Class: PureCDB::Reader

Inherits:
Base
  • Object
show all
Includes:
Enumerable
Defined in:
lib/purecdb/reader.rb

Overview

Read 32 bit or 64 bit CDB files.

Constant Summary

Constants inherited from Base

Base::CDB64_MAGIC, Base::DEFAULT_HASHPTR_SIZE, Base::DEFAULT_LENGTH_SIZE, Base::DEFAULT_NUM_HASHES

Instance Attribute Summary

Attributes inherited from Base

#hashptr_size, #length_size, #mode, #num_hashes

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from Base

#hash, #hash_size, #hashref_size, #set_mode, #set_stream

Constructor Details

#initialize(target, *options) ⇒ Reader

Open a CDB file for reading.

:call-seq:

r = PureCDB::Reader.new(file)
r = PureCDB::Reader.new(file, options)
PureCDB::Reader.new(file)  {|r| ... }
PureCDB::Reader.new(file, options) {|r| ... }

file can be a String or any object that meets the minimum requirements, which means having #sysseek, #sysopen to and #sysclose which does not arbitrarily sttop access ot it.

If Mmap is available, the code will attempt to use it if target is a filename



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# File 'lib/purecdb/reader.rb', line 29

def initialize target, *options
  if target.is_a?(String)
    @name = target
    @io = File.new(target,"rb")
    raise "Unable to open file #{target}" if !@io
  else
    set_stream(target)
  end
  
  @io.sysseek(-8,IO::SEEK_END)
  tail = @io.sysread(8)
  raise "Unable to read trailing 8 bytes for magic cookie" if tail.size != 8
  mode = tail == CDB64_MAGIC ? 64 : 32

  super *options
  if @mode == :detect
    set_mode(mode)
  elsif @mode != mode
    raise "#{mode}bit mode detected in file; options request #{@mode}bit mode"
  end

  @m = FFI::Mmap.new(target,"r", FFI::Mmap::MAP_SHARED) rescue nil
  read_hashes

  raise "Invalid File (Hashes are all empty)" if @hashes.uniq == [0]

  if block_given?
    yield(self)
    close
  else
  end
end

Class Method Details

.open(target, *options, &block) ⇒ Object

Alternative to PureCDB::Reader.new(target,options) ..



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# File 'lib/purecdb/reader.rb', line 77

def self.open(target, *options, &block)
  Reader.new(target, *options, &block)
end

Instance Method Details

#close ⇒ Object

Close the CDB file



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# File 'lib/purecdb/reader.rb', line 84

def close
  @io.close if @io
  @m.unmap if @m
  @m = nil
  @io = nil
end

#each ⇒ Object

Iterate over all key/value pairs in the order they occur in the file. This is not sorted or insertion order.

each will yield each key,value pair separately even when a key is duplicate.



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# File 'lib/purecdb/reader.rb', line 96

def each
  pos = hash_size
  hoff0 = @hashes[0]
  while pos < hoff0
    key, value = *read_entry(pos)
    yield(key,value)
    pos += key.length + value.length + hashref_size
  end
end

#mmap? ⇒ Boolean

Is the file mmap’ed? Note that this may in theory return true right after opening the file, but return false after attempting to read if the attempt to read from the mmap object fails for whatever reason.

I’m not sure that can ever happen, but to be 100% sure, check after a lookup

Returns:

  • (Boolean) 


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# File 'lib/purecdb/reader.rb', line 70

def mmap?
   @m.nil? == false
end

#values(key) ⇒ Object

Returns all values for key in an array



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# File 'lib/purecdb/reader.rb', line 107

def values(key)
  h = hash(key)

  hoff = @hashes[(h % 256)*2]
  hlen = @hashes[(h % 256)*2 + 1]

  return [] if hlen == 0
  off = (h / 256) % hlen

  vals = []

  # FIXME: Is this potentially an infinite loop (if full)?
  # Easy to avoid by exiting if off reaches the same value twice.

  while
      (slot = read(hoff + off * hashref_size .. hoff + off * hashref_size + hashref_size - 1)) &&
      (dslot = ary_unpack(slot,2)) && dslot[1] != 0

    if dslot[0] == h
      pos = dslot[1]

      rkey, value = read_entry(pos)
      if rkey == key
        vals << value
      end
    end
    off = (off + 1) % hlen
  end
  return vals
end