1ei_connect(3) C Library Functions ei_connect(3)
2
6 ei_connect - Communicate with distributed Erlang.
7
9 Note:
10 The support for VxWorks is deprecated as of OTP 22, and will be removed
11 in OTP 23.
12 This module enables C-programs to communicate with Erlang nodes, using
15 the Erlang distribution over TCP/IP.
16 A C-node appears to Erlang as a hidden node. That is, Erlang processes
18 that know the name of the C-node can communicate with it in a normal
19 manner, but the node name is not shown in the listing provided by
20 erlang:nodes/0 in ERTS.
21 The environment variable ERL_EPMD_PORT can be used to indicate which
23 logical cluster a C-node belongs to.
24
26 Most functions appear in a version with the suffix _tmo appended to the
27 function name. Those functions take an extra argument, a time-out in
28 milliseconds. The semantics is this: for each communication primitive
29 involved in the operation, if the primitive does not complete within
30 the time specified, the function returns an error and erl_errno is set
31 to ETIMEDOUT. With communication primitive is meant an operation on the
32 socket, like connect, accept, recv, or send.
33 Clearly the time-outs are for implementing fault tolerance, not to keep
35 hard real-time promises. The _tmo functions are for detecting non-
36 responsive peers and to avoid blocking on socket operations.
37 A time-out value of 0 (zero) means that time-outs are disabled. Calling
39 a _tmo function with the last argument as 0 is therefore the same thing
40 as calling the function without the _tmo suffix.
41 As with all other functions starting with ei_, you are not expected to
43 put the socket in non-blocking mode yourself in the program. Every use
44 of non-blocking mode is embedded inside the time-out functions. The
45 socket will always be back in blocking mode after the operations are
46 completed (regardless of the result). To avoid problems, leave the
47 socket options alone. ei handles any socket options that need modifica‐
48 tion.
49 In all other senses, the _tmo functions inherit all the return values
51 and the semantics from the functions without the _tmo suffix.
52
54 By default ei supplies a TCP/IPv4 socket interface that is used when
55 communicating. The user can however plug in his/her own IPv4 socket
56 implementation. This, for example, in order to communicate over TLS. A
57 user supplied socket implementation is plugged in by passing a callback
58 structure to either ei_connect_init_ussi() or ei_connect_xinit_ussi().
59 All callbacks in the ei_socket_callbacks structure should return zero
61 on success; and a posix error code on failure.
62 The addr argument of the listen, accept, and connect callbacks refer to
64 appropriate address structure for currently used protocol. Currently ei
65 only supports IPv4. That is, at this time addr always points to a
66 struct sockaddr_in structure.
67 The ei_socket_callbacks structure may be enlarged in the future. All
69 fields not set, needs to be zeroed out.
70 typedef struct {
72 int flags;
73 int (*socket)(void **ctx, void *setup_ctx);
74 int (*close)(void *ctx);
75 int (*listen)(void *ctx, void *addr, int *len, int backlog);
76 int (*accept)(void **ctx, void *addr, int *len, unsigned tmo);
77 int (*connect)(void *ctx, void *addr, int len, unsigned tmo);
78 int (*writev)(void *ctx, const void *iov, int iovcnt, ssize_t *len, unsigned tmo);
79 int (*write)(void *ctx, const char *buf, ssize_t *len, unsigned tmo);
80 int (*read)(void *ctx, char *buf, ssize_t *len, unsigned tmo);
81 int (*handshake_packet_header_size)(void *ctx, int *sz);
82 int (*connect_handshake_complete)(void *ctx);
83 int (*accept_handshake_complete)(void *ctx);
84 int (*get_fd)(void *ctx, int *fd);
85 } ei_socket_callbacks;
86 flags:
89 Flags informing ei about the behaviour of the callbacks. Flags
90 should be bitwise or:ed together. If no flag, is set, the flags
91 field should contain 0. Currently, supported flags:
92 EI_SCLBK_FLG_FULL_IMPL:
94 If set, the accept(), connect(), writev(), write(), and read()
95 callbacks implements timeouts. The timeout is passed in the tmo
96 argument and is given in milli seconds. Note that the tmo argu‐
97 ment to these callbacks differ from the timeout arguments in the
98 ei API. Zero means a zero timeout. That is, poll and timeout
99 immediately unless the operation is successful. EI_SCLBK_INF_TMO
100 (max unsigned) means infinite timeout. The file descriptor is in
101 blocking mode when a callback is called, and it must be in block‐
102 ing mode when the callback returns.
