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/qstring.h"
  85 #include "qemu/cutils.h"
  86 #include "qemu/option.h"
  87
  88 /*
  89  * Convert @key to a list index.
  90  * Convert all leading decimal digits to a (non-negative) number,
  91  * capped at INT_MAX.
  92  * If @end is non-null, assign a pointer to the first character after
  93  * the number to *@end.
  94  * Else, fail if any characters follow.
  95  * On success, return the converted number.
  96  * On failure, return a negative value.
  97  * Note: since only digits are converted, no two keys can map to the
  98  * same number, except by overflow to INT_MAX.
  99  */
 100 static int key_to_index(const char *key, const char **end)
 101 {
 102     int ret;
 103     unsigned long index;
 104
 105     if (*key < '0' || *key > '9') {
 106         return -EINVAL;
 107     }
 108     ret = qemu_strtoul(key, end, 10, &index);
 109     if (ret) {
 110         return ret == -ERANGE ? INT_MAX : ret;
 111     }
 112     return index <= INT_MAX ? index : INT_MAX;
 113 }
 114
 115 /*
 116  * Ensure @cur maps @key_in_cur the right way.
 117  * If @value is null, it needs to map to a QDict, else to this
 118  * QString.
 119  * If @cur doesn't have @key_in_cur, put an empty QDict or @value,
 120  * respectively.
 121  * Else, if it needs to map to a QDict, and already does, do nothing.
 122  * Else, if it needs to map to this QString, and already maps to a
 123  * QString, replace it by @value.
 124  * Else, fail because we have conflicting needs on how to map
 125  * @key_in_cur.
 126  * In any case, take over the reference to @value, i.e. if the caller
 127  * wants to hold on to a reference, it needs to QINCREF().
 128  * Use @key up to @key_cursor to identify the key in error messages.
 129  * On success, return the mapped value.
 130  * On failure, store an error through @errp and return NULL.
 131  */
 132 static QObject *keyval_parse_put(QDict *cur,
 133                                  const char *key_in_cur, QString *value,
 134                                  const char *key, const char *key_cursor,
 135                                  Error **errp)
 136 {
 137     QObject *old, *new;
 138
 139     old = qdict_get(cur, key_in_cur);
 140     if (old) {
 141         if (qobject_type(old) != (value ? QTYPE_QSTRING : QTYPE_QDICT)) {
 142             error_setg(errp, "Parameters '%.*s.*' used inconsistently",
 143                        (int)(key_cursor - key), key);
 144             QDECREF(value);
 145             return NULL;
 146         }
 147         if (!value) {
 148             return old;         /* already QDict, do nothing */
 149         }
 150         new = QOBJECT(value);   /* replacement */
 151     } else {
 152         new = value ? QOBJECT(value) : QOBJECT(qdict_new());
 153     }
 154     qdict_put_obj(cur, key_in_cur, new);
 155     return new;
 156 }
 157
 158 /*
 159  * Parse one KEY=VALUE from @params, store result in @qdict.
 160  * The first fragment of KEY applies to @qdict.  Subsequent fragments
 161  * apply to nested QDicts, which are created on demand.  @implied_key
 162  * is as in keyval_parse().
 163  * On success, return a pointer to the next KEY=VALUE, or else to '\0'.
 164  * On failure, return NULL.
 165  */
 166 static const char *keyval_parse_one(QDict *qdict, const char *params,
 167                                     const char *implied_key,
 168                                     Error **errp)
 169 {
 170     const char *key, *key_end, *s, *end;
 171     size_t len;
 172     char key_in_cur[128];
 173     QDict *cur;
 174     int ret;
 175     QObject *next;
 176     QString *val;
 177
 178     key = params;
 179     len = strcspn(params, "=,");
 180     if (implied_key && len && key[len] != '=') {
 181         /* Desugar implied key */
 182         key = implied_key;
 183         len = strlen(implied_key);
 184     }
 185     key_end = key + len;
 186
 187     /*
 188      * Loop over key fragments: @s points to current fragment, it
 189      * applies to @cur.  @key_in_cur[] holds the previous fragment.
 190      */
 191     cur = qdict;
 192     s = key;
 193     for (;;) {
 194         /* Want a key index (unless it's first) or a QAPI name */
 195         if (s != key && key_to_index(s, &end) >= 0) {
 196             len = end - s;
 197         } else {
 198             ret = parse_qapi_name(s, false);
 199             len = ret < 0 ? 0 : ret;
 200         }
 201         assert(s + len <= key_end);
 202         if (!len || (s + len < key_end && s[len] != '.')) {
 203             assert(key != implied_key);
 204             error_setg(errp, "Invalid parameter '%.*s'",
 205                        (int)(key_end - key), key);
 206             return NULL;
 207         }
 208         if (len >= sizeof(key_in_cur)) {
 209             assert(key != implied_key);
 210             error_setg(errp, "Parameter%s '%.*s' is too long",
 211                        s != key || s + len != key_end ? " fragment" : "",
 212                        (int)len, s);
 213             return NULL;
 214         }
 215
 216         if (s != key) {
 217             next = keyval_parse_put(cur, key_in_cur, NULL,
 218                                     key, s - 1, errp);
 219             if (!next) {
 220                 return NULL;
 221             }
 222             cur = qobject_to_qdict(next);
 223             assert(cur);
 224         }
 225
 226         memcpy(key_in_cur, s, len);
 227         key_in_cur[len] = 0;
 228         s += len;
 229
 230         if (*s != '.') {
 231             break;
 232         }
 233         s++;
 234     }
 235
 236     if (key == implied_key) {
 237         assert(!*s);
 238         s = params;
 239     } else {
 240         if (*s != '=') {
 241             error_setg(errp, "Expected '=' after parameter '%.*s'",
 242                        (int)(s - key), key);
 243             return NULL;
 244         }
 245         s++;
 246     }
 247
 248     val = qstring_new();
 249     for (;;) {
 250         if (!*s) {
 251             break;
 252         } else if (*s == ',') {
 253             s++;
 254             if (*s != ',') {
 255                 break;
 256             }
 257         }
 258         qstring_append_chr(val, *s++);
 259     }
 260
 261     if (!keyval_parse_put(cur, key_in_cur, val, key, key_end, errp)) {
 262         return NULL;
 263     }
 264     return s;
 265 }
 266
 267 static char *reassemble_key(GSList *key)
 268 {
 269     GString *s = g_string_new("");
 270     GSList *p;
 271
 272     for (p = key; p; p = p->next) {
 273         g_string_prepend_c(s, '.');
 274         g_string_prepend(s, (char *)p->data);
 275     }
 276
 277     return g_string_free(s, FALSE);
 278 }
 279
 280 /*
 281  * Listify @cur recursively.
