LWAPP: Modernize packet parsing style. #1368
Open
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
The first revision of print-lwapp.c supposedly implemented draft-ohara-capwap-lwapp-04, all subsequent revisions made various code clean-ups only and the differences between the I-D and RFC 5412 seem to be purely editorial. However, the current implementation has substantial discrepancies with the specification. Moreover, several aspects of the specification are plainly not implementable due to various technical issues. The matter is, RFC 5412 was published for posterity rather than implementation: CAPWAP superseded LWAPP before the latter was complete. Before time is good for a more substantial reorganization of tcpdump decoders, clean the LWAPP decoder up once more and make it follow the specification better where practicable. Improve various comments. Define ND_LONGJMP_FROM_TCHECK. In lwapp_transport_header rename version to ver_rid_cfl and rearrange the associated macros for clarity. lwapp_control_print() and lwapp_data_print() each parse an LWAPP transport header in a slightly different way. Move the common code to a new function, lwapp_print(), and make it the only function exported from the decoder. To print the value of "length", the old common code used UDP payload length for ndo_vflag == 0 and LWAPP transport header payload length otherwise; in the new function make it the latter in both cases. Ibid., add diagnostics to flag unexpected fragmentation in the transport header. Ibid., use the transport header C bit instead of UDP ports to tell control and data frames apart. Rename lwapp_message_header to lwapp_msgelem_header to match the data it represents. Add a registry of message elements and specify the minimum length where possible. Implement a new function, permitted_msg_elem(), to tell whether a message element is valid for a message type. Fix lwapp_control_print() to iterate over message elements rather than messages and use the new props to validate and to print control messages a bit better. In lwapp_data_print() remove the mention of AP identity field because the function does not actually implement it. Ibid., do not require the transport payload length to be greater or equal to the transport header length and do not subtract the latter from the former for the hex dump because the former does not include the latter (this recovers the overlooked last 6 bytes of the payload in the output); require the transport payload end and the UDP payload end to be the same. With these changes made lwapp_data_print() becomes equivalent to just print_unknown_data(), so remove the former function. Since these clean-ups affect most of the code, in the same go reindent the entire file in a more sensible way. Update the tests.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
It took much longer than I originally expected.