Florian Ragwitz > NanoMsg-Raw-0.02 > NanoMsg::Raw

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NAME ^

NanoMsg::Raw - Low-level interface to the nanomsg scalability protocols library

SYNOPSIS ^

    use NanoMsg::Raw;

    my $sb = nn_socket(AF_SP, NN_PAIR);
    nn_bind($sb, 'inproc://foo');
    nn_send($sb, 'bar');

    my $sc = nn_socket(AF_SP, NN_PAIR);
    nn_connect($sc, 'inproc://foo');
    nn_recv($sc, my $buf);
    is $buf, 'bar';

DESCRIPTION ^

NanoMsg::Raw is a binding to the nanomsg C library. The goal of this module is to provide a very low-level and manual interface to all the functionality of the nanomsg library. It doesn't intend to provide a convenient high-level API, integration with event loops, or the like. Those are intended to be implemented as separate abstractions on top of NanoMsg::Raw.

The nanomsg C library is a high-performance implementation of several "scalability protocols". Scalability protocol's job is to define how multiple applications communicate to form a single distributed application. Implementation of following scalability protocols is available at the moment:

Scalability protocols are layered on top of transport layer in the network stack. At the moment, nanomsg library supports following transports:

FUNCTIONS ^

nn_socket($domain, $protocol)

    my $s = nn_socket(AF_SP, NN_PAIR);
    die nn_errno unless defined $s;

Creates a nanomsg socket with specified $domain and $protocol. Returns a file descriptor for the newly created socket.

Following domains are defined at the moment:

The $protocol parameter defines the type of the socket, which in turn determines the exact semantics of the socket. See "Protocols" to get the list of available protocols and their socket types.

The newly created socket is initially not associated with any endpoints. In order to establish a message flow at least one endpoint has to be added to the socket using nn_bind or nn_connect.

Also note that type argument as found in standard socket function is omitted from nn_socket. All the SP sockets are message-based and thus of SOCK_SEQPACKET type.

If the function succeeds file descriptor of the new socket is returned. Otherwise, undef is returned and nn_errno is set to to one of the values defined below.

Note that file descriptors returned by nn_socket function are not standard file descriptors and will exhibit undefined behaviour when used with system functions. Moreover, it may happen that a system file descriptor and file descriptor of an SP socket will incidentally collide (be equal).

nn_close($s)

    nn_close($s) or die nn_errno;

Closes the socket $s. Any buffered inbound messages that were not yet received by the application will be discarded. The library will try to deliver any outstanding outbound messages for the time specified by NN_LINGER socket option. The call will block in the meantime.

If the function succeeds, a true value is returned. Otherwise, undef is returned and nn_errno is set to to one of the values defined below.

nn_setsockopt($s, $level, $option, $value)

    nn_setsockopt($s, NN_SOL_SOCKET, NN_LINGER, 1000) or die nn_errno;
    nn_setsockopt($s, NN_SOL_SOCKET, NN_SUB_SUBSCRIBE, 'ABC') or die nn_errno;

Sets the $value of the socket option $option. The $level argument specifies the protocol level at which the option resides. For generic socket-level options use the NN_SOL_SOCKET level. For socket-type-specific options use the socket type for the $level argument (e.g. NN_SUB). For transport-specific options use the ID of the transport as the $level argument (e.g. NN_TCP).

If the function succeeds a true value is returned. Otherwise, undef is returned and nn_errno is set to to one of the values defined below.

These are the generic socket-level (NN_SOL_SOCKET level) options:

nn_getsockopt($s, $level, $option)

    my $linger = unpack 'i', nn_getsockopt($s, NN_SOL_SOCKET, NN_LINGER) || die nn_errno;

Retrieves the value for the socket option $option. The $level argument specifies the protocol level at which the option resides. For generic socket-level options use the NN_SOL_SOCKET level. For socket-type-specific options use the socket type for the $level argument (e.g. NN_SUB). For transport-specific options use ID of the transport as the $level argument (e.g. NN_TCP).

The function returns a packed string representing the requested socket option, or undef on error, with one of the following reasons for the error placed in nn_errno.

