taylor · February 6, 2014 02:13 · Feb 6, 2014
diff --git a/string_io.ex b/string_io.ex
@@ -0,0 +1,186 @@
+defmodule StringIO do
+  def new(string) when is_binary(string) do
+    spawn_link(fn -> string_io_process(string) end)
+  end
+
+  def string_io_process(string) do
+    loop(:infinity, String.to_char_list!(string))
+  end
+
+  def loop(wait, buf) do
+    receive do
+      { :io_request, from, reply_as, req } ->
+        p = :erlang.process_flag(:priority, :normal)
+        buf = io_request(from, reply_as, req, buf)
+        :erlang.process_flag(:priority, p)
+        loop(wait, buf)
+      :stop ->
+        receive after: (2 -> :ok)
+        :erlang.process_flag(:priority, :low)
+        loop(0, buf)
+      _ ->
+        loop(0, buf)
+    end
+  end
+
+  defp io_request(from, reply_as, req, buf) do
+    { reply, buf1 } = io_request(req, buf)
+    io_reply(from, reply_as, reply)
+    buf1
+  end
+
+  defp io_reply(from, reply_as, reply) do
+    send from, { :io_reply, reply_as, reply }
+  end
+
+  defp io_request({ :put_chars, chars }, buf) do
+    { :ok, [chars|buf] }
+  end
+
+  defp io_request({ :put_chars, m, f, as }, buf) do
+    chars = apply(m, f, as)
+    { :ok, [chars|buf] }
+  end
+
+  defp io_request({ :put_chars, _enc, chars }, buf) do
+    io_request({ :put_chars, chars }, buf)
+  end
+
+  defp io_request({ :put_chars, _enc, mod, func, args }, buf) do
+    io_request({ :put_chars, mod, func, args }, buf)
+  end
+
+  defp io_request({ :get_chars, _enc, prompt, n }, buf) when n >= 0 do
+    io_request({ :get_chars, prompt, n }, buf)
+  end
+
+  defp io_request({ :get_chars, _prompt, n }, buf) when n >= 0 do
+    get_chars(n, buf)
+  end
+
+  defp io_request({ :get_line, _enc, prompt }, buf) do
+    io_request({ :get_line, prompt }, buf)
+  end
+
+  defp io_request({ :get_line, _prompt }, buf) do
+    get_line(buf)
+  end
+
+  defp io_request({ :get_until, _encoding, prompt, mod, fun, args}, buf) do
+    io_request({ :get_until, prompt, mod, fun, args}, buf)
+  end
+
+  defp io_request({ :get_until, _prompt, mod, fun, args }, buf) do
+    get_until(mod, fun, args, buf)
+  end
+
+  defp io_request({ :setopts, _opts }, buf) do
+    { :ok, buf }
+  end
+
+  defp io_request(:getopts, buf) do
+    { { :error, :enotsup }, buf }
+  end
+
+  defp io_request({ :get_geometry, :columns }, buf) do
+    { { :error, :enotsup }, buf }
+  end
+
+  defp io_request({ :get_geometry, :rows }, buf) do
+    { { :error, :enotsup }, buf }
+  end
+
+  defp io_request({ :requests, reqs }, buf) do
+    io_requests(reqs, { :ok, buf })
+  end
+
+  defp io_request(_, buf) do
+    { { :error, :request }, buf }
+  end
+
+  defp io_requests([r|rs], { :ok, buf }) do
+    io_requests(rs, io_request(r, buf))
+  end
+
+  defp io_requests(_, result) do
+    result
+  end
+
+  defp get_line(buf) do
+    case buf do
+      [] ->
+        { :eof, [] }
+      _ ->
+        { line, rest } = Enum.split_while(buf, fn(char) -> char != ?\n end)
+        case rest do
+          [] ->
+            { String.from_char_list!(line), [] }
+          [_|t] ->
+            { String.from_char_list!(line) <> "\n", t }
+        end
+    end
+  end
+
+  defp get_chars(n, buf) do
+    case buf do
+      [] ->
+        { :eof, [] }
+      _ ->
+        { chars, rest } = Enum.split(buf, n)
+        { String.from_char_list!(chars), rest }
+    end
+  end
+
+  defp get_until(mod, fun, args, buf) do
+    do_get_until(buf, mod, fun, args)
+  end
+
+  defp do_get_until([], mod, fun, args, continuation \\ [])
+
+  defp do_get_until([], mod, fun, args, continuation) do
+    case apply(mod, fun, [continuation, :eof | args]) do
+      { :done, result, rest_chars } ->
+        { result, rest_chars }
+      { :more, next_continuation } ->
+        do_get_until([], mod, fun, args, next_continuation)
+    end
+  end
+
+  defp do_get_until(input, mod, fun, args, continuation) do
+    { line, rest } = Enum.split_while(input, fn(char) -> char != ?\n end)
+
+    case rest do
+      [] ->
+        case apply(mod, fun, [continuation, line | args]) do
+          { :done, result, rest_chars } ->
+            { result, rest_chars }
+          { :more, next_continuation } ->
+            do_get_until([], mod, fun, args, next_continuation)
+        end
+      [_|t] ->
+        case apply(mod, fun, [continuation, line ++ '\n' | args]) do
+          { :done, result, rest_chars } ->
+            { result, rest_chars ++ t }
+          { :more, next_continuation } ->
+            do_get_until(t, mod, fun, args, next_continuation)
+        end
+    end
+  end
+end
+
+ExUnit.start
+
+defmodule StringIOTest do
+  use ExUnit.Case
+
+  test "the truth" do
+    f = StringIO.new "abc\ndef\n"
+    assert IO.read(f, :line) == "abc\n"
+    assert IO.read(f, :line) == "def\n"
+    assert IO.read(f, :line) == :eof
+
+    assert IO.write(f, "hello\n") == :ok
+    assert IO.read(f, :line) == "hello\n"
+    assert IO.read(f, :line) == :eof
+  end
+end
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