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authorMax Kellermann <max@duempel.org>2014-08-11 20:57:14 +0200
committerMax Kellermann <max@duempel.org>2014-08-11 21:48:25 +0200
commit45c139cfb36fd0801faded97683aa7faa83809b1 (patch)
treee9dc546db5b0a0429f8799875f0fc27bb6649358 /src/fs
parent3a111e5d744f875cde11fe755d03d3df3519f8a2 (diff)
downloadmpd-45c139cfb36fd0801faded97683aa7faa83809b1.tar.gz
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fs/io/PeekReader: new utility class
Diffstat (limited to 'src/fs')
-rw-r--r--src/fs/io/PeekReader.cxx60
-rw-r--r--src/fs/io/PeekReader.hxx52
2 files changed, 112 insertions, 0 deletions
diff --git a/src/fs/io/PeekReader.cxx b/src/fs/io/PeekReader.cxx
new file mode 100644
index 000000000..2e8042ab6
--- /dev/null
+++ b/src/fs/io/PeekReader.cxx
@@ -0,0 +1,60 @@
+/*
+ * 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 "PeekReader.hxx"
+
+#include <algorithm>
+
+#include <assert.h>
+#include <string.h>
+
+const void *
+PeekReader::Peek(size_t size, Error &error)
+{
+ assert(size > 0);
+ assert(size < sizeof(buffer));
+ assert(buffer_size == 0);
+ assert(buffer_position == 0);
+
+ do {
+ size_t nbytes = next.Read(buffer + buffer_size,
+ size - buffer_size, error);
+ if (nbytes == 0)
+ return nullptr;
+
+ buffer_size += nbytes;
+ } while (buffer_size < size);
+
+ return buffer;
+}
+
+size_t
+PeekReader::Read(void *data, size_t size, Error &error)
+{
+ size_t buffer_remaining = buffer_size - buffer_position;
+ if (buffer_remaining > 0) {
+ size_t nbytes = std::min(buffer_remaining, size);
+ memcpy(data, buffer + buffer_position, nbytes);
+ buffer_position += nbytes;
+ return nbytes;
+ }
+
+ return next.Read(data, size, error);
+}
diff --git a/src/fs/io/PeekReader.hxx b/src/fs/io/PeekReader.hxx
new file mode 100644
index 000000000..27e7ff7c1
--- /dev/null
+++ b/src/fs/io/PeekReader.hxx
@@ -0,0 +1,52 @@
+/*
+ * 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.
+ */
+
+#ifndef MPD_PEEK_READER_HXX
+#define MPD_PEEK_READER_HXX
+
+#include "check.h"
+#include "Reader.hxx"
+
+#include <stdint.h>
+
+class AutoGunzipReader;
+
+/**
+ * A filter that allows the caller to peek the first few bytes without
+ * consuming them. The first call must be Peek(), and the following
+ * Read() will deliver the same bytes again.
+ */
+class PeekReader final : public Reader {
+ Reader &next;
+
+ size_t buffer_size, buffer_position;
+
+ uint8_t buffer[64];
+
+public:
+ PeekReader(Reader &_next)
+ :next(_next), buffer_size(0), buffer_position(0) {}
+
+ const void *Peek(size_t size, Error &error);
+
+ /* virtual methods from class Reader */
+ virtual size_t Read(void *data, size_t size, Error &error) override;
+};
+
+#endif