Add base64 decoding function

.gitmodules

@@ -7,3 +7,6 @@
 [submodule "subprojects/SQLiteCpp/SQLiteCpp"]
 	path = subprojects/SQLiteCpp/SQLiteCpp
 	url = https://github.com/SRombauts/SQLiteCpp.git
+[submodule "src/gnulib"]
+	path = src/gnulib
+	url = git://git.savannah.gnu.org/gnulib.git

meson.build

@@ -1,4 +1,4 @@
-project('orotool', 'cpp',
+project('orotool', 'cpp', 'c',
   version: '0.1.0',
   meson_version: '>=0.49.2',
   default_options: ['buildtype=debug', 'cpp_std=gnu++17'],

src/gnulib

@@ -0,0 +1 @@
+Subproject commit 444acd314f6c4a1fb7ea7412a54b8ea5fc0ad7c2

src/meson.build

@@ -27,6 +27,10 @@ project_config_file = configure_file(
 	configuration: conf,
 )
 
+gnulib_conf = configuration_data()
+gnulib_conf.set('_GL_ATTRIBUTE_CONST', '__attribute__ ((__const__))')
+configure_file(output : 'config.h', configuration : gnulib_conf)
+
 lib_deps = [
   restc_cpp_dep,
   sqlitecpp_dep,
@@ -47,6 +51,8 @@ executable(meson.project_name(),
   'timer_items.cpp',
   'timer_icons.cpp',
   'oro/originsdb.cpp',
+  'gnulib/lib/base64.c',
+  'oro/base64.cpp',
   project_config_file,
   install: true,
   dependencies: lib_deps,

src/oro/base64.cpp

@@ -0,0 +1,31 @@
+#include "base64.hpp"
+#include <config.h>
+#define restrict __restrict__
+#include "gnulib/lib/base64.h"
+#include <cassert>
+#include <stdexcept>
+
+#if defined(base64_decode)
+#	undef base64_decode
+#endif
+
+namespace oro {
+
+std::vector<char> base64_decode (std::string_view text) {
+	base64_decode_context ctx;
+	base64_decode_ctx_init(&ctx);
+	std::vector<char> retval(3 * (text.size() / 4) + 3);
+
+	size_t out_size = retval.size();
+	const bool success = base64_decode_ctx(&ctx, text.data(), text.size(), retval.data(), &out_size);
+	if (not success)
+		throw std::runtime_error("Base64 decode failed");
+
+	assert(out_size <= retval.size());
+	retval.resize(out_size);
+	return retval;
+}
+
+} //namespace oro
+
+#undef restrict

src/oro/base64.hpp

@@ -0,0 +1,10 @@
+#pragma once
+
+#include <string_view>
+#include <vector>
+
+namespace oro {
+
+std::vector<char> base64_decode (std::string_view text);
+
+} //namespace oro