diff --git a/src/Checksum.cc b/src/Checksum.cc
index 66c2f0f9..2d4862e1 100644
--- a/src/Checksum.cc
+++ b/src/Checksum.cc
@@ -37,15 +37,13 @@
 
 namespace aria2 {
 
-Checksum::Checksum
-(const std::string& hashType,
- const std::string& digest)
-    : hashType_(hashType),
-      digest_(digest)
+Checksum::Checksum(std::string hashType, std::string digest)
+  : hashType_(std::move(hashType)),
+    digest_(std::move(digest))
 {}
 
 Checksum::Checksum()
-    : hashType_("sha-1")
+  : hashType_("sha-1")
 {}
 
 Checksum::~Checksum() {}
@@ -55,14 +53,14 @@ bool Checksum::isEmpty() const
   return digest_.empty();
 }
 
-void Checksum::setDigest(const std::string& digest)
+void Checksum::setDigest(std::string digest)
 {
-  digest_ = digest;
+  digest_ = std::move(digest);
 }
 
-void Checksum::setHashType(const std::string& hashType)
+void Checksum::setHashType(std::string hashType)
 {
-  hashType_ = hashType;
+  hashType_ = std::move(hashType);
 }
 
 void Checksum::swap(Checksum& other)
diff --git a/src/Checksum.h b/src/Checksum.h
index 147a3c09..686f44a9 100644
--- a/src/Checksum.h
+++ b/src/Checksum.h
@@ -47,19 +47,19 @@ private:
   std::string digest_;
 public:
   // digest_ is raw byte array of hash value, not ascii hexadecimal notation.
-  Checksum(const std::string& hashType, const std::string& digest);
+  Checksum(std::string hashType, std::string digest);
   Checksum();
   ~Checksum();
 
   bool isEmpty() const;
 
-  void setDigest(const std::string& md);
+  void setDigest(std::string md);
   const std::string& getDigest() const
   {
     return digest_;
   }
 
-  void setHashType(const std::string& type);
+  void setHashType(std::string type);
   const std::string& getHashType() const
   {
     return hashType_;
diff --git a/src/ChunkChecksum.cc b/src/ChunkChecksum.cc
index 68e76b1e..3a081778 100644
--- a/src/ChunkChecksum.cc
+++ b/src/ChunkChecksum.cc
@@ -40,12 +40,12 @@ namespace aria2 {
 ChunkChecksum::ChunkChecksum():pieceLength_(0) {}
 
 ChunkChecksum::ChunkChecksum
-(const std::string& hashType,
- const std::vector<std::string>& pieceHashes,
+(std::string hashType,
+ std::vector<std::string> pieceHashes,
  int32_t pieceLength)
-    : hashType_(hashType),
-      pieceHashes_(pieceHashes),
-      pieceLength_(pieceLength)
+  : hashType_(std::move(hashType)),
+    pieceHashes_(std::move(pieceHashes)),
+    pieceLength_(pieceLength)
 {}
 
 bool ChunkChecksum::validateChunk
@@ -75,9 +75,9 @@ const std::string& ChunkChecksum::getPieceHash(size_t index) const
   }
 }
 
-void ChunkChecksum::setHashType(const std::string& hashType)
+void ChunkChecksum::setHashType(std::string hashType)
 {
-  hashType_ = hashType;
+  hashType_ = std::move(hashType);
 }
 
 void ChunkChecksum::setPieceHashes(std::vector<std::string> pieceHashes)
diff --git a/src/ChunkChecksum.h b/src/ChunkChecksum.h
index 4d82528a..14acac85 100644
--- a/src/ChunkChecksum.h
+++ b/src/ChunkChecksum.h
@@ -51,8 +51,8 @@ public:
   ChunkChecksum();
 
   ChunkChecksum
-  (const std::string& hashType,
-   const std::vector<std::string>& pieceHashes,
+  (std::string hashType,
+   std::vector<std::string> pieceHashes,
    int32_t pieceLength);
 
   bool validateChunk(const std::string& actualDigest,
@@ -70,7 +70,7 @@ public:
     return pieceHashes_;
   }
 
-  void setHashType(const std::string& hashType);
+  void setHashType(std::string hashType);
   const std::string& getHashType() const
   {
     return hashType_;
diff --git a/src/ExpatXmlParser.cc b/src/ExpatXmlParser.cc
index 36ccec53..70e8691f 100644
--- a/src/ExpatXmlParser.cc
+++ b/src/ExpatXmlParser.cc
@@ -109,10 +109,10 @@ void mlEndElement(void* userData, const char* nsName)
   SessionData* sd = reinterpret_cast<SessionData*>(userData);
   std::string characters;
   if(sd->psm->needsCharactersBuffering()) {
-    characters = sd->charactersStack.front();
+    characters = std::move(sd->charactersStack.front());
     sd->charactersStack.pop_front();
   }
-  sd->psm->endElement(localname, prefix, nsUri, characters);
+  sd->psm->endElement(localname, prefix, nsUri, std::move(characters));
   delete [] nsUri;
 }
 } // namespace
diff --git a/src/MetalinkParserController.cc b/src/MetalinkParserController.cc
index edf7fe09..e3fbd598 100644
--- a/src/MetalinkParserController.cc
+++ b/src/MetalinkParserController.cc
@@ -85,7 +85,7 @@ void MetalinkParserController::newEntryTransaction()
 #endif // ENABLE_MESSAGE_DIGEST
 }
 
-void MetalinkParserController::setFileNameOfEntry(const std::string& filename)
+void MetalinkParserController::setFileNameOfEntry(std::string filename)
 {
   if(!tEntry_) {
     return;
@@ -109,28 +109,28 @@ void MetalinkParserController::setFileLengthOfEntry(int64_t length)
   tEntry_->sizeKnown = true;
 }
 
-void MetalinkParserController::setVersionOfEntry(const std::string& version)
+void MetalinkParserController::setVersionOfEntry(std::string version)
 {
   if(!tEntry_) {
     return;
   }
-  tEntry_->version = version;
+  tEntry_->version = std::move(version);
 }
 
-void MetalinkParserController::setLanguageOfEntry(const std::string& language)
+void MetalinkParserController::setLanguageOfEntry(std::string language)
 {
   if(!tEntry_) {
     return;
   }
-  tEntry_->languages.push_back(language);
+  tEntry_->languages.push_back(std::move(language));
 }
 
-void MetalinkParserController::setOSOfEntry(const std::string& os)
+void MetalinkParserController::setOSOfEntry(std::string os)
 {
   if(!tEntry_) {
     return;
   }
-  tEntry_->oses.push_back(os);
+  tEntry_->oses.push_back(std::move(os));
 }
 
 void MetalinkParserController::setMaxConnectionsOfEntry(int maxConnections)
@@ -174,7 +174,7 @@ void MetalinkParserController::newResourceTransaction()
   tResource_ = make_unique<MetalinkResource>();
 }
 