103 If not set, ei will implement the timeout using select() in order
105 to determine when to call the callbacks and when to time out. The
106 tmo arguments of the accept(), connect(), writev(), write(), and
107 read() callbacks should be ignored. The callbacks may be called
108 in non-blocking mode. The callbacks are not allowed to change
109 between blocking and non-blocking mode. In order for this to
110 work, select() needs to interact with the socket primitives used
111 the same way as it interacts with the ordinary socket primitives.
112 If this is not the case, the callbacks need to implement timeouts
113 and this flag should be set.
114 More flags may be introduced in the future.
116 int (*socket)(void **ctx, void *setup_ctx):
118 Create a socket and a context for the socket.
119 On success it should set *ctx to point to a context for the created
121 socket. This context will be passed to all other socket callbacks.
122 This function will be passed the same setup_context as passed to
123 the preceeding ei_connect_init_ussi() or ei_connect_xinit_ussi()
124 call.
125 Note:
127 During the lifetime of a socket, the pointer *ctx has to remain the
128 same. That is, it cannot later be relocated.
129 This callback is mandatory.
132 int (*close)(void *ctx):
134 Close the socket identified by ctx and destroy the context.
135 This callback is mandatory.
137 int (*listen)(void *ctx, void *addr, int *len, int backlog):
139 Bind the socket identified by ctx to a local interface and then
140 listen on it.
141 The addr and len arguments are both input and output arguments.
143 When called addr points to an address structure of lenght *len con‐
144 taining information on how to bind the socket. Uppon return this
145 callback should have updated the structure referred by addr with
146 information on how the socket actually was bound. *len should be
147 updated to reflect the size of *addr updated. backlog identifies
148 the size of the backlog for the listen socket.
149 This callback is mandatory.
151 int (*accept)(void **ctx, void *addr, int *len, unsigned tmo):
153 Accept connections on the listen socket identified by *ctx.
154 When a connection is accepted, a new context for the accepted con‐
156 nection should be created and *ctx should be updated to point to
157 the new context for the accepted connection. When called addr
158 points to an uninitialized address structure of lenght *len. Uppon
159 return this callback should have updated this structure with infor‐
160 mation about the client address. *len should be updated to reflect
161 the size of *addr updated.
162 If the EI_SCLBK_FLG_FULL_IMPL flag has been set, tmo contains time‐
164 out time in milliseconds.
165 Note:
167 During the lifetime of a socket, the pointer *ctx has to remain the
168 same. That is, it cannot later be relocated.
169 This callback is mandatory.
172 int (*connect)(void *ctx, void *addr, int len, unsigned tmo):
174 Connect the socket identified by ctx to the address identified by
175 addr.
176 When called addr points to an address structure of lenght len con‐
178 taining information on where to connect.
179 If the EI_SCLBK_FLG_FULL_IMPL flag has been set, tmo contains time‐
181 out time in milliseconds.
182 This callback is mandatory.
184 int (*writev)(void *ctx, const void *iov, long iovcnt, ssize_t *len,
186 unsigned tmo):
187 Write data on the connected socket identified by ctx.
188 iov points to an array of struct iovec structures of length iovcnt
190 containing data to write to the socket. On success, this callback
191 should set *len to the amount of bytes successfully written on the
192 socket.
193 If the EI_SCLBK_FLG_FULL_IMPL flag has been set, tmo contains time‐
195 out time in milliseconds.
196 This callback is optional. Set the writev field in the the
198 ei_socket_callbacks structure to NULL if not implemented.
