From 75e8c9b7c7f2f10d9b7f479d45f58d81ea729d30 Mon Sep 17 00:00:00 2001
From: Zack Rusin <zack@kde.org>
Date: Thu, 25 Aug 2011 00:02:20 -0400
Subject: [PATCH] Make sure that the size of the compressed length is constant.

size_t can differ between 32 and 64 bit systems.
Plus add some documentation about the file format.
---
 trace_snappyfile.cpp | 32 +++++++++++++++++++++++++++++---
 trace_snappyfile.hpp |  6 ++++--
 2 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/trace_snappyfile.cpp b/trace_snappyfile.cpp
index 45cd95a..2dc5cb3 100644
--- a/trace_snappyfile.cpp
+++ b/trace_snappyfile.cpp
@@ -7,6 +7,32 @@
 
 using namespace Trace;
 
+/*
+ * Snappy file format.
+ * -------------------
+ *
+ * Snappy at its core is just a compressoin algorithm so we're
+ * creating a new file format which uses snappy compression
+ * to hold the trace data.
+ *
+ * The file is composed of a number of chunks, they are:
+ * chunk {
+ *     uint32 - specifying the length of the compressed data
+ *     compressed data
+ * }
+ * File can contain any number of such chunks.
+ * The default size of an uncompressed chunk is specified in
+ * SNAPPY_CHUNK_SIZE.
+ *
+ * Note:
+ * Currently the default size for a a to-be-compressed data is
+ * 1mb, meaning that the compressed data will be <= 1mb.
+ * The reason it's 1mb is because it seems
+ * to offer a pretty good compression/disk io speed ratio
+ * but that might change.
+ *
+ */
+
 SnappyFile::SnappyFile(const std::string &filename,
                               File::Mode mode)
     : File(),
@@ -172,14 +198,14 @@ void SnappyFile::createCache(size_t size)
     m_cacheSize = size;
 }
 
-void SnappyFile::writeCompressedLength(size_t value)
+void SnappyFile::writeCompressedLength(uint32_t value)
 {
     m_stream.write((char*)&value, sizeof value);
 }
 
-size_t SnappyFile::readCompressedLength()
+uint32_t SnappyFile::readCompressedLength()
 {
-    size_t len;
+    uint32_t len;
     m_stream.read((char*)&len, sizeof len);
     return len;
 }
diff --git a/trace_snappyfile.hpp b/trace_snappyfile.hpp
index 0cafa98..601bc12 100644
--- a/trace_snappyfile.hpp
+++ b/trace_snappyfile.hpp
@@ -6,6 +6,8 @@
 #include <string>
 #include <fstream>
 
+#include <stdint.h>
+
 namespace snappy {
     class File;
 }
@@ -42,8 +44,8 @@ private:
     }
     void flushCache();
     void createCache(size_t size);
-    void writeCompressedLength(size_t num);
-    size_t readCompressedLength();
+    void writeCompressedLength(uint32_t  num);
+    uint32_t readCompressedLength();
 private:
     std::fstream m_stream;
     char *m_cache;
-- 
2.43.0