6 class SSHFileError < StandardError; end
8 ## this is a file-like interface to a file that actually lives on the
9 ## other end of an ssh connection. it works by using wc, head and tail
10 ## to simulate (buffered) random access. on a fast connection, this
11 ## can have a good bandwidth, but the latency is pretty terrible:
12 ## about 1 second (!) per request. luckily, we're either just reading
13 ## straight through the mbox (an import) or we're reading a few
14 ## messages at a time (viewing messages) so the latency is not a problem.
16 ## all of the methods here can throw SSHFileErrors, SocketErrors,
17 ## Net::SSH::Exceptions and Errno::ENOENTs.
19 ## debugging TODO: remove me
23 module_function :debug
25 ## a simple buffer of contiguous data
36 def empty?; @start.nil?; end
37 def start; @start; end
38 def endd; @start + @buf.length; end
40 def add data, offset=endd
41 #MBox::debug "+ adding #{data.length} bytes; size will be #{size + data.length}; limit #{SSHFile::MAX_BUF_SIZE}"
49 raise "non-continguous data added to buffer (data #{offset}:#{offset + data.length}, buf range #{start}:#{endd})" if offset + data.length < start || offset > endd
52 @buf = data[0 ... (start - offset)] + @buf
55 return if offset + data.length < endd
56 @buf += data[(endd - offset) .. -1]
61 raise "only ranges supported due to programmer's laziness" unless o.is_a? Range
62 @buf[Range.new(o.first - @start, o.last - @start, o.exclude_end?)]
65 def index what, start=0
66 x = @buf.index(what, start - @start)
67 x.nil? ? nil : x + @start
69 def rindex what, start=0
70 x = @buf.rindex(what, start - @start)
71 x.nil? ? nil : x + @start
74 def size; empty? ? 0 : @buf.size; end
75 def to_s; empty? ? "<empty>" : "[#{start}, #{endd})"; end # for debugging
78 ## the file-like interface to a remote file
80 MAX_BUF_SIZE = 1024 * 1024 # bytes
81 MAX_TRANSFER_SIZE = 1024 * 64
82 REASONABLE_TRANSFER_SIZE = 1024 * 32
83 SIZE_CHECK_INTERVAL = 60 * 1 # seconds
85 def initialize host, fn, ssh_opts={}
96 def broken?; !@broken_msg.nil?; end
99 @say_id = BufferManager.say s, @say_id if BufferManager.instantiated?
105 BufferManager.clear @say_id if BufferManager.instantiated?
111 raise SSHFileError, @broken_msg if broken?
113 say "Opening SSH connection to #{@host}..."
116 #raise SSHFileError, "simulated SSH file error"
117 #@session = Net::SSH.start @host, @ssh_opts
119 say "Starting SSH shell..."
120 # @shell = @session.shell.sync
122 say "Checking for #@fn..."
124 raise Errno::ENOENT, @fn
125 raise Errno::ENOENT, @fn unless @shell.test("-e #@fn").status == 0
131 def eof?; @offset >= size; end
132 def eof; eof?; end # lame but IO's method is named this and rmail calls that
133 def seek loc; @offset = loc; end
134 def tell; @offset; end
138 if @file_size.nil? || (Time.now - @last_size_check) > SIZE_CHECK_INTERVAL
139 @last_size_check = Time.now
140 @file_size = do_remote("wc -c #@fn").split.first.to_i
147 make_buf_include @offset
148 expand_buf_forward while @buf.index("\n", @offset).nil? && @buf.endd < size
149 returning(@buf[@offset .. (@buf.index("\n", @offset) || -1)]) { |line| @offset += line.length }
154 make_buf_include @offset, n
155 @buf[@offset ... (@offset += n)]
160 def do_remote cmd, expected_size=0
164 MBox::debug "sending command: #{cmd.inspect}"
166 result = @shell.send_command cmd
167 raise SSHFileError, "Failure during remote command #{cmd.inspect}: #{result.stderr[0 .. 100]}" unless result.status == 0
168 rescue Net::SSH::Exception # these happen occasionally for no apparent reason. gotta love that nondeterminism!
169 retry if (retries += 1) < 3
172 rescue Net::SSH::Exception, SSHFileError, Errno::ENOENT => e
173 @broken_msg = e.message
179 def get_bytes offset, size
180 do_remote "tail -c +#{offset + 1} #@fn | head -c #{size}", size
183 def expand_buf_forward n=REASONABLE_TRANSFER_SIZE
184 @buf.add get_bytes(@buf.endd, n)
187 ## try our best to transfer somewhere between
188 ## REASONABLE_TRANSFER_SIZE and MAX_TRANSFER_SIZE bytes
189 def make_buf_include offset, size=0
190 good_size = [size, REASONABLE_TRANSFER_SIZE].max
192 trans_start, trans_size =
195 elsif offset < @buf.start
196 if @buf.start - offset <= good_size
197 start = [@buf.start - good_size, 0].max
198 [start, @buf.start - start]
199 elsif @buf.start - offset < MAX_TRANSFER_SIZE
200 [offset, @buf.start - offset]
202 MBox::debug "clearing SSH buffer because buf.start #{@buf.start} - offset #{offset} >= #{MAX_TRANSFER_SIZE}"
207 return if [offset + size, self.size].min <= @buf.endd # whoohoo!
208 if offset - @buf.endd <= good_size
209 [@buf.endd, good_size]
210 elsif offset - @buf.endd < MAX_TRANSFER_SIZE
211 [@buf.endd, offset - @buf.endd]
213 MBox::debug "clearing SSH buffer because offset #{offset} - buf.end #{@buf.endd} >= #{MAX_TRANSFER_SIZE}"
219 @buf.clear! if @buf.size > MAX_BUF_SIZE
220 @buf.add get_bytes(trans_start, trans_size), trans_start