199 int (*write)(void *ctx, const char *buf, ssize_t *len, unsigned tmo):
201 Write data on the connected socket identified by ctx.
202 When called buf points to a buffer of length *len containing the
204 data to write on the socket. On success, this callback should set
205 *len to the amount of bytes successfully written on the socket.
206 If the EI_SCLBK_FLG_FULL_IMPL flag has been set, tmo contains time‐
208 out time in milliseconds.
209 This callback is mandatory.
211 int (*read)(void *ctx, char *buf, ssize_t *len, unsigned tmo):
213 Read data on the connected socket identified by ctx.
214 buf points to a buffer of length *len where the read data should be
216 placed. On success, this callback should update *len to the amount
217 of bytes successfully read on the socket.
218 If the EI_SCLBK_FLG_FULL_IMPL flag has been set, tmo contains time‐
220 out time in milliseconds.
221 This callback is mandatory.
223 int (*handshake_packet_header_size)(void *ctx, int *sz):
225 Inform about handshake packet header size to use during the Erlang
226 distribution handshake.
227 On success, *sz should be set to the handshake packet header size
229 to use. Valid values are 2 and 4. Erlang TCP distribution use a
230 handshake packet size of 2 and Erlang TLS distribution use a hand‐
231 shake packet size of 4.
232 This callback is mandatory.
234 int (*connect_handshake_complete)(void *ctx):
236 Called when a locally started handshake has completed successfully.
237 This callback is optional. Set the connect_handshake_complete field
239 in the ei_socket_callbacks structure to NULL if not implemented.
240 int (*accept_handshake_complete)(void *ctx):
242 Called when a remotely started handshake has completed success‐
243 fully.
244 This callback is optional. Set the accept_handshake_complete field
246 in the ei_socket_callbacks structure to NULL if not implemented.
247 int (*get_fd)(void *ctx, int *fd):
249 Inform about file descriptor used by the socket which is identified
250 by ctx.
251 Note:
253 During the lifetime of a socket, the file descriptor has to remain
254 the same. That is, repeated calls to this callback with the same con‐
255 text should always report the same file descriptor.
256 The file descriptor has to be a real file descriptor. That is, no
258 other operation should be able to get the same file descriptor until
259 it has been released by the close() callback.
260 This callback is mandatory.
263
265 struct hostent *ei_gethostbyaddr(const char *addr, int len, int type)
266 struct hostent *ei_gethostbyaddr_r(const char *addr, int length, int
267 type, struct hostent *hostp, char *buffer, int buflen, int
268 *h_errnop)
269 struct hostent *ei_gethostbyname(const char *name)
270 struct hostent *ei_gethostbyname_r(const char *name, struct hostent
271 *hostp, char *buffer, int buflen, int *h_errnop)
272 Convenience functions for some common name lookup functions.
274 int ei_accept(ei_cnode *ec, int listensock, ErlConnect *conp)
276 Used by a server process to accept a connection from a client
278 process.
279 * ec is the C-node structure.
281 * listensock is an open socket descriptor on which listen()
283 has previously been called.
284 * conp is a pointer to an ErlConnect struct, described as fol‐
286 lows:
287 typedef struct {
289 char ipadr[4];
290 char nodename[MAXNODELEN];
291 } ErlConnect;
292 On success, conp is filled in with the address and node name of
295 the connecting client and a file descriptor is returned. On
296 failure, ERL_ERROR is returned and erl_errno is set to EIO.
297 int ei_accept_tmo(ei_cnode *ec, int listensock, ErlConnect *conp,
299 unsigned timeout_ms)
300 Equivalent to ei_accept with an optional time-out argument, see
302 the description at the beginning of this manual page.
303 int ei_close_connection(int fd)
305 Closes a previously opened connection or listen socket.
307 int ei_connect(ei_cnode* ec, char *nodename)
309 int ei_xconnect(ei_cnode* ec, Erl_IpAddr adr, char *alivename)
310 Sets up a connection to an Erlang node.
312 ei_xconnect() requires the IP address of the remote host and the
314 alive name of the remote node to be specified. ei_connect() pro‐
315 vides an alternative interface and determines the information
316 from the node name provided.
