1ei_connect(3) C Library Functions ei_connect(3)
2
6 ei_connect - Communicate with distributed Erlang.
7
9 This module enables C-programs to communicate with Erlang nodes, using
10 the Erlang distribution over TCP/IP.
11 A C-node appears to Erlang as a hidden node. That is, Erlang processes
13 that know the name of the C-node can communicate with it in a normal
14 manner, but the node name is not shown in the listing provided by er‐
15 lang:nodes/0 in ERTS.
16 The environment variable ERL_EPMD_PORT can be used to indicate which
18 logical cluster a C-node belongs to.
19
21 Most functions appear in a version with the suffix _tmo appended to the
22 function name. Those functions take an extra argument, a time-out in
23 milliseconds. The semantics is this: for each communication primitive
24 involved in the operation, if the primitive does not complete within
25 the time specified, the function returns an error and erl_errno is set
26 to ETIMEDOUT. With communication primitive is meant an operation on the
27 socket, like connect, accept, recv, or send.
28 Clearly the time-outs are for implementing fault tolerance, not to keep
30 hard real-time promises. The _tmo functions are for detecting non-re‐
31 sponsive peers and to avoid blocking on socket operations.
32 A time-out value of 0 (zero) means that time-outs are disabled. Calling
34 a _tmo function with the last argument as 0 is therefore the same thing
35 as calling the function without the _tmo suffix.
36 As with all other functions starting with ei_, you are not expected to
38 put the socket in non-blocking mode yourself in the program. Every use
39 of non-blocking mode is embedded inside the time-out functions. The
40 socket will always be back in blocking mode after the operations are
41 completed (regardless of the result). To avoid problems, leave the
42 socket options alone. ei handles any socket options that need modifica‐
43 tion.
44 In all other senses, the _tmo functions inherit all the return values
46 and the semantics from the functions without the _tmo suffix.
47
49 By default ei supplies a TCP/IPv4 socket interface that is used when
50 communicating. The user can however plug in his/her own IPv4 socket im‐
51 plementation. This, for example, in order to communicate over TLS. A
52 user supplied socket implementation is plugged in by passing a callback
53 structure to either ei_connect_init_ussi() or ei_connect_xinit_ussi().
54 All callbacks in the ei_socket_callbacks structure should return zero
56 on success; and a posix error code on failure.
57 The addr argument of the listen, accept, and connect callbacks refer to
59 appropriate address structure for currently used protocol. Currently ei
60 only supports IPv4. That is, at this time addr always points to a
61 struct sockaddr_in structure.
62 The ei_socket_callbacks structure may be enlarged in the future. All
64 fields not set, needs to be zeroed out. Currently the following fields
65 exist:
66 flags:
68 Flags informing ei about the behaviour of the callbacks. Flags
69 should be bitwise or:ed together. If no flag, is set, the flags
70 field should contain 0. Currently, supported flags:
71 EI_SCLBK_FLG_FULL_IMPL:
73 If set, the accept(), connect(), writev(), write(), and read()
74 callbacks implements timeouts. The timeout is passed in the tmo
75 argument and is given in milli seconds. Note that the tmo argu‐
76 ment to these callbacks differ from the timeout arguments in the
77 ei API. Zero means a zero timeout. That is, poll and timeout im‐
78 mediately unless the operation is successful. EI_SCLBK_INF_TMO
79 (max unsigned) means infinite timeout. The file descriptor is in
80 blocking mode when a callback is called, and it must be in block‐
81 ing mode when the callback returns.
82 If not set, ei will implement the timeout using select() in order
84 to determine when to call the callbacks and when to time out. The
85 tmo arguments of the accept(), connect(), writev(), write(), and
86 read() callbacks should be ignored. The callbacks may be called
87 in non-blocking mode. The callbacks are not allowed to change be‐
88 tween blocking and non-blocking mode. In order for this to work,
89 select() needs to interact with the socket primitives used the
90 same way as it interacts with the ordinary socket primitives. If
91 this is not the case, the callbacks need to implement timeouts
92 and this flag should be set.
93 More flags may be introduced in the future.
95 int (*socket)(void **ctx, void *setup_ctx):
97 Create a socket and a context for the socket.
98 On success it should set *ctx to point to a context for the created
100 socket. This context will be passed to all other socket callbacks.
101 This function will be passed the same setup_context as passed to
102 the preceding ei_connect_init_ussi() or ei_connect_xinit_ussi()
103 call.
104 Note:
106 During the lifetime of a socket, the pointer *ctx has to remain the
107 same. That is, it cannot later be relocated.
108 This callback is mandatory.
111 int (*close)(void *ctx):
113 Close the socket identified by ctx and destroy the context.
114 This callback is mandatory.
116 int (*listen)(void *ctx, void *addr, int *len, int backlog):
118 Bind the socket identified by ctx to a local interface and then
119 listen on it.
