structhostent*ei_gethostbyaddr(constchar*addr,intlen,inttype)structhostent*ei_gethostbyaddr_r(constchar*addr,intlength,inttype,structhostent*hostp,char*buffer,intbuflen,int*h_errnop)structhostent*ei_gethostbyname(constchar*name)structhostent*ei_gethostbyname_r(constchar*name,structhostent*hostp,char*buffer,intbuflen,int*h_errnop)
Convenience functions for some common name lookup functions.
intei_accept(ei_cnode*ec,intlistensock,ErlConnect*conp)
Types:
ei_cnodeErlConnect
Used by a server process to accept a connection from a client process.
* ec is the C-node structure.
* listensock is an open socket descriptor on which listen() has previously been called.
* conp is a pointer to an ErlConnect struct.
On success, conp is filled in with the address and node name of the connecting client and a file
descriptor is returned. On failure, ERL_ERROR is returned and erl_errno is set to EIO.
intei_accept_tmo(ei_cnode*ec,intlistensock,ErlConnect*conp,unsignedtimeout_ms)
Types:
ei_cnodeErlConnect
Equivalent to ei_accept with an optional time-out argument, see the description at the beginning
of this manual page.
intei_close_connection(intfd)
Closes a previously opened connection or listen socket.
intei_connect(ei_cnode*ec,char*nodename)intei_xconnect(ei_cnode*ec,Erl_IpAddradr,char*alivename)intei_connect_host_port(ei_cnode*ec,char*hostname,intport)intei_xconnect_host_port(ei_cnode*ec,Erl_IpAddradr,intport)
Types:
ei_cnodeErl_IpAddr
Sets up a connection to an Erlang node.
ei_xconnect() requires the IP address of the remote host and the alive name of the remote node to
be specified. ei_connect() provides an alternative interface and determines the information from
the node name provided. The ei_xconnect_host_port() function provides yet another alternative that
will work even if there is no EPMD instance on the host where the remote node is running. The
ei_xconnect_host_port() function requires the IP address and port of the remote node to be
specified. The ei_connect_host_port() function is an alternative to ei_xconnect_host_port() that
lets the user specify a hostname instead of an IP address.
* adr is the 32-bit IP address of the remote host.
* alive is the alivename of the remote node.
* node is the name of the remote node.
* port is the port number of the remote node.
These functions return an open file descriptor on success, or a negative value indicating that an
error occurred. In the latter case they set erl_errno to one of the following:
EHOSTUNREACH:
The remote host node is unreachable.
ENOMEM:
No more memory is available.
EIO:
I/O error.
Also, errno values from socket(2) and connect(2) system calls may be propagated into erl_errno.
Example:
#define NODE "madonna@chivas.du.etx.ericsson.se"
#define ALIVE "madonna"
#define IP_ADDR "150.236.14.75"
/*** Variant 1 ***/
int fd = ei_connect(&ec, NODE);
/*** Variant 2 ***/
struct in_addr addr;
addr.s_addr = inet_addr(IP_ADDR);
fd = ei_xconnect(&ec, &addr, ALIVE);
intei_connect_init(ei_cnode*ec,constchar*this_node_name,constchar*cookie,shortcreation)intei_connect_init_ussi(ei_cnode*ec,constchar*this_node_name,constchar*cookie,shortcreation,ei_socket_callbacks*cbs,intcbs_sz,void*setup_context)intei_connect_xinit(ei_cnode*ec,constchar*thishostname,constchar*thisalivename,constchar*thisnodename,Erl_IpAddrthisipaddr,constchar*cookie,shortcreation)intei_connect_xinit_ussi(ei_cnode*ec,constchar*thishostname,constchar*thisalivename,constchar*thisnodename,Erl_IpAddrthisipaddr,constchar*cookie,shortcreation,ei_socket_callbacks*cbs,intcbs_sz,void*setup_context)
Types:
ei_cnodeErl_IpAddrei_socket_callbacks
Initializes the ec structure, to identify the node name and cookie of the server. One of them must
be called before other functions that works on the ei_cnode type or a file descriptor associated
with a connection to another node is used.
