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55320a29833f2884d304ee8da8fb372ad86b9a4f
qemu/qobject/json-parser.c
Paolo Bonzini 55320a2983 json-streamer: do not heap-allocate JSONToken 
This is not needed with a push parser.  Since it processes tokens
immediately, the JSONToken can be created directly on the stack
and does not need to copy the lexer's string data.

Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20260626101727.1727389-6-pbonzini@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
2026-07-02 13:55:41 +02:00

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/*
* JSON Parser
*
* Copyright IBM, Corp. 2009
*
* Authors:
* Anthony Liguori <aliguori@us.ibm.com>
*
* This work is licensed under the terms of the GNU LGPL, version 2.1 or later.
* See the COPYING.LIB file in the top-level directory.
*
*/
#include "qemu/osdep.h"
#include "qemu/ctype.h"
#include "qemu/cutils.h"
#include "qemu/unicode.h"
#include "qapi/error.h"
#include "qobject/qbool.h"
#include "qobject/qdict.h"
#include "qobject/qlist.h"
#include "qobject/qnull.h"
#include "qobject/qnum.h"
#include "qobject/qstring.h"
#include "json-parser-int.h"
/*
* The JSON parser is a push parser, returning a completed top-level
* object, an error, or NULL (if the object is incomplete and no error
* happened) after every token. Therefore it has an explicit
* representation of its parser stack; each stack entry consists of a
* parser state and a QObject: - a QList, for an array that is being
* added to - a QDict, for a dictionary that is being added to - a
* QString, for the key of the next pair that will be added to a QDict
*
* The stack represents an arbitrary nesting of arrays and dictionaries
* (whose next key has been parsed); it can also have a dictionary whose
* next key has not been parsed, but that can only happen at the top level.
* Because of this, the stack contents are always of the form
* "(QList | QDict QString)* QDict?".
*
* An empty stack represents the beginning of the parsing process, with
* start state BEFORE_VALUE.
*/
typedef enum JSONParserState {
AFTER_LCURLY,
AFTER_LSQUARE,
BEFORE_KEY,
BEFORE_VALUE,
END_OF_KEY,
END_OF_VALUE,
} JSONParserState;
typedef struct JSONParserStackEntry {
/*
* State when the container is completed or, for the top of the stack,
* entry state for the next token.
*/
JSONParserState state;
/*
* A QString with the last parsed key, or a QList/QDict for the current
* container.
*/
QObject *partial;
} JSONParserStackEntry;
/*
* This is the JSON grammar that's parsed, with the state transition and
* action at each point of the grammar. While this is not a formal
* description, "-> action" represents the pseudocode of the action
* and "-> STATE" sets the top stack entry's state to STATE.
*
* The state alone is enough to tell you what to parse; the state plus
* the type of the top of stack tells you which action to take.
*
* // The initial state is BEFORE_VALUE.
* input := value -> END_OF_VALUE -> return parsed value
* (input | END_OF_INPUT)
*
* // entered on BEFORE_VALUE; after any of these rules are processed, the
* // parser has completed a QObject and is in the END_OF_VALUE state.
* //
* // When the parser reaches the END_OF_VALUE state, it examines the
* // top of the stack to see if it's coming from "input" (stack empty),
* // "array_items" (TOS is a QList) or "dict_pairs" (TOS is a QString; the
* // item below will be a QDict). It then proceeds with the corresponding
* // actions, which will be one of:
* // - return parsed value
* // - add value to QList
* // - pop QString with the key, add key/value to the QDict
* value := literal -> END_OF_VALUE
* | '[' -> push empty QList -> AFTER_LSQUARE
* after_lsquare -> END_OF_VALUE
* | '{' -> push empty QDict -> AFTER_LCURLY
* after_lcurly -> END_OF_VALUE
*
* // non-recursive values, entered on BEFORE_VALUE
* literal := INTEGER -> END_OF_VALUE
* | FLOAT -> END_OF_VALUE
* | KEYWORD -> END_OF_VALUE
* | STRING -> END_OF_VALUE
* | INTERP -> END_OF_VALUE
*
* // entered on AFTER_LSQUARE
* after_lsquare := ']' -> pop completed QList -> END_OF_VALUE
* | ϵ -> BEFORE_VALUE
* array_items -> END_OF_VALUE
*
* // entered on BEFORE_VALUE, with TOS being a QList
* array_items := value -> add value to QList -> END_OF_VALUE
* (']' -> pop completed QList -> END_OF_VALUE
* | ',' -> BEFORE_VALUE
* array_items) -> END_OF_VALUE
*
* // entered on AFTER_LCURLY
* after_lcurly := '}' -> pop completed QDict -> END_OF_VALUE
* | ϵ -> BEFORE_KEY
* dict_pairs -> END_OF_VALUE
*
* // entered on BEFORE_KEY, with TOS being a QDict
* dict_pairs := (STRING | INTERP) -> push QString -> END_OF_KEY
* ':' -> BEFORE_VALUE
* value -> pop QString + add pair to QDict -> END_OF_VALUE
* ('}' -> pop completed QDict -> END_OF_VALUE
* | ',' -> BEFORE_KEY
* dict_pairs) -> END_OF_VALUE
*
* Parse errors ignore the token. json_parser_reset() can be
* called to restart parsing from scratch, with an empty stack.
