Class: Net::SSH::Buffer

Inherits:
Object
  • Object
show all
Defined in:
lib/net/ssh/buffer.rb

Overview

Net::SSH::Buffer is a flexible class for building and parsing binary data packets. It provides a stream-like interface for sequentially reading data items from the buffer, as well as a useful helper method for building binary packets given a signature.

Writing to a buffer always appends to the end, regardless of where the read cursor is. Reading, on the other hand, always begins at the first byte of the buffer and increments the read cursor, with subsequent reads taking up where the last left off.

As a consumer of the Net::SSH library, you will rarely come into contact with these buffer objects directly, but it could happen. Also, if you are ever implementing a protocol on top of SSH (e.g. SFTP), this buffer class can be quite handy.

Direct Known Subclasses

Packet

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(content = "") ⇒ Buffer

Creates a new buffer, initialized to the given content. The position is initialized to the beginning of the buffer.



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# File 'lib/net/ssh/buffer.rb', line 70

def initialize(content="")
  @content = content.to_s
  @position = 0
end

Instance Attribute Details

#content ⇒ Object (readonly)

exposes the raw content of the buffer



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# File 'lib/net/ssh/buffer.rb', line 63

def content
  @content
end

#position ⇒ Object

the current position of the pointer in the buffer



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# File 'lib/net/ssh/buffer.rb', line 66

def position
  @position
end

Class Method Details

.from(*args) ⇒ Object

This is a convenience method for creating and populating a new buffer from a single command. The arguments must be even in length, with the first of each pair of arguments being a symbol naming the type of the data that follows. If the type is :raw, the value is written directly to the hash.

b = Buffer.from(:byte, 1, :string, "hello", :raw, "\1\2\3\4")
#-> "\1\0\0\0\5hello\1\2\3\4"

The supported data types are:

  • :raw => write the next value verbatim (#write)

  • :int64 => write an 8-byte integer (#write_int64)

  • :long => write a 4-byte integer (#write_long)

  • :byte => write a single byte (#write_byte)

  • :string => write a 4-byte length followed by character data (#write_string)

  • :bool => write a single byte, interpreted as a boolean (#write_bool)

  • :bignum => write an SSH-encoded bignum (#write_bignum)

  • :key => write an SSH-encoded key value (#write_key)

Any of these, except for :raw, accepts an Array argument, to make it easier to write multiple values of the same type in a briefer manner.

Raises:

  • (ArgumentError) 


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# File 'lib/net/ssh/buffer.rb', line 43

def self.from(*args)
  raise ArgumentError, "odd number of arguments given" unless args.length % 2 == 0

  buffer = new
  0.step(args.length-1, 2) do |index|
    type = args[index]
    value = args[index+1]
    if type == :raw
      buffer.append(value.to_s)
    elsif Array === value
      buffer.send("write_#{type}", *value)
    else
      buffer.send("write_#{type}", value)
    end
  end

  buffer
end

Instance Method Details

#==(buffer) ⇒ Object

Compares the contents of the two buffers, returning true only if they are identical in size and content.



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# File 'lib/net/ssh/buffer.rb', line 93

def ==(buffer)
  to_s == buffer.to_s
end

#append(text) ⇒ Object

Appends the given text to the end of the buffer. Does not alter the read position. Returns the buffer object itself.



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# File 'lib/net/ssh/buffer.rb', line 142

def append(text)
  @content << text
  self
end

#available ⇒ Object

Returns the number of bytes available to be read (e.g., how many bytes remain between the current position and the end of the buffer).



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# File 'lib/net/ssh/buffer.rb', line 82

def available
  length - position
end

#clear! ⇒ Object

Resets the buffer, making it empty. Also, resets the read position to 0.



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# File 'lib/net/ssh/buffer.rb', line 116

def clear!
  @content = ""
  @position = 0
end

#consume!(n = position) ⇒ Object

Consumes n bytes from the buffer, where n is the current position unless otherwise specified. This is useful for removing data from the buffer that has previously been read, when you are expecting more data to be appended. It helps to keep the size of buffers down when they would otherwise tend to grow without bound.

Returns the buffer object itself.



