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 alternate types and type 'any', where the
  69  * visitor's expectation isn't clear.  Code visiting such types needs
  70  * to do the conversion itself, but only when using this keyval
  71  * visitor.  Awkward.  Alternate types without a string member don't
  72  * work at all.
  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 "qapi/util.h"
  86 #include "qemu/cutils.h"
  87 #include "qemu/option.h"
  88
  89 /*
  90  * Convert @key to a list index.
  91  * Convert all leading decimal digits to a (non-negative) number,
  92  * capped at INT_MAX.
  93  * If @end is non-null, assign a pointer to the first character after
  94  * the number to *@end.
  95  * Else, fail if any characters follow.
  96  * On success, return the converted number.
  97  * On failure, return a negative value.
  98  * Note: since only digits are converted, no two keys can map to the
  99  * same number, except by overflow to INT_MAX.
 100  */
 101 static int key_to_index(const char *key, const char **end)
 102 {
 103     int ret;
 104     unsigned long index;
 105
 106     if (*key < '0' || *key > '9') {
 107         return -EINVAL;
 108     }
 109     ret = qemu_strtoul(key, end, 10, &index);
 110     if (ret) {
 111         return ret == -ERANGE ? INT_MAX : ret;
 112     }
 113     return index <= INT_MAX ? index : INT_MAX;
 114 }
 115
 116 /*
 117  * Ensure @cur maps @key_in_cur the right way.
 118  * If @value is null, it needs to map to a QDict, else to this
 119  * QString.
 120  * If @cur doesn't have @key_in_cur, put an empty QDict or @value,
 121  * respectively.
 122  * Else, if it needs to map to a QDict, and already does, do nothing.
 123  * Else, if it needs to map to this QString, and already maps to a
 124  * QString, replace it by @value.
 125  * Else, fail because we have conflicting needs on how to map
 126  * @key_in_cur.
 127  * In any case, take over the reference to @value, i.e. if the caller
 128  * wants to hold on to a reference, it needs to QINCREF().
 129  * Use @key up to @key_cursor to identify the key in error messages.
 130  * On success, return the mapped value.
 131  * On failure, store an error through @errp and return NULL.
 132  */
 133 static QObject *keyval_parse_put(QDict *cur,
 134                                  const char *key_in_cur, QString *value,
 135                                  const char *key, const char *key_cursor,
 136                                  Error **errp)
 137 {
 138     QObject *old, *new;
 139
 140     old = qdict_get(cur, key_in_cur);
 141     if (old) {
 142         if (qobject_type(old) != (value ? QTYPE_QSTRING : QTYPE_QDICT)) {
 143             error_setg(errp, "Parameters '%.*s.*' used inconsistently",
 144                        (int)(key_cursor - key), key);
 145             QDECREF(value);
 146             return NULL;
 147         }
 148         if (!value) {
 149             return old;         /* already QDict, do nothing */
 150         }
 151         new = QOBJECT(value);   /* replacement */
 152     } else {
 153         new = value ? QOBJECT(value) : QOBJECT(qdict_new());
 154     }
 155     qdict_put_obj(cur, key_in_cur, new);
 156     return new;
 157 }
 158
 159 /*
 160  * Parse one KEY=VALUE from @params, store result in @qdict.
 161  * The first fragment of KEY applies to @qdict.  Subsequent fragments
 162  * apply to nested QDicts, which are created on demand.  @implied_key
 163  * is as in keyval_parse().
 164  * On success, return a pointer to the next KEY=VALUE, or else to '\0'.
 165  * On failure, return NULL.
