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7 ============================================================================================
9 ============================================================================================
10 --------------------------------------------------------------------------------------------
11 RIC Message Router -- RMR
12 --------------------------------------------------------------------------------------------
18 The RIC Message Router (RMR) is a library for peer-to-peer
19 communication. Applications use the library to send and
20 receive messages where the message routing and endpoint
21 selection is based on the message type rather than DNS host
22 name-IP port combinations. The library provides the following
26 * Routing and endpoint selection is based on *message type.*
28 * Application is insulated from the underlying transport
29 mechanism and/or protocols.
31 * Message distribution (round robin or fanout) is selectable
34 * Route management updates are received and processed
35 asynchronously and without overt application involvement.
43 RMR's main purpose is to provide an application with the
44 ability to send and receive messages to/from other peer
45 applications with minimal effort on the application's part.
46 To achieve this, RMR manages all endpoint information,
47 connections, and routing information necessary to establish
48 and maintain communication. From the application's point of
49 view, all that is required to send a message is to allocate
50 (via RMR) a message buffer, add the payload data, and set the
51 message type. To receive a message, the application needs
52 only to invoke the receive function; when a message arrives a
53 message buffer will be returned as the function result.
59 Applications are required to place a message type into a
60 message before sending, and may optionally add a subscription
61 ID when appropriate. The combination of message type, and
62 subscription ID are refered to as the *message key,* and is
63 used to match an entry in a routing table which provides the
64 possible endpoints expecting to receive messages with the
71 An endpoint from RMR's perspective is an application to which
72 RMR may establish a connection, and expect to send messages
73 with one or more defined message keys. Each entry in the
74 route table consists of one or more endpoint groups, called
75 round robin groups. When a message matches a specific entry,
76 the entry's groups are used to select the destination of the
77 message. A message is sent once to each group, with messages
78 being *balanced* across the endpoints of a group via round
79 robin selection. Care should be taken when defining multiple
80 groups for a message type as there is extra overhead required
81 and thus the overall message latency is somewhat increased.
87 Route table information is made available to RMR a static
88 file (loaded once), or by updates sent from a separate route
89 manager application. If a static table is provided, it is
90 loaded during RMR initialization and will remain in use until
91 an external process connects and delivers a route table
92 update (often referred to as a dynamic update). Dynamic
93 updates are listened for in a separate process thread and
94 applied automatically; the application does not need to allow
95 for, or trigger, updates.
98 Latency And Throughput
99 ----------------------
101 While providing insulation from the underlying message
102 transport mechanics, RMR must also do so in such a manner
103 that message latency and throughput are not impacted. In
104 general, the RMR induced overhead, incurred due to the
105 process of selecting an endpoint for each message, is minimal
106 and should not impact the overall latency or throughput of
107 the application. This impact has been measured with test
108 applications running on the same physical host and the
109 average latency through RMR for a message was on the order of
112 As an application's throughput increases, it becomes easy for
113 the application to overrun the underlying transport mechanism
114 (e.g. NNG), consume all available TCP transmit buffers, or
115 otherwise find itself in a situation where a send might not
116 immediately complete. RMR offers different *modes* which
117 allow the application to manage these states based on the
118 overall needs of the application. These modes are discussed
119 in the *Configuration* section of this document.
125 To use, the RMR based application simply needs to initialise
126 the RMR environment, wait for RMR to have received a routing
127 table (become ready), and then invoke either the send or
128 receive functions. These steps, and some behind the scenes
129 details, are described in the following paragraphs.
135 The RMR function ``rmr_init()`` is used to set up the RMR
136 environment and must be called before messages can be sent or
137 received. One of the few parameters that the application must
138 communicate to RMR is the port number that will be used as
139 the listen port for new connections. The port number is
140 passed on the initialisation function call and a TCP listen
141 socket will be opened with this port. If the port is already
142 in use RMR will report a failure; the application will need
143 to reinitialise with a different port number, abort, or take
144 some other action appropriate for the application.
146 In addition to creating a TCP listen port, RMR will start a
147 process thread which will be responsible for receiving
148 dynamic updates to the route table. This thread also causes a
149 TCP listen port to be opened as it is expected that the
150 process which generates route table updates will connect and
151 send new information when needed. The route table update port
152 is **not** supplied by the application, but is supplied via
153 an environment variable as this value is likely determined by
154 the mechanism which is starting and configuring the
161 On successful initialisation, a void pointer, often called a
162 *handle* by some programming languages, is returned to the
163 application. This is a reference to the RMR control
164 information and must be passed as the first parameter on most
165 RMR function calls. RMR refers to this as the context, or
172 An application which is only receiving messages does not need
173 to wait for RMR to *become ready* after the call to the
174 initialization function. However, before the application can
175 successfully send a message, RMR must have loaded a route
176 table, and the application must wait for RMR to report that
177 it has done so. The RMR function ``rmr_ready()`` will return
178 the value *true* (1) when a complete route table has been
179 loaded and can be used to determine the endpoint for a send
186 The process of receiving is fairly straight forward. The
187 application invokes the RMR ``rmr_rcv_msg()`` function which
188 will block until a message is received. The function returns
189 a pointer to a message block which provides all of the
190 details about the message. Specifically, the application has
191 access to the following information either directly or
195 * The payload (actual data)
197 * The total payload length in bytes
199 * The number of bytes of the payload which contain valid data
201 * The message type and subscription ID values
203 * The hostname and IP address of the source of the message
208 * Tracing data (if provided)
216 The message payload contains the *raw* data that was sent by
217 the peer application. The format will likely depend on the
218 message type, and is expected to be known by the application.