*/
#define BUG_ON(cond) assert(!(cond))
/**
* TODO
*
* 0) make errors meaningful again
* 1) add geometry information to tokens
* 3) should we return a parsed size?
* 4) deal with premature EOI
*/
static inline JSONParserStackEntry *current_entry(JSONParserContext *ctxt)
{
return g_queue_peek_tail(ctxt->stack);
}
static void push_entry(JSONParserContext *ctxt, QObject *partial,
JSONParserState state)
{
JSONParserStackEntry *entry = g_new(JSONParserStackEntry, 1);
entry->partial = partial;
entry->state = state;
g_queue_push_tail(ctxt->stack, entry);
}
/* Drop the top entry and return the new top entry. */
static JSONParserStackEntry *pop_entry(JSONParserContext *ctxt)
{
JSONParserStackEntry *entry = g_queue_pop_tail(ctxt->stack);
g_free(entry);
return current_entry(ctxt);
}
/**
* Error handler
*/
static void G_GNUC_PRINTF(3, 4) parse_error(JSONParserContext *ctxt,
const JSONToken *token,
const char *msg, ...)
{
va_list ap;
char message[1024];
if (ctxt->err) {
return;
}
va_start(ap, msg);
vsnprintf(message, sizeof(message), msg, ap);
va_end(ap);
error_setg(&ctxt->err, "JSON parse error, %s", message);
}
static int cvt4hex(const char *s)
{
int cp, i;
cp = 0;
for (i = 0; i < 4; i++) {
if (!qemu_isxdigit(s[i])) {
return -1;
}
cp <<= 4;
if (s[i] >= '0' && s[i] <= '9') {
cp |= s[i] - '0';
} else if (s[i] >= 'a' && s[i] <= 'f') {
cp |= 10 + s[i] - 'a';
} else if (s[i] >= 'A' && s[i] <= 'F') {
cp |= 10 + s[i] - 'A';
} else {
return -1;
}
}
return cp;
}
/**
* parse_string(): Parse a JSON string
*
* From RFC 8259 "The JavaScript Object Notation (JSON) Data
* Interchange Format":
*
* char = unescaped /
* escape (
* %x22 / ; " quotation mark U+0022
* %x5C / ; \ reverse solidus U+005C
* %x2F / ; / solidus U+002F
* %x62 / ; b backspace U+0008
* %x66 / ; f form feed U+000C
* %x6E / ; n line feed U+000A
* %x72 / ; r carriage return U+000D
* %x74 / ; t tab U+0009
* %x75 4HEXDIG ) ; uXXXX U+XXXX
* escape = %x5C ; \
* quotation-mark = %x22 ; "
* unescaped = %x20-21 / %x23-5B / %x5D-10FFFF
*
* Extensions over RFC 8259:
* - Extra escape sequence in strings:
* 0x27 (apostrophe) is recognized after escape, too
* - Single-quoted strings:
* Like double-quoted strings, except they're delimited by %x27
* (apostrophe) instead of %x22 (quotation mark), and can't contain
* unescaped apostrophe, but can contain unescaped quotation mark.
*
* Note:
* - Encoding is modified UTF-8.
* - Invalid Unicode characters are rejected.
* - Control characters \x00..\x1F are rejected by the lexer.