 166  */
 167 static const char *keyval_parse_one(QDict *qdict, const char *params,
 168                                     const char *implied_key,
 169                                     Error **errp)
 170 {
 171     const char *key, *key_end, *s, *end;
 172     size_t len;
 173     char key_in_cur[128];
 174     QDict *cur;
 175     int ret;
 176     QObject *next;
 177     QString *val;
 178
 179     key = params;
 180     len = strcspn(params, "=,");
 181     if (implied_key && len && key[len] != '=') {
 182         /* Desugar implied key */
 183         key = implied_key;
 184         len = strlen(implied_key);
 185     }
 186     key_end = key + len;
 187
 188     /*
 189      * Loop over key fragments: @s points to current fragment, it
 190      * applies to @cur.  @key_in_cur[] holds the previous fragment.
 191      */
 192     cur = qdict;
 193     s = key;
 194     for (;;) {
 195         /* Want a key index (unless it's first) or a QAPI name */
 196         if (s != key && key_to_index(s, &end) >= 0) {
 197             len = end - s;
 198         } else {
 199             ret = parse_qapi_name(s, false);
 200             len = ret < 0 ? 0 : ret;
 201         }
 202         assert(s + len <= key_end);
 203         if (!len || (s + len < key_end && s[len] != '.')) {
 204             assert(key != implied_key);
 205             error_setg(errp, "Invalid parameter '%.*s'",
 206                        (int)(key_end - key), key);
 207             return NULL;
 208         }
 209         if (len >= sizeof(key_in_cur)) {
 210             assert(key != implied_key);
 211             error_setg(errp, "Parameter%s '%.*s' is too long",
 212                        s != key || s + len != key_end ? " fragment" : "",
 213                        (int)len, s);
 214             return NULL;
 215         }
 216
 217         if (s != key) {
 218             next = keyval_parse_put(cur, key_in_cur, NULL,
 219                                     key, s - 1, errp);
 220             if (!next) {
 221                 return NULL;
 222             }
 223             cur = qobject_to_qdict(next);
 224             assert(cur);
 225         }
 226
 227         memcpy(key_in_cur, s, len);
 228         key_in_cur[len] = 0;
 229         s += len;
 230
 231         if (*s != '.') {
 232             break;
 233         }
 234         s++;
 235     }
 236
 237     if (key == implied_key) {
 238         assert(!*s);
 239         s = params;
 240     } else {
 241         if (*s != '=') {
 242             error_setg(errp, "Expected '=' after parameter '%.*s'",
 243                        (int)(s - key), key);
 244             return NULL;
 245         }
 246         s++;
 247     }
 248
 249     val = qstring_new();
 250     for (;;) {
 251         if (!*s) {
 252             break;
 253         } else if (*s == ',') {
 254             s++;
 255             if (*s != ',') {
 256                 break;
 257             }
 258         }
 259         qstring_append_chr(val, *s++);
 260     }
 261
 262     if (!keyval_parse_put(cur, key_in_cur, val, key, key_end, errp)) {
 263         return NULL;
 264     }
 265     return s;
 266 }
 267
 268 static char *reassemble_key(GSList *key)
 269 {
 270     GString *s = g_string_new("");
 271     GSList *p;
 272
 273     for (p = key; p; p = p->next) {
 274         g_string_prepend_c(s, '.');
 275         g_string_prepend(s, (char *)p->data);
 276     }
 277
 278     return g_string_free(s, FALSE);
 279 }
 280
 281 /*
 282  * Listify @cur recursively.
 283  * Replace QDicts whose keys are all valid list indexes by QLists.
 284  * @key_of_cur is the list of key fragments leading up to @cur.
 285  * On success, return either @cur or its replacement.
 286  * On failure, store an error through @errp and return NULL.
 287  */
 288 static QObject *keyval_listify(QDict *cur, GSList *key_of_cur, Error **errp)
 289 {
 290     GSList key_node;
 291     bool has_index, has_member;
 292     const QDictEntry *ent;
 293     QDict *qdict;
 294     QObject *val;
 295     char *key;
 296     size_t nelt;
 297     QObject **elt;
 298     int index, max_index, i;
 299     QList *list;
 300
 301     key_node.next = key_of_cur;
 302
 303     /*
 304      * Recursively listify @cur's members, and figure out whether @cur
 305      * itself is to be listified.
