util/keyval.c

   1 /*
   2  * Parsing KEY=VALUE,... strings
   3  *
   4  * Copyright (C) 2017 Red Hat Inc.
   5  *
   6  * Authors:
   7  *  Markus Armbruster <armbru@redhat.com>,
   8  *
   9  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  10  * See the COPYING file in the top-level directory.
  11  */
  12
  13 /*
  14  * KEY=VALUE,... syntax:
  15  *
  16  *   key-vals     = [ key-val { ',' key-val } [ ',' ] ]
  17  *   key-val      = key '=' val
  18  *   key          = key-fragment { '.' key-fragment }
  19  *   key-fragment = / [^=,.]* /
  20  *   val          = { / [^,]* / | ',,' }
  21  *
  22  * Semantics defined by reduction to JSON:
  23  *
  24  *   key-vals specifies a JSON object, i.e. a tree whose root is an
  25  *   object, inner nodes other than the root are objects or arrays,
  26  *   and leaves are strings.
  27  *
  28  *   Each key-val = key-fragment '.' ... '=' val specifies a path from
  29  *   root to a leaf (left of '='), and the leaf's value (right of
  30  *   '=').
  31  *
  32  *   A path from the root is defined recursively:
  33  *       L '.' key-fragment is a child of the node denoted by path L
  34  *       key-fragment is a child of the tree root
  35  *   If key-fragment is numeric, the parent is an array and the child
  36  *   is its key-fragment-th member, counting from zero.
  37  *   Else, the parent is an object, and the child is its member named
  38  *   key-fragment.
  39  *
  40  *   This constrains inner nodes to be either array or object.  The
  41  *   constraints must be satisfiable.  Counter-example: a.b=1,a=2 is
  42  *   not, because root.a must be an object to satisfy a.b=1 and a
  43  *   string to satisfy a=2.
  44  *
  45  *   Array subscripts can occur in any order, but the set of
  46  *   subscripts must not have gaps.  For instance, a.1=v is not okay,
  47  *   because root.a[0] is missing.
  48  *
  49  *   If multiple key-val denote the same leaf, the last one determines
  50  *   the value.
  51  *
  52  * Key-fragments must be valid QAPI names or consist only of decimal
  53  * digits.
  54  *
  55  * The length of any key-fragment must be between 1 and 127.
  56  *
  57  * Design flaw: there is no way to denote an empty array or non-root
  58  * object.  While interpreting "key absent" as empty seems natural
  59  * (removing a key-val from the input string removes the member when
  60  * there are more, so why not when it's the last), it doesn't work:
  61  * "key absent" already means "optional object/array absent", which
  62  * isn't the same as "empty object/array present".
  63  *
  64  * Design flaw: scalar values can only be strings; there is no way to
  65  * denote numbers, true, false or null.  The special QObject input
  66  * visitor returned by qobject_input_visitor_new_keyval() mostly hides
  67  * this by automatically converting strings to the type the visitor
  68  * expects.  Breaks down for type 'any', where the visitor's
  69  * expectation isn't clear.  Code visiting 'any' needs to do the
  70  * conversion itself, but only when using this keyval visitor.
  71  * Awkward.  Note that we carefully restrict alternate types to avoid
  72  * similar ambiguity.
  73  *
  74  * Additional syntax for use with an implied key:
  75  *
  76  *   key-vals-ik  = val-no-key [ ',' key-vals ]
  77  *   val-no-key   = / [^=,]* /
  78  *
  79  * where no-key is syntactic sugar for implied-key=val-no-key.
  80  */
  81
  82 #include "qemu/osdep.h"
  83 #include "qapi/error.h"
  84 #include "qapi/qmp/qdict.h"
  85 #include "qapi/qmp/qlist.h"
  86 #include "qapi/qmp/qstring.h"
  87 #include "qemu/cutils.h"
  88 #include "qemu/option.h"
  89
  90 /*
  91  * Convert @key to a list index.
  92  * Convert all leading decimal digits to a (non-negative) number,
  93  * capped at INT_MAX.
  94  * If @end is non-null, assign a pointer to the first character after
  95  * the number to *@end.
  96  * Else, fail if any characters follow.
  97  * On success, return the converted number.
  98  * On failure, return a negative value.
  99  * Note: since only digits are converted, no two keys can map to the
 100  * same number, except by overflow to INT_MAX.
 101  */
 102 static int key_to_index(const char *key, const char **end)
 103 {
 104     int ret;
 105     unsigned long index;
 106
 107     if (*key < '0' || *key > '9') {
 108         return -EINVAL;
 109     }
 110     ret = qemu_strtoul(key, end, 10, &index);
 111     if (ret) {
 112         return ret == -ERANGE ? INT_MAX : ret;
 113     }
 114     return index <= INT_MAX ? index : INT_MAX;
 115 }
 116
 117 /*
 118  * Ensure @cur maps @key_in_cur the right way.
 119  * If @value is null, it needs to map to a QDict, else to this
 120  * QString.
 121  * If @cur doesn't have @key_in_cur, put an empty QDict or @value,
 122  * respectively.
