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qemu-e2k/json-parser.c
Michael Roth 65c0f1e955 json-parser: don't replicate tokens at each level of recursion 
Currently, when parsing a stream of tokens we make a copy of the token
list at the beginning of each level of recursion so that we do not
modify the original list in cases where we need to fall back to an
earlier state.

In the worst case, we will only read 1 or 2 tokens off the list before
recursing again, which means an upper bound of roughly N^2 token allocations.

For a "reasonably" sized QMP request (in this a QMP representation of
cirrus_vga's device state, generated via QIDL, being passed in via
qom-set), this caused my 16GB's of memory to be exhausted before any
noticeable progress was made by the parser.

This patch works around the issue by using single copy of the token list
in the form of an indexable array so that we can save/restore state by
manipulating indices.

A subsequent commit adds a "large_dict" test case which exhibits the
same behavior as above. With this patch applied the test case successfully
completes in under a second.

Tested with valgrind, make check, and QMP.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
2012-08-16 13:41:15 -05:00

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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 <stdarg.h>
#include "qemu-common.h"
#include "qstring.h"
#include "qint.h"
#include "qdict.h"
#include "qlist.h"
#include "qfloat.h"
#include "qbool.h"
#include "json-parser.h"
#include "json-lexer.h"
#include "qerror.h"
typedef struct JSONParserContext
{
Error *err;
struct {
QObject **buf;
size_t pos;
size_t count;
} tokens;
} JSONParserContext;
#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 QObject *parse_value(JSONParserContext *ctxt, va_list *ap);
/**
* Token manipulators
*
* tokens are dictionaries that contain a type, a string value, and geometry information
* about a token identified by the lexer. These are routines that make working with
* these objects a bit easier.
*/
static const char *token_get_value(QObject *obj)
{
return qdict_get_str(qobject_to_qdict(obj), "token");
}
static JSONTokenType token_get_type(QObject *obj)
{
return qdict_get_int(qobject_to_qdict(obj), "type");
}
static int token_is_operator(QObject *obj, char op)
{
const char *val;
if (token_get_type(obj) != JSON_OPERATOR) {
return 0;
}
val = token_get_value(obj);
return (val[0] == op) && (val[1] == 0);
}
static int token_is_keyword(QObject *obj, const char *value)
{
if (token_get_type(obj) != JSON_KEYWORD) {
return 0;
}
return strcmp(token_get_value(obj), value) == 0;
}
static int token_is_escape(QObject *obj, const char *value)
{
if (token_get_type(obj) != JSON_ESCAPE) {
return 0;
}
return (strcmp(token_get_value(obj), value) == 0);
}
/**
* Error handler
*/
static void GCC_FMT_ATTR(3, 4) parse_error(JSONParserContext *ctxt,
QObject *token, const char *msg, ...)
{
va_list ap;
char message[1024];
va_start(ap, msg);
vsnprintf(message, sizeof(message), msg, ap);
va_end(ap);
if (ctxt->err) {
error_free(ctxt->err);
ctxt->err = NULL;
}
error_set(&ctxt->err, QERR_JSON_PARSE_ERROR, message);
}
/**
* String helpers
*
* These helpers are used to unescape strings.