*/
static QString *parse_string(JSONParserContext *ctxt, const JSONToken *token)
{
const char *ptr = token->str;
GString *str;
char quote;
const char *beg;
int cp, trailing;
char *end;
ssize_t len;
char utf8_buf[5];
assert(*ptr == '"' || *ptr == '\'');
quote = *ptr++;
str = g_string_new(NULL);
while (*ptr != quote) {
assert(*ptr);
switch (*ptr) {
case '\\':
beg = ptr++;
switch (*ptr++) {
case '"':
g_string_append_c(str, '"');
break;
case '\'':
g_string_append_c(str, '\'');
break;
case '\\':
g_string_append_c(str, '\\');
break;
case '/':
g_string_append_c(str, '/');
break;
case 'b':
g_string_append_c(str, '\b');
break;
case 'f':
g_string_append_c(str, '\f');
break;
case 'n':
g_string_append_c(str, '\n');
break;
case 'r':
g_string_append_c(str, '\r');
break;
case 't':
g_string_append_c(str, '\t');
break;
case 'u':
cp = cvt4hex(ptr);
ptr += 4;
/* handle surrogate pairs */
if (cp >= 0xD800 && cp <= 0xDBFF
&& ptr[0] == '\\' && ptr[1] == 'u') {
/* leading surrogate followed by \u */
cp = 0x10000 + ((cp & 0x3FF) << 10);
trailing = cvt4hex(ptr + 2);
if (trailing >= 0xDC00 && trailing <= 0xDFFF) {
/* followed by trailing surrogate */
cp |= trailing & 0x3FF;
ptr += 6;
} else {
cp = -1; /* invalid */
}
}
if (mod_utf8_encode(utf8_buf, sizeof(utf8_buf), cp) < 0) {
parse_error(ctxt, token,
"%.*s is not a valid Unicode character",
(int)(ptr - beg), beg);
goto out;
}
g_string_append(str, utf8_buf);
break;
default:
parse_error(ctxt, token, "invalid escape sequence in string");
goto out;
}
break;
case '%':
if (ctxt->ap) {
if (ptr[1] != '%') {
parse_error(ctxt, token, "can't interpolate into string");
goto out;
}
ptr++;
}
/* fall through */
default:
cp = mod_utf8_codepoint(ptr, 6, &end);
if (cp < 0) {
parse_error(ctxt, token, "invalid UTF-8 sequence in string");
goto out;
}
ptr = end;
len = mod_utf8_encode(utf8_buf, sizeof(utf8_buf), cp);
assert(len >= 0);
g_string_append(str, utf8_buf);
}
}
return qstring_from_gstring(str);
out:
g_string_free(str, true);
return NULL;
}
/* Terminals */
static QObject *parse_keyword(JSONParserContext *ctxt, const JSONToken *token)
{
assert(token && token->type == JSON_KEYWORD);
if (!strcmp(token->str, "true")) {
return QOBJECT(qbool_from_bool(true));
} else if (!strcmp(token->str, "false")) {
return QOBJECT(qbool_from_bool(false));
} else if (!strcmp(token->str, "null")) {
return QOBJECT(qnull());
}
parse_error(ctxt, token, "invalid keyword '%s'", token->str);
return NULL;
}
static QObject *parse_interpolation(JSONParserContext *ctxt,
const JSONToken *token)
{
assert(token && token->type == JSON_INTERP);
if (!strcmp(token->str, "%p")) {
return va_arg(*ctxt->ap, QObject *);
} else if (!strcmp(token->str, "%i")) {
return QOBJECT(qbool_from_bool(va_arg(*ctxt->ap, int)));
} else if (!strcmp(token->str, "%d")) {
return QOBJECT(qnum_from_int(va_arg(*ctxt->ap, int)));
} else if (!strcmp(token->str, "%ld")) {
return QOBJECT(qnum_from_int(va_arg(*ctxt->ap, long)));
} else if (!strcmp(token->str, "%lld")) {
return QOBJECT(qnum_from_int(va_arg(*ctxt->ap, long long)));
} else if (!strcmp(token->str, "%" PRId64)) {
return QOBJECT(qnum_from_int(va_arg(*ctxt->ap, int64_t)));
} else if (!strcmp(token->str, "%u")) {
return QOBJECT(qnum_from_uint(va_arg(*ctxt->ap, unsigned int)));
} else if (!strcmp(token->str, "%lu")) {
return QOBJECT(qnum_from_uint(va_arg(*ctxt->ap, unsigned long)));
} else if (!strcmp(token->str, "%llu")) {
return QOBJECT(qnum_from_uint(va_arg(*ctxt->ap, unsigned long long)));
} else if (!strcmp(token->str, "%" PRIu64)) {
return QOBJECT(qnum_from_uint(va_arg(*ctxt->ap, uint64_t)));
} else if (!strcmp(token->str, "%s")) {
return QOBJECT(qstring_from_str(va_arg(*ctxt->ap, const char *)));
} else if (!strcmp(token->str, "%f")) {
return QOBJECT(qnum_from_double(va_arg(*ctxt->ap, double)));
}
parse_error(ctxt, token, "invalid interpolation '%s'", token->str);
return NULL;
}
static QObject *parse_literal(JSONParserContext *ctxt, const JSONToken *token)
{
assert(token);
switch (token->type) {
case JSON_STRING:
return QOBJECT(parse_string(ctxt, token));
case JSON_INTEGER: {
/*
* Represent JSON_INTEGER as QNUM_I64 if possible, else as
* QNUM_U64, else as QNUM_DOUBLE. Note that qemu_strtoi64()
* and qemu_strtou64() fail with ERANGE when it's not
* possible.
