WiFi.monitor Module

Since Origin / Contributor Maintainer Source
2017-12-20 Philip Gladstone Philip Gladstone wifi_monitor.c

This is an optional module that is only included if LUA_USE_MODULES_WIFI_MONITOR is defined in the user_modules.h file. This module provides access to the monitor mode features of the ESP8266 chipset. In particular, it provides access to received WiFi management frames.

This module is not for casual use -- it requires an understanding of IEEE802.11 management protocols.

wifi.monitor.start()

This registers a callback function to be called whenever a management frame is received. Note that this can be at quite a high rate, so some limited filtering is provided before the callback is invoked. Only the first 110 bytes or so of the frame are returned -- this is an SDK restriction. Any connected ap/station will be disconnected.

Syntax

wifi.monitor.start([filter parameters,] mgmt_frame_callback)

Parameters

  • filter parameters. This is a byte offset (1 based) into the underlying data structure, a value to match against, and an optional mask to use for matching. The data structure used for filtering is 12 bytes of radio header, and then the actual frame. The first byte of the frame is therefore numbered 13. The filter values of 13, 0x80 will just extract beacon frames.
  • mgmt_frame_callback is a function which is invoked with a single argument which is a wifi.packet object which has many methods and attributes.

Returns

nothing.

Example

wifi.monitor.channel(6)
wifi.monitor.start(13, 0x80, function(pkt)
    print ('Beacon: ' .. pkt.bssid_hex .. " '" .. pkt[0] .. "' ch " .. pkt[3]:byte(1))
end)

wifi.monitor.stop()

This disables the monitor mode and returns to normal operation. There are no parameters and no return value.

Syntax

wifi.monitor.stop()

wifi.monitor.channel()

This sets the channel number to monitor. Note that in many applications you will want to step through the channel numbers at regular intervals. Beacon frames (in particular) are typically sent every 102 milliseconds, so a switch time of (say) 150 milliseconds seems to work well.

Syntax

wifi.monitor.channel(channel)

Parameters

  • channel sets the channel number in the range 1 to 15.

Returns

nothing.

wifi.packet object

This object provides access to the raw packet data and also many methods to extract data from the packet in a simple way.

packet:radio_byte()

This is like the string.byte method, except that it gives access to the bytes of the radio header.

Syntax

packet:radio_byte(n)

Parameters

  • n the byte number (1 based) to get from the radio header portion of the packet

Returns

0-255 as the value of the byte nothing if the offset is not within the radio header.

packet:frame_byte()

This is like the string.byte method, except that it gives access to the bytes of the received frame.

Syntax

packet:frame_byte(n)

Parameters

  • n the byte number (1 based) to get from the received frame.

Returns

0-255 as the value of the byte nothing if the offset is not within the received frame.

packet:radio_sub()

This is like the string.sub method, except that it gives access to the bytes of the radio header.

Syntax

packet:radio_sub(start, end)

Parameters

Same rules as for string.sub except that it operates on the radio header.

Returns

A string according to the string.sub rules.

packet:frame_sub()

This is like the string.sub method, except that it gives access to the bytes of the received frame.

Syntax

packet:frame_sub(start, end)

Parameters

Same rules as for string.sub except that it operates on the received frame.

Returns

A string according to the string.sub rules.

packet:radio_subhex()

This is like the string.sub method, except that it gives access to the bytes of the radio header. It also converts them into hex efficiently.

Syntax

packet:radio_subhex(start, end [, seperator])

Parameters

Same rules as for string.sub except that it operates on the radio header. - seperator is an optional sting which is placed between the individual hex pairs returned.

Returns

A string according to the string.sub rules, converted into hex with possible inserted spacers.

packet:frame_sub()

This is like the string.sub method, except that it gives access to the bytes of the received frame.

Syntax

packet:frame_subhex(start, end [, seperator])

Parameters

Same rules as for string.sub except that it operates on the received frame. - seperator is an optional sting which is placed between the individual hex pairs returned.

Returns

A string according to the string.sub rules, converted into hex with possible inserted spacers.

packet:ie_table()

This returns a table of the information elements from the management frame. The table keys values are the information element numbers (0 - 255). Note that IE0 is the SSID. This method is mostly only useful if you need to determine which information elements were in the management frame.

Syntax

packet:ie_table()

Parameters

None.

Returns

A table with all the information elements in it.

Example

print ("SSID", packet:ie_table()[0])

Note that this is possibly the worst way of getting the SSID.

Alternative

The packet object itself can be indexed to extract the information elements.

Example

print ("SSID", packet[0])

This is more efficient than the above approach, but requires you to remember that IE0 is the SSID.

packet.<attribute>

The packet object has many attributes on it. These allow easy access to all the fields, though not an easy way to enumerate them. All integers are unsigned except where noted. Information Elements are only returned if they are completely within the captured frame. This can mean that for some frames, some of the information elements can be missing.

When a string is returned as the value of a field, it can (and often is) be a binary string with embedded nulls. All information elements are returned as strings even if they are only one byte long and look like a number in the specification. This is purely to make the interface consistent. Note that even SSIDs can contain embedded nulls.

