qemu/json-lexer.c
Michael Roth b011f61931 json-lexer: make lexer error-recovery more deterministic
Currently when we reach an error state we effectively flush everything
fed to the lexer, which can put us in a state where we keep feeding
tokens into the parser at arbitrary offsets in the stream. This makes it
difficult for the lexer/tokenizer/parser to get back in sync when bad
input is made by the client.

With these changes we emit an error state/token up to the tokenizer as
soon as we reach an error state, and continue processing any data passed
in rather than bailing out. The reset token will be used to reset the
tokenizer and parser, such that they'll recover state as soon as the
lexer begins generating valid token sequences again.

We also map chr(192,193,245-255) to an error state here, since they are
invalid UTF-8 characters. QMP guest proxy/agent will use chr(255) to
force a flush/reset of previous input for reliable delivery of certain
events, so also we document that thoroughly here.

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
2011-06-07 13:52:11 -05:00

373 lines
9.2 KiB
C

/*
* JSON lexer
*
* 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 "qstring.h"
#include "qlist.h"
#include "qdict.h"
#include "qint.h"
#include "qemu-common.h"
#include "json-lexer.h"
#define MAX_TOKEN_SIZE (64ULL << 20)
/*
* \"([^\\\"]|(\\\"\\'\\\\\\/\\b\\f\\n\\r\\t\\u[0-9a-fA-F][0-9a-fA-F][0-9a-fA-F][0-9a-fA-F]))*\"
* '([^\\']|(\\\"\\'\\\\\\/\\b\\f\\n\\r\\t\\u[0-9a-fA-F][0-9a-fA-F][0-9a-fA-F][0-9a-fA-F]))*'
* 0|([1-9][0-9]*(.[0-9]+)?([eE]([-+])?[0-9]+))
* [{}\[\],:]
* [a-z]+
*
*/
enum json_lexer_state {
IN_ERROR = 0,
IN_DQ_UCODE3,
IN_DQ_UCODE2,
IN_DQ_UCODE1,
IN_DQ_UCODE0,
IN_DQ_STRING_ESCAPE,
IN_DQ_STRING,
IN_SQ_UCODE3,
IN_SQ_UCODE2,
IN_SQ_UCODE1,
IN_SQ_UCODE0,
IN_SQ_STRING_ESCAPE,
IN_SQ_STRING,
IN_ZERO,
IN_DIGITS,
IN_DIGIT,
IN_EXP_E,
IN_MANTISSA,
IN_MANTISSA_DIGITS,
IN_NONZERO_NUMBER,
IN_NEG_NONZERO_NUMBER,
IN_KEYWORD,
IN_ESCAPE,
IN_ESCAPE_L,
IN_ESCAPE_LL,
IN_ESCAPE_I,
IN_ESCAPE_I6,
IN_ESCAPE_I64,
IN_WHITESPACE,
IN_START,
};
#define TERMINAL(state) [0 ... 0x7F] = (state)
/* Return whether TERMINAL is a terminal state and the transition to it
from OLD_STATE required lookahead. This happens whenever the table
below uses the TERMINAL macro. */
#define TERMINAL_NEEDED_LOOKAHEAD(old_state, terminal) \
(json_lexer[(old_state)][0] == (terminal))
static const uint8_t json_lexer[][256] = {
/* double quote string */
[IN_DQ_UCODE3] = {
['0' ... '9'] = IN_DQ_STRING,
['a' ... 'f'] = IN_DQ_STRING,
['A' ... 'F'] = IN_DQ_STRING,
},
[IN_DQ_UCODE2] = {
['0' ... '9'] = IN_DQ_UCODE3,
['a' ... 'f'] = IN_DQ_UCODE3,
['A' ... 'F'] = IN_DQ_UCODE3,
},
[IN_DQ_UCODE1] = {
['0' ... '9'] = IN_DQ_UCODE2,
['a' ... 'f'] = IN_DQ_UCODE2,
['A' ... 'F'] = IN_DQ_UCODE2,
},
[IN_DQ_UCODE0] = {
