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qjson: Convert to parser to recursive descent
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We backtrack in parse_value(), even though JSON is LL(1) and thus can
be parsed by straightforward recursive descent.  Do exactly that.

Based on an almost-correct patch from Paolo Bonzini.

Signed-off-by: Paolo Bonzini <[email protected]>
Signed-off-by: Markus Armbruster <[email protected]>
Message-Id: <[email protected]>
Reviewed-by: Eric Blake <[email protected]>
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Markus Armbruster committed Nov 26, 2015
1 parent d2ca7c0 commit d538b25
Showing 1 changed file with 47 additions and 118 deletions.
165 changes: 47 additions & 118 deletions qobject/json-parser.c
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Original file line number Diff line number Diff line change
Expand Up @@ -265,23 +265,6 @@ static QObject *parser_context_peek_token(JSONParserContext *ctxt)
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;
Expand Down Expand Up @@ -333,7 +316,6 @@ static void parser_context_free(JSONParserContext *ctxt)
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) {
Expand Down Expand Up @@ -371,7 +353,6 @@ static int parse_pair(JSONParserContext *ctxt, QDict *dict, va_list *ap)
return 0;

out:
parser_context_restore(ctxt, saved_ctxt);
qobject_decref(key);

return -1;
Expand All @@ -381,16 +362,9 @@ 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_get_type(token) != JSON_LCURLY) {
goto out;
}
assert(token && token_get_type(token) == JSON_LCURLY);

dict = qdict_new();

Expand Down Expand Up @@ -434,7 +408,6 @@ static QObject *parse_object(JSONParserContext *ctxt, va_list *ap)
return QOBJECT(dict);

out:
parser_context_restore(ctxt, saved_ctxt);
QDECREF(dict);
return NULL;
}
Expand All @@ -443,16 +416,9 @@ 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_get_type(token) != JSON_LSQUARE) {
goto out;
}
assert(token && token_get_type(token) == JSON_LSQUARE);

list = qlist_new();

Expand Down Expand Up @@ -506,109 +472,72 @@ static QObject *parse_array(JSONParserContext *ctxt, va_list *ap)
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);
QObject *token;
const char *val;

token = parser_context_pop_token(ctxt);
if (token == NULL) {
goto out;
}

if (token_get_type(token) != JSON_KEYWORD) {
goto out;
}

assert(token && token_get_type(token) == JSON_KEYWORD);
val = token_get_value(token);

if (!strcmp(val, "true")) {
ret = QOBJECT(qbool_from_bool(true));
return QOBJECT(qbool_from_bool(true));
} else if (!strcmp(val, "false")) {
ret = QOBJECT(qbool_from_bool(false));
return QOBJECT(qbool_from_bool(false));
} else if (!strcmp(val, "null")) {
ret = qnull();
} else {
parse_error(ctxt, token, "invalid keyword '%s'", val);
goto out;
return qnull();
}

return ret;

out:
parser_context_restore(ctxt, saved_ctxt);

parse_error(ctxt, token, "invalid keyword '%s'", val);
return NULL;
}

static QObject *parse_escape(JSONParserContext *ctxt, va_list *ap)
{
QObject *token = NULL, *obj;
JSONParserContext saved_ctxt = parser_context_save(ctxt);
QObject *token;
const char *val;

if (ap == NULL) {
goto out;
return NULL;
}

token = parser_context_pop_token(ctxt);
if (token == NULL) {
goto out;
}

if (token_get_type(token) != JSON_ESCAPE) {
goto out;
}

assert(token && token_get_type(token) == JSON_ESCAPE);
val = token_get_value(token);

if (!strcmp(val, "%p")) {
obj = va_arg(*ap, QObject *);
return va_arg(*ap, QObject *);
} else if (!strcmp(val, "%i")) {
obj = QOBJECT(qbool_from_bool(va_arg(*ap, int)));
return QOBJECT(qbool_from_bool(va_arg(*ap, int)));
} else if (!strcmp(val, "%d")) {
obj = QOBJECT(qint_from_int(va_arg(*ap, int)));
return QOBJECT(qint_from_int(va_arg(*ap, int)));
} else if (!strcmp(val, "%ld")) {
obj = QOBJECT(qint_from_int(va_arg(*ap, long)));
return QOBJECT(qint_from_int(va_arg(*ap, long)));
} else if (!strcmp(val, "%lld") ||
!strcmp(val, "%I64d")) {
obj = QOBJECT(qint_from_int(va_arg(*ap, long long)));
return QOBJECT(qint_from_int(va_arg(*ap, long long)));
} else if (!strcmp(val, "%s")) {
obj = QOBJECT(qstring_from_str(va_arg(*ap, const char *)));
return QOBJECT(qstring_from_str(va_arg(*ap, const char *)));
} else if (!strcmp(val, "%f")) {
obj = QOBJECT(qfloat_from_double(va_arg(*ap, double)));
} else {
goto out;
return QOBJECT(qfloat_from_double(va_arg(*ap, double)));
}

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);
QObject *token;

token = parser_context_pop_token(ctxt);
if (token == NULL) {
goto out;
}
assert(token);

switch (token_get_type(token)) {
case JSON_STRING:
obj = QOBJECT(qstring_from_escaped_str(ctxt, token));
break;
return QOBJECT(qstring_from_escaped_str(ctxt, token));
case JSON_INTEGER: {
/* A possibility exists that this is a whole-valued float where the
* fractional part was left out due to being 0 (.0). It's not a big
Expand All @@ -627,46 +556,46 @@ static QObject *parse_literal(JSONParserContext *ctxt)
errno = 0; /* strtoll doesn't set errno on success */
value = strtoll(token_get_value(token), NULL, 10);
if (errno != ERANGE) {
obj = QOBJECT(qint_from_int(value));
break;
return QOBJECT(qint_from_int(value));
}
/* fall through to JSON_FLOAT */
}
case JSON_FLOAT:
/* FIXME dependent on locale */
obj = QOBJECT(qfloat_from_double(strtod(token_get_value(token), NULL)));
break;
return QOBJECT(qfloat_from_double(strtod(token_get_value(token),
NULL)));
default:
goto out;
abort();
}

return obj;

out:
parser_context_restore(ctxt, saved_ctxt);

return NULL;
}

static QObject *parse_value(JSONParserContext *ctxt, va_list *ap)
{
QObject *obj;
QObject *token;

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);
token = parser_context_peek_token(ctxt);
if (token == NULL) {
parse_error(ctxt, NULL, "premature EOI");
return NULL;
}

return obj;
switch (token_get_type(token)) {
case JSON_LCURLY:
return parse_object(ctxt, ap);
case JSON_LSQUARE:
return parse_array(ctxt, ap);
case JSON_ESCAPE:
return parse_escape(ctxt, ap);
case JSON_INTEGER:
case JSON_FLOAT:
case JSON_STRING:
return parse_literal(ctxt);
case JSON_KEYWORD:
return parse_keyword(ctxt);
default:
parse_error(ctxt, token, "expecting value");
return NULL;
}
}

QObject *json_parser_parse(QList *tokens, va_list *ap)
Expand Down

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