Class: CSV::StreamBuf

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

Overview

Buffered stream.

EXAMPLE 1 – an IO.

class MyBuf < StreamBuf
  # Do initialize myself before a super class.  Super class might call my
  # method 'read'. (Could be awful for C++ user. :-)
  def initialize(s)
    @s = s
    super()
  end

  # define my own 'read' method.
  # CAUTION: Returning nil means EnfOfStream.
  def read(size)
    @s.read(size)
  end

  # release buffers. in Ruby which has GC, you do not have to call this...
  def terminate
    @s = nil
    super()
  end
end

buf = MyBuf.new(STDIN)
my_str = ''
p buf[0, 0]               # => '' (null string)
p buf[0]                  # => 97 (char code of 'a')
p buf[0, 1]               # => 'a'
my_str = buf[0, 5]
p my_str                  # => 'abcde' (5 chars)
p buf[0, 6]               # => "abcde\n" (6 chars)
p buf[0, 7]               # => "abcde\n" (6 chars)
p buf.drop(3)             # => 3 (dropped chars)
p buf.get(0, 2)           # => 'de' (2 chars)
p buf.is_eos?             # => false (is not EOS here)
p buf.drop(5)             # => 3 (dropped chars)
p buf.is_eos?             # => true (is EOS here)
p buf[0]                  # => nil (is EOS here)

EXAMPLE 2 – String.

This is a conceptual example.  No pros with this.

class StrBuf < StreamBuf
  def initialize(s)
    @str = s
    @idx = 0
    super()
  end

  def read(size)
    str = @str[@idx, size]
    @idx += str.size
    str
  end
end

Direct Known Subclasses

IOBuf

Instance Method Summary collapse

Constructor Details

#initialize ⇒ StreamBuf

WARN: Do not instantiate this class directly. Define your own class which derives this class and define ‘read’ instance method.



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# File 'lib/csv.rb', line 888

def initialize
  @buf_list = []
  @cur_buf = @buf_tail_idx = -1
  @offset = 0
  @is_eos = false
  add_buf
  @cur_buf = @buf_tail_idx
end

Instance Method Details

#[](idx, n = nil) ⇒ Object Also known as: get

get a char or a partial string from the stream. idx: index of a string to specify a start point of a string to get. unlike String instance, idx < 0 returns nil. n: size of a string to get. returns char at idx if n == nil. returns a partial string, from idx to (idx + n) if n != nil. at EOF, the string size could not equal to arg n.



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# File 'lib/csv.rb', line 803

def [](idx, n = nil) 
  if idx < 0
    return nil
  end
  if (idx_is_eos?(idx))
    if n and (@offset + idx == buf_size(@cur_buf))
      # Like a String, 'abc'[4, 1] returns nil and
      # 'abc'[3, 1] returns '' not nil.
      return ''
    else
      return nil
    end
  end
  my_buf = @cur_buf
  my_offset = @offset
  next_idx = idx
  while (my_offset + next_idx >= buf_size(my_buf))
    if (my_buf == @buf_tail_idx)
      unless add_buf
        break
      end
    end
    next_idx = my_offset + next_idx - buf_size(my_buf)
    my_buf += 1
    my_offset = 0
  end
  loc = my_offset + next_idx
  if !n
    return @buf_list[my_buf][loc]           # Fixnum of char code.
  elsif (loc + n - 1 < buf_size(my_buf))
    return @buf_list[my_buf][loc, n]        # String.
  else # should do loop insted of (tail) recursive call...
    res = @buf_list[my_buf][loc, BufSize]
    size_added = buf_size(my_buf) - loc
    if size_added > 0
      idx += size_added
      n -= size_added
      ret = self[idx, n]
      if ret
        res << ret
      end
    end
    return res
  end
end

#drop(n) ⇒ Object

drop a string from the stream. returns dropped size. at EOF, dropped size might not equals to arg n. Once you drop the head of the stream, access to the dropped part via [] or get returns nil.



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# File 'lib/csv.rb', line 854

def drop(n)
  if is_eos?
    return 0
  end
  size_dropped = 0
  while (n > 0)
    if !@is_eos or (@cur_buf != @buf_tail_idx)
      if (@offset + n < buf_size(@cur_buf))
        size_dropped += n
        @offset += n
        n = 0
      else
        size = buf_size(@cur_buf) - @offset
        size_dropped += size
        n -= size
        @offset = 0
        unless rel_buf
          unless add_buf
            break
          end
          @cur_buf = @buf_tail_idx
        end
      end
    end
  end
  size_dropped
end

#is_eos? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/csv.rb', line 882

def is_eos?
  return idx_is_eos?(0)
end