Pluggable libheimbase interface for DBs and misc libheimbase enhancements

[Code reviewed by Love Hörnquist Åstrand <lha@kth.se>]

    Added heim_db_*() entry points for dealing with databases, and
    make krb5_aname_to_localname() use it.

    The following enhancements to libheimbase are included:

     - Add heim_data_t and heim_string_t "reference" variants to
       avoid memory copies of potentially large data/strings.

       See heim_data_ref_create() and heim_string_ref_create().

     - Added enhancements to heim_array_t to allow their use for
       queues and stacks, and to improve performance.  See
       heim_array_insert_value().

     - Added XPath-like accessors for heim_object_t.  See
       heim_path_get(), heim_path_copy(), heim_path_create(), and
       heim_path_delete().  These are used extensively in the DB
       framework's generic composition of ACID support and in the
       test_base program

     - Made libheimbase more consistent with Core Foundation naming
       conventions.  See heim_{dict, array}_{get, copy}_value() and
       heim_path_{get, copy}().

     - Added functionality to and fixed bugs in base/json.c:
        - heim_serialize();
        - depth limit for JSON parsing (for DoS protection);
        - pretty-printing;
        - JSON compliance (see below);
        - flag options for parsing and serializing; these are needed
          because of impedance mismatches between heim_object_t and
          JSON (e.g., heim_dict_t allows non-string keys, but JSON
          does not; heimbase supports binary data, while JSON does
          not).

     - Added heim_error_enomem().

     - Enhanced the test_base program to test new functionality and
       to use heim_path*() to better test JSON encoding.  This
       includes some fuzz testing of JSON parsing, and running the
       test under valgrind.

     - Started to add doxygen documentation for libheimbase (but doc
       build for libheimbase is still incomplete).

    Note that there's still some incomplete JSON support:

     - JSON string quoting is not fully implemented;

     - libheimbase lacks support for real numbers, while JSON has
       it -- otherwise libheimbase is a superset of JSON,
       specifically in that any heim_object_t can be a key for an
       associative array.

    The following DB backends are supported natively:

     - "sorted-text", a binary search of sorted (in C locale), flat
       text files;

     - "json", a backend that stores DB contents serialized as JSON
       (this is intended for configuration-like contents).

    The DB framework supports:

     - multiple key/value tables per-DB
     - ACID transactions

    The DB framework also natively implements ACID transactions for
    any DB backends that a) do not provide transactions natively, b)
    do provide lock/unlock/sync methods (even on Windows).  This
    includes autocommit of DB updates outside transactions.

    Future DB enhancements may include:

     - add backends for various DB types (BDB, CDB, MDB, ...);

     - make libhdb use heim_db_t;

     - add a command-line tool for interfacing to databases via
       libheimbase (e.g., to get/set/delete values, create/copy/
       backup DBs, inspect history, check integrity);

     - framework-level transaction logging (with redo and undo
       logging), for generic incremental replication;

     - framework-level DB integrity checking.

       We could store a MAC of the XOR of a hash function applied to
       {key, value} for every entry in the DB, then use this to check
       DB integrity incrementally during incremental replication, as
       well as for the whole DB.

base/string.c

@@ -39,11 +39,37 @@
 static void
 string_dealloc(void *ptr)
 {
+    heim_string_t s = ptr;
+    heim_string_free_f_t *deallocp;
+    heim_string_free_f_t dealloc;
+
+    if (*(const char *)ptr != '\0')
+	return;
+
+    /* Possible string ref */
+    deallocp = _heim_get_isaextra(s, 0);
+    dealloc = *deallocp;
+    if (dealloc != NULL) {
+	char **strp = _heim_get_isaextra(s, 1);
+	dealloc(*strp);
+    }
 }
 
 static int
 string_cmp(void *a, void *b)
 {
+    if (*(char *)a == '\0') {
+	char **strp = _heim_get_isaextra(a, 1);
+
+	if (*strp != NULL)
+	    a = *strp; /* a is a string ref */
+    }
+    if (*(char *)b == '\0') {
+	char **strp = _heim_get_isaextra(b, 1);
+
+	if (*strp != NULL)
+	    b = *strp; /* b is a string ref */
+    }
     return strcmp(a, b);
 }
 
@@ -82,6 +108,43 @@ heim_string_create(const char *string)
     return heim_string_create_with_bytes(string, strlen(string));
 }
 
+/**
+ * Create a string object without copying the source.
+ *
+ * @param string the string to referenced, must be UTF-8
+ * @param dealloc the function to use to release the referece to the string
+ *
+ * @return string object
+ */
+
+heim_string_t
+heim_string_ref_create(const char *string, heim_string_free_f_t dealloc)
+{
+    heim_string_t s;
+    heim_string_free_f_t *deallocp;
+
+    s = _heim_alloc_object(&_heim_string_object, 1);
+    if (s) {
+	const char **strp;
+
+	((char *)s)[0] = '\0';
+	deallocp = _heim_get_isaextra(s, 0);
+	*deallocp = dealloc;
+	strp = _heim_get_isaextra(s, 1);
+	*strp = string;
+    }
+    return s;
+}
+
+/**
+ * Create a string object
+ *
+ * @param string the string to create, must be an utf8 string
+ * @param len the length of the string
+ *
+ * @return string object
+ */
+
 heim_string_t
 heim_string_create_with_bytes(const void *data, size_t len)
 {
@@ -118,6 +181,14 @@ heim_string_get_type_id(void)
 const char *
 heim_string_get_utf8(heim_string_t string)
 {
+    if (*(const char *)string == '\0') {
+	const char **strp;
+
+	/* String ref */
+	strp = _heim_get_isaextra(string, 1);
+	if (*strp != NULL)
+	    return *strp;
+    }
     return (const char *)string;
 }