From 36ca9d01fbd9cd996472f4ebcbceb25b955d707c Mon Sep 17 00:00:00 2001
From: Max Kellermann <max@musicpd.org>
Date: Mon, 20 Aug 2018 15:21:05 +0200
Subject: [PATCH] util/ForeignFifoBuffer: shift the buffer in MoveFrom() on
 demand

The API documentation says "move as much data as possible", and if
there is room at the head of the buffer, we should use that if the
room after the tail is not large enough.
---
 src/util/ForeignFifoBuffer.hxx | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/util/ForeignFifoBuffer.hxx b/src/util/ForeignFifoBuffer.hxx
index da0058ad3..bcc2b9d67 100644
--- a/src/util/ForeignFifoBuffer.hxx
+++ b/src/util/ForeignFifoBuffer.hxx
@@ -223,6 +223,15 @@ public:
 	size_type MoveFrom(ForeignFifoBuffer<T> &src) noexcept {
 		auto r = src.Read();
 		auto w = Write();
+
+		if (w.size < r.size && head > 0) {
+			/* if the source contains more data than we
+			   can append at the tail, try to make more
+			   room by shifting the head to 0 */
+			Shift();
+			w = Write();
+		}
+
 		size_t n = std::min(r.size, w.size);
 
 		std::move(r.data, r.data + n, w.data);