 123  * Else, if it needs to map to a QDict, and already does, do nothing.
 124  * Else, if it needs to map to this QString, and already maps to a
 125  * QString, replace it by @value.
 126  * Else, fail because we have conflicting needs on how to map
 127  * @key_in_cur.
 128  * In any case, take over the reference to @value, i.e. if the caller
 129  * wants to hold on to a reference, it needs to qobject_ref().
 130  * Use @key up to @key_cursor to identify the key in error messages.
 131  * On success, return the mapped value.
 132  * On failure, store an error through @errp and return NULL.
 133  */
 134 static QObject *keyval_parse_put(QDict *cur,
 135                                  const char *key_in_cur, QString *value,
 136                                  const char *key, const char *key_cursor,
 137                                  Error **errp)
 138 {
 139     QObject *old, *new;
 140
 141     old = qdict_get(cur, key_in_cur);
 142     if (old) {
 143         if (qobject_type(old) != (value ? QTYPE_QSTRING : QTYPE_QDICT)) {
 144             error_setg(errp, "Parameters '%.*s.*' used inconsistently",
 145                        (int)(key_cursor - key), key);
 146             qobject_unref(value);
 147             return NULL;
 148         }
 149         if (!value) {
 150             return old;         /* already QDict, do nothing */
 151         }
 152         new = QOBJECT(value);   /* replacement */
 153     } else {
 154         new = value ? QOBJECT(value) : QOBJECT(qdict_new());
 155     }
 156     qdict_put_obj(cur, key_in_cur, new);
 157     return new;
 158 }
 159
 160 /*
 161  * Parse one KEY=VALUE from @params, store result in @qdict.
 162  * The first fragment of KEY applies to @qdict.  Subsequent fragments
 163  * apply to nested QDicts, which are created on demand.  @implied_key
 164  * is as in keyval_parse().
 165  * On success, return a pointer to the next KEY=VALUE, or else to '\0'.
 166  * On failure, return NULL.
 167  */
 168 static const char *keyval_parse_one(QDict *qdict, const char *params,
 169                                     const char *implied_key,
 170                                     Error **errp)
 171 {
 172     const char *key, *key_end, *s, *end;
 173     size_t len;
 174     char key_in_cur[128];
 175     QDict *cur;
 176     int ret;
 177     QObject *next;
 178     QString *val;
 179
 180     key = params;
 181     len = strcspn(params, "=,");
 182     if (implied_key && len && key[len] != '=') {
 183         /* Desugar implied key */
 184         key = implied_key;
 185         len = strlen(implied_key);
 186     }
 187     key_end = key + len;
 188
 189     /*
 190      * Loop over key fragments: @s points to current fragment, it
 191      * applies to @cur.  @key_in_cur[] holds the previous fragment.
 192      */
 193     cur = qdict;
 194     s = key;
 195     for (;;) {
 196         /* Want a key index (unless it's first) or a QAPI name */
 197         if (s != key && key_to_index(s, &end) >= 0) {
 198             len = end - s;
 199         } else {
 200             ret = parse_qapi_name(s, false);
 201             len = ret < 0 ? 0 : ret;
 202         }
 203         assert(s + len <= key_end);
 204         if (!len || (s + len < key_end && s[len] != '.')) {
 205             assert(key != implied_key);
 206             error_setg(errp, "Invalid parameter '%.*s'",
 207                        (int)(key_end - key), key);
 208             return NULL;
 209         }
 210         if (len >= sizeof(key_in_cur)) {
 211             assert(key != implied_key);
 212             error_setg(errp, "Parameter%s '%.*s' is too long",
 213                        s != key || s + len != key_end ? " fragment" : "",
 214                        (int)len, s);
 215             return NULL;
 216         }
 217
 218         if (s != key) {
 219             next = keyval_parse_put(cur, key_in_cur, NULL,
 220                                     key, s - 1, errp);
 221             if (!next) {
 222                 return NULL;
 223             }
 224             cur = qobject_to(QDict, next);
 225             assert(cur);
 226         }
 227
 228         memcpy(key_in_cur, s, len);
 229         key_in_cur[len] = 0;
 230         s += len;
 231
 232         if (*s != '.') {
 233             break;
 234         }
 235         s++;
 236     }
 237
 238     if (key == implied_key) {
 239         assert(!*s);
 240         s = params;
 241     } else {
 242         if (*s != '=') {
 243             error_setg(errp, "Expected '=' after parameter '%.*s'",
 244                        (int)(s - key), key);
 245             return NULL;
 246         }
 247         s++;
 248     }
 249
 250     val = qstring_new();
 251     for (;;) {
 252         if (!*s) {
 253             break;
 254         } else if (*s == ',') {
 255             s++;
 256             if (*s != ',') {
 257                 break;
 258             }
 259         }
 260         qstring_append_chr(val, *s++);
 261     }
 262
 263     if (!keyval_parse_put(cur, key_in_cur, val, key, key_end, errp)) {
 264         return NULL;
 265     }
 266     return s;
 267 }
 268
 269 static char *reassemble_key(GSList *key)
 270 {
 271     GString *s = g_string_new("");
 272     GSList *p;
 273
 274     for (p = key; p; p = p->next) {
 275         g_string_prepend_c(s, '.');
 276         g_string_prepend(s, (char *)p->data);
 277     }
 278
 279     return g_string_free(s, FALSE);
 280 }
 281
 282 /*
 283  * Listify @cur recursively.