-void MetalinkParserController::setURLOfResource(const std::string& url)
+void MetalinkParserController::setURLOfResource(std::string url)
 {
   if(!tResource_) {
     return;
@@ -182,16 +182,17 @@ void MetalinkParserController::setURLOfResource(const std::string& url)
   std::string u = uri::joinUri(baseUri_, url);
   uri_split_result us;
   if(uri_split(&us, u.c_str()) == 0) {
-    tResource_->url = u;
+    tResource_->url = std::move(u);
     if(tResource_->type == MetalinkResource::TYPE_UNKNOWN) {
-      setTypeOfResource(uri::getFieldString(us, USR_SCHEME, u.c_str()));
+      setTypeOfResource(uri::getFieldString(us, USR_SCHEME,
+                                            tResource_->url.c_str()));
     }
   } else {
-    tResource_->url = url;
+    tResource_->url = std::move(url);
   }
 }
 
-void MetalinkParserController::setTypeOfResource(const std::string& type)
+void MetalinkParserController::setTypeOfResource(std::string type)
 {
   if(!tResource_) {
     return;
@@ -210,12 +211,12 @@ void MetalinkParserController::setTypeOfResource(const std::string& type)
   }
 }
 
-void MetalinkParserController::setLocationOfResource(const std::string& location)
+void MetalinkParserController::setLocationOfResource(std::string location)
 {
   if(!tResource_) {
     return;
   }
-  tResource_->location = location;
+  tResource_->location = std::move(location);
 }
 
 void MetalinkParserController::setPriorityOfResource(int priority)
@@ -270,7 +271,7 @@ void MetalinkParserController::newChecksumTransaction()
 #endif // ENABLE_MESSAGE_DIGEST
 }
 
-void MetalinkParserController::setTypeOfChecksum(const std::string& type)
+void MetalinkParserController::setTypeOfChecksum(std::string type)
 {
 #ifdef ENABLE_MESSAGE_DIGEST
   if(!tChecksum_) {
@@ -278,14 +279,14 @@ void MetalinkParserController::setTypeOfChecksum(const std::string& type)
   }
   std::string calgo = MessageDigest::getCanonicalHashType(type);
   if(MessageDigest::supports(calgo)) {
-    tChecksum_->setHashType(calgo);
+    tChecksum_->setHashType(std::move(calgo));
   } else {
     cancelChecksumTransaction();
   }
 #endif // ENABLE_MESSAGE_DIGEST
 }
 
-void MetalinkParserController::setHashOfChecksum(const std::string& md)
+void MetalinkParserController::setHashOfChecksum(std::string md)
 {
 #ifdef ENABLE_MESSAGE_DIGEST
   if(!tChecksum_) {
@@ -332,7 +333,7 @@ void MetalinkParserController::newChunkChecksumTransactionV4()
 #endif // ENABLE_MESSAGE_DIGEST
 }
 
-void MetalinkParserController::setTypeOfChunkChecksumV4(const std::string& type)
+void MetalinkParserController::setTypeOfChunkChecksumV4(std::string type)
 {
 #ifdef ENABLE_MESSAGE_DIGEST
   if(!tChunkChecksumV4_) {
@@ -340,7 +341,7 @@ void MetalinkParserController::setTypeOfChunkChecksumV4(const std::string& type)
   }
   std::string calgo = MessageDigest::getCanonicalHashType(type);
   if(MessageDigest::supports(calgo)) {
-    tChunkChecksumV4_->setHashType(calgo);
+    tChunkChecksumV4_->setHashType(std::move(calgo));
   } else {
     cancelChunkChecksumTransactionV4();
   }
@@ -361,7 +362,7 @@ void MetalinkParserController::setLengthOfChunkChecksumV4(size_t length)
 #endif // ENABLE_MESSAGE_DIGEST
 }
 
-void MetalinkParserController::addHashOfChunkChecksumV4(const std::string& md)
+void MetalinkParserController::addHashOfChunkChecksumV4(std::string md)
 {
 #ifdef ENABLE_MESSAGE_DIGEST
   if(!tChunkChecksumV4_) {
@@ -409,7 +410,7 @@ void MetalinkParserController::newChunkChecksumTransaction()
 #endif // ENABLE_MESSAGE_DIGEST
 }
 
-void MetalinkParserController::setTypeOfChunkChecksum(const std::string& type)
+void MetalinkParserController::setTypeOfChunkChecksum(std::string type)
 {
 #ifdef ENABLE_MESSAGE_DIGEST
   if(!tChunkChecksum_) {
@@ -417,7 +418,7 @@ void MetalinkParserController::setTypeOfChunkChecksum(const std::string& type)
   }
   std::string calgo = MessageDigest::getCanonicalHashType(type);
   if(MessageDigest::supports(calgo)) {
-    tChunkChecksum_->setHashType(calgo);
+    tChunkChecksum_->setHashType(std::move(calgo));
   } else {
     cancelChunkChecksumTransaction();
   }
@@ -438,14 +439,15 @@ void MetalinkParserController::setLengthOfChunkChecksum(size_t length)
 #endif // ENABLE_MESSAGE_DIGEST
 }
 
-void MetalinkParserController::addHashOfChunkChecksum(size_t order, const std::string& md)
+void MetalinkParserController::addHashOfChunkChecksum(size_t order,
+                                                      std::string md)
 {
 #ifdef ENABLE_MESSAGE_DIGEST
   if(!tChunkChecksum_) {
     return;
   }
   if(MessageDigest::isValidHash(tChunkChecksum_->getHashType(), md)) {
-    tempChunkChecksums_.push_back(std::make_pair(order, md));
+    tempChunkChecksums_.push_back(std::make_pair(order, std::move(md)));
   } else {
     cancelChunkChecksumTransaction();
   }
@@ -462,7 +464,7 @@ void MetalinkParserController::createNewHashOfChunkChecksum(size_t order)
 #endif // ENABLE_MESSAGE_DIGEST
 }
 
-void MetalinkParserController::setMessageDigestOfChunkChecksum(const std::string& md)
+void MetalinkParserController::setMessageDigestOfChunkChecksum(std::string md)
 {
 #ifdef ENABLE_MESSAGE_DIGEST
   if(!tChunkChecksum_) {
@@ -524,28 +526,28 @@ void MetalinkParserController::newSignatureTransaction()
   tSignature_ = make_unique<Signature>();
 }
 
-void MetalinkParserController::setTypeOfSignature(const std::string& type)
+void MetalinkParserController::setTypeOfSignature(std::string type)
 {
   if(!tSignature_) {
     return;
   }
-  tSignature_->setType(type);
+  tSignature_->setType(std::move(type));
 }
 
-void MetalinkParserController::setFileOfSignature(const std::string& file)
+void MetalinkParserController::setFileOfSignature(std::string file)
 {
   if(!tSignature_) {
     return;
   }
-  tSignature_->setFile(file);
+  tSignature_->setFile(std::move(file));
 }
 
-void MetalinkParserController::setBodyOfSignature(const std::string& body)
+void MetalinkParserController::setBodyOfSignature(std::string body)
 {
   if(!tSignature_) {
     return;
   }
-  tSignature_->setBody(body);
+  tSignature_->setBody(std::move(body));
 }
 
 void MetalinkParserController::commitSignatureTransaction()
@@ -569,33 +571,32 @@ void MetalinkParserController::newMetaurlTransaction()
   tMetaurl_ = make_unique<MetalinkMetaurl>();
 }
 
