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doc: sort dgram alphabetically
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Reorders, with no contextual changes, the dgram documentation
alphabetically.

PR-URL: #3662
Reviewed-By: Evan Lucas <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Jeremiah Senkpiel <[email protected]>
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@tflanagan @rvagg
tflanagan authored and rvagg committed Nov 13, 2015
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301 changes: 149 additions & 152 deletions doc/api/dgram.markdown
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Original file line number Diff line number Diff line change
Expand Up @@ -20,66 +20,11 @@ You have to change it to this:
s.addMembership('224.0.0.114');
});


## dgram.createSocket(type[, callback])

* `type` String. Either 'udp4' or 'udp6'
* `callback` Function. Attached as a listener to `message` events.
Optional
* Returns: Socket object

Creates a datagram Socket of the specified types. Valid types are `udp4`
and `udp6`.

Takes an optional callback which is added as a listener for `message` events.

Call `socket.bind()` if you want to receive datagrams. `socket.bind()` will
bind to the "all interfaces" address on a random port (it does the right thing
for both `udp4` and `udp6` sockets). You can then retrieve the address and port
with `socket.address().address` and `socket.address().port`.

## dgram.createSocket(options[, callback])
* `options` Object
* `callback` Function. Attached as a listener to `message` events.
* Returns: Socket object

The `options` object should contain a `type` field of either `udp4` or `udp6`
and an optional boolean `reuseAddr` field.

When `reuseAddr` is `true` `socket.bind()` will reuse the address, even if
another process has already bound a socket on it. `reuseAddr` defaults to
`false`.

Takes an optional callback which is added as a listener for `message` events.

Call `socket.bind()` if you want to receive datagrams. `socket.bind()` will
bind to the "all interfaces" address on a random port (it does the right thing
for both `udp4` and `udp6` sockets). You can then retrieve the address and port
with `socket.address().address` and `socket.address().port`.

## Class: dgram.Socket

The dgram Socket class encapsulates the datagram functionality. It
should be created via `dgram.createSocket(...)`

### Event: 'message'

* `msg` Buffer object. The message
* `rinfo` Object. Remote address information

Emitted when a new datagram is available on a socket. `msg` is a `Buffer` and
`rinfo` is an object with the sender's address information:

socket.on('message', function(msg, rinfo) {
console.log('Received %d bytes from %s:%d\n',
msg.length, rinfo.address, rinfo.port);
});

### Event: 'listening'

Emitted when a socket starts listening for datagrams. This happens as soon as UDP sockets
are created.

### Event: 'close'

Emitted after a socket is closed with `close()`. No new `message` events will be emitted
Expand All @@ -91,72 +36,38 @@ on this socket.

Emitted when an error occurs.

### socket.send(buf, offset, length, port, address[, callback])

* `buf` Buffer object or string. Message to be sent
* `offset` Integer. Offset in the buffer where the message starts.
* `length` Integer. Number of bytes in the message.
* `port` Integer. Destination port.
* `address` String. Destination hostname or IP address.
* `callback` Function. Called when the message has been sent. Optional.

For UDP sockets, the destination port and address must be specified. A string
may be supplied for the `address` parameter, and it will be resolved with DNS.

If the address is omitted or is an empty string, `'0.0.0.0'` or `'::0'` is used
instead. Depending on the network configuration, those defaults may or may not
work; it's best to be explicit about the destination address.
### Event: 'listening'

If the socket has not been previously bound with a call to `bind`, it gets
assigned a random port number and is bound to the "all interfaces" address
(`'0.0.0.0'` for `udp4` sockets, `'::0'` for `udp6` sockets.)
Emitted when a socket starts listening for datagrams. This happens as soon as UDP sockets
are created.

An optional callback may be specified to detect DNS errors or for determining
when it's safe to reuse the `buf` object. Note that DNS lookups delay the time
to send for at least one tick. The only way to know for sure that the datagram
has been sent is by using a callback. If an error occurs and a callback is
given, the error will be the first argument to the callback. If a callback is
not given, the error is emitted as an `'error'` event on the `socket` object.
### Event: 'message'

With consideration for multi-byte characters, `offset` and `length` will
be calculated with respect to
[byte length](buffer.html#buffer_class_method_buffer_bytelength_string_encoding)
and not the character position.
* `msg` Buffer object. The message
* `rinfo` Object. Remote address information

Example of sending a UDP packet to a random port on `localhost`;
Emitted when a new datagram is available on a socket. `msg` is a `Buffer` and
`rinfo` is an object with the sender's address information:

var dgram = require('dgram');
var message = new Buffer("Some bytes");
var client = dgram.createSocket("udp4");
client.send(message, 0, message.length, 41234, "localhost", function(err) {
client.close();
socket.on('message', function(msg, rinfo) {
console.log('Received %d bytes from %s:%d\n',
msg.length, rinfo.address, rinfo.port);
});

**A Note about UDP datagram size**
### socket.addMembership(multicastAddress[, multicastInterface])

The maximum size of an `IPv4/v6` datagram depends on the `MTU` (_Maximum Transmission Unit_)
and on the `Payload Length` field size.
* `multicastAddress` String
* `multicastInterface` String, Optional

- The `Payload Length` field is `16 bits` wide, which means that a normal payload
cannot be larger than 64K octets including internet header and data
(65,507 bytes = 65,535 − 8 bytes UDP header − 20 bytes IP header);
this is generally true for loopback interfaces, but such long datagrams
are impractical for most hosts and networks.
Tells the kernel to join a multicast group with `IP_ADD_MEMBERSHIP` socket option.

