add read and write file validators CLIUtils#249

Signed-off-by: Rafi Wiener <[email protected]>

README.md

@@ -337,6 +337,8 @@ CLI11 has several Validators built in that perform some common checks
 -   `CLI::Transformer(...)`: 🚧 Modify the input using a map.  See [Transforming Validators](#transforming-validators) for more details.
 -   `CLI::CheckedTransformer(...)`: 🚧 Modify the input using a map, and Require that the input is either in the set or already one of the outputs of the set. See [Transforming Validators](#transforming-validators) for more details.
 -   `CLI::ExistingFile`: Requires that the file exists if given.
+-   `CLI::ExistingReadFile`: Requires that the file given exists and have permission to read it.
+-   `CLI::ExistingWriteFile`: Requires that the file given exists and have permission to write to it.
 -   `CLI::ExistingDirectory`: Requires that the directory exists.
 -   `CLI::ExistingPath`: Requires that the path (file or directory) exists.
 -   `CLI::NonexistentPath`: Requires that the path does not exist.

include/CLI/Validators.hpp

@@ -216,8 +216,8 @@ namespace detail {
 /// Check for an existing file (returns error message if check fails)
 class ExistingFileValidator : public Validator {
   public:
-    ExistingFileValidator() : Validator("FILE") {
-        func_ = [](std::string &filename) {
+    ExistingFileValidator(unsigned short mode = 0) : Validator("FILE") {
+        func_ = [mode](std::string &filename) {
             struct stat buffer;
             bool exist = stat(filename.c_str(), &buffer) == 0;
             bool is_dir = (buffer.st_mode & S_IFDIR) != 0;
@@ -226,6 +226,9 @@ class ExistingFileValidator : public Validator {
             } else if(is_dir) {
                 return "File is actually a directory: " + filename;
             }
+            if (mode && !(buffer.st_mode & mode)) {
+                return "File doesn't have the wanted permission: " + filename;
+            }
             return std::string();
         };
     }
@@ -328,6 +331,12 @@ class PositiveNumber : public Validator {
 /// Check for existing file (returns error message if check fails)
 const detail::ExistingFileValidator ExistingFile;
 
+/// Check that the file exist and available for read
+const detail::ExistingFileValidator ExistingReadFile(S_IREAD);
+
+/// Check that the file exist and available for write
+const detail::ExistingFileValidator ExistingWriteFile(S_IWRITE);
+
 /// Check for an existing directory (returns error message if check fails)
 const detail::ExistingDirectoryValidator ExistingDirectory;