mex: create_symlink()

Author: scivision

private/get_mex_sources.m

@@ -12,6 +12,7 @@
 
 srcs = {fullfile(top, "src/is_char_device.cpp"), ...
   fullfile(top, "src/set_permissions.cpp"), ...
+  fullfile(top, "src/create_symlink.cpp"), ...
   [fullfile(top, "src/is_rosetta.cpp"), mac], ...
   [fullfile(top, "src/windows_shortname.cpp"), win]
 };

src/create_symlink.cpp

@@ -0,0 +1,115 @@
+#include "mex.hpp"
+#include "mexAdapter.hpp"
+
+#include <string>
+// note: <string_view> causes compile failures with MSVC at least
+
+#include <vector>
+#include <memory>
+
+#if defined(_WIN32)
+# define WIN32_LEAN_AND_MEAN
+# include <windows.h>
+#else
+# include <unistd.h> // for symlink()
+#endif
+
+#if __has_include(<filesystem>)
+# include <filesystem>
+# include <system_error>
+#endif
+
+
+bool fs_create_symlink(std::string target, std::string link)
+{
+  // confusing program errors if target is "" -- we'd never make such a symlink in real use.
+  if(target.empty())
+    return false;
+
+  // macOS needs empty check to avoid SIGABRT
+  if(link.empty())
+    return false;
+
+#if defined(__MINGW32__) || (defined(_WIN32) && !defined(__cpp_lib_filesystem))
+
+  const DWORD attr = GetFileAttributesA(target.data());
+// https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-getfileattributesa
+// https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants
+
+  if (attr == INVALID_FILE_ATTRIBUTES)
+    return false;
+
+  DWORD p = SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE;
+  if(attr & FILE_ATTRIBUTE_DIRECTORY)
+    p |= SYMBOLIC_LINK_FLAG_DIRECTORY;
+
+  return CreateSymbolicLinkA(link.data(), target.data(), p);
+#elif defined(__cpp_lib_filesystem)
+  std::error_code ec;
+  std::filesystem::path t(target);
+
+  bool isdir = std::filesystem::is_directory(t, ec);
+  if (ec)
+    return false;
+
+  isdir
+    ? std::filesystem::create_directory_symlink(t, link, ec)
+    : std::filesystem::create_symlink(t, link, ec);
+
+  return !ec;
+#else
+  // https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man2/symlink.2.html
+  // https://linux.die.net/man/3/symlink
+  return symlink(target.data(), link.data()) == 0;
+#endif
+
+}
+
+
+class MexFunction : public matlab::mex::Function {
+public:
+  void operator()(matlab::mex::ArgumentList outputs, matlab::mex::ArgumentList inputs) {
+// boilerplate engine & ArrayFactory setup
+    std::shared_ptr<matlab::engine::MATLABEngine> matlabEng = getEngine();
+
+    matlab::data::ArrayFactory factory;
+// wrangle inputs
+    std::string target, link;
+
+    if (inputs.size() != 2) {
+      matlabEng->feval(u"error", 0,
+        std::vector<matlab::data::Array>({ factory.createScalar("Two inputs required") }));
+    }
+
+    if ((inputs[0].getType() == matlab::data::ArrayType::MATLAB_STRING && inputs[0].getNumberOfElements() == 1)){
+        matlab::data::TypedArray<matlab::data::MATLABString> stringArr = inputs[0];
+        target = stringArr[0];
+    } else if (inputs[0].getType() == matlab::data::ArrayType::CHAR){
+        matlab::data::CharArray charArr = inputs[0];
+        target.assign(charArr.begin(), charArr.end());
+    } else {
+        matlabEng->feval(u"error", 0,
+        std::vector<matlab::data::Array>({ factory.createScalar("Mex: First input must be a scalar string or char vector") }));
+    }
+
+     if ((inputs[1].getType() == matlab::data::ArrayType::MATLAB_STRING && inputs[1].getNumberOfElements() == 1)){
+        matlab::data::TypedArray<matlab::data::MATLABString> stringArr = inputs[1];
+        link = stringArr[0];
+    } else if (inputs[1].getType() == matlab::data::ArrayType::CHAR){
+        matlab::data::CharArray charArr = inputs[1];
+        link.assign(charArr.begin(), charArr.end());
+    } else {
+        matlabEng->feval(u"error", 0,
+        std::vector<matlab::data::Array>({ factory.createScalar("Mex: Second input must be a scalar string or char vector") }));
+    }
+
+// actual function algorithm / computation
+    bool y = fs_create_symlink(target, link);
+
+// convert to Matlab output
+// https://www.mathworks.com/help/matlab/matlab_external/create-matlab-array-with-matlab-data-cpp-api.html
+// https://www.mathworks.com/help/matlab/apiref/matlab.data.arrayfactory.html
+
+    outputs[0] = factory.createScalar<bool>(y);
+  }
+};