-void MetalinkParserController::setURLOfMetaurl(const std::string& url)
+void MetalinkParserController::setURLOfMetaurl(std::string url)
 {
   if(!tMetaurl_) {
     return;
   }
 #ifdef ENABLE_BITTORRENT
   if(magnet::parse(url)) {
-    tMetaurl_->url = url;
+    tMetaurl_->url = std::move(url);
   } else
 #endif // ENABLE_BITTORRENT
     {
       std::string u = uri::joinUri(baseUri_, url);
       if(uri_split(nullptr, u.c_str()) == 0) {
-        tMetaurl_->url = u;
+        tMetaurl_->url = std::move(u);
       } else {
-        tMetaurl_->url = url;
+        tMetaurl_->url = std::move(url);
       }
     }
 }
 
-void MetalinkParserController::setMediatypeOfMetaurl
-(const std::string& mediatype)
+void MetalinkParserController::setMediatypeOfMetaurl(std::string mediatype)
 {
   if(!tMetaurl_) {
     return;
   }
-  tMetaurl_->mediatype = mediatype;
+  tMetaurl_->mediatype = std::move(mediatype);
 }
 
 void MetalinkParserController::setPriorityOfMetaurl(int priority)
@@ -606,12 +607,12 @@ void MetalinkParserController::setPriorityOfMetaurl(int priority)
   tMetaurl_->priority = priority;
 }
 
-void MetalinkParserController::setNameOfMetaurl(const std::string& name)
+void MetalinkParserController::setNameOfMetaurl(std::string name)
 {
   if(!tMetaurl_) {
     return;
   }
-  tMetaurl_->name = name;
+  tMetaurl_->name = std::move(name);
 }
 
 void MetalinkParserController::commitMetaurlTransaction()
diff --git a/src/MetalinkParserController.h b/src/MetalinkParserController.h
index 12fd6f4f..4ff11fff 100644
--- a/src/MetalinkParserController.h
+++ b/src/MetalinkParserController.h
@@ -92,15 +92,15 @@ public:
 
   void newEntryTransaction();
 
-  void setFileNameOfEntry(const std::string& filename);
+  void setFileNameOfEntry(std::string filename);
 
   void setFileLengthOfEntry(int64_t length);
 
-  void setVersionOfEntry(const std::string& version);
+  void setVersionOfEntry(std::string version);
 
-  void setLanguageOfEntry(const std::string& language);
+  void setLanguageOfEntry(std::string language);
 
-  void setOSOfEntry(const std::string& os);
+  void setOSOfEntry(std::string os);
 
   void setMaxConnectionsOfEntry(int maxConnections);
 
@@ -110,11 +110,11 @@ public:
 
   void newResourceTransaction();
 
-  void setURLOfResource(const std::string& url);
+  void setURLOfResource(std::string url);
 
-  void setTypeOfResource(const std::string& type);
+  void setTypeOfResource(std::string type);
 
-  void setLocationOfResource(const std::string& location);
+  void setLocationOfResource(std::string location);
 
   void setPriorityOfResource(int priority);
 
@@ -126,9 +126,9 @@ public:
 
   void newChecksumTransaction();
 
-  void setTypeOfChecksum(const std::string& type);
+  void setTypeOfChecksum(std::string type);
 
-  void setHashOfChecksum(const std::string& md);
+  void setHashOfChecksum(std::string md);
 
   void commitChecksumTransaction();
 
@@ -136,11 +136,11 @@ public:
 
   void newChunkChecksumTransactionV4(); // Metalink4Spec
 
-  void setTypeOfChunkChecksumV4(const std::string& type); // Metalink4Spec
+  void setTypeOfChunkChecksumV4(std::string type); // Metalink4Spec
 
   void setLengthOfChunkChecksumV4(size_t length); // Metalink4Spec
 
-  void addHashOfChunkChecksumV4(const std::string& md); // Metalink4Spec
+  void addHashOfChunkChecksumV4(std::string md); // Metalink4Spec
 
   void commitChunkChecksumTransactionV4(); // Metalink4Spec
 
@@ -148,15 +148,15 @@ public:
 
   void newChunkChecksumTransaction(); // Metalink3Spec
 
-  void setTypeOfChunkChecksum(const std::string& type); // Metalink3Spec
+  void setTypeOfChunkChecksum(std::string type); // Metalink3Spec
 
   void setLengthOfChunkChecksum(size_t length); // Metalink3Spec
 
-  void addHashOfChunkChecksum(size_t order, const std::string& md);// Metalink3Spec
+  void addHashOfChunkChecksum(size_t order, std::string md);// Metalink3Spec
 
   void createNewHashOfChunkChecksum(size_t order); // Metalink3Spec
 
-  void setMessageDigestOfChunkChecksum(const std::string& md); // Metalink3Spec
+  void setMessageDigestOfChunkChecksum(std::string md); // Metalink3Spec
 
   void addHashOfChunkChecksum(); // Metalink3Spec
 
@@ -166,11 +166,11 @@ public:
 
   void newSignatureTransaction();
 
-  void setTypeOfSignature(const std::string& type);
+  void setTypeOfSignature(std::string type);
 
-  void setFileOfSignature(const std::string& file);
+  void setFileOfSignature(std::string file);
 
-  void setBodyOfSignature(const std::string& body);
+  void setBodyOfSignature(std::string body);
 
   void commitSignatureTransaction();
 
@@ -178,21 +178,21 @@ public:
 
   void newMetaurlTransaction();
 
-  void setURLOfMetaurl(const std::string& url);
+  void setURLOfMetaurl(std::string url);
 
-  void setMediatypeOfMetaurl(const std::string& mediatype);
+  void setMediatypeOfMetaurl(std::string mediatype);
 
   void setPriorityOfMetaurl(int priority);
 
-  void setNameOfMetaurl(const std::string& name);
+  void setNameOfMetaurl(std::string name);
 
   void commitMetaurlTransaction();
 
   void cancelMetaurlTransaction();
 
-  void setBaseUri(const std::string& baseUri)
+  void setBaseUri(std::string baseUri)
   {
-    baseUri_ = baseUri;
+    baseUri_ = std::move(baseUri);
   }
 };
 
diff --git a/src/MetalinkParserState.h b/src/MetalinkParserState.h
index 844597f4..5693adf2 100644
--- a/src/MetalinkParserState.h
+++ b/src/MetalinkParserState.h
@@ -62,7 +62,7 @@ public:
    const char* localname,
    const char* prefix,
    const char* nsUri,
-   const std::string& characters) {}
+   std::string characters) {}
 
   virtual bool needsCharactersBuffering() const
   {
diff --git a/src/MetalinkParserStateMachine.cc b/src/MetalinkParserStateMachine.cc
index 2f4fd242..4c637ebd 100644
--- a/src/MetalinkParserStateMachine.cc
+++ b/src/MetalinkParserStateMachine.cc
@@ -268,9 +268,9 @@ void MetalinkParserStateMachine::newEntryTransaction()
   ctrl_->newEntryTransaction();
 }
 
