340 lines
11 KiB
Ruby
340 lines
11 KiB
Ruby
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require 'net/ssh/ruby_compat'
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require 'net/ssh/transport/openssl'
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module Net; module SSH
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# Net::SSH::Buffer is a flexible class for building and parsing binary
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# data packets. It provides a stream-like interface for sequentially
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# reading data items from the buffer, as well as a useful helper method
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# for building binary packets given a signature.
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#
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# Writing to a buffer always appends to the end, regardless of where the
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# read cursor is. Reading, on the other hand, always begins at the first
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# byte of the buffer and increments the read cursor, with subsequent reads
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# taking up where the last left off.
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#
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# As a consumer of the Net::SSH library, you will rarely come into contact
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# with these buffer objects directly, but it could happen. Also, if you
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# are ever implementing a protocol on top of SSH (e.g. SFTP), this buffer
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# class can be quite handy.
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class Buffer
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# This is a convenience method for creating and populating a new buffer
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# from a single command. The arguments must be even in length, with the
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# first of each pair of arguments being a symbol naming the type of the
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# data that follows. If the type is :raw, the value is written directly
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# to the hash.
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#
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# b = Buffer.from(:byte, 1, :string, "hello", :raw, "\1\2\3\4")
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# #-> "\1\0\0\0\5hello\1\2\3\4"
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#
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# The supported data types are:
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#
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# * :raw => write the next value verbatim (#write)
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# * :int64 => write an 8-byte integer (#write_int64)
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# * :long => write a 4-byte integer (#write_long)
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# * :byte => write a single byte (#write_byte)
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# * :string => write a 4-byte length followed by character data (#write_string)
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# * :bool => write a single byte, interpreted as a boolean (#write_bool)
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# * :bignum => write an SSH-encoded bignum (#write_bignum)
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# * :key => write an SSH-encoded key value (#write_key)
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#
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# Any of these, except for :raw, accepts an Array argument, to make it
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# easier to write multiple values of the same type in a briefer manner.
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def self.from(*args)
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raise ArgumentError, "odd number of arguments given" unless args.length % 2 == 0
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buffer = new
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0.step(args.length-1, 2) do |index|
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type = args[index]
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value = args[index+1]
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if type == :raw
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buffer.append(value.to_s)
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elsif Array === value
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buffer.send("write_#{type}", *value)
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else
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buffer.send("write_#{type}", value)
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end
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end
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buffer
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end
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# exposes the raw content of the buffer
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attr_reader :content
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# the current position of the pointer in the buffer
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attr_accessor :position
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# Creates a new buffer, initialized to the given content. The position
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# is initialized to the beginning of the buffer.
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def initialize(content="")
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@content = content.to_s
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@position = 0
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end
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# Returns the length of the buffer's content.
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def length
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@content.length
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end
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# Returns the number of bytes available to be read (e.g., how many bytes
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# remain between the current position and the end of the buffer).
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def available
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length - position
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end
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# Returns a copy of the buffer's content.
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def to_s
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(@content || "").dup
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end
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# Compares the contents of the two buffers, returning +true+ only if they
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# are identical in size and content.
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def ==(buffer)
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to_s == buffer.to_s
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end
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# Returns +true+ if the buffer contains no data (e.g., it is of zero length).
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def empty?
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@content.empty?
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end
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# Resets the pointer to the start of the buffer. Subsequent reads will
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# begin at position 0.
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def reset!
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@position = 0
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end
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# Returns true if the pointer is at the end of the buffer. Subsequent
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# reads will return nil, in this case.
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def eof?
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@position >= length
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end
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# Resets the buffer, making it empty. Also, resets the read position to
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# 0.
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def clear!
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@content = ""
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@position = 0
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end
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# Consumes n bytes from the buffer, where n is the current position
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# unless otherwise specified. This is useful for removing data from the
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# buffer that has previously been read, when you are expecting more data
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# to be appended. It helps to keep the size of buffers down when they
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# would otherwise tend to grow without bound.
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#
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# Returns the buffer object itself.
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def consume!(n=position)
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if n >= length
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# optimize for a fairly common case
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clear!
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elsif n > 0
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@content = @content[n..-1] || ""
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@position -= n
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@position = 0 if @position < 0
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end
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self
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end
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# Appends the given text to the end of the buffer. Does not alter the
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# read position. Returns the buffer object itself.
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def append(text)
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@content << text
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self
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end
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# Returns all text from the current pointer to the end of the buffer as
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# a new Net::SSH::Buffer object.
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def remainder_as_buffer
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Buffer.new(@content[@position..-1])
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end
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# Reads all data up to and including the given pattern, which may be a
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# String, Fixnum, or Regexp and is interpreted exactly as String#index
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# does. Returns nil if nothing matches. Increments the position to point
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# immediately after the pattern, if it does match. Returns all data up to
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# and including the text that matched the pattern.