* ec is a structure containing information about the C-node. It is used in other ei functions
for connecting and receiving data.
* this_node_name is the name of the C-node (the name before '@' in the full node name).
* cookie is the cookie for the node.
* creation identifies a specific instance of a C-node. It can help prevent the node from
receiving messages sent to an earlier process with the same registered name.
* thishostname is the name of the machine we are running on. If long names are to be used, they
are to be fully qualified (that is, durin.erix.ericsson.se instead of durin).
* thisalivename is the name of the local C-node (the name before '@' in the full node name). Can
be NULL (from OTP 23) to get a dynamically assigned name from the peer node.
* thisnodename is the full name of the local C-node, that is, mynode@myhost. Can be NULL if
thisalivename is NULL.
* thispaddr if the IP address of the host.
* cbs is a pointer to a callback structure implementing and alternative socket interface.
* cbs_sz is the size of the structure pointed to by cbs.
* setup_context is a pointer to a structure that will be passed as second argument to the socket
callback in the cbs structure.
A C-node acting as a server is assigned a creation number when it calls ei_publish().
A connection is closed by simply closing the socket. For information about how to close the socket
gracefully (when there are outgoing packets before close), see the relevant system documentation.
These functions return a negative value indicating that an error occurred.
Example1:
int n = 0;
struct in_addr addr;
ei_cnode ec;
addr.s_addr = inet_addr("150.236.14.75");
if (ei_connect_xinit(&ec,
"chivas",
"madonna",
"madonna@chivas.du.etx.ericsson.se",
&addr;
"cookie...",
n++) < 0) {
fprintf(stderr,"ERROR when initializing: %d",erl_errno);
exit(-1);
}
Example2:
if (ei_connect_init(&ec, "madonna", "cookie...", n++) < 0) {
fprintf(stderr,"ERROR when initializing: %d",erl_errno);
exit(-1);
}
intei_connect_tmo(ei_cnode*ec,char*nodename,unsignedtimeout_ms)intei_xconnect_tmo(ei_cnode*ec,Erl_IpAddradr,char*alivename,unsignedtimeout_ms)intei_connect_host_port_tmo(ei_cnode*ec,char*hostname,intport,unsignedms)intei_xconnect_host_port_tmo(ei_cnode*ec,Erl_IpAddradr,intport,unsignedms)
Types:
ei_cnodeErl_IpAddr
Equivalent to ei_connect, ei_xconnect, ei_connect_host_port and ei_xconnect_host_port with an
optional time-out argument, see the description at the beginning of this manual page.
intei_get_tracelevel(void)voidei_set_tracelevel(intlevel)
Used to set tracing on the distribution. The levels are different verbosity levels. A higher level
means more information. See also section Debug Information.
These functions are not thread safe.
intei_listen(ei_cnode*ec,int*port,intbacklog)intei_xlisten(ei_cnode*ec,Erl_IpAddradr,int*port,intbacklog)
Types:
ei_cnodeErl_IpAddr
Used by a server process to setup a listen socket which later can be used for accepting
connections from client processes.
* ec is the C-node structure.
* adr is local interface to bind to.
* port is a pointer to an integer containing the port number to bind to. If *port equals 0 when
calling ei_listen(), the socket will be bound to an ephemeral port. On success, ei_listen()
will update the value of *port to the port actually bound to.
* backlog is maximum backlog of pending connections.
ei_listen will create a socket, bind to a port on the local interface identified by adr (or all
local interfaces if ei_listen() is called), and mark the socket as a passive socket (that is, a
socket that will be used for accepting incoming connections).