*/
static void wchar_to_utf8(uint16_t wchar, char *buffer, size_t buffer_length)
{
if (wchar <= 0x007F) {
BUG_ON(buffer_length < 2);
buffer[0] = wchar & 0x7F;
buffer[1] = 0;
} else if (wchar <= 0x07FF) {
BUG_ON(buffer_length < 3);
buffer[0] = 0xC0 | ((wchar >> 6) & 0x1F);
buffer[1] = 0x80 | (wchar & 0x3F);
buffer[2] = 0;
} else {
BUG_ON(buffer_length < 4);
buffer[0] = 0xE0 | ((wchar >> 12) & 0x0F);
buffer[1] = 0x80 | ((wchar >> 6) & 0x3F);
buffer[2] = 0x80 | (wchar & 0x3F);
buffer[3] = 0;
}
}
static int hex2decimal(char ch)
{
if (ch >= '0' && ch <= '9') {
return (ch - '0');
} else if (ch >= 'a' && ch <= 'f') {
return 10 + (ch - 'a');
} else if (ch >= 'A' && ch <= 'F') {
return 10 + (ch - 'A');
}
return -1;
}
/**
* parse_string(): Parse a json string and return a QObject
*
* string
* ""
* " chars "
* chars
* char
* char chars
* char
* any-Unicode-character-
* except-"-or-\-or-
* control-character
* \"
* \\
* \/
* \b
* \f
* \n
* \r
* \t
* \u four-hex-digits
*/
static QString *qstring_from_escaped_str(JSONParserContext *ctxt, QObject *token)
{
const char *ptr = token_get_value(token);
QString *str;
int double_quote = 1;
if (*ptr == '"') {
double_quote = 1;
} else {
double_quote = 0;
}
ptr++;
str = qstring_new();
while (*ptr &&
((double_quote && *ptr != '"') || (!double_quote && *ptr != '\''))) {
if (*ptr == '\\') {
ptr++;
switch (*ptr) {
case '"':
qstring_append(str, "\"");
ptr++;
break;
case '\'':
qstring_append(str, "'");
ptr++;
break;
case '\\':
qstring_append(str, "\\");
ptr++;
break;
case '/':
qstring_append(str, "/");
ptr++;
break;
case 'b':
qstring_append(str, "\b");
ptr++;
break;
case 'f':
qstring_append(str, "\f");
ptr++;
break;
case 'n':
qstring_append(str, "\n");
ptr++;
break;
case 'r':
qstring_append(str, "\r");
ptr++;
break;
case 't':
qstring_append(str, "\t");
ptr++;
break;
case 'u': {
uint16_t unicode_char = 0;
char utf8_char[4];
int i = 0;
ptr++;
for (i = 0; i < 4; i++) {
if (qemu_isxdigit(*ptr)) {
unicode_char |= hex2decimal(*ptr) << ((3 - i) * 4);
} else {
parse_error(ctxt, token,
"invalid hex escape sequence in string");
goto out;
}
ptr++;
}
wchar_to_utf8(unicode_char, utf8_char, sizeof(utf8_char));
qstring_append(str, utf8_char);
} break;
default:
parse_error(ctxt, token, "invalid escape sequence in string");
goto out;
}
} else {
char dummy[2];
dummy[0] = *ptr++;
dummy[1] = 0;
qstring_append(str, dummy);
}
}
return str;
out:
QDECREF(str);
return NULL;
}
static QObject *parser_context_pop_token(JSONParserContext *ctxt)
{
QObject *token;
g_assert(ctxt->tokens.pos < ctxt->tokens.count);
token = ctxt->tokens.buf[ctxt->tokens.pos];
ctxt->tokens.pos++;
return token;
}
/* Note: parser_context_{peek|pop}_token do not increment the
* token object's refcount. In both cases the references will continue
* to be tracked and cleaned up in parser_context_free(), so do not
* attempt to free the token object.
*/
static QObject *parser_context_peek_token(JSONParserContext *ctxt)
{
QObject *token;
g_assert(ctxt->tokens.pos < ctxt->tokens.count);
token = ctxt->tokens.buf[ctxt->tokens.pos];
return token;
}
static JSONParserContext parser_context_save(JSONParserContext *ctxt)
{
JSONParserContext saved_ctxt = {0};
saved_ctxt.tokens.pos = ctxt->tokens.pos;
saved_ctxt.tokens.count = ctxt->tokens.count;
saved_ctxt.tokens.buf = ctxt->tokens.buf;
return saved_ctxt;
}
static void parser_context_restore(JSONParserContext *ctxt,
JSONParserContext saved_ctxt)
{
ctxt->tokens.pos = saved_ctxt.tokens.pos;
ctxt->tokens.count = saved_ctxt.tokens.count;
ctxt->tokens.buf = saved_ctxt.tokens.buf;
}
static void tokens_append_from_iter(QObject *obj, void *opaque)
{
JSONParserContext *ctxt = opaque;
