Create a symlink instead of copying the file when deployFile is requested with source and target paths inside the AppDir

include/linuxdeploy/util/misc.h

@@ -6,10 +6,33 @@
 #include <sstream>
 #include <string>
 #include <vector>
+#include <boost/filesystem.hpp>
 
 namespace linuxdeploy {
     namespace util {
         namespace misc {
+            static bool path_contains_file(boost::filesystem::path dir, boost::filesystem::path file) {
+                // If dir ends with "/" and isn't the root directory, then the final
+                // component returned by iterators will include "." and will interfere
+                // with the std::equal check below, so we strip it before proceeding.
+                if (dir.filename() == ".")
+                    dir.remove_filename();
+                // We're also not interested in the file's name.
+                assert(file.has_filename());
+                file.remove_filename();
+
+                // If dir has more components than file, then file can't possibly
+                // reside in dir.
+                auto dir_len = std::distance(dir.begin(), dir.end());
+                auto file_len = std::distance(file.begin(), file.end());
+                if (dir_len > file_len)
+                    return false;
+
+                // This stops checking when it reaches dir.end(), so it's OK if file
+                // has more directory components afterward. They won't be checked.
+                return std::equal(dir.begin(), dir.end(), file.begin());
+            };
+
             static inline bool ltrim(std::string& s, char to_trim = ' ') {
                 // TODO: find more efficient way to check whether elements have been removed
                 size_t initialLength = s.length();

src/core/appdir.cpp

@@ -20,6 +20,7 @@
 #include "excludelist.h"
 
 using namespace linuxdeploy::core;
+using namespace linuxdeploy::util::misc;
 using namespace linuxdeploy::core::log;
 
 using namespace cimg_library;
@@ -159,8 +160,10 @@ namespace linuxdeploy {
                             const auto& from = pair.first;
                             const auto& to = pair.second;
 
-                            if (!copyFile(from, to))
-                                success = false;
+                            if (path_contains_file(appDirPath, from)) {
+                                success = bf::exists(to) || symlinkFile(from, to, true); // create a symbolic link
+                            } else
+                                success = copyFile(from, to); // copy the file
 
                             copyOperations.erase(copyOperations.begin());
                         }