120 The addr and len arguments are both input and output arguments.
122 When called addr points to an address structure of length *len con‐
123 taining information on how to bind the socket. Upon return this
124 callback should have updated the structure referred by addr with
125 information on how the socket actually was bound. *len should be
126 updated to reflect the size of *addr updated. backlog identifies
127 the size of the backlog for the listen socket.
128 This callback is mandatory.
130 int (*accept)(void **ctx, void *addr, int *len, unsigned tmo):
132 Accept connections on the listen socket identified by *ctx.
133 When a connection is accepted, a new context for the accepted con‐
135 nection should be created and *ctx should be updated to point to
136 the new context for the accepted connection. When called addr
137 points to an uninitialized address structure of length *len. Upon
138 return this callback should have updated this structure with infor‐
139 mation about the client address. *len should be updated to reflect
140 the size of *addr updated.
141 If the EI_SCLBK_FLG_FULL_IMPL flag has been set, tmo contains time‐
143 out time in milliseconds.
144 Note:
146 During the lifetime of a socket, the pointer *ctx has to remain the
147 same. That is, it cannot later be relocated.
148 This callback is mandatory.
151 int (*connect)(void *ctx, void *addr, int len, unsigned tmo):
153 Connect the socket identified by ctx to the address identified by
154 addr.
155 When called addr points to an address structure of length len con‐
157 taining information on where to connect.
158 If the EI_SCLBK_FLG_FULL_IMPL flag has been set, tmo contains time‐
160 out time in milliseconds.
161 This callback is mandatory.
163 int (*writev)(void *ctx, const void *iov, long iovcnt, ssize_t *len,
165 unsigned tmo):
166 Write data on the connected socket identified by ctx.
167 iov points to an array of struct iovec structures of length iovcnt
169 containing data to write to the socket. On success, this callback
170 should set *len to the amount of bytes successfully written on the
171 socket.
172 If the EI_SCLBK_FLG_FULL_IMPL flag has been set, tmo contains time‐
174 out time in milliseconds.
175 This callback is optional. Set the writev field in the the
177 ei_socket_callbacks structure to NULL if not implemented.
178 int (*write)(void *ctx, const char *buf, ssize_t *len, unsigned tmo):
180 Write data on the connected socket identified by ctx.
181 When called buf points to a buffer of length *len containing the
183 data to write on the socket. On success, this callback should set
184 *len to the amount of bytes successfully written on the socket.
185 If the EI_SCLBK_FLG_FULL_IMPL flag has been set, tmo contains time‐
187 out time in milliseconds.
188 This callback is mandatory.
190 int (*read)(void *ctx, char *buf, ssize_t *len, unsigned tmo):
192 Read data on the connected socket identified by ctx.
193 buf points to a buffer of length *len where the read data should be
195 placed. On success, this callback should update *len to the amount
196 of bytes successfully read on the socket.
197 If the EI_SCLBK_FLG_FULL_IMPL flag has been set, tmo contains time‐
199 out time in milliseconds.
200 This callback is mandatory.
202 int (*handshake_packet_header_size)(void *ctx, int *sz):
204 Inform about handshake packet header size to use during the Erlang
205 distribution handshake.
206 On success, *sz should be set to the handshake packet header size
208 to use. Valid values are 2 and 4. Erlang TCP distribution use a
209 handshake packet size of 2 and Erlang TLS distribution use a hand‐
210 shake packet size of 4.
211 This callback is mandatory.
213 int (*connect_handshake_complete)(void *ctx):
215 Called when a locally started handshake has completed successfully.
216 This callback is optional. Set the connect_handshake_complete field
218 in the ei_socket_callbacks structure to NULL if not implemented.
219 int (*accept_handshake_complete)(void *ctx):
221 Called when a remotely started handshake has completed success‐
222 fully.
223 This callback is optional. Set the accept_handshake_complete field
225 in the ei_socket_callbacks structure to NULL if not implemented.
226 int (*get_fd)(void *ctx, int *fd):
228 Inform about file descriptor used by the socket which is identified
229 by ctx.
230 Note:
232 During the lifetime of a socket, the file descriptor has to remain
233 the same. That is, repeated calls to this callback with the same con‐
234 text should always report the same file descriptor.
235 The file descriptor has to be a real file descriptor. That is, no
237 other operation should be able to get the same file descriptor until
238 it has been released by the close() callback.
239 This callback is mandatory.
242
244 ei_cnode:
245 Opaque data type representing a C-node. A ei_cnode structure is
246 initialized by calling ei_connect_init() or friends.
