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 ## sharing a ssh connection to one machines between sources seems to
79 ## create lots of broken situations: commands returning bizarre (large
80 ## positive integer) return codes despite working; commands
81 ## occasionally not working, etc. i suspect this is because of the
82 ## fragile nature of the ssh syncshell.
84 ## at any rate, we now open up one ssh connection per file, which is
85 ## probably silly in the extreme case.
87 ## the file-like interface to a remote file
89 MAX_BUF_SIZE = 1024 * 1024 # bytes
90 MAX_TRANSFER_SIZE = 1024 * 128
91 REASONABLE_TRANSFER_SIZE = 1024 * 32
92 SIZE_CHECK_INTERVAL = 60 * 1 # seconds
94 def initialize host, fn, ssh_opts={}
104 @shell_mutex = Mutex.new
107 def to_s; "mbox+ssh://#@host/#@fn"; end ## TODO: remove thisis EVILness
108 def broken?; !@broken_msg.nil?; end
110 ## TODO: share this code with imap
112 @say_id = BufferManager.say s, @say_id if BufferManager.instantiated?
116 BufferManager.clear @say_id if BufferManager.instantiated?
119 private :say, :shutup
122 raise SSHFileError, @broken_msg if broken?
124 @shell_mutex.synchronize do
128 say "Opening SSH connection to #{@host}..."
129 #raise SSHFileError, "simulated SSH file error"
130 session = Net::SSH.start @host, @ssh_opts
131 say "Starting SSH shell..."
132 @shell = session.shell.sync
133 say "Checking for #@fn..."
134 raise Errno::ENOENT, @fn unless @shell.test("-e #@fn").status == 0
141 def eof?; @offset >= size; end
142 def eof; eof?; end # lame but IO's method is named this and rmail calls that
143 def seek loc; @offset = loc; end
144 def tell; @offset; end
148 if @file_size.nil? || (Time.now - @last_size_check) > SIZE_CHECK_INTERVAL
149 @last_size_check = Time.now
150 @file_size = do_remote("wc -c #@fn").split.first.to_i
157 make_buf_include @offset
158 expand_buf_forward while @buf.index("\n", @offset).nil? && @buf.endd < size
159 returning(@buf[@offset .. (@buf.index("\n", @offset) || -1)]) { |line| @offset += line.length }
164 make_buf_include @offset, n
165 @buf[@offset ... (@offset += n)]
170 def do_remote cmd, expected_size=0
174 # MBox::debug "sending command: #{cmd.inspect}"
176 result = @shell.send_command cmd
177 result = @shell.sync { @shell.send_command cmd }
178 raise SSHFileError, "Failure during remote command #{cmd.inspect}: #{(result.stderr || result.stdout || "")[0 .. 100]}" unless result.status == 0
179 rescue Net::SSH::Exception # these happen occasionally for no apparent reason. gotta love that nondeterminism!
180 retry if (retries += 1) <= 3
183 if (retries += 1) <= e
189 rescue Net::SSH::Exception, SSHFileError, Errno::ENOENT => e
190 @broken_msg = e.message
196 def get_bytes offset, size
197 do_remote "tail -c +#{offset + 1} #@fn | head -c #{size}", size
200 def expand_buf_forward n=REASONABLE_TRANSFER_SIZE
201 @buf.add get_bytes(@buf.endd, n)
204 ## try our best to transfer somewhere between
205 ## REASONABLE_TRANSFER_SIZE and MAX_TRANSFER_SIZE bytes
206 def make_buf_include offset, size=0
207 good_size = [size, REASONABLE_TRANSFER_SIZE].max
209 trans_start, trans_size =
212 elsif offset < @buf.start
213 if @buf.start - offset <= good_size
214 start = [@buf.start - good_size, 0].max
215 [start, @buf.start - start]
216 elsif @buf.start - offset < MAX_TRANSFER_SIZE
217 [offset, @buf.start - offset]
219 MBox::debug "clearing SSH buffer because buf.start #{@buf.start} - offset #{offset} >= #{MAX_TRANSFER_SIZE}"
224 return if [offset + size, self.size].min <= @buf.endd # whoohoo!
225 if offset - @buf.endd <= good_size
226 [@buf.endd, good_size]
227 elsif offset - @buf.endd < MAX_TRANSFER_SIZE
228 [@buf.endd, offset - @buf.endd]
230 MBox::debug "clearing SSH buffer because offset #{offset} - buf.end #{@buf.endd} >= #{MAX_TRANSFER_SIZE}"
236 @buf.clear! if @buf.size > MAX_BUF_SIZE
237 @buf.add get_bytes(trans_start, trans_size), trans_start