Allow metadata to be written incrementally.

[cumulus.git] / store.h

diff --git a/store.h b/store.h
index 6acee7f..1ef5db4 100644 (file)
--- a/store.h
+++ b/store.h
@@ -6,8 +6,8 @@
  * is built on top of libtar, and represents segments as TAR files and objects
  * as files within them. */
 
-#ifndef _LBS_TARSTORE_H
-#define _LBS_TARSTORE_H
+#ifndef _LBS_STORE_H
+#define _LBS_STORE_H
 
 #include <stdint.h>
 #include <libtar.h>
@@ -20,6 +20,9 @@
 #include <sstream>
 
 #include "sha1.h"
+#include "ref.h"
+
+class LbsObject;
 
 /* In memory datatype to represent key/value pairs of information, such as file
  * metadata.  Currently implemented as map<string, string>. */
@@ -57,7 +60,6 @@ public:
 private:
     size_t size;
     std::string segment_name;
-    std::ostringstream checksums;
     TAR *t;
 };
 
@@ -71,9 +73,8 @@ public:
     // (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);
+    ObjectReference write_object(const char *data, size_t len,
+                                 const std::string &group = "");
 
     // Ensure all segments have been fully written.
     void sync();
@@ -82,17 +83,12 @@ private:
     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);
 
@@ -101,4 +97,46 @@ private:
     std::string object_reference_to_segment(const std::string &object);
 };
 
-#endif // _LBS_TARSTORE_H
+/* An in-memory representation of an object, which can be incrementally built
+ * before it is written out to a segment. */
+class LbsObject {
+public:
+    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.
+    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);
+
+    // Compute the checksum of an object, and include it in the object
+    // reference.  This should be called after write(), and the data specified
+    // by set_data() must remain valid through the call to checksum().
+    void checksum();
+
+    // 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 ref.to_string(); }
+    ObjectReference get_ref() { return ref; }
+
+private:
+    std::string group;
+    const char *data;
+    size_t data_len;
+
+    bool written;
+    ObjectReference ref;
+};
+
+#endif // _LBS_STORE_H