*
* qnum_get_int() will then work for any signed 64-bit
* JSON_INTEGER, qnum_get_uint() for any unsigned 64-bit
* integer, and qnum_get_double() both for any JSON_INTEGER
* and any JSON_FLOAT (with precision loss for integers beyond
* 53 bits)
*/
int ret;
int64_t value;
uint64_t uvalue;
ret = qemu_strtoi64(token->str, NULL, 10, &value);
if (!ret) {
return QOBJECT(qnum_from_int(value));
}
assert(ret == -ERANGE);
if (token->str[0] != '-') {
ret = qemu_strtou64(token->str, NULL, 10, &uvalue);
if (!ret) {
return QOBJECT(qnum_from_uint(uvalue));
}
assert(ret == -ERANGE);
}
}
/* fall through to JSON_FLOAT */
case JSON_FLOAT:
/* FIXME dependent on locale; a pervasive issue in QEMU */
/* FIXME our lexer matches RFC 8259 in forbidding Inf or NaN,
* but those might be useful extensions beyond JSON */
return QOBJECT(qnum_from_double(strtod(token->str, NULL)));
default:
abort();
}
}
/* Parsing state machine */
static QObject *parse_begin_value(JSONParserContext *ctxt,
const JSONToken *token)
{
switch (token->type) {
case JSON_LCURLY:
push_entry(ctxt, QOBJECT(qdict_new()), AFTER_LCURLY);
return NULL;
case JSON_LSQUARE:
push_entry(ctxt, QOBJECT(qlist_new()), AFTER_LSQUARE);
return NULL;
case JSON_INTERP:
return parse_interpolation(ctxt, token);
case JSON_INTEGER:
case JSON_FLOAT:
case JSON_STRING:
return parse_literal(ctxt, token);
case JSON_KEYWORD:
return parse_keyword(ctxt, token);
default:
parse_error(ctxt, token, "expecting value");
return NULL;
}
}
static QObject *parse_token(JSONParserContext *ctxt, const JSONToken *token)
{
JSONParserStackEntry *entry;
JSONParserState state;
QString *key;
QObject *key_obj = NULL, *value = NULL;
entry = current_entry(ctxt);
state = entry ? entry->state : BEFORE_VALUE;
switch (state) {
case AFTER_LCURLY:
/* Grab '}' for empty object or fall through to BEFORE_KEY */
assert(qobject_type(entry->partial) == QTYPE_QDICT);
if (token->type == JSON_RCURLY) {
value = entry->partial;
entry = pop_entry(ctxt);
break;
}
entry->state = BEFORE_KEY;
/* fall through */
case BEFORE_KEY:
/* Expecting object key */
assert(qobject_type(entry->partial) == QTYPE_QDICT);
if (token->type != JSON_STRING && token->type != JSON_INTERP) {
parse_error(ctxt, token, "expecting key");
return NULL;
}
key_obj = parse_begin_value(ctxt, token);
if (!key_obj) {
/* Parse error already reported */
} else if (qobject_type(key_obj) != QTYPE_QSTRING) {
/* An interpolation was valid syntactically but not %s */
parse_error(ctxt, token, "key is not a string in object");
} else {
/* Store key in a special entry on the stack */
push_entry(ctxt, key_obj, END_OF_KEY);
}
return NULL;
case END_OF_KEY:
/* Expecting ':' after key */
assert(qobject_type(entry->partial) == QTYPE_QSTRING);
if (token->type == JSON_COLON) {
entry->state = BEFORE_VALUE;
} else {
parse_error(ctxt, token, "expecting ':'");
}
return NULL;
case AFTER_LSQUARE:
/* Grab ']' for empty array or fall through to BEFORE_VALUE */
assert(qobject_type(entry->partial) == QTYPE_QLIST);
if (token->type == JSON_RSQUARE) {
value = entry->partial;
entry = pop_entry(ctxt);
break;
}
entry->state = BEFORE_VALUE;
/* fall through */
