diff --git a/src/bacnet/basic/service/h_apdu.c b/src/bacnet/basic/service/h_apdu.c
index 3c50d24d..53f0ef59 100644
--- a/src/bacnet/basic/service/h_apdu.c
+++ b/src/bacnet/basic/service/h_apdu.c
@@ -554,10 +554,12 @@ static bool apdu_unconfirmed_dcc_disabled(uint8_t service_choice)
  * @param apdu [in] The apdu portion of the request, to be processed.
  * @param apdu_len [in] The total (remaining) length of the apdu.
  */
-void apdu_handler(BACNET_ADDRESS *src,
+void apdu_handler(
+    BACNET_ADDRESS *src,
     uint8_t *apdu, /* APDU data */
     uint16_t apdu_len)
 {
+    BACNET_PDU_TYPE pdu_type;
     BACNET_CONFIRMED_SERVICE_DATA service_data = { 0 };
     uint8_t service_choice = 0;
     uint8_t *service_request = NULL;
@@ -572,157 +574,166 @@ void apdu_handler(BACNET_ADDRESS *src,
     bool server = false;
 #endif
 
-    if (apdu) {
-        /* PDU Type */
-        switch (apdu[0] & 0xF0) {
-            case PDU_TYPE_CONFIRMED_SERVICE_REQUEST:
-                len = apdu_decode_confirmed_service_request(&apdu[0], apdu_len,
-                    &service_data, &service_choice, &service_request,
-                    &service_request_len);
-                if (len == 0) {
-                    /* service data unable to be decoded - simply drop */
-                    break;
-                }
-                if (apdu_confirmed_dcc_disabled(service_choice)) {
-                    /* When network communications are completely disabled,
-                       only DeviceCommunicationControl and ReinitializeDevice
-                       APDUs shall be processed and no messages shall be
-                       initiated. */
-                    break;
-                }
-                if ((service_choice < MAX_BACNET_CONFIRMED_SERVICE) &&
-                    (Confirmed_Function[service_choice])) {
-                    Confirmed_Function[service_choice](service_request,
-                        service_request_len, src, &service_data);
-                } else if (Unrecognized_Service_Handler) {
-                    Unrecognized_Service_Handler(service_request,
-                        service_request_len, src, &service_data);
-                }
-                break;
-            case PDU_TYPE_UNCONFIRMED_SERVICE_REQUEST:
-                if (apdu_len < 2) {
-                    break;
-                }
-                service_choice = apdu[1];
-                service_request = &apdu[2];
-                service_request_len = apdu_len - 2;
-                if (apdu_unconfirmed_dcc_disabled(service_choice)) {
-                    /* When network communications are disabled,
-                        only DeviceCommunicationControl and
-                        ReinitializeDevice APDUs shall be processed and no
-                        messages shall be initiated. If communications have
-                        been initiation disabled, then WhoIs may be
-                        processed. */
-                    break;
-                }
-                if (service_choice < MAX_BACNET_UNCONFIRMED_SERVICE) {
-                    if (Unconfirmed_Function[service_choice]) {
-                        Unconfirmed_Function[service_choice](
-                            service_request, service_request_len, src);
-                    }
-                }
-                break;
-#if !BACNET_SVC_SERVER
-            case PDU_TYPE_SIMPLE_ACK:
-                if (apdu_len < 3) {
-                    break;
-                }
-                invoke_id = apdu[1];
-                service_choice = apdu[2];
-                if (apdu_confirmed_simple_ack_service(service_choice)) {
-                    if (Confirmed_ACK_Function[service_choice].simple !=
-                        NULL) {
-                        Confirmed_ACK_Function[service_choice].simple(
-                            src, invoke_id);
-                    }
-                    tsm_free_invoke_id(invoke_id);
-                }
-                break;
-            case PDU_TYPE_COMPLEX_ACK:
-                if (apdu_len < 3) {
-                    break;
-                }
-                service_ack_data.segmented_message =
-                    (apdu[0] & BIT(3)) ? true : false;
-                service_ack_data.more_follows =
-                    (apdu[0] & BIT(2)) ? true : false;
-                invoke_id = service_ack_data.invoke_id = apdu[1];
-                len = 2;
-                if (service_ack_data.segmented_message) {
-                    service_ack_data.sequence_number = apdu[len++];
-                    service_ack_data.proposed_window_number = apdu[len++];
-                }
-                service_choice = apdu[len++];
-                service_request = &apdu[len];
-                service_request_len = apdu_len - (uint16_t)len;
-                if (!apdu_confirmed_simple_ack_service(service_choice)) {
-                    if (service_choice < MAX_BACNET_CONFIRMED_SERVICE) {
-                        if (Confirmed_ACK_Function[service_choice]
-                            .complex != NULL) {
-                            Confirmed_ACK_Function[service_choice].complex(
-                                service_request, service_request_len, src,
-                                &service_ack_data);
-                        }
-                    }
-                    tsm_free_invoke_id(invoke_id);
-                }
-                break;
-            case PDU_TYPE_SEGMENT_ACK:
-                /* FIXME: what about a denial of service attack here?
