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-rw-r--r--src/input/plugins/RewindInputPlugin.cxx156
1 files changed, 156 insertions, 0 deletions
diff --git a/src/input/plugins/RewindInputPlugin.cxx b/src/input/plugins/RewindInputPlugin.cxx
new file mode 100644
index 000000000..95f604044
--- /dev/null
+++ b/src/input/plugins/RewindInputPlugin.cxx
@@ -0,0 +1,156 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "RewindInputPlugin.hxx"
+#include "../ProxyInputStream.hxx"
+
+#include <assert.h>
+#include <string.h>
+
+class RewindInputStream final : public ProxyInputStream {
+ /**
+ * The read position within the buffer. Undefined as long as
+ * ReadingFromBuffer() returns false.
+ */
+ size_t head;
+
+ /**
+ * The write/append position within the buffer.
+ */
+ size_t tail;
+
+ /**
+ * The size of this buffer is the maximum number of bytes
+ * which can be rewinded cheaply without passing the "seek"
+ * call to CURL.
+ *
+ * The origin of this buffer is always the beginning of the
+ * stream (offset 0).
+ */
+ char buffer[64 * 1024];
+
+public:
+ RewindInputStream(InputStream *_input)
+ :ProxyInputStream(_input),
+ tail(0) {
+ }
+
+ /* virtual methods from InputStream */
+
+ void Update() override {
+ if (!ReadingFromBuffer())
+ ProxyInputStream::Update();
+ }
+
+ bool IsEOF() override {
+ return !ReadingFromBuffer() && ProxyInputStream::IsEOF();
+ }
+
+ size_t Read(void *ptr, size_t size, Error &error) override;
+ bool Seek(offset_type offset, Error &error) override;
+
+private:
+ /**
+ * Are we currently reading from the buffer, and does the
+ * buffer contain more data for the next read operation?
+ */
+ bool ReadingFromBuffer() const {
+ return tail > 0 && offset < input.GetOffset();
+ }
+};
+
+size_t
+RewindInputStream::Read(void *ptr, size_t read_size, Error &error)
+{
+ if (ReadingFromBuffer()) {
+ /* buffered read */
+
+ assert(head == (size_t)offset);
+ assert(tail == (size_t)input.GetOffset());
+
+ if (read_size > tail - head)
+ read_size = tail - head;
+
+ memcpy(ptr, buffer + head, read_size);
+ head += read_size;
+ offset += read_size;
+
+ return read_size;
+ } else {
+ /* pass method call to underlying stream */
+
+ size_t nbytes = input.Read(ptr, read_size, error);
+
+ if (input.GetOffset() > (offset_type)sizeof(buffer))
+ /* disable buffering */
+ tail = 0;
+ else if (tail == (size_t)offset) {
+ /* append to buffer */
+
+ memcpy(buffer + tail, ptr, nbytes);
+ tail += nbytes;
+
+ assert(tail == (size_t)input.GetOffset());
+ }
+
+ CopyAttributes();
+
+ return nbytes;
+ }
+}
+
+bool
+RewindInputStream::Seek(offset_type new_offset,
+ Error &error)
+{
+ assert(IsReady());
+
+ if (tail > 0 && new_offset <= (offset_type)tail) {
+ /* buffered seek */
+
+ assert(!ReadingFromBuffer() ||
+ head == (size_t)offset);
+ assert(tail == (size_t)input.GetOffset());
+
+ head = (size_t)new_offset;
+ offset = new_offset;
+
+ return true;
+ } else {
+ /* disable the buffer, because input has left the
+ buffered range now */
+ tail = 0;
+
+ return ProxyInputStream::Seek(new_offset, error);
+ }
+}
+
+InputStream *
+input_rewind_open(InputStream *is)
+{
+ assert(is != nullptr);
+ assert(!is->IsReady() || is->GetOffset() == 0);
+
+ if (is->IsReady() && is->IsSeekable())
+ /* seekable resources don't need this plugin */
+ return is;
+
+ return new RewindInputStream(is);
+}