247 ei_socket_callbacks:
249 typedef struct {
252 int flags;
253 int (*socket)(void **ctx, void *setup_ctx);
254 int (*close)(void *ctx);
255 int (*listen)(void *ctx, void *addr, int *len, int backlog);
256 int (*accept)(void **ctx, void *addr, int *len, unsigned tmo);
257 int (*connect)(void *ctx, void *addr, int len, unsigned tmo);
258 int (*writev)(void *ctx, const void *iov, int iovcnt, ssize_t *len, unsigned tmo);
259 int (*write)(void *ctx, const char *buf, ssize_t *len, unsigned tmo);
260 int (*read)(void *ctx, char *buf, ssize_t *len, unsigned tmo);
261 int (*handshake_packet_header_size)(void *ctx, int *sz);
262 int (*connect_handshake_complete)(void *ctx);
263 int (*accept_handshake_complete)(void *ctx);
264 int (*get_fd)(void *ctx, int *fd);
265 } ei_socket_callbacks;
266 Callbacks functions for a User Supplied Socket Implementation .
268 Documentation of each field can be found in the User Supplied
269 Socket Implementation section above.
270 ErlConnect:
272 typedef struct {
275 char ipadr[4]; /* Ip v4 address in network byte order */
276 char nodename[MAXNODELEN];
277 } ErlConnect;
278 IP v4 address and nodename.
280 Erl_IpAddr:
282 typedef struct {
285 unsigned s_addr; /* Ip v4 address in network byte order */
286 } Erl_IpAddr;
287 IP v4 address.
289 erlang_msg:
291 typedef struct {
294 long msgtype;
295 erlang_pid from;
296 erlang_pid to;
297 char toname[MAXATOMLEN+1];
298 char cookie[MAXATOMLEN+1];
299 erlang_trace token;
300 } erlang_msg;
301 Information about a message received via ei_receive_msg() or
303 friends.
304
306 struct hostent *ei_gethostbyaddr(const char *addr, int len, int type)
307 struct hostent *ei_gethostbyaddr_r(const char *addr, int length, int
308 type, struct hostent *hostp, char *buffer, int buflen, int *h_er‐
309 rnop)
310 struct hostent *ei_gethostbyname(const char *name)
311 struct hostent *ei_gethostbyname_r(const char *name, struct hostent
312 *hostp, char *buffer, int buflen, int *h_errnop)
313 Convenience functions for some common name lookup functions.
315 int ei_accept(ei_cnode *ec, int listensock, ErlConnect *conp)
317 Types:
319 ei_cnode
321 ErlConnect
322 Used by a server process to accept a connection from a client
324 process.
325 * ec is the C-node structure.
327 * listensock is an open socket descriptor on which listen()
329 has previously been called.
330 * conp is a pointer to an ErlConnect struct.
332 On success, conp is filled in with the address and node name of
334 the connecting client and a file descriptor is returned. On
335 failure, ERL_ERROR is returned and erl_errno is set to EIO.
336 int ei_accept_tmo(ei_cnode *ec, int listensock, ErlConnect *conp, un‐
338 signed timeout_ms)
339 Types:
341 ei_cnode
343 ErlConnect
344 Equivalent to ei_accept with an optional time-out argument, see
346 the description at the beginning of this manual page.
347 int ei_close_connection(int fd)
349 Closes a previously opened connection or listen socket.
351 int ei_connect(ei_cnode* ec, char *nodename)
353 int ei_xconnect(ei_cnode* ec, Erl_IpAddr adr, char *alivename)
354 int ei_connect_host_port(ei_cnode* ec, char *hostname, int port)
355 int ei_xconnect_host_port(ei_cnode* ec, Erl_IpAddr adr, int port)
356 Types:
358 ei_cnode
360 Erl_IpAddr
361 Sets up a connection to an Erlang node.
363 ei_xconnect() requires the IP address of the remote host and the
365 alive name of the remote node to be specified. ei_connect() pro‐
366 vides an alternative interface and determines the information
367 from the node name provided. The ei_xconnect_host_port() func‐
368 tion provides yet another alternative that will work even if
369 there is no EPMD instance on the host where the remote node is
370 running. The ei_xconnect_host_port() function requires the IP
371 address and port of the remote node to be specified. The ei_con‐
372 nect_host_port() function is an alternative to ei_xcon‐
373 nect_host_port() that lets the user specify a hostname instead
374 of an IP address.
375 * adr is the 32-bit IP address of the remote host.
377 * alive is the alivename of the remote node.
379 * node is the name of the remote node.
381 * port is the port number of the remote node.
383 These functions return an open file descriptor on success, or a
385 negative value indicating that an error occurred. In the latter
386 case they set erl_errno to one of the following:
387 EHOSTUNREACH:
389 The remote host node is unreachable.
390 ENOMEM:
392 No more memory is available.
393 EIO:
395 I/O error.
396 Also, errno values from socket(2) and connect(2) system calls
398 may be propagated into erl_errno.
