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Add explicit state management.
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For partial parsing support, we need to remember what we were doing so that we
can continue parsing. This commit adds an enum with all our parsing states and a
states stack to store the current states.
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@canatella
canatella committed Dec 29, 2016
1 parent 62220ad commit 621d48c
Showing 1 changed file with 122 additions and 11 deletions.
133 changes: 122 additions & 11 deletions json11.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -344,8 +344,30 @@ struct JsonParserPriv final {
const JsonParse strategy;
std::stack<Json> values;

enum State {
EXPECT_VALUE,
VALUE_STRING,
VALUE_NUMBER,
VALUE_TRUE,
VALUE_FALSE,
VALUE_NULL,
VALUE_COMMENT,
VALUE_OBJECT,
OBJECT_KEY_OR_END,
OBJECT_COMMA_OR_END,
OBJECT_KEY,
OBJECT_COLON,
OBJECT_VALUE,
VALUE_ARRAY,
ARRAY_VALUE_OR_END,
ARRAY_COMMA_OR_END,
ARRAY_VALUE
};
std::stack<State> states;

JsonParserPriv(string str, string &err, const JsonParse strategy):
str(str), err(err), strategy(strategy) {
push_state(EXPECT_VALUE);
}

/* fail(msg, err_ret = Json())
Expand All @@ -359,6 +381,7 @@ struct JsonParserPriv final {
template <typename T>
void fail(string &&msg, const T err_ret) {
if (!failed) {
pop_state();
err = std::move(msg);
}

Expand All @@ -367,6 +390,7 @@ struct JsonParserPriv final {
values.push(err_ret);

failed = true;
assert(states.size() > 0);
}

/* stop(msg, err_ret = Json())
Expand All @@ -391,6 +415,33 @@ struct JsonParserPriv final {
return i == str.size();
}

/* set_state()
*
* Set current parsing state.
*/
void set_state(State state) {
states.pop();
states.push(state);
}

/* push_state()
*
* push new current parsing state.
*/
void push_state(State state) {
states.push(state);
}

/* pop_state()
*
* Set current parsing state.
*/
void pop_state() {
states.pop();
}

#define assert_state(S) assert(states.top() == S)

/* consume_whitespace()
*
* Advance until the current character is non-whitespace.
Expand All @@ -405,6 +456,7 @@ struct JsonParserPriv final {
* Advance comments (c-style inline and multiline).
*/
void consume_comment() {
assert_state(VALUE_COMMENT);
bool comment_found = false;
if (str[i] == '/') {
i++;
Expand Down Expand Up @@ -446,6 +498,7 @@ struct JsonParserPriv final {
else
return fail("malformed comment", false);
}
pop_state();
values.push(comment_found);
}

Expand All @@ -458,6 +511,7 @@ struct JsonParserPriv final {
if(strategy == JsonParse::COMMENTS) {
bool comment_found = false;
do {
push_state(VALUE_COMMENT);
consume_comment();
if (need_data)
break;
Expand Down Expand Up @@ -515,6 +569,8 @@ struct JsonParserPriv final {
* Parse a string, starting at the current position.
*/
void parse_string() {
assert_state(VALUE_STRING);

string out;
long last_escaped_codepoint = -1;
while (true) {
Expand All @@ -525,6 +581,7 @@ struct JsonParserPriv final {

if (ch == '"') {
encode_utf8(last_escaped_codepoint, out);
pop_state();
values.push(out);
return;
}
Expand Down Expand Up @@ -609,6 +666,7 @@ struct JsonParserPriv final {
* Parse a double.
*/
void parse_number() {
assert_state(VALUE_NUMBER);
size_t start_pos = i;

if (str[i] == '-')
Expand Down Expand Up @@ -641,6 +699,7 @@ struct JsonParserPriv final {

if (str[i] != '.' && str[i] != 'e' && str[i] != 'E'
&& (i - start_pos) <= static_cast<size_t>(std::numeric_limits<int>::digits10)) {
pop_state();
return values.push(std::atoi(str.c_str() + start_pos));
}

Expand Down Expand Up @@ -690,6 +749,7 @@ struct JsonParserPriv final {
}
}

pop_state();
return values.push(std::strtod(str.c_str() + start_pos, nullptr));
}

Expand All @@ -707,6 +767,7 @@ struct JsonParserPriv final {

if (str.compare(i, expected.length(), expected) == 0) {
i += expected.length();
pop_state();
return values.push(res);
} else {
return fail("parse error: expected " + expected + ", got " + str.substr(i, expected.length()));
Expand All @@ -718,6 +779,7 @@ struct JsonParserPriv final {
* Parse a json true value.
*/
void parse_true() {
assert_state(VALUE_TRUE);
expect("true", true);
}

Expand All @@ -726,6 +788,7 @@ struct JsonParserPriv final {
* Parse a json false value.
*/
void parse_false() {
assert_state(VALUE_FALSE);
expect("false", false);
}