Just what is in the packed string depends on $level and $option; see the list of socket options for details; A common case is that the option is an integer, in which case the result is a packed integer, which you can decode using unpack with the i (or I) format.

This function can be used to retrieve the values for all the generic socket-level (NN_SOL_SOCKET) options documented in nn_getsockopt and also supports these additional generic socket-level options that can only be retrieved but not set:

nn_bind($s, $addr)

    my $eid = nn_bind($s, 'inproc://test');
    die nn_errno unless defined $eid;

Adds a local endpoint to the socket $s. The endpoint can be then used by other applications to connect to.

The $addr argument consists of two parts as follows: transport://address. The transport specifies the underlying transport protocol to use. The meaning of the address part is specific to the underlying transport protocol.

See "Transports" for a list of available transport protocols.

The maximum length of the $addr parameter is specified by NN_SOCKADDR_MAX constant.

Note that nn_bind and nn_connect may be called multiple times on the same socket thus allowing the socket to communicate with multiple heterogeneous endpoints.

If the function succeeds, an endpoint ID is returned. Endpoint ID can be later used to remove the endpoint from the socket via nn_shutdown function.

If the function fails, undef is returned and nn_errno is set to to one of the values defined below.

nn_connect($s, $addr)

    my $eid = nn_connect($s, 'inproc://test');
    die nn_errno unless defined $eid;

Adds a remote endpoint to the socket $s. The library would then try to connect to the specified remote endpoint.

The $addr argument consists of two parts as follows: transport://address. The transport specifies the underlying transport protocol to use. The meaning of the address part is specific to the underlying transport protocol.

See "Protocols" for a list of available transport protocols.

The maximum length of the $addr parameter is specified by NN_SOCKADDR_MAX constant.

Note that nn_connect and nn_bind may be called multiple times on the same socket thus allowing the socket to communicate with multiple heterogeneous endpoints.

If the function succeeds, an endpoint ID is returned. Endpoint ID can be later used to remove the endpoint from the socket via nn_shutdown function.

If the function fails, undef is returned and nn_errno is set to to one of the values defined below.

nn_shutdown($s, $eid)

    nn_shutdown($s, $eid) or die nn_errno;

Removes an endpoint from socket $s. The eid parameter specifies the ID of the endpoint to remove as returned by prior call to nn_bind or nn_connect.

The nn_shutdown call will return immediately. However, the library will try to deliver any outstanding outbound messages to the endpoint for the time specified by the NN_LINGER socket option.

If the function succeeds, a true value is returned. Otherwise, undef is returned and nn_errno is set to to one of the values defined below.

nn_send($s, $data, $flags=0)

    my $bytes_sent = nn_send($s, 'foo');
    die nn_errno unless defined $bytes_sent;

This function will send a message containing the provided $data to the socket $s.

$data can either be anything that can be used as a byte string in perl or a message buffer instance allocated by nn_allocmsg. In case of a message buffer instance the instance will be deallocated and invalidated by the nn_send function. The buffer will be an instance of NanoMsg::Raw::Message::Freed after the call to nn_send.

Which of the peers the message will be sent to is determined by the particular socket type.

The $flags argument, which defaults to 0, is a combination of the flags defined below:

If the function succeeds, the number of bytes in the message is returned. Otherwise, a undef is returned and nn_errno is set to to one of the values defined below.

nn_recv($s, $data, $length=NN_MSG, $flags=0)

    my $bytes_received = nn_recv($s, my $buf, 256);
    die nn_errno unless defined $bytes_received;

Receive a message from the socket $s and store it in the buffer $buf. Any bytes exceeding the length specified by the $length argument will be truncated.

Alternatively, nn_recv can allocate a message buffer instance for you. To do so, set the $length parameter to NN_MSG (the default).

The $flags argument, which defaults to 0, is a combination of the flags defined below:

If the function succeeds number of bytes in the message is returned. Otherwise, undef is returned and nn_errno is set to to one of the values defined below.

nn_sendmsg($s, $flags, $data1, $data2, ..., $dataN)

    my $bytes_sent = nn_sendmsg($s, 0, 'foo', 'bar');
    die nn_errno unless defined $bytes_sent;

This function is a fine-grained alternative to nn_send. It allows sending multiple data buffers that make up a single message without having to create another temporary buffer to hold the concatenation of the different message parts.