219 A direct pointer to the payload is available from the message
220 buffer (see appendix B for specific message buffer details).
222 Two payload-related length values are also directly
223 available: the total payload length, and the number of bytes
224 actually filled with data. The used length is set by the
225 caller, and may or not be an accurate value. The total
226 payload length is determined when the buffer is created for
227 sending, and is the maximum number of bytes that the
228 application may modify should the buffer be used to return a
232 Message Type and Subscription ID
233 --------------------------------
235 The message type and subscription ID are both directly
236 available from the message buffer, and are the values which
237 were used to by RMR in the sending application to select the
238 endpoint. If the application resends the message, as opposed
239 to returning the message buffer as a response, the message
240 number and/or the subscription ID might need to be changed to
241 avoid potential issues[1].
247 The source, or sender information, is indirectly available to
248 the application via the ``rmr_get_src()`` and
249 ``rmr_get_ip()`` functions. The former returns a string
250 containing ``hostname:port,`` while the string
251 ``ip:port`` is returned by the latter.
257 The message buffer contains a fixed length set of bytes which
258 applications can set to track related messages across the
259 application concept of a transaction. RMR will use the
260 transaction ID for matching a response message when the
261 ``rmr_call()`` function is used to send a message.
267 RMR supports the addition of an optional trace information to
268 any message. The presence and size is controlled by the
269 application, and can vary from message to message if desired.
270 The actual contents of the trace information is determined by
271 the application; RMR provides only the means to set, extract,
272 and obtain a direct reference to the trace bytes. The trace
273 data field in a message buffer is discussed in greater detail
274 in the *Trace Data* section.
280 Sending requires only slightly more work on the part of the
281 application than receiving a message. The application must
282 allocate an RMR message buffer, populate the message payload
283 with data, set the message type and length, and optionally
284 set the subscription ID. Information such as the source IP
285 address, hostname, and port are automatically added to the
286 message buffer by RMR, so there is no need for the
287 application to worry about these.
290 Message Buffer Allocation
291 -------------------------
293 The function ``rmr_msg_alloc()`` allocates a *zero copy*
294 buffer and returns a pointer to the RMR ``rmr_mbuf_t``
295 structure. The message buffer provides direct access to the
296 payload, length, message type and subscription ID fields. The
297 buffer must be preallocated in order to allow the underlying
298 transport mechanism to allocate the payload space from its
299 internal memory pool; this eliminates multiple copies as the
300 message is sent, and thus is more efficient.
302 If a message buffer has been received, and the application
303 wishes to use the buffer to send a response, or to forward
304 the buffer to another application, a new buffer does **not**
305 need to be allocated. The application may set the necessary
306 information (message type, etc.), and adjust the payload, as
307 is necessary and then pass the message buffer to
308 ``rmr_send_msg()`` or ``rmr_rts_msg()`` to be sent or
309 returned to the sender.
312 Populating the Message Buffer
313 -----------------------------
315 The application has direct access to several of the message
316 buffer fields, and should set them appropriately.
326 This is the number of bytes that the application placed into
327 the payload. Setting length to 0 is allowed, and length may
328 be less than the allocated payload size.
332 The message type that RMR will use to determine the endpoint
333 used as the target of the send.
337 The subscription ID if the message is to be routed based on
338 the combination of message type and subscription ID. If no
339 subscription ID is valid for the message, the application
340 should set the field with the RMR constant
345 The application should obtain the reference (pointer) to the
346 payload from the message buffer and place any data into the
347 payload. The application is responsible for ensuring that the
348 maximum payload size is not exceeded. The application may
349 obtain the maximum size via the ``rmr_payload_size()``
354 Optionally, the application may add trace information to the
361 Sending a Message Buffer
362 ------------------------
364 Once the application has populated the necessary bits of a
365 message, it may be sent by passing the buffer to the
366 ``rmr_send_msg()`` function. This function will select an
367 endpoint to receive the message, based on message type and
368 subscription ID, and will pass the message to the underlying
369 transport mechanism for actual transmission on the
370 connection. (Depending on the underlying transport mechanism,
371 the actual connection to the endpoint may happen at the time
372 of the first message sent to the endpoint, and thus the
373 latency of the first send might be longer than expected.)