399 Example:
401 #define NODE "madonna@chivas.du.etx.ericsson.se"
403 #define ALIVE "madonna"
404 #define IP_ADDR "150.236.14.75"
405 /*** Variant 1 ***/
407 int fd = ei_connect(&ec, NODE);
408 /*** Variant 2 ***/
410 struct in_addr addr;
411 addr.s_addr = inet_addr(IP_ADDR);
412 fd = ei_xconnect(&ec, &addr, ALIVE);
413 int ei_connect_init(ei_cnode* ec, const char* this_node_name, const
416 char *cookie, unsigned creation)
417 int ei_connect_init_ussi(ei_cnode* ec, const char* this_node_name,
418 const char *cookie, unsigned creation, ei_socket_callbacks *cbs, int
419 cbs_sz, void *setup_context)
420 int ei_connect_xinit(ei_cnode* ec, const char *thishostname, const char
421 *thisalivename, const char *thisnodename, Erl_IpAddr thisipaddr, const
422 char *cookie, unsigned creation)
423 int ei_connect_xinit_ussi(ei_cnode* ec, const char *thishostname, const
424 char *thisalivename, const char *thisnodename, Erl_IpAddr thisipaddr,
425 const char *cookie, unsigned creation, ei_socket_callbacks *cbs, int
426 cbs_sz, void *setup_context)
427 Types:
429 ei_cnode
431 Erl_IpAddr
432 ei_socket_callbacks
433 Initializes the ec structure, to identify the node name and
435 cookie of the server. One of them must be called before other
436 functions that works on the ei_cnode type or a file descriptor
437 associated with a connection to another node is used.
438 * ec is a structure containing information about the C-node.
440 It is used in other ei functions for connecting and receiv‐
441 ing data.
442 * this_node_name is the name of the C-node (the name before
444 '@' in the full node name).
445 * cookie is the cookie for the node.
447 * creation identifies a specific instance of a C-node. It can
449 help prevent the node from receiving messages sent to an
450 earlier process with the same registered name.
451 Note:
453 The type of the creation argument was changed from short (16
454 bit) to unsigned int (32 bit) in OTP 25. This should cause no
455 practical problem other than maybe a compiler warning.
456 * thishostname is the name of the machine we are running on.
459 If long names are to be used, they are to be fully qualified
460 (that is, durin.erix.ericsson.se instead of durin).
461 * thisalivename is the name of the local C-node (the name be‐
463 fore '@' in the full node name). Can be NULL (from OTP 23)
464 to get a dynamically assigned name from the peer node.
465 * thisnodename is the full name of the local C-node, that is,
467 mynode@myhost. Can be NULL if thisalivename is NULL.
468 * thispaddr if the IP address of the host.
470 * cbs is a pointer to a callback structure implementing and
472 alternative socket interface.
473 * cbs_sz is the size of the structure pointed to by cbs.
475 * setup_context is a pointer to a structure that will be
477 passed as second argument to the socket callback in the cbs
478 structure.
479 A C-node acting as a server is assigned a creation number when
481 it calls ei_publish().
482 A connection is closed by simply closing the socket. For infor‐
484 mation about how to close the socket gracefully (when there are
485 outgoing packets before close), see the relevant system documen‐
486 tation.
487 These functions return a negative value indicating that an error
489 occurred.
490 Example 1:
492 unsigned n = 0;
494 struct in_addr addr;
495 ei_cnode ec;
496 addr.s_addr = inet_addr("150.236.14.75");
497 if (ei_connect_xinit(&ec,
498 "chivas",
499 "madonna",
500 "madonna@chivas.du.etx.ericsson.se",
501 &addr;
502 "cookie...",
503 n++) < 0) {
504 fprintf(stderr,"ERROR when initializing: %d",erl_errno);
505 exit(-1);
506 }
507 Example 2:
510 if (ei_connect_init(&ec, "madonna", "cookie...", n++) < 0) {
512 fprintf(stderr,"ERROR when initializing: %d",erl_errno);
513 exit(-1);
514 }
515 int ei_connect_tmo(ei_cnode* ec, char *nodename, unsigned timeout_ms)
518 int ei_xconnect_tmo(ei_cnode* ec, Erl_IpAddr adr, char *alivename, un‐
519 signed timeout_ms)
520 int ei_connect_host_port_tmo(ei_cnode* ec, char *hostname, int port,
521 unsigned ms)
522 int ei_xconnect_host_port_tmo(ei_cnode* ec, Erl_IpAddr adr, int port,
523 unsigned ms)
524 Types:
526 ei_cnode
528 Erl_IpAddr
529 Equivalent to ei_connect, ei_xconnect, ei_connect_host_port and
531 ei_xconnect_host_port with an optional time-out argument, see
532 the description at the beginning of this manual page.
533 int ei_get_tracelevel(void)
535 void ei_set_tracelevel(int level)
536 Used to set tracing on the distribution. The levels are differ‐
538 ent verbosity levels. A higher level means more information. See
539 also section Debug Information.
540 These functions are not thread safe.
542 int ei_listen(ei_cnode *ec, int *port, int backlog)
544 int ei_xlisten(ei_cnode *ec, Erl_IpAddr adr, int *port, int backlog)
545 Types:
547 ei_cnode
549 Erl_IpAddr
550 Used by a server process to setup a listen socket which later
552 can be used for accepting connections from client processes.
