Implement File.readable? and .writable? in Win32 (#14420)

Co-authored-by: Johannes Müller <straightshoota@gmail.com>

spec/std/file_spec.cr

@@ -31,6 +31,17 @@ private def normalize_permissions(permissions, *, directory)
   {% end %}
 end
 
+# TODO: Find a better way to execute specs involving file permissions when
+# running as a privileged user. Compiling a program and running a separate
+# process would be a lot of overhead.
+private def pending_if_superuser!
+  {% if flag?(:unix) %}
+    if LibC.getuid == 0
+      pending! "Spec cannot run as superuser"
+    end
+  {% end %}
+end
+
 describe "File" do
   it "gets path" do
     path = datapath("test_file.txt")
@@ -217,6 +228,27 @@ describe "File" do
     it "gives false when a component of the path is a file" do
       File.readable?(datapath("dir", "test_file.txt", "")).should be_false
     end
+
+    # win32 doesn't have a way to make files unreadable via chmod
+    {% unless flag?(:win32) %}
+      it "gives false when the file has no read permissions" do
+        with_tempfile("unreadable.txt") do |path|
+          File.write(path, "")
+          File.chmod(path, 0o222)
+          pending_if_superuser!
+          File.readable?(path).should be_false
+        end
+      end
+
+      it "gives false when the file has no permissions" do
+        with_tempfile("unaccessible.txt") do |path|
+          File.write(path, "")
+          File.chmod(path, 0o000)
+          pending_if_superuser!
+          File.readable?(path).should be_false
+        end
+      end
+    {% end %}
   end
 
   describe "writable?" do
@@ -231,6 +263,15 @@ describe "File" do
     it "gives false when a component of the path is a file" do
       File.writable?(datapath("dir", "test_file.txt", "")).should be_false
     end
+
+    it "gives false when the file has no write permissions" do
+      with_tempfile("readonly.txt") do |path|
+        File.write(path, "")
+        File.chmod(path, 0o444)
+        pending_if_superuser!
+        File.writable?(path).should be_false
+      end
+    end
   end
 
   describe "file?" do
@@ -991,14 +1032,7 @@ describe "File" do
       with_tempfile("file.txt") do |path|
         File.touch(path)
         File.chmod(path, File::Permissions::None)
-        {% if flag?(:unix) %}
-          # TODO: Find a better way to execute this spec when running as privileged
-          # user. Compiling a program and running a separate process would be a
-          # lot of overhead.
-          if LibC.getuid == 0
-            pending! "Spec cannot run as superuser"
-          end
-        {% end %}
+        pending_if_superuser!
         expect_raises(File::AccessDeniedError, "Error opening file with mode 'r': '#{path.inspect_unquoted}'") { File.read(path) }
       end
     end
@@ -1008,14 +1042,7 @@ describe "File" do
     with_tempfile("file.txt") do |path|
       File.touch(path)
       File.chmod(path, File::Permissions::None)
-      {% if flag?(:unix) %}
-        # TODO: Find a better way to execute this spec when running as privileged
-        # user. Compiling a program and running a separate process would be a
-        # lot of overhead.
-        if LibC.getuid == 0
-          pending! "Spec cannot run as superuser"
-        end
-      {% end %}
+      pending_if_superuser!
       expect_raises(File::AccessDeniedError, "Error opening file with mode 'w': '#{path.inspect_unquoted}'") { File.write(path, "foo") }
     end
   end

src/crystal/system/win32/file.cr

@@ -177,23 +177,28 @@ module Crystal::System::File
     if follow_symlinks
       path = realpath?(path) || return false
     end
-    accessible?(path, 0)
+    accessible?(path, check_writable: false)
   end
 
   def self.readable?(path) : Bool
-    accessible?(path, 4)
+    accessible?(path, check_writable: false)
   end
 
   def self.writable?(path) : Bool
-    accessible?(path, 2)
+    accessible?(path, check_writable: true)
   end
 
   def self.executable?(path) : Bool
     LibC.GetBinaryTypeW(System.to_wstr(path), out result) != 0
   end
 
-  private def self.accessible?(path, mode)
-    LibC._waccess_s(System.to_wstr(path), mode) == 0
+  private def self.accessible?(path, *, check_writable)
+    attributes = LibC.GetFileAttributesW(System.to_wstr(path))
+    return false if attributes == LibC::INVALID_FILE_ATTRIBUTES
+    return true if attributes.bits_set?(LibC::FILE_ATTRIBUTE_DIRECTORY)
+    return false if check_writable && attributes.bits_set?(LibC::FILE_ATTRIBUTE_READONLY)
+
+    true
   end
 
   def self.chown(path : String, uid : Int32, gid : Int32, follow_symlinks : Bool) : Nil

src/lib_c/x86_64-windows-msvc/c/io.cr

@@ -2,7 +2,6 @@ require "c/stdint"
 
 lib LibC
   fun _close(fd : Int) : Int
-  fun _waccess_s(path : WCHAR*, mode : Int) : ErrnoT
   fun _wexecvp(cmdname : WCHAR*, argv : WCHAR**) : IntPtrT
   fun _get_osfhandle(fd : Int) : IntPtrT
   fun _dup2(fd1 : Int, fd2 : Int) : Int
@@ -14,6 +13,7 @@ lib LibC
   fun _read(fd : Int, buffer : UInt8*, count : UInt) : Int
   fun _lseeki64(fd : Int, offset : Int64, origin : Int) : Int64
   fun _wopen(filename : WCHAR*, oflag : Int, ...) : Int
+  fun _waccess_s(path : WCHAR*, mode : Int) : ErrnoT
   fun _wchmod(filename : WCHAR*, pmode : Int) : Int
   fun _wunlink(filename : WCHAR*) : Int
   fun _wmktemp_s(template : WCHAR*, sizeInChars : SizeT) : ErrnoT