 284  * Replace QDicts whose keys are all valid list indexes by QLists.
 285  * @key_of_cur is the list of key fragments leading up to @cur.
 286  * On success, return either @cur or its replacement.
 287  * On failure, store an error through @errp and return NULL.
 288  */
 289 static QObject *keyval_listify(QDict *cur, GSList *key_of_cur, Error **errp)
 290 {
 291     GSList key_node;
 292     bool has_index, has_member;
 293     const QDictEntry *ent;
 294     QDict *qdict;
 295     QObject *val;
 296     char *key;
 297     size_t nelt;
 298     QObject **elt;
 299     int index, max_index, i;
 300     QList *list;
 301
 302     key_node.next = key_of_cur;
 303
 304     /*
 305      * Recursively listify @cur's members, and figure out whether @cur
 306      * itself is to be listified.
 307      */
 308     has_index = false;
 309     has_member = false;
 310     for (ent = qdict_first(cur); ent; ent = qdict_next(cur, ent)) {
 311         if (key_to_index(ent->key, NULL) >= 0) {
 312             has_index = true;
 313         } else {
 314             has_member = true;
 315         }
 316
 317         qdict = qobject_to(QDict, ent->value);
 318         if (!qdict) {
 319             continue;
 320         }
 321
 322         key_node.data = ent->key;
 323         val = keyval_listify(qdict, &key_node, errp);
 324         if (!val) {
 325             return NULL;
 326         }
 327         if (val != ent->value) {
 328             qdict_put_obj(cur, ent->key, val);
 329         }
 330     }
 331
 332     if (has_index && has_member) {
 333         key = reassemble_key(key_of_cur);
 334         error_setg(errp, "Parameters '%s*' used inconsistently", key);
 335         g_free(key);
 336         return NULL;
 337     }
 338     if (!has_index) {
 339         return QOBJECT(cur);
 340     }
 341
 342     /* Copy @cur's values to @elt[] */
 343     nelt = qdict_size(cur) + 1; /* one extra, for use as sentinel */
 344     elt = g_new0(QObject *, nelt);
 345     max_index = -1;
 346     for (ent = qdict_first(cur); ent; ent = qdict_next(cur, ent)) {
 347         index = key_to_index(ent->key, NULL);
 348         assert(index >= 0);
 349         if (index > max_index) {
 350             max_index = index;
 351         }
 352         /*
 353          * We iterate @nelt times.  If we get one exceeding @nelt
 354          * here, we will put less than @nelt values into @elt[],
 355          * triggering the error in the next loop.
 356          */
 357         if ((size_t)index >= nelt - 1) {
 358             continue;
 359         }
 360         /* Even though dict keys are distinct, indexes need not be */
 361         elt[index] = ent->value;
 362     }
 363
 364     /*
 365      * Make a list from @elt[], reporting the first missing element,
 366      * if any.
 367      * If we dropped an index >= nelt in the previous loop, this loop
 368      * will run into the sentinel and report index @nelt missing.
 369      */
 370     list = qlist_new();
 371     assert(!elt[nelt-1]);       /* need the sentinel to be null */
 372     for (i = 0; i < MIN(nelt, max_index + 1); i++) {
 373         if (!elt[i]) {
 374             key = reassemble_key(key_of_cur);
 375             error_setg(errp, "Parameter '%s%d' missing", key, i);
 376             g_free(key);
 377             g_free(elt);
 378             qobject_unref(list);
 379             return NULL;
 380         }
 381         qobject_ref(elt[i]);
 382         qlist_append_obj(list, elt[i]);
 383     }
 384
 385     g_free(elt);
 386     return QOBJECT(list);
 387 }
 388
 389 /*
 390  * Parse @params in QEMU's traditional KEY=VALUE,... syntax.
 391  * If @implied_key, the first KEY= can be omitted.  @implied_key is
 392  * implied then, and VALUE can't be empty or contain ',' or '='.
 393  * On success, return a dictionary of the parsed keys and values.
 394  * On failure, store an error through @errp and return NULL.
 395  */
 396 QDict *keyval_parse(const char *params, const char *implied_key,
 397                     Error **errp)
 398 {
 399     QDict *qdict = qdict_new();
 400     QObject *listified;
 401     const char *s;
 402
 403     s = params;
 404     while (*s) {
 405         s = keyval_parse_one(qdict, s, implied_key, errp);
 406         if (!s) {
 407             qobject_unref(qdict);
 408             return NULL;
 409         }
 410         implied_key = NULL;
 411     }
 412
 413     listified = keyval_listify(qdict, NULL, errp);
 414     if (!listified) {
 415         qobject_unref(qdict);
 416         return NULL;
 417     }
 418     assert(listified == QOBJECT(qdict));
 419     return qdict;
 420 }