class SF::Packet

SF::Packet
Reference
Object

Overview

Utility class to build blocks of data to transfer over the network

Packets provide a safe and easy way to serialize data, in order to send it over the network using sockets (SF::TcpSocket, SF::UdpSocket).

Packets solve 2 fundamental problems that arise when transferring data over the network:

data is interpreted correctly according to the endianness
the bounds of the packet are preserved (one send == one receive)

The SF::Packet class provides both input and output, using #read and #write methods.

It is recommended to use only fixed-size types (like Int32, etc.), to avoid possible differences between the sender and the receiver.

Usage example:

x = 24u32
s = "hello"
d = 5.89

# Group the variables to send into a packet
packet = SF::Packet.new
packet.write x
packet.write s
packet.write d

# Send it over the network (socket is a valid SF::TcpSocket)
socket.send packet

# -----------------------------------------------------------------

# Receive the packet at the other end
packet = SF::Packet.new
socket.receive(packet)

# Extract the variables contained in the packet
x = packet.read UInt32
s = packet.read String
d = packet.read Float64
if packet.valid?
  # Data extracted successfully...
end

Packets have overloads of #read and #write methods for standard types:

Bool
Fixed-size integer types (Int8/16/32/64, UInt8/16/32/64)
Floating point numbers (Float32/64)
String

Like standard streams, it is also possible to define your own overloads of these methods in order to handle your custom types.

struct MyStruct
  number : Float32
  integer : Int8
  str : String
end

class SF::Packet
  def write(m : MyStruct)
    write m.number
    write m.integer
    write m.str
  end

  def read(type : MyStruct.class) : MyStruct
    MyStruct.new(packet.read(Float32), packet.read(Int8), packet.read(String))
  end
end

See also: SF::TcpSocket, SF::UdpSocket

Defined in:

network/obj.cr

Constructors

.new
Default constructor

Instance Method Summary

#append(data : Slice)
Append data to the end of the packet
#clear
Clear the packet
#data : Pointer(Void)
Get a pointer to the data contained in the packet
#data_size : Int32
Get the size of the data contained in the packet
#dup : Packet
Returns a shallow copy of this object.
#end_of_packet : Bool
Tell if the reading position has reached the end of the packet
#finalize
Virtual destructor
#read(type : Bool.class) : Bool
Read data from the packet.
#read(type : Int8.class) : Int8
Read data from the packet.
#read(type : UInt8.class) : UInt8
Read data from the packet.
#read(type : Int16.class) : Int16
Read data from the packet.
#read(type : UInt16.class) : UInt16
Read data from the packet.
#read(type : Int32.class) : Int32
Read data from the packet.
#read(type : UInt32.class) : UInt32
Read data from the packet.
#read(type : Int64.class) : Int64
Read data from the packet.
#read(type : UInt64.class) : UInt64
Read data from the packet.
#read(type : Float32.class) : Float32
Read data from the packet.
#read(type : Float64.class) : Float64
Read data from the packet.
#read(type : String.class) : String
Read data from the packet.
#valid? : Bool
Test the validity of the packet, for reading
#write(data : Bool)
Write data into the packet
#write(data : Int8)
Write data into the packet
#write(data : UInt8)
Write data into the packet
#write(data : Int16)
Write data into the packet
#write(data : UInt16)
Write data into the packet
#write(data : Int32)
Write data into the packet
#write(data : UInt32)
Write data into the packet
#write(data : Int64)
Write data into the packet
#write(data : UInt64)
Write data into the packet
#write(data : Float32)
Write data into the packet
#write(data : Float64)
Write data into the packet
#write(data : String)
Write data into the packet

Constructor Detail

def self.new #

Default constructor

Creates an empty packet.

[View source]

Instance Method Detail

def append(data : Slice) #

Append data to the end of the packet

data - Pointer to the sequence of bytes to append
size_in_bytes - Number of bytes to append

See also: #clear

[View source]

def clear #

Clear the packet

After calling Clear, the packet is empty.

See also: #append

[View source]

def data : Pointer(Void) #

Get a pointer to the data contained in the packet

WARNING The returned pointer may become invalid after you append data to the packet, therefore it should never be stored. The return pointer is NULL if the packet is empty.

Returns: Pointer to the data

See also: #data_size

[View source]

def data_size : Int32 #

Get the size of the data contained in the packet

This function returns the number of bytes pointed to by what data returns.

Returns: Data size, in bytes

See also: #data

[View source]

def dup : Packet #

Description copied from class Reference

Returns a shallow copy of this object.

This allocates a new object and copies the contents of self into it.

[View source]

def end_of_packet : Bool #

Tell if the reading position has reached the end of the packet

This function is useful to know if there is some data left to be read, without actually reading it.

Returns: True if all data was read, false otherwise

See also: operator bool

[View source]

def finalize #

Virtual destructor

[View source]

def read(type : Bool.class) : Bool #