On success, a file descriptor is returned which can be used in a call to ei_accept(). On failure,
ERL_ERROR is returned and erl_errno is set to EIO.
intei_make_pid(ei_cnode*ec,erlang_pid*pid)
Types:
ei_cnodeerlang_pid
Creates a new process identifier in the argument pid. This process identifier refers to a
conseptual process residing on the C-node identified by the argument ec. On success 0 is returned.
On failure ERL_ERROR is returned and erl_errno is set.
The C-node identified by ec must have been initialized and must have received a name prior to the
call to ei_make_pid(). Initialization of the C-node is done by a call to ei_connect_init() or
friends. If the name is dynamically assigned from the peer node, the C-node also has to be
connected.
intei_make_ref(ei_cnode*ec,erlang_ref*ref)
Types:
ei_cnodeerlang_ref
Creates a new reference in the argument ref. This reference originates from the C-node identified
by the argument ec. On success 0 is returned. On failure ERL_ERROR is returned and erl_errno is
set.
The C-node identified by ec must have been initialized and must have received a name prior to the
call to ei_make_ref(). Initialization of the C-node is done by a call to ei_connect_init() or
friends. If the name is dynamically assigned from the peer node, the C-node also has to be
connected.
intei_publish(ei_cnode*ec,intport)
Types:
ei_cnode
Used by a server process to register with the local name server EPMD, thereby allowing other
processes to send messages by using the registered name. Before calling either of these functions,
the process should have called bind() and listen() on an open socket.
* ec is the C-node structure.
* port is the local name to register, and is to be the same as the port number that was
previously bound to the socket.
* addr is the 32-bit IP address of the local host.
To unregister with EPMD, simply close the returned descriptor. Do not use ei_unpublish(), which is
deprecated anyway.
On success, the function returns a descriptor connecting the calling process to EPMD. On failure,
-1 is returned and erl_errno is set to EIO.
Also, errno values from socket(2) and connect(2) system calls may be propagated into erl_errno.
intei_publish_tmo(ei_cnode*ec,intport,unsignedtimeout_ms)
Types:
ei_cnode
Equivalent to ei_publish with an optional time-out argument, see the description at the beginning
of this manual page.
intei_receive(intfd,unsignedchar*bufp,intbufsize)
Receives a message consisting of a sequence of bytes in the Erlang external format.
* fd is an open descriptor to an Erlang connection. It is obtained from a previous ei_connect or
ei_accept.
* bufp is a buffer large enough to hold the expected message.
* bufsize indicates the size of bufp.
If a tick occurs, that is, the Erlang node on the other end of the connection has polled this node
to see if it is still alive, the function returns ERL_TICK and no message is placed in the buffer.
Also, erl_errno is set to EAGAIN.
On success, the message is placed in the specified buffer and the function returns the number of
bytes actually read. On failure, the function returns ERL_ERROR and sets erl_errno to one of the
following:
EAGAIN:
Temporary error: Try again.
EMSGSIZE:
Buffer is too small.
EIO:
I/O error.
intei_receive_encoded(intfd,char**mbufp,int*bufsz,erlang_msg*msg,int*msglen)
Types:
erlang_msg
This function is retained for compatibility with code generated by the interface compiler and with
code following examples in the same application.
In essence, the function performs the same operation as ei_xreceive_msg, but instead of using an
ei_x_buff, the function expects a pointer to a character pointer (mbufp), where the character
pointer is to point to a memory area allocated by malloc. Argument bufsz is to be a pointer to an
integer containing the exact size (in bytes) of the memory area. The function may reallocate the
memory area and will in such cases put the new size in *bufsz and update *mbufp.
Returns either ERL_TICK or the msgtype field of the erlang_msg*msg. The length of the message is
put in *msglen. On error a value <0 is returned.
It is recommended to use ei_xreceive_msg instead when possible, for the sake of readability.
