Reimplement canonical in terms of GetFinalPathNameByHandleW on Windows.

This moves the common part of v3 and v4 canonical() to a separate
function and changes the Windows implementation to use
GetFinalPathNameByHandleW system call. As a side effect, this converts
drive names to upper case, which makes paths more interoperable.

Additionally, on POSIX systems, avoid adding a trailing directory
separator if the input path has one (which may be the case in v4). This
is consistent with libstdc++ and MSVC implementations of std::filesystem.

Fixes https://github.com/boostorg/filesystem/issues/325.

doc/release_history.html

@@ -40,6 +40,13 @@
   </tr>
 </table>
 
+<h2>1.87.0</h2>
+<ul>
+  <li>As was announced in 1.84.0, Windows versions prior to 10 are no longer supported.</li>
+  <li>On Windows, <code>canonical</code> is now based on the <code>GetFinalPathNameByHandleW</code> WinAPI function. As a side effect, drive letters are converted to upper case, which makes the resulting paths more interoperable. (<a href="https://github.com/boostorg/filesystem/issues/325">#325</a>)</li>
+  <li><b>v4:</b> <code>canonical</code> no longer produces a trailing directory separator in the resulting path, if the input path has one.</li>
+</ul>
+
 <h2>1.86.0</h2>
 <ul>
   <li><code>is_empty</code> operation is now better protected against concurrent filesystem modifications.</li>

src/operations.cpp

@@ -263,11 +263,11 @@ namespace {
 // The number of retries remove_all should make if it detects that the directory it is about to enter has been replaced with a symlink or a regular file
 BOOST_CONSTEXPR_OR_CONST unsigned int remove_all_directory_replaced_retry_count = 5u;
 
-#if defined(BOOST_POSIX_API)
-
 // Size of a small buffer for a path that can be placed on stack, in character code units
 BOOST_CONSTEXPR_OR_CONST std::size_t small_path_size = 1024u;
 
+#if defined(BOOST_POSIX_API)
+
 // Absolute maximum path length, in character code units, that we're willing to accept from various system calls.
 // This value is arbitrary, it is supposed to be a hard limit to avoid memory exhaustion
 // in some of the algorithms below in case of some corrupted or maliciously broken filesystem.
@@ -2383,7 +2383,7 @@ inline path convert_nt_path_to_win32_path(const wchar_t* nt_path, std::size_t si
         (
             // Check if the following is a drive letter
             (
-                detail::is_letter(nt_path[pos]) && nt_path[pos + 1u] == colon &&
+                nt_path[pos + 1u] == colon && detail::is_letter(nt_path[pos]) &&
                 ((size - pos) == 2u || detail::is_directory_separator(nt_path[pos + 2u]))
             ) ||
             // Check for an "incorrect" syntax for UNC path junction points
@@ -2565,15 +2565,11 @@ path absolute_v4(path const& p, path const& base, system::error_code* ec)
     return res;
 }
 
-BOOST_FILESYSTEM_DECL
-path canonical_v3(path const& p, path const& base, system::error_code* ec)
+namespace {
+
+inline path canonical_common(path& source, system::error_code* ec)
 {
-    path source(detail::absolute_v3(p, base, ec));
-    if (ec && *ec)
-    {
-    return_empty_path:
-        return path();
-    }
+#if defined(BOOST_POSIX_API)
 
     system::error_code local_ec;
     file_status st(detail::status_impl(source, &local_ec));
@@ -2590,7 +2586,9 @@ path canonical_v3(path const& p, path const& base, system::error_code* ec)
             BOOST_FILESYSTEM_THROW(filesystem_error("boost::filesystem::canonical", source, local_ec));
 
         *ec = local_ec;
-        goto return_empty_path;
+
+    return_empty_path:
+        return path();
     }
 
     path root(source.root_path());
@@ -2602,6 +2600,8 @@ path canonical_v3(path const& p, path const& base, system::error_code* ec)
     {
         for (path::iterator itr(source.begin()), end(source.end()); itr != end; path_algorithms::increment_v4(itr))
         {
+            if (itr->empty())
+                continue;
             if (path_algorithms::compare_v4(*itr, dot_p) == 0)
                 continue;
             if (path_algorithms::compare_v4(*itr, dot_dot_p) == 0)
@@ -2624,12 +2624,6 @@ path canonical_v3(path const& p, path const& base, system::error_code* ec)
 
             path_algorithms::append_v4(result, *itr);
 