553 * ec is the C-node structure.
555 * adr is local interface to bind to.
557 * port is a pointer to an integer containing the port number
559 to bind to. If *port equals 0 when calling ei_listen(), the
560 socket will be bound to an ephemeral port. On success,
561 ei_listen() will update the value of *port to the port actu‐
562 ally bound to.
563 * backlog is maximum backlog of pending connections.
565 ei_listen will create a socket, bind to a port on the local in‐
567 terface identified by adr (or all local interfaces if ei_lis‐
568 ten() is called), and mark the socket as a passive socket (that
569 is, a socket that will be used for accepting incoming connec‐
570 tions).
571 On success, a file descriptor is returned which can be used in a
573 call to ei_accept(). On failure, ERL_ERROR is returned and
574 erl_errno is set to EIO.
575 int ei_make_pid(ei_cnode *ec, erlang_pid *pid)
577 Types:
579 ei_cnode
581 erlang_pid
582 Creates a new process identifier in the argument pid. This
584 process identifier refers to a conseptual process residing on
585 the C-node identified by the argument ec. On success 0 is re‐
586 turned. On failure ERL_ERROR is returned and erl_errno is set.
587 The C-node identified by ec must have been initialized and must
589 have received a name prior to the call to ei_make_pid(). Ini‐
590 tialization of the C-node is done by a call to ei_connect_init()
591 or friends. If the name is dynamically assigned from the peer
592 node, the C-node also has to be connected.
593 int ei_make_ref(ei_cnode *ec, erlang_ref *ref)
595 Types:
597 ei_cnode
599 erlang_ref
600 Creates a new reference in the argument ref. This reference
602 originates from the C-node identified by the argument ec. On
603 success 0 is returned. On failure ERL_ERROR is returned and
604 erl_errno is set.
605 The C-node identified by ec must have been initialized and must
607 have received a name prior to the call to ei_make_ref(). Ini‐
608 tialization of the C-node is done by a call to ei_connect_init()
609 or friends. If the name is dynamically assigned from the peer
610 node, the C-node also has to be connected.
611 int ei_publish(ei_cnode *ec, int port)
613 Types:
615 ei_cnode
617 Used by a server process to register with the local name server
619 EPMD, thereby allowing other processes to send messages by using
620 the registered name. Before calling either of these functions,
621 the process should have called bind() and listen() on an open
622 socket.
623 * ec is the C-node structure.
625 * port is the local name to register, and is to be the same as
627 the port number that was previously bound to the socket.
628 * addr is the 32-bit IP address of the local host.
630 To unregister with EPMD, simply close the returned descriptor.
632 Do not use ei_unpublish(), which is deprecated anyway.
633 On success, the function returns a descriptor connecting the
635 calling process to EPMD. On failure, -1 is returned and erl_er‐
636 rno is set to EIO.
637 Also, errno values from socket(2) and connect(2) system calls
639 may be propagated into erl_errno.
640 int ei_publish_tmo(ei_cnode *ec, int port, unsigned timeout_ms)
642 Types:
644 ei_cnode
646 Equivalent to ei_publish with an optional time-out argument, see
648 the description at the beginning of this manual page.
649 int ei_receive(int fd, unsigned char* bufp, int bufsize)
651 Receives a message consisting of a sequence of bytes in the Er‐
653 lang external format.
654 * fd is an open descriptor to an Erlang connection. It is ob‐
656 tained from a previous ei_connect or ei_accept.
657 * bufp is a buffer large enough to hold the expected message.
659 * bufsize indicates the size of bufp.
661 If a tick occurs, that is, the Erlang node on the other end of
663 the connection has polled this node to see if it is still alive,
664 the function returns ERL_TICK and no message is placed in the
665 buffer. Also, erl_errno is set to EAGAIN.
666 On success, the message is placed in the specified buffer and
668 the function returns the number of bytes actually read. On fail‐
669 ure, the function returns ERL_ERROR and sets erl_errno to one of
670 the following:
671 EAGAIN:
673 Temporary error: Try again.
674 EMSGSIZE:
676 Buffer is too small.
677 EIO:
679 I/O error.
680 int ei_receive_encoded(int fd, char **mbufp, int *bufsz, erlang_msg
682 *msg, int *msglen)
683 Types:
685 erlang_msg
687 This function is retained for compatibility with code generated
689 by the interface compiler and with code following examples in
690 the same application.
691 In essence, the function performs the same operation as ei_xre‐
693 ceive_msg, but instead of using an ei_x_buff, the function ex‐
694 pects a pointer to a character pointer (mbufp), where the char‐
695 acter pointer is to point to a memory area allocated by malloc.
696 Argument bufsz is to be a pointer to an integer containing the
697 exact size (in bytes) of the memory area. The function may re‐
698 allocate the memory area and will in such cases put the new size
699 in *bufsz and update *mbufp.