However, the function will be retained in the interface for compatibility and will not be removed
in future releases without prior notice.
intei_receive_encoded_tmo(intfd,char**mbufp,int*bufsz,erlang_msg*msg,int*msglen,unsignedtimeout_ms)
Types:
erlang_msg
Equivalent to ei_receive_encoded with an optional time-out argument, see the description at the
beginning of this manual page.
intei_receive_msg(intfd,erlang_msg*msg,ei_x_buff*x)intei_xreceive_msg(intfd,erlang_msg*msg,ei_x_buff*x)
Types:
ei_x_bufferlang_msg
Receives a message to the buffer in x. ei_xreceive_msg allows the buffer in x to grow, but
ei_receive_msg fails if the message is larger than the pre-allocated buffer in x.
* fd is an open descriptor to an Erlang connection.
* msg is a pointer to an erlang_msg structure and contains information on the message received.
* x is buffer obtained from ei_x_new.
On success, the functions return ERL_MSG and the msg struct is initialized.
msgtype identifies the type of message, and is one of the following:
ERL_SEND:
Indicates that an ordinary send operation has occurred. msg->to contains the pid of the
recipient (the C-node).
ERL_REG_SEND:
A registered send operation occurred. msg->from contains the pid of the sender.
ERL_LINK or ERL_UNLINK:
msg->to and msg->from contain the pids of the sender and recipient of the link or unlink.
ERL_EXIT:
Indicates a broken link. msg->to and msg->from contain the pids of the linked processes.
The return value is the same as for ei_receive.
intei_receive_msg_tmo(intfd,erlang_msg*msg,ei_x_buff*x,unsignedimeout_ms)intei_xreceive_msg_tmo(intfd,erlang_msg*msg,ei_x_buff*x,unsignedtimeout_ms)
Types:
ei_x_bufferlang_msg
Equivalent to ei_receive_msg and ei_xreceive_msg with an optional time-out argument, see the
description at the beginning of this manual page.
intei_receive_tmo(intfd,unsignedchar*bufp,intbufsize,unsignedtimeout_ms)
Equivalent to ei_receive with an optional time-out argument, see the description at the beginning
of this manual page.
intei_reg_send(ei_cnode*ec,intfd,char*server_name,char*buf,intlen)
Types:
ei_cnode
Sends an Erlang term to a registered process.
* fd is an open descriptor to an Erlang connection.
* server_name is the registered name of the intended recipient.
* buf is the buffer containing the term in binary format.
* len is the length of the message in bytes.
Returns 0 if successful, otherwise -1. In the latter case it sets erl_errno to EIO.
Example:
Send the atom "ok" to the process "worker":
ei_x_buff x;
ei_x_new_with_version(&x);
ei_x_encode_atom(&x, "ok");
if (ei_reg_send(&ec, fd, x.buff, x.index) < 0)
handle_error();
intei_reg_send_tmo(ei_cnode*ec,intfd,char*server_name,char*buf,intlen,unsignedtimeout_ms)
Types:
ei_cnode
Equivalent to ei_reg_send with an optional time-out argument, see the description at the beginning
of this manual page.
intei_rpc(ei_cnode*ec,intfd,char*mod,char*fun,constchar*argbuf,intargbuflen,ei_x_buff*x)intei_rpc_to(ei_cnode*ec,intfd,char*mod,char*fun,constchar*argbuf,intargbuflen)intei_xrpc_to(ei_cnode*ec,intfd,char*mod,char*fun,constchar*argbuf,intargbuflen,intflags)intei_rpc_from(ei_cnode*ec,intfd,inttimeout,erlang_msg*msg,ei_x_buff*x)
Types:
ei_cnodeei_x_bufferlang_msg
Supports calling Erlang functions on remote nodes. ei_rpc_to() sends an RPC request to a remote
node and ei_rpc_from() receives the results of such a call. ei_rpc() combines the functionality of
these two functions by sending an RPC request and waiting for the results.
