Add ability to write to STDIN

Needs:

- Integration test
- README docs

Notably, the hard part about this might not be writing the values to stdin, but rather dealing with the fact that most interactive processes behave VERY differently when run without a TTY. There are workarounds such as using the `script` command line tool, however integrating with a TTY shall be an exercise for the reader.

lib/rundoc/code_command/background.rb

@@ -7,3 +7,4 @@ class Rundoc::CodeCommand::Background
 require "rundoc/code_command/background/wait"
 require "rundoc/code_command/background/log/clear"
 require "rundoc/code_command/background/log/read"
+require "rundoc/code_command/background/stdin_write"

lib/rundoc/code_command/background/process_spawn.rb

@@ -53,6 +53,7 @@ def initialize(command, timeout: 5, log: Tempfile.new("log"), out: "2>&1")
       @log = Pathname.new(log)
       @log.dirname.mkpath
       FileUtils.touch(@log)
+      @pipe_output, @pipe_input = IO.pipe
 
       @command = "/usr/bin/env bash -c #{@command.shellescape} >> #{@log} #{out}"
       @pid = nil
@@ -78,8 +79,23 @@ def alive?
       false
     end
 
+    def write(contents, timeout: timeout_value, wait: nil, ending: $/)
+      contents = contents + $/ if ending
+      begin
+        Timeout.timeout(Integer(timeout)) do
+          @pipe_input.print(contents)
+          @pipe_input.flush
+        end
+      rescue Timeout::Error
+        raise "Timeout (#{timeout}s) waiting to write #{contents} to stdin. Log contents:\n'#{log.read}'"
+      end
+      wait(wait, timeout)
+      contents
+    end
+
     def stop
       return unless alive?
+      @pipe_input.close
       Process.kill("TERM", -Process.getpgid(@pid))
       Process.wait(@pid)
     end
@@ -89,7 +105,7 @@ def check_alive!
     end
 
     private def call
-      @pid ||= Process.spawn(@command, pgroup: true)
+      @pid ||= Process.spawn(@command, pgroup: true, in: @pipe_output)
     end
   end
 end

lib/rundoc/code_command/background/stdin_write.rb

@@ -0,0 +1,37 @@
+class Rundoc::CodeCommand::Background
+  # Will send contents to the background process via STDIN along with a newline
+  #
+  #
+  class StdinWrite < Rundoc::CodeCommand
+    def initialize(contents, name:, wait:, timeout: 5, ending: $/)
+      @contents = contents
+      @ending = ending
+      @spawn = Rundoc::CodeCommand::Background::ProcessSpawn.find(name)
+      @wait = wait
+      @timeout_value = Integer(timeout)
+      @contents_written = nil
+    end
+
+    # The command is rendered (`:::>-`) by the output of the `def call` method.
+    def to_md(env = {})
+      writecontents
+    end
+
+    # The contents produced by the command (`:::->`) are rendered by the `def to_md` method.
+    def call(env = {})
+      writecontents
+      output = @spawn.log.read
+      output
+    end
+
+    def writecontents
+      @contents_written ||= @spawn.write(
+        contents,
+        wait: @wait,
+        ending: @ending,
+        timeout: @timeout_value
+      )
+    end
+  end
+end
+Rundoc.register_code_command(:"background.writeln", Rundoc::CodeCommand::Background::Wait)

test/rundoc/code_commands/background_test.rb

@@ -1,11 +1,41 @@
 require "test_helper"
 
 class BackgroundTest < Minitest::Test
+
+  def test_stdin_with_cat_echo
+    Dir.mktmpdir do |dir|
+      Dir.chdir(dir) do
+        background_start = Rundoc::CodeCommand::Background::Start.new("cat",
+          name: "cat",
+        )
+        output = background_start.call
+
+        output = Rundoc::CodeCommand::Background::StdinWrite.new(
+          "hello there",
+          name: "cat",
+          wait: "hello"
+        ).call
+        assert_equal("hello there" + $/, output)
+
+        output = Rundoc::CodeCommand::Background::Log::Clear.new(
+          name: "cat"
+        ).call
+
+        output = Rundoc::CodeCommand::Background::StdinWrite.new(
+          "general kenobi",
+          name: "cat",
+          wait: "general"
+        ).call
+        assert_equal("general kenobi" + $/, output)
+      end
+    end
+  end
+
   def test_process_spawn_gc
     Dir.mktmpdir do |dir|
       Dir.chdir(dir) do
         file = "foo.txt"
-        `echo 'foo' >> #{file}`
+        run!("echo 'foo' >> #{file}")
 
         background_start = Rundoc::CodeCommand::Background::Start.new("tail -f #{file}",
           name: "tail2",
@@ -30,7 +60,7 @@ def test_background_start
     Dir.mktmpdir do |dir|
       Dir.chdir(dir) do
         file = "foo.txt"
-        `echo 'foo' >> #{file}`
+        run!("echo 'foo' >> #{file}")
 
         background_start = Rundoc::CodeCommand::Background::Start.new("tail -f #{file}",
           name: "tail",
@@ -49,7 +79,7 @@ def test_background_start
         output = log_clear.call
         assert_equal("", output)
 
-        `echo 'bar' >> #{file}`
+        run!("echo 'bar' >> #{file}")
 
         log_read = Rundoc::CodeCommand::Background::Log::Read.new(name: "tail")
         output = log_read.call