1 files changed, 251 insertions, 0 deletions
diff --git a/src/input/plugins/RewindInputPlugin.cxx b/src/input/plugins/RewindInputPlugin.cxx
new file mode 100644
index 000000000..1a930ac53
--- /dev/null
+++ b/src/input/plugins/RewindInputPlugin.cxx
@@ -0,0 +1,251 @@
+/*
+ * 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 "../InputStream.hxx"
+#include "../InputPlugin.hxx"
+
+#include <assert.h>
+#include <string.h>
+#include <stdio.h>
+
+extern const InputPlugin rewind_input_plugin;
+
+struct RewindInputStream {
+	InputStream base;
+
+	InputStream *input;
+
+	/**
+	 * 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];
+
+	RewindInputStream(InputStream *_input)
+		:base(rewind_input_plugin, _input->uri.c_str(),
+		      _input->mutex, _input->cond),
+		 input(_input), tail(0) {
+	}
+
+	~RewindInputStream() {
+		input->Close();
+	}
+
+	/**
+	 * 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 && base.offset < input->offset;
+	}
+
+	/**
+	 * Copy public attributes from the underlying input stream to the
+	 * "rewind" input stream.  This function is called when a method of
+	 * the underlying stream has returned, which may have modified these
+	 * attributes.
+	 */
+	void CopyAttributes() {
+		InputStream *dest = &base;
+		const InputStream *src = input;
+
+		assert(dest != src);
+
+		bool dest_ready = dest->ready;
+
+		dest->ready = src->ready;
+		dest->seekable = src->seekable;
+		dest->size = src->size;
+		dest->offset = src->offset;
+
+		if (!dest_ready && src->ready)
+			dest->mime = src->mime;
+	}
+};
+
+static void
+input_rewind_close(InputStream *is)
+{
+	RewindInputStream *r = (RewindInputStream *)is;
+
+	delete r;
+}
+
+static bool
+input_rewind_check(InputStream *is, Error &error)
+{
+	RewindInputStream *r = (RewindInputStream *)is;
+
+	return r->input->Check(error);
+}
+
+static void
+input_rewind_update(InputStream *is)
+{
+	RewindInputStream *r = (RewindInputStream *)is;
+
+	if (!r->ReadingFromBuffer())
+		r->CopyAttributes();
+}
+
+static Tag *
+input_rewind_tag(InputStream *is)
+{
+	RewindInputStream *r = (RewindInputStream *)is;
+
+	return r->input->ReadTag();
+}
+
+static bool
+input_rewind_available(InputStream *is)
+{
+	RewindInputStream *r = (RewindInputStream *)is;
+
+	return r->input->IsAvailable();
+}
+
+static size_t
+input_rewind_read(InputStream *is, void *ptr, size_t size,
+		  Error &error)
+{
+	RewindInputStream *r = (RewindInputStream *)is;
+
+	if (r->ReadingFromBuffer()) {
+		/* buffered read */
+
+		assert(r->head == (size_t)is->offset);
+		assert(r->tail == (size_t)r->input->offset);
+
+		if (size > r->tail - r->head)
+			size = r->tail - r->head;
+
+		memcpy(ptr, r->buffer + r->head, size);
+		r->head += size;
+		is->offset += size;
+
+		return size;
+	} else {
+		/* pass method call to underlying stream */
+
+		size_t nbytes = r->input->Read(ptr, size, error);
+
+		if (r->input->offset > (InputPlugin::offset_type)sizeof(r->buffer))
+			/* disable buffering */
+			r->tail = 0;
+		else if (r->tail == (size_t)is->offset) {
+			/* append to buffer */
+
+			memcpy(r->buffer + r->tail, ptr, nbytes);
+			r->tail += nbytes;
+
+			assert(r->tail == (size_t)r->input->offset);
+		}
+
+		r->CopyAttributes();
+
+		return nbytes;
+	}
+}
+
+static bool
+input_rewind_eof(InputStream *is)
+{
+	RewindInputStream *r = (RewindInputStream *)is;
+
+	return !r->ReadingFromBuffer() && r->input->IsEOF();
+}
+
+static bool
+input_rewind_seek(InputStream *is, InputPlugin::offset_type offset,
+		  int whence,
+		  Error &error)
+{
+	RewindInputStream *r = (RewindInputStream *)is;
+
+	assert(is->ready);
+
+	if (whence == SEEK_SET && r->tail > 0 &&
+	    offset <= (InputPlugin::offset_type)r->tail) {
+		/* buffered seek */
+
+		assert(!r->ReadingFromBuffer() ||
+		       r->head == (size_t)is->offset);
+		assert(r->tail == (size_t)r->input->offset);
+
+		r->head = (size_t)offset;
+		is->offset = offset;
+
+		return true;
+	} else {
+		bool success = r->input->Seek(offset, whence, error);
+		r->CopyAttributes();
+
+		/* disable the buffer, because r->input has left the
+		   buffered range now */
+		r->tail = 0;
+
+		return success;
+	}
+}
+
+const InputPlugin rewind_input_plugin = {
+	nullptr,
+	nullptr,
+	nullptr,
+	nullptr,
+	input_rewind_close,
+	input_rewind_check,
+	input_rewind_update,
+	input_rewind_tag,
+	input_rewind_available,
+	input_rewind_read,
+	input_rewind_eof,
+	input_rewind_seek,
+};
+
+InputStream *
+input_rewind_open(InputStream *is)
+{
+	assert(is != nullptr);
+	assert(is->offset == 0);
+
+	if (is->seekable)
+		/* seekable resources don't need this plugin */
+		return is;
+
+	RewindInputStream *c = new RewindInputStream(is);
+	return &c->base;
+}