The ei_xrpc_to() function is equivalent to ei_rpc_to() when its flags parameter is set to 0. When
the flags parameter of ei_xrpc_to() is set to EI_RPC_FETCH_STDOUT, stdout (standard output) data
are forwarded. See the documentation for the flags parameter for more information about the
EI_RPC_FETCH_STDOUT flag.
rpc:call/4 in Kernel.
* ec is the C-node structure previously initiated by a call to ei_connect_init() or
ei_connect_xinit().
* fd is an open descriptor to an Erlang connection.
* timeout is the maximum time (in milliseconds) to wait for results. Specify ERL_NO_TIMEOUT to
wait forever. ei_rpc() waits infinitely for the answer, that is, the call will never time out.
* mod is the name of the module containing the function to be run on the remote node.
* fun is the name of the function to run.
* argbuf is a pointer to a buffer with an encoded Erlang list, without a version magic number,
containing the arguments to be passed to the function.
* argbuflen is the length of the buffer containing the encoded Erlang list.
* msg is structure of type erlang_msg and contains information on the message received. For a
description of the erlang_msg format, see ei_receive_msg.
* x points to the dynamic buffer that receives the result. For ei_rpc() this is the result
without the version magic number. For an ei_rpc_from() call the result consists of a version
magic number and a 2-tuple. The 2-tuple can be in one of the following two forms:
{rex,Reply}:
This response value means that the RPC has completed. The result value is the Reply term.
This is the only type of response that one can get from an RPC triggered by a call to
ei_rpc_to() or ei_xrpc_to() without the EI_RPC_FETCH_STDOUT flag. If the RPC was triggered
by a call to ei_xrpc_to() with the EI_RPC_FETCH_STDOUT flag set, then all forwarded stdout
data has been received.
{rex_stdout,StdOutUTF8Binary}:
This response value can only be obtained if the RPC call was triggered by a call to
ei_xrpc_to() with the EI_RPC_FETCH_STDOUT flag set. This response value means that forwarded
stdout data has been received. The stdout data is stored in a binary and is UTF-8 encoded.
One may need to call ei_rpc_from() multiple times to read all the stdout data. The stdout
data is received in the same order as it was written. All forwarded stdout data have been
received when a {rex,Reply} tuple has been obtained from an ei_rpc_from() call.
* flags The flag EI_RPC_FETCH_STDOUT is currently the only flag that is supported by
ei_xrpc_to(). When EI_RPC_FETCH_STDOUT is set, the called function is executed in a new
process with a group leader that forwards all stdout data. This means that stdout data that
are written during the execution of the called function, by the called function and by
descendant processes, will be forwarded (given that the group leader has not been changed by a
call to erlang:group_leader/2). The forwarded stdout data need to be collected by a sequence
of calls to ei_rpc_from(). See the description of the x parameter for how ei_rpc_from() is
used to receive stdout data. See the documentation of the the I/O protocol, for more
information about the group leader concept.
Note:
The flag EI_RPC_FETCH_STDOUT only works when interacting with a node with a version greater or
equal to OTP-24.
ei_rpc() returns the number of bytes in the result on success and -1 on failure. ei_rpc_from()
returns the number of bytes, otherwise one of ERL_TICK, ERL_TIMEOUT, and ERL_ERROR. The functions
ei_rpc_to() and ei_xrpc_to() returns 0 if successful, otherwise -1. When failing, all four
functions set erl_errno to one of the following:
EIO:
I/O error.
ETIMEDOUT:
Time-out expired.
EAGAIN:
Temporary error: Try again.