The scalars containing the data to be sent ($data1, $data2, ..., $dataN) can either be anything that can be used as a byte string in perl or a message buffer instance allocated by nn_allocmsg. In case of a message buffer instance the instance will be deallocated and invalidated by the nn_sendmsg function. The buffers will be a instances of NanoMsg::Raw::Message::Freed after the call to nn_sendmsg.

When using message buffer instances, only one buffer may be provided.

To which of the peers will the message be sent to is determined by the particular socket type.

The $flags argument is a combination of the flags defined below:

If the function succeeds number of bytes in the message is returned. Otherwise, undef is returned and nn_errno is set to to one of the values defined below.

In the future, nn_sendmsg might allow for sending along additional control data.

nn_recvmsg($s, $flags, $data1 => $len1, $data2 => $len2, ..., $dataN => $lenN)

    my $bytes_received = nn_recvmsg($s, 0, my $buf1 => 256, my $buf2 => 1024);
    die nn_errno unless defined $bytes_received;

This function is a fine-grained alternative to nn_recv. It allows receiving a single message into multiple data buffers of different sizes, eliminating the need to create copies of part of the received message in some cases.

The scalars in which to receive the message data ($buf1, $buf2, ..., $bufN) will be filled with as many bytes of data as is specified by the length parameter following them in the argument list ($len1, $len2, ..., $lenN).

Alternatively, nn_recvmsg can allocate a message buffer instance for you. To do so, set the length parameter of a buffer to to NN_MSG. In this case, only one receive buffer can be provided.

The $flags argument is a combination of the flags defined below:

In the future, nn_recvmsg might allow for receiving additional control data.

nn_allocmsg($size, $type)

    my $msg = nn_allocmsg(3, 0) or die nn_errno;
    $msg->copy('foo');
    nn_send($s, $msg);

Allocate a message of the specified $size to be sent in zero-copy fashion. The content of the message is undefined after allocation and it should be filled in by the user. While nn_send and nn_sendmsg allow to send arbitrary buffers, buffers allocated using nn_allocmsg can be more efficient for large messages as they allow for using zero-copy techniques.

The $type parameter specifies type of allocation mechanism to use. Zero is the default one. However, individual transport mechanisms may define their own allocation mechanisms, such as allocating in shared memory or allocating a memory block pinned down to a physical memory address. Such allocation, when used with the transport that defines them, should be more efficient than the default allocation mechanism.

If the function succeeds a newly allocated message buffer instance (an object instance of the class NanoMsg::Raw::Message) is returned. Otherwise, undef is returned and nn_errno is set to to one of the values defined below.

nn_errno()

Returns value of errno after the last call to any nanomsg function in the current thread. This function can be used in the same way the $! global variable is be used for many other system and library calls.

The return value can be used in numeric context, for example to compare it with error code constants such as EAGAIN, or in a string context, to retrieve a textual message describing the error.

nn_strerror($errno)

Returns a textual representation of the error described by the nummeric $errno provided. It shouldn't normally be necessary to ever call this function, as using nn_errno in string context is basically equivalent to nn_strerror(nn_errno).

nn_device($s1, $s2)

    nn_device($s1, $s2) or die;

Starts a device to forward messages between two sockets. If both sockets are valid, the nn_device function loops and sends and messages received from $s1 to $s2 and vice versa. If only one socket is valid and the other is undef, nn_device works in a loopback mode — it loops and sends any messages received from the socket back to itself.

The function loops until it hits an error. In such case it returns undef and sets nn_errno to one of the values defined below.

nn_term()

    nn_term();

To help with shutdown of multi-threaded programs the nn_term function is provided. It informs all the open sockets that process termination is underway.

If a socket is blocked inside a blocking function, such as nn_recv, it will be unblocked and the ETERM error will be returned to the user. Similarly, any subsequent attempt to invoke a socket function other than nn_close after nn_term was called will result in an ETERM error.

If waiting for NN_SNDFD or NN_RCVFD using a polling function, such as poll or select, the call will unblock with both NN_SNDFD and NN_RCVFD signaled.

