refactor(main): move file operation functions to new source (#2124)

src/file_handler.cpp

@@ -0,0 +1,69 @@
+/**
+ * @file file_handler.cpp
+ * @brief File handling functions.
+ */
+
+// standard includes
+#include <filesystem>
+#include <fstream>
+
+// local includes
+#include "file_handler.h"
+#include "logging.h"
+
+namespace file_handler {
+
+  /**
+   * @brief Read a file to string.
+   * @param path The path of the file.
+   * @return `std::string` : The contents of the file.
+   *
+   * EXAMPLES:
+   * ```cpp
+   * std::string contents = read_file("path/to/file");
+   * ```
+   */
+  std::string
+  read_file(const char *path) {
+    if (!std::filesystem::exists(path)) {
+      BOOST_LOG(debug) << "Missing file: " << path;
+      return {};
+    }
+
+    std::ifstream in(path);
+
+    std::string input;
+    std::string base64_cert;
+
+    while (!in.eof()) {
+      std::getline(in, input);
+      base64_cert += input + '\n';
+    }
+
+    return base64_cert;
+  }
+
+  /**
+   * @brief Writes a file.
+   * @param path The path of the file.
+   * @param contents The contents to write.
+   * @return `int` : `0` on success, `-1` on failure.
+   *
+   * EXAMPLES:
+   * ```cpp
+   * int write_status = write_file("path/to/file", "file contents");
+   * ```
+   */
+  int
+  write_file(const char *path, const std::string_view &contents) {
+    std::ofstream out(path);
+
+    if (!out.is_open()) {
+      return -1;
+    }
+
+    out << contents;
+
+    return 0;
+  }
+}  // namespace file_handler