libcamera: utils: Add a C++ dirname implementation

Provide a std::string based implementation which conforms to the
behaviour of the dirname() fucntion defined by POSIX.

Tests are added to cover expected corner cases of the implementation.

Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

2 files changed, 49 insertions, 0 deletions

diff --git a/src/libcamera/include/utils.h b/src/libcamera/include/utils.h
index 080ea661..94059776 100644
--- a/src/libcamera/include/utils.h
+++ b/src/libcamera/include/utils.h
@@ -33,6 +33,7 @@ namespace utils {
 const char *basename(const char *path);
 
 char *secure_getenv(const char *name);
+std::string dirname(const std::string &path);
 
 template<class InputIt1, class InputIt2>
 unsigned int set_overlap(InputIt1 first1, InputIt1 last1,
diff --git a/src/libcamera/utils.cpp b/src/libcamera/utils.cpp
index 453e3b3b..f566e88c 100644
--- a/src/libcamera/utils.cpp
+++ b/src/libcamera/utils.cpp
@@ -71,6 +71,54 @@ char *secure_getenv(const char *name)
 }
 
 /**
+ * \brief Identify the dirname portion of a path
+ * \param[in] path The full path to parse
+ *
+ * This function conforms with the behaviour of the %dirname() function as
+ * defined by POSIX.
+ *
+ * \return A string of the directory component of the path
+ */
+std::string dirname(const std::string &path)
+{
+	if (path.empty())
+		return ".";
+
+	/*
+	 * Skip all trailing slashes. If the path is only made of slashes,
+	 * return "/".
+	 */
+	size_t pos = path.size() - 1;
+	while (path[pos] == '/') {
+		if (!pos)
+			return "/";
+		pos--;
+	}
+
+	/*
+	 * Find the previous slash. If the path contains no non-trailing slash,
+	 * return ".".
+	 */
+	while (path[pos] != '/') {
+		if (!pos)
+			return ".";
+		pos--;
+	}
+
+	/*
+	 * Return the directory name up to (but not including) any trailing
+	 * slash. If this would result in an empty string, return "/".
+	 */
+	while (path[pos] == '/') {
+		if (!pos)
+			return "/";
+		pos--;
+	}
+
+	return path.substr(0, pos + 1);
+}
+
+/**
  * \fn libcamera::utils::set_overlap(InputIt1 first1, InputIt1 last1,
  *				     InputIt2 first2, InputIt2 last2)
  * \brief Count the number of elements in the intersection of two ranges