Class: IParty::MaxMind::LazyReader

Inherits:
Object
  • Object
show all
Defined in:
lib/iparty/max_mind/lazy_reader.rb

Overview

A low memory file reader for MaxMindDB (mmdb) files. Avoids reading the database into memory. Has a lower memory footprint but slower lookup times.

Constant Summary collapse

METADATA_MAX_SIZE = 
128 * 1024

Instance Method Summary collapse

Constructor Details

#initialize(path) ⇒ LazyReader

Returns a new instance of LazyReader.



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# File 'lib/iparty/max_mind/lazy_reader.rb', line 10

def initialize path
  @mutex = Mutex.new
  @file = File.open(path, "rb")
end

Instance Method Details

#[](pos, length = 1) ⇒ Object 



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# File 'lib/iparty/max_mind/lazy_reader.rb', line 15

def [] pos, length = 1
  atomic_read(length, pos)
end

#atomic_read(length, pos) ⇒ Object 



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# File 'lib/iparty/max_mind/lazy_reader.rb', line 34

def atomic_read length, pos
  # Prefer `pread` in environments where it is available. `pread` provides atomic file access across processes.
  if @file.respond_to?(:pread)
    @file.pread(length, pos)
  else
    @mutex.synchronize do
      @file.seek(pos)
      @file.read(length)
    end
  end
end

#close ⇒ Object 



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# File 'lib/iparty/max_mind/lazy_reader.rb', line 19

def close
  @file.close
end

#closed? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/iparty/max_mind/lazy_reader.rb', line 23

def closed?
  @file.closed?
end

#rindex(search) ⇒ Object 



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# File 'lib/iparty/max_mind/lazy_reader.rb', line 27

def rindex search
  base = [0, @file.size - METADATA_MAX_SIZE].max
  tail = atomic_read(METADATA_MAX_SIZE, base)
  pos = tail.rindex(search)
  base + pos unless pos.nil?
end