case BEFORE_VALUE:
/* Expecting value */
assert(!entry || qobject_type(entry->partial) != QTYPE_QDICT);
value = parse_begin_value(ctxt, token);
if (!value) {
/* Error or '['/'{' */
return NULL;
}
/* Return value or insert it into a container */
break;
case END_OF_VALUE:
/* Grab ',' or ']' for array; ',' or '}' for object */
if (qobject_to(QList, entry->partial)) {
/* Array */
if (token->type != JSON_RSQUARE) {
if (token->type == JSON_COMMA) {
entry->state = BEFORE_VALUE;
} else {
parse_error(ctxt, token, "expected ',' or ']'");
}
return NULL;
}
} else if (qobject_to(QDict, entry->partial)) {
/* Object */
if (token->type != JSON_RCURLY) {
if (token->type == JSON_COMMA) {
entry->state = BEFORE_KEY;
} else {
parse_error(ctxt, token, "expected ',' or '}'");
}
return NULL;
}
} else {
g_assert_not_reached();
}
/* Got ']' or '}'; return full value or insert into parent container */
value = entry->partial;
entry = pop_entry(ctxt);
break;
}
assert(value);
if (entry == NULL) {
/* Parse stack now empty, the top-level value is complete. */
return value;
}
/*
* Parse stack is not empty and entry->partial is the top of stack.
* It's a QString with the key (and a QDict is below it) if we're
* parsing an object, or a QList if we're parsing an array.
*/
key = qobject_to(QString, entry->partial);
if (key) {
const char *key_str;
QDict *dict;
/* Pop off key, and store (key, value) in QDict. */
entry = pop_entry(ctxt);
dict = qobject_to(QDict, entry->partial);
assert(dict);
key_str = qstring_get_str(key);
if (qdict_haskey(dict, key_str)) {
parse_error(ctxt, token, "duplicate key");
qobject_unref(value);
return NULL;
}
qdict_put_obj(dict, key_str, value);
qobject_unref(key);
} else {
/* Array, just store value in the QList. */
qlist_append_obj(qobject_to(QList, entry->partial), value);
}
entry->state = END_OF_VALUE;
return NULL;
}
void json_parser_reset(JSONParserContext *ctxt)
{
JSONParserStackEntry *entry;
ctxt->err = NULL;
while ((entry = g_queue_pop_tail(ctxt->stack)) != NULL) {
qobject_unref(entry->partial);
g_free(entry);
}
}
void json_parser_init(JSONParserContext *ctxt, va_list *ap)
{
ctxt->stack = g_queue_new();
ctxt->ap = ap;
json_parser_reset(ctxt);
}
void json_parser_destroy(JSONParserContext *ctxt)
{
json_parser_reset(ctxt);
g_queue_free(ctxt->stack);
ctxt->stack = NULL;
}
/*
* Advance the parser based on the token that is passed.
* Return the finished top-level value if the token completes it, else
* NULL.
* Once an error is returned, the function must not be called again
* without first resetting the parser.
*/
QObject *json_parser_feed(JSONParserContext *ctxt, const JSONToken *token,
Error **errp)
{
QObject *result = NULL;
assert(!ctxt->err);
switch (token->type) {
case JSON_ERROR:
parse_error(ctxt, token, "stray '%s'", token->str);
break;
case JSON_END_OF_INPUT:
/* Check for premature end of input */
if (!g_queue_is_empty(ctxt->stack)) {
parse_error(ctxt, token, "premature end of input");
}
break;
default:
result = parse_token(ctxt, token);
break;
}
error_propagate(errp, ctxt->err);
return result;
}
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