The nn_term function itself is non-blocking.

WARNING ^

nanomsg, the c library this module is based on, is still in alpha stage!

Protocols ^

One-to-one protocol

Pair protocol is the simplest and least scalable scalability protocol. It allows scaling by breaking the application in exactly two pieces. For example, if a monolithic application handles both accounting and agenda of HR department, it can be split into two applications (accounting vs. HR) that are run on two separate servers. These applications can then communicate via PAIR sockets.

The downside of this protocol is that its scaling properties are very limited. Splitting the application into two pieces allows to scale to two servers. To add the third server to the cluster, application has to be split once more, say be separating HR functionality into hiring module and salary computation module. Whenever possible, try to use one of the more scalable protocols instead.

Socket Types

Socket Options

No protocol-specific socket options are defined at the moment.

Request/reply protocol

This protocol is used to distribute the workload among multiple stateless workers.

Socket Types

Socket Options

Publish/subscribe protocol

Broadcasts messages to multiple destinations.

Socket Types

Socket Options

Survey protocol

Allows to broadcast a survey to multiple locations and gather the responses.

Socket Types

Socket Options

Pipeline protocol

Fair queues messages from the previous processing step and load balances them among instances of the next processing step.

Socket Types

Socket Options

No protocol-specific socket options are defined at the moment.

Message bus protocol

Broadcasts messages from any node to all other nodes in the topology. The socket should never receives messages that it sent itself.

This pattern scales only to local level (within a single machine or within a single LAN). Trying to scale it further can result in overloading individual nodes with messages.

WARNING: For bus topology to function correctly, the user is responsible for ensuring that path from each node to any other node exists within the topology.

Raw (AF_SP_RAW) BUS socket never send the message to the peer it was received from.

Socket Types

Socket Options

There are no options defined at the moment.

Transports ^

In-process transport

The in-process transport allows to send messages between threads or modules inside a process. In-process address is an arbitrary case-sensitive string preceded by inproc:// protocol specifier. All in-process addresses are visible from any module within the process. They are not visible from outside of the process.

The overall buffer size for an inproc connection is determined by the NN_RCVBUF socket option on the receiving end of the connection. The NN_SNDBUF socket option is ignored. In addition to the buffer, one message of arbitrary size will fit into the buffer. That way, even messages larger than the buffer can be transfered via inproc connection.

This transport's ID is NN_INPROC.

Inter-process transport

The inter-process transport allows for sending messages between processes within a single box. The implementation uses native IPC mechanism provided by the local operating system and the IPC addresses are thus OS-specific.

On POSIX-compliant systems, UNIX domain sockets are used and IPC addresses are file references. Note that both relative (ipc://test.ipc) and absolute (ipc:///tmp/test.ipc) paths may be used. Also note that access rights on the IPC files must be set in such a way that the appropriate applications can actually use them.

On Windows, named pipes are used for IPC. IPC address is an arbitrary case-insensitive string containing any character except for backslash. Internally, address ipc://test means that named pipe \\.\pipe\test will be used.

This transport's ID is NN_IPC.

TCP transport

The TCP transport allows for passing message over the network using simple reliable one-to-one connections. TCP is the most widely used transport protocol, it is virtually ubiquitous and thus the transport of choice for communication over the network.

When binding a TCP socket address of the form tcp://interface:port should be used. Port is the TCP port number to use. Interface is one of the following (optionally placed within square brackets):

When connecting a TCP socket address of the form tcp://interface;address:port should be used. Port is the TCP port number to use. Interface is optional and specifies which local network interface to use. If not specified, OS will select an appropriate interface itself. If specified it can be one of the following (optionally placed within square brackets):

Finally, address specifies the remote address to connect to. It can be one of the following (optionally placed within square brackets):

This transport's ID is NN_TCP.

Socket Options

Constants ^

In addition to all the error constants and NN_ constants used in the documentation of the individual functions, protocols, and transports, the following constants are available:

SEE ALSO ^

AUTHORS ^

COPYRIGHT AND LICENSE ^

This software is Copyright (c) 2013 by Florian Ragwitz.

This is free software, licensed under:

  The MIT (X11) License
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