fix: max filepath length on windows (#16552)

# Description

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Windows traditionally limits many file operations to `MAX_PATH` (260
characters). Deeply nested plugin packages can exceed this limit during
`.whl` extraction, leaving files missing and causing the plugin to fail
to load.

This change adds a shared extended_path helper that prepares paths for
Windows file operations using the extended-length prefixes `\\?\` or
`\\?\UNC\`. The helper is used for ZIP archive I/O and extraction
destinations, including plugin wheel extraction. This avoids relying on
the Windows long-path setting, which changes machine-wide settings.

Paths remain unprefixed outside file operations. Code that bypasses the
shared ZIP helpers may still require separate long-path handling.

See [Microsoft's documentation on path length
limitation](https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation?tabs=registry)

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## Tests

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changes made in this PR.
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Tested on Windows 11 by using a portable installation of OrcaSlicer and
placing it in some really long filepath length e.g.
`C:/somename/<240 characters long folder path>/OrcaSlicer` and then
running and trying to install any plugin locally or on OrcaCloud.

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src/libslic3r/Utils.hpp

@@ -842,6 +842,13 @@ void load_string_file(const boost::filesystem::path& p, std::string& str);
 
 bool check_layer_id_pattern(const std::string& pattern, int layer_id);
 
+// On Windows, return an equivalent path carrying the extended-length ("\\?\" / "\\?\UNC\")
+// prefix so the Win32 APIs accept it past MAX_PATH even when LongPathsEnabled is off. The path
+// is made absolute and lexically normalized first, because the prefix disables normalisation.
+// A path that is already extended (or a device path) is returned unchanged; on other platforms,
+// or when an absolute path cannot be formed, the input is returned unchanged.
+boost::filesystem::path extended_path(const boost::filesystem::path& path);
+
 } // namespace Slic3r
 
 #if WIN32

src/libslic3r/miniz_extension.cpp

@@ -17,6 +17,7 @@
 
 #if defined(_MSC_VER) || defined(__MINGW64__)
 #include "boost/nowide/cstdio.hpp"
+#include "boost/nowide/convert.hpp"
 #endif
 
 #include "I18N.hpp"
@@ -62,7 +63,11 @@ bool open_zip(mz_zip_archive *zip, const char *fname, bool isread)
 
     FILE *f = nullptr;
 #if defined(_MSC_VER) || defined(__MINGW64__)
-    f = boost::nowide::fopen(fname, mode);
+    // fname is UTF-8 (the nowide contract). Route it through the shared extended-path helper so an
+    // archive stored past MAX_PATH opens even with LongPathsEnabled off.
+    const std::wstring wide_path = boost::nowide::widen(fname);
+    const std::string  extended  = boost::nowide::narrow(Slic3r::extended_path(boost::filesystem::path(wide_path)).wstring());
+    f = boost::nowide::fopen(extended.c_str(), mode);
 #elif defined(__GNUC__) && defined(_LARGEFILE64_SOURCE)
     f = fopen64(fname, mode);
 #else
@@ -101,6 +106,14 @@ bool close_zip(mz_zip_archive *zip, bool isread)
     }
     return ret;
 }
+
+#ifdef WIN32
+// mz_file_write_func writing an extracted entry into an already-open FILE*.
+size_t mz_write_to_cfile(void *opaque, mz_uint64 /*file_ofs*/, const void *buffer, size_t size)
+{
+    return std::fwrite(buffer, 1, size, static_cast<FILE *>(opaque));
+}
+#endif
 }
 
 bool open_zip_reader(mz_zip_archive *zip, const std::string &fname)
@@ -116,6 +129,36 @@ bool open_zip_writer(mz_zip_archive *zip, const std::string &fname)
 bool close_zip_reader(mz_zip_archive *zip) { return close_zip(zip, true); }
 bool close_zip_writer(mz_zip_archive *zip) { return close_zip(zip, false); }
 