700 Returns either ERL_TICK or the msgtype field of the erlang_msg
702 *msg. The length of the message is put in *msglen. On error a
703 value < 0 is returned.
704 It is recommended to use ei_xreceive_msg instead when possible,
706 for the sake of readability. However, the function will be re‐
707 tained in the interface for compatibility and will not be re‐
708 moved in future releases without prior notice.
709 int ei_receive_encoded_tmo(int fd, char **mbufp, int *bufsz, er‐
711 lang_msg *msg, int *msglen, unsigned timeout_ms)
712 Types:
714 erlang_msg
716 Equivalent to ei_receive_encoded with an optional time-out argu‐
718 ment, see the description at the beginning of this manual page.
719 int ei_receive_msg(int fd, erlang_msg* msg, ei_x_buff* x)
721 int ei_xreceive_msg(int fd, erlang_msg* msg, ei_x_buff* x)
722 Types:
724 ei_x_buff
726 erlang_msg
727 Receives a message to the buffer in x. ei_xreceive_msg allows
729 the buffer in x to grow, but ei_receive_msg fails if the message
730 is larger than the pre-allocated buffer in x.
731 * fd is an open descriptor to an Erlang connection.
733 * msg is a pointer to an erlang_msg structure and contains in‐
735 formation on the message received.
736 * x is buffer obtained from ei_x_new.
738 On success, the functions return ERL_MSG and the msg struct is
740 initialized.
741 msgtype identifies the type of message, and is one of the fol‐
743 lowing:
744 ERL_SEND:
746 Indicates that an ordinary send operation has occurred.
747 msg->to contains the pid of the recipient (the C-node).
748 ERL_REG_SEND:
750 A registered send operation occurred. msg->from contains the
751 pid of the sender.
752 ERL_LINK or ERL_UNLINK:
754 msg->to and msg->from contain the pids of the sender and re‐
755 cipient of the link or unlink.
756 ERL_EXIT:
758 Indicates a broken link. msg->to and msg->from contain the
759 pids of the linked processes.
760 The return value is the same as for ei_receive.
762 int ei_receive_msg_tmo(int fd, erlang_msg* msg, ei_x_buff* x, unsigned
764 imeout_ms)
765 int ei_xreceive_msg_tmo(int fd, erlang_msg* msg, ei_x_buff* x, unsigned
766 timeout_ms)
767 Types:
769 ei_x_buff
771 erlang_msg
772 Equivalent to ei_receive_msg and ei_xreceive_msg with an op‐
774 tional time-out argument, see the description at the beginning
775 of this manual page.
776 int ei_receive_tmo(int fd, unsigned char* bufp, int bufsize, unsigned
778 timeout_ms)
779 Equivalent to ei_receive with an optional time-out argument, see
781 the description at the beginning of this manual page.
782 int ei_reg_send(ei_cnode* ec, int fd, char* server_name, char* buf, int
784 len)
785 Types:
787 ei_cnode
789 Sends an Erlang term to a registered process.
791 * fd is an open descriptor to an Erlang connection.
793 * server_name is the registered name of the intended recipi‐
795 ent.
796 * buf is the buffer containing the term in binary format.
798 * len is the length of the message in bytes.
800 Returns 0 if successful, otherwise -1. In the latter case it
802 sets erl_errno to EIO.
803 Example:
805 Send the atom "ok" to the process "worker":
807 ei_x_buff x;
809 ei_x_new_with_version(&x);
810 ei_x_encode_atom(&x, "ok");
811 if (ei_reg_send(&ec, fd, x.buff, x.index) < 0)
812 handle_error();
813 int ei_reg_send_tmo(ei_cnode* ec, int fd, char* server_name, char* buf,
816 int len, unsigned timeout_ms)
817 Types:
819 ei_cnode
821 Equivalent to ei_reg_send with an optional time-out argument,
823 see the description at the beginning of this manual page.
824 int ei_rpc(ei_cnode *ec, int fd, char *mod, char *fun, const char *arg‐
826 buf, int argbuflen, ei_x_buff *x)
827 int ei_rpc_to(ei_cnode *ec, int fd, char *mod, char *fun, const char
828 *argbuf, int argbuflen)
829 int ei_xrpc_to(ei_cnode *ec, int fd, char *mod, char *fun, const char
830 *argbuf, int argbuflen, int flags)
831 int ei_rpc_from(ei_cnode *ec, int fd, int timeout, erlang_msg *msg,
832 ei_x_buff *x)
833 Types:
835 ei_cnode
837 ei_x_buff
838 erlang_msg
839 Supports calling Erlang functions on remote nodes. ei_rpc_to()
841 sends an RPC request to a remote node and ei_rpc_from() receives
842 the results of such a call. ei_rpc() combines the functionality
843 of these two functions by sending an RPC request and waiting for
844 the results.