g_assert(ctxt->tokens.pos < ctxt->tokens.count);
ctxt->tokens.buf[ctxt->tokens.pos++] = obj;
qobject_incref(obj);
}
static JSONParserContext *parser_context_new(QList *tokens)
{
JSONParserContext *ctxt;
size_t count;
if (!tokens) {
return NULL;
}
count = qlist_size(tokens);
if (count == 0) {
return NULL;
}
ctxt = g_malloc0(sizeof(JSONParserContext));
ctxt->tokens.pos = 0;
ctxt->tokens.count = count;
ctxt->tokens.buf = g_malloc(count * sizeof(QObject *));
qlist_iter(tokens, tokens_append_from_iter, ctxt);
ctxt->tokens.pos = 0;
return ctxt;
}
/* to support error propagation, ctxt->err must be freed separately */
static void parser_context_free(JSONParserContext *ctxt)
{
int i;
if (ctxt) {
for (i = 0; i < ctxt->tokens.count; i++) {
qobject_decref(ctxt->tokens.buf[i]);
}
g_free(ctxt->tokens.buf);
g_free(ctxt);
}
}
/**
* Parsing rules
*/
static int parse_pair(JSONParserContext *ctxt, QDict *dict, va_list *ap)
{
QObject *key = NULL, *token = NULL, *value, *peek;
JSONParserContext saved_ctxt = parser_context_save(ctxt);
peek = parser_context_peek_token(ctxt);
if (peek == NULL) {
parse_error(ctxt, NULL, "premature EOI");
goto out;
}
key = parse_value(ctxt, ap);
if (!key || qobject_type(key) != QTYPE_QSTRING) {
parse_error(ctxt, peek, "key is not a string in object");
goto out;
}
token = parser_context_pop_token(ctxt);
if (token == NULL) {
parse_error(ctxt, NULL, "premature EOI");
goto out;
}
if (!token_is_operator(token, ':')) {
parse_error(ctxt, token, "missing : in object pair");
goto out;
}
value = parse_value(ctxt, ap);
if (value == NULL) {
parse_error(ctxt, token, "Missing value in dict");
goto out;
}
qdict_put_obj(dict, qstring_get_str(qobject_to_qstring(key)), value);
qobject_decref(key);
return 0;
out:
parser_context_restore(ctxt, saved_ctxt);
qobject_decref(key);
return -1;
}
static QObject *parse_object(JSONParserContext *ctxt, va_list *ap)
{
QDict *dict = NULL;
QObject *token, *peek;
JSONParserContext saved_ctxt = parser_context_save(ctxt);
token = parser_context_pop_token(ctxt);
if (token == NULL) {
goto out;
}
if (!token_is_operator(token, '{')) {
goto out;
}
token = NULL;
dict = qdict_new();
peek = parser_context_peek_token(ctxt);
if (peek == NULL) {
parse_error(ctxt, NULL, "premature EOI");
goto out;
}
if (!token_is_operator(peek, '}')) {
if (parse_pair(ctxt, dict, ap) == -1) {
goto out;
}
token = parser_context_pop_token(ctxt);
if (token == NULL) {
parse_error(ctxt, NULL, "premature EOI");
goto out;
}
while (!token_is_operator(token, '}')) {
if (!token_is_operator(token, ',')) {
parse_error(ctxt, token, "expected separator in dict");
goto out;
}
token = NULL;
if (parse_pair(ctxt, dict, ap) == -1) {
goto out;
}
token = parser_context_pop_token(ctxt);
if (token == NULL) {
parse_error(ctxt, NULL, "premature EOI");
goto out;
}
}
token = NULL;
} else {
token = parser_context_pop_token(ctxt);
token = NULL;
}
return QOBJECT(dict);
out:
parser_context_restore(ctxt, saved_ctxt);
QDECREF(dict);
return NULL;
}
static QObject *parse_array(JSONParserContext *ctxt, va_list *ap)
{
QList *list = NULL;
QObject *token, *peek;
JSONParserContext saved_ctxt = parser_context_save(ctxt);
token = parser_context_pop_token(ctxt);
if (token == NULL) {
goto out;
}
if (!token_is_operator(token, '[')) {
token = NULL;
goto out;
}
token = NULL;
list = qlist_new();
peek = parser_context_peek_token(ctxt);
if (peek == NULL) {
parse_error(ctxt, NULL, "premature EOI");
goto out;
}
if (!token_is_operator(peek, ']')) {
QObject *obj;
obj = parse_value(ctxt, ap);
if (obj == NULL) {
parse_error(ctxt, token, "expecting value");
goto out;
}
qlist_append_obj(list, obj);
token = parser_context_pop_token(ctxt);
if (token == NULL) {
parse_error(ctxt, NULL, "premature EOI");