Expand All @@ -734,6 +797,7 @@ struct JsonParserPriv final {
* Parse a json null value.
*/
void parse_null() {
assert_state(VALUE_NULL);
expect("null", Json());
}

Expand All @@ -742,10 +806,16 @@ struct JsonParserPriv final {
* Parse a json object value.
*/
void parse_object() {
assert(states.top() >= VALUE_OBJECT && states.top() <= OBJECT_VALUE);

map<string, Json> data;

set_state(OBJECT_KEY_OR_END);
char ch = get_next_token();
if (ch == '}')
if (ch == '}') {
pop_state();
return values.push(data);
}

while (1) {
if (need_data)
Expand All @@ -754,6 +824,8 @@ struct JsonParserPriv final {
if (ch != '"')
return fail("expected '\"' in object, got " + esc(ch));

set_state(OBJECT_KEY);
push_state(VALUE_STRING);
parse_string();
if (need_data)
return;
Expand All @@ -764,13 +836,16 @@ struct JsonParserPriv final {
if (failed)
return values.push(Json());

set_state(OBJECT_COLON);
ch = get_next_token();
if (need_data)
return;

if (ch != ':')
return fail("expected ':' in object, got " + esc(ch));

set_state(OBJECT_VALUE);
push_state(EXPECT_VALUE);
parse_json();
if (need_data)
return;
Expand All @@ -783,12 +858,14 @@ struct JsonParserPriv final {

data[std::move(key)] = value;

set_state(OBJECT_COMMA_OR_END);
ch = get_next_token();
if (need_data)
return;

if (ch == '}') {
values.push(data);
pop_state();
break;
}

Expand All @@ -804,17 +881,27 @@ struct JsonParserPriv final {
* Parse a json array value.
*/
void parse_array() {
assert(states.top() >= VALUE_ARRAY && states.top() <= ARRAY_VALUE);

vector<Json> data;

set_state(ARRAY_VALUE_OR_END);
char ch = get_next_token();

if (ch == ']')
if (ch == ']') {
pop_state();
return values.push(data);
}

while (1) {
if (need_data)
return;

i--;

set_state(ARRAY_VALUE);
push_state(EXPECT_VALUE);

parse_json();
if (need_data)
return;
Expand All @@ -826,12 +913,14 @@ struct JsonParserPriv final {
return values.push(Json());
data.push_back(value);

set_state(ARRAY_COMMA_OR_END);
ch = get_next_token();
if (need_data)
return;

if (ch == ']') {
values.push(data);
pop_state();
break;
}

Expand All @@ -848,6 +937,8 @@ struct JsonParserPriv final {
* Parse any JSON value.
*/
void parse_json() {
assert_state(EXPECT_VALUE);

if (values.size() > max_depth) {
return fail("exceeded maximum nesting depth");
}
Expand All @@ -858,26 +949,39 @@ struct JsonParserPriv final {

if (ch == '-' || (ch >= '0' && ch <= '9')) {
i--;
set_state(VALUE_NUMBER);
return parse_number();
}

if (ch == 't')
if (ch == 't') {
set_state(VALUE_TRUE);
return parse_true();
}

if (ch == 'f')
if (ch == 'f') {
set_state(VALUE_FALSE);
return parse_false();
}

if (ch == 'n')
if (ch == 'n') {
set_state(VALUE_NULL);
return parse_null();
}

if (ch == '"')
if (ch == '"') {
set_state(VALUE_STRING);
return parse_string();
}

if (ch == '{')
if (ch == '{') {
set_state(VALUE_OBJECT);
return parse_object();
}

if (ch == '[')
if (ch == '[') {
set_state(VALUE_ARRAY);
return parse_array();
}

return fail("expected value, got " + esc(ch));
}
Expand Down Expand Up @@ -906,13 +1010,15 @@ Json JsonParser::json() const {

Json Json::parse(const string &in, string &err, JsonParse strategy) {
JsonParserPriv parser { in, err, strategy };
assert(parser.states.size() == 1);

parser.eof = true;
parser.parse_json();

// Check for any trailing garbage
parser.consume_garbage();
if (parser.i != in.size()) {
parser.fail("unexpected trailing " + esc(in[parser.i]));
err = "unexpected trailing " + esc(in[parser.i]);
return Json();
}

Expand All @@ -923,8 +1029,10 @@ Json Json::parse(const string &in, string &err, JsonParse strategy) {
}

#ifndef NDEBUG
if (!parser.failed)
if (!parser.failed) {
assert(parser.values.size() == 1);
assert(parser.states.empty());
}
#endif
return parser.values.top();
}
Expand Down Expand Up @@ -952,8 +1060,11 @@ vector<Json> Json::parse_multi(const string &in,
parser.values.pop();
// Check for another object
parser.consume_garbage();
if (!parser.failed && !parser.need_data)
if (!parser.failed && !parser.need_data) {
assert(parser.states.empty());
parser.push_state(JsonParserPriv::EXPECT_VALUE);
parser_stop_pos = parser.i;
}
}
return json_vec;
}
Expand Down

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