diff --git a/src/packet/gtp1_utils.h b/src/packet/gtp1_utils.h
index db4ed2b..3ca4235 100644
--- a/src/packet/gtp1_utils.h
+++ b/src/packet/gtp1_utils.h
@@ -99,7 +99,7 @@ static inline uint8_t gtp1_hdr_get_version(const struct gtp1_hdr *gtp)
     return (gtp->flags & GTP1_FLAG_VERSION) >> 5;
 }
 
-static inline uint8_t gtp1_hdr_get_protocol(const struct gtp1_hdr *gtp)
+static inline uint8_t gtp1_hdr_get_proto(const struct gtp1_hdr *gtp)
 {
     return (gtp->flags & GTP1_FLAG_PROTOCOL) >> 4;
 }
@@ -178,15 +178,6 @@ static inline uint8_t gtp1_hdr_get_next_ext_type(const struct gtp1_hdr *gtp)
     }
 }
 
-static inline uint8_t peek_gtp_version(const char *data, uint16_t len)
-{
-    if (data == NULL || len == 0)
-    {
-        return 0;
-    }
-    return ((*(uint8_t *)data) >> 5) & 0x07;
-}
-
 // include gtp fixed header and optional headers and extension headers
 static inline uint16_t calc_gtp1_hdr_len(const char *data, uint16_t len)
 {
@@ -248,7 +239,7 @@ static inline void gtp1_hdr_set_version(struct gtp1_hdr *gtp, uint8_t version)
     gtp->flags = (gtp->flags & ~GTP1_FLAG_VERSION) | (version << 5);
 }
 
-static inline void gtp1_hdr_set_protocol(struct gtp1_hdr *gtp, uint8_t protocol_type)
+static inline void gtp1_hdr_set_proto(struct gtp1_hdr *gtp, uint8_t protocol_type)
 {
     gtp->flags = (gtp->flags & ~GTP1_FLAG_PROTOCOL) | (protocol_type << 4);
 }
@@ -321,11 +312,13 @@ static inline void gtp1_hdr_set_next_ext_type(struct gtp1_hdr *gtp, uint8_t next
 
 static inline int gtp1_hdr_to_str(const struct gtp1_hdr *gtp, char *buf, size_t len)
 {
+    memset(buf, 0, len);
+
     int used = 0;
     used += snprintf(buf + used, len - used, "GTP: flags=0x%02x (version=%u, protocol=%u, reserved=%u, ext_flag=%u, seq_flag=%u, npdu_flag=%u), msg_type=0x%02x, msg_len=%u, teid=%u",
                      gtp1_hdr_get_flags(gtp),
                      gtp1_hdr_get_version(gtp),
-                     gtp1_hdr_get_protocol(gtp),
+                     gtp1_hdr_get_proto(gtp),
                      gtp1_hdr_get_reserved(gtp),
                      gtp1_hdr_get_ext_flag(gtp),
                      gtp1_hdr_get_seq_flag(gtp),
diff --git a/src/packet/gtp2_utils.h b/src/packet/gtp2_utils.h
index 41661f6..c7e6cf5 100644
--- a/src/packet/gtp2_utils.h
+++ b/src/packet/gtp2_utils.h
@@ -242,6 +242,8 @@ static inline void gtp2_hdr_set_spare(struct gtp2_hdr *gtp, uint8_t spare)
 
