Add normalizePath, absolutePath and tests

lib/pure/os.nim

@@ -283,8 +283,11 @@ proc setCurrentDir*(newDir: string) {.inline, tags: [].} =
 
 proc expandFilename*(filename: string): string {.rtl, extern: "nos$1",
   tags: [ReadDirEffect].} =
-  ## Returns the full (`absolute`:idx:) path of the file `filename`,
+  ## Returns the full (`absolute`:idx:) path of an existing file `filename`,
   ## raises OSError in case of an error.
+  ##
+  ## To create absolute paths from any path (existing or not) see
+  ## `<#absolutePath>`_.
   when defined(windows):
     var bufsize = MAX_PATH.int32
     when useWinUnicode:
@@ -323,6 +326,52 @@ proc expandFilename*(filename: string): string {.rtl, extern: "nos$1",
       result = $r
       c_free(cast[pointer](r))
 
+proc normalizePath*(path: string): string =
+  ## Normalize an UNIX path.
+  ##
+  ## Consecutive slashes (/) are collapsed, including an initial double slash.
+  ##
+  ## On relative paths, double dot (..) sequences are collapsed if possible.
+  ## On absolute paths they are always collapsed.
+  ##
+  ## Warning: URL-encoded and Unicode attempts at directory traversal are not detected.
+  ## Triple dot is not handled.
+  let is_abs = path[0] == DirSep
+  var stack: seq[string] = @[]
+  for p in split(path, {DirSep}):
+    case p
+    of "", ".":
+      continue
+    of "..":
+      if stack.len == 0:
+        if is_abs:
+          discard  # collapse all double dots on absoluta paths
+        else:
+          stack.add(p)
+      elif stack[^1] == "..":
+        stack.add(p)
+      else:
+        discard stack.pop()
+    else:
+      stack.add(p)
+
+  if is_abs:
+    result = DirSep & join(stack, $DirSep)
+  elif stack.len > 0:
+    result = join(stack, $DirSep)
+  else:
+    result = "."
+
+proc absolutePath*(path: string): string =
+  ## Returns the normalized, (`absolute`:idx:) version of `path`, based on
+  ## the current directory. See `<#normalizePath>`_
+  if path.isAbsolute:
+    result = path
+  else:
+    result = joinPath(getCurrentDir(), path)
+  if result.len > 1 and result[^1] == DirSep:
+    result = result[0..^2]
+
 when defined(Windows):
   proc openHandle(path: string, followSymlink=true): Handle =
     var flags = FILE_FLAG_BACKUP_SEMANTICS or FILE_ATTRIBUTE_NORMAL

tests/stdlib/tos.nim

@@ -42,11 +42,16 @@ Raises
 true
 true
 true
+
+[Suite] normalizePath
+
+[Suite] absolutePath
+
 '''
 """
 # test os path creation, iteration, and deletion
 
-import os, strutils
+import os, strutils, unittest
 
 let files = @["these.txt", "are.x", "testing.r", "files.q"]
 let dirs = @["some", "created", "test", "dirs"]
@@ -129,3 +134,54 @@ echo fileExists("../dest/a/b/file.txt")
 
 echo fileExists("../dest/a/b/c/fileC.txt")
 removeDir("../dest")
+
+suite "normalizePath":
+  test "normalizePath relative":
+    check normalizePath(".") == "."
+    check normalizePath("..") == ".."
+    check normalizePath("../") == ".."
+    check normalizePath("../..") == "../.."
+    check normalizePath("../a/..") == ".."
+    check normalizePath("../a/../") == ".."
+    check normalizePath("./") == "."
+
+  test "normalizePath absolute":
+    check normalizePath("/") == "/"
+    check normalizePath("/.") == "/"
+    check normalizePath("/..") == "/"
+    check normalizePath("/../") == "/"
+    check normalizePath("/../..") == "/"
+    check normalizePath("/../../") == "/"
+    check normalizePath("/../../../") == "/"
+    check normalizePath("/./") == "/"
+    check normalizePath("//") == "/"
+    check normalizePath("///") == "/"
+    check normalizePath("/a//b") == "/a/b"
+    check normalizePath("/a///b") == "/a/b"
+    check normalizePath("/a/b/c/..") == "/a/b"
+    check normalizePath("/a/b/c/../") == "/a/b"
+
+when defined(Linux) or defined(osx):
+
+  suite "absolutePath":
+    setup:
+      let cwd = getCurrentDir()
+
+    test "absolutePath /":
+      setCurrentDir("/")
+      check absolutePath("foo") == "/foo"
+      check absolutePath("") == "/"
+      #check absolutePath(".") == "/"
+      check absolutePath("/") == "/"
+
+    test "absolutePath /tmp":
+      setCurrentDir("/tmp")
+      check absolutePath("foo") == "/tmp/foo"
+      check absolutePath("") == "/tmp"
+      #check absolutePath(".") == "/tmp"
+      check absolutePath("/") == "/"
+      #check absolutePath("foo/..") == "/tmp/foo"
+      #check absolutePath("../..") == "/tmp/foo"
+
+    teardown:
+      setCurrentDir(cwd)