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# File 'lib/net/ssh/buffer.rb', line 128

def consume!(n=position)
  if n >= length
    # optimize for a fairly common case
    clear!
  elsif n > 0
    @content = @content[n..-1] || ""
    @position -= n
    @position = 0 if @position < 0
  end
  self
end

#empty? ⇒ Boolean

Returns true if the buffer contains no data (e.g., it is of zero length).

Returns:

  • (Boolean) 


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# File 'lib/net/ssh/buffer.rb', line 98

def empty?
  @content.empty?
end

#eof? ⇒ Boolean

Returns true if the pointer is at the end of the buffer. Subsequent reads will return nil, in this case.

Returns:

  • (Boolean) 


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# File 'lib/net/ssh/buffer.rb', line 110

def eof?
  @position >= length
end

#length ⇒ Object

Returns the length of the buffer’s content.



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# File 'lib/net/ssh/buffer.rb', line 76

def length
  @content.length
end

#read(count = nil) ⇒ Object

Reads and returns the next count bytes from the buffer, starting from the read position. If count is nil, this will return all remaining text in the buffer. This method will increment the pointer.



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# File 'lib/net/ssh/buffer.rb', line 171

def read(count=nil)
  count ||= length
  count = length - @position if @position + count > length
  @position += count
  @content[@position-count, count]
end

#read!(count = nil) ⇒ Object

Reads (as #read) and returns the given number of bytes from the buffer, and then consumes (as #consume!) all data up to the new read position.



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# File 'lib/net/ssh/buffer.rb', line 180

def read!(count=nil)
  data = read(count)
  consume!
  data
end

#read_bignum ⇒ Object

Read a bignum (OpenSSL::BN) from the buffer, in SSH2 format. It is essentially just a string, which is reinterpreted to be a bignum in binary format.



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# File 'lib/net/ssh/buffer.rb', line 228

def read_bignum
  data = read_string
  return unless data
  OpenSSL::BN.new(data, 2)
end

#read_bool ⇒ Object

Read a single byte and convert it into a boolean, using ‘C’ rules (i.e., zero is false, non-zero is true).



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# File 'lib/net/ssh/buffer.rb', line 220

def read_bool
  b = read_byte or return nil
  b != 0
end

#read_buffer ⇒ Object

Reads the next string from the buffer, and returns a new Buffer object that wraps it.



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# File 'lib/net/ssh/buffer.rb', line 267

def read_buffer
  Buffer.new(read_string)
end

#read_byte ⇒ Object

Read and return the next byte in the buffer. Returns nil if called at the end of the buffer.



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# File 'lib/net/ssh/buffer.rb', line 205

def read_byte
  b = read(1) or return nil
  b.getbyte(0)
end

#read_int64 ⇒ Object

Return the next 8 bytes as a 64-bit integer (in network byte order). Returns nil if there are less than 8 bytes remaining to be read in the buffer.



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# File 'lib/net/ssh/buffer.rb', line 189

def read_int64
  hi = read_long or return nil
  lo = read_long or return nil
  return (hi << 32) + lo
end

#read_key ⇒ Object

Read a key from the buffer. The key will start with a string describing its type. The remainder of the key is defined by the type that was read.



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# File 'lib/net/ssh/buffer.rb', line 237

def read_key
  type = read_string
  return (type ? read_keyblob(type) : nil)
end

#read_keyblob(type) ⇒ Object

Read a keyblob of the given type from the buffer, and return it as a key. Only RSA and DSA keys are supported.



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# File 'lib/net/ssh/buffer.rb', line 244

def read_keyblob(type)
  case type
    when "ssh-dss"
      key = OpenSSL::PKey::DSA.new
      key.p = read_bignum
      key.q = read_bignum
      key.g = read_bignum
      key.pub_key = read_bignum

    when "ssh-rsa"
      key = OpenSSL::PKey::RSA.new
      key.e = read_bignum
      key.n = read_bignum

    else
      raise NotImplementedError, "unsupported key type `#{type}'"
  end

  return key
end

#read_long ⇒ Object

Return the next four bytes as a long integer (in network byte order). Returns nil if there are less than 4 bytes remaining to be read in the buffer.



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# File 'lib/net/ssh/buffer.rb', line 198

def read_long
  b = read(4) or return nil
  b.unpack("N").first
end

#read_string ⇒ Object

Read and return an SSH2-encoded string. The string starts with a long integer that describes the number of bytes remaining in the string. Returns nil if there are not enough bytes to satisfy the request.