317 * addr is the 32-bit IP address of the remote host.
319 * alive is the alivename of the remote node.
321 * node is the name of the remote node.
323 These functions return an open file descriptor on success, or a
325 negative value indicating that an error occurred. In the latter
326 case they set erl_errno to one of the following:
327 EHOSTUNREACH:
329 The remote host node is unreachable.
330 ENOMEM:
332 No more memory is available.
333 EIO:
335 I/O error.
336 Also, errno values from socket(2) and connect(2) system calls
338 may be propagated into erl_errno.
339 Example:
341 #define NODE "madonna@chivas.du.etx.ericsson.se"
343 #define ALIVE "madonna"
344 #define IP_ADDR "150.236.14.75"
345 /*** Variant 1 ***/
347 int fd = ei_connect(&ec, NODE);
348 /*** Variant 2 ***/
350 struct in_addr addr;
351 addr.s_addr = inet_addr(IP_ADDR);
352 fd = ei_xconnect(&ec, &addr, ALIVE);
353 int ei_connect_init(ei_cnode* ec, const char* this_node_name, const
356 char *cookie, short creation)
357 int ei_connect_init_ussi(ei_cnode* ec, const char* this_node_name,
358 const char *cookie, short creation, ei_socket_callbacks *cbs, int
359 cbs_sz, void *setup_context)
360 int ei_connect_xinit(ei_cnode* ec, const char *thishostname, const char
361 *thisalivename, const char *thisnodename, Erl_IpAddr thisipaddr, const
362 char *cookie, short creation)
363 int ei_connect_xinit_ussi(ei_cnode* ec, const char *thishostname, const
364 char *thisalivename, const char *thisnodename, Erl_IpAddr thisipaddr,
365 const char *cookie, short creation, ei_socket_callbacks *cbs, int
366 cbs_sz, void *setup_context)
367 Initializes the ec structure, to identify the node name and
369 cookie of the server. One of them must be called before other
370 functions that works on the ei_cnode type or a file descriptor
371 associated with a connection to another node is used.
372 * ec is a structure containing information about the C-node.
374 It is used in other ei functions for connecting and receiv‐
375 ing data.
376 * this_node_name is the registered name of the process (the
378 name before '@').
379 * cookie is the cookie for the node.
381 * creation identifies a specific instance of a C-node. It can
383 help prevent the node from receiving messages sent to an
384 earlier process with the same registered name.
385 * thishostname is the name of the machine we are running on.
387 If long names are to be used, they are to be fully qualified
388 (that is, durin.erix.ericsson.se instead of durin).
389 * thisalivename is the registered name of the process.
391 * thisnodename is the full name of the node, that is, ein‐
393 ode@durin.
394 * thispaddr if the IP address of the host.
396 * cbs is a pointer to a callback structure implementing and
398 alternative socket interface.
399 * cbs_sz is the size of the structure pointed to by cbs.
401 * setup_context is a pointer to a structure that will be
403 passed as second argument to the socket callback in the cbs
404 structure.
405 A C-node acting as a server is assigned a creation number when
407 it calls ei_publish().
408 A connection is closed by simply closing the socket. For infor‐
410 mation about how to close the socket gracefully (when there are
411 outgoing packets before close), see the relevant system documen‐
412 tation.
413 These functions return a negative value indicating that an error
415 occurred.