-void MetalinkParserStateMachine::setFileNameOfEntry(const std::string& filename)
+void MetalinkParserStateMachine::setFileNameOfEntry(std::string filename)
 {
-  ctrl_->setFileNameOfEntry(filename);
+  ctrl_->setFileNameOfEntry(std::move(filename));
 }
 
 void MetalinkParserStateMachine::setFileLengthOfEntry(int64_t length)
@@ -278,19 +278,19 @@ void MetalinkParserStateMachine::setFileLengthOfEntry(int64_t length)
   ctrl_->setFileLengthOfEntry(length);
 }
 
-void MetalinkParserStateMachine::setVersionOfEntry(const std::string& version)
+void MetalinkParserStateMachine::setVersionOfEntry(std::string version)
 {
-  ctrl_->setVersionOfEntry(version);
+  ctrl_->setVersionOfEntry(std::move(version));
 }
 
-void MetalinkParserStateMachine::setLanguageOfEntry(const std::string& language)
+void MetalinkParserStateMachine::setLanguageOfEntry(std::string language)
 {
-  ctrl_->setLanguageOfEntry(language);
+  ctrl_->setLanguageOfEntry(std::move(language));
 }
 
-void MetalinkParserStateMachine::setOSOfEntry(const std::string& os)
+void MetalinkParserStateMachine::setOSOfEntry(std::string os)
 {
-  ctrl_->setOSOfEntry(os);
+  ctrl_->setOSOfEntry(std::move(os));
 }
 
 void MetalinkParserStateMachine::setMaxConnectionsOfEntry(int maxConnections)
@@ -313,20 +313,19 @@ void MetalinkParserStateMachine::newResourceTransaction()
   ctrl_->newResourceTransaction();
 }
 
-void MetalinkParserStateMachine::setURLOfResource(const std::string& url)
+void MetalinkParserStateMachine::setURLOfResource(std::string url)
 {
-  ctrl_->setURLOfResource(url);
+  ctrl_->setURLOfResource(std::move(url));
 }
 
-void MetalinkParserStateMachine::setTypeOfResource(const std::string& type)
+void MetalinkParserStateMachine::setTypeOfResource(std::string type)
 {
-  ctrl_->setTypeOfResource(type);
+  ctrl_->setTypeOfResource(std::move(type));
 }
 
-void MetalinkParserStateMachine::setLocationOfResource
-(const std::string& location)
+void MetalinkParserStateMachine::setLocationOfResource(std::string location)
 {
-  ctrl_->setLocationOfResource(location);
+  ctrl_->setLocationOfResource(std::move(location));
 }
 
 void MetalinkParserStateMachine::setPriorityOfResource(int priority)
@@ -354,14 +353,14 @@ void MetalinkParserStateMachine::newChecksumTransaction()
   ctrl_->newChecksumTransaction();
 }
 
-void MetalinkParserStateMachine::setTypeOfChecksum(const std::string& type)
+void MetalinkParserStateMachine::setTypeOfChecksum(std::string type)
 {
-  ctrl_->setTypeOfChecksum(type);
+  ctrl_->setTypeOfChecksum(std::move(type));
 }
 
-void MetalinkParserStateMachine::setHashOfChecksum(const std::string& md)
+void MetalinkParserStateMachine::setHashOfChecksum(std::string md)
 {
-  ctrl_->setHashOfChecksum(md);
+  ctrl_->setHashOfChecksum(std::move(md));
 }
 
 void MetalinkParserStateMachine::commitChecksumTransaction()
@@ -384,15 +383,14 @@ void MetalinkParserStateMachine::setLengthOfChunkChecksumV4(size_t length)
   ctrl_->setLengthOfChunkChecksumV4(length);
 }
 
-void MetalinkParserStateMachine::setTypeOfChunkChecksumV4
-(const std::string& type)
+void MetalinkParserStateMachine::setTypeOfChunkChecksumV4(std::string type)
 {
-  ctrl_->setTypeOfChunkChecksumV4(type);
+  ctrl_->setTypeOfChunkChecksumV4(std::move(type));
 }
 
-void MetalinkParserStateMachine::addHashOfChunkChecksumV4(const std::string& md)
+void MetalinkParserStateMachine::addHashOfChunkChecksumV4(std::string md)
 {
-  ctrl_->addHashOfChunkChecksumV4(md);
+  ctrl_->addHashOfChunkChecksumV4(std::move(md));
 }
 
 void MetalinkParserStateMachine::commitChunkChecksumTransactionV4()
@@ -415,9 +413,9 @@ void MetalinkParserStateMachine::setLengthOfChunkChecksum(size_t length)
   ctrl_->setLengthOfChunkChecksum(length);
 }
 
-void MetalinkParserStateMachine::setTypeOfChunkChecksum(const std::string& type)
+void MetalinkParserStateMachine::setTypeOfChunkChecksum(std::string type)
 {
-  ctrl_->setTypeOfChunkChecksum(type);
+  ctrl_->setTypeOfChunkChecksum(std::move(type));
 }
 
 void MetalinkParserStateMachine::createNewHashOfChunkChecksum(size_t order)
@@ -425,10 +423,9 @@ void MetalinkParserStateMachine::createNewHashOfChunkChecksum(size_t order)
   ctrl_->createNewHashOfChunkChecksum(order);
 }
 
-void MetalinkParserStateMachine::setMessageDigestOfChunkChecksum
-(const std::string& md)
+void MetalinkParserStateMachine::setMessageDigestOfChunkChecksum(std::string md)
 {
-  ctrl_->setMessageDigestOfChunkChecksum(md);
+  ctrl_->setMessageDigestOfChunkChecksum(std::move(md));
 }
 
 void MetalinkParserStateMachine::addHashOfChunkChecksum()
@@ -451,19 +448,19 @@ void MetalinkParserStateMachine::newSignatureTransaction()
   ctrl_->newSignatureTransaction();
 }
 
-void MetalinkParserStateMachine::setTypeOfSignature(const std::string& type)
+void MetalinkParserStateMachine::setTypeOfSignature(std::string type)
 {
-  ctrl_->setTypeOfSignature(type);
+  ctrl_->setTypeOfSignature(std::move(type));
 }
 
-void MetalinkParserStateMachine::setFileOfSignature(const std::string& file)
+void MetalinkParserStateMachine::setFileOfSignature(std::string file)
 {
-  ctrl_->setFileOfSignature(file);
+  ctrl_->setFileOfSignature(std::move(file));
 }
 
-void MetalinkParserStateMachine::setBodyOfSignature(const std::string& body)
+void MetalinkParserStateMachine::setBodyOfSignature(std::string body)
 {
-  ctrl_->setBodyOfSignature(body);
+  ctrl_->setBodyOfSignature(std::move(body));
 }
 
 void MetalinkParserStateMachine::commitSignatureTransaction()
@@ -481,15 +478,14 @@ void MetalinkParserStateMachine::newMetaurlTransaction()
   ctrl_->newMetaurlTransaction();
 }
 
-void MetalinkParserStateMachine::setURLOfMetaurl(const std::string& url)
+void MetalinkParserStateMachine::setURLOfMetaurl(std::string url)
 {
-  ctrl_->setURLOfMetaurl(url);
+  ctrl_->setURLOfMetaurl(std::move(url));
 }
 
