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parser.c: Extract json_match_keyword #996

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Merged
byroot merged 1 commit into from
Jun 5, 2026
+29 −25
Merged

parser.c: Extract json_match_keyword #996

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52 changes: 28 additions & 24 deletions ext/json/ext/parser/parser.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1425,9 +1425,7 @@ static inline VALUE json_parse_positive_number(JSON_ParserState *state, JSON_Par

static inline VALUE json_parse_negative_number(JSON_ParserState *state, JSON_ParserConfig *config)
{
const char *start = state->cursor;
state->cursor++;
return json_parse_number(state, config, true, start);
return json_parse_number(state, config, true, state->cursor - 1);
}

// How many values (array elements, or interleaved object keys+values) have been
Expand All @@ -1452,6 +1450,22 @@ static inline void json_value_completed(json_frame *frame)
frame->phase = (enum json_frame_phase) frame->type;
}

static inline bool json_match_keyword(JSON_ParserState *state, const char *keyword, size_t offset)
{
// It is assumed that since `keyword` is always a literal, the compiler is able to constantize this
// `strlen` and several other computations in that routine, such as eliminating the `if (resumable)` branch.
Comment on lines +1453 to +1456
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@eregon eregon Jun 5, 2026

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An ALWAYS_INLINE (I think available from CRuby headers) would help guarantee that, vs depending on the compiler inlining heuristics.
(inline doesn't mean to inline but just tolerate multiple definitions of it)

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@byroot byroot Jun 5, 2026

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yeah we have a shim for it.

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@eregon eregon Jun 5, 2026

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#998 if it's helpful


size_t len = strlen(keyword);

// Note: memcmp with a small power of two and a literal string compile to an integer comparison /
// That's why we sometime compare starting from the first byte and sometimes from the second.
if (rest(state) >= len && (memcmp(state->cursor + offset, keyword + offset, len - offset) == 0)) {
state->cursor += len;
return true;
}
return false;
}

// Parse an arbitrary JSON value iteratively. This is a state machine driven
// entirely by the top frame's phase so it can stop at any value boundary and
// resume purely from the frame stack. A JSON_FRAME_ROOT frame sits at the
Expand All @@ -1475,27 +1489,23 @@ static VALUE json_parse_any(JSON_ParserState *state, JSON_ParserConfig *config)

switch (peek(state)) {
case 'n':
if (rest(state) >= 4 && (memcmp(state->cursor, "null", 4) == 0)) {
state->cursor += 4;
if (json_match_keyword(state, "null", 0)) {
json_push_value(state, config, Qnil);
json_value_completed(frame);
break;
}

raise_parse_error("unexpected token %s", state);
case 't':
if (rest(state) >= 4 && (memcmp(state->cursor, "true", 4) == 0)) {
state->cursor += 4;
if (json_match_keyword(state, "true", 0)) {
json_push_value(state, config, Qtrue);
json_value_completed(frame);
break;
}

raise_parse_error("unexpected token %s", state);
case 'f':
// Note: memcmp with a small power of two compile to an integer comparison
if (rest(state) >= 5 && (memcmp(state->cursor + 1, "alse", 4) == 0)) {
state->cursor += 5;
if (json_match_keyword(state, "false", 1)) {
json_push_value(state, config, Qfalse);
json_value_completed(frame);
break;
Expand All @@ -1504,35 +1514,29 @@ static VALUE json_parse_any(JSON_ParserState *state, JSON_ParserConfig *config)
raise_parse_error("unexpected token %s", state);
case 'N':
// Note: memcmp with a small power of two compile to an integer comparison
if (config->allow_nan && rest(state) >= 3 && (memcmp(state->cursor + 1, "aN", 2) == 0)) {
state->cursor += 3;
if (config->allow_nan && json_match_keyword(state, "NaN", 1)) {
json_push_value(state, config, CNaN);
json_value_completed(frame);
break;
}

raise_parse_error("unexpected token %s", state);
case 'I':
if (config->allow_nan && rest(state) >= 8 && (memcmp(state->cursor, "Infinity", 8) == 0)) {
state->cursor += 8;
if (config->allow_nan && json_match_keyword(state, "Infinity", 0)) {
json_push_value(state, config, CInfinity);
json_value_completed(frame);
break;
}

raise_parse_error("unexpected token %s", state);
case '-': {
// Note: memcmp with a small power of two compile to an integer comparison
if (rest(state) >= 9 && (memcmp(state->cursor + 1, "Infinity", 8) == 0)) {
if (config->allow_nan) {
state->cursor += 9;
json_push_value(state, config, CMinusInfinity);
json_value_completed(frame);
break;
} else {
raise_parse_error("unexpected token %s", state);
}
state->cursor++;
if (config->allow_nan && json_match_keyword(state, "Infinity", 0)) {
json_push_value(state, config, CMinusInfinity);
json_value_completed(frame);
break;
}

json_push_value(state, config, json_parse_negative_number(state, config));
json_value_completed(frame);
break;
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2 changes: 1 addition & 1 deletion test/json/json_ext_parser_test.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -26,7 +26,7 @@ def test_error_messages

ex = assert_raise(ParserError) { parse('-Infinity something') }
unless RUBY_PLATFORM =~ /java/
assert_equal "unexpected token '-Infinity' at line 1 column 1", ex.message
assert_equal "invalid number: '-Infinity' at line 1 column 1", ex.message
end

ex = assert_raise(ParserError) { parse('NaN something') }
Expand Down
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