416 Example 1:
418 int n = 0;
420 struct in_addr addr;
421 ei_cnode ec;
422 addr.s_addr = inet_addr("150.236.14.75");
423 if (ei_connect_xinit(&ec,
424 "chivas",
425 "madonna",
426 "madonna@chivas.du.etx.ericsson.se",
427 &addr;
428 "cookie...",
429 n++) < 0) {
430 fprintf(stderr,"ERROR when initializing: %d",erl_errno);
431 exit(-1);
432 }
433 Example 2:
436 if (ei_connect_init(&ec, "madonna", "cookie...", n++) < 0) {
438 fprintf(stderr,"ERROR when initializing: %d",erl_errno);
439 exit(-1);
440 }
441 int ei_connect_tmo(ei_cnode* ec, char *nodename, unsigned timeout_ms)
444 int ei_xconnect_tmo(ei_cnode* ec, Erl_IpAddr adr, char *alivename,
445 unsigned timeout_ms)
446 Equivalent to ei_connect and ei_xconnect with an optional time-
448 out argument, see the description at the beginning of this man‐
449 ual page.
450 int ei_get_tracelevel(void)
452 void ei_set_tracelevel(int level)
453 Used to set tracing on the distribution. The levels are differ‐
455 ent verbosity levels. A higher level means more information. See
456 also section Debug Information.
457 These functions are not thread safe.
459 int ei_listen(ei_cnode *ec, int *port, int backlog)
461 int ei_xlisten(ei_cnode *ec, Erl_IpAddr adr, int *port, int backlog)
462 Used by a server process to setup a listen socket which later
464 can be used for accepting connections from client processes.
465 * ec is the C-node structure.
467 * adr is local interface to bind to.
469 * port is a pointer to an integer containing the port number
471 to bind to. If *port equals 0 when calling ei_listen(), the
472 socket will be bound to an ephemeral port. On success,
473 ei_listen() will update the value of *port to the port actu‐
474 ally bound to.
475 * backlog is maximum backlog of pending connections.
477 ei_listen will create a socket, bind to a port on the local
479 interface identified by adr (or all local interfaces if ei_lis‐
480 ten() is called), and mark the socket as a passive socket (that
481 is, a socket that will be used for accepting incoming connec‐
482 tions).
483 On success, a file descriptor is returned which can be used in a
485 call to ei_accept(). On failure, ERL_ERROR is returned and
486 erl_errno is set to EIO.
487 int ei_publish(ei_cnode *ec, int port)
489 Used by a server process to register with the local name server
491 EPMD, thereby allowing other processes to send messages by using
492 the registered name. Before calling either of these functions,
493 the process should have called bind() and listen() on an open
494 socket.
495 * ec is the C-node structure.
497 * port is the local name to register, and is to be the same as
499 the port number that was previously bound to the socket.
500 * addr is the 32-bit IP address of the local host.
502 To unregister with EPMD, simply close the returned descriptor.
504 Do not use ei_unpublish(), which is deprecated anyway.
505 On success, the function returns a descriptor connecting the
507 calling process to EPMD. On failure, -1 is returned and
508 erl_errno is set to EIO.
509 Also, errno values from socket(2) and connect(2) system calls
511 may be propagated into erl_errno.
512 int ei_publish_tmo(ei_cnode *ec, int port, unsigned timeout_ms)
514 Equivalent to ei_publish with an optional time-out argument, see
516 the description at the beginning of this manual page.
517 int ei_receive(int fd, unsigned char* bufp, int bufsize)
519 Receives a message consisting of a sequence of bytes in the
521 Erlang external format.
522 * fd is an open descriptor to an Erlang connection. It is
524 obtained from a previous ei_connect or ei_accept.
525 * bufp is a buffer large enough to hold the expected message.
527 * bufsize indicates the size of bufp.
529 If a tick occurs, that is, the Erlang node on the other end of
531 the connection has polled this node to see if it is still alive,
532 the function returns ERL_TICK and no message is placed in the
533 buffer. Also, erl_errno is set to EAGAIN.
534 On success, the message is placed in the specified buffer and
536 the function returns the number of bytes actually read. On fail‐
537 ure, the function returns ERL_ERROR and sets erl_errno to one of
538 the following:
539 EAGAIN:
541 Temporary error: Try again.
542 EMSGSIZE:
544 Buffer is too small.
545 EIO:
547 I/O error.
548 int ei_receive_encoded(int fd, char **mbufp, int *bufsz, erlang_msg
550 *msg, int *msglen)
551 This function is retained for compatibility with code generated
553 by the interface compiler and with code following examples in
554 the same application.
