In order to avoid stashing all the tokens corresponding to a JSON value, embed the parsing stack and state machine in JSONParser. This is more efficient and allows for more prompt error recovery; it also does not make the code substantially larger than the current recursive descent parser, though the state machine is probably a bit harder to follow.
The stack consists of QLists and QDicts corresponding to open brackets and braces, plus optionally a QString with the current key on top of each QDict. After each value is parsed, it is added to the top array or dictionary or, if the stack is empty, json_parser_feed returns the complete QObject. For now, json-streamer.c keeps tracking the tokens up until braces and brackets are balanced, and then shoves the whole queue of tokens into the push parser. The only logic change is that JSON_END_OF_INPUT always triggers the emptying of the queue; the parser takes notice and checks that there is nothing on the stack. Not using brace_count and bracket_count for this is the first step towards improved separation of concerns between json-parser.c and json-streamer.c. Signed-off-by: Paolo Bonzini <[email protected]> --- include/qobject/json-parser.h | 6 + qobject/json-parser-int.h | 4 +- qobject/json-parser.c | 430 +++++++++++++++++----------------- qobject/json-streamer.c | 21 +- 4 files changed, 245 insertions(+), 216 deletions(-) diff --git a/include/qobject/json-parser.h b/include/qobject/json-parser.h index 7345a9bd5cb..05346fa816b 100644 --- a/include/qobject/json-parser.h +++ b/include/qobject/json-parser.h @@ -20,6 +20,12 @@ typedef struct JSONLexer { int x, y; } JSONLexer; +typedef struct JSONParserContext { + Error *err; + GQueue *stack; + va_list *ap; +} JSONParserContext; + typedef struct JSONMessageParser { void (*emit)(void *opaque, QObject *json, Error *err); void *opaque; diff --git a/qobject/json-parser-int.h b/qobject/json-parser-int.h index 8c01f236276..05e2e8e1831 100644 --- a/qobject/json-parser-int.h +++ b/qobject/json-parser-int.h @@ -49,6 +49,8 @@ void json_message_process_token(JSONLexer *lexer, GString *input, /* json-parser.c */ JSONToken *json_token(JSONTokenType type, int x, int y, GString *tokstr); -QObject *json_parser_parse(GQueue *tokens, va_list *ap, Error **errp); +void json_parser_init(JSONParserContext *ctxt, va_list *ap); +QObject *json_parser_feed(JSONParserContext *ctxt, const JSONToken *token, Error **errp); +void json_parser_destroy(JSONParserContext *ctxt); #endif diff --git a/qobject/json-parser.c b/qobject/json-parser.c index eabc9f8358c..338f0c5aae6 100644 --- a/qobject/json-parser.c +++ b/qobject/json-parser.c @@ -31,12 +31,36 @@ struct JSONToken { char str[]; }; -typedef struct JSONParserContext { - Error *err; - JSONToken *current; - GQueue *buf; - va_list *ap; -} JSONParserContext; +/* + * Objects: { } | { members } + * - Empty: { -> AFTER_LCURLY -> } + * - Non-empty: { -> AFTER_LCURLY -> BEFORE_KEY -> string -> END_OF_KEY -> : -> + * BEFORE_VALUE -> value -> END_OF_VALUE -> , -> BEFORE_KEY -> ... -> } + * + * Arrays: [ ] | [ elements ] + * - Empty: [ -> AFTER_LSQUARE -> ] + * - Non-empty: [ -> AFTER_LSQUARE -> BEFORE_VALUE -> value -> END_OF_VALUE -> , -> + * BEFORE_VALUE -> ... -> ] + * + * The two cases for END_OF_VALUE are distinguished based on the type of QObject at + * top-of-stack. + */ +typedef enum JSONParserState { + AFTER_LCURLY, + AFTER_LSQUARE, + BEFORE_KEY, + BEFORE_VALUE, + END_OF_KEY, + END_OF_VALUE, +} JSONParserState; + +typedef struct JSONParserStackEntry { + /* A QString with the last parsed key, or a QList/QDict for the current container. */ + QObject *partial; + + /* Needed to distinguish whether the parser is waiting for a colon or comma. */ + JSONParserState state; +} JSONParserStackEntry; #define BUG_ON(cond) assert(!