fileutils: add isPathRelative(), default root to loadFile()

Make it easier to use relative paths across the daemon.

Change-Id: I53fe0b384d48d0dde9ad11a9e0c03714c7ad3766
Reviewed-by: Guillaume Roguez <guillaume.roguez@savoirfairelinux.com>

src/fileutils.cpp

@@ -290,11 +290,21 @@ writeTime(const std::string& path)
 #endif
 }
 
+bool isPathRelative(const std::string& path)
+{
+#ifndef _WIN32
+    return not path.empty() and not (path[0] == '/');
+#else
+    return not path.empty() and path.find(":") == std::string::npos;
+#endif
+}
+
 std::vector<uint8_t>
-loadFile(const std::string& path)
+loadFile(const std::string& path, const std::string& default_dir)
 {
+    bool isRelative {not default_dir.empty() and isPathRelative(path)};
     std::vector<uint8_t> buffer;
-    std::ifstream file(path, std::ios::binary);
+    std::ifstream file(isRelative ? default_dir + DIR_SEPARATOR_STR + path : path, std::ios::binary);
     if (!file)
         throw std::runtime_error("Can't read file: "+path);
     file.seekg(0, std::ios::end);

src/fileutils.h

@@ -26,11 +26,11 @@
 #include <chrono>
 #include <cstdio>
 
-#ifndef RING_UWP
-#define PROTECTED_GETENV(str) ({char *envvar_ = getenv((str)); \
-                                                   envvar_ ? envvar_ : "";})
-#else
-#define PROTECTED_GETENV(str) ({char *envvar_ = "" })
+#ifndef RING_UWP
+#define PROTECTED_GETENV(str) ({char *envvar_ = getenv((str)); \
+                                                   envvar_ ? envvar_ : "";})
+#else
+#define PROTECTED_GETENV(str) ({char *envvar_ = "" })
 #endif
 
 #define XDG_DATA_HOME           (PROTECTED_GETENV("XDG_DATA_HOME"))
@@ -70,6 +70,8 @@ namespace ring { namespace fileutils {
 
     bool recursive_mkdir(const std::string& path, mode_t mode=0755);
 
+    bool isPathRelative(const std::string& path);
+
     bool isFile(const std::string& path);
     bool isDirectory(const std::string& path);
 
@@ -84,7 +86,11 @@ namespace ring { namespace fileutils {
      */
     std::vector<std::string> readDirectory(const std::string &dir);
 
-    std::vector<uint8_t> loadFile(const std::string& path);
+    /**
+     * Read the full content of a file at path.
+     * If path is relative, it is appended to default_dir.
+     */
+    std::vector<uint8_t> loadFile(const std::string& path, const std::string& default_dir = {});
     void saveFile(const std::string& path, const std::vector<uint8_t>& data, mode_t mode=0644);
 
     struct FileHandle {