From 859ceb25d0beedbe3d048d6c48a1628af389717c Mon Sep 17 00:00:00 2001
From: NiteHawk <n1tehawk@users.noreply.github.com>
Date: Tue, 18 Oct 2016 18:41:33 +0200
Subject: [PATCH 1/3] Implement lfs.realpath()

For POSIX systems, the function is a straightforward wrapper
around realpath() - see "man 3 realpath".
On Windows, the CRT function `_fullpath` gets used instead,
see https://msdn.microsoft.com/en-us/library/506720ff.aspx
---
 src/lfs.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/src/lfs.c b/src/lfs.c
index 25122a3..37cd532 100644
--- a/src/lfs.c
+++ b/src/lfs.c
@@ -909,6 +909,35 @@ static int link_info (lua_State *L) {
         return ret;
 }
 
+/*
+** Retrieve canonicalized absolute pathname using realpath()
+** Upon success the function returns the resolved path, otherwise the return
+** values are `nil`, an error message (string) and the error number.
+**
+** Note that the Windows implementation differs from the POSIX function,
+** for example it doesn't test if the resolved path is actually reachable.
+** E.g. "C:\foo\..\bar" will happily resolve to "C:\bar",
+** even if neither C:\foo nor C:\bar exist.
+*/
+static int get_realpath (lua_State *L) {
+        const char *path = luaL_checkstring (L, 1);
+        char *resolved;
+#ifdef _WIN32
+        resolved = _fullpath(NULL, path, 0);
+#else
+        resolved = realpath(path, NULL);
+#endif
+        if (resolved) {
+                lua_pushstring(L, resolved);
+                free(resolved);
+                return 1;
+        }
+        /* an error occured */
+        lua_pushnil(L);
+        lua_pushfstring(L, "lfs.realpath('%s') failed: %s", path, strerror(errno));
+        lua_pushinteger(L, errno);
+        return 3;
+}
 
 /*
 ** Assumes the table is on top of the stack.
@@ -931,6 +960,7 @@ static const struct luaL_Reg fslib[] = {
         {"link", make_link},
         {"lock", file_lock},
         {"mkdir", make_dir},
+        {"realpath", get_realpath},
         {"rmdir", remove_dir},
         {"symlinkattributes", link_info},
         {"setmode", lfs_f_setmode},

From 84628e479a6dc657f7b4bc1fab0fba50196921fe Mon Sep 17 00:00:00 2001
From: NiteHawk <n1tehawk@users.noreply.github.com>
Date: Tue, 18 Oct 2016 18:44:23 +0200
Subject: [PATCH 2/3] Add test cases for lfs.realpath()

---
 tests/test.lua | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/tests/test.lua b/tests/test.lua
index 10810fe..fa2cfd5 100644
--- a/tests/test.lua
+++ b/tests/test.lua
@@ -65,6 +65,20 @@ f:close()
 io.write(".")
 io.flush()
 
+-- Check that realpath can resolve the parent of tmpdir (= "current")
+assert(lfs.realpath(tmpdir..sep.."..") == current)
+
+-- Non-existent paths will error on POSIX (errno 2), but not on Windows!
+local ok, err = lfs.realpath("C:\\foo\\..\\bar")
+if not ok then
+        assert(err:match("No such file or directory"))
+else
+        assert(ok == "C:\\bar")
+end
+
+io.write(".")
+io.flush()
+
 -- Change access time
 local testdate = os.time({ year = 2007, day = 10, month = 2, hour=0})
 assert (lfs.touch (tmpfile, testdate))
@@ -95,6 +109,7 @@ if lfs.link (tmpfile, "_a_link_for_test_", true) then
   assert (lfs.symlinkattributes("_a_link_for_test_", "target") == tmpfile)
   assert (lfs.link (tmpfile, "_a_hard_link_for_test_"))
   assert (lfs.attributes (tmpfile, "nlink") == 2)
+  assert (lfs.realpath"_a_link_for_test_" == tmpfile)
   assert (os.remove"_a_link_for_test_")
   assert (os.remove"_a_hard_link_for_test_")
 end

From 2ad5d9aae9c987250e7e98752b7bd9fa7d0e2c91 Mon Sep 17 00:00:00 2001
From: NiteHawk <n1tehawk@users.noreply.github.com>
Date: Wed, 19 Oct 2016 13:41:24 +0200
Subject: [PATCH 3/3] Fixup: Add missing documentation line

(Squash with 859ceb2)
---
 src/lfs.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/lfs.c b/src/lfs.c
index 37cd532..1b7b9fa 100644
--- a/src/lfs.c
+++ b/src/lfs.c
@@ -12,6 +12,7 @@
 **   lfs.lock (fh, mode)
 **   lfs.lock_dir (path)
 **   lfs.mkdir (path)
+**   lfs.realpath (path)
 **   lfs.rmdir (path)
 **   lfs.setmode (filepath, mode)
 **   lfs.symlinkattributes (filepath [, attributename])