375 On success, the send function will return a reference to a
376 message buffer; the status within that message buffer will
377 indicate what the message buffer contains. When the status is
378 ``RMR_OK`` the reference is to a **new** message buffer for
379 the application to use for the next send; the payload size is
380 the same as the payload size allocated for the message that
381 was just sent. This is a convenience as it eliminates the
382 need for the application to call the message allocation
383 function at some point in the future, and assumes the
384 application will send many messages which will require the
385 same payload dimensions.
387 If the message contains any status other than ``RMR_OK,``
388 then the message could **not** be sent, and the reference is
389 to the unsent message buffer. The value of the status will
390 indicate whether the nature of the failure was transient (
391 ``RMR_ERR_RETRY``) or not. Transient failures are likely to
392 be successful if the application attempts to send the message
393 at a later time. Unfortunately, it is impossible for RMR to
394 know the exact transient failure (e.g. connection being
395 established, or TCP buffer shortage), and thus it is not
396 possible to communicate how long the application should wait
397 before attempting to resend, if the application wishes to
398 resend the message. (More discussion with respect to message
399 retries can be found in the *Handling Failures* section.)
405 Several forms of usage fall into a more advanced category and
406 are described in the following sections. These include
407 blocking call, return to sender and wormhole functions.
413 The RMR function ``rmr_call()`` sends a message in the exact
414 same manner as the ``rmr_send_msg()()`` function, with the
415 endpoint selection based on the message key. But unlike the
416 send function, ``rmr_call()`` will block and wait for a
417 response from the application that is selected to receive the
418 message. The matching message is determined by the
419 transaction ID which the application must place into the
420 message buffer prior to invoking ``rmr_call()``. Similarly,
421 the responding application must ensure that the same
422 transaction ID is placed into the message buffer before
423 returning its response.
425 The return from the call is a message buffer with the
426 response message; there is no difference between a message
427 buffer returned by the receive function and one returned by
428 the ``rmr_call()`` function. If a response is not received in
429 a reasonable amount of time, a nil message buffer is returned
430 to the calling application.
436 Because of the nature of RMR's routing policies, it is
437 generally not possible for an application to control exactly
438 which endpoint is sent a message. There are cases, such as
439 responding to a message delivered via ``rmr_call()`` that the
440 application must send a message and guarantee that RMR routes
441 it to an exact destination. To enable this, RMR provides the
442 ``rmr_rts_msg(),`` return to sender, function. Upon receipt
443 of any message, an application may alter the payload, and if
444 necessary the message type and subscription ID, and pass the
445 altered message buffer to the ``rmr_rts_msg()`` function to
446 return the altered message to the application which sent it.
447 When this function is used, RMR will examine the message
448 buffer for the source information and use that to select the
449 connection on which to write the response.
455 The basic call mechanism described above is **not** thread
456 safe, as it is not possible to guarantee that a response
457 message is delivered to the correct thread. The RMR function
458 ``rmr_mt_call()`` accepts an additional parameter which
459 identifies the calling thread in order to ensure that the
460 response is delivered properly. In addition, the application
461 must specifically initialise the multi-threaded call
462 environment by passing the ``RMRFL_MTCALL`` flag as an option
463 to the ``rmr_init()`` function.
465 One advantage of the multi-threaded call capability in RMR is
466 the fact that only the calling thread is blocked. Messages
467 received which are not responses to the call are continued to
468 be delivered via normal ``rmr_rcv_msg()`` calls.
470 While the process is blocked waiting for the response, it is
471 entirely possible that asynchronous, non-matching, messages
472 will arrive. When this happens, RMR will queues the messages
473 and return them to the application over the next calls to
480 As was mentioned earlier, the design of RMR is to eliminate
481 the need for an application to know a specific endpoint, even
482 when a response message is being sent. In some rare cases it
483 may be necessary for an application to establish a direct
484 connection to an RMR-based application rather than relying on
485 message type and subscription ID based routing. The
486 *wormhole* functions provide an application with the ability
487 to create a direct connection and then to send and receive
488 messages across the connection. The following are the RMR
489 functions which provide wormhole communications:
499 Open a connection to an endpoint. Name or IP address and port
500 of the endpoint is supplied. Returns a wormhole ID that the
501 application must use when sending a direct message.
503 * - **rmr_wh_send_msg**
505 Sends an RMR message buffer to the connected application. The
506 message type and subscription ID may be set in the message,
507 but RMR will ignore both.
511 Closes the direct connection.
520 The vast majority of states reported by RMR are fatal; if
521 encountered during setup or initialization, then it is
522 unlikely that any message oriented processing should
523 continue, and when encountered on a message operation
524 continued operation on that message should be abandoned.
