Compatibility with the new SSHKit::Command API

An upcoming version of SSHKit changes its API for accessing stdout and stderr
data. This commit introduces a facade to normalize the API differences in the
various SSHKit versions, so both the new and old APIs can be supported.

Also, since SSHKit now `clear`s stdout/stderr data instead of assigning a new
blank value, our old technique of a simple `Command#dup` does not protect us
from mutations to the output strings. Use `Marshal` to do a deep copy instead.

CHANGELOG.md

@@ -1,6 +1,7 @@
 ## Next release
 
 * Your contribution here!
+* Changes to ensure compatibility with the upcoming version of SSHKit.
 * Explicitly specify UTF-8 encoding for source files, for Ruby 1.9.3 compatibility.
 
 ## 0.3.0 (2015-03-28)

lib/airbrussh/command_output.rb

@@ -0,0 +1,42 @@
+module Airbrussh
+  # A facade that provides access to stdout and stderr command output of
+  # sshkit commands. This is needed to normalize the API differences in
+  # various sshkit versions.
+  class CommandOutput
+    def self.for(command)
+      if command.respond_to?(:clear_stdout_lines)
+        Modern.new(command)
+      else
+        Legacy.new(command)
+      end
+    end
+
+    attr_reader :command
+
+    def initialize(command)
+      @command = command
+    end
+  end
+
+  class Legacy < CommandOutput
+    # The stderr/stdout methods provided by the command object have the current
+    # "chunk" as received over the wire. Since there may be more chunks
+    # appended and we don't want to print duplicates, clear the current data.
+    def each_line(stream, &block)
+      output = command.public_send(stream)
+      return if output.empty?
+      output.lines.to_a.each(&block)
+      command.public_send("#{stream}=", "")
+    end
+  end
+
+  class Modern < CommandOutput
+    # Newer versions of sshkit take care of clearing the output with the
+    # clear_stdout_lines/clear_stderr_lines methods.
+    def each_line(stream, &block)
+      lines = command.public_send("clear_#{stream}_lines")
+      return if lines.join.empty?
+      lines.each(&block)
+    end
+  end
+end

lib/airbrussh/formatter.rb

@@ -1,4 +1,5 @@
 # encoding: UTF-8
+require "airbrussh/command_output"
 require "airbrussh/console"
 require "colorize"
 require "ostruct"
@@ -79,8 +80,8 @@ def write_log_file_delimiter
 
     def write(obj)
       # SSHKit's :pretty formatter mutates the stdout and stderr data in the
-      # command obj. So we need to dup it to ensure our copy is unscathed.
-      @log_file_formatter << obj.dup
+      # command obj. So we need to clone it to ensure our copy is unscathed.
+      @log_file_formatter << deep_copy(obj)
 
       case obj
       when SSHKit::Command    then write_command(obj)
@@ -136,20 +137,10 @@ def write_command_output(command, number)
       # Use a bit of meta-programming here, since stderr and stdout logic
       # are identical except for different method names.
       %w(stderr stdout).each do |stream|
-
         next unless config.public_send("command_output_#{stream}?")
-        output = command.public_send(stream)
-        next if output.empty?
-
-        output.lines.each do |line|
+        CommandOutput.for(command).each_line(stream) do |line|
           print_line "      #{number} #{line.chomp}"
         end
-
-        # The stderr/stdout data provided by the command object is the current
-        # "chunk" as received over the wire. Since there may be more chunks
-        # appended and we don't want to print duplicates, clear the current
-        # data.
-        command.public_send("#{stream}=", "")
       end
     end
 
@@ -234,5 +225,9 @@ def clock
     def config
       Airbrussh.configuration
     end
+
+    def deep_copy(obj)
+      Marshal.load(Marshal.dump(obj))
+    end
   end
 end