Add a new object-oriented wrapper for building object references.

[cumulus.git] / ref.h

diff --git a/ref.h b/ref.h
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+/* LBS: An LFS-inspired filesystem backup system
+ * Copyright (C) 2007  Michael Vrable
+ *
+ * Backups are structured as a collection of objects, which may refer to other
+ * objects.  Object references are used to name other objects or parts of them.
+ * This file defines the class for representing object references and the
+ * textual representation of these references. */
+
+#ifndef _LBS_REF_H
+#define _LBS_REF_H
+
+#include <string>
+
+/* ======================== Object Reference Syntax ========================
+ *
+ * Segments are groups of objects.  Segments are named by UUID, which is a
+ * 128-bit value.  The text representation is
+ *    <segment> ::= xxxxxxxx-xxxx-xxxx-xxxxxxxxxxxxxxxxx
+ * where each <x> is a lowercase hexadecimal digit ([0-9a-f]).
+ *
+ * Each object within a segment is assigned a sequence number, which is given
+ * as a hexadecimal value:
+ *    <object-seq> ::= xxxxxxxx
+ *
+ * An object can be uniquely named by the combination of segment name and
+ * object sequence number:
+ *    <object-name> ::= <segment> "/" <object-seq>
+ * Example: "cf47429e-a503-43ac-9c31-bb3175fbb820/0000002b"
+ *
+ * An object name may optionally be suffixed with a checksum, which allows
+ * checking the integrity of the referenced object.
+ *    <checksum> ::= <checksum-alg> "=" <checksum-value>
+ * Currently the only checksum-alg is "sha1", but others may be defined later.
+ * <checksum-value> is a hexadecimal string.  If included, the checksum is
+ * enclosed in parentheses.
+ *
+ * Each object is stored as a string of bytes, and object reference may specify
+ * a substring rather than the entire string using a range specifier.  If no
+ * range specifier is given, then by default the entire object is used.
+ *    <range> ::= <start> "+" <length>
+ * Both <start> and <length> are decimal values.  If included, the range is
+ * enclosed in brackets.
+ *
+ * When both a checksum and a range are included, note that the checksum is
+ * taken over the entire original object, before the range is taken into
+ * account.
+ *
+ * The full syntax for an object reference is:
+ *    <object-reference>
+ *      ::= <object-name> [ "(" <checksum> ")" ] [ "[" <range> "]" ]
+ * Example: "cf47429e-a503-43ac-9c31-bb3175fbb820/0000002b(sha1=b9f5d0a21b8d07356723f041f5463dec892654af)[1024+512]"
+ *
+ * Finally, in specific circumstances, and indirect reference may be used.  In
+ * cases where data could be listed directly, instead an object reference can
+ * be given, prefixed with "@", which indicates that the data stored at the
+ * referenced object should be treated as being included.
+ *    <indirect-reference> ::= "@" <object-reference>
+ */
+
+/* Generate a fresh UUID, suitable for use as a segment name. */
+std::string generate_uuid();
+
+/* Class representing an object reference, which allows it to be manipulated
+ * and converted to and from the text representation. */
+class ObjectReference {
+public:
+    ObjectReference(const std::string& segment, int sequence);
+
+    std::string to_string() const;
+
+    std::string get_segment() const { return segment; }
+    void set_segment(const std::string& segment) { this->segment = segment; }
+
+    bool has_checksum() const { return checksum_valid; }
+    std::string get_checksum() const { return checksum; }
+    void clear_checksum() { checksum = ""; checksum_valid = false; }
+    void set_checksum(const std::string& checksum)
+        { this->checksum = checksum; checksum_valid = true; }
+
+    bool has_range() const { return range_valid; }
+    size_t get_range_start() const { return range_start; }
+    size_t get_range_length() const { return range_length; }
+    void clear_range() { range_start = range_length = 0; range_valid = false; }
+    void set_range(size_t start, size_t length)
+        { range_start = start; range_length = length; range_valid = true; }
+
+private:
+    std::string segment, object, checksum;
+    size_t range_start, range_length;
+    bool checksum_valid, range_valid;
+};
+
+#endif // _LBS_REF_H