525 Specifically with regard to message sending, it is very
526 likely that the underlying transport mechanism will report a
527 *soft,* or transient, failure which might be successful if
528 the operation is retried at a later point in time. The
529 paragraphs below discuss the methods that an application
530 might deal with these soft failures.
536 When a soft failure is reported, the returned message buffer
537 returned by the RMR function will be ``RMR_ERR_RETRY.`` These
538 types of failures can occur for various reasons; one of two
539 reasons is typically the underlying cause:
542 * The session to the targeted recipient (endpoint) is not
545 * The transport mechanism buffer pool is full and cannot
546 accept another buffer.
550 Unfortunately, it is not possible for RMR to determine which
551 of these two cases is occurring, and equally as unfortunate
552 the time to resolve each is different. The first, no
553 connection, may require up to a second before a message can
554 be accepted, while a rejection because of buffer shortage is
555 likely to resolve in less than a millisecond.
561 The action which an application takes when a soft failure is
562 reported ultimately depends on the nature of the application
563 with respect to factors such as tolerance to extended message
564 latency, dropped messages, and over all message rate.
570 In an effort to reduce the workload of an application
571 developer, RMR has a default retry policy such that RMR will
572 attempt to retransmit a message up to 1000 times when a soft
573 failure is reported. These retries generally take less than 1
574 millisecond (if all 1000 are attempted) and in most cases
575 eliminates nearly all reported soft failures to the
576 application. When using this mode, it might allow the
577 application to simply treat all bad return values from a send
578 attempt as permanent failures.
580 If an application is so sensitive to any delay in RMR, or the
581 underlying transport mechanism, it is possible to set RMR to
582 return a failure immediately on any kind of error (permanent
583 failures are always reported without retry). In this mode,
584 RMR will still set the state in the message buffer to
585 ``RMR_ERR_RETRY,`` but will **not** make any attempts to
586 resend the message. This zero-retry policy is enabled by
587 invoking the ``rmr_set_stimeout()`` with a value of 0; this
588 can be done once immediately after ``rmr_init()`` is invoked.
590 Regardless of the retry mode which the application sets, it
591 will ultimately be up to the application to handle failures
592 by queuing the message internally for resend, retrying
593 immediately, or dropping the send attempt all together. As
594 stated before, only the application can determine how to best
595 handle send failures.
601 RMR will return the state of processing for message based
602 operations (send/receive) as the status in the message
603 buffer. For non-message operations, state is returned to the
604 caller as the integer return value for all functions which
605 are not expected to return a pointer (e.g.
606 ``rmr_init()``.) The following are the RMR state constants
607 and a brief description of their meaning.
617 state is good; operation finished successfully
619 * - **RMR_ERR_BADARG**
621 argument passed to function was unusable
623 * - **RMR_ERR_NOENDPT**
625 send/call could not find an endpoint based on msg type
627 * - **RMR_ERR_EMPTY**
629 msg received had no payload; attempt to send an empty message
631 * - **RMR_ERR_NOHDR**
633 message didn't contain a valid header
635 * - **RMR_ERR_SENDFAILED**
637 send failed; errno may contain the transport provider reason
639 * - **RMR_ERR_CALLFAILED**
641 unable to send the message for a call function; errno may
642 contain the transport provider reason
644 * - **RMR_ERR_NOWHOPEN**
646 no wormholes are open
650 the wormhole id provided was invalid
652 * - **RMR_ERR_OVERFLOW**
654 operation would have busted through a buffer/field size
656 * - **RMR_ERR_RETRY**
658 request (send/call/rts) failed, but caller should retry
659 (EAGAIN for wrappers)
661 * - **RMR_ERR_RCVFAILED**
663 receive failed (hard error)
665 * - **RMR_ERR_TIMEOUT**
667 response message not received in a reasonable amount of time
669 * - **RMR_ERR_UNSET**
671 the message hasn't been populated with a transport buffer
673 * - **RMR_ERR_TRUNC**
675 length in the received buffer is longer than the size of the
676 allocated payload, received message likely truncated (length
677 set by sender could be wrong, but we can't know that)
679 * - **RMR_ERR_INITFAILED**
681 initialisation of something (probably message) failed
683 * - **RMR_ERR_NOTSUPP**
685 the request is not supported, or RMR was not initialised for
690 Depending on the underlying transport mechanism, and the
691 nature of the call that RMR attempted, the system
692 ``errno`` value might reflect additional detail about the
693 failure. Applications should **not** rely on errno as some
694 transport mechanisms do not set it with any consistency.
697 Configuration and Control
698 =========================
700 With the assumption that most RMR based applications will be
701 executed in a containerised environment, there are some
702 underlying mechanics which the developer may need to know in
703 order to properly provide a configuration specification to
704 the container management system. The following paragraphs
705 briefly discuss these.
712 RMR requires two (2) TCP listen ports: one for general
713 application-to-application communications and one for
714 route-table updates. The general communication port is
715 specified by the application at the time RMR is initialised.
