`class Window`

Flow control window for managing HTTP/2 data flow.

Definitions

`DEFAULT_CAPACITY = 0xFFFF`

When an HTTP/2 connection is first established, new streams are created with an initial flow-control window size of 65,535 octets. The connection flow-control window is also 65,535 octets.

`def initialize(capacity = DEFAULT_CAPACITY)`

Initialize a new flow control window.

Signature

parameter　capacity　Integer: The initial window size, typically from the settings.

Implementation

def initialize(capacity = DEFAULT_CAPACITY)
	# This is the main field required:
	@available = capacity
	
	# These two fields are primarily used for efficiently sending window updates:
	@used = 0
	@capacity = capacity
end

`def full?`

The window is completely full?

Implementation

def full?
	@available <= 0
end

`def capacity=(value)`

When the value of SETTINGS_INITIAL_WINDOW_SIZE changes, a receiver MUST adjust the size of all stream flow-control windows that it maintains by the difference between the new value and the old value.

Implementation

def capacity= value
	difference = value - @capacity
	
	# An endpoint MUST treat a change to SETTINGS_INITIAL_WINDOW_SIZE that causes any flow-control window to exceed the maximum size as a connection error of type FLOW_CONTROL_ERROR.
	if (@available + difference) > MAXIMUM_ALLOWED_WINDOW_SIZE
		raise FlowControlError, "Changing window size by #{difference} caused overflow: #{@available + difference} > #{MAXIMUM_ALLOWED_WINDOW_SIZE}!"
	end
	
	@available += difference
	@capacity = value
end

`def consume(amount)`

Consume a specific amount from the available window.

Signature

parameter　amount　Integer: The amount to consume from the window.

Implementation

def consume(amount)
	@available -= amount
	@used += amount
end

`def available?`

Check if there is available window capacity.

Signature

returns　Boolean: True if there is available capacity.

Implementation

def available?
	@available > 0
end

`def expand(amount)`

Expand the window by a specific amount.

Signature

parameter　amount　Integer: The amount to expand the window by.
raises　FlowControlError: If expansion would cause overflow.

Implementation

def expand(amount)
	available = @available + amount
	
	if available > MAXIMUM_ALLOWED_WINDOW_SIZE
		raise FlowControlError, "Expanding window by #{amount} caused overflow: #{available} > #{MAXIMUM_ALLOWED_WINDOW_SIZE}!"
	end
	
	# puts "expand(#{amount}) @available=#{@available}"
	@available += amount
	@used -= amount
end

`def wanted`

Get the amount of window that should be reclaimed.

Signature

returns　Integer: The amount of used window space.

Implementation

def wanted
	@used
end

`def limited?`

Check if the window is limited and needs updating.

Signature

returns　Boolean: True if available capacity is less than half of total capacity.

Implementation

def limited?
	@available < (@capacity / 2)
end

`def inspect`

Get a string representation of the window.

Signature

returns　String: Human-readable window information.

Implementation

def inspect
	"\#<#{self.class} available=#{@available} used=#{@used} capacity=#{@capacity}#{limited? ? " limited" : nil}>"
end