-            // If we don't have an absolute path yet then don't check symlink status.
-            // This avoids checking "C:" which is "the current directory on drive C"
-            // and hence not what we want to check/resolve here.
-            if (!result.is_absolute())
-                continue;
-
             st = detail::symlink_status_impl(result, ec);
             if (ec && *ec)
                 goto return_empty_path;
@@ -2656,7 +2650,7 @@ path canonical_v3(path const& p, path const& base, system::error_code* ec)
                         if (path_algorithms::compare_v4(*itr, dot_p) != 0)
                             path_algorithms::append_v4(link, *itr);
                     }
-                    source = link;
+                    source = std::move(link);
                     root = source.root_path();
                 }
                 else // link is relative
@@ -2672,7 +2666,7 @@ path canonical_v3(path const& p, path const& base, system::error_code* ec)
                         if (path_algorithms::compare_v4(*itr, dot_p) != 0)
                             path_algorithms::append_v4(new_source, *itr);
                     }
-                    source = new_source;
+                    source = std::move(new_source);
                 }
 
                 // symlink causes scan to be restarted
@@ -2688,6 +2682,122 @@ path canonical_v3(path const& p, path const& base, system::error_code* ec)
 
     BOOST_ASSERT_MSG(result.is_absolute(), "canonical() implementation error; please report");
     return result;
+
+#else // defined(BOOST_POSIX_API)
+
+    unique_handle h(create_file_handle(
+        source.c_str(),
+        FILE_READ_ATTRIBUTES | FILE_READ_EA,
+        FILE_SHARE_DELETE | FILE_SHARE_READ | FILE_SHARE_WRITE,
+        nullptr, // lpSecurityAttributes
+        OPEN_EXISTING,
+        FILE_FLAG_BACKUP_SEMANTICS));
+
+    DWORD err;
+    if (!h)
+    {
+        err = ::GetLastError();
+
+    fail_err:
+        emit_error(err, source, ec, "boost::filesystem::canonical");
+        return path();
+    }
+
+    WCHAR path_small_buf[small_path_size];
+    std::unique_ptr< WCHAR[] > path_large_buf;
+    WCHAR* path_buf = path_small_buf;
+    DWORD path_buf_size = sizeof(path_small_buf) / sizeof(*path_small_buf);
+    DWORD flags = FILE_NAME_NORMALIZED;
+    DWORD path_len;
+
+    while (true)
+    {
+        path_len = ::GetFinalPathNameByHandleW(h.get(), path_buf, path_buf_size, flags);
+        if (path_len > 0)
+        {
+            if (path_len < path_buf_size)
+                break;
+
+            // The buffer is not large enough, path_len is the required buffer size, including the terminating zero
+            path_large_buf.reset(new WCHAR[path_len]);
+            path_buf = path_large_buf.get();
+            path_buf_size = path_len;
+        }
+        else
+        {
+            err = ::GetLastError();
+            if (BOOST_UNLIKELY(err == ERROR_PATH_NOT_FOUND && (flags & VOLUME_NAME_NT) == 0u))
+            {
+                // Drive letter does not exist for the file, obtain an NT path for it
+                flags |= VOLUME_NAME_NT;
+                continue;
+            }
+
+            goto fail_err;
+        }
+    }
+
+    path result;
+    if ((flags & VOLUME_NAME_NT) == 0u)
+    {
+        // If the input path did not contain a long path prefix, convert
+        // "\\?\X:" to "X:" and "\\?\UNC\" to "\\". Otherwise, preserve the prefix.
+        const path::value_type* source_str = source.c_str();
+        if (source.size() < 4u ||
+            source_str[0] != path::preferred_separator ||
+            source_str[1] != path::preferred_separator ||
+            source_str[2] != questionmark ||
+            source_str[3] != path::preferred_separator)
+        {
+            if (path_len >= 6u &&
+                path_buf[0] == path::preferred_separator &&
+                path_buf[1] == path::preferred_separator &&
+                path_buf[2] == questionmark &&
+                path_buf[3] == path::preferred_separator)
+            {
+                if (path_buf[5] == colon && detail::is_letter(path_buf[4]))
+                {
+                    path_buf += 4;
+                    path_len -= 4u;
+                }
+                else if (path_len >= 8u &&
+                    (path_buf[4] == L'U' || path_buf[4] == L'u') &&
+                    (path_buf[5] == L'N' || path_buf[5] == L'n') &&
+                    (path_buf[6] == L'C' || path_buf[6] == L'c') &&
+                    path_buf[7] == path::preferred_separator)
+                {
+                    path_buf += 6;
+                    path_len -= 6u;
+                    path_buf[0] = path::preferred_separator;
+                }
+            }
+        }
+
+        result.assign(path_buf, path_buf + path_len);
+    }
+    else
+    {
+        // Convert NT path to a Win32 path
+        result.assign(L"\\\\?\\GLOBALROOT");
+        result.concat(path_buf, path_buf + path_len);
+    }
+
+    BOOST_ASSERT_MSG(result.is_absolute(), "canonical() implementation error; please report");
+    return result;
+
+#endif // defined(BOOST_POSIX_API)
+}
+
+} // unnamed namespace
+
+BOOST_FILESYSTEM_DECL
+path canonical_v3(path const& p, path const& base, system::error_code* ec)
+{
+    path source(detail::absolute_v3(p, base, ec));
+    if (ec && *ec)
+        return path();
+
+    return detail::canonical_common(source, ec);
 }
 