['0' ... '9'] = IN_DQ_UCODE1,
['a' ... 'f'] = IN_DQ_UCODE1,
['A' ... 'F'] = IN_DQ_UCODE1,
},
[IN_DQ_STRING_ESCAPE] = {
['b'] = IN_DQ_STRING,
['f'] = IN_DQ_STRING,
['n'] = IN_DQ_STRING,
['r'] = IN_DQ_STRING,
['t'] = IN_DQ_STRING,
['/'] = IN_DQ_STRING,
['\\'] = IN_DQ_STRING,
['\''] = IN_DQ_STRING,
['\"'] = IN_DQ_STRING,
['u'] = IN_DQ_UCODE0,
},
[IN_DQ_STRING] = {
[1 ... 0xBF] = IN_DQ_STRING,
[0xC2 ... 0xF4] = IN_DQ_STRING,
['\\'] = IN_DQ_STRING_ESCAPE,
['"'] = JSON_STRING,
},
/* single quote string */
[IN_SQ_UCODE3] = {
['0' ... '9'] = IN_SQ_STRING,
['a' ... 'f'] = IN_SQ_STRING,
['A' ... 'F'] = IN_SQ_STRING,
},
[IN_SQ_UCODE2] = {
['0' ... '9'] = IN_SQ_UCODE3,
['a' ... 'f'] = IN_SQ_UCODE3,
['A' ... 'F'] = IN_SQ_UCODE3,
},
[IN_SQ_UCODE1] = {
['0' ... '9'] = IN_SQ_UCODE2,
['a' ... 'f'] = IN_SQ_UCODE2,
['A' ... 'F'] = IN_SQ_UCODE2,
},
[IN_SQ_UCODE0] = {
['0' ... '9'] = IN_SQ_UCODE1,
['a' ... 'f'] = IN_SQ_UCODE1,
['A' ... 'F'] = IN_SQ_UCODE1,
},
[IN_SQ_STRING_ESCAPE] = {
['b'] = IN_SQ_STRING,
['f'] = IN_SQ_STRING,
['n'] = IN_SQ_STRING,
['r'] = IN_SQ_STRING,
['t'] = IN_SQ_STRING,
['/'] = IN_DQ_STRING,
['\\'] = IN_DQ_STRING,
['\''] = IN_SQ_STRING,
['\"'] = IN_SQ_STRING,
['u'] = IN_SQ_UCODE0,
},
[IN_SQ_STRING] = {
[1 ... 0xBF] = IN_SQ_STRING,
[0xC2 ... 0xF4] = IN_SQ_STRING,
['\\'] = IN_SQ_STRING_ESCAPE,
['\''] = JSON_STRING,
},
/* Zero */
[IN_ZERO] = {
TERMINAL(JSON_INTEGER),
['0' ... '9'] = IN_ERROR,
['.'] = IN_MANTISSA,
},
/* Float */
[IN_DIGITS] = {
TERMINAL(JSON_FLOAT),
['0' ... '9'] = IN_DIGITS,
},
[IN_DIGIT] = {
['0' ... '9'] = IN_DIGITS,
},
[IN_EXP_E] = {
['-'] = IN_DIGIT,
['+'] = IN_DIGIT,
['0' ... '9'] = IN_DIGITS,
},
[IN_MANTISSA_DIGITS] = {
TERMINAL(JSON_FLOAT),
['0' ... '9'] = IN_MANTISSA_DIGITS,
['e'] = IN_EXP_E,
['E'] = IN_EXP_E,
},
[IN_MANTISSA] = {
['0' ... '9'] = IN_MANTISSA_DIGITS,
},
/* Number */
[IN_NONZERO_NUMBER] = {
TERMINAL(JSON_INTEGER),
['0' ... '9'] = IN_NONZERO_NUMBER,
['e'] = IN_EXP_E,
['E'] = IN_EXP_E,
['.'] = IN_MANTISSA,
},
[IN_NEG_NONZERO_NUMBER] = {
['0'] = IN_ZERO,
['1' ... '9'] = IN_NONZERO_NUMBER,
},
/* keywords */
[IN_KEYWORD] = {
TERMINAL(JSON_KEYWORD),
['a' ... 'z'] = IN_KEYWORD,
},
/* whitespace */
[IN_WHITESPACE] = {
TERMINAL(JSON_SKIP),
[' '] = IN_WHITESPACE,
['\t'] = IN_WHITESPACE,
['\r'] = IN_WHITESPACE,
['\n'] = IN_WHITESPACE,
},
/* escape */
[IN_ESCAPE_LL] = {
['d'] = JSON_ESCAPE,
},
[IN_ESCAPE_L] = {
['d'] = JSON_ESCAPE,
['l'] = IN_ESCAPE_LL,
},
[IN_ESCAPE_I64] = {
['d'] = JSON_ESCAPE,
},
[IN_ESCAPE_I6] = {
['4'] = IN_ESCAPE_I64,
},
[IN_ESCAPE_I] = {
['6'] = IN_ESCAPE_I6,
},
[IN_ESCAPE] = {
['d'] = JSON_ESCAPE,
['i'] = JSON_ESCAPE,
['p'] = JSON_ESCAPE,
['s'] = JSON_ESCAPE,
['f'] = JSON_ESCAPE,
['l'] = IN_ESCAPE_L,
['I'] = IN_ESCAPE_I,
},
/* top level rule */
[IN_START] = {
['"'] = IN_DQ_STRING,
['\''] = IN_SQ_STRING,
