qemu/qobject/json-lexer.c
Markus Armbruster 852dfa76b8 json: Clean up how lexer consumes "end of input"
When the lexer isn't in its start state at the end of input, it's
working on a token.  To flush it out, it needs to transit to its start
state on "end of input" lookahead.

There are two ways to the start state, depending on the current state:

* If the lexer is in a TERMINAL(JSON_FOO) state, it can emit a
  JSON_FOO token.

* Else, it can go to IN_ERROR state, and emit a JSON_ERROR token.

There are complications, however:

* The transition to IN_ERROR state consumes the input character and
  adds it to the JSON_ERROR token.  The latter is inappropriate for
  the "end of input" character, so we suppress that.  See also recent
  commit a2ec6be72b "json: Fix lexer to include the bad character in
  JSON_ERROR token".

* The transition to a TERMINAL(JSON_FOO) state doesn't consume the
  input character.  In that case, the lexer normally loops until it is
  consumed.  We have to suppress that for the "end of input" input
  character.  If we didn't, the lexer would consume it by entering
  IN_ERROR state, emitting a bogus JSON_ERROR token.  We fixed that in
  commit bd3924a33a.

However, simply breaking the loop this way assumes that the lexer
needs exactly one state transition to reach its start state.  That
assumption is correct now, but it's unclean, and I'll soon break it.
Clean up: instead of breaking the loop after one iteration, break it
after it reached the start state.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20180831075841.13363-3-armbru@redhat.com>
2018-09-24 18:06:09 +02:00

