SocketRecvBuffer: Eliminate memmove

Since we don't try to read into buffer if buffer is not empty, we
don't have to memmove things.  This commit mostly rewrites
SocketRecvBuffer.

src/DownloadCommand.cc

@@ -187,7 +187,7 @@ bool DownloadCommand::executeInternal() {
                                getSocketRecvBuffer()->getBufferLength());
       bufSize = streamFilter_->getBytesProcessed();
     }
-    getSocketRecvBuffer()->shiftBuffer(bufSize);
+    getSocketRecvBuffer()->drain(bufSize);
     peerStat_->updateDownloadLength(bufSize);
     getDownloadContext()->updateDownloadLength(bufSize);
   }

src/HttpConnection.cc

@@ -157,12 +157,12 @@ std::unique_ptr<HttpResponse> HttpConnection::receiveResponse()
     httpResponse->setHttpHeader(proc->getResult());
     httpResponse->setHttpRequest(outstandingHttpRequests_.front()->
                                  popHttpRequest());
-    socketRecvBuffer_->shiftBuffer(proc->getLastBytesProcessed());
+    socketRecvBuffer_->drain(proc->getLastBytesProcessed());
     outstandingHttpRequests_.pop_front();
     return httpResponse;
   }
 
-  socketRecvBuffer_->shiftBuffer(proc->getLastBytesProcessed());
+  socketRecvBuffer_->drain(proc->getLastBytesProcessed());
   return nullptr;
 }
 

src/HttpServer.cc

@@ -142,7 +142,7 @@ bool HttpServer::receiveRequest()
     lastRequestHeader_ = headerProcessor_->getResult();
     A2_LOG_INFO(fmt("HTTP Server received request\n%s",
                     headerProcessor_->getHeaderString().c_str()));
-    socketRecvBuffer_->shiftBuffer(headerProcessor_->getLastBytesProcessed());
+    socketRecvBuffer_->drain(headerProcessor_->getLastBytesProcessed());
     bodyConsumed_ = 0;
     if(setupResponseRecv() < 0) {
       A2_LOG_INFO("Request path is invaild. Ignore the request body.");
@@ -175,7 +175,7 @@ bool HttpServer::receiveRequest()
     }
     return true;
   } else {
-    socketRecvBuffer_->shiftBuffer(headerProcessor_->getLastBytesProcessed());
+    socketRecvBuffer_->drain(headerProcessor_->getLastBytesProcessed());
     return false;
   }
 }
@@ -197,7 +197,7 @@ bool HttpServer::receiveBody()
   if(lastBody_) {
     lastBody_->writeData(socketRecvBuffer_->getBuffer(), length, 0);
   }
-  socketRecvBuffer_->shiftBuffer(length);
+  socketRecvBuffer_->drain(length);
   bodyConsumed_ += length;
   return lastContentLength_ == bodyConsumed_;
 }

src/HttpSkipResponseCommand.cc

@@ -138,7 +138,7 @@ bool HttpSkipResponseCommand::executeInternal()
                                  getSocketRecvBuffer()->getBufferLength());
         bufSize = streamFilter_->getBytesProcessed();
       }
-      getSocketRecvBuffer()->shiftBuffer(bufSize);
+      getSocketRecvBuffer()->drain(bufSize);
     }
     if(totalLength_ != 0 && eof) {
       throw DL_RETRY_EX(EX_GOT_EOF);

src/SocketRecvBuffer.cc

@@ -39,17 +39,11 @@
 
 #include "SocketCore.h"
 #include "LogFactory.h"
-#include "a2functional.h"
 
 namespace aria2 {
 
-SocketRecvBuffer::SocketRecvBuffer
-(std::shared_ptr<SocketCore> socket,
- size_t capacity)
-  : socket_(std::move(socket)),
-    capacity_(capacity),
-    buf_(make_unique<unsigned char[]>(capacity_)),
-    bufLen_(0)
+SocketRecvBuffer::SocketRecvBuffer(std::shared_ptr<SocketCore> socket)
+  : socket_(std::move(socket)), pos_(buf_.data()), last_(pos_)
 {}
 
 SocketRecvBuffer::~SocketRecvBuffer()
@@ -57,21 +51,28 @@ SocketRecvBuffer::~SocketRecvBuffer()
 
 ssize_t SocketRecvBuffer::recv()
 {
-  size_t len = capacity_ - bufLen_;
-  if(len > 0) {
-    socket_->readData(buf_.get() + bufLen_, len);
-    bufLen_ += len;
-  } else {
+  size_t n = std::end(buf_) - last_;
+  if (n == 0) {
     A2_LOG_DEBUG("Buffer full");
+    return 0;
   }
-  return len;
+  socket_->readData(last_, n);
+  last_ += n;
+  return n;
 }
 
-void SocketRecvBuffer::shiftBuffer(size_t offset)
+void SocketRecvBuffer::drain(size_t n)
 {
-  assert(offset <= bufLen_);
-  memmove(buf_.get(), buf_.get() + offset, bufLen_ - offset);
-  bufLen_ -= offset;
+  assert(pos_ + n <= last_);
+  pos_ += n;
+  if (pos_ == last_) {
+    truncateBuffer();
+  }
+}
+
+void SocketRecvBuffer::truncateBuffer()
+{
+  pos_ = last_ = buf_.data();
 }
 
 } // namespace aria2

src/SocketRecvBuffer.h

@@ -38,6 +38,7 @@
 #include "common.h"
 
 #include <memory>
+#include <array>
 
 namespace aria2 {
 
@@ -45,21 +46,17 @@ class SocketCore;
 
 class SocketRecvBuffer {
 public:
-  SocketRecvBuffer
-  (std::shared_ptr<SocketCore> socket,
-   size_t capacity = 16*1024);
+  SocketRecvBuffer(std::shared_ptr<SocketCore> socket);
   ~SocketRecvBuffer();
   // Reads data from socket as much as capacity allows. Returns the
   // number of bytes read.
   ssize_t recv();
-  // Shifts buffer by offset bytes. offset must satisfy offset <=
-  // getBufferLength().
-  void shiftBuffer(size_t offset);
   // Truncates the contents of buffer to 0.
-  void clearBuffer()
-  {
-    bufLen_ = 0;
-  }
+  void truncateBuffer();
+  // Drains first n bytes of data from buffer.  It is an programmer's
+  // responsibility to ensure that n is smaller or equal to the
+  // buffered data.
+  void drain(size_t n);
 
   const std::shared_ptr<SocketCore>& getSocket() const
   {
@@ -68,25 +65,24 @@ public:
 
   const unsigned char* getBuffer() const
   {
-    return buf_.get();
+    return pos_;
   }
 
   size_t getBufferLength() const
   {
-    return bufLen_;
+    return last_ - pos_;
   }
 
   bool bufferEmpty() const
   {
-    return bufLen_ == 0;
+    return pos_ == last_;
   }
 
-  void pushBuffer(const unsigned char* data, size_t len);
 private:
+  std::array<unsigned char, 16384> buf_;
   std::shared_ptr<SocketCore> socket_;
-  size_t capacity_;
-  std::unique_ptr<unsigned char[]> buf_;
-  size_t bufLen_;
+  unsigned char *pos_;
+  unsigned char *last_;
 };
 
 } // namespace aria2