-void MetalinkParserStateMachine::setMediatypeOfMetaurl
-(const std::string& mediatype)
+void MetalinkParserStateMachine::setMediatypeOfMetaurl(std::string mediatype)
 {
-  ctrl_->setMediatypeOfMetaurl(mediatype);
+  ctrl_->setMediatypeOfMetaurl(std::move(mediatype));
 }
 
 void MetalinkParserStateMachine::setPriorityOfMetaurl(int priority)
@@ -497,9 +493,9 @@ void MetalinkParserStateMachine::setPriorityOfMetaurl(int priority)
   ctrl_->setPriorityOfMetaurl(priority);
 }
 
-void MetalinkParserStateMachine::setNameOfMetaurl(const std::string& name)
+void MetalinkParserStateMachine::setNameOfMetaurl(std::string name)
 {
-  ctrl_->setNameOfMetaurl(name);
+  ctrl_->setNameOfMetaurl(std::move(name));
 }
 
 void MetalinkParserStateMachine::commitMetaurlTransaction()
@@ -525,9 +521,10 @@ void MetalinkParserStateMachine::endElement
 (const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
-  stateStack_.top()->endElement(this, localname, prefix, nsUri, characters);
+  stateStack_.top()->endElement(this, localname, prefix, nsUri,
+                                std::move(characters));
   stateStack_.pop();
 }
 
@@ -536,10 +533,10 @@ bool MetalinkParserStateMachine::needsCharactersBuffering() const
   return stateStack_.top()->needsCharactersBuffering();
 }
 
-void MetalinkParserStateMachine::logError(const std::string& log)
+void MetalinkParserStateMachine::logError(std::string log)
 {
   if(errors_.size() < 10) {
-    errors_.push_back(log);
+    errors_.push_back(std::move(log));
   }
 }
 
@@ -557,9 +554,9 @@ std::unique_ptr<Metalinker> MetalinkParserStateMachine::getResult()
   return ctrl_->getResult();
 }
 
-void MetalinkParserStateMachine::setBaseUri(const std::string& uri)
+void MetalinkParserStateMachine::setBaseUri(std::string uri)
 {
-  ctrl_->setBaseUri(uri);
+  ctrl_->setBaseUri(std::move(uri));
 }
 
 } // namespace aria2
diff --git a/src/MetalinkParserStateMachine.h b/src/MetalinkParserStateMachine.h
index ad7c1456..68ba4d9c 100644
--- a/src/MetalinkParserStateMachine.h
+++ b/src/MetalinkParserStateMachine.h
@@ -109,7 +109,7 @@ public:
   (const char* localname,
    const char* prefix,
    const char* nsUri,
-   const std::string& characters) CXX11_OVERRIDE;
+   std::string characters) CXX11_OVERRIDE;
 
   virtual void reset() CXX11_OVERRIDE;
 
@@ -159,15 +159,15 @@ public:
 
   void newEntryTransaction();
 
-  void setFileNameOfEntry(const std::string& filename);
+  void setFileNameOfEntry(std::string filename);
 
   void setFileLengthOfEntry(int64_t length);
 
-  void setVersionOfEntry(const std::string& version);
+  void setVersionOfEntry(std::string version);
 
-  void setLanguageOfEntry(const std::string& language);
+  void setLanguageOfEntry(std::string language);
 
-  void setOSOfEntry(const std::string& os);
+  void setOSOfEntry(std::string os);
 
   void setMaxConnectionsOfEntry(int maxConnections); // Metalink3Spec
 
@@ -177,11 +177,11 @@ public:
 
   void newResourceTransaction();
 
-  void setURLOfResource(const std::string& url);
+  void setURLOfResource(std::string url);
 
-  void setTypeOfResource(const std::string& type);
+  void setTypeOfResource(std::string type);
 
-  void setLocationOfResource(const std::string& location);
+  void setLocationOfResource(std::string location);
 
   void setPriorityOfResource(int priority);
 
@@ -193,9 +193,9 @@ public:
 
   void newChecksumTransaction();
 
-  void setTypeOfChecksum(const std::string& type);
+  void setTypeOfChecksum(std::string type);
 
-  void setHashOfChecksum(const std::string& md);
+  void setHashOfChecksum(std::string md);
 
   void commitChecksumTransaction();
 
@@ -205,9 +205,9 @@ public:
 
   void setLengthOfChunkChecksumV4(size_t length); // Metalink4Spec
 
-  void setTypeOfChunkChecksumV4(const std::string& type); // Metalink4Spec
+  void setTypeOfChunkChecksumV4(std::string type); // Metalink4Spec
 
-  void addHashOfChunkChecksumV4(const std::string& md); // Metalink4Spec
+  void addHashOfChunkChecksumV4(std::string md); // Metalink4Spec
 
   void commitChunkChecksumTransactionV4(); // Metalink4Spec
 
@@ -217,11 +217,11 @@ public:
 
   void setLengthOfChunkChecksum(size_t length); // Metalink3Spec
 
-  void setTypeOfChunkChecksum(const std::string& type); // Metalink3Spec
+  void setTypeOfChunkChecksum(std::string type); // Metalink3Spec
 
   void createNewHashOfChunkChecksum(size_t order); // Metalink3Spec
 
-  void setMessageDigestOfChunkChecksum(const std::string& md); // Metalink3Spec
+  void setMessageDigestOfChunkChecksum(std::string md); // Metalink3Spec
 
   void addHashOfChunkChecksum(); // Metalink3Spec
 
@@ -231,11 +231,11 @@ public:
 
   void newSignatureTransaction();
 
-  void setTypeOfSignature(const std::string& type);
+  void setTypeOfSignature(std::string type);
 
-  void setFileOfSignature(const std::string& file);
+  void setFileOfSignature(std::string file);
 
-  void setBodyOfSignature(const std::string& body);
+  void setBodyOfSignature(std::string body);
 
   void commitSignatureTransaction();
 
@@ -243,20 +243,20 @@ public:
 
   void newMetaurlTransaction();
 
-  void setURLOfMetaurl(const std::string& url);
+  void setURLOfMetaurl(std::string url);
 
-  void setMediatypeOfMetaurl(const std::string& mediatype);
+  void setMediatypeOfMetaurl(std::string mediatype);
 
   void setPriorityOfMetaurl(int priority);
 
-  void setNameOfMetaurl(const std::string& name);
+  void setNameOfMetaurl(std::string name);
 
   void commitMetaurlTransaction();
 
   void cancelMetaurlTransaction();
 
   // Only stores first 10 errors.
-  void logError(const std::string& log);
+  void logError(std::string log);
 
   const std::vector<std::string>& getErrors() const
   {
@@ -267,7 +267,7 @@ public:
 
   std::unique_ptr<Metalinker> getResult();
 
-  void setBaseUri(const std::string& uri);
+  void setBaseUri(std::string uri);
 };
 