716 The port used to listen for route table updates is likely to
717 be a constant port shared by all applications provided they
718 are running in separate containers. To that end, the port
719 number defaults to 4561, but can be configured with an
720 environment variable (see later paragraph in this section).
726 RMR is typically host name agnostic. Route table entries may
727 contain endpoints defined either by host name or IP address.
728 In the container world the concept of a *service name* might
729 exist, and likely is different than a host name. RMR's only
730 requirement with respect to host names is that a name used on
731 a route table entry must be resolvable via the
732 ``gethostbyname`` system call.
735 Environment Variables
736 ---------------------
738 Several environment variables are recognised by RMR which, in
739 general, are used to define interfaces and listen ports (e.g.
740 the route table update listen port), or debugging
741 information. Generally this information is system controlled
742 and thus RMR expects this information to be defined in the
743 environment rather than provided by the application. The
744 following is a list of the environment variables which RMR
755 The interface to bind to listen ports to. If not defined
756 0.0.0.0 (all interfaces) is assumed.
760 This variabe supplies the host:port (or address:port) of the
761 Route Manager (route table generator) process. RMR will
762 attempt to connect to this address port combination and
763 request a route table. If it is desired to prevent RMR from
764 attempting to request a dynamic route table, the value of
765 this variable should be set to "-1." If not set
766 ``routemgr`` is assumed.
770 This is the port which RMR's route table collector thread
771 will use to listen for RMR messages from the route manager
772 (route table generator). By default this is 4561, and must be
773 unique for each RMR process running on the host/container.
775 * - **RMR_RTREQ_FREQ**
777 When a new route table is needed, the frequency that RMR
778 sends a route table request to the Route Manager defaults to
779 5 seconds. This variable can be used to set the frequency to
780 a value between 1 and 300 seconds inclusive.
784 Where RMR expects to find the name of the seed (static) route
785 table. If not defined no static table is read.
787 * - **RMR_RTG_ISRAW**
789 If the value set to 0, RMR expects the route table manager
790 messages to be messages with and RMR header. If this is not
791 defined messages are assumed to be "raw" (without an RMR
794 * - **RMR_VCTL_FILE**
796 Provides a file which is used to set the verbose level of the
797 route table collection thread. The first line of the file is
798 read and expected to contain an integer value to set the
799 verbose level. The value may be changed at any time and the
800 route table thread will adjust accordingly.
802 * - **RMR_SRC_NAMEONLY**
804 If the value of this variable is greater than 0, RMR will not
805 permit the IP address to be sent as the message source. Only
806 the host name will be sent as the source in the message
816 RMR does **not** use any logging libraries; any error or
817 warning messages are written to standard error. RMR messages
818 are written with one of three prefix strings:
828 The event is of a critical nature and it is unlikely that RMR
829 will continue to operate correctly if at all. It is almost
830 certain that immediate action will be needed to resolve the
835 The event is not expected and RMR is not able to handle it.
836 There is a small chance that continued operation will be
837 negatively impacted. Eventual action to diagnose and correct
838 the issue will be necessary.
842 The event was not expected by RMR, but can be worked round.
843 Normal operation will continue, but it is recommended that
844 the cause of the problem be investigated.
854 [1] It is entirely possible to design a routing table, and
855 application group, such that the same message type is is
856 left unchanged and the message is forwarded by an
857 application after updating the payload. This type of
858 behaviour is often referred to as service chaining, and can
859 be done without any "knowledge" by an application with
860 respect to where the message goes next. Service chaining is
861 supported by RMR in as much as it allows the message to be
862 resent, but the actual complexities of designing and
863 implementing service chaining lie with the route table
871 Appendix A -- Quick Reference
872 =============================
874 Please refer to the RMR manual pages on the Read the Docs
877 https://docs.o-ran-sc.org/projects/o-ran-sc-ric-plt-lib-rmr/en/latest/index.html
881 Appendix B -- Message Buffer Details
882 ====================================
884 The RMR message buffer is a C structure which is exposed in
885 the ``rmr.h`` header file. It is used to manage a message
886 received from a peer endpoint, or a message that is being
887 sent to a peer. Fields include payload length, amount of
888 payload actually used, status, and a reference to the
889 payload. There are also fields which the application should
890 ignore, and could be hidden in the header file, but we chose
891 not to. These fields include a reference to the RMR header
892 information, and to the underlying transport mechanism
893 message struct which may or may not be the same as the RMR
900 The following is the C structure. Readers are cautioned to
901 examine the ``rmr.h`` header file directly; the information
902 here may be out of date (old document in some cache), and
903 thus it may be incorrect.
