diff --git a/core-test/app/communication-client.c b/core-test/app/communication-client.c
index 1bb10fe..dde96c9 100644
--- a/core-test/app/communication-client.c
+++ b/core-test/app/communication-client.c
@@ -35,6 +35,7 @@ int main (int argc, char *argv[], char *env[])
         return EXIT_FAILURE;
     }
 
+    printf ("msg to send: %s\n", MSG);
     if (app_write (&srv, MSG, strlen(MSG)) < 0) {
         handle_err("main", "app_write < 0");
         return EXIT_FAILURE;
diff --git a/core/communication.c b/core/communication.c
index d66cb16..95ff7b5 100644
--- a/core/communication.c
+++ b/core/communication.c
@@ -1,6 +1,7 @@
 #include "communication.h"
 #include "usocket.h"
 #include "msg-format.h"
+#include "utils.h"
 
 #include <assert.h>
 #include <stdio.h>
@@ -46,11 +47,15 @@ int srv_init (int argc, char **argv, char **env
 int srv_accept (struct service *srv, struct process *p)
 {
     usock_accept (srv->service_fd, &p->proc_fd);
+    char *buf;
+    size_t msgsize = BUFSIZ;
 
-    char buf[3];
-    msg_format_ack (buf);
+    srv_read (p, &buf, &msgsize);
 
-    srv_write (p, buf, 3);
+    msgsize = 0;
+    msg_format_ack (buf, NULL, &msgsize);
+
+    srv_write (p, buf, msgsize);
 
     return 0;
 }
@@ -106,12 +111,12 @@ int app_connection (int argc, char **argv, char **env
     app_write (srv, send_buffer, msize);
 
     char *buffer;
-    size_t read_msg_size;
+    size_t read_msg_size = BUFSIZ;
 
     app_read (srv, &buffer, &read_msg_size);
 
-    assert (read_msg_size == 3);
     assert (buffer[0] == MSG_TYPE_ACK);
+    assert (read_msg_size == 3);
 
     return 0;
 }
diff --git a/core/msg-format.c b/core/msg-format.c
index 26eae8d..2e55ba6 100644
--- a/core/msg-format.c
+++ b/core/msg-format.c
@@ -22,17 +22,18 @@ int msg_format_con (char *buf, const char *constr, size_t *msgsize)
     short final_size = (short) *msgsize;
     memcpy (buf + 1, &final_size, 2);
     memcpy (buf + 3, constr, *msgsize);
-
+    *msgsize += 3;
     return 0;
 }
 
 // [type]   [len]
 // 4        0
-int msg_format_ack (char *buf)
+int msg_format_ack (char *buf, const char *constr, size_t *msgsize)
 {
     assert (buf != NULL);
     memset(buf, 0, 3);
     buf[0] = MSG_TYPE_ACK;
 
+    *msgsize += 3;
     return 0;
 }
diff --git a/core/msg-format.h b/core/msg-format.h
index a815db5..26424bf 100644
--- a/core/msg-format.h
+++ b/core/msg-format.h
@@ -8,6 +8,6 @@
 #define MSG_TYPE_ACK 4
 
 int msg_format_con (char *buf, const char *constr, size_t *msgsize);
-int msg_format_ack (char *buf);
+int msg_format_ack (char *buf, const char *constr, size_t *msgsize);
 
 #endif
diff --git a/core/usocket.c b/core/usocket.c
index 4c42e35..b28dca2 100644
--- a/core/usocket.c
+++ b/core/usocket.c
@@ -1,4 +1,5 @@
 #include "usocket.h"
+#include "utils.h"
 #include <stdio.h>
 #include <stdlib.h>
 #include <errno.h>
@@ -10,13 +11,15 @@
 
 int usock_send (const int fd, const char *buf, const int msize)
 {
+    print_hexa ("msg send", (unsigned char *)buf, msize);
+    printf ("msg to send: (%d) \n", msize);
+    fflush(stdout);
+
     int ret = 0;
     //printf ("%ld bytes to write\n", msize);
     ret = send (fd, buf, msize, 0);
-    if (ret <= 0) {
-        fprintf (stderr, "usock_send: file %s line %d send ret <= 0\n"
-                , __FILE__, __LINE__);
-    }
+    if (ret <= 0)
+        handle_err ("usock_send", "send ret <= 0");
     return ret;
 }
 
@@ -37,6 +40,8 @@ int usock_recv (const int fd, char **buf, size_t *msize)
 
     if (*buf == NULL) {
         // do not allocate too much memory
+        if (*msize > BUFSIZ)
+            handle_err ("usock_recv", "msize > BUFSIZ");
         *buf = malloc ((*msize < BUFSIZ) ? *msize : BUFSIZ);
     }
 
@@ -48,6 +53,7 @@ int usock_recv (const int fd, char **buf, size_t *msize)
         return ret;
     }
     *msize = (size_t) ret;
+    print_hexa ("msg recv", (unsigned char *)*buf, *msize);
     return ret;
 }
 
diff --git a/core/utils.c b/core/utils.c
new file mode 100644
index 0000000..2c0bcb0
--- /dev/null
+++ b/core/utils.c
@@ -0,0 +1,22 @@
+#include "utils.h"
+
+void print_hexa (const char *prefix, unsigned char *val, size_t size)
+{
+    if (! val)
+        return ;
+
+    size_t i;
+    for(i = 0; i < size; i++)
+    {
+        if(! (i % 4))
+            printf("\n%s (%ld) ", prefix, size);
+        printf("%2x ", val[i]);
+    }
+    printf("\n");
+}
+
+
+void mprint_hexa (char *prefix, unsigned char *buf, size_t length)
+{
+    print_hexa (prefix, buf, length);
+}
diff --git a/core/utils.h b/core/utils.h
new file mode 100644
index 0000000..a55cccd
--- /dev/null
+++ b/core/utils.h
@@ -0,0 +1,11 @@
+#ifndef __UTIL_H__
+#define __UTIL_H__
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+void print_hexa (const char *prefix, unsigned char *val, size_t size);
+void mprint_hexa (char *prefix, unsigned char *buf, size_t length);
+
+#endif