555 In essence, the function performs the same operation as ei_xre‐
557 ceive_msg, but instead of using an ei_x_buff, the function
558 expects a pointer to a character pointer (mbufp), where the
559 character pointer is to point to a memory area allocated by mal‐
560 loc. Argument bufsz is to be a pointer to an integer containing
561 the exact size (in bytes) of the memory area. The function may
562 reallocate the memory area and will in such cases put the new
563 size in *bufsz and update *mbufp.
564 Returns either ERL_TICK or the msgtype field of the erlang_msg
566 *msg. The length of the message is put in *msglen. On error a
567 value < 0 is returned.
568 It is recommended to use ei_xreceive_msg instead when possible,
570 for the sake of readability. However, the function will be
571 retained in the interface for compatibility and will not be
572 removed in future releases without prior notice.
573 int ei_receive_encoded_tmo(int fd, char **mbufp, int *bufsz,
575 erlang_msg *msg, int *msglen, unsigned timeout_ms)
576 Equivalent to ei_receive_encoded with an optional time-out argu‐
578 ment, see the description at the beginning of this manual page.
579 int ei_receive_msg(int fd, erlang_msg* msg, ei_x_buff* x)
581 int ei_xreceive_msg(int fd, erlang_msg* msg, ei_x_buff* x)
582 Receives a message to the buffer in x. ei_xreceive_msg allows
584 the buffer in x to grow, but ei_receive_msg fails if the message
585 is larger than the pre-allocated buffer in x.
586 * fd is an open descriptor to an Erlang connection.
588 * msg is a pointer to an erlang_msg structure and contains
590 information on the message received.
591 * x is buffer obtained from ei_x_new.
593 On success, the functions return ERL_MSG and the msg struct is
595 initialized. erlang_msg is defined as follows:
596 typedef struct {
598 long msgtype;
599 erlang_pid from;
600 erlang_pid to;
601 char toname[MAXATOMLEN+1];
602 char cookie[MAXATOMLEN+1];
603 erlang_trace token;
604 } erlang_msg;
605 msgtype identifies the type of message, and is one of the fol‐
608 lowing:
609 ERL_SEND:
611 Indicates that an ordinary send operation has occurred.
612 msg->to contains the pid of the recipient (the C-node).
613 ERL_REG_SEND:
615 A registered send operation occurred. msg->from contains the
616 pid of the sender.
617 ERL_LINK or ERL_UNLINK:
619 msg->to and msg->from contain the pids of the sender and
620 recipient of the link or unlink.
621 ERL_EXIT:
623 Indicates a broken link. msg->to and msg->from contain the
624 pids of the linked processes.
625 The return value is the same as for ei_receive.
627 int ei_receive_msg_tmo(int fd, erlang_msg* msg, ei_x_buff* x, unsigned
629 imeout_ms)
630 int ei_xreceive_msg_tmo(int fd, erlang_msg* msg, ei_x_buff* x, unsigned
631 timeout_ms)
632 Equivalent to ei_receive_msg and ei_xreceive_msg with an
634 optional time-out argument, see the description at the beginning
635 of this manual page.
636 int ei_receive_tmo(int fd, unsigned char* bufp, int bufsize, unsigned
638 timeout_ms)
639 Equivalent to ei_receive with an optional time-out argument, see
641 the description at the beginning of this manual page.
642 int ei_reg_send(ei_cnode* ec, int fd, char* server_name, char* buf, int
644 len)
645 Sends an Erlang term to a registered process.
647 * fd is an open descriptor to an Erlang connection.
649 * server_name is the registered name of the intended recipi‐
651 ent.
652 * buf is the buffer containing the term in binary format.
654 * len is the length of the message in bytes.
656 Returns 0 if successful, otherwise -1. In the latter case it
658 sets erl_errno to EIO.