910 int state; // state of processing
911 int mtype; // message type
912 int len; // length of data in the payload (send or received)
913 unsigned char* payload; // transported data
914 unsigned char* xaction; // pointer to fixed length transaction id bytes
915 int sub_id; // subscription id
916 int tp_state; // transport state (errno)
918 // these things are off limits to the user application
919 void* tp_buf; // underlying transport allocated pointer (e.g. nng message)
920 void* header; // internal message header (whole buffer: header+payload)
921 unsigned char* id; // if we need an ID in the message separate from the xaction id
922 int flags; // various MFL_ (private) flags as needed
923 int alloc_len; // the length of the allocated space (hdr+payload)
924 void* ring; // ring this buffer should be queued back to
925 int rts_fd; // SI fd for return to sender
926 int cookie; // cookie to detect user misuse of free'd msg
932 State vs Transport State
933 ------------------------
935 The state field reflects the state at the time the message
936 buffer is returned to the calling application. For a send
937 operation, if the state is not ``RMR_OK`` then the message
938 buffer references the payload that could not be sent, and
939 when the state is ``RMR_OK`` the buffer references a *fresh*
940 payload that the application may fill in.
942 When the state is not ``RMR_OK,`` C programmes may examine
943 the global ``errno`` value which RMR will have left set, if
944 it was set, by the underlying transport mechanism. In some
945 cases, wrapper modules are not able to directly access the
946 C-library ``errno`` value, and to assist with possible
947 transport error details, the send and receive operations
948 populate ``tp_state`` with the value of ``errno.``
950 Regardless of whether the application makes use of the
951 ``tp_state,`` or the ``errno`` value, it should be noted that
952 the underlying transport mechanism may not actually update
953 the errno value; in other words: it might not be accurate. In
954 addition, RMR populates the ``tp_state`` value in the message
955 buffer **only** when the state is not ``RMR_OK.``
961 The transaction field was exposed in the first version of
962 RMR, and in hindsight this shouldn't have been done. Rather
963 than break any existing code the reference was left, but
964 additional fields such as trace data, were not directly
965 exposed to the application. The application developer is
966 strongly encouraged to use the functions which get and set
967 the transaction ID rather than using the pointer directly;
968 any data overruns will not be detected if the reference is
971 In contrast, the payload reference should be used directly by
972 the application in the interest of speed and ease of
973 programming. The same care to prevent writing more bytes to
974 the payload buffer than it can hold must be taken by the
975 application. By the nature of the allocation of the payload
976 in transport space, RMR is unable to add guard bytes and/or
977 test for data overrun.
983 When RMR sends the application's message, the message buffer
984 is **not** transmitted. The transport buffer (tp_buf) which
985 contains the RMR header and application payload is the only
986 set of bytes which are transmitted. While it may seem to the
987 caller like the function ``rmr_send_msg()`` is returning a
988 new message buffer, the same struct is reused and only a new
989 transport buffer is allocated. The intent is to keep the
990 alloc/free cycles to a minimum.
994 Appendix C -- Glossary
995 ======================
997 Many terms in networking can be interpreted with multiple
998 meanings, and several terms used in various RMR documentation
999 are RMR specific. The following definitions are the meanings
1000 of terms used within RMR documentation and should help the
1001 reader to understand the intent of meaning.
1010 A programme which uses RMR to send and/or receive messages
1011 to/from another RMR based application.
1013 * - **Critical error**
1015 An error that RMR has encountered which will prevent further
1016 successful processing by RMR. Critical errors usually
1017 indicate that the application should abort.
1021 An RMR based application that is defined as being capable of
1022 receiving one or more types of messages (as defined by a
1025 * - **Environment variable**
1027 A key/value pair which is set externally to the application,
1028 but which is available to the application (and referenced
1029 libraries) through the ``getenv`` system call. Environment
1030 variables are the main method of communicating information
1031 such as port numbers to RMR.
1035 An abnormal condition that RMR has encountered, but will not
1036 affect the overall processing by RMR, but may impact certain
1037 aspects such as the ability to communicate with a specific
1038 endpoint. Errors generally indicate that something, usually
1039 external to RMR, must be addressed.
1043 The name of the host as returned by the ``gethostbyname``
1044 system call. In a containerised environment this might be the
1045 container or service name depending on how the container is
1046 started. From RMR's point of view, a host name can be used to
1047 resolve an *endpoint* definition in a *route* table.)
1051 Internet protocol. A low level transmission protocol which
1052 governs the transmission of datagrams across network
1055 * - **Listen socket**
1057 A *TCP* socket used to await incoming connection requests.
1058 Listen sockets are defined by an interface and port number
1059 combination where the port number is unique for the
1064 A series of bytes transmitted from the application to another
1065 RMR based application. A message is comprised of RMR specific
1066 data (a header), and application data (a payload).
1068 * - **Message buffer**
1070 A data structure used to describe a message which is to be
1071 sent or has been received. The message buffer includes the
1072 payload length, message type, message source, and other
1075 * - **Message type**
1077 A signed integer (0-32000) which identifies the type of
1078 message being transmitted, and is one of the two components
1079 of a *routing key.* See *Subscription ID.*
1083 The portion of a message which holds the user data to be
1084 transmitted to the remote *endpoint.* The payload contents
1085 are completely application defined.