(cond)) @@ -49,7 +73,29 @@ typedef struct JSONParserContext { * 4) deal with premature EOI */ -static QObject *parse_value(JSONParserContext *ctxt, const JSONToken *token); +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); +} + +/* Note that entry->partial does *not* lose its reference count even if value == NULL. */ +static JSONParserStackEntry *pop_entry(JSONParserContext *ctxt, QObject **value) +{ + JSONParserStackEntry *entry = g_queue_pop_tail(ctxt->stack); + if (value) { + *value = entry->partial; + } + g_free(entry); + return current_entry(ctxt); +} /** * Error handler @@ -235,189 +281,7 @@ out: return NULL; } -/* Note: the token object returned by parser_context_pop_token is - * deleted as soon as parser_context_pop_token is called again. - */ -static const JSONToken *parser_context_pop_token(JSONParserContext *ctxt) -{ - g_free(ctxt->current); - ctxt->current = g_queue_pop_head(ctxt->buf); - return ctxt->current; -} - -/** - * Parsing rules - */ -static int parse_pair(JSONParserContext *ctxt, const JSONToken *token, QDict *dict) -{ - QObject *key_obj = NULL; - QString *key; - QObject *value; - - key_obj = parse_value(ctxt, token); - key = qobject_to(QString, key_obj); - if (!key) { - parse_error(ctxt, token, "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->type != JSON_COLON) { - parse_error(ctxt, token, "missing : in object pair"); - goto out; - } - - token = parser_context_pop_token(ctxt); - if (token == NULL) { - parse_error(ctxt, NULL, "premature EOI"); - goto out; - } - - value = parse_value(ctxt, token); - if (value == NULL) { - parse_error(ctxt, token, "Missing value in dict"); - goto out; - } - - if (qdict_haskey(dict, qstring_get_str(key))) { - parse_error(ctxt, token, "duplicate key"); - goto out; - } - - qdict_put_obj(dict, qstring_get_str(key), value); - - qobject_unref(key_obj); - return 0; - -out: - qobject_unref(key_obj); - return -1; -} - -static QObject *parse_object(JSONParserContext *ctxt) -{ - QDict *dict = NULL; - const JSONToken *token; - - dict = qdict_new(); - - token = parser_context_pop_token(ctxt); - if (token == NULL) { - parse_error(ctxt, NULL, "premature EOI"); - goto out; - } - - if (token->type != JSON_RCURLY) { - if (parse_pair(ctxt, token, dict) == -1) { - goto out; - } - - token = parser_context_pop_token(ctxt); - if (token == NULL) { - parse_error(ctxt, NULL, "premature EOI"); - goto out; - } - - while (token->type != JSON_RCURLY) { - if (token->type != JSON_COMMA) { - parse_error(ctxt, token, "expected separator in dict"); - goto out; - } - - token = parser_context_pop_token(ctxt); - if (token == NULL) { - parse_error(ctxt, NULL, "premature EOI"); - goto out; - } - - if (parse_pair(ctxt, token, dict) == -1) { - goto out; - } - - token = parser_context_pop_token(ctxt); - if (token == NULL) { - parse_error(ctxt, NULL, "premature EOI"); - goto out; - } - } - } - - return QOBJECT(dict); - -out: - qobject_unref(dict); - return NULL; -} - -static QObject *parse_array(JSONParserContext *ctxt) -{ - QList *list = NULL; - const JSONToken *token; - - list = qlist_new(); - - token = parser_context_pop_token(ctxt); - if (token == NULL) { - parse_error(ctxt, NULL, "premature EOI"); - goto out; - } - - if (token->type != JSON_RSQUARE) { - QObject *obj; - - obj = parse_value(ctxt, token); - 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->type != JSON_RSQUARE) { - if (token->type != JSON_COMMA) { - parse_error(ctxt, token, "expected separator in list"); - goto out; - } - - token = parser_context_pop_token(ctxt); - if (token == NULL) { - parse_error(ctxt, NULL, "premature EOI"); - goto out; - } - - obj = parse_value(ctxt, token); - 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; - } - } - } - - return QOBJECT(list); - -out: - qobject_unref(list); - return NULL; -} +/* Terminals */ static QObject *parse_keyword(JSONParserContext *ctxt, const JSONToken *token) { @@ -516,13 +380,17 @@ static QObject *parse_literal(JSONParserContext *ctxt, const JSONToken *token) } } -static QObject *parse_value(JSONParserContext *ctxt, const JSONToken *token) +/* Parsing state machine */ + +static QObject *parse_begin_value(JSONParserContext *ctxt, const JSONToken *token) { switch (token->type) { case JSON_LCURLY: - return parse_object(ctxt); + push_entry(ctxt, QOBJECT(qdict_new()), AFTER_LCURLY); + return NULL; case JSON_LSQUARE: - return parse_array(ctxt); + push_entry(ctxt, QOBJECT(qlist_new()), AFTER_LSQUARE); + return NULL; case JSON_INTERP: return parse_interpolation(ctxt, token); case JSON_INTEGER: @@ -537,6 +405,130 @@ static QObject *parse_value(JSONParserContext *ctxt, const JSONToken *token) } } +static QObject *json_parser_parse_token(JSONParserContext *ctxt, const JSONToken *token) +{ + JSONParserStackEntry *entry; + JSONParserState state; + QString *key; + QObject *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 */ + if (token->type == JSON_RCURLY) { + entry = pop_entry(ctxt, &value); + break; + } + entry->state = BEFORE_KEY; + /* fall through */ + + case BEFORE_KEY: + /* Expecting object key */ + if (token->type == JSON_STRING) { + key = parse_string(ctxt, token); + if (!key) { + return NULL; + } + + /* Store key in a special entry on the stack */ + push_entry(ctxt, QOBJECT(key), END_OF_KEY); + } else { + parse_error(ctxt, token, "expecting key"); + } + return NULL; + + case END_OF_KEY: + /* Expecting ':' after key */ + 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 */ + if (token->type == JSON_RSQUARE) { + entry = pop_entry(ctxt, &value); + break; + } + entry->state = BEFORE_VALUE; + /* fall through */ + + case BEFORE_VALUE: + /* Expecting value */ + 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 value or insert into parent container */ + entry = pop_entry(ctxt, &value); + break; + } + + assert(value); + if (entry == NULL) { + /* The toplevel value is complete. */ + return value; + } + + key = qobject_to(QString, entry->partial); + if (key) { + const char *key_str; + QDict *dict; + + entry = pop_entry(ctxt, NULL); + 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 { + /* Add to array */ + qlist_append_obj(qobject_to(QList, entry->partial), value); + } + + entry->state = END_OF_VALUE; + return NULL; +} + JSONToken *json_token(JSONTokenType type, int x, int y, GString *tokstr) { JSONToken *token = g_malloc(sizeof(JSONToken) + tokstr->len + 1); @@ -549,27 +541,43 @@ JSONToken *json_token(JSONTokenType type, int x, int y, GString *tokstr) return token; } -QObject *json_parser_parse(GQueue *tokens, va_list *ap, Error **errp) +void json_parser_init(JSONParserContext *ctxt, va_list *ap) { - JSONParserContext ctxt = { .buf = tokens, .ap = ap }; - QObject *result; - const JSONToken *token; + ctxt->err = NULL; + ctxt->stack = g_queue_new(); + ctxt->ap = ap; +} - token = parser_context_pop_token(&ctxt); - if (token == NULL) { - parse_error(&ctxt, NULL, "premature EOI"); - return NULL; +void json_parser_destroy(JSONParserContext *ctxt) +{ + JSONParserStackEntry *entry; + + while ((entry = g_queue_pop_tail(ctxt->stack)) != NULL) { + qobject_unref(entry->partial); + g_free(entry); + } + g_queue_free(ctxt->stack); + ctxt->stack = NULL; +} + +QObject *json_parser_feed(JSONParserContext *ctxt, const JSONToken *token, Error **errp) +{ + QObject *result = NULL; + + assert(!ctxt->err); + switch (token->type) { + 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 = json_parser_parse_token(ctxt, token); + break; } - result = parse_value(&ctxt, token); - assert(ctxt.err || g_queue_is_empty(ctxt.buf)); - - error_propagate(errp, ctxt.err); - - while (!g_queue_is_empty(ctxt.buf)) { - parser_context_pop_token(&ctxt); - } - g_free(ctxt.current); - + error_propagate(errp, ctxt->err); return result; } diff --git a/qobject/json-streamer.c b/qobject/json-streamer.c index b93d97b995f..6c93e6fd78d 100644 --- a/qobject/json-streamer.c +++ b/qobject/json-streamer.c @@ -32,6 +32,7 @@ void json_message_process_token(JSONLexer *lexer, GString *input, JSONTokenType type, int x, int y) { JSONMessageParser *parser = container_of(lexer, JSONMessageParser, lexer); + JSONParserContext ctxt; QObject *json = NULL; Error *err = NULL; JSONToken *token; @@ -56,8 +57,7 @@ void json_message_process_token(JSONLexer *lexer, GString *input, if (g_queue_is_empty(&parser->tokens)) { return; } - json = json_parser_parse(&parser->tokens, parser->ap, &err); - goto out_emit; + break; default: break; } @@ -85,11 +85,24 @@ void json_message_process_token(JSONLexer *lexer, GString *input, g_queue_push_tail(&parser->tokens, token); if ((parser->brace_count > 0 || parser->bracket_count > 0) - && parser->brace_count >= 0 && parser->bracket_count >= 0) { + && parser->brace_count >= 0 && parser->bracket_count >= 0 + && type != JSON_END_OF_INPUT) { return; } - json = json_parser_parse(&parser->tokens, parser->ap, &err); + json_parser_init(&ctxt, parser->ap); + + /* Process all tokens in the queue */ + while (!g_queue_is_empty(&parser->tokens)) { + token = g_queue_pop_head(&parser->tokens); + json = json_parser_feed(&ctxt, token, &err); + g_free(token); + if (json || err) { + break; + } + } + + json_parser_destroy(&ctxt); out_emit: parser->brace_count = 0; -- 2.52.0