659 Example:
661 Send the atom "ok" to the process "worker":
663 ei_x_buff x;
665 ei_x_new_with_version(&x);
666 ei_x_encode_atom(&x, "ok");
667 if (ei_reg_send(&ec, fd, x.buff, x.index) < 0)
668 handle_error();
669 int ei_reg_send_tmo(ei_cnode* ec, int fd, char* server_name, char* buf,
672 int len, unsigned timeout_ms)
673 Equivalent to ei_reg_send with an optional time-out argument,
675 see the description at the beginning of this manual page.
676 int ei_rpc(ei_cnode *ec, int fd, char *mod, char *fun, const char *arg‐
678 buf, int argbuflen, ei_x_buff *x)
679 int ei_rpc_to(ei_cnode *ec, int fd, char *mod, char *fun, const char
680 *argbuf, int argbuflen)
681 int ei_rpc_from(ei_cnode *ec, int fd, int timeout, erlang_msg *msg,
682 ei_x_buff *x)
683 Supports calling Erlang functions on remote nodes. ei_rpc_to()
685 sends an RPC request to a remote node and ei_rpc_from() receives
686 the results of such a call. ei_rpc() combines the functionality
687 of these two functions by sending an RPC request and waiting for
688 the results. See also rpc:call/4 in Kernel.
689 * ec is the C-node structure previously initiated by a call to
691 ei_connect_init() or ei_connect_xinit().
692 * fd is an open descriptor to an Erlang connection.
694 * timeout is the maximum time (in milliseconds) to wait for
696 results. Specify ERL_NO_TIMEOUT to wait forever. ei_rpc()
697 waits infinitely for the answer, that is, the call will
698 never time out.
699 * mod is the name of the module containing the function to be
701 run on the remote node.
702 * fun is the name of the function to run.
704 * argbuf is a pointer to a buffer with an encoded Erlang list,
706 without a version magic number, containing the arguments to
707 be passed to the function.
708 * argbuflen is the length of the buffer containing the encoded
710 Erlang list.
711 * msg is structure of type erlang_msg and contains information
713 on the message received. For a description of the erlang_msg
714 format, see ei_receive_msg.
715 * x points to the dynamic buffer that receives the result. For
717 ei_rpc() this is the result without the version magic num‐
718 ber. For ei_rpc_from() the result returns a version magic
719 number and a 2-tuple {rex,Reply}.
720 ei_rpc() returns the number of bytes in the result on success
722 and -1 on failure. ei_rpc_from() returns the number of bytes,
723 otherwise one of ERL_TICK, ERL_TIMEOUT, and ERL_ERROR. When
724 failing, all three functions set erl_errno to one of the follow‐
725 ing:
726 EIO:
728 I/O error.
729 ETIMEDOUT:
731 Time-out expired.
732 EAGAIN:
734 Temporary error: Try again.
735 Example:
737 Check to see if an Erlang process is alive:
739 int index = 0, is_alive;
741 ei_x_buff args, result;
742 ei_x_new(&result);
744 ei_x_new(&args);
745 ei_x_encode_list_header(&args, 1);
746 ei_x_encode_pid(&args, &check_pid);
747 ei_x_encode_empty_list(&args);
748 if (ei_rpc(&ec, fd, "erlang", "is_process_alive",
750 args.buff, args.index, &result) < 0)
751 handle_error();
752 if (ei_decode_version(result.buff, &index) < 0
754 || ei_decode_bool(result.buff, &index, &is_alive) < 0)
755 handle_error();
756 erlang_pid *ei_self(ei_cnode *ec)
759 Retrieves the pid of the C-node. Every C-node has a (pseudo) pid
761 used in ei_send_reg, ei_rpc, and others. This is contained in a
762 field in the ec structure. It will be safe for a long time to
763 fetch this field directly from the ei_cnode structure.
764 int ei_send(int fd, erlang_pid* to, char* buf, int len)
766 Sends an Erlang term to a process.
768 * fd is an open descriptor to an Erlang connection.
