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class SF::Packet
inherits Reference #

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

Class methods#

.new #

Default constructor

Creates an empty packet.

View source

Methods#

#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

#clear #

Clear the packet

After calling Clear, the packet is empty.

See also: append

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#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

#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

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#dup : Packet #

Returns a shallow copy of this object.

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

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#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

#finalize #

Virtual destructor

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

Read data from the packet. The expected type corresponds to what was actually sent.

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#read(type : Float32.class) : Float32 #

Read data from the packet. The expected type corresponds to what was actually sent.

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#read(type : String.class) : String #

Read data from the packet. The expected type corresponds to what was actually sent.

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#read(type : Float64.class) : Float64 #

Read data from the packet. The expected type corresponds to what was actually sent.

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#read(type : UInt64.class) : UInt64 #

Read data from the packet. The expected type corresponds to what was actually sent.

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#read(type : Int64.class) : Int64 #

Read data from the packet. The expected type corresponds to what was actually sent.

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#read(type : UInt32.class) : UInt32 #

Read data from the packet. The expected type corresponds to what was actually sent.

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#read(type : Int32.class) : Int32 #

Read data from the packet. The expected type corresponds to what was actually sent.

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#read(type : UInt16.class) : UInt16 #

Read data from the packet. The expected type corresponds to what was actually sent.

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#read(type : Int16.class) : Int16 #

Read data from the packet. The expected type corresponds to what was actually sent.

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#read(type : UInt8.class) : UInt8 #

Read data from the packet. The expected type corresponds to what was actually sent.

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#read(type : Int8.class) : Int8 #

Read data from the packet. The expected type corresponds to what was actually sent.

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#valid? : Bool #

Test the validity of the packet, for reading

This operator allows to test the packet as a boolean variable, to check if a reading operation was successful.

A packet will be in an invalid state if it has no more data to read.

This behavior is the same as standard C++ streams.

Usage example:

x = packet.read(Float32)
if packet.valid?
   # ok, x was extracted successfully
end

Returns: True if last data extraction from packet was successful

See also: end_of_packet

View source

#write(data : String) #

Write data into the packet

View source

#write(data : Float64) #

Write data into the packet

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#write(data : Float32) #

Write data into the packet

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#write(data : UInt64) #

Write data into the packet

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#write(data : Int64) #

Write data into the packet

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#write(data : UInt32) #

Write data into the packet

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#write(data : Int32) #

Write data into the packet

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#write(data : UInt16) #

Write data into the packet

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#write(data : Int16) #

Write data into the packet

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#write(data : UInt8) #

Write data into the packet

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#write(data : Int8) #

Write data into the packet

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#write(data : Bool) #

Write data into the packet

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