+bool extract_zip_entry_to_file(mz_zip_archive *zip, mz_uint file_index, const boost::filesystem::path &dest_path)
+{
+    if (!zip)
+        return false;
+#ifdef WIN32
+    // Open the destination ourselves with a Windows extended-length path: miniz's narrow
+    // extract_to_file cannot be relied on past MAX_PATH with LongPathsEnabled off, and its wide
+    // variant takes a plain (unprefixed) path and a text-mode stream. This keeps the write binary.
+    FILE *file = ::_wfopen(Slic3r::extended_path(dest_path).wstring().c_str(), L"wb");
+    if (!file) {
+        zip->m_last_error = MZ_ZIP_FILE_OPEN_FAILED;
+        return false;
+    }
+
+    const bool written = mz_zip_reader_extract_to_callback(zip, file_index, mz_write_to_cfile, file, 0) != 0;
+    const bool closed  = std::fclose(file) == 0;
+    if (!written || !closed) {
+        if (written && !closed)
+            zip->m_last_error = MZ_ZIP_FILE_CLOSE_FAILED;
+        // Drop the partial entry rather than leave a truncated file behind.
+        boost::system::error_code ec;
+        boost::filesystem::remove(Slic3r::extended_path(dest_path), ec);
+        return false;
+    }
+    return true;
+#else
+    return mz_zip_reader_extract_to_file(zip, file_index, dest_path.string().c_str(), 0) != 0;
+#endif
+}
+
 std::string decode_archive_entry_path(mz_zip_archive *zip, const mz_zip_archive_file_stat &stat)
 {
     if (stat.m_is_utf8)
@@ -156,10 +199,13 @@ bool extract_archive_confined(const std::string &zip_path_utf8, const std::strin
         }
         const std::string dest_file = dest_dir + "/" + stat.m_filename;
         try {
+            // Use the extended-length form for every filesystem call so entries under a destination
+            // past MAX_PATH are created even with LongPathsEnabled off.
+            const boost::filesystem::path dest_path(dest_file);
+            const boost::filesystem::path io_dest = extended_path(dest_path);
             if (stat.m_is_directory) {
-                const boost::filesystem::path dest_path(dest_file);
-                if (!boost::filesystem::exists(dest_path))
-                    boost::filesystem::create_directories(dest_path);
+                if (!boost::filesystem::exists(io_dest))
+                    boost::filesystem::create_directories(io_dest);
                 continue;
             }
             if (stat.m_uncomp_size == 0) {
@@ -167,10 +213,9 @@ bool extract_archive_confined(const std::string &zip_path_utf8, const std::strin
                 continue;
             }
             // Replace a symlink at the destination rather than writing through it.
-            const boost::filesystem::path dest_path(dest_file);
-            if (boost::filesystem::is_symlink(boost::filesystem::symlink_status(dest_path)))
-                boost::filesystem::remove(dest_path);
-            if (!mz_zip_reader_extract_to_file(&archive, stat.m_file_index, dest_file.c_str(), 0)) {
+            if (boost::filesystem::is_symlink(boost::filesystem::symlink_status(io_dest)))
+                boost::filesystem::remove(io_dest);
+            if (!extract_zip_entry_to_file(&archive, stat.m_file_index, dest_path)) {
                 BOOST_LOG_TRIVIAL(error) << "Unzip: extract file " << stat.m_filename << " to dest " << dest_file << " failed";
                 close_zip_reader(&archive);
                 return false;

src/libslic3r/miniz_extension.hpp

@@ -1,6 +1,7 @@
 #ifndef MINIZ_EXTENSION_HPP
 #define MINIZ_EXTENSION_HPP
 
+#include <boost/filesystem/path.hpp>
 #include <string>
 #include <miniz.h>
 
@@ -13,6 +14,10 @@ bool close_zip_writer(mz_zip_archive *zip);
 std::string decode_archive_entry_path(mz_zip_archive *zip, const mz_zip_archive_file_stat &stat);
 // Extracts every entry of the archive under dest_dir. Nothing is written if any entry would resolve outside dest_dir.
 bool extract_archive_confined(const std::string &zip_path_utf8, const std::string &dest_dir);
+// Extracts one entry into dest_path, binary-safe and overwriting. On Windows the destination is
+// opened through an extended-length path so it works past MAX_PATH even with LongPathsEnabled off;
+// a partial file is removed if the write fails. False for a directory/unsupported entry or on error.
+bool extract_zip_entry_to_file(mz_zip_archive *zip, mz_uint file_index, const boost::filesystem::path &dest_path);
 
 class MZ_Archive {
 public:

src/libslic3r/utils.cpp

@@ -2254,5 +2254,45 @@ bool check_layer_id_pattern(const std::string& pattern, int layer_id){
     return mod >= 0 && mod < count;
 }
 
