os.isCygwinPty: Fix a bug, replace kernel32 call, and optimize

lib/std/fs/file.zig

@@ -379,6 +379,9 @@ pub const File = struct {
             const rc = windows.ntdll.NtQueryInformationFile(self.handle, &io_status_block, &info, @sizeOf(windows.FILE_ALL_INFORMATION), .FileAllInformation);
             switch (rc) {
                 .SUCCESS => {},
+                // Buffer overflow here indicates that there is more information available than was able to be stored in the buffer
+                // size provided. This is treated as success because the type of variable-length information that this would be relevant for
+                // (name, volume name, etc) we don't care about.
                 .BUFFER_OVERFLOW => {},
                 .INVALID_PARAMETER => unreachable,
                 .ACCESS_DENIED => return error.AccessDenied,
@@ -830,6 +833,9 @@ pub const File = struct {
                     const rc = windows.ntdll.NtQueryInformationFile(self.handle, &io_status_block, &info, @sizeOf(windows.FILE_ALL_INFORMATION), .FileAllInformation);
                     switch (rc) {
                         .SUCCESS => {},
+                        // Buffer overflow here indicates that there is more information available than was able to be stored in the buffer
+                        // size provided. This is treated as success because the type of variable-length information that this would be relevant for
+                        // (name, volume name, etc) we don't care about.
                         .BUFFER_OVERFLOW => {},
                         .INVALID_PARAMETER => unreachable,
                         .ACCESS_DENIED => return error.AccessDenied,

lib/std/os.zig

@@ -3217,22 +3217,48 @@ pub fn isatty(handle: fd_t) bool {
 pub fn isCygwinPty(handle: fd_t) bool {
     if (builtin.os.tag != .windows) return false;
 
-    const size = @sizeOf(windows.FILE_NAME_INFO);
-    var name_info_bytes align(@alignOf(windows.FILE_NAME_INFO)) = [_]u8{0} ** (size + windows.MAX_PATH);
+    // If this is a MSYS2/cygwin pty, then it will be a named pipe with a name in one of these formats:
+    //   msys-[...]-ptyN-[...]
+    //   cygwin-[...]-ptyN-[...]
+    //
+    // Example: msys-1888ae32e00d56aa-pty0-to-master
+
+    // First, just check that the handle is a named pipe.
+    // This allows us to avoid the more costly NtQueryInformationFile call
+    // for handles that aren't named pipes.
+    {
+        var io_status: windows.IO_STATUS_BLOCK = undefined;
+        var device_info: windows.FILE_FS_DEVICE_INFORMATION = undefined;
+        const rc = windows.ntdll.NtQueryVolumeInformationFile(handle, &io_status, &device_info, @sizeOf(windows.FILE_FS_DEVICE_INFORMATION), .FileFsDeviceInformation);
+        switch (rc) {
+            .SUCCESS => {},
+            else => return false,
+        }
+        if (device_info.DeviceType != windows.FILE_DEVICE_NAMED_PIPE) return false;
+    }
 
-    if (windows.kernel32.GetFileInformationByHandleEx(
-        handle,
-        windows.FileNameInfo,
-        @ptrCast(*anyopaque, &name_info_bytes),
-        name_info_bytes.len,
-    ) == 0) {
-        return false;
+    const name_bytes_offset = @offsetOf(windows.FILE_NAME_INFO, "FileName");
+    // `NAME_MAX` UTF-16 code units (2 bytes each)
+    // Note: This buffer may not be long enough to handle *all* possible paths (PATH_MAX_WIDE would be necessary for that),
+    //       but because we only care about certain paths and we know they must be within a reasonable length,
+    //       we can use this smaller buffer and just return false on any error from NtQueryInformationFile.
+    const num_name_bytes = windows.MAX_PATH * 2;
+    var name_info_bytes align(@alignOf(windows.FILE_NAME_INFO)) = [_]u8{0} ** (name_bytes_offset + num_name_bytes);
+
+    var io_status_block: windows.IO_STATUS_BLOCK = undefined;
+    const rc = windows.ntdll.NtQueryInformationFile(handle, &io_status_block, &name_info_bytes, @intCast(u32, name_info_bytes.len), .FileNameInformation);
+    switch (rc) {
+        .SUCCESS => {},
+        .INVALID_PARAMETER => unreachable,
+        else => return false,
     }
 
