* Copyright (C) 2006 Michael Vrable
*
* Backup data is stored in a collection of objects, which are grouped together
- * into segments for storage purposes. This file provides interfaces for
- * reading and writing objects and segments. */
+ * into segments for storage purposes. This implementation of the object store
+ * is built on top of libtar, and represents segments as TAR files and objects
+ * as files within them. */
-#ifndef _LBS_STORE_H
-#define _LBS_STORE_H
+#ifndef _LBS_TARSTORE_H
+#define _LBS_TARSTORE_H
#include <stdint.h>
+#include <libtar.h>
-#include <exception>
+#include <list>
#include <map>
+#include <set>
#include <string>
+#include <iostream>
#include <sstream>
+#include "sha1.h"
+
+class LbsObject;
+
/* In memory datatype to represent key/value pairs of information, such as file
* metadata. Currently implemented as map<string, string>. */
typedef std::map<std::string, std::string> dictionary;
std::string getError() const { return error; }
};
-/* OutputStream is an abstract interface for writing data without seeking.
- * Output could be to a file, to an object within a segment, or even to a
- * memory buffer to help serialize data. */
-class OutputStream {
+/* A simple wrapper around a single TAR file to represent a segment. Objects
+ * may only be written out all at once, since the tar header must be written
+ * first; incremental writing is not supported. */
+class Tarfile {
public:
- OutputStream();
- virtual ~OutputStream() { }
-
- // Write the given data buffer
- void write(const void *data, size_t len);
-
- // Return the total number of bytes written so far
- int64_t get_pos() const { return bytes_written; }
-
- // Convenience functions for writing other data types. Values are always
- // written out in little-endian order.
- void write_u8(uint8_t val);
- void write_u16(uint16_t val);
- void write_u32(uint32_t val);
- void write_u64(uint64_t val);
-
- void write_s32(int32_t val) { write_u32((uint32_t)val); }
- void write_s64(int64_t val) { write_u64((uint64_t)val); }
+ Tarfile(const std::string &path, const std::string &segment);
+ ~Tarfile();
- void write_varint(uint64_t val);
+ void write_object(int id, const char *data, size_t len);
- void write_string(const std::string &s);
- void write_dictionary(const dictionary &d);
+ // Return an estimate of the size of the file.
+ size_t size_estimate() { return size; }
-protected:
- // Function which actually causes a write: must be overridden by
- // implementation.
- virtual void write_internal(const void *data, size_t len) = 0;
+ void internal_write_object(const std::string &path,
+ const char *data, size_t len);
private:
- int64_t bytes_written;
+ size_t size;
+ std::string segment_name;
+ std::ostringstream checksums;
+ TAR *t;
};
-/* An OutputStream implementation which writes data to memory and returns the
- * result as a string. */
-class StringOutputStream : public OutputStream {
+class TarSegmentStore {
public:
- StringOutputStream();
- std::string contents() const { return buf.str(); }
+ // New segments will be stored in the given directory.
+ TarSegmentStore(const std::string &path) { this->path = path; }
+ ~TarSegmentStore() { sync(); }
-protected:
- virtual void write_internal(const void *data, size_t len);
+ // Writes an object to segment in the store, and returns the name
+ // (segment/object) to refer to it. The optional parameter group can be
+ // used to control object placement; objects with different group
+ // parameters are kept in separate segments.
+ std::string write_object(const char *data, size_t len,
+ const std::string &group = "",
+ const std::list<std::string> &refs = norefs);
+
+ // Ensure all segments have been fully written.
+ void sync();
private:
- std::stringstream buf;
+ struct segment_info {
+ Tarfile *file;
+ std::string name; // UUID
+ std::set<std::string> refs; // Other segments this one refers to
+ int count; // Objects written to this segment
+ };
+
+ std::string path;
+ std::map<std::string, struct segment_info *> segments;
+
+ // An empty list which can be used as an argument to write_object to
+ // indicate that this object depends on no others.
+ static std::list<std::string> norefs;
+
+ // Ensure that all segments in the given group have been fully written.
+ void close_segment(const std::string &group);
+
+ // Parse an object reference string and return just the segment name
+ // portion.
+ std::string object_reference_to_segment(const std::string &object);
};
-/* An OutputStream implementation which writes data via the C stdio layer. */
-class FileOutputStream : public OutputStream {
+/* An in-memory representation of an object, which can be incrementally built
+ * before it is written out to a segment. */
+class LbsObject {
public:
- explicit FileOutputStream(FILE *file);
- virtual ~FileOutputStream();
-
-protected:
- virtual void write_internal(const void *data, size_t len);
+ LbsObject();
+ ~LbsObject();
+
+ // If an object is placed in a group, it will be written out to segments
+ // only containing other objects in the same group. A group name is simply
+ // a string.
+ //std::string get_group() const { return group; }
+ void set_group(const std::string &g) { group = g; }
+
+ // Data in an object must be written all at once, and cannot be generated
+ // incrementally. Data can be an arbitrary block of binary data of any
+ // size. The pointer to the data need only remain valid until write() is
+ // called.
+ //const char *get_data() const { return data; }
+ //size_t get_data_len() const { return data_len; }
+ void set_data(const char *d, size_t len) { data = d; data_len = len; }
+
+ // Write an object to a segment, thus making it permanent. This function
+ // can be called at most once.
+ void write(TarSegmentStore *store);
+
+ // An object is assigned a permanent name once it has been written to a
+ // segment. Until that time, its name cannot be determined.
+ std::string get_name() const { return name; }
+
+ // Logically, one object may reference other objects (such as a metadata
+ // listing referncing actual file data blocks). Such references should be
+ // noted explicitly. It may eventually be used to build up a tree of
+ // checksums for later verifying integrity.
+ void add_reference(const LbsObject *o);
private:
- FILE *f;
-};
+ std::string group;
+ const char *data;
+ size_t data_len;
-/* Simple wrappers that encode integers using a StringOutputStream and return
- * the encoded result. */
-std::string encode_u16(uint16_t val);
-std::string encode_u32(uint32_t val);
-std::string encode_u64(uint64_t val);
+ bool written;
+ std::string name;
+
+ std::set<std::string> refs;
+};
-#endif // _LBS_STORE_H
+#endif // _LBS_TARSTORE_H
projects / cumulus.git / blobdiff