+boost::filesystem::path extended_path(const boost::filesystem::path& path) {
+#ifdef WIN32
+    namespace fs = boost::filesystem;
+
+    // Already extended, or an explicit device path (which is not subject to MAX_PATH and must not
+    // be absolutized or normalized): leave it alone.
+    {
+        fs::path prefix_candidate = path;
+        const std::wstring native = prefix_candidate.make_preferred().wstring();
+        if (native.rfind(L"\\\\?\\", 0) == 0 || native.rfind(L"\\\\.\\", 0) == 0)
+            return fs::path(native);
+    }
+
+    fs::path absolute = path;
+    if (!absolute.is_absolute()) {
+        boost::system::error_code ec;
+        absolute = fs::absolute(absolute, ec);
+        if (ec)
+            return path; // can't form a valid prefixed path from a relative one
+    }
+
+    // A trailing separator is redundant to the Win32 APIs, but lexically_normal() would rewrite it
+    // as a "." element, which the "\\?\" prefix (normalisation off) takes literally. Drop it first.
+    while (absolute.has_relative_path() && absolute.filename() == ".")
+        absolute = absolute.parent_path();
+
+    // The "\\?\" prefix turns off Win32 normalisation, so do it here first.
+    absolute = absolute.lexically_normal();
+
+    // Extended paths only recognize backslash separators.
+    const std::wstring native = absolute.make_preferred().wstring();
+    if (native.empty())
+        return path;
+    if (native.rfind(L"\\\\", 0) == 0)
+        return fs::path(L"\\\\?\\UNC\\" + native.substr(2)); // \\server\share\... -> \\?\UNC\server\share\...
+    return fs::path(L"\\\\?\\" + native);                    // C:\dir\... -> \\?\C:\dir\...
+#else
+    return path;
+#endif
+}
 
 }; // namespace Slic3r

src/slic3r/plugin/PluginFsUtils.cpp

@@ -34,10 +34,6 @@
 #include <unordered_set>
 #include <vector>
 
-#ifdef WIN32
-#include <boost/locale/encoding_utf.hpp>
-#endif
-
 namespace Slic3r {
 
 const char* const INSTALL_STATE_FILE = ".install_state.json";
@@ -665,7 +661,7 @@ bool extract_zip_to_directory(const boost::filesystem::path& zip_path, const boo
     namespace fs = boost::filesystem;
 
     boost::system::error_code ec;
-    fs::create_directories(destination, ec);
+    fs::create_directories(extended_path(destination), ec);
     if (ec) {
         error = "Failed to create plugin staging directory: " + ec.message();
         return false;
@@ -709,7 +705,7 @@ bool extract_zip_to_directory(const boost::filesystem::path& zip_path, const boo
 
         const fs::path output_path = destination / relative_path;
         if (stat.m_is_directory || mz_zip_reader_is_file_a_directory(&reader.archive, stat.m_file_index)) {
-            fs::create_directories(output_path, ec);
+            fs::create_directories(extended_path(output_path), ec);
             if (ec) {
                 error = "Failed to create plugin zip directory " + output_path.string() + ": " + ec.message();
                 return false;
@@ -717,26 +713,19 @@ bool extract_zip_to_directory(const boost::filesystem::path& zip_path, const boo
             continue;
         }
 
-        fs::create_directories(output_path.parent_path(), ec);
+        fs::create_directories(extended_path(output_path.parent_path()), ec);
         if (ec) {
             error = "Failed to create plugin zip parent directory " + output_path.parent_path().string() + ": " + ec.message();
             return false;
         }
 
-        if (fs::exists(output_path, ec) && fs::is_directory(output_path, ec)) {
+        if (fs::exists(extended_path(output_path), ec) && fs::is_directory(extended_path(output_path), ec)) {
             error = "Plugin zip file conflicts with an existing directory: " + output_path.string();
             return false;
         }
 
-        const std::string encoded_output_path = encode_path(output_path.string().c_str());
-        mz_bool extracted = mz_zip_reader_extract_to_file(&reader.archive, stat.m_file_index, encoded_output_path.c_str(), 0);
-#ifdef WIN32
-        if (!extracted) {
-            const std::wstring wide_output_path = boost::locale::conv::utf_to_utf<wchar_t>(output_path.generic_string());
-            extracted = mz_zip_reader_extract_to_file_w(&reader.archive, stat.m_file_index, wide_output_path.c_str(), 0);
-        }
-#endif
-        if (!extracted) {
+        // Shared with the rest of the archive code: long-path capable and binary-safe.
+        if (!extract_zip_entry_to_file(&reader.archive, stat.m_file_index, output_path)) {
             error = "Failed to extract plugin zip entry " + relative_key + ": " +
                     MZ_Archive::get_errorstr(mz_zip_get_last_error(&reader.archive));
             return false;