocketTCP_sendStruct(&conn->sock, res_head));
+    try_void(EncryptedSocketTCP_sendStruct(&conn->sock, &res));
+
+    Return RESULT_VOID;
+}
diff --git a/src/server/request_handlers/Login.c b/src/server/responses/Login.c
similarity index 92%
rename from src/server/request_handlers/Login.c
rename to src/server/responses/Login.c
index 1a5be35..869f00c 100644
--- a/src/server/request_handlers/Login.c
+++ b/src/server/responses/Login.c
@@ -1,4 +1,4 @@
-#include "request_handlers.h"
+#include "responses.h"
 
 #define LOGGER conn->server->logger
 #define LOG_FUNC conn->server->log_func
@@ -23,11 +23,12 @@ declare_RequestHandler(Login)
 
     // validate username
     str username_str = str_null;
-    str username_check_error = validateUsername_cstr(req.username, &username_str);
-    if(username_check_error.data){
+    str name_error_str = validateUsername_cstr(req.username, &username_str);
+    if(name_error_str.data){
+        Defer(str_free(name_error_str));
         try_void(sendErrorMessage(log_ctx, conn, res_head,
             LogSeverity_Warn,
-            username_check_error
+            name_error_str
         ));
         Return RESULT_VOID;
     }
diff --git a/src/server/request_handlers/Register.c b/src/server/responses/Register.c
similarity index 90%
rename from src/server/request_handlers/Register.c
rename to src/server/responses/Register.c
index e60e1a4..c8a432e 100644
--- a/src/server/request_handlers/Register.c
+++ b/src/server/responses/Register.c
@@ -1,4 +1,4 @@
-#include "request_handlers.h"
+#include "responses.h"
 
 #define LOGGER conn->server->logger
 #define LOG_FUNC conn->server->log_func
@@ -23,11 +23,12 @@ declare_RequestHandler(Register)
 
     // validate username
     str username_str = str_null;
-    str username_check_error = validateUsername_cstr(req.username, &username_str);
-    if(username_check_error.data){
+    str name_error_str = validateUsername_cstr(req.username, &username_str);
+    if(name_error_str.data){
+        Defer(str_free(name_error_str));
         try_void(sendErrorMessage(log_ctx, conn, res_head, 
             LogSeverity_Warn,
-            username_check_error
+            name_error_str
         ));
         Return RESULT_VOID;
     }
@@ -59,7 +60,7 @@ declare_RequestHandler(Register)
 
     memcpy(user.token, req.token, sizeof(req.token));
     
-    DateTime_getUTC(&user.registration_time);
+    DateTime_getUTC(&user.registration_time_utc);
     
     // save new user to db and cache
     try(u64 user_id, u, idb_pushRow(conn->server->db_users_table, &user));
diff --git a/src/server/responses/SendMessage.c b/src/server/responses/SendMessage.c
new file mode 100644
index 0000000..796567c
--- /dev/null
+++ b/src/server/responses/SendMessage.c
@@ -0,0 +1,23 @@
+#include "responses.h"
+
+#define LOGGER conn->server->logger
+#define LOG_FUNC conn->server->log_func
+
+declare_RequestHandler(SendMessage)
+{
+    Deferral(4);
+    logInfo(log_ctx, "requested %s", req_type_name);
+    
+    // receive request
+    SendMessageRequest req;
+    try_void(PacketHeader_validateContentSize(req_head, sizeof(req)));
+    try_void(EncryptedSocketTCP_recvStruct(&conn->sock, &req));
+
+    // send response
+    SendMessageResponse res;
+    SendMessageResponse_construct(&res, res_head, );
+    try_void(EncryptedSocketTCP_sendStruct(&conn->sock, res_head));
+    try_void(EncryptedSocketTCP_sendStruct(&conn->sock, &res));
+
+    Return RESULT_VOID;
+}
diff --git a/src/server/request_handlers/ServerPublicInfo.c b/src/server/responses/ServerPublicInfo.c
similarity index 97%
rename from src/server/request_handlers/ServerPublicInfo.c
rename to src/server/responses/ServerPublicInfo.c
index b8dc0d8..86a88ed 100644
--- a/src/server/request_handlers/ServerPublicInfo.c
+++ b/src/server/responses/ServerPublicInfo.c
@@ -1,4 +1,4 @@
-#include "request_handlers.h"
+#include "responses.h"
 
 #define LOGGER conn->server->logger
 #define LOG_FUNC conn->server->log_func
diff --git a/src/server/request_handlers/request_handlers.h b/src/server/responses/responses.h
similarity index 100%
rename from src/server/request_handlers/request_handlers.h
rename to src/server/responses/responses.h
diff --git a/src/server/request_handlers/send_error.c b/src/server/responses/send_error.c
similarity index 98%
rename from src/server/request_handlers/send_error.c
rename to src/server/responses/send_error.c
index e19a838..1532bd4 100644
--- a/src/server/request_handlers/send_error.c
+++ b/src/server/responses/send_error.c
@@ -1,4 +1,4 @@
-#include "request_handlers.h"
+#include "responses.h"
 
 #define LOGGER conn->server->logger
 #define LOG_FUNC conn->server->log_func
diff --git a/src/server/request_handlers/template b/src/server/responses/template
similarity index 95%
rename from src/server/request_handlers/template
rename to src/server/responses/template
index 5ff1a88..48fc380 100644
--- a/src/server/request_handlers/template
+++ b/src/server/responses/template
@@ -1,4 +1,4 @@
-#include "request_handlers.h"
+#include "responses.h"
 
 #define LOGGER conn->server->logger
 #define LOG_FUNC conn->server->log_func
diff --git a/src/server/server.c b/src/server/server.c
index a9eb513..d58d54c 100644
--- a/src/server/server.c
+++ b/src/server/server.c
@@ -5,7 +5,7 @@
 #include "server/server_internal.h"
 #include "config.h"
 #include "network/tcp-chat-protocol/v1.h"
-#include "server/request_handlers/request_handlers.h"
+#include "server/responses/responses.h"
 
 static void* handleConnection(void* _args);
 static Result(void) try_handleConnection(ConnectionHandlerArgs* args, cstr log_ctx);
diff --git a/src/server/server_internal.h b/src/server/server_internal.h
index 0c033f0..2593b31 100644
--- a/src/server/server_internal.h
+++ b/src/server/server_internal.h
@@ -7,7 +7,7 @@
 #include "cryptography/RSA.h"
 #include "network/encrypted_sockets.h"
 #include "db/idb.h"
-#include "server/db_tables.h"
+#include "db/tables.h"
 
 typedef struct ClientConnection ClientConnection;