 306      */
 307     has_index = false;
 308     has_member = false;
 309     for (ent = qdict_first(cur); ent; ent = qdict_next(cur, ent)) {
 310         if (key_to_index(ent->key, NULL) >= 0) {
 311             has_index = true;
 312         } else {
 313             has_member = true;
 314         }
 315
 316         qdict = qobject_to_qdict(ent->value);
 317         if (!qdict) {
 318             continue;
 319         }
 320
 321         key_node.data = ent->key;
 322         val = keyval_listify(qdict, &key_node, errp);
 323         if (!val) {
 324             return NULL;
 325         }
 326         if (val != ent->value) {
 327             qdict_put_obj(cur, ent->key, val);
 328         }
 329     }
 330
 331     if (has_index && has_member) {
 332         key = reassemble_key(key_of_cur);
 333         error_setg(errp, "Parameters '%s*' used inconsistently", key);
 334         g_free(key);
 335         return NULL;
 336     }
 337     if (!has_index) {
 338         return QOBJECT(cur);
 339     }
 340
 341     /* Copy @cur's values to @elt[] */
 342     nelt = qdict_size(cur) + 1; /* one extra, for use as sentinel */
 343     elt = g_new0(QObject *, nelt);
 344     max_index = -1;
 345     for (ent = qdict_first(cur); ent; ent = qdict_next(cur, ent)) {
 346         index = key_to_index(ent->key, NULL);
 347         assert(index >= 0);
 348         if (index > max_index) {
 349             max_index = index;
 350         }
 351         /*
 352          * We iterate @nelt times.  If we get one exceeding @nelt
 353          * here, we will put less than @nelt values into @elt[],
 354          * triggering the error in the next loop.
 355          */
 356         if ((size_t)index >= nelt - 1) {
 357             continue;
 358         }
 359         /* Even though dict keys are distinct, indexes need not be */
 360         elt[index] = ent->value;
 361     }
 362
 363     /*
 364      * Make a list from @elt[], reporting the first missing element,
 365      * if any.
 366      * If we dropped an index >= nelt in the previous loop, this loop
 367      * will run into the sentinel and report index @nelt missing.
 368      */
 369     list = qlist_new();
 370     assert(!elt[nelt-1]);       /* need the sentinel to be null */
 371     for (i = 0; i < MIN(nelt, max_index + 1); i++) {
 372         if (!elt[i]) {
 373             key = reassemble_key(key_of_cur);
 374             error_setg(errp, "Parameter '%s%d' missing", key, i);
 375             g_free(key);
 376             g_free(elt);
 377             QDECREF(list);
 378             return NULL;
 379         }
 380         qobject_incref(elt[i]);
 381         qlist_append_obj(list, elt[i]);
 382     }
 383
 384     g_free(elt);
 385     return QOBJECT(list);
 386 }
 387
 388 /*
 389  * Parse @params in QEMU's traditional KEY=VALUE,... syntax.
 390  * If @implied_key, the first KEY= can be omitted.  @implied_key is
 391  * implied then, and VALUE can't be empty or contain ',' or '='.
 392  * On success, return a dictionary of the parsed keys and values.
 393  * On failure, store an error through @errp and return NULL.
 394  */
 395 QDict *keyval_parse(const char *params, const char *implied_key,
 396                     Error **errp)
 397 {
 398     QDict *qdict = qdict_new();
 399     QObject *listified;
 400     const char *s;
 401
 402     s = params;
 403     while (*s) {
 404         s = keyval_parse_one(qdict, s, implied_key, errp);
 405         if (!s) {
 406             QDECREF(qdict);
 407             return NULL;
 408         }
 409         implied_key = NULL;
 410     }
 411
 412     listified = keyval_listify(qdict, NULL, errp);
 413     if (!listified) {
 414         QDECREF(qdict);
 415         return NULL;
 416     }
 417     assert(listified == QOBJECT(qdict));
 418     return qdict;
 419 }