From d1c48192cbff3cdc9168854c115d2d421068fb01 Mon Sep 17 00:00:00 2001
From: Kohei Suzuki <eagletmt@gmail.com>
Date: Sat, 17 Dec 2016 15:00:04 +0900
Subject: Add File.readlink

---
 README.md    |  2 +-
 src/file.c   | 31 +++++++++++++++++++++++++++++++
 test/file.rb | 16 ++++++++++++++++
 3 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 604361f25..e007393a9 100644
--- a/README.md
+++ b/README.md
@@ -134,7 +134,7 @@ Add the line below to your `build_config.rb`:
 | File.pipe?                  |   o      | FileTest |
 | File.readable?              |          | FileTest |
 | File.readable_real?         |          | FileTest |
-| File.readlink               |          |      |
+| File.readlink               |   o      |      |
 | File.realdirpath            |          |      |
 | File.realpath               |   o      |      |
 | File.rename                 |   o      |      |
diff --git a/src/file.c b/src/file.c
index 2131db654..a1c965638 100644
--- a/src/file.c
+++ b/src/file.c
@@ -353,6 +353,36 @@ mrb_file_s_chmod(mrb_state *mrb, mrb_value klass) {
   return mrb_fixnum_value(argc);
 }
 
+static mrb_value
+mrb_file_s_readlink(mrb_state *mrb, mrb_value klass) {
+#if defined(_WIN32) || defined(_WIN64)
+  mrb_raise(mrb, E_NOTIMP_ERROR, "readlink is not supported on this platform");
+  return mrb_nil_value(); // unreachable
+#else
+  char *path, *buf;
+  size_t bufsize = 100;
+  ssize_t rc;
+  mrb_value ret;
+  int ai = mrb_gc_arena_save(mrb);
+
+  mrb_get_args(mrb, "z", &path);
+
+  buf = mrb_malloc(mrb, bufsize);
+  while ((rc = readlink(path, buf, bufsize)) == bufsize && rc != -1) {
+    bufsize *= 2;
+    buf = mrb_realloc(mrb, buf, bufsize);
+  }
+  if (rc == -1) {
+    mrb_sys_fail(mrb, path);
+  }
+  ret = mrb_str_new(mrb, buf, rc);
+  mrb_free(mrb, buf);
+
+  mrb_gc_arena_restore(mrb, ai);
+  return ret;
+#endif
+}
+
 void
 mrb_init_file(mrb_state *mrb)
 {
@@ -367,6 +397,7 @@ mrb_init_file(mrb_state *mrb)
   mrb_define_class_method(mrb, file, "rename", mrb_file_s_rename, MRB_ARGS_REQ(2));
   mrb_define_class_method(mrb, file, "symlink", mrb_file_s_symlink, MRB_ARGS_REQ(2));
   mrb_define_class_method(mrb, file, "chmod", mrb_file_s_chmod, MRB_ARGS_REQ(1) | MRB_ARGS_REST());
+  mrb_define_class_method(mrb, file, "readlink", mrb_file_s_readlink, MRB_ARGS_REQ(1));
 
   mrb_define_class_method(mrb, file, "dirname",   mrb_file_dirname,    MRB_ARGS_REQ(1));
   mrb_define_class_method(mrb, file, "basename",  mrb_file_basename,   MRB_ARGS_REQ(1));
diff --git a/test/file.rb b/test/file.rb
index f5607bbaa..58c16bbfe 100644
--- a/test/file.rb
+++ b/test/file.rb
@@ -91,6 +91,22 @@ assert('File.realpath') do
   end
 end
 
+assert("File.readlink") do
+  begin
+    assert_equal 'hoge', File.readlink($mrbtest_io_symlinkname)
+  rescue NotImplementedError => e
+    skip e.message
+  end
+end
+
+assert("File.readlink fails with non-symlink") do
+  begin
+    assert_raise(RuntimeError) { File.readlink($mrbtest_io_rfname) }
+  rescue NotImplementedError => e
+    skip e.message
+  end
+end
+
 assert('File TEST CLEANUP') do
   assert_nil MRubyIOTestUtil.io_test_cleanup
 end
-- 
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