goto out;
}
while (!token_is_operator(token, ']')) {
if (!token_is_operator(token, ',')) {
parse_error(ctxt, token, "expected separator in list");
goto out;
}
token = NULL;
obj = parse_value(ctxt, ap);
if (obj == NULL) {
parse_error(ctxt, token, "expecting value");
goto out;
}
qlist_append_obj(list, obj);
token = parser_context_pop_token(ctxt);
if (token == NULL) {
parse_error(ctxt, NULL, "premature EOI");
goto out;
}
}
token = NULL;
} else {
token = parser_context_pop_token(ctxt);
token = NULL;
}
return QOBJECT(list);
out:
parser_context_restore(ctxt, saved_ctxt);
QDECREF(list);
return NULL;
}
static QObject *parse_keyword(JSONParserContext *ctxt)
{
QObject *token, *ret;
JSONParserContext saved_ctxt = parser_context_save(ctxt);
token = parser_context_pop_token(ctxt);
if (token == NULL) {
goto out;
}
if (token_get_type(token) != JSON_KEYWORD) {
goto out;
}
if (token_is_keyword(token, "true")) {
ret = QOBJECT(qbool_from_int(true));
} else if (token_is_keyword(token, "false")) {
ret = QOBJECT(qbool_from_int(false));
} else {
parse_error(ctxt, token, "invalid keyword `%s'", token_get_value(token));
goto out;
}
return ret;
out:
parser_context_restore(ctxt, saved_ctxt);
return NULL;
}
static QObject *parse_escape(JSONParserContext *ctxt, va_list *ap)
{
QObject *token = NULL, *obj;
JSONParserContext saved_ctxt = parser_context_save(ctxt);
if (ap == NULL) {
goto out;
}
token = parser_context_pop_token(ctxt);
if (token == NULL) {
goto out;
}
if (token_is_escape(token, "%p")) {
obj = va_arg(*ap, QObject *);
} else if (token_is_escape(token, "%i")) {
obj = QOBJECT(qbool_from_int(va_arg(*ap, int)));
} else if (token_is_escape(token, "%d")) {
obj = QOBJECT(qint_from_int(va_arg(*ap, int)));
} else if (token_is_escape(token, "%ld")) {
obj = QOBJECT(qint_from_int(va_arg(*ap, long)));
} else if (token_is_escape(token, "%lld") ||
token_is_escape(token, "%I64d")) {
obj = QOBJECT(qint_from_int(va_arg(*ap, long long)));
} else if (token_is_escape(token, "%s")) {
obj = QOBJECT(qstring_from_str(va_arg(*ap, const char *)));
} else if (token_is_escape(token, "%f")) {
obj = QOBJECT(qfloat_from_double(va_arg(*ap, double)));
} else {
goto out;
}
return obj;
out:
parser_context_restore(ctxt, saved_ctxt);
return NULL;
}
static QObject *parse_literal(JSONParserContext *ctxt)
{
QObject *token, *obj;
JSONParserContext saved_ctxt = parser_context_save(ctxt);
token = parser_context_pop_token(ctxt);
if (token == NULL) {
goto out;
}
switch (token_get_type(token)) {
case JSON_STRING:
obj = QOBJECT(qstring_from_escaped_str(ctxt, token));
break;
case JSON_INTEGER:
obj = QOBJECT(qint_from_int(strtoll(token_get_value(token), NULL, 10)));
break;
case JSON_FLOAT:
/* FIXME dependent on locale */
obj = QOBJECT(qfloat_from_double(strtod(token_get_value(token), NULL)));
break;
default:
goto out;
}
return obj;
out:
parser_context_restore(ctxt, saved_ctxt);
return NULL;
}
static QObject *parse_value(JSONParserContext *ctxt, va_list *ap)
{
QObject *obj;
obj = parse_object(ctxt, ap);
if (obj == NULL) {
obj = parse_array(ctxt, ap);
}
if (obj == NULL) {
obj = parse_escape(ctxt, ap);
}
if (obj == NULL) {
obj = parse_keyword(ctxt);
}
if (obj == NULL) {
obj = parse_literal(ctxt);
}
return obj;
}
QObject *json_parser_parse(QList *tokens, va_list *ap)
{
return json_parser_parse_err(tokens, ap, NULL);
}
QObject *json_parser_parse_err(QList *tokens, va_list *ap, Error **errp)
{
JSONParserContext *ctxt = parser_context_new(tokens);
QObject *result;
if (!ctxt) {
return NULL;
}
result = parse_value(ctxt, ap);
error_propagate(errp, ctxt->err);
parser_context_free(ctxt);
return result;
}
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