-                   we could check src to see if that matched the tsm */
-                tsm_free_invoke_id(invoke_id);
-                break;
-            case PDU_TYPE_ERROR:
-                if (apdu_len < 3) {
-                    break;
-                }
-                invoke_id = apdu[1];
-                service_choice = apdu[2];
-                if (apdu_complex_error(service_choice)) {
-                    if (Error_Function[service_choice].complex) {
-                        Error_Function[service_choice].complex(src,
-                            invoke_id, service_choice, &apdu[3],
-                            apdu_len - 3);
-                    }
-                } else if (service_choice < MAX_BACNET_CONFIRMED_SERVICE) {
-                    len = bacerror_decode_error_class_and_code(
-                        &apdu[3], apdu_len - 3, &error_class, &error_code);
-                    if ((len != 0) &&
-                        (Error_Function[service_choice].error)) {
-                        Error_Function[service_choice].error(src, invoke_id,
-                            (BACNET_ERROR_CLASS)error_class,
-                            (BACNET_ERROR_CODE)error_code);
-                    }
-                }
-                tsm_free_invoke_id(invoke_id);
-                break;
-            case PDU_TYPE_REJECT:
-                if (apdu_len < 3) {
-                    break;
-                }
-                invoke_id = apdu[1];
-                reason = apdu[2];
-                if (Reject_Function) {
-                    Reject_Function(src, invoke_id, reason);
-                }
-                tsm_free_invoke_id(invoke_id);
-                break;
-            case PDU_TYPE_ABORT:
-                if (apdu_len < 3) {
-                    break;
-                }
-                server = apdu[0] & 0x01;
-                invoke_id = apdu[1];
-                reason = apdu[2];
-                if (Abort_Function) {
-                    Abort_Function(src, invoke_id, reason, server);
-                }
-                tsm_free_invoke_id(invoke_id);
-                break;
-#endif
-            default:
-                break;
-        }
+    if (!apdu) {
+        return;
+    }
+    if (apdu_len == 0) {
+        return;
+    }
+    pdu_type = apdu[0] & 0xF0;
+    switch (pdu_type) {
+        case PDU_TYPE_CONFIRMED_SERVICE_REQUEST:
+            len = apdu_decode_confirmed_service_request(
+                apdu, apdu_len, &service_data, &service_choice,
+                &service_request, &service_request_len);
+            if (len == 0) {
+                /* service data unable to be decoded - simply drop */
+                break;
+            }
+            if (apdu_confirmed_dcc_disabled(service_choice)) {
+                /* When network communications are completely disabled,
+                    only DeviceCommunicationControl and ReinitializeDevice
+                    APDUs shall be processed and no messages shall be
+                    initiated. */
+                break;
+            }
+            if ((service_choice < MAX_BACNET_CONFIRMED_SERVICE) &&
+                (Confirmed_Function[service_choice])) {
+                Confirmed_Function[service_choice](
+                    service_request, service_request_len, src, &service_data);
+            } else if (Unrecognized_Service_Handler) {
+                Unrecognized_Service_Handler(
+                    service_request, service_request_len, src, &service_data);
+            }
+            break;
+        case PDU_TYPE_UNCONFIRMED_SERVICE_REQUEST:
+            if (apdu_len < 2) {
+                break;
+            }
+            service_choice = apdu[1];
+            /* prepare the service request buffer and length */
+            service_request_len = apdu_len - 2;
+            service_request = &apdu[2];
+            if (apdu_unconfirmed_dcc_disabled(service_choice)) {
+                /* When network communications are disabled,
+                    only DeviceCommunicationControl and
+                    ReinitializeDevice APDUs shall be processed and no
+                    messages shall be initiated. If communications have
+                    been initiation disabled, then WhoIs may be
+                    processed. */
+                break;
+            }
+            if (service_choice < MAX_BACNET_UNCONFIRMED_SERVICE) {
+                if (Unconfirmed_Function[service_choice]) {
