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/error.c

@@ -75,6 +75,13 @@ struct heim_type_data _heim_error_object = {
     error_hash
 };
 
+heim_error_t
+heim_error_enomem(void)
+{
+    /* This is an immediate object; see heim_number_create() */
+    return (heim_error_t)heim_number_create(ENOMEM);
+}
+
 heim_error_t
 heim_error_create(int error_code, const char *fmt, ...)
 {
@@ -94,14 +101,17 @@ heim_error_createv(int error_code, const char *fmt, va_list ap)
     heim_error_t e;
     char *str;
     int len;
+    int save_errno = errno;
 
     str = malloc(1024);
+    errno = save_errno;
     if (str == NULL)
-        return NULL;
+        return heim_error_enomem();
     len = vsnprintf(str, 1024, fmt, ap);
+    errno = save_errno;
     if (len < 0) {
         free(str);
-	return NULL;
+	return NULL; /* XXX We should have a special heim_error_t for this */
     }
 
     e = _heim_alloc_object(&_heim_error_object, sizeof(struct heim_error));
@@ -111,12 +121,18 @@ heim_error_createv(int error_code, const char *fmt, va_list ap)
     }
     free(str);
 
+    errno = save_errno;
     return e;
 }
 
 heim_string_t
 heim_error_copy_string(heim_error_t error)
 {
+    if (heim_get_tid(error) != HEIM_TID_ERROR) {
+	if (heim_get_tid(error) == heim_number_get_type_id())
+	    return __heim_string_constant(strerror(heim_number_get_int((heim_number_t)error)));
+	heim_abort("invalid heim_error_t");
+    }
     /* XXX concat all strings */
     return heim_retain(error->msg);
 }
@@ -124,12 +140,22 @@ heim_error_copy_string(heim_error_t error)
 int
 heim_error_get_code(heim_error_t error)
 {
+    if (heim_get_tid(error) != HEIM_TID_ERROR) {
+	if (heim_get_tid(error) == heim_number_get_type_id())
+	    return heim_number_get_int((heim_number_t)error);
+	heim_abort("invalid heim_error_t");
+    }
     return error->error_code;
 }
 
 heim_error_t
 heim_error_append(heim_error_t top, heim_error_t append)
 {
+    if (heim_get_tid(top) != HEIM_TID_ERROR) {
+	if (heim_get_tid(top) == heim_number_get_type_id())
+	    return top;
+	heim_abort("invalid heim_error_t");
+    }
     if (top->next)
 	heim_release(top->next);
     top->next = heim_retain(append);