introduce std.os.windows.QueryObjectName

Author: rohlem

lib/std/os/windows.zig

@@ -952,6 +952,46 @@ pub fn SetFilePointerEx_CURRENT_get(handle: HANDLE) SetFilePointerError!u64 {
     return @bitCast(u64, result);
 }
 
+pub fn QueryObjectName(
+    Handle: HANDLE,
+    out_buffer: []u16,
+    ReturnLength: ?PULONG, //returned in bytes
+) ![:0]u16 {
+    const alignment = @alignOf(OBJECT_NAME_INFORMATION);
+    const begin_addr = @ptrToInt(out_buffer.ptr);
+    const aligned_begin_addr = std.mem.alignForward(begin_addr, alignment);
+    const alignment_step = aligned_begin_addr - begin_addr;
+    const aligned_raw_buffer = @alignCast(alignment, std.mem.sliceAsBytes(out_buffer)[alignment_step..out_buffer.len*@sizeOf(u16)]);
+    if(aligned_raw_buffer.len < @sizeOf(OBJECT_NAME_INFORMATION)) return error.BufferTooSmall; //this would result in .INFO_LENGTH_MISMATCH
+    
+    var info = @ptrCast(*OBJECT_NAME_INFORMATION, aligned_raw_buffer);
+    info.* = undefined; //all of the fields we read will be overwritten, and the result string is placed in the same buffer after the struct
+    const out_buffer_length = std.math.cast(ULONG, aligned_raw_buffer.len) catch |e| std.math.maxInt(u32); //we'll just use as much of it as we can
+    const rc = ntdll.NtQueryObject(Handle, .ObjectNameInformation, out_buffer.ptr, out_buffer_length, ReturnLength); //buffer size is specified in u16...
+    switch(rc){
+        .SUCCESS => if(info.Name.Buffer) |buffer| return buffer[0..@divExact(info.Name.Length, 2):0] //... but result length is specified in u8
+            else return error.Unnamed,
+        .ACCESS_DENIED => return error.AccessDenied,
+        .INVALID_HANDLE => return error.InvalidHandle,
+        .BUFFER_OVERFLOW, .BUFFER_TOO_SMALL => return error.NameTooLong,
+        .INFO_LENGTH_MISMATCH => unreachable, //aligned_raw_buffer.len < @sizeOf(OBJECT_NAME_INFORMATION) already checked previously
+        else => |e| return unexpectedStatus(e),
+    }
+}
+test "QueryObjectName" {
+    const file: std.fs.File = try std.fs.openSelfExe(.{}); //any file will do; canonicalization works on NTFS junctions and symlinks, hardlinks remain separate paths.
+    defer file.close();
+    var out_buffer align(16) = std.mem.zeroes([1<<10]u16); //make this big enough for the test runner exe path
+    var required_length: ULONG = undefined;
+
+    _ = try QueryObjectName(file.handle, out_buffer[0..], &required_length);
+    required_length = @divExact(required_length, 2);
+    _ = try QueryObjectName(file.handle, out_buffer[0..required_length], null);
+    std.testing.expect(null == QueryObjectName(file.handle, out_buffer[0..required_length-1], null)
+        catch |e| switch(e) {error.NameTooLong => null, else => unreachable});
+    _ = try QueryObjectName(file.handle, out_buffer[0..required_length+1], null);
+}
+
 pub const GetFinalPathNameByHandleError = error {
         BadPathName,
         FileNotFound,
@@ -963,7 +1003,9 @@ pub const GetFinalPathNameByHandleError = error {
     else
         error {
             AccessDenied,
-            SystemResources,
+            BufferTooSmall,
+            InvalidHandle,
+            Unnamed,
         };
 
 /// Specifies how to format volume path in the result of `GetFinalPathNameByHandle`.
@@ -1147,7 +1189,7 @@ test "GetFinalPathNameByHandle" {
 
     const selfExeFile: std.fs.File = try std.fs.openSelfExe(.{}); //any file would do
 
-    var buffer = std.mem.zeroes([1<<10]u16); //make this big enough for the current directory
+    var buffer = std.mem.zeroes([1<<10]u16); //make this big enough for the test runner exe path
 
     //check with sufficient size
     const dos_length = try S.check(selfExeFile, buffer[0..], .{.volume_name = .Dos});

lib/std/os/windows/bits.zig

@@ -65,6 +65,7 @@ pub const SIZE_T = usize;
 pub const TCHAR = if (UNICODE) WCHAR else u8;
 pub const UINT = c_uint;
 pub const ULONG_PTR = usize;
+pub const PULONG = *ULONG;
 pub const LONG_PTR = isize;
 pub const DWORD_PTR = ULONG_PTR;
 pub const UNICODE = false;
@@ -1178,7 +1179,7 @@ pub const OBJ_VALID_ATTRIBUTES = 0x000003F2;
 pub const UNICODE_STRING = extern struct {
     Length: c_ushort,
     MaximumLength: c_ushort,
-    Buffer: [*]WCHAR,
+    Buffer: ?[*]WCHAR,
 };
 
 const ACTIVATION_CONTEXT_DATA = opaque {};
@@ -1606,3 +1607,18 @@ pub const IOCTL_MOUNTMGR_QUERY_POINTS: ULONG = 0x6d0008;
 pub const SD_RECEIVE = 0;
 pub const SD_SEND = 1;
 pub const SD_BOTH = 2;
+
+pub const OBJECT_INFORMATION_CLASS = extern enum {
+    ObjectBasicInformation = 0,
+    ObjectNameInformation = 1,
+    ObjectTypeInformation = 2,
+    ObjectTypesInformation = 3,
+    ObjectHandleFlagInformation = 4,
+    ObjectSessionInformation = 5,
+    MaxObjectInfoClass,
+};
+
+pub const OBJECT_NAME_INFORMATION = extern struct {
+    Name: UNICODE_STRING,
+};
+pub const POBJECT_NAME_INFORMATION = *OBJECT_NAME_INFORMATION;

lib/std/os/windows/ntdll.zig

@@ -113,3 +113,10 @@ pub extern "NtDll" fn NtWaitForKeyedEvent(
 ) callconv(WINAPI) NTSTATUS;
 
 pub extern "NtDll" fn RtlSetCurrentDirectory_U(PathName: *UNICODE_STRING) callconv(WINAPI) NTSTATUS;
+
+pub extern "NtDll" fn NtQueryObject(
+    Handle: HANDLE,
+    ObjectInformationClass: OBJECT_INFORMATION_CLASS,
+    ObjectInformation: PVOID,
+    ObjectInformationLength: ULONG,
+    ReturnLength: ?PULONG) NTSTATUS;