From d17c9b3591ba822df3af341a0d4cf5f004413f4a Mon Sep 17 00:00:00 2001
From: Jakub Konka <kubkon@jakubkonka.com>
Date: Tue, 14 Jul 2020 08:45:04 +0200
Subject: [PATCH] Fix incorrect byte format of REPARSE_DATA_BUFFER struct

---
 lib/std/os.zig              | 22 ++++++++++++-------
 lib/std/os/windows/bits.zig | 42 ++++++++++++++++++-------------------
 2 files changed, 36 insertions(+), 28 deletions(-)

diff --git a/lib/std/os.zig b/lib/std/os.zig
index 75254b52c8..24de1d83f2 100644
--- a/lib/std/os.zig
+++ b/lib/std/os.zig
@@ -2394,11 +2394,10 @@ pub const readlinkC = @compileError("deprecated: renamed to readlinkZ");
 /// See also `readlinkZ`.
 pub fn readlinkW(file_path: [*:0]const u16, out_buffer: []u8) ReadLinkError![]u8 {
     const w = windows;
-    const access_mode: w.DWORD = 0;
     const sharing = w.FILE_SHARE_DELETE | w.FILE_SHARE_READ | w.FILE_SHARE_WRITE;
     const disposition = w.OPEN_EXISTING;
     const flags = w.FILE_FLAG_BACKUP_SEMANTICS | w.FILE_FLAG_OPEN_REPARSE_POINT;
-    const handle = w.CreateFileW(file_path, access_mode, sharing, null, disposition, flags, null) catch |err| {
+    const handle = w.CreateFileW(file_path, 0, sharing, null, disposition, flags, null) catch |err| {
         switch (err) {
             error.SharingViolation => return error.AccessDenied,
             error.PathAlreadyExists => unreachable,
@@ -2406,22 +2405,31 @@ pub fn readlinkW(file_path: [*:0]const u16, out_buffer: []u8) ReadLinkError![]u8
             else => |e| return e,
         }
     };
-    var reparse_buf: [w.MAXIMUM_REPARSE_DATA_BUFFER_SIZE]u8 = undefined;
+    var reparse_buf align(@alignOf(w.REPARSE_DATA_BUFFER)) = [_]u8{0} ** (w.MAXIMUM_REPARSE_DATA_BUFFER_SIZE);
     _ = try w.DeviceIoControl(handle, w.FSCTL_GET_REPARSE_POINT, null, reparse_buf[0..], null);
-    const reparse_struct = mem.bytesAsValue(w.REPARSE_DATA_BUFFER, reparse_buf[0..@sizeOf(w.REPARSE_DATA_BUFFER)]);
+    const reparse_struct = @ptrCast(*const w.REPARSE_DATA_BUFFER, &reparse_buf[0]);
     switch (reparse_struct.ReparseTag) {
         w.IO_REPARSE_TAG_SYMLINK => {
-            std.debug.warn("got symlink!", .{});
+            const alignment = @alignOf(w.SymbolicLinkReparseBuffer);
+            const buf = @ptrCast(*const w.SymbolicLinkReparseBuffer, @alignCast(alignment, &reparse_struct.DataBuffer[0]));
+            const offset = buf.SubstituteNameOffset / 2;
+            const len = buf.SubstituteNameLength / 2;
+            const f = buf.Flags;
+            const path_buf = @as([*]const u16, &buf.PathBuffer);
+            std.debug.warn("got symlink => offset={}, len={}, flags = {}, {}\n", .{ offset, len, f, w.SYMLINK_FLAG_RELATIVE });
+            // TODO handle absolute paths and namespace prefix
+            const out_len = std.unicode.utf16leToUtf8(out_buffer, path_buf[offset .. offset + len]) catch unreachable;
+            std.debug.warn("got symlink => utf8={}\n", .{out_buffer[0..out_len]});
+            return out_buffer[0..out_len];
         },
         w.IO_REPARSE_TAG_MOUNT_POINT => {
-            std.debug.warn("got mount point!", .{});
+            @panic("TODO parse mount point");
         },
         else => |value| {
             std.debug.warn("unsupported symlink type: {}", .{value});
             return error.UnsupportedSymlinkType;
         },
     }
-    @panic("Oh no!");
 }
 
 /// Same as `readlink` except `file_path` is null-terminated.
diff --git a/lib/std/os/windows/bits.zig b/lib/std/os/windows/bits.zig
index fef9af9bda..66ea5bb512 100644
--- a/lib/std/os/windows/bits.zig
+++ b/lib/std/os/windows/bits.zig
@@ -1544,31 +1544,31 @@ pub const RTL_OSVERSIONINFOW = OSVERSIONINFOW;
 pub const PRTL_OSVERSIONINFOW = *RTL_OSVERSIONINFOW;
 
 pub const REPARSE_DATA_BUFFER = extern struct {
-    ReparseTag: ULONG, ReparseDataLength: USHORT, Reserved: USHORT, u: extern union {
-        SymbolicLinkReparseBuffer: extern struct {
-            SubstituteNameOffset: USHORT,
-            SubstituteNameLength: USHORT,
-            PrintNameOffset: USHORT,
-            PrintNameLength: USHORT,
-            Flags: ULONG,
-            PathBuffer: [1]WCHAR,
-        },
-        MountPointReparseBuffer: extern struct {
-            SubstituteNameOffset: USHORT,
-            SubstituteNameLength: USHORT,
-            PrintNameOffset: USHORT,
-            PrintNameLength: USHORT,
-            PathBuffer: [1]WCHAR,
-        },
-        GenericReparseBuffer: extern struct {
-            DataBuffer: [1]UCHAR,
-        },
-    }
+    ReparseTag: ULONG,
+    ReparseDataLength: USHORT,
+    Reserved: USHORT,
+    DataBuffer: [1]UCHAR,
 };
-pub const MAXIMUM_REPARSE_DATA_BUFFER_SIZE: usize = 16 * 1024;
+pub const SymbolicLinkReparseBuffer = extern struct {
+    SubstituteNameOffset: USHORT,
+    SubstituteNameLength: USHORT,
+    PrintNameOffset: USHORT,
+    PrintNameLength: USHORT,
+    Flags: ULONG,
+    PathBuffer: [1]WCHAR,
+};
+pub const MountPointReparseBuffer = extern struct {
+    SubstituteNameOffset: USHORT,
+    SubstituteNameLength: USHORT,
+    PrintNameOffset: USHORT,
+    PrintNameLength: USHORT,
+    PathBuffer: [1]WCHAR,
+};
+pub const MAXIMUM_REPARSE_DATA_BUFFER_SIZE: ULONG = 16 * 1024;
 pub const FSCTL_GET_REPARSE_POINT: DWORD = 0x900a8;
 pub const IO_REPARSE_TAG_SYMLINK: ULONG = 0xa000000c;
 pub const IO_REPARSE_TAG_MOUNT_POINT: ULONG = 0xa0000003;
+pub const SYMLINK_FLAG_RELATIVE: ULONG = 0x1;
 
 pub const SYMBOLIC_LINK_FLAG_FILE: DWORD = 0x0;
 pub const SYMBOLIC_LINK_FLAG_DIRECTORY: DWORD = 0x1;