     const name_info = @ptrCast(*const windows.FILE_NAME_INFO, &name_info_bytes[0]);
-    const name_bytes = name_info_bytes[size .. size + @as(usize, name_info.FileNameLength)];
+    const name_bytes = name_info_bytes[name_bytes_offset .. name_bytes_offset + @as(usize, name_info.FileNameLength)];
     const name_wide = mem.bytesAsSlice(u16, name_bytes);
-    return mem.indexOf(u16, name_wide, &[_]u16{ 'm', 's', 'y', 's', '-' }) != null or
+    // Note: The name we get from NtQueryInformationFile will be prefixed with a '\', e.g. \msys-1888ae32e00d56aa-pty0-to-master
+    return (mem.startsWith(u16, name_wide, &[_]u16{ '\\', 'm', 's', 'y', 's', '-' }) or
+        mem.startsWith(u16, name_wide, &[_]u16{ '\\', 'c', 'y', 'g', 'w', 'i', 'n', '-' })) and
         mem.indexOf(u16, name_wide, &[_]u16{ '-', 'p', 't', 'y' }) != null;
 }
 

lib/std/os/windows.zig

@@ -2472,6 +2472,29 @@ pub const FILE_INFORMATION_CLASS = enum(c_int) {
     FileMaximumInformation,
 };
 
+pub const FILE_FS_DEVICE_INFORMATION = extern struct {
+    DeviceType: DEVICE_TYPE,
+    Characteristics: ULONG,
+};
+
+pub const FS_INFORMATION_CLASS = enum(c_int) {
+    FileFsVolumeInformation = 1,
+    FileFsLabelInformation,
+    FileFsSizeInformation,
+    FileFsDeviceInformation,
+    FileFsAttributeInformation,
+    FileFsControlInformation,
+    FileFsFullSizeInformation,
+    FileFsObjectIdInformation,
+    FileFsDriverPathInformation,
+    FileFsVolumeFlagsInformation,
+    FileFsSectorSizeInformation,
+    FileFsDataCopyInformation,
+    FileFsMetadataSizeInformation,
+    FileFsFullSizeInformationEx,
+    FileFsMaximumInformation,
+};
+
 pub const OVERLAPPED = extern struct {
     Internal: ULONG_PTR,
     InternalHigh: ULONG_PTR,

lib/std/os/windows/ntdll.zig

@@ -18,6 +18,7 @@ const IO_STATUS_BLOCK = windows.IO_STATUS_BLOCK;
 const LARGE_INTEGER = windows.LARGE_INTEGER;
 const OBJECT_INFORMATION_CLASS = windows.OBJECT_INFORMATION_CLASS;
 const FILE_INFORMATION_CLASS = windows.FILE_INFORMATION_CLASS;
+const FS_INFORMATION_CLASS = windows.FS_INFORMATION_CLASS;
 const UNICODE_STRING = windows.UNICODE_STRING;
 const RTL_OSVERSIONINFOW = windows.RTL_OSVERSIONINFOW;
 const FILE_BASIC_INFORMATION = windows.FILE_BASIC_INFORMATION;
@@ -232,6 +233,14 @@ pub extern "ntdll" fn NtQueryObject(
     ReturnLength: ?*ULONG,
 ) callconv(WINAPI) NTSTATUS;
 
+pub extern "ntdll" fn NtQueryVolumeInformationFile(
+    FileHandle: HANDLE,
+    IoStatusBlock: *IO_STATUS_BLOCK,
+    FsInformation: *anyopaque,
+    Length: ULONG,
+    FsInformationClass: FS_INFORMATION_CLASS,
+) callconv(WINAPI) NTSTATUS;
+
 pub extern "ntdll" fn RtlWakeAddressAll(
     Address: ?*const anyopaque,
 ) callconv(WINAPI) void;