Attribute name Type
aggregation Integer
ampdu_cnt Integer
association_id Integer
authentication_algorithm Integer
authentication_transaction Integer
beacon_interval Integer
beacon_interval Integer
bssid String
bssid_hex String
bssidmatch0 Integer
bssidmatch1 Integer
capability Integer
channel Integer
current_ap String
cwb Integer
dmatch0 Integer
dmatch1 Integer
dstmac String
dstmac_hex String
duration Integer
fec_coding Integer
frame String (the entire received frame)
frame_hex String
fromds Integer
header String (the fixed part of the management frame)
ht_length Integer
ie_20_40_bss_coexistence String
ie_20_40_bss_intolerant_channel_report String
ie_advertisement_protocol String
ie_aid String
ie_antenna String
ie_ap_channel_report String
ie_authenticated_mesh_peering_exchange String
ie_beacon_timing String
ie_bss_ac_access_delay String
ie_bss_available_admission_capacity String
ie_bss_average_access_delay String
ie_bss_load String
ie_bss_max_idle_period String
ie_cf_parameter_set String
ie_challenge_text String
ie_channel_switch_announcement String
ie_channel_switch_timing String
ie_channel_switch_wrapper String
ie_channel_usage String
ie_collocated_interference_report String
ie_congestion_notification String
ie_country String
ie_destination_uri String
ie_diagnostic_report String
ie_diagnostic_request String
ie_dms_request String
ie_dms_response String
ie_dse_registered_location String
ie_dsss_parameter_set String
ie_edca_parameter_set String
ie_emergency_alart_identifier String
ie_erp_information String
ie_event_report String
ie_event_request String
ie_expedited_bandwidth_request String
ie_extended_bss_load String
ie_extended_capabilities String
ie_extended_channel_switch_announcement String
ie_extended_supported_rates String
ie_fast_bss_transition String
ie_fh_parameter_set String
ie_fms_descriptor String
ie_fms_request String
ie_fms_response String
ie_gann String
ie_he_capabilities String
ie_hopping_pattern_parameters String
ie_hopping_pattern_table String
ie_ht_capabilities String
ie_ht_operation String
ie_ibss_dfs String
ie_ibss_parameter_set String
ie_interworking String
ie_link_identifier String
ie_location_parameters String
ie_management_mic String
ie_mccaop String
ie_mccaop_advertisement String
ie_mccaop_advertisement_overview String
ie_mccaop_setup_reply String
ie_mccaop_setup_request String
ie_measurement_pilot_transmission String
ie_measurement_report String
ie_measurement_request String
ie_mesh_awake_window String
ie_mesh_channel_switch_parameters String
ie_mesh_configuration String
ie_mesh_id String
ie_mesh_link_metric_report String
ie_mesh_peering_management String
ie_mic String
ie_mobility_domain String
ie_multiple_bssid String
ie_multiple_bssid_index String
ie_neighbor_report String
ie_nontransmitted_bssid_capability String
ie_operating_mode_notification String
ie_overlapping_bss_scan_parameters String
ie_perr String
ie_power_capability String
ie_power_constraint String
ie_prep String
ie_preq String
ie_proxy_update String
ie_proxy_update_confirmation String
ie_pti_control String
ie_qos_capability String
ie_qos_map_set String
ie_qos_traffic_capability String
ie_quiet String
ie_quiet_channel String
ie_rann String
ie_rcpi String
ie_request String
ie_ric_data String
ie_ric_descriptor String
ie_rm_enabled_capacities String
ie_roaming_consortium String
ie_rsn String
ie_rsni String
ie_schedule String
ie_secondary_channel_offset String
ie_ssid String
ie_ssid_list String
ie_supported_channels String
ie_supported_operating_classes String
ie_supported_rates String
ie_tclas String
ie_tclas_processing String
ie_tfs_request String
ie_tfs_response String
ie_tim String
ie_tim_broadcast_request String
ie_tim_broadcast_response String
ie_time_advertisement String
ie_time_zone String
ie_timeout_interval String
ie_tpc_report String
ie_tpc_request String
ie_tpu_buffer_status String
ie_ts_delay String
ie_tspec String
ie_uapsd_coexistence String
ie_vendor_specific String
ie_vht_capabilities String
ie_vht_operation String
ie_vht_transmit_power_envelope String
ie_wakeup_schedule String
ie_wide_bandwidth_channel_switch String
ie_wnm_sleep_mode String
is_group Integer
legacy_length Integer
listen_interval Integer
mcs Integer
moredata Integer
moreflag Integer
not_counding Integer
number Integer
order Integer
protectedframe Integer
protocol Integer
pwrmgmt Integer
radio String (the entire radio header)
rate Integer
reason Integer
retry Integer
rssi Signed Integer
rxend_state Integer
sgi Integer
sig_mode Integer
smoothing Integer
srcmac String
srcmac_hex String
status Integer
stbc Integer
subtype Integer
timestamp String
tods Integer
type Integer

If you don't know what some of the attributes are, then you probably need to read the IEEE 802.11 specifications and other supporting material.

Example

print ("SSID", packet.ie_ssid)

The Radio Header

The Radio Header has been mentioned above as a 12 byte structure. The layout is shown below. The only comments are in Chinese.

struct {
    signed rssi:8;//表示该包的信号强度
    unsigned rate:4;
    unsigned is_group:1;
    unsigned:1;
    unsigned sig_mode:2;//表示该包是否是11n 的包,0 表示非11n,非0 表示11n
    unsigned legacy_length:12;//如果不是11n 的包,它表示包的长度
    unsigned damatch0:1;
    unsigned damatch1:1;
    unsigned bssidmatch0:1;
    unsigned bssidmatch1:1;
    unsigned MCS:7;//如果是11n 的包,它表示包的调制编码序列,有效值:0-76
    unsigned CWB:1;//如果是11n 的包,它表示是否为HT40 的包
    unsigned HT_length:16;//如果是11n 的包,它表示包的长度
    unsigned Smoothing:1;
    unsigned Not_Sounding:1;
    unsigned:1;
    unsigned Aggregation:1;
    unsigned STBC:2;
    unsigned FEC_CODING:1;//如果是11n 的包,它表示是否为LDPC 的包
    unsigned SGI:1;
    unsigned rxend_state:8;
    unsigned ampdu_cnt:8;
    unsigned channel:4;//表示该包所在的信道
    unsigned:12;
}