1089 A set of information which defines the current state of the
1090 underlying transport connections that RMR is managing. The
1091 application will be give a context reference (pointer) that
1092 is supplied to most RMR functions as the first parameter.
1096 The method of selecting an *endpoint* from a list such that
1097 all *endpoints* are selected before starting at the head of
1102 A series of "rules" which define the possible *endpoints* for
1105 * - **Route table manager**
1107 An application responsible for building a *route table* and
1108 then distributing it to all applicable RMR based
1113 The process of selecting an *endpoint* which will be the
1114 recipient of a message.
1118 A combination of *message type* and *subscription ID* which
1119 RMR uses to select the destination *endpoint* when sending a
1124 The sender of a message.
1126 * - **Subscription ID**
1128 A signed integer value (0-32000) which identifies the
1129 subscription characteristic of a message. It is used in
1130 conjunction with the *message type* to determine the *routing
1135 The *endpoint* selected to receive a message.
1139 Transmission Control Protocol. A connection based internet
1140 protocol which provides for lossless packet transportation,
1145 Also called a *process thread, or pthread.* This is a
1146 lightweight process which executes in concurrently with the
1147 application and shares the same address space. RMR uses
1148 threads to manage asynchronous functions such as route table
1151 * - **Trace information**
1153 An optional portion of the message buffer that the
1154 application may populate with data that allows for tracing
1155 the progress of the transaction or application activity
1156 across components. RMR makes no use of this data.
1158 * - **Transaction ID**
1160 A fixed number of bytes in the *message* buffer) which the
1161 application may populate with information related to the
1162 transaction. RMR makes use of the transaction ID for matching
1163 response messages with the &c function is used to send a
1166 * - **Transient failure**
1168 An error state that is believed to be short lived and that
1169 the operation, if retried by the application, might be
1170 successful. C programmers will recognise this as
1175 A warning occurs when RMR has encountered something that it
1176 believes isn't correct, but has a defined work round.
1180 A direct connection managed by RMR between the user
1181 application and a remote, RMR based, application.
1187 Appendix D -- Code Examples
1188 ===========================
1190 The following snippet of code illustrate some of the basic
1191 operation of the RMR library. Please refer to the examples
1192 and test directories in the RMR repository for complete RMR
1199 The following code segment shows how a message buffer can be
1200 allocated, populated, and sent. The snippet also illustrates
1201 how the result from the ``rmr_send_msg()`` function is used
1202 to send the next message. It does not illustrate error and/or
1214 #include <sys/epoll.h>
1217 #include <rmr/rmr.h>
1219 int main( int argc, char** argv ) {
1220 void* mrc; // msg router context
1221 struct epoll_event events[1]; // list of events to give to epoll
1222 struct epoll_event epe; // event definition for event to listen to
1223 int ep_fd = -1; // epoll's file des (given to epoll_wait)
1224 int rcv_fd; // file des for epoll checks
1225 int nready; // number of events ready for receive
1226 rmr_mbuf_t* sbuf; // send buffer
1227 rmr_mbuf_t* rbuf; // received buffer
1230 char* listen_port = "43086";
1231 int delay = 1000000; // mu-sec delay between messages
1233 int stats_freq = 100;
1235 if( argc > 1 ) { // simplistic arg picking
1236 listen_port = argv[1];
1239 delay = atoi( argv[2] );
1242 mtype = atoi( argv[3] );
1245 fprintf( stderr, "<DEMO> listen port: %s; mtype: %d; delay: %d\\n",
1246 listen_port, mtype, delay );
1248 if( (mrc = rmr_init( listen_port, 1400, RMRFL_NONE )) == NULL ) {
1249 fprintf( stderr, "<DEMO> unable to initialise RMR\\n" );
1253 rcv_fd = rmr_get_rcvfd( mrc ); // set up epoll things, start by getting the FD from RMR
1255 fprintf( stderr, "<DEMO> unable to set up polling fd\\n" );
1258 if( (ep_fd = epoll_create1( 0 )) < 0 ) {
1259 fprintf( stderr, "[FAIL] unable to create epoll fd: %d\\n", errno );
1262 epe.events = EPOLLIN;
1263 epe.data.fd = rcv_fd;
1265 if( epoll_ctl( ep_fd, EPOLL_CTL_ADD, rcv_fd, &epe ) != 0 ) {
1266 fprintf( stderr, "[FAIL] epoll_ctl status not 0 : %s\\n", strerror( errno ) );