 282  * Replace QDicts whose keys are all valid list indexes by QLists.
 283  * @key_of_cur is the list of key fragments leading up to @cur.
 284  * On success, return either @cur or its replacement.
 285  * On failure, store an error through @errp and return NULL.
 286  */
 287 static QObject *keyval_listify(QDict *cur, GSList *key_of_cur, Error **errp)
 288 {
 289     GSList key_node;
 290     bool has_index, has_member;
 291     const QDictEntry *ent;
 292     QDict *qdict;
 293     QObject *val;
 294     char *key;
 295     size_t nelt;
 296     QObject **elt;
 297     int index, max_index, i;
 298     QList *list;
 299
 300     key_node.next = key_of_cur;
 301
 302     /*
 303      * Recursively listify @cur's members, and figure out whether @cur
 304      * itself is to be listified.
 305      */
 306     has_index = false;
 307     has_member = false;
 308     for (ent = qdict_first(cur); ent; ent = qdict_next(cur, ent)) {
 309         if (key_to_index(ent->key, NULL) >= 0) {
 310             has_index = true;
 311         } else {
 312             has_member = true;
 313         }
 314
 315         qdict = qobject_to_qdict(ent->value);
 316         if (!qdict) {
 317             continue;
 318         }
 319
 320         key_node.data = ent->key;
 321         val = keyval_listify(qdict, &key_node, errp);
 322         if (!val) {
 323             return NULL;
 324         }
 325         if (val != ent->value) {
 326             qdict_put_obj(cur, ent->key, val);
 327         }
 328     }
 329
 330     if (has_index && has_member) {
 331         key = reassemble_key(key_of_cur);
 332         error_setg(errp, "Parameters '%s*' used inconsistently", key);
 333         g_free(key);
 334         return NULL;
 335     }
 336     if (!has_index) {
 337         return QOBJECT(cur);
 338     }
 339
 340     /* Copy @cur's values to @elt[] */
 341     nelt = qdict_size(cur) + 1; /* one extra, for use as sentinel */
 342     elt = g_new0(QObject *, nelt);
 343     max_index = -1;
 344     for (ent = qdict_first(cur); ent; ent = qdict_next(cur, ent)) {
 345         index = key_to_index(ent->key, NULL);
 346         assert(index >= 0);
 347         if (index > max_index) {
 348             max_index = index;
 349         }
 350         /*
 351          * We iterate @nelt times.  If we get one exceeding @nelt
 352          * here, we will put less than @nelt values into @elt[],
 353          * triggering the error in the next loop.
 354          */
 355         if ((size_t)index >= nelt - 1) {
 356             continue;
 357         }
 358         /* Even though dict keys are distinct, indexes need not be */
 359         elt[index] = ent->value;
 360     }
 361
 362     /*
 363      * Make a list from @elt[], reporting the first missing element,
 364      * if any.
 365      * If we dropped an index >= nelt in the previous loop, this loop
 366      * will run into the sentinel and report index @nelt missing.
 367      */
 368     list = qlist_new();
 369     assert(!elt[nelt-1]);       /* need the sentinel to be null */
 370     for (i = 0; i < MIN(nelt, max_index + 1); i++) {
 371         if (!elt[i]) {
 372             key = reassemble_key(key_of_cur);
 373             error_setg(errp, "Parameter '%s%d' missing", key, i);
 374             g_free(key);
 375             g_free(elt);
 376             QDECREF(list);
 377             return NULL;
 378         }
 379         qobject_incref(elt[i]);
 380         qlist_append_obj(list, elt[i]);
 381     }
 382
 383     g_free(elt);
 384     return QOBJECT(list);
 385 }
 386
 387 /*
 388  * Parse @params in QEMU's traditional KEY=VALUE,... syntax.
 389  * If @implied_key, the first KEY= can be omitted.  @implied_key is
 390  * implied then, and VALUE can't be empty or contain ',' or '='.
 391  * On success, return a dictionary of the parsed keys and values.
 392  * On failure, store an error through @errp and return NULL.
 393  */
 394 QDict *keyval_parse(const char *params, const char *implied_key,
 395                     Error **errp)
 396 {
 397     QDict *qdict = qdict_new();
 398     QObject *listified;
 399     const char *s;
 400
 401     s = params;
 402     while (*s) {
 403         s = keyval_parse_one(qdict, s, implied_key, errp);
 404         if (!s) {
 405             QDECREF(qdict);
 406             return NULL;
 407         }
 408         implied_key = NULL;
 409     }
 410
 411     listified = keyval_listify(qdict, NULL, errp);
 412     if (!listified) {
 413         QDECREF(qdict);
 414         return NULL;
 415     }
 416     assert(listified == QOBJECT(qdict));
 417     return qdict;
 418 }