845 The ei_xrpc_to() function is equivalent to ei_rpc_to() when its
847 flags parameter is set to 0. When the flags parameter of
848 ei_xrpc_to() is set to EI_RPC_FETCH_STDOUT, stdout (standard
849 output) data are forwarded. See the documentation for the flags
850 parameter for more information about the EI_RPC_FETCH_STDOUT
851 flag.
852 rpc:call/4 in Kernel.
854 * ec is the C-node structure previously initiated by a call to
856 ei_connect_init() or ei_connect_xinit().
857 * fd is an open descriptor to an Erlang connection.
859 * timeout is the maximum time (in milliseconds) to wait for
861 results. Specify ERL_NO_TIMEOUT to wait forever. ei_rpc()
862 waits infinitely for the answer, that is, the call will
863 never time out.
864 * mod is the name of the module containing the function to be
866 run on the remote node.
867 * fun is the name of the function to run.
869 * argbuf is a pointer to a buffer with an encoded Erlang list,
871 without a version magic number, containing the arguments to
872 be passed to the function.
873 * argbuflen is the length of the buffer containing the encoded
875 Erlang list.
876 * msg is structure of type erlang_msg and contains information
878 on the message received. For a description of the erlang_msg
879 format, see ei_receive_msg.
880 * x points to the dynamic buffer that receives the result. For
882 ei_rpc() this is the result without the version magic num‐
883 ber. For an ei_rpc_from() call the result consists of a ver‐
884 sion magic number and a 2-tuple. The 2-tuple can be in one
885 of the following two forms:
886 {rex,Reply}:
888 This response value means that the RPC has completed. The
889 result value is the Reply term. This is the only type of
890 response that one can get from an RPC triggered by a call
891 to ei_rpc_to() or ei_xrpc_to() without the
892 EI_RPC_FETCH_STDOUT flag. If the RPC was triggered by a
893 call to ei_xrpc_to() with the EI_RPC_FETCH_STDOUT flag
894 set, then all forwarded stdout data has been received.
895 {rex_stdout,StdOutUTF8Binary}:
897 This response value can only be obtained if the RPC call
898 was triggered by a call to ei_xrpc_to() with the
899 EI_RPC_FETCH_STDOUT flag set. This response value means
900 that forwarded stdout data has been received. The stdout
901 data is stored in a binary and is UTF-8 encoded. One may
902 need to call ei_rpc_from() multiple times to read all the
903 stdout data. The stdout data is received in the same order
904 as it was written. All forwarded stdout data have been re‐
905 ceived when a {rex,Reply} tuple has been obtained from an
906 ei_rpc_from() call.
907 * flags The flag EI_RPC_FETCH_STDOUT is currently the only
909 flag that is supported by ei_xrpc_to(). When
910 EI_RPC_FETCH_STDOUT is set, the called function is executed
911 in a new process with a group leader that forwards all std‐
912 out data. This means that stdout data that are written dur‐
913 ing the execution of the called function, by the called
914 function and by descendant processes, will be forwarded
915 (given that the group leader has not been changed by a call
916 to erlang:group_leader/2). The forwarded stdout data need to
917 be collected by a sequence of calls to ei_rpc_from(). See
918 the description of the x parameter for how ei_rpc_from() is
919 used to receive stdout data. See the documentation of the
920 the I/O protocol, for more information about the group
921 leader concept.
922 Note:
924 The flag EI_RPC_FETCH_STDOUT only works when interacting with
925 a node with a version greater or equal to OTP-24.
926 ei_rpc() returns the number of bytes in the result on success
929 and -1 on failure. ei_rpc_from() returns the number of bytes,
930 otherwise one of ERL_TICK, ERL_TIMEOUT, and ERL_ERROR. The func‐
931 tions ei_rpc_to() and ei_xrpc_to() returns 0 if successful, oth‐
932 erwise -1. When failing, all four functions set erl_errno to one
933 of the following:
934 EIO:
936 I/O error.
937 ETIMEDOUT:
939 Time-out expired.
940 EAGAIN:
942 Temporary error: Try again.
943 Example:
945 Check to see if an Erlang process is alive:
947 int index = 0, is_alive;
949 ei_x_buff args, result;
950 ei_x_new(&result);
952 ei_x_new(&args);
953 ei_x_encode_list_header(&args, 1);
954 ei_x_encode_pid(&args, &check_pid);
955 ei_x_encode_empty_list(&args);
956 if (ei_rpc(&ec, fd, "erlang", "is_process_alive",
958 args.buff, args.index, &result) < 0)
959 handle_error();
960 if (ei_decode_version(result.buff, &index) < 0
962 || ei_decode_bool(result.buff, &index, &is_alive) < 0)
963 handle_error();
964 erlang_pid *ei_self(ei_cnode *ec)
967 Types:
969 ei_cnode
971 erlang_pid
972 Retrieves a generic pid of the C-node. Every C-node has a
974 (pseudo) pid used in ei_send_reg, ei_rpc(), and others. This is
975 contained in a field in the ec structure. Do not modify this
976 structure.