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def read_to(pattern)
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index = @content.index(pattern, @position) or return nil
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length = case pattern
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when String then pattern.length
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when Fixnum then 1
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when Regexp then $&.length
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end
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index && read(index+length)
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end
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# Reads and returns the next +count+ bytes from the buffer, starting from
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# the read position. If +count+ is +nil+, this will return all remaining
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# text in the buffer. This method will increment the pointer.
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def read(count=nil)
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count ||= length
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count = length - @position if @position + count > length
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@position += count
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@content[@position-count, count]
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end
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# Reads (as #read) and returns the given number of bytes from the buffer,
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# and then consumes (as #consume!) all data up to the new read position.
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def read!(count=nil)
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data = read(count)
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consume!
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data
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end
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# Return the next 8 bytes as a 64-bit integer (in network byte order).
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# Returns nil if there are less than 8 bytes remaining to be read in the
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# buffer.
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def read_int64
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hi = read_long or return nil
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lo = read_long or return nil
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return (hi << 32) + lo
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end
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# Return the next four bytes as a long integer (in network byte order).
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# Returns nil if there are less than 4 bytes remaining to be read in the
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# buffer.
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def read_long
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b = read(4) or return nil
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b.unpack("N").first
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end
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# Read and return the next byte in the buffer. Returns nil if called at
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# the end of the buffer.
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def read_byte
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b = read(1) or return nil
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b.getbyte(0)
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end
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# Read and return an SSH2-encoded string. The string starts with a long
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# integer that describes the number of bytes remaining in the string.
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# Returns nil if there are not enough bytes to satisfy the request.
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def read_string
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length = read_long or return nil
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read(length)
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end
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# Read a single byte and convert it into a boolean, using 'C' rules
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# (i.e., zero is false, non-zero is true).
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def read_bool
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b = read_byte or return nil
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b != 0
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end
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# Read a bignum (OpenSSL::BN) from the buffer, in SSH2 format. It is
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# essentially just a string, which is reinterpreted to be a bignum in
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# binary format.
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def read_bignum
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data = read_string
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return unless data
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OpenSSL::BN.new(data, 2)
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end
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# Read a key from the buffer. The key will start with a string
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# describing its type. The remainder of the key is defined by the
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# type that was read.
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def read_key
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type = read_string
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return (type ? read_keyblob(type) : nil)
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end
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# Read a keyblob of the given type from the buffer, and return it as
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# a key. Only RSA and DSA keys are supported.
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def read_keyblob(type)
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case type
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when "ssh-dss"
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key = OpenSSL::PKey::DSA.new
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key.p = read_bignum
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key.q = read_bignum
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key.g = read_bignum
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key.pub_key = read_bignum
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when "ssh-rsa"
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key = OpenSSL::PKey::RSA.new
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key.e = read_bignum
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key.n = read_bignum
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else
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raise NotImplementedError, "unsupported key type `#{type}'"
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end
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return key
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end
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# Reads the next string from the buffer, and returns a new Buffer
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# object that wraps it.
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def read_buffer
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Buffer.new(read_string)
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end
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# Writes the given data literally into the string. Does not alter the
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# read position. Returns the buffer object.
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def write(*data)
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data.each { |datum| @content << datum }
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self
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end
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# Writes each argument to the buffer as a network-byte-order-encoded
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# 64-bit integer (8 bytes). Does not alter the read position. Returns the
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# buffer object.
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def write_int64(*n)
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n.each do |i|
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hi = (i >> 32) & 0xFFFFFFFF
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lo = i & 0xFFFFFFFF
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@content << [hi, lo].pack("N2")
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end
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self
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end
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# Writes each argument to the buffer as a network-byte-order-encoded
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# long (4-byte) integer. Does not alter the read position. Returns the
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# buffer object.
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def write_long(*n)
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@content << n.pack("N*")
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self
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end
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# Writes each argument to the buffer as a byte. Does not alter the read
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# position. Returns the buffer object.
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def write_byte(*n)
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n.each { |b| @content << b.chr }
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self
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end
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# Writes each argument to the buffer as an SSH2-encoded string. Each
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# string is prefixed by its length, encoded as a 4-byte long integer.
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# Does not alter the read position. Returns the buffer object.
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def write_string(*text)
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text.each do |string|
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s = string.to_s
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write_long(s.length)
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write(s)
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end
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self
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end
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# Writes each argument to the buffer as a (C-style) boolean, with 1
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# meaning true, and 0 meaning false. Does not alter the read position.
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# Returns the buffer object.
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def write_bool(*b)
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b.each { |v| @content << (v ? "\1" : "\0") }
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self
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end
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# Writes each argument to the buffer as a bignum (SSH2-style). No
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# checking is done to ensure that the arguments are, in fact, bignums.
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# Does not alter the read position. Returns the buffer object.
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def write_bignum(*n)
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@content << n.map { |b| b.to_ssh }.join
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self
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end
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# Writes the given arguments to the buffer as SSH2-encoded keys. Does not
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# alter the read position. Returns the buffer object.
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def write_key(*key)
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key.each { |k| append(k.to_blob) }
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self
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end
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end
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end; end;
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