+                    Unconfirmed_Function[service_choice](
+                        service_request, service_request_len, src);
+                }
+            }
+            break;
+#if !BACNET_SVC_SERVER
+        case PDU_TYPE_SIMPLE_ACK:
+            if (apdu_len < 3) {
+                break;
+            }
+            invoke_id = apdu[1];
+            service_choice = apdu[2];
+            if (apdu_confirmed_simple_ack_service(service_choice)) {
+                if (Confirmed_ACK_Function[service_choice].simple != NULL) {
+                    Confirmed_ACK_Function[service_choice].simple(
+                        src, invoke_id);
+                }
+                tsm_free_invoke_id(invoke_id);
+            }
+            break;
+        case PDU_TYPE_COMPLEX_ACK:
+            if (apdu_len < 3) {
+                break;
+            }
+            service_ack_data.segmented_message =
+                (apdu[0] & BIT(3)) ? true : false;
+            service_ack_data.more_follows = (apdu[0] & BIT(2)) ? true : false;
+            invoke_id = service_ack_data.invoke_id = apdu[1];
+            len = 2;
+            if (service_ack_data.segmented_message) {
+                if (apdu_len < 5) {
+                    break;
+                }
+                service_ack_data.sequence_number = apdu[len++];
+                service_ack_data.proposed_window_number = apdu[len++];
+            }
+            service_choice = apdu[len++];
+            /* prepare the service request buffer and length */
+            service_request_len = apdu_len - (uint16_t)len;
+            service_request = &apdu[len];
+            if (!apdu_confirmed_simple_ack_service(service_choice)) {
+                if (service_choice < MAX_BACNET_CONFIRMED_SERVICE) {
+                    if (Confirmed_ACK_Function[service_choice].complex !=
+                        NULL) {
+                        Confirmed_ACK_Function[service_choice].complex(
+                            service_request, service_request_len, src,
+                            &service_ack_data);
+                    }
+                }
+                tsm_free_invoke_id(invoke_id);
+            }
+            break;
+        case PDU_TYPE_SEGMENT_ACK:
+            /* FIXME: what about a denial of service attack here?
+                we could check src to see if that matched the tsm */
+            tsm_free_invoke_id(invoke_id);
+            break;
+        case PDU_TYPE_ERROR:
+            if (apdu_len < 3) {
+                break;
+            }
+            invoke_id = apdu[1];
+            service_choice = apdu[2];
+            /* prepare the service request buffer and length */
+            service_request_len = apdu_len - 3;
+            service_request = &apdu[3];
+            if (apdu_complex_error(service_choice)) {
+                if (Error_Function[service_choice].complex) {
+                    Error_Function[service_choice].complex(
+                        src, invoke_id, service_choice, service_request,
+                        service_request_len);
+                }
+            } else if (service_choice < MAX_BACNET_CONFIRMED_SERVICE) {
+                len = bacerror_decode_error_class_and_code(
+                    service_request, service_request_len, &error_class,
+                    &error_code);
+                if ((len != 0) && (Error_Function[service_choice].error)) {
+                    Error_Function[service_choice].error(
+                        src, invoke_id, (BACNET_ERROR_CLASS)error_class,
+                        (BACNET_ERROR_CODE)error_code);
+                }
+            }
+            tsm_free_invoke_id(invoke_id);
+            break;
+        case PDU_TYPE_REJECT:
+            if (apdu_len < 3) {
+                break;
+            }
+            invoke_id = apdu[1];
+            reason = apdu[2];
+            if (Reject_Function) {
+                Reject_Function(src, invoke_id, reason);
+            }
+            tsm_free_invoke_id(invoke_id);
+            break;
+        case PDU_TYPE_ABORT:
+            if (apdu_len < 3) {
+                break;
+            }
+            server = apdu[0] & 0x01;
+            invoke_id = apdu[1];
+            reason = apdu[2];
+            if (Abort_Function) {
+                Abort_Function(src, invoke_id, reason, server);
+            }
+            tsm_free_invoke_id(invoke_id);
+            break;
+#endif
+        default:
+            break;
     }
-    return;
 }