 static inline int gtp2_hdr_to_str(const struct gtp2_hdr *gtp, char *buf, size_t len)
 {
+    memset(buf, 0, len);
+
     int used = 0;
     used += snprintf(buf + used, len - used, "GTP: flags=0x%02x (version=%u, piggyback=%u, teid_flag=%u, spare_flag=%u), msg_type=0x%02x, msg_len=%u",
                      gtp2_hdr_get_flags(gtp),
diff --git a/src/packet/gtp_utils.h b/src/packet/gtp_utils.h
new file mode 100644
index 0000000..8b0fc00
--- /dev/null
+++ b/src/packet/gtp_utils.h
@@ -0,0 +1,51 @@
+#pragma once
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+#include "gtp1_utils.h"
+#include "gtp2_utils.h"
+
+// return GTP version 0 or 1
+// return 255 if not GTP
+static inline uint8_t peek_gtp_version(const char *data, uint16_t len)
+{
+    if (data == NULL || len == 0)
+    {
+        return 255;
+    }
+
+    return ((*(uint8_t *)data) >> 5) & 0x07;
+}
+
+static inline uint16_t calc_gtp_hdr_len(const char *data, uint32_t len)
+{
+    switch (peek_gtp_version(data, len))
+    {
+    case 1:
+        return calc_gtp1_hdr_len(data, len);
+    case 2:
+        return calc_gtp2_hdr_len(data, len);
+    default:
+        return 0;
+    }
+}
+
+static inline int gtp_hdr_to_str(const char *hdr, uint16_t len, char *buf, size_t size)
+{
+    switch (peek_gtp_version(hdr, len))
+    {
+    case 1:
+        return gtp1_hdr_to_str((const struct gtp1_hdr *)hdr, buf, size);
+    case 2:
+        return gtp2_hdr_to_str((const struct gtp2_hdr *)hdr, buf, size);
+    default:
+        return 0;
+    }
+}
+
+#ifdef __cplusplus
+}
+#endif
diff --git a/src/packet/packet_build.cpp b/src/packet/packet_build.cpp
index a3609b1..ead36b0 100644
--- a/src/packet/packet_build.cpp
+++ b/src/packet/packet_build.cpp
@@ -6,8 +6,7 @@
 #include "udp_utils.h"
 #include "ip4_utils.h"
 #include "ip6_utils.h"
-#include "gtp1_utils.h"
-#include "gtp2_utils.h"
+#include "gtp_utils.h"
 #include "packet_def.h"
 #include "packet_utils.h"
 #include "packet_layer.h"
diff --git a/src/packet/packet_parse.cpp b/src/packet/packet_parse.cpp
index b52e8b7..88fc6a5 100644
--- a/src/packet/packet_parse.cpp
+++ b/src/packet/packet_parse.cpp
@@ -11,8 +11,7 @@
 #include "tcp_utils.h"
 #include "ip4_utils.h"
 #include "ip6_utils.h"
-#include "gtp1_utils.h"
-#include "gtp2_utils.h"
+#include "gtp_utils.h"
 #include "mpls_utils.h"
 #include "l2tp_utils.h"
 #include "vlan_utils.h"
@@ -689,7 +688,7 @@ static inline const char *parse_gre(struct packet *pkt, const char *data, uint16
     {
         return data;
     }
-    uint16_t next_proto = gre_hdr_get_proto((const struct gre_hdr *)data);
+    uint16_t next_proto = peek_gre_proto(data, len);
     SET_LAYER(pkt, layer, LAYER_PROTO_GRE, hdr_len, data, len, 0);
 
     return parse_l3(pkt, next_proto, layer->pld_ptr, layer->pld_len);
@@ -856,7 +855,7 @@ static inline const char *parse_gtp_u(struct packet *pkt, const char *data, uint
         return data;
     }
 