- The `MTU` is the largest size a given link layer technology can support for datagrams.
For any link, `IPv4` mandates a minimum `MTU` of `68` octets, while the recommended `MTU`
for IPv4 is `576` (typically recommended as the `MTU` for dial-up type applications),
whether they arrive whole or in fragments.
If `multicastInterface` is not specified, the OS will try to add membership to all valid
interfaces.

For `IPv6`, the minimum `MTU` is `1280` octets, however, the mandatory minimum
fragment reassembly buffer size is `1500` octets.
The value of `68` octets is very small, since most current link layer technologies have
a minimum `MTU` of `1500` (like Ethernet).
### socket.address()

Note that it's impossible to know in advance the MTU of each link through which
a packet might travel, and that generally sending a datagram greater than
the (receiver) `MTU` won't work (the packet gets silently dropped, without
informing the source that the data did not reach its intended recipient).
Returns an object containing the address information for a socket. For UDP sockets,
this object will contain `address` , `family` and `port`.

### socket.bind([port][, address][, callback])

Expand Down Expand Up @@ -204,7 +115,6 @@ Example of a UDP server listening on port 41234:
server.bind(41234);
// server listening 0.0.0.0:41234


### socket.bind(options[, callback])

* `options` {Object} - Required. Supports the following properties:
Expand All @@ -230,16 +140,90 @@ shown below.
exclusive: true
});


### socket.close([callback])

Close the underlying socket and stop listening for data on it. If a callback is
provided, it is added as a listener for the ['close'](#dgram_event_close) event.

### socket.address()
### socket.dropMembership(multicastAddress[, multicastInterface])

Returns an object containing the address information for a socket. For UDP sockets,
this object will contain `address` , `family` and `port`.
* `multicastAddress` String
* `multicastInterface` String, Optional

Opposite of `addMembership` - tells the kernel to leave a multicast group with
`IP_DROP_MEMBERSHIP` socket option. This is automatically called by the kernel
when the socket is closed or process terminates, so most apps will never need to call
this.

If `multicastInterface` is not specified, the OS will try to drop membership to all valid
interfaces.

### socket.send(buf, offset, length, port, address[, callback])

* `buf` Buffer object or string. Message to be sent
* `offset` Integer. Offset in the buffer where the message starts.
* `length` Integer. Number of bytes in the message.
* `port` Integer. Destination port.
* `address` String. Destination hostname or IP address.
* `callback` Function. Called when the message has been sent. Optional.

For UDP sockets, the destination port and address must be specified. A string
may be supplied for the `address` parameter, and it will be resolved with DNS.

If the address is omitted or is an empty string, `'0.0.0.0'` or `'::0'` is used
instead. Depending on the network configuration, those defaults may or may not
work; it's best to be explicit about the destination address.

If the socket has not been previously bound with a call to `bind`, it gets
assigned a random port number and is bound to the "all interfaces" address
(`'0.0.0.0'` for `udp4` sockets, `'::0'` for `udp6` sockets.)

An optional callback may be specified to detect DNS errors or for determining
when it's safe to reuse the `buf` object. Note that DNS lookups delay the time
to send for at least one tick. The only way to know for sure that the datagram
has been sent is by using a callback. If an error occurs and a callback is
given, the error will be the first argument to the callback. If a callback is
not given, the error is emitted as an `'error'` event on the `socket` object.

With consideration for multi-byte characters, `offset` and `length` will
be calculated with respect to
[byte length](buffer.html#buffer_class_method_buffer_bytelength_string_encoding)
and not the character position.

Example of sending a UDP packet to a random port on `localhost`;

var dgram = require('dgram');
var message = new Buffer("Some bytes");
var client = dgram.createSocket("udp4");
client.send(message, 0, message.length, 41234, "localhost", function(err) {
client.close();
});

**A Note about UDP datagram size**

The maximum size of an `IPv4/v6` datagram depends on the `MTU` (_Maximum Transmission Unit_)
and on the `Payload Length` field size.

- The `Payload Length` field is `16 bits` wide, which means that a normal payload
cannot be larger than 64K octets including internet header and data
(65,507 bytes = 65,535 − 8 bytes UDP header − 20 bytes IP header);
this is generally true for loopback interfaces, but such long datagrams
are impractical for most hosts and networks.

- The `MTU` is the largest size a given link layer technology can support for datagrams.
For any link, `IPv4` mandates a minimum `MTU` of `68` octets, while the recommended `MTU`
for IPv4 is `576` (typically recommended as the `MTU` for dial-up type applications),
whether they arrive whole or in fragments.