 } //  namespace aria2
diff --git a/src/MetalinkParserStateV3Impl.cc b/src/MetalinkParserStateV3Impl.cc
index f92ae51a..5b658999 100644
--- a/src/MetalinkParserStateV3Impl.cc
+++ b/src/MetalinkParserStateV3Impl.cc
@@ -134,7 +134,7 @@ void FileMetalinkParserState::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
   psm->commitEntryTransaction();
 }
@@ -144,7 +144,7 @@ void SizeMetalinkParserState::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
   // current metalink specification doesn't require size element.
   int64_t size;
@@ -159,9 +159,9 @@ void VersionMetalinkParserState::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
-  psm->setVersionOfEntry(characters);
+  psm->setVersionOfEntry(std::move(characters));
 }
 
 void LanguageMetalinkParserState::endElement
@@ -169,9 +169,9 @@ void LanguageMetalinkParserState::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
-  psm->setLanguageOfEntry(characters);
+  psm->setLanguageOfEntry(std::move(characters));
 }
 
 void OSMetalinkParserState::endElement
@@ -179,9 +179,9 @@ void OSMetalinkParserState::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
-  psm->setOSOfEntry(characters);
+  psm->setOSOfEntry(std::move(characters));
 }
 
 void VerificationMetalinkParserState::beginElement
@@ -259,9 +259,9 @@ void HashMetalinkParserState::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
-  psm->setHashOfChecksum(characters);
+  psm->setHashOfChecksum(std::move(characters));
   psm->commitChecksumTransaction();
 }
 
@@ -296,7 +296,7 @@ void PiecesMetalinkParserState::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
   psm->commitChunkChecksumTransaction();
 }
@@ -306,9 +306,9 @@ void PieceHashMetalinkParserState::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
-  psm->setMessageDigestOfChunkChecksum(characters);
+  psm->setMessageDigestOfChunkChecksum(std::move(characters));
   psm->addHashOfChunkChecksum();
 }
 
@@ -317,9 +317,9 @@ void SignatureMetalinkParserState::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
-  psm->setBodyOfSignature(characters);
+  psm->setBodyOfSignature(std::move(characters));
   psm->commitSignatureTransaction();
 }
 
@@ -391,9 +391,9 @@ void URLMetalinkParserState::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
-  psm->setURLOfResource(characters);
+  psm->setURLOfResource(std::move(characters));
   psm->commitResourceTransaction();
 }
 
diff --git a/src/MetalinkParserStateV3Impl.h b/src/MetalinkParserStateV3Impl.h
index dcac3d70..787a91b5 100644
--- a/src/MetalinkParserStateV3Impl.h
+++ b/src/MetalinkParserStateV3Impl.h
@@ -80,7 +80,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
@@ -95,7 +95,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
@@ -110,7 +110,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
@@ -125,7 +125,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
@@ -140,7 +140,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
@@ -170,7 +170,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
@@ -191,7 +191,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
@@ -206,7 +206,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-			  const std::string& characters) CXX11_OVERRIDE;
+			  std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
@@ -221,7 +221,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
@@ -251,7 +251,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
diff --git a/src/MetalinkParserStateV4Impl.cc b/src/MetalinkParserStateV4Impl.cc
index cb186b94..a10e5d88 100644
--- a/src/MetalinkParserStateV4Impl.cc
+++ b/src/MetalinkParserStateV4Impl.cc
@@ -223,7 +223,7 @@ void FileMetalinkParserStateV4::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
   psm->commitEntryTransaction();
 }
@@ -233,7 +233,7 @@ void SizeMetalinkParserStateV4::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
   int64_t size;
   if(util::parseLLIntNoThrow(size, characters) && size >= 0 &&
@@ -250,9 +250,9 @@ void VersionMetalinkParserStateV4::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
-  psm->setVersionOfEntry(characters);
+  psm->setVersionOfEntry(std::move(characters));
 }
 
 void LanguageMetalinkParserStateV4::endElement
@@ -260,9 +260,9 @@ void LanguageMetalinkParserStateV4::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
-  psm->setLanguageOfEntry(characters);
+  psm->setLanguageOfEntry(std::move(characters));
 }
 
 void OSMetalinkParserStateV4::endElement
@@ -270,9 +270,9 @@ void OSMetalinkParserStateV4::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
-  psm->setOSOfEntry(characters);
+  psm->setOSOfEntry(std::move(characters));
 }
 
 void HashMetalinkParserStateV4::endElement
@@ -280,9 +280,9 @@ void HashMetalinkParserStateV4::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
-  psm->setHashOfChecksum(characters);
+  psm->setHashOfChecksum(std::move(characters));
   psm->commitChecksumTransaction();
 }
 
@@ -305,7 +305,7 @@ void PiecesMetalinkParserStateV4::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
   psm->commitChunkChecksumTransactionV4();
 }
@@ -315,9 +315,9 @@ void PieceHashMetalinkParserStateV4::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
-  psm->addHashOfChunkChecksumV4(characters);
+  psm->addHashOfChunkChecksumV4(std::move(characters));
 }
 
 void SignatureMetalinkParserStateV4::endElement
@@ -325,9 +325,9 @@ void SignatureMetalinkParserStateV4::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
-  psm->setBodyOfSignature(characters);
+  psm->setBodyOfSignature(std::move(characters));
   psm->commitSignatureTransaction();
 }
 
@@ -336,9 +336,9 @@ void URLMetalinkParserStateV4::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
-  psm->setURLOfResource(characters);
+  psm->setURLOfResource(std::move(characters));
   psm->commitResourceTransaction();
 }
 
@@ -347,9 +347,9 @@ void MetaurlMetalinkParserStateV4::endElement
  const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
-  psm->setURLOfMetaurl(characters);
+  psm->setURLOfMetaurl(std::move(characters));
   psm->commitMetaurlTransaction();
 }
 
diff --git a/src/MetalinkParserStateV4Impl.h b/src/MetalinkParserStateV4Impl.h
index 123d2f8f..e791884b 100644
--- a/src/MetalinkParserStateV4Impl.h
+++ b/src/MetalinkParserStateV4Impl.h
@@ -65,7 +65,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
@@ -80,7 +80,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
@@ -95,7 +95,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
@@ -110,7 +110,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
@@ -125,7 +125,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
@@ -140,7 +140,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
@@ -161,7 +161,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
@@ -176,7 +176,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-			  const std::string& characters) CXX11_OVERRIDE;
+			  std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
@@ -191,7 +191,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
@@ -206,7 +206,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
@@ -221,7 +221,7 @@ public:
                           const char* localname,
                           const char* prefix,
                           const char* nsUri,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   {
diff --git a/src/ParserStateMachine.h b/src/ParserStateMachine.h
index bdf0084f..48b4e953 100644
--- a/src/ParserStateMachine.h
+++ b/src/ParserStateMachine.h
@@ -62,7 +62,7 @@ public:
   (const char* localname,
    const char* prefix,
    const char* nsUri,
-   const std::string& characters) = 0;
+   std::string characters) = 0;
 
   // Resets internal state of the object and make it ready for new
   // parser session.
diff --git a/src/Signature.cc b/src/Signature.cc
index c12303e0..3226abc5 100644
--- a/src/Signature.cc
+++ b/src/Signature.cc
@@ -42,19 +42,19 @@ Signature::Signature() {}
 
 Signature::~Signature() {}
 
-void Signature::setType(const std::string& type)
+void Signature::setType(std::string type)
 {
-  type_ = type;
+  type_ = std::move(type);
 }
 
