Avoid copying in ZipReader::readFileToString()

Resolves: #290

Author: adazem009

src/internal/scratch3reader.cpp

@@ -558,7 +558,9 @@ void Scratch3Reader::read()
     if (m_zipReader->open()) {
         // Parse the JSON
         try {
-            m_json = json::parse(m_zipReader->readFileToString("project.json"));
+            std::string jsonStr;
+            m_zipReader->readFileToString("project.json", jsonStr);
+            m_json = json::parse(jsonStr);
         } catch (std::exception &e) {
             printErr("invalid JSON file", e.what());
         }

src/internal/zipreader.cpp

@@ -48,17 +48,14 @@ size_t ZipReader::readFile(const std::string &fileName, void **buf)
     return bufsize;
 }
 
-std::string ZipReader::readFileToString(const std::string &fileName)
+void ZipReader::readFileToString(const std::string &fileName, std::string &dst)
 {
     void *buf = nullptr;
     size_t bufsize = readFile(fileName, &buf);
 
     if (buf) {
-        std::string ret(reinterpret_cast<char *>(buf), bufsize);
+        dst.assign(reinterpret_cast<char *>(buf), bufsize);
         free(buf);
-
-        return ret;
-    }
-
-    return "";
+    } else
+        dst = "";
 }

src/internal/zipreader.h

@@ -20,7 +20,7 @@ class ZipReader
         void close();
 
         size_t readFile(const std::string &fileName, void **buf);
-        std::string readFileToString(const std::string &fileName);
+        void readFileToString(const std::string &fileName, std::string &dst);
 
     private:
         std::string m_fileName;

test/zip/zip_test.cpp

@@ -8,7 +8,9 @@ inline std::string readSb3Json(const std::string &fileName)
     ZipReader reader(fileName);
     reader.open();
 
-    return reader.readFileToString("project.json");
+    std::string ret;
+    reader.readFileToString("project.json", ret);
+    return ret;
 }
 
 TEST(ZipTest, NonexistentProject)