 BOOST_FILESYSTEM_DECL
@@ -2695,124 +2805,9 @@ path canonical_v4(path const& p, path const& base, system::error_code* ec)
 {
     path source(detail::absolute_v4(p, base, ec));
     if (ec && *ec)
-    {
-    return_empty_path:
         return path();
-    }
 
-    system::error_code local_ec;
-    file_status st(detail::status_impl(source, &local_ec));
-
-    if (st.type() == fs::file_not_found)
-    {
-        local_ec = system::errc::make_error_code(system::errc::no_such_file_or_directory);
-        goto fail_local_ec;
-    }
-    else if (local_ec)
-    {
-    fail_local_ec:
-        if (!ec)
-            BOOST_FILESYSTEM_THROW(filesystem_error("boost::filesystem::canonical", source, local_ec));
-
-        *ec = local_ec;
-        goto return_empty_path;
-    }
-
-    path root(source.root_path());
-    path const& dot_p = dot_path();
-    path const& dot_dot_p = dot_dot_path();
-    unsigned int symlinks_allowed = symloop_max;
-    path result;
-    while (true)
-    {
-        for (path::iterator itr(source.begin()), end(source.end()); itr != end; path_algorithms::increment_v4(itr))
-        {
-            if (path_algorithms::compare_v4(*itr, dot_p) == 0)
-                continue;
-            if (path_algorithms::compare_v4(*itr, dot_dot_p) == 0)
-            {
-                if (path_algorithms::compare_v4(result, root) != 0)
-                    result.remove_filename_and_trailing_separators();
-                continue;
-            }
-
-            if (itr->size() == 1u && detail::is_directory_separator(itr->native()[0]))
-            {
-                // Convert generic separator returned by the iterator for the root directory to
-                // the preferred separator. This is important on Windows, as in some cases,
-                // like paths for network shares and cloud storage mount points GetFileAttributesW
-                // will return "file not found" if the path contains forward slashes.
-                result += path::preferred_separator;
-                // We don't need to check for a symlink after adding a separator.
-                continue;
-            }
-
-            path_algorithms::append_v4(result, *itr);
-
-            // If we don't have an absolute path yet then don't check symlink status.
-            // This avoids checking "C:" which is "the current directory on drive C"
-            // and hence not what we want to check/resolve here.
-            if (!result.is_absolute())
-                continue;
-
-            st = detail::symlink_status_impl(result, ec);
-            if (ec && *ec)
-                goto return_empty_path;
-
-            if (is_symlink(st))
-            {
-                if (symlinks_allowed == 0)
-                {
-                    local_ec = system::errc::make_error_code(system::errc::too_many_symbolic_link_levels);
-                    goto fail_local_ec;
-                }
-
-                --symlinks_allowed;
-
-                path link(detail::read_symlink(result, ec));
-                if (ec && *ec)
-                    goto return_empty_path;
-                result.remove_filename_and_trailing_separators();
-
-                if (link.is_absolute())
-                {
-                    for (path_algorithms::increment_v4(itr); itr != end; path_algorithms::increment_v4(itr))
-                    {
-                        if (path_algorithms::compare_v4(*itr, dot_p) != 0)
-                            path_algorithms::append_v4(link, *itr);
-                    }
-                    source = link;
-                    root = source.root_path();
-                }
-                else // link is relative
-                {
-                    link.remove_trailing_separator();
-                    if (path_algorithms::compare_v4(link, dot_p) == 0)
-                        continue;
-
-                    path new_source(result);
-                    path_algorithms::append_v4(new_source, link);
-                    for (path_algorithms::increment_v4(itr); itr != end; path_algorithms::increment_v4(itr))
-                    {
-                        if (path_algorithms::compare_v4(*itr, dot_p) != 0)
-                            path_algorithms::append_v4(new_source, *itr);
-                    }
-                    source = new_source;
-                }
-
-                // symlink causes scan to be restarted
-                goto restart_scan;
-            }
-        }
-
-        break;
-
-    restart_scan:
-        result.clear();
-    }
-
-    BOOST_ASSERT_MSG(result.is_absolute(), "canonical() implementation error; please report");
-    return result;
+    return detail::canonical_common(source, ec);
 }
 