-void Signature::setFile(const std::string& file)
+void Signature::setFile(std::string file)
 {
-  file_ = file;
+  file_ = std::move(file);
 }
 
-void Signature::setBody(const std::string& body)
+void Signature::setBody(std::string body)
 {
-  body_ = body;
+  body_ = std::move(body);
 }
 
 bool Signature::save(const std::string& filepath) const
diff --git a/src/Signature.h b/src/Signature.h
index 940f89e5..60b46d03 100644
--- a/src/Signature.h
+++ b/src/Signature.h
@@ -53,21 +53,21 @@ public:
 
   ~Signature();
 
-  void setType(const std::string& type);
+  void setType(std::string type);
 
   const std::string& getType() const
   {
     return type_;
   }
 
-  void setFile(const std::string& file);
+  void setFile(std::string file);
 
   const std::string& getFile() const
   {
     return file_;
   }
 
-  void setBody(const std::string& body);
+  void setBody(std::string body);
 
   const std::string& getBody() const
   {
diff --git a/src/Xml2XmlParser.cc b/src/Xml2XmlParser.cc
index bcc87827..8e611771 100644
--- a/src/Xml2XmlParser.cc
+++ b/src/Xml2XmlParser.cc
@@ -97,7 +97,7 @@ void mlEndElement
   SessionData* sd = reinterpret_cast<SessionData*>(userData);
   std::string characters;
   if(sd->psm->needsCharactersBuffering()) {
-    characters = sd->charactersStack.front();
+    characters = std::move(sd->charactersStack.front());
     sd->charactersStack.pop_front();
   }
   sd->psm->endElement
diff --git a/src/XmlRpcRequestParserState.h b/src/XmlRpcRequestParserState.h
index 4dfb9dae..832ed652 100644
--- a/src/XmlRpcRequestParserState.h
+++ b/src/XmlRpcRequestParserState.h
@@ -58,7 +58,7 @@ public:
 
   virtual void endElement(XmlRpcRequestParserStateMachine* psm,
                           const char* name,
-                          const std::string& characters) = 0;
+                          std::string characters) = 0;
 
   virtual bool needsCharactersBuffering() const = 0;
 };
diff --git a/src/XmlRpcRequestParserStateImpl.cc b/src/XmlRpcRequestParserStateImpl.cc
index d263f663..255587fd 100644
--- a/src/XmlRpcRequestParserStateImpl.cc
+++ b/src/XmlRpcRequestParserStateImpl.cc
@@ -63,7 +63,7 @@ void InitialXmlRpcRequestParserState::beginElement
 void InitialXmlRpcRequestParserState::endElement
 (XmlRpcRequestParserStateMachine* psm,
  const char* name,
- const std::string& characters)
+ std::string characters)
 {}
 
 // UnknownElementXmlRpcRequestParserState
@@ -106,9 +106,9 @@ void MethodNameXmlRpcRequestParserState::beginElement
 void MethodNameXmlRpcRequestParserState::endElement
 (XmlRpcRequestParserStateMachine* psm,
  const char* name,
- const std::string& characters)
+ std::string characters)
 {
-  psm->setMethodName(characters);
+  psm->setMethodName(std::move(characters));
 }
 
 // ParamsXmlRpcRequestParserState
@@ -143,7 +143,7 @@ void ParamXmlRpcRequestParserState::beginElement
 void ParamXmlRpcRequestParserState::endElement
 (XmlRpcRequestParserStateMachine* psm,
  const char* name,
- const std::string& characters)
+ std::string characters)
 {
   psm->popArrayFrame();
 }
@@ -175,13 +175,13 @@ void ValueXmlRpcRequestParserState::beginElement
 void ValueXmlRpcRequestParserState::endElement
 (XmlRpcRequestParserStateMachine* psm,
  const char* name,
- const std::string& characters)
+ std::string characters)
 {
   // XML-RPC specification says that if no data type tag is used, the
   // data must be treated as string.  To prevent from overwriting
   // current frame value, we first check it is still null.
   if(!psm->getCurrentFrameValue() && !characters.empty()) {
-    psm->setCurrentFrameValue(String::g(characters));
+    psm->setCurrentFrameValue(String::g(std::move(characters)));
   }
 }
 
@@ -198,7 +198,7 @@ void IntXmlRpcRequestParserState::beginElement
 void IntXmlRpcRequestParserState::endElement
 (XmlRpcRequestParserStateMachine* psm,
  const char* name,
- const std::string& characters)
+ std::string characters)
 {
   int32_t value;
   if(util::parseIntNoThrow(value, characters)) {
@@ -221,9 +221,9 @@ void StringXmlRpcRequestParserState::beginElement
 void StringXmlRpcRequestParserState::endElement
 (XmlRpcRequestParserStateMachine* psm,
  const char* name,
- const std::string& characters)
+ std::string characters)
 {
-  psm->setCurrentFrameValue(String::g(characters));
+  psm->setCurrentFrameValue(String::g(std::move(characters)));
 }
 
 // Base64XmlRpcRequestParserState
@@ -239,7 +239,7 @@ void Base64XmlRpcRequestParserState::beginElement
 void Base64XmlRpcRequestParserState::endElement
 (XmlRpcRequestParserStateMachine* psm,
  const char* name,
- const std::string& characters)
+ std::string characters)
 {
   psm->setCurrentFrameValue
     (String::g(base64::decode(characters.begin(), characters.end())));
@@ -279,7 +279,7 @@ void MemberXmlRpcRequestParserState::beginElement
 void MemberXmlRpcRequestParserState::endElement
 (XmlRpcRequestParserStateMachine* psm,
  const char* name,
- const std::string& characters)
+ std::string characters)
 {
   psm->popStructFrame();
 }
@@ -297,9 +297,9 @@ void NameXmlRpcRequestParserState::beginElement
 void NameXmlRpcRequestParserState::endElement
 (XmlRpcRequestParserStateMachine* psm,
  const char* name,
- const std::string& characters)
+ std::string characters)
 {
-  psm->setCurrentFrameName(characters);
+  psm->setCurrentFrameName(std::move(characters));
 }
 
 // ArrayXmlRpcRequestParserState
@@ -336,9 +336,9 @@ void DataXmlRpcRequestParserState::beginElement
 void ArrayValueXmlRpcRequestParserState::endElement
 (XmlRpcRequestParserStateMachine* psm,
  const char* name,
- const std::string& characters)
+ std::string characters)
 {
-  ValueXmlRpcRequestParserState::endElement(psm, name, characters);
+  ValueXmlRpcRequestParserState::endElement(psm, name, std::move(characters));
   psm->popArrayFrame();
 }
 
diff --git a/src/XmlRpcRequestParserStateImpl.h b/src/XmlRpcRequestParserStateImpl.h
index a9aa0b46..fb34bbd2 100644
--- a/src/XmlRpcRequestParserStateImpl.h
+++ b/src/XmlRpcRequestParserStateImpl.h
@@ -49,7 +49,7 @@ public:
 
   virtual void endElement(XmlRpcRequestParserStateMachine* psm,
                           const char* name,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   { return false; }
@@ -63,7 +63,7 @@ public:
 