977 On success a pointer to the process identifier is returned. On
979 failure NULL is returned and erl_errno is set.
980 The C-node identified by ec must have been initialized and must
982 have received a name prior to the call to ei_self(). Initializa‐
983 tion of the C-node is done by a call to ei_connect_init() or
984 friends. If the name is dynamically assigned from the peer node,
985 the C-node also has to be connected.
986 int ei_send(int fd, erlang_pid* to, char* buf, int len)
988 Types:
990 erlang_pid
992 Sends an Erlang term to a process.
994 * fd is an open descriptor to an Erlang connection.
996 * to is the pid of the intended recipient of the message.
998 * buf is the buffer containing the term in binary format.
1000 * len is the length of the message in bytes.
1002 Returns 0 if successful, otherwise -1. In the latter case it
1004 sets erl_errno to EIO.
1005 int ei_send_encoded(int fd, erlang_pid* to, char* buf, int len)
1007 Types:
1009 erlang_pid
1011 Works exactly as ei_send, the alternative name is retained for
1013 backward compatibility. The function will not be removed without
1014 prior notice.
1015 int ei_send_encoded_tmo(int fd, erlang_pid* to, char* buf, int len, un‐
1017 signed timeout_ms)
1018 Types:
1020 erlang_pid
1022 Equivalent to ei_send_encoded with an optional time-out argu‐
1024 ment, see the description at the beginning of this manual page.
1025 int ei_send_reg_encoded(int fd, const erlang_pid *from, const char *to,
1027 const char *buf, int len)
1028 Types:
1030 erlang_pid
1032 This function is retained for compatibility with code generated
1034 by the interface compiler and with code following examples in
1035 the same application.
1036 The function works as ei_reg_send with one exception. Instead of
1038 taking ei_cnode as first argument, it takes a second argument,
1039 an erlang_pid, which is to be the process identifier of the
1040 sending process (in the Erlang distribution protocol).
1041 A suitable erlang_pid can be retrieved from the ei_cnode struc‐
1043 ture by calling ei_self(cnode_pointer).
1044 int ei_send_reg_encoded_tmo(int fd, const erlang_pid *from, const char
1046 *to, const char *buf, int len, unsigned timeout_ms)
1047 Types:
1049 erlang_pid
1051 Equivalent to ei_send_reg_encoded with an optional time-out ar‐
1053 gument, see the description at the beginning of this manual
1054 page.
1055 int ei_send_tmo(int fd, erlang_pid* to, char* buf, int len, unsigned
1057 timeout_ms)
1058 Types:
1060 erlang_pid
1062 Equivalent to ei_send with an optional time-out argument, see
1064 the description at the beginning of this manual page.
1065 const char *ei_thisnodename(ei_cnode *ec)
1067 const char *ei_thishostname(ei_cnode *ec)
1068 const char *ei_thisalivename(ei_cnode *ec)
1069 Types:
1071 ei_cnode
1073 Can be used to retrieve information about the C-node. These val‐
1075 ues are initially set with ei_connect_init() or ei_con‐
1076 nect_xinit().
1077 These function simply fetch the appropriate field from the ec
1079 structure. Read the field directly will probably be safe for a
1080 long time, so these functions are not really needed.
1081 int ei_unpublish(ei_cnode *ec)
1083 Types:
1085 ei_cnode
1087 Can be called by a process to unregister a specified node from
1089 EPMD on the local host. This is, however, usually not allowed,
1090 unless EPMD was started with flag -relaxed_command_check, which
1091 it normally is not.
1092 To unregister a node you have published, you should close the
1094 descriptor that was returned by ei_publish().
1095 Warning:
1097 This function is deprecated and will be removed in a future re‐
1098 lease.
1099 ec is the node structure of the node to unregister.
1102 If the node was successfully unregistered from EPMD, the func‐
1104 tion returns 0. Otherwise, -1 is returned and erl_errno is set
1105 to EIO.
1106 int ei_unpublish_tmo(ei_cnode *ec, unsigned timeout_ms)
1108 Types:
1110 ei_cnode
1112 Equivalent to ei_unpublish with an optional time-out argument,
1114 see the description at the beginning of this manual page.
1115
1117 If a connection attempt fails, the following can be checked:
1118 * erl_errno.
1120 * That the correct cookie was used
1122 * That EPMD is running
1124 * That the remote Erlang node on the other side is running the same
1126 version of Erlang as the ei library
1127 * That environment variable ERL_EPMD_PORT is set correctly
1129 The connection attempt can be traced by setting a trace level by either
1131 using ei_set_tracelevel or by setting environment variable
1132 EI_TRACELEVEL. The trace levels have the following messages:
1133 * 1: Verbose error messages
1135 * 2: Above messages and verbose warning messages
1137 * 3: Above messages and progress reports for connection handling
1139 * 4: Above messages and progress reports for communication
1141 * 5: Above messages and progress reports for data conversion
1143Ericsson AB erl_interface 5.4 ei_connect(3)