Class: PackfileReader::PackfileHeader

Inherits:
Object
  • Object
show all
Defined in:
lib/packfile_reader/packfile_header.rb

Overview

Defines a class for the HEADER portion of a git packfile From: git-scm.com/docs/pack-format

A header appears at the beginning and consists of the following:

4-byte signature:

The signature is: {'P', 'A', 'C', 'K'}

4-byte version number (network byte order):

Git currently accepts version number 2 or 3 but generates version 2 only.

4-byte number of objects contained in the pack (network byte order)

Observation: we cannot have more than 4G versions ;-) and more than 4G objects in a pack.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(packfile_io) ⇒ PackfileHeader

Creates a new PackfileHeader instance reading data from the beginning of a packfile. It fails if it cannot parse the data or if the signature does not match the expected ‘PACK’ string

Params:

packfile_io

the opened packfile handler in binary format (usually the output of File.open(‘path’, ‘rb’))



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# File 'lib/packfile_reader/packfile_header.rb', line 28

def initialize(packfile_io)
  begin
    go_to_start(packfile_io)
    @sign = parse_sign(packfile_io)
    @version = parse_version(packfile_io)
    @n_entries = parse_n_entries(packfile_io)
  rescue
    raise 'Invalid packfile. Cannot parse header'
  end
  raise "Invalid signature. Got '#{@sign}' expected 'PACK'" unless @sign == 'PACK'
end

Instance Attribute Details

#n_entries ⇒ Object (readonly)

how many objects in the packfile



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# File 'lib/packfile_reader/packfile_header.rb', line 20

def n_entries
  @n_entries
end

#sign ⇒ Object (readonly)

signature (must be PACK)



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# File 'lib/packfile_reader/packfile_header.rb', line 19

def sign
  @sign
end

#version ⇒ Object (readonly)

version of the packfile



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# File 'lib/packfile_reader/packfile_header.rb', line 18

def version
  @version
end

Instance Method Details

#to_s ⇒ Object 



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# File 'lib/packfile_reader/packfile_header.rb', line 40

def to_s
  <<~EOS.strip
  Packfile Headers
  - Signature: #{@sign}
  - Version: #{@version}
  - Entries: #{@n_entries}
  EOS
end