   virtual void endElement(XmlRpcRequestParserStateMachine* psm,
                           const char* name,
-                          const std::string& characters) CXX11_OVERRIDE {}
+                          std::string characters) CXX11_OVERRIDE {}
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   { return false; }
@@ -77,7 +77,7 @@ public:
 
   virtual void endElement(XmlRpcRequestParserStateMachine* psm,
                           const char* name,
-                          const std::string& characters) CXX11_OVERRIDE {}
+                          std::string characters) CXX11_OVERRIDE {}
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   { return false; }
@@ -91,7 +91,7 @@ public:
 
   virtual void endElement(XmlRpcRequestParserStateMachine* psm,
                           const char* name,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE { return true; }
 };
@@ -103,7 +103,7 @@ class ParamsXmlRpcRequestParserState:public XmlRpcRequestParserState {
 
   virtual void endElement(XmlRpcRequestParserStateMachine* psm,
                           const char* name,
-                          const std::string& characters) CXX11_OVERRIDE {}
+                          std::string characters) CXX11_OVERRIDE {}
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   { return false; }
@@ -116,7 +116,7 @@ class ParamXmlRpcRequestParserState:public XmlRpcRequestParserState {
 
   virtual void endElement(XmlRpcRequestParserStateMachine* psm,
                           const char* name,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   { return false; }
@@ -129,7 +129,7 @@ class ValueXmlRpcRequestParserState:public XmlRpcRequestParserState {
 protected:
   virtual void endElement(XmlRpcRequestParserStateMachine* psm,
                           const char* name,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE { return true; }
 };
@@ -141,7 +141,7 @@ class IntXmlRpcRequestParserState:public XmlRpcRequestParserState {
 
   virtual void endElement(XmlRpcRequestParserStateMachine* psm,
                           const char* name,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE { return true; }
 };
@@ -153,7 +153,7 @@ class StringXmlRpcRequestParserState:public XmlRpcRequestParserState {
 
   virtual void endElement(XmlRpcRequestParserStateMachine* psm,
                           const char* name,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE { return true; }
 };
@@ -165,7 +165,7 @@ class Base64XmlRpcRequestParserState:public XmlRpcRequestParserState {
 
   virtual void endElement(XmlRpcRequestParserStateMachine* psm,
                           const char* name,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE { return true; }
 };
@@ -177,7 +177,7 @@ class StructXmlRpcRequestParserState:public XmlRpcRequestParserState {
 
   virtual void endElement(XmlRpcRequestParserStateMachine* psm,
                           const char* name,
-                          const std::string& characters) CXX11_OVERRIDE {}
+                          std::string characters) CXX11_OVERRIDE {}
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   { return false; }
@@ -190,7 +190,7 @@ class MemberXmlRpcRequestParserState:public XmlRpcRequestParserState {
 
   virtual void endElement(XmlRpcRequestParserStateMachine* psm,
                           const char* name,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   { return false; }
@@ -203,7 +203,7 @@ class NameXmlRpcRequestParserState:public XmlRpcRequestParserState {
 
   virtual void endElement(XmlRpcRequestParserStateMachine* psm,
                           const char* name,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE { return true; }
 };
@@ -215,7 +215,7 @@ class ArrayXmlRpcRequestParserState:public XmlRpcRequestParserState {
 
   virtual void endElement(XmlRpcRequestParserStateMachine* psm,
                           const char* name,
-                          const std::string& characters) CXX11_OVERRIDE {}
+                          std::string characters) CXX11_OVERRIDE {}
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   { return false; }
@@ -228,7 +228,7 @@ class DataXmlRpcRequestParserState:public XmlRpcRequestParserState {
 
   virtual void endElement(XmlRpcRequestParserStateMachine* psm,
                           const char* name,
-                          const std::string& characters) CXX11_OVERRIDE {}
+                          std::string characters) CXX11_OVERRIDE {}
 
   virtual bool needsCharactersBuffering() const CXX11_OVERRIDE
   { return false; }
@@ -237,7 +237,7 @@ class DataXmlRpcRequestParserState:public XmlRpcRequestParserState {
 class ArrayValueXmlRpcRequestParserState:public ValueXmlRpcRequestParserState {
   virtual void endElement(XmlRpcRequestParserStateMachine* psm,
                           const char* name,
-                          const std::string& characters) CXX11_OVERRIDE;
+                          std::string characters) CXX11_OVERRIDE;
 };
 
 } // namespace rpc
diff --git a/src/XmlRpcRequestParserStateMachine.cc b/src/XmlRpcRequestParserStateMachine.cc
index 466e4ef0..d3e2e1fb 100644
--- a/src/XmlRpcRequestParserStateMachine.cc
+++ b/src/XmlRpcRequestParserStateMachine.cc
@@ -117,16 +117,15 @@ void XmlRpcRequestParserStateMachine::endElement
 (const char* localname,
  const char* prefix,
  const char* nsUri,
- const std::string& characters)
+ std::string characters)
 {
-  stateStack_.top()->endElement(this, localname, characters);
+  stateStack_.top()->endElement(this, localname, std::move(characters));
   stateStack_.pop();
 }
 
-void XmlRpcRequestParserStateMachine::setMethodName
-(const std::string& methodName)
+void XmlRpcRequestParserStateMachine::setMethodName(std::string methodName)
 {
-  controller_->setMethodName(methodName);
+  controller_->setMethodName(std::move(methodName));
 }
 
 const std::string& XmlRpcRequestParserStateMachine::getMethodName() const
@@ -167,10 +166,9 @@ XmlRpcRequestParserStateMachine::popCurrentFrameValue()
   return controller_->popCurrentFrameValue();
 }
 
-void XmlRpcRequestParserStateMachine::setCurrentFrameName
-(const std::string& name)
+void XmlRpcRequestParserStateMachine::setCurrentFrameName(std::string name)
 {
-  controller_->setCurrentFrameName(name);
+  controller_->setCurrentFrameName(std::move(name));
 }
 
 void XmlRpcRequestParserStateMachine::pushUnknownElementState()
diff --git a/src/XmlRpcRequestParserStateMachine.h b/src/XmlRpcRequestParserStateMachine.h
index cbc0f419..0798d2d4 100644
--- a/src/XmlRpcRequestParserStateMachine.h
+++ b/src/XmlRpcRequestParserStateMachine.h
@@ -68,11 +68,11 @@ public:
   (const char* localname,
    const char* prefix,
    const char* nsUri,
-   const std::string& characters) CXX11_OVERRIDE;
+   std::string characters) CXX11_OVERRIDE;
 
   virtual void reset() CXX11_OVERRIDE;
 
-  void setMethodName(const std::string& methodName);
+  void setMethodName(std::string methodName);
   const std::string& getMethodName() const;
   void popArrayFrame();
   void popStructFrame();
@@ -80,7 +80,7 @@ public:
   void setCurrentFrameValue(std::unique_ptr<ValueBase> value);
   const std::unique_ptr<ValueBase>& getCurrentFrameValue() const;
   std::unique_ptr<ValueBase> popCurrentFrameValue();
-  void setCurrentFrameName(const std::string& name);
+  void setCurrentFrameName(std::string name);
 
   void pushUnknownElementState();
   void pushMethodCallState();