1270 sbuf = rmr_alloc_msg( mrc, 256 ); // alloc 1st send buf; subsequent bufs alloc on send
1271 rbuf = NULL; // don't need to alloc receive buffer
1273 while( ! rmr_ready( mrc ) ) { // must have route table
1274 sleep( 1 ); // wait til we get one
1276 fprintf( stderr, "<DEMO> rmr is ready\\n" );
1279 while( 1 ) { // send messages until the cows come home
1280 snprintf( sbuf->payload, 200,
1281 "count=%d received= %d ts=%lld %d stand up and cheer!", // create the payload
1282 count, rcvd_count, (long long) time( NULL ), rand() );
1284 sbuf->mtype = mtype; // fill in the message bits
1285 sbuf->len = strlen( sbuf->payload ) + 1; // send full ascii-z string
1287 sbuf = rmr_send_msg( mrc, sbuf ); // send & get next buf to fill in
1288 while( sbuf->state == RMR_ERR_RETRY ) { // soft failure (device busy?) retry
1289 sbuf = rmr_send_msg( mrc, sbuf ); // w/ simple spin that doesn't give up
1293 // check to see if anything was received and pull all messages in
1294 while( (nready = epoll_wait( ep_fd, events, 1, 0 )) > 0 ) { // 0 is non-blocking
1295 if( events[0].data.fd == rcv_fd ) { // waiting on 1 thing, so [0] is ok
1297 rbuf = rmr_rcv_msg( mrc, rbuf ); // receive and ignore; just count
1304 if( (count % stats_freq) == 0 ) { // occasional stats out to tty
1305 fprintf( stderr, "<DEMO> sent %d received %d\\n", count, rcvd_count );
1318 The receiver code is even simpler than the sender code as it
1319 does not need to wait for a route table to arrive (only
1320 senders need to do that), nor does it need to allocate an
1321 initial buffer. The example assumes that the sender is
1322 transmitting a zero terminated string as the payload.
1334 #include <rmr/rmr.h>
1337 int main( int argc, char** argv ) {
1338 void* mrc; // msg router context
1339 long long total = 0;
1340 rmr_mbuf_t* msg = NULL; // message received
1341 int stat_freq = 10; // write stats after reciving this many messages
1343 char* listen_port = "4560"; // default to what has become the standard RMR port
1344 long long count = 0;
1346 long long empty = 0;
1349 listen_port = argv[1];
1352 stat_freq = atoi( argv[2] );
1354 fprintf( stderr, "<DEMO> listening on port: %s\\n", listen_port );
1355 fprintf( stderr, "<DEMO> stats will be reported every %d messages\\n", stat_freq );
1357 mrc = rmr_init( listen_port, RMR_MAX_RCV_BYTES, RMRFL_NONE );
1359 fprintf( stderr, "<DEMO> ABORT: unable to initialise RMr\\n" );
1363 while( ! rmr_ready( mrc ) ) { // wait for RMR to get a route table
1364 fprintf( stderr, "<DEMO> waiting for ready\\n" );
1367 fprintf( stderr, "<DEMO> rmr now shows ready\\n" );
1369 while( 1 ) { // receive until killed
1370 msg = rmr_rcv_msg( mrc, msg ); // block until one arrives
1373 if( msg->state == RMR_OK ) {
1374 count++; // nothing fancy, just count
1382 if( (count % stat_freq) == 0 ) {
1383 fprintf( stderr, "<DEMO> total received: %lld; errors: %lld; empty: %lld\\n",
1384 count, bad, empty );
1392 Receive and Send Sample
1393 -----------------------
1395 The following code snippet receives messages and responds to
1396 the sender if the message type is odd. The code illustrates
1397 how the received message may be used to return a message to
1398 the source. Variable type definitions are omitted for clarity
1399 and should be obvious.
1401 It should also be noted that things like the message type
1402 which id returned to the sender (99) is a random value that
1403 these applications would have agreed on in advance and is
1404 **not** an RMR definition.
1409 mrc = rmr_init( listen_port, MAX_BUF_SZ, RMRFL_NOFLAGS );
1410 rmr_set_stimeout( mrc, 1 ); // allow RMR to retry failed sends for ~1ms
1412 while( ! rmr_ready( mrc ) ) { // we send, therefore we need a route table
1416 mbuf = NULL; // ensure our buffer pointer is nil for 1st call
1419 mbuf = rmr_rcv_msg( mrc, mbuf ); // wait for message
1421 if( mbuf == NULL || mbuf->state != RMR_OK ) {
1425 if( mbuf->mtype % 2 ) { // respond to odd message types
1426 plen = rmr_payload_size( mbuf ); // max size
1428 // reset necessary fields in msg
1429 mbuf->mtype = 99; // response type
1430 mbuf->sub_id = RMR_VOID_SUBID; // we turn subid off
1431 mbuf->len = snprintf( mbuf->payload, plen, "pong: %s", get_info() );
1433 mbuf = rmr_rts_msg( mrc, mbuf ); // return to sender
1434 if( mbuf == NULL || mbuf->state != RMR_OK ) {
1435 fprintf( stderr, "return to sender failed\\n" );
1440 fprintf( stderr, "abort: receive failure\\n" );
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