-    uint16_t hdr_len = calc_gtp1_hdr_len(data, len);
+    uint16_t hdr_len = calc_gtp_hdr_len(data, len);
     if (unlikely(hdr_len == 0 || hdr_len > len))
     {
         PACKET_LOG_DATA_INSUFFICIENCY(pkt, LAYER_PROTO_GTP_U);
@@ -886,20 +885,7 @@ static inline const char *parse_gtp_u(struct packet *pkt, const char *data, uint
 static inline const char *parse_gtp_c(struct packet *pkt, const char *data, uint16_t len)
 {
     // GTPv1-C or GTPv2-C
-    uint16_t hdr_len = 0;
-    uint8_t version = peek_gtp_version(data, len);
-    switch (version)
-    {
-    case 1:
-        hdr_len = calc_gtp1_hdr_len(data, len);
-        break;
-    case 2:
-        hdr_len = calc_gtp2_hdr_len(data, len);
-        break;
-    default:
-        return data;
-    }
-
+    uint16_t hdr_len = calc_gtp_hdr_len(data, len);
     if (unlikely(hdr_len == 0 || hdr_len > len))
     {
         PACKET_LOG_DATA_INSUFFICIENCY(pkt, LAYER_PROTO_GTP_C);
@@ -1033,7 +1019,7 @@ void packet_print(const struct packet *pkt)
         case LAYER_PROTO_IPAH:
             break;
         case LAYER_PROTO_GRE:
-            used = gre_hdr_to_str((const struct gre_hdr *)layer->hdr_ptr, buffer, sizeof(buffer));
+            used = gre_hdr_to_str(layer->hdr_ptr, layer->hdr_len, buffer, sizeof(buffer));
             break;
         case LAYER_PROTO_UDP:
             used = udp_hdr_to_str((const struct udphdr *)layer->hdr_ptr, buffer, sizeof(buffer));
@@ -1050,14 +1036,7 @@ void packet_print(const struct packet *pkt)
             break;
         case LAYER_PROTO_GTP_C:
         case LAYER_PROTO_GTP_U:
-            if (peek_gtp_version(layer->hdr_ptr, layer->hdr_len) == 1)
-            {
-                used = gtp1_hdr_to_str((const struct gtp1_hdr *)layer->hdr_ptr, buffer, sizeof(buffer));
-            }
-            if (peek_gtp_version(layer->hdr_ptr, layer->hdr_len) == 2)
-            {
-                used = gtp2_hdr_to_str((const struct gtp2_hdr *)layer->hdr_ptr, buffer, sizeof(buffer));
-            }
+            used = gtp_hdr_to_str(layer->hdr_ptr, layer->hdr_len, buffer, sizeof(buffer));
             break;
         default:
             break;
diff --git a/src/packet/test/gtest_gtp1_utils.cpp b/src/packet/test/gtest_gtp1_utils.cpp
index 8d917e8..231dd1c 100644
--- a/src/packet/test/gtest_gtp1_utils.cpp
+++ b/src/packet/test/gtest_gtp1_utils.cpp
@@ -132,7 +132,7 @@ TEST(GTP1_UTILS, C_GET)
     EXPECT_TRUE(calc_gtp1_hdr_len((const char *)gtp1_c, sizeof(gtp1_c)) == 12);
     EXPECT_TRUE(gtp1_hdr_get_flags(hdr) == 0x32);
     EXPECT_TRUE(gtp1_hdr_get_version(hdr) == 1);
-    EXPECT_TRUE(gtp1_hdr_get_protocol(hdr) == 1);
+    EXPECT_TRUE(gtp1_hdr_get_proto(hdr) == 1);
     EXPECT_TRUE(gtp1_hdr_get_reserved(hdr) == 0);
     EXPECT_TRUE(gtp1_hdr_get_ext_flag(hdr) == 0);
     EXPECT_TRUE(gtp1_hdr_get_seq_flag(hdr) == 1);
@@ -156,7 +156,7 @@ TEST(GTP1_UTILS, C_SET)
     struct gtp1_hdr *hdr = (struct gtp1_hdr *)buff;
     gtp1_hdr_set_flags(hdr, 0x32);
     gtp1_hdr_set_version(hdr, 1);
-    gtp1_hdr_set_protocol(hdr, 1);
+    gtp1_hdr_set_proto(hdr, 1);
     gtp1_hdr_set_reserved(hdr, 0);
     gtp1_hdr_set_ext_flag(hdr, 0);
     gtp1_hdr_set_seq_flag(hdr, 1);
@@ -197,7 +197,7 @@ TEST(GTP1_UTILS, U_GET)
     EXPECT_TRUE(calc_gtp1_hdr_len((const char *)gtp1_u, sizeof(gtp1_u)) == 8);
     EXPECT_TRUE(gtp1_hdr_get_flags(hdr) == 0x30);
     EXPECT_TRUE(gtp1_hdr_get_version(hdr) == 1);
-    EXPECT_TRUE(gtp1_hdr_get_protocol(hdr) == 1);
+    EXPECT_TRUE(gtp1_hdr_get_proto(hdr) == 1);
     EXPECT_TRUE(gtp1_hdr_get_reserved(hdr) == 0);
     EXPECT_TRUE(gtp1_hdr_get_ext_flag(hdr) == 0);
     EXPECT_TRUE(gtp1_hdr_get_seq_flag(hdr) == 0);
@@ -221,7 +221,7 @@ TEST(GTP1_UTILS, U_SET)
     struct gtp1_hdr *hdr = (struct gtp1_hdr *)buff;
     gtp1_hdr_set_flags(hdr, 0x30);
     gtp1_hdr_set_version(hdr, 1);
-    gtp1_hdr_set_protocol(hdr, 1);
+    gtp1_hdr_set_proto(hdr, 1);
     gtp1_hdr_set_reserved(hdr, 0);
     gtp1_hdr_set_ext_flag(hdr, 0);
     gtp1_hdr_set_seq_flag(hdr, 0);