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# File 'lib/net/ssh/buffer.rb', line 213

def read_string
  length = read_long or return nil
  read(length)
end

#read_to(pattern) ⇒ Object

Reads all data up to and including the given pattern, which may be a String, Fixnum, or Regexp and is interpreted exactly as String#index does. Returns nil if nothing matches. Increments the position to point immediately after the pattern, if it does match. Returns all data up to and including the text that matched the pattern.



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# File 'lib/net/ssh/buffer.rb', line 158

def read_to(pattern)
  index = @content.index(pattern, @position) or return nil
  length = case pattern
    when String then pattern.length
    when Fixnum then 1
    when Regexp then $&.length
  end
  index && read(index+length)
end

#remainder_as_buffer ⇒ Object

Returns all text from the current pointer to the end of the buffer as a new Net::SSH::Buffer object.



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# File 'lib/net/ssh/buffer.rb', line 149

def remainder_as_buffer
  Buffer.new(@content[@position..-1])
end

#reset! ⇒ Object

Resets the pointer to the start of the buffer. Subsequent reads will begin at position 0.



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# File 'lib/net/ssh/buffer.rb', line 104

def reset!
  @position = 0
end

#to_s ⇒ Object

Returns a copy of the buffer’s content.



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# File 'lib/net/ssh/buffer.rb', line 87

def to_s
  (@content || "").dup
end

#write(*data) ⇒ Object

Writes the given data literally into the string. Does not alter the read position. Returns the buffer object.



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# File 'lib/net/ssh/buffer.rb', line 273

def write(*data)
  data.each { |datum| @content << datum }
  self
end

#write_bignum(*n) ⇒ Object

Writes each argument to the buffer as a bignum (SSH2-style). No checking is done to ensure that the arguments are, in fact, bignums. Does not alter the read position. Returns the buffer object.



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# File 'lib/net/ssh/buffer.rb', line 328

def write_bignum(*n)
  @content << n.map { |b| b.to_ssh }.join
  self
end

#write_bool(*b) ⇒ Object

Writes each argument to the buffer as a (C-style) boolean, with 1 meaning true, and 0 meaning false. Does not alter the read position. Returns the buffer object.



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# File 'lib/net/ssh/buffer.rb', line 320

def write_bool(*b)
  b.each { |v| @content << (v ? "\1" : "\0") }
  self
end

#write_byte(*n) ⇒ Object

Writes each argument to the buffer as a byte. Does not alter the read position. Returns the buffer object.



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# File 'lib/net/ssh/buffer.rb', line 300

def write_byte(*n)
  n.each { |b| @content << b.chr }
  self
end

#write_int64(*n) ⇒ Object

Writes each argument to the buffer as a network-byte-order-encoded 64-bit integer (8 bytes). Does not alter the read position. Returns the buffer object.



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# File 'lib/net/ssh/buffer.rb', line 281

def write_int64(*n)
  n.each do |i|
    hi = (i >> 32) & 0xFFFFFFFF
    lo = i & 0xFFFFFFFF
    @content << [hi, lo].pack("N2")
  end
  self
end

#write_key(*key) ⇒ Object

Writes the given arguments to the buffer as SSH2-encoded keys. Does not alter the read position. Returns the buffer object.



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# File 'lib/net/ssh/buffer.rb', line 335

def write_key(*key)
  key.each { |k| append(k.to_blob) }
  self
end

#write_long(*n) ⇒ Object

Writes each argument to the buffer as a network-byte-order-encoded long (4-byte) integer. Does not alter the read position. Returns the buffer object.



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# File 'lib/net/ssh/buffer.rb', line 293

def write_long(*n)
  @content << n.pack("N*")
  self
end

#write_string(*text) ⇒ Object

Writes each argument to the buffer as an SSH2-encoded string. Each string is prefixed by its length, encoded as a 4-byte long integer. Does not alter the read position. Returns the buffer object.



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# File 'lib/net/ssh/buffer.rb', line 308

def write_string(*text)
  text.each do |string|
    s = string.to_s
    write_long(s.length)
    write(s)
  end
  self
end