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# Copyright, 2014, by Samuel G. D. Williams. <http://www.codeotaku.com>
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
module Process
class Daemon
# This is a special file instance which provides the ability to read a log file from the end backwards.
class LogFile < File
# Yields the lines of a log file in reverse order, once the yield statement returns true, stops, and returns the lines in order.
def tail_log
lines = []
seek_end
reverse_each_line do |line|
lines << line
break if block_given? and yield line
end
return lines.reverse
end
private
# Seek to the end of the file
def seek_end(offset = 0)
seek(offset, IO::SEEK_END)
end
# Read a chunk of data and then move the file pointer backwards.
#
# Calling this function multiple times will return new data and traverse the file backwards.
#
def read_reverse(length)
offset = tell
if offset == 0
return nil
end
start = [0, offset-length].max
seek(start, IO::SEEK_SET)
buf = read(offset-start)
seek(start, IO::SEEK_SET)
return buf
end
REVERSE_BUFFER_SIZE = 128
# This function is very similar to gets but it works in reverse.
#
# You can use it to efficiently read a file line by line backwards.
#
# It returns nil when there are no more lines.
def reverse_gets(sep_string=$/)
end_pos = tell
offset = nil
buf = ""
while offset == nil
chunk = read_reverse(REVERSE_BUFFER_SIZE)
return (buf == "" ? nil : buf) if chunk == nil
buf = chunk + buf
# Don't consider the last newline.
offset = buf.rindex(sep_string, -(sep_string.length + 1))
end
# Don't include newline:
offset += 1
line = buf[offset...buf.size]
seek((end_pos - buf.size) + offset, IO::SEEK_SET)
return line
end
# Similar to each_line but works in reverse. Don't forget to call
# seek_end before you start!
def reverse_each_line(sep_string=$/, &block)
return to_enum(:reverse_each_line) unless block_given?
line = reverse_gets(sep_string)
while line != nil
yield line
line = reverse_gets(sep_string)
end
end
end
end
end
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