357 lines
10 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 "qemu/osdep.h"
#include "json-parser-int.h"
#define MAX_TOKEN_SIZE (64ULL << 20)
/*
* From RFC 8259 "The JavaScript Object Notation (JSON) Data
* Interchange Format", with [comments in brackets]:
*
* The set of tokens includes six structural characters, strings,
* numbers, and three literal names.
*
* These are the six structural characters:
*
* begin-array = ws %x5B ws ; [ left square bracket
* begin-object = ws %x7B ws ; { left curly bracket
* end-array = ws %x5D ws ; ] right square bracket
* end-object = ws %x7D ws ; } right curly bracket
* name-separator = ws %x3A ws ; : colon
* value-separator = ws %x2C ws ; , comma
*
* Insignificant whitespace is allowed before or after any of the six
* structural characters.
* [This lexer accepts it before or after any token, which is actually
* the same, as the grammar always has structural characters between
* other tokens.]
*
* ws = *(
* %x20 / ; Space
* %x09 / ; Horizontal tab
* %x0A / ; Line feed or New line
* %x0D ) ; Carriage return
*
* [...] three literal names:
* false null true
* [This lexer accepts [a-z]+, and leaves rejecting unknown literal
* names to the parser.]
*
* [Numbers:]
*
* number = [ minus ] int [ frac ] [ exp ]
* decimal-point = %x2E ; .
* digit1-9 = %x31-39 ; 1-9
* e = %x65 / %x45 ; e E
* exp = e [ minus / plus ] 1*DIGIT
* frac = decimal-point 1*DIGIT
* int = zero / ( digit1-9 *DIGIT )
* minus = %x2D ; -
* plus = %x2B ; +
* zero = %x30 ; 0
*
* [Strings:]
* string = quotation-mark *char quotation-mark
*
* 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
* [This lexer accepts any non-control character after escape, and
* leaves rejecting invalid ones to the parser.]
*
*
* 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.
* - Interpolation, if enabled:
* The lexer accepts %[A-Za-z0-9]*, and leaves rejecting invalid
* ones to the parser.
*
* Note:
* - Input must be encoded in modified UTF-8.
* - Decoding and validating is left to the parser.
*/
enum json_lexer_state {
IN_ERROR = 0, /* must really be 0, see json_lexer[] */
IN_DQ_STRING_ESCAPE,
IN_DQ_STRING,
IN_SQ_STRING_ESCAPE,
IN_SQ_STRING,
IN_ZERO,
IN_EXP_DIGITS,
IN_EXP_SIGN,
IN_EXP_E,
IN_MANTISSA,
IN_MANTISSA_DIGITS,
IN_DIGITS,
IN_SIGN,
IN_KEYWORD,
IN_INTERP,
IN_WHITESPACE,
IN_START,
IN_START_INTERP, /* must be IN_START + 1 */
};
QEMU_BUILD_BUG_ON((int)JSON_MIN <= (int)IN_START_INTERP);
QEMU_BUILD_BUG_ON(IN_START_INTERP != IN_START + 1);
#define TERMINAL(state) [0 ... 0xFF] = (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) \
(terminal != IN_ERROR && json_lexer[(old_state)][0] == (terminal))
static const uint8_t json_lexer[][256] = {
/* Relies on default initialization to IN_ERROR! */
/* double quote string */
[IN_DQ_STRING_ESCAPE] = {
[0x20 ... 0xFD] = IN_DQ_STRING,
},
[IN_DQ_STRING] = {
[0x20 ... 0xFD] = IN_DQ_STRING,
['\\'] = IN_DQ_STRING_ESCAPE,
['"'] = JSON_STRING,
},
/* single quote string */
[IN_SQ_STRING_ESCAPE] = {
[0x20 ... 0xFD] = IN_SQ_STRING,
},
[IN_SQ_STRING] = {
[0x20 ... 0xFD] = IN_SQ_STRING,
['\\'] = IN_SQ_STRING_ESCAPE,
['\''] = JSON_STRING,
},
/* Zero */
[IN_ZERO] = {
TERMINAL(JSON_INTEGER),
['0' ... '9'] = IN_ERROR,
['.'] = IN_MANTISSA,
},
/* Float */
[IN_EXP_DIGITS] = {
TERMINAL(JSON_FLOAT),
['0' ... '9'] = IN_EXP_DIGITS,
},
[IN_EXP_SIGN] = {
['0' ... '9'] = IN_EXP_DIGITS,
},
[IN_EXP_E] = {
['-'] = IN_EXP_SIGN,
['+'] = IN_EXP_SIGN,
['0' ... '9'] = IN_EXP_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_DIGITS] = {
TERMINAL(JSON_INTEGER),
['0' ... '9'] = IN_DIGITS,
['e'] = IN_EXP_E,
['E'] = IN_EXP_E,
['.'] = IN_MANTISSA,
},
[IN_SIGN] = {
['0'] = IN_ZERO,
['1' ... '9'] = IN_DIGITS,
},
/* 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,
},
/* interpolation */
[IN_INTERP] = {
TERMINAL(JSON_INTERP),
['A' ... 'Z'] = IN_INTERP,
['a' ... 'z'] = IN_INTERP,
['0' ... '9'] = IN_INTERP,
},
/*
* Two start states:
* - IN_START recognizes JSON tokens with our string extensions
* - IN_START_INTERP additionally recognizes interpolation.
*/
[IN_START ... IN_START_INTERP] = {
['"'] = IN_DQ_STRING,
['\''] = IN_SQ_STRING,
['0'] = IN_ZERO,
['1' ... '9'] = IN_DIGITS,
['-'] = IN_SIGN,
['{'] = JSON_LCURLY,
['}'] = JSON_RCURLY,
['['] = JSON_LSQUARE,
[']'] = JSON_RSQUARE,
[','] = JSON_COMMA,
[':'] = JSON_COLON,
['a' ... 'z'] = IN_KEYWORD,
[' '] = IN_WHITESPACE,
['\t'] = IN_WHITESPACE,
['\r'] = IN_WHITESPACE,
['\n'] = IN_WHITESPACE,
},
[IN_START_INTERP]['%'] = IN_INTERP,
};
void json_lexer_init(JSONLexer *lexer, bool enable_interpolation)
{
lexer->start_state = lexer->state = enable_interpolation
? IN_START_INTERP : IN_START;
lexer->token = g_string_sized_new(3);
lexer->x = lexer->y = 0;
}
static void json_lexer_feed_char(JSONLexer *lexer, char ch, bool flush)
{
int new_state;
bool char_consumed = false;
lexer->x++;
if (ch == '\n') {
lexer->x = 0;
lexer->y++;
}
while (flush ? lexer->state != lexer->start_state : !char_consumed) {
assert(lexer->state <= ARRAY_SIZE(json_lexer));
new_state = json_lexer[lexer->state][(uint8_t)ch];
char_consumed = !flush
&& !TERMINAL_NEEDED_LOOKAHEAD(lexer->state, new_state);
if (char_consumed) {
g_string_append_c(lexer->token, ch);
}
switch (new_state) {
case JSON_LCURLY:
case JSON_RCURLY:
case JSON_LSQUARE:
case JSON_RSQUARE:
case JSON_COLON:
case JSON_COMMA:
case JSON_INTERP:
case JSON_INTEGER:
case JSON_FLOAT:
case JSON_KEYWORD:
case JSON_STRING:
json_message_process_token(lexer, lexer->token, new_state,
lexer->x, lexer->y);
/* fall through */
case JSON_SKIP:
g_string_truncate(lexer->token, 0);
new_state = lexer->start_state;
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
* parser by emitting a JSON_ERROR token, then reset lexer 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.
*/
json_message_process_token(lexer, lexer->token, JSON_ERROR,
lexer->x, lexer->y);
g_string_truncate(lexer->token, 0);
lexer->state = lexer->start_state;
return;
default:
break;
}
lexer->state = new_state;
}
/* Do not let a single token grow to an arbitrarily large size,
* this is a security consideration.
*/
if (lexer->token->len > MAX_TOKEN_SIZE) {
json_message_process_token(lexer, lexer->token, lexer->state,
lexer->x, lexer->y);
g_string_truncate(lexer->token, 0);
lexer->state = lexer->start_state;
}
}
void json_lexer_feed(JSONLexer *lexer, const char *buffer, size_t size)
{
size_t i;
for (i = 0; i < size; i++) {
json_lexer_feed_char(lexer, buffer[i], false);
}
}
void json_lexer_flush(JSONLexer *lexer)
{
json_lexer_feed_char(lexer, 0, true);
assert(lexer->state == lexer->start_state);
json_message_process_token(lexer, lexer->token, JSON_END_OF_INPUT,
lexer->x, lexer->y);
}
void json_lexer_destroy(JSONLexer *lexer)
{
g_string_free(lexer->token, true);
}