Net::SSH::Buffer

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.

Methods

Public Class

from
new

Public Instance

Attributes

content	[R]	exposes the raw content of the buffer
position	[RW]	the current position of the pointer in the buffer

Public Class methods

from (*args)

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.

# 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

new (content="")

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

# File lib/net/ssh/buffer.rb, line 70
def initialize(content="")
  @content = content.to_s
  @position = 0
end

Public Instance methods

== (buffer)

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

# File lib/net/ssh/buffer.rb, line 93
def ==(buffer)
  to_s == buffer.to_s
end

append (text)

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

# File lib/net/ssh/buffer.rb, line 142
def append(text)
  @content << text
  self
end

available ()

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).

# File lib/net/ssh/buffer.rb, line 82
def available
  length - position
end

clear! ()

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

# File lib/net/ssh/buffer.rb, line 116
def clear!
  @content = ""
  @position = 0
end

consume! (n=position)

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.

# 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? ()

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

# File lib/net/ssh/buffer.rb, line 98
def empty?
  @content.empty?
end

eof? ()

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

# File lib/net/ssh/buffer.rb, line 110
def eof?
  @position >= length
end

length ()

Returns the length of the buffer's content.

# File lib/net/ssh/buffer.rb, line 76
def length
  @content.length
end

read (count=nil)

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.

# 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)

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.

# File lib/net/ssh/buffer.rb, line 180
def read!(count=nil)
  data = read(count)
  consume!
  data
end

read_bignum ()

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.

# 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 ()

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

# File lib/net/ssh/buffer.rb, line 220
def read_bool
  b = read_byte or return nil
  b != 0
end

read_buffer ()

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

# File lib/net/ssh/buffer.rb, line 277
def read_buffer
  Buffer.new(read_string)
end

read_byte ()

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

# File lib/net/ssh/buffer.rb, line 205
def read_byte
  b = read(1) or return nil
  b.getbyte(0)
end

read_int64 ()

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.

# 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 ()

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.

# File lib/net/ssh/buffer.rb, line 237
def read_key
  type = read_string
  return (type ? read_keyblob(type) : nil)
end

read_keyblob (type)

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

# File lib/net/ssh/buffer.rb, line 244
def read_keyblob(type)
  case type
    when /^ssh-dss(-cert-v01@openssh\.com)?$/
      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(-cert-v01@openssh\.com)?$/
      key = OpenSSL::PKey::RSA.new
      key.e = read_bignum
      key.n = read_bignum

    when /^ecdsa\-sha2\-(\w*)$/, /^ssh-ed25519(-cert-v01@openssh.com)?$/
      unless defined?(OpenSSL::PKey::EC)
        raise NotImplementedError, "unsupported key type `#{type}'"
      else
        begin
          key = OpenSSL::PKey::EC.read_keyblob($1, self)
        rescue OpenSSL::PKey::ECError
          raise NotImplementedError, "unsupported key type `#{type}'"
        end
      end
    else
      raise NotImplementedError, "unsupported key type `#{type}'"
  end

  return key
end

read_long ()

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.

# File lib/net/ssh/buffer.rb, line 198
def read_long
  b = read(4) or return nil
  b.unpack("N").first
end

read_string ()

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.

# File lib/net/ssh/buffer.rb, line 213
def read_string
  length = read_long or return nil
  read(length)
end

read_to (pattern)

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.

# 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 ()

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

# File lib/net/ssh/buffer.rb, line 149
def remainder_as_buffer
  Buffer.new(@content[@position..-1])
end

reset! ()

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

# File lib/net/ssh/buffer.rb, line 104
def reset!
  @position = 0
end

to_s ()

Returns a copy of the buffer's content.

# File lib/net/ssh/buffer.rb, line 87
def to_s
  (@content || "").dup
end

write (*data)

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

# File lib/net/ssh/buffer.rb, line 283
def write(*data)
  data.each { |datum| @content << datum }
  self
end

write_bignum (*n)

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.

# File lib/net/ssh/buffer.rb, line 338
def write_bignum(*n)
  @content << n.map { |b| b.to_ssh }.join
  self
end

write_bool (*b)

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.

# File lib/net/ssh/buffer.rb, line 330
def write_bool(*b)
  b.each { |v| @content << (v ? "\11"" : "\00"") }
  self
end

write_byte (*n)

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

# File lib/net/ssh/buffer.rb, line 310
def write_byte(*n)
  n.each { |b| @content << b.chr }
  self
end

write_int64 (*n)

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.

# File lib/net/ssh/buffer.rb, line 291
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)

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

# File lib/net/ssh/buffer.rb, line 345
def write_key(*key)
  key.each { |k| append(k.to_blob) }
  self
end

write_long (*n)

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.

# File lib/net/ssh/buffer.rb, line 303
def write_long(*n)
  @content << n.pack("N*")
  self
end

write_string (*text)

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.

# File lib/net/ssh/buffer.rb, line 318
def write_string(*text)
  text.each do |string|
    s = string.to_s
    write_long(s.bytesize)
    write(s)
  end
  self
end