ei_connect

Convenience functions for some common name lookup functions.

Used by a server process to accept a connection from a client process.

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.

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.

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:

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.

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 and ei_xconnect 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 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.

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.

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:

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.

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:

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.

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.

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:

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.

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.