ei_connect

Convenience functions for some common name lookup functions.

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, described as follows:

  typedef struct {
    char ipadr[4];             
    char nodename[MAXNODELEN];
  } ErlConnect;

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.

Equivalent to ei_accept with an optional time-out argument, see the description at the beginning of this manual page.

Closes a previously opened connection or listen socket.

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);

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 registered name of the process (the name before '@').

• 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 registered name of the process.

• thisnodename is the full name of the node, that is, einode@durin.

• 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.

Example 1:

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);
}

Example 2:

if (ei_connect_init(&ec, "madonna", "cookie...", n++) < 0) {
    fprintf(stderr,"ERROR when initializing: %d",erl_errno);
    exit(-1);
}

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.

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.

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.

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.

Equivalent to ei_publish with an optional time-out argument, see the description at the beginning of this manual page.

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.

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.

Equivalent to ei_receive_encoded with an optional time-out argument, see the description at the beginning of this manual page.

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. erlang_msg is defined as follows:

typedef struct {
    long msgtype;
    erlang_pid from;
    erlang_pid to;
    char toname[MAXATOMLEN+1];
    char cookie[MAXATOMLEN+1];
    erlang_trace token;
} erlang_msg;

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.

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.

Equivalent to ei_receive with an optional time-out argument, see the description at the beginning of this manual page.

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();

Equivalent to ei_reg_send with an optional time-out argument, see the description at the beginning of this manual page.

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. See also 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 ei_rpc_from() the result returns a version magic number and a 2-tuple {rex,Reply}.

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. When failing, all three 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();

Retrieves the 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. It will be safe for a long time to fetch this field directly from the ei_cnode structure.

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.

Works exactly as ei_send, the alternative name is retained for backward compatibility. The function will not be removed without prior notice.

Equivalent to ei_send_encoded with an optional time-out argument, see the description at the beginning of this manual page.

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 constructed from the ei_cnode structure by the following example code:

ei_cnode ec;
erlang_pid *self;
int fd; /* the connection fd */
...
self = ei_self(&ec);
self->num = fd;

Equivalent to ei_send_reg_encoded with an optional time-out argument, see the description at the beginning of this manual page.

Equivalent to ei_send with an optional time-out argument, see the description at the beginning of this manual page.

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.

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().

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.

Equivalent to ei_unpublish with an optional time-out argument, see the description at the beginning of this manual page.