For `IPv6`, the minimum `MTU` is `1280` octets, however, the mandatory minimum
fragment reassembly buffer size is `1500` octets.
The value of `68` octets is very small, since most current link layer technologies have
a minimum `MTU` of `1500` (like Ethernet).

Note that it's impossible to know in advance the MTU of each link through which
a packet might travel, and that generally sending a datagram greater than
the (receiver) `MTU` won't work (the packet gets silently dropped, without
informing the source that the data did not reach its intended recipient).

### socket.setBroadcast(flag)

Expand All @@ -248,18 +232,12 @@ this object will contain `address` , `family` and `port`.
Sets or clears the `SO_BROADCAST` socket option. When this option is set, UDP packets
may be sent to a local interface's broadcast address.

### socket.setTTL(ttl)

* `ttl` Integer
### socket.setMulticastLoopback(flag)

Sets the `IP_TTL` socket option. TTL stands for "Time to Live," but in this context it
specifies the number of IP hops that a packet is allowed to go through. Each router or
gateway that forwards a packet decrements the TTL. If the TTL is decremented to 0 by a
router, it will not be forwarded. Changing TTL values is typically done for network
probes or when multicasting.
* `flag` Boolean

The argument to `setTTL()` is a number of hops between 1 and 255. The default on most
systems is 64.
Sets or clears the `IP_MULTICAST_LOOP` socket option. When this option is set, multicast
packets will also be received on the local interface.

### socket.setMulticastTTL(ttl)

Expand All @@ -273,35 +251,26 @@ decrements the TTL. If the TTL is decremented to 0 by a router, it will not be f
The argument to `setMulticastTTL()` is a number of hops between 0 and 255. The default on most
systems is 1.

### socket.setMulticastLoopback(flag)

* `flag` Boolean

Sets or clears the `IP_MULTICAST_LOOP` socket option. When this option is set, multicast
packets will also be received on the local interface.

### socket.addMembership(multicastAddress[, multicastInterface])

* `multicastAddress` String
* `multicastInterface` String, Optional
### socket.setTTL(ttl)

Tells the kernel to join a multicast group with `IP_ADD_MEMBERSHIP` socket option.
* `ttl` Integer

If `multicastInterface` is not specified, the OS will try to add membership to all valid
interfaces.
Sets the `IP_TTL` socket option. TTL stands for "Time to Live," but in this context it
specifies the number of IP hops that a packet is allowed to go through. Each router or
gateway that forwards a packet decrements the TTL. If the TTL is decremented to 0 by a
router, it will not be forwarded. Changing TTL values is typically done for network
probes or when multicasting.

### socket.dropMembership(multicastAddress[, multicastInterface])
The argument to `setTTL()` is a number of hops between 1 and 255. The default on most
systems is 64.

* `multicastAddress` String
* `multicastInterface` String, Optional
### socket.ref()

Opposite of `addMembership` - tells the kernel to leave a multicast group with
`IP_DROP_MEMBERSHIP` socket option. This is automatically called by the kernel
when the socket is closed or process terminates, so most apps will never need to call
this.
Opposite of `unref`, calling `ref` on a previously `unref`d socket will *not*
let the program exit if it's the only socket left (the default behavior). If
the socket is `ref`d calling `ref` again will have no effect.

If `multicastInterface` is not specified, the OS will try to drop membership to all valid
interfaces.
Returns `socket`.

### socket.unref()

Expand All @@ -311,10 +280,38 @@ active socket in the event system. If the socket is already `unref`d calling

Returns `socket`.

### socket.ref()
## dgram.createSocket(options[, callback])
* `options` Object
* `callback` Function. Attached as a listener to `message` events.
* Returns: Socket object

Opposite of `unref`, calling `ref` on a previously `unref`d socket will *not*
let the program exit if it's the only socket left (the default behavior). If
the socket is `ref`d calling `ref` again will have no effect.
The `options` object should contain a `type` field of either `udp4` or `udp6`
and an optional boolean `reuseAddr` field.

Returns `socket`.
When `reuseAddr` is `true` `socket.bind()` will reuse the address, even if
another process has already bound a socket on it. `reuseAddr` defaults to
`false`.

Takes an optional callback which is added as a listener for `message` events.

Call `socket.bind()` if you want to receive datagrams. `socket.bind()` will
bind to the "all interfaces" address on a random port (it does the right thing
for both `udp4` and `udp6` sockets). You can then retrieve the address and port
with `socket.address().address` and `socket.address().port`.

## dgram.createSocket(type[, callback])

* `type` String. Either 'udp4' or 'udp6'
* `callback` Function. Attached as a listener to `message` events.
Optional
* Returns: Socket object

Creates a datagram Socket of the specified types. Valid types are `udp4`
and `udp6`.

Takes an optional callback which is added as a listener for `message` events.

Call `socket.bind()` if you want to receive datagrams. `socket.bind()` will
bind to the "all interfaces" address on a random port (it does the right thing
for both `udp4` and `udp6` sockets). You can then retrieve the address and port
with `socket.address().address` and `socket.address().port`.

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