Example:
Check to see if an Erlang process is alive:
int index = 0, is_alive;
ei_x_buff args, result;
ei_x_new(&result);
ei_x_new(&args);
ei_x_encode_list_header(&args, 1);
ei_x_encode_pid(&args, &check_pid);
ei_x_encode_empty_list(&args);
if (ei_rpc(&ec, fd, "erlang", "is_process_alive",
args.buff, args.index, &result) < 0)
handle_error();
if (ei_decode_version(result.buff, &index) < 0
|| ei_decode_bool(result.buff, &index, &is_alive) < 0)
handle_error();
erlang_pid*ei_self(ei_cnode*ec)
Types:
ei_cnodeerlang_pid
Retrieves a generic pid of the C-node. Every C-node has a (pseudo) pid used in ei_send_reg,
ei_rpc(), and others. This is contained in a field in the ec structure. Do not modify this
structure.
On success a pointer to the process identifier is returned. On failure NULL is returned and
erl_errno is set.
The C-node identified by ec must have been initialized and must have received a name prior to the
call to ei_self(). Initialization of the C-node is done by a call to ei_connect_init() or friends.
If the name is dynamically assigned from the peer node, the C-node also has to be connected.
intei_send(intfd,erlang_pid*to,char*buf,intlen)
Types:
erlang_pid
Sends an Erlang term to a process.
* fd is an open descriptor to an Erlang connection.
* to is the pid of the intended recipient of the message.
* buf is the buffer containing the term in binary format.
* len is the length of the message in bytes.
Returns 0 if successful, otherwise -1. In the latter case it sets erl_errno to EIO.
intei_send_encoded(intfd,erlang_pid*to,char*buf,intlen)
Types:
erlang_pid
Works exactly as ei_send, the alternative name is retained for backward compatibility. The
function will not be removed without prior notice.
intei_send_encoded_tmo(intfd,erlang_pid*to,char*buf,intlen,unsignedtimeout_ms)
Types:
erlang_pid
Equivalent to ei_send_encoded with an optional time-out argument, see the description at the
beginning of this manual page.
intei_send_reg_encoded(intfd,consterlang_pid*from,constchar*to,constchar*buf,intlen)
Types:
erlang_pid
This function is retained for compatibility with code generated by the interface compiler and with
code following examples in the same application.
The function works as ei_reg_send with one exception. Instead of taking ei_cnode as first
argument, it takes a second argument, an erlang_pid, which is to be the process identifier of the
sending process (in the Erlang distribution protocol).
A suitable erlang_pid can be retrieved from the ei_cnode structure by calling
ei_self(cnode_pointer).
intei_send_reg_encoded_tmo(intfd,consterlang_pid*from,constchar*to,constchar*buf,intlen,unsignedtimeout_ms)
Types:
erlang_pid
Equivalent to ei_send_reg_encoded with an optional time-out argument, see the description at the
beginning of this manual page.
intei_send_tmo(intfd,erlang_pid*to,char*buf,intlen,unsignedtimeout_ms)
Types:
erlang_pid
Equivalent to ei_send with an optional time-out argument, see the description at the beginning of
this manual page.
constchar*ei_thisnodename(ei_cnode*ec)constchar*ei_thishostname(ei_cnode*ec)constchar*ei_thisalivename(ei_cnode*ec)
Types:
ei_cnode
Can be used to retrieve information about the C-node. These values are initially set with
ei_connect_init() or ei_connect_xinit().
These function simply fetch the appropriate field from the ec structure. Read the field directly
will probably be safe for a long time, so these functions are not really needed.
intei_unpublish(ei_cnode*ec)
Types:
ei_cnode
Can be called by a process to unregister a specified node from EPMD on the local host. This is,
however, usually not allowed, unless EPMD was started with flag -relaxed_command_check, which it
normally is not.
To unregister a node you have published, you should close the descriptor that was returned by
ei_publish().
Warning:
This function is deprecated and will be removed in a future release.
ec is the node structure of the node to unregister.
If the node was successfully unregistered from EPMD, the function returns 0. Otherwise, -1 is
returned and erl_errno is set to EIO.
intei_unpublish_tmo(ei_cnode*ec,unsignedtimeout_ms)
Types:
ei_cnode
Equivalent to ei_unpublish with an optional time-out argument, see the description at the
beginning of this manual page.
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