Implemented config and crypto infrastructure (#2)

Added config file read/write infrastructure with RapidJSON.
Added key pair generation and sign/verify helper with libsodium.

src/conf.cpp

@@ -0,0 +1,61 @@
+#include <cstdio>
+#include <iostream>
+#include <fstream>
+#include <unistd.h>
+#include "lib/rapidjson/document.h"
+#include "lib/rapidjson/istreamwrapper.h"
+#include "lib/rapidjson/ostreamwrapper.h"
+#include "lib/rapidjson/writer.h"
+#include "conf.h"
+
+using namespace std;
+using namespace rapidjson;
+
+namespace conf
+{
+
+static const char * configPath;
+
+string get_full_path(const char *filename)
+{
+    string fullpath = configPath;
+    fullpath += filename;
+    return fullpath;
+}
+
+void load(const char *filename, Document &d)
+{
+    ifstream ifs(get_full_path(filename));
+    IStreamWrapper isw(ifs);
+
+    d.ParseStream(isw);
+}
+
+void save(const char *filename, Document &d)
+{
+    ofstream ofs(get_full_path(filename));
+    OStreamWrapper osw(ofs);
+
+    Writer<OStreamWrapper> writer(osw);
+    d.Accept(writer);
+}
+
+string get_exec_path()
+{
+    char buf[PATH_MAX + 1];
+    if (readlink("/proc/self/exe", buf, sizeof(buf) - 1) == -1)
+        throw string("readlink() failed");
+    string str(buf);
+    return str.substr(0, str.rfind('/') + 1);
+}
+
+int init()
+{
+    string execPath = get_exec_path();
+    char * confPathChar = (char *)malloc(execPath.size() + 1);
+    strcpy(confPathChar, &execPath[0]);
+    configPath = confPathChar;
+    return 1;
+}
+
+} // namespace conf