diff --git a/src/algo_naive.c b/src/algo_naive.c
index b391634..40d220c 100644
--- a/src/algo_naive.c
+++ b/src/algo_naive.c
@@ -300,7 +300,7 @@ int on_err(struct evt_core_ctx* ctx, struct evt_core_fdinfo* fdinfo) {
   // 3. If appears in the read waiting queue, remove it
   g_queue_remove_all (app_ctx->read_waiting, &(fdinfo->fd));
 
-  return 1;
+  return 0;
 }
 
 void algo_naive(struct algo_skel* as) {
diff --git a/src/donar_client.c b/src/donar_client.c
index 7145ffd..6ac5d8f 100644
--- a/src/donar_client.c
+++ b/src/donar_client.c
@@ -18,6 +18,7 @@ void init_tcp_client(struct donar_client_ctx* ctx, int i) {
 
   while (1) {
     fdinfo.fd = create_tcp_client("127.0.0.1", "9050");
+    perror("1");
     if (fdinfo.fd < 0) goto failed_socks5;
     ctx->client_sock[i].fd = fdinfo.fd;
     ctx->client_sock[i].state = SOCKS5_STATE_NEW;
@@ -25,6 +26,7 @@ void init_tcp_client(struct donar_client_ctx* ctx, int i) {
     evt_core_add_fd (&(ctx->evts), &fdinfo);
     //@FIXME: We suppose that we will be able to do the whole write at once which is wrong
     err = socks5_handshake_syn(fdinfo.fd);
+    perror("2");
     if (err) goto failed_socks5;
 
     break;
@@ -57,16 +59,21 @@ int configure_tcp_clients(struct evt_core_ctx* ctx, struct evt_core_fdinfo* fdin
     case SOCKS5_STATE_NEW:
       //@FIXME: We suppose that we will be able to do the whole read at once which is wrong
       err = socks5_handshake_ack (fdinfo->fd);
+      perror("3");
       if (err < 0) goto on_socks5_err;
       //@FIXME: We suppose that we will be able to do the whole write at once which is wrong too
       err = socks5_connect_dns(fdinfo->fd, target_host, app_ctx->ports[pos]);
+      perror("4");
       if (err < 0) goto on_socks5_err;
       app_ctx->client_sock[pos].state = SOCKS5_STATE_ACK;
       printf("Socket %d/%d %s:%d is connecting...\n", pos+1, CLIENT_PORT_SIZE, target_host, app_ctx->ports[pos]);
       break;
     case SOCKS5_STATE_ACK:
       //@FIXME: We suppose that we will be able to do the whole read at once which is wrong too
+      perror("5");
       err = socks5_reply (fdinfo->fd);
+      fprintf(stderr, "captured err: %d\n", err);
+      perror("6");
       if (err < 0) goto on_socks5_err;
       app_ctx->client_sock[pos].state = SOCKS5_STATE_RDY;
       int sock1, sock2;
@@ -74,7 +81,9 @@ int configure_tcp_clients(struct evt_core_ctx* ctx, struct evt_core_fdinfo* fdin
       sock2 = dup(fdinfo->fd);
       if (sock1 < 0 || sock2 < 0) goto on_socks5_err;
       void* fdcat = evt_core_rm_fd (ctx, fdinfo->fd);
-      if (fdcat == NULL) goto on_socks5_err;
+      if (fdcat == NULL) {
+        exit(EXIT_FAILURE);
+      }
 
       struct evt_core_fdinfo fdinfo = {0};
       struct evt_core_cat cat = {0};
@@ -107,6 +116,7 @@ on_socks5_err:
     perror("An error occured while connecting to an Onion Service");
     app_ctx->client_sock[pos].state = SOCKS5_STATE_ERR;
     evt_core_rm_fd (ctx, fdinfo->fd);
+    perror("0");
     sleep(2);
     init_tcp_client (app_ctx, pos);
     return 1;
@@ -119,6 +129,7 @@ void donar_client(struct donar_client_ctx* ctx, struct algo_skel* algo,
     .app_ctx = ctx,
     .free_app_ctx = NULL,
     .cb = configure_tcp_clients,
+    .err_cb = NULL,
     .name = "configure-socks5",
     .flags = EPOLLIN | EPOLLET,
     .socklist = NULL
diff --git a/src/evt_core.c b/src/evt_core.c
index c87680b..4ef18af 100644
--- a/src/evt_core.c
+++ b/src/evt_core.c
@@ -112,7 +112,10 @@ struct evt_core_cat* evt_core_rm_fd(struct evt_core_ctx* ctx, int fd) {
   // 2. Update category
   for (int i = 0; i < cat->socklist->len; i++) {
     if (g_array_index(cat->socklist, struct evt_core_fdinfo*, i) == fdinfo) {
-      printf("Remove fd\n");
+      if (fdinfo->fd != fd) {
+        fprintf(stderr, "Logic error in updating file descriptor list\n");
+        exit(EXIT_FAILURE);
+      }
       g_array_remove_index(cat->socklist, i);
     }
   }
diff --git a/src/socks5.c b/src/socks5.c
index 925b1f8..2e450e1 100644
--- a/src/socks5.c
+++ b/src/socks5.c
@@ -39,8 +39,14 @@ int socks5_handshake_ack(int sock) {
 }
 
 int socks5_reply(int sock) {
+    int res;
     struct server_reply sr = {0};
-    read_entity(sock, &sr, sizeof(uint8_t) * 4);
+    res = read_entity(sock, &sr, sizeof(uint8_t) * 4);
+    if (res == -1) {
+      perror("read_entity");
+      exit(EXIT_FAILURE);
+    }
+
     switch(sr.atyp) {
         case ATYP_IPV4:
             if (read_entity(sock, sr.bind_addr.ipv4, sizeof(uint8_t) * 4) == -1)
@@ -60,7 +66,11 @@ int socks5_reply(int sock) {
             fprintf(stderr, "Unsupported ATYP in server reply\n");
             return -128;
     }
-    read_entity(sock, &sr.port, sizeof(uint16_t));
+    res = read_entity(sock, &sr.port, sizeof(uint16_t));
+    if (res == -1) {
+      perror("read_entity");
+      exit(EXIT_FAILURE);
+    }
 
     if (sr.rep < 0 || sr.rep > 0x08) {
       fprintf(stderr, "Invalid reply field\n");