770 * to is the pid of the intended recipient of the message.
772 * buf is the buffer containing the term in binary format.
774 * len is the length of the message in bytes.
776 Returns 0 if successful, otherwise -1. In the latter case it
778 sets erl_errno to EIO.
779 int ei_send_encoded(int fd, erlang_pid* to, char* buf, int len)
781 Works exactly as ei_send, the alternative name is retained for
783 backward compatibility. The function will not be removed without
784 prior notice.
785 int ei_send_encoded_tmo(int fd, erlang_pid* to, char* buf, int len,
787 unsigned timeout_ms)
788 Equivalent to ei_send_encoded with an optional time-out argu‐
790 ment, see the description at the beginning of this manual page.
791 int ei_send_reg_encoded(int fd, const erlang_pid *from, const char *to,
793 const char *buf, int len)
794 This function is retained for compatibility with code generated
796 by the interface compiler and with code following examples in
797 the same application.
798 The function works as ei_reg_send with one exception. Instead of
800 taking ei_cnode as first argument, it takes a second argument,
801 an erlang_pid, which is to be the process identifier of the
802 sending process (in the Erlang distribution protocol).
803 A suitable erlang_pid can be constructed from the ei_cnode
805 structure by the following example code:
806 ei_cnode ec;
808 erlang_pid *self;
809 int fd; /* the connection fd */
810 self = ei_self(&ec);
811 self->num = fd;
812 int ei_send_reg_encoded_tmo(int fd, const erlang_pid *from, const char
815 *to, const char *buf, int len)
816 Equivalent to ei_send_reg_encoded with an optional time-out
818 argument, see the description at the beginning of this manual
819 page.
820 int ei_send_tmo(int fd, erlang_pid* to, char* buf, int len, unsigned
822 timeout_ms)
823 Equivalent to ei_send with an optional time-out argument, see
825 the description at the beginning of this manual page.
826 const char *ei_thisnodename(ei_cnode *ec)
828 const char *ei_thishostname(ei_cnode *ec)
829 const char *ei_thisalivename(ei_cnode *ec)
830 Can be used to retrieve information about the C-node. These val‐
832 ues are initially set with ei_connect_init() or ei_con‐
833 nect_xinit().
834 These function simply fetch the appropriate field from the ec
836 structure. Read the field directly will probably be safe for a
837 long time, so these functions are not really needed.
838 int ei_unpublish(ei_cnode *ec)
840 Can be called by a process to unregister a specified node from
842 EPMD on the local host. This is, however, usually not allowed,
843 unless EPMD was started with flag -relaxed_command_check, which
844 it normally is not.
845 To unregister a node you have published, you should close the
847 descriptor that was returned by ei_publish().
848 Warning:
850 This function is deprecated and will be removed in a future
851 release.
852 ec is the node structure of the node to unregister.
855 If the node was successfully unregistered from EPMD, the func‐
857 tion returns 0. Otherwise, -1 is returned and erl_errno is set
858 to EIO.
859 int ei_unpublish_tmo(ei_cnode *ec, unsigned timeout_ms)
861 Equivalent to ei_unpublish with an optional time-out argument,
863 see the description at the beginning of this manual page.
864
866 If a connection attempt fails, the following can be checked:
867 * erl_errno.
869 * That the correct cookie was used
871 * That EPMD is running
873 * That the remote Erlang node on the other side is running the same
875 version of Erlang as the ei library
876 * That environment variable ERL_EPMD_PORT is set correctly
878 The connection attempt can be traced by setting a trace level by either
880 using ei_set_tracelevel or by setting environment variable
881 EI_TRACELEVEL. The trace levels have the following messages:
882 * 1: Verbose error messages
884 * 2: Above messages and verbose warning messages
886 * 3: Above messages and progress reports for connection handling
888 * 4: Above messages and progress reports for communication
890 * 5: Above messages and progress reports for data conversion
892Ericsson AB erl_interface 3.13.2 ei_connect(3)