This file attempts to describe the contents of the aprsc
source tree. When adding files, please describe them here. Thanks!
aprsc.c
Contains a command line parser, the main signal handler, and
a small main loop, which only calls time() to update a global
"now" variable (to reduce the amount of system calls). At startup
it reads the configuration and starts up the accept thread,
which in turns starts worker threads. It can also trigger
reconfiguring and log reopening on when signals are received,
and start a graceful shutdown.
accept.c
Contains the accept thread, which listens on the configured TCP/UDP
sockets, accepts (or denies) new connections, and passes them
to the worker thread with least existing connections. When
a lot of connections arrive quickly, multiple connections
are transferred to a worker in a single transaction to reduce
lock congestion.
worker.c
worker.h
Contains the body of the worker thread. worker.h defines most
of the interesting data structures and is a good place to
start digging.
Worker threads process incoming and outgoing data. There are 1..n
workers, where N is 1 to 4 (more really doesn't make sense at this
point, and 1 is probably good too). Incoming data is parsed,
preprocessed, and passed on to the dupecheck thread which
marks duplicate packets as such. Dupecheck returns the packets to
the workers which then pass on them to the right clients.
ssl.c
SSL/TLS encryption and authentication code for APRS-IS sockets.
sctp.c
SCTP protocol support. sctp(7) says: "Like TCP, SCTP provides
reliable, connection oriented data delivery with congestion control.
Unlike TCP, SCTP also provides message boundary preservation,
ordered and unordered message delivery, multi-streaming and
multi-homing."
login.c
Contains a login_handler() function which is called by the
worker thread to process an incoming "user" command from
a new client.
uplink.c
The uplink management thread takes care of connecting to
remote upstream servers as needed. It also contains the handlers
necessary for logging in to a server. After a successful connect()
the connection is passed to a worker thread, but the login
handshake incoming data handlers for the login phase can be found
in uplink.c.
incoming.c
Contains the incoming_handler() function which is called
by the worker thread to process incoming APRS-IS data
line by line. Decodes basic IS packet format and calls
the Q construct processor and the APRS decoder.
outgoing.c
Checks which outgoing packets should be sent to each client by
calling filter functions, and does the actual sending.
filter.c
APRS-IS filter used by the outgoing packet processing.
It tells if the packet should be sent out on given client socket,
depending on the user's preferences.
parse_aprs.c
A simple APRS parser for aprsc. Translated from Ham::APRS::FAP
perl module (by OH2KKU). Only needs to get lat/lng out of the
packet, and classify the type of the packet, other features would
be unnecessary in this application, and slow down the parser.
Called by incoming.c.
parse_qc.c
Parses and possibly generates a new Q construct, or modifies
an existing one. Called by incoming.c.
messaging.c
Contains utility functions for processing received APRS text
messages and generating new messages.
clientlist.c
Clientlist contains a list of connected clients, along with their
verification status. It is updated when clients connect or disconnect,
and lookups are made more often by the Q construct algorithm.
This list is maintained so that the login handler can find duplicate
verified logins, and that the Q construct handler can lookup
verified logins without locking and walking the other worker thread's
client list.
client_heard.c
The client's heard list contains a list of stations heard by
a given client. It's used for message routing by the
message destination callsign.
The module also maintains a list of callsigns which have transmitted
messages to a given client. The list is used to pass courtesy
positions to the client.
The heard list is only called by the worker thread operating
on that client socket, so it shouldn't need any locking at all.
config.c
Code to read (and reread) configuration using the services
provided by cfgfile.c. Validates configuration and takes
it into use. Contains global configuration variables.
http.c
HTTP server implemented using libevent2. Runs in a single thread,
event-driven, provides access to the status page and HTTP
position uploads.
--- Libraries ---
The following source code files have rather clean APIs, are not specific to
to the aprsc project, and are usablein other projects as such.
netlib.c
A few network socket utility functions.
xpoll.c
A wrapper for different select/poll/epoll implementations.
Currently only contains support for poll(). Should maybe
support select() for ancient systems. The following platform-
specific APIs would provide improved performance: epoll()
on Linux 2.6, kqueue on new *BSD, /dev/poll on new Solaris
releases. Written for the aprsc project by Heikki Hannikainen,
OH7LZB.
passcode.c
aprs_passcode() function to calculate the checksum used as the
"password" int the APRS-IS login command. Released to the
open source APRS community by Steve Dimse, K4HG, on April 11,
2000. Obtained from the aprsd sources, which are GPL.
acl.c
Access list code for limiting server access based on IP address.
hlog.c
A logging library written by Heikki Hannikainen, OH7LZB,
for some old project. Supports logging to syslog, stderr,
and a log file, with configurable log levels and rotation
(reopen on SIGHUP).
hmalloc.c
malloc/realloc/free/strdup wrappers with error checking.
Please use these in this project. Written by Hessu, OH7LZB.
cfgfile.c
A configuration file parser written by Tomi Manninen, OH2BNS,
originally for the node(1) program in the ax25-utils package.
keyhash.c
Various attempts at keyhashing.
Contains algorithms:
- FNV-1a
- CRC32
Currently using FNV-1a
rwlock.c
A schoolbook pthread rwlock implementation for systems
lacking one (Solaris 2.6 to name one).
From the book "Programming with POSIX Threads", by
David R. Butenhof. Appears in modified and GPL'ed form in at
least the Bacula sources.
inet_ntop.c, inet_pton.c, getnameinfo.c, gai_strerror.c:
Backup instances of IPv4/IPv6 agnostic resolver library just
in case the operating system does not have it.
(From ZMailer by Matti Aarnio, OH2MQK)
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