Fill buffer before allocating more

[folly.git] / folly / io / Cursor.h

diff --git a/folly/io/Cursor.h b/folly/io/Cursor.h
index c16c6a45692bf41736ecb6a6b731b1032e3f6450..32d65605262905be0b2be9f400ee15ce4b767683 100644 (file)
--- a/folly/io/Cursor.h
+++ b/folly/io/Cursor.h
@@ -975,7 +975,15 @@ class QueueAppender : public detail::Writable<QueueAppender> {
 
   using detail::Writable<QueueAppender>::pushAtMost;
   size_t pushAtMost(const uint8_t* buf, size_t len) {
-    size_t remaining = len;
+    // Fill the current buffer
+    const size_t copyLength = std::min(len, length());
+    if (copyLength != 0) {
+      memcpy(writableData(), buf, copyLength);
+      append(copyLength);
+      buf += copyLength;
+    }
+    // Allocate more buffers as necessary
+    size_t remaining = len - copyLength;
     while (remaining != 0) {
       auto p = queue_->preallocate(std::min(remaining, growth_),
                                    growth_,