['0'] = IN_ZERO,
['1' ... '9'] = IN_NONZERO_NUMBER,
['-'] = IN_NEG_NONZERO_NUMBER,
['{'] = JSON_OPERATOR,
['}'] = JSON_OPERATOR,
['['] = JSON_OPERATOR,
[']'] = JSON_OPERATOR,
[','] = JSON_OPERATOR,
[':'] = JSON_OPERATOR,
['a' ... 'z'] = IN_KEYWORD,
['%'] = IN_ESCAPE,
[' '] = IN_WHITESPACE,
['\t'] = IN_WHITESPACE,
['\r'] = IN_WHITESPACE,
['\n'] = IN_WHITESPACE,
},
};
void json_lexer_init(JSONLexer *lexer, JSONLexerEmitter func)
{
lexer->emit = func;
lexer->state = IN_START;
lexer->token = qstring_new();
lexer->x = lexer->y = 0;
}
static int json_lexer_feed_char(JSONLexer *lexer, char ch, bool flush)
{
int char_consumed, new_state;
lexer->x++;
if (ch == '\n') {
lexer->x = 0;
lexer->y++;
}
do {
new_state = json_lexer[lexer->state][(uint8_t)ch];
char_consumed = !TERMINAL_NEEDED_LOOKAHEAD(lexer->state, new_state);
if (char_consumed) {
qstring_append_chr(lexer->token, ch);
}
switch (new_state) {
case JSON_OPERATOR:
case JSON_ESCAPE:
case JSON_INTEGER:
case JSON_FLOAT:
case JSON_KEYWORD:
case JSON_STRING:
lexer->emit(lexer, lexer->token, new_state, lexer->x, lexer->y);
case JSON_SKIP:
QDECREF(lexer->token);
lexer->token = qstring_new();
new_state = IN_START;
break;
case IN_ERROR:
/* XXX: To avoid having previous bad input leaving the parser in an
* unresponsive state where we consume unpredictable amounts of
* subsequent "good" input, percolate this error state up to the
* tokenizer/parser by forcing a NULL object to be emitted, then
* reset state.
*
* Also note that this handling is required for reliable channel
* negotiation between QMP and the guest agent, since chr(0xFF)
* is placed at the beginning of certain events to ensure proper
* delivery when the channel is in an unknown state. chr(0xFF) is
* never a valid ASCII/UTF-8 sequence, so this should reliably
* induce an error/flush state.
*/
lexer->emit(lexer, lexer->token, JSON_ERROR, lexer->x, lexer->y);
QDECREF(lexer->token);
lexer->token = qstring_new();
new_state = IN_START;
lexer->state = new_state;
return 0;
default:
break;
}
lexer->state = new_state;
} while (!char_consumed && !flush);
/* Do not let a single token grow to an arbitrarily large size,
* this is a security consideration.
*/
if (lexer->token->length > MAX_TOKEN_SIZE) {
lexer->emit(lexer, lexer->token, lexer->state, lexer->x, lexer->y);
QDECREF(lexer->token);
lexer->token = qstring_new();
lexer->state = IN_START;
}
return 0;
}
int json_lexer_feed(JSONLexer *lexer, const char *buffer, size_t size)
{
size_t i;
for (i = 0; i < size; i++) {
int err;
err = json_lexer_feed_char(lexer, buffer[i], false);
if (err < 0) {
return err;
}
}
return 0;
}
int json_lexer_flush(JSONLexer *lexer)
{
return lexer->state == IN_START ? 0 : json_lexer_feed_char(lexer, 0, true);
}
void json_lexer_destroy(JSONLexer *lexer)
{
QDECREF(lexer->token);
}