Dissecting a field with a mixed content

dissector

asked 2020-08-27 08:46:51 +0000

dottedmag
3 ●1 ●5

I'm writing a dissector for a protocol, and have stumbled upon the following field:

rxRSSIVal IN

RSSI measurement of the received frame. This is a signed 8-bit value.

Values from RSSI_RESERVED_START to 124 are reserved.

All values below RSSI_RESERVED_START are received power in dBms.

RSSI_NOT_AVAILABLE - RSSI measurement not available

RSSI_MAX_POWER_SATURATED - Receiver saturated. RSSI too high to measure precisely

RSSI_BELOW_SENSITIVITY - No signal detected. The RSSI is too low to measure precisely.

I understand how to mark reserved values as invalid via expert field.

How can I format other values in the packet tree node? I looked at various field types and none of them seem to fit. Is there a custom field type where dissector code can control the displayed value?

Ideally I'd also like to be able to support filtering myproto.rxrssi=max_power_saturated and myproto.rxrssi=10, but I'm not sure it is feasible.

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ti = proto_tree_add_item_ret_uint(tree,... hf_myproto_rxrssi,...., &rssi); subtree = proto_item_add_subtree(ti, ...); if (rssi >= RSSI_RESERVED_START && rssi < 124) { ti = proto_tree_add_item(subtree, ... hf_myproto_rxrssi_reserved, ....); proto_item_set_generated(ti); //optional, this creates square brackets around the field } else

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You could use a value string for the 3 enumerated values in the sub item.

grahamb ( 2020-08-27 12:24:20 +0000 )edit

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