 BOOST_FILESYSTEM_DECL

test/operations_test.cpp

@@ -1781,15 +1781,9 @@ void canonical_basic_tests()
     BOOST_TEST(ok);
 
     // non-symlink tests; also see canonical_symlink_tests()
-#if BOOST_FILESYSTEM_VERSION == 3
     BOOST_TEST_EQ(fs::canonical(""), fs::current_path());
     BOOST_TEST_EQ(fs::canonical("", fs::current_path()), fs::current_path());
     BOOST_TEST_EQ(fs::canonical("", ""), fs::current_path());
-#else
-    BOOST_TEST_EQ(fs::canonical(""), fs::current_path() / fs::path());
-    BOOST_TEST_EQ(fs::canonical("", fs::current_path()), fs::current_path() / fs::path());
-    BOOST_TEST_EQ(fs::canonical("", ""), fs::current_path() / fs::path());
-#endif
     BOOST_TEST_EQ(fs::canonical(fs::current_path()), fs::current_path());
     BOOST_TEST_EQ(fs::canonical(fs::current_path(), ""), fs::current_path());
     BOOST_TEST_EQ(fs::canonical(fs::current_path(), "no-such-file"), fs::current_path());
@@ -1836,6 +1830,23 @@ void canonical_basic_tests()
     // Test Windows long paths
     fs::path long_path = make_long_path(dir / L"f0");
     BOOST_TEST_EQ(fs::canonical(long_path), long_path);
+
+    // Test that canonical() consistently converts drive letters to upper case.
+    // https://github.com/boostorg/filesystem/issues/325
+    {
+        fs::path::string_type root_path = dir.root_path().native(), lc_root_path, uc_root_path;
+        for (fs::path::string_type::value_type c : root_path)
+        {
+            fs::path::string_type::value_type lc = c, uc = c;
+            if (lc >= L'A' && lc <= L'Z')
+                lc += L'a' - L'A';
+            if (uc >= L'a' && uc <= L'z')
+                uc -= L'a' - L'A';
+            lc_root_path.push_back(lc);
+            uc_root_path.push_back(uc);
+        }
+        BOOST_TEST_EQ(fs::canonical(fs::path(lc_root_path) / dir.relative_path()), fs::canonical(fs::path(uc_root_path) / dir.relative_path()));
+    }
 #endif
 }
 
@@ -2829,7 +2840,7 @@ void weakly_canonical_basic_tests()
     BOOST_TEST_EQ(fs::weakly_canonical("..//foo", d1), dir / "foo");
 
 #ifdef BOOST_WINDOWS_API
-    BOOST_TEST_EQ(fs::weakly_canonical("c:/no-such/foo/bar"), fs::path("c:/no-such/foo/bar"));
+    BOOST_TEST_EQ(fs::weakly_canonical("c:/no-such/foo/bar"), fs::path("C:/no-such/foo/bar"));
 
     // Test Windows long paths
     fs::path long_path = make_long_path(dir / L"f0");