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improving JSON decoder
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@jvde-github
jvde-github committed Jan 18, 2025
1 parent 6871445 commit ca6fc2c
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Showing 2 changed files with 126 additions and 50 deletions.
174 changes: 125 additions & 49 deletions JSON/Parser.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -20,110 +20,166 @@

#include "Parser.h"

namespace JSON {
namespace JSON
{

// Parser -- Build JSON object from String

void Parser::error(const std::string& err, int pos) {
void Parser::error(const std::string &err, int pos)
{
const int char_limit = 40;
int from = MAX(pos - char_limit, 0);
int to = MIN(pos + char_limit, json.size());

std::stringstream ss;
for (int i = from; i < to; i++) {
for (int i = from; i < to; i++)
{
char c = json[i];
char d = (c == '\t' || c == '\r' || c == '\n') ? ' ' : c;
ss << d;
}
ss << std::endl
<< std::string(MIN(char_limit, pos), ' ') << "^" << std::endl
<< std::string(MIN(char_limit, pos), ' ') << "^" << std::endl;
throw std::runtime_error("JSON parsing error: " + err);
<< std::string(MIN(char_limit, pos), ' ') << "^" << std::endl
<< std::string(MIN(char_limit, pos), ' ') << "^" << std::endl;
throw std::runtime_error("syntax error in JSON: " + err);
}

// Lex analysis

void Parser::skip_whitespace(int& ptr) {
while (ptr < json.size() && std::isspace(json[ptr])) ptr++;
void Parser::skip_whitespace(int &ptr)
{
while (ptr < json.size() && std::isspace(json[ptr]))
ptr++;
}

void Parser::tokenizer() {
void Parser::tokenizer()
{

tokens.clear();
std::string s;
int ptr = 0;

while (ptr < json.size()) {
while (ptr < json.size())
{

skip_whitespace(ptr);
if (ptr == json.size()) break;
if (ptr == json.size())
break;

char c = json[ptr];

// number
if (std::isdigit(c) || c == '-') {
if (std::isdigit(c) || c == '-')
{
bool floating = false;
int start_idx = ptr;
bool scientific = false;

s.clear();

do {
if (json[ptr] == '.') {
do
{
if (json[ptr] == '.')
{
if (floating || start_idx == ptr || !std::isdigit(json[ptr - 1]))
error("malformed number", ptr);
else
floating = true;
}
else if ((json[ptr] == 'e' || json[ptr] == 'E') && !scientific) {
else if ((json[ptr] == 'e' || json[ptr] == 'E') && !scientific)
{
if (!std::isdigit(json[ptr - 1]) && json[ptr - 1] != '.')
error("malformed number", ptr);

scientific = floating = true;

s += json[ptr++];
if (ptr != json.size() && (json[ptr] == '+' || json[ptr] == '-')) {
if (ptr != json.size() && (json[ptr] == '+' || json[ptr] == '-'))
{
s += json[ptr++];
}

if (ptr == json.size() || !std::isdigit(json[ptr]))
error("malformed number", ptr);
}

s += json[ptr++];

} while (ptr != json.size() && (std::isdigit(json[ptr]) || json[ptr] == '.' || json[ptr] == 'e' || json[ptr] == 'E'));

tokens.push_back(Token(floating ? TokenType::FloatingPoint : TokenType::Integer, s, ptr));
}
// string
else if (c == '\"') {
else if (c == '\"')
{
s.clear();
ptr++;

while (ptr != json.size() && json[ptr] != '\"' && json[ptr] != '\n' && json[ptr] != '\r') {
if (json[ptr] == '\\') {
if (++ptr == json.size()) error("line ends in string literal escape sequence", ptr);
if (json[ptr] != '\"') {
Error() << "Cannot parse JSON string: " << json;
error("escape sequence not supported\\allowed", ptr);
while (ptr != json.size() && json[ptr] != '\"' && json[ptr] != '\n' && json[ptr] != '\r')
{
char c = json[ptr];
if (c == '\\')
{
if (++ptr == json.size())
error("line ends in string literal escape sequence", ptr);
c = json[ptr];
switch (c)
{
case '\"':
break;
case '\\':
break;
case '/':
break;
case 'b':
c = '\b';
break;
case 'f':
c = '\f';
break;
case 'n':
c = '\n';
break;
case 'r':
c = '\r';
break;
case 't':
c = '\t';
break;
case 'u':
{
if (ptr + 4 >= json.size())
error("line ends in string literal unicode escape sequence", ptr);
std::string hex = json.substr(ptr + 1, 4);
for (int i = 0; i < 4; i++)
if (!std::isxdigit(hex[i]))
error("illegal unicode escape sequence", ptr);
c = std::stoi(hex, nullptr, 16);
ptr += 4;
break;
}
default:
error("illegal escape sequence " + std::to_string((int)(c)), ptr);
}

}
s += json[ptr++];
s += c;
ptr++;
};

if (json.size() == ptr || json[ptr] != '\"') error("line ends in string literal", ptr);
if (json.size() == ptr || json[ptr] != '\"')
error("line ends in string literal", ptr);

tokens.push_back(Token(TokenType::String, s, ptr));
ptr++;
}
// keyword
else if (isalpha(c)) {
else if (isalpha(c))
{

s.clear();

while (ptr != json.size() && isalpha(json[ptr])) s += json[ptr++];
while (ptr != json.size() && isalpha(json[ptr]))
s += json[ptr++];

if (s == "true")
tokens.push_back(Token(TokenType::True, "", ptr));
Expand All @@ -135,8 +191,10 @@ namespace JSON {
error("illegal identifier : \"" + s + "\"", ptr);
}
// special characters
else {
switch (c) {
else
{
switch (c)
{
case '{':
tokens.push_back(Token(TokenType::LeftBrace, "", ptr));
break;
Expand Down Expand Up @@ -167,39 +225,50 @@ namespace JSON {

// Parsing functions

void Parser::error_parser(const std::string& err) {
void Parser::error_parser(const std::string &err)
{
error(err, tokens[MIN(tokens.size() - 1, idx)].pos);
}

bool Parser::is_match(TokenType t) {
if (idx >= tokens.size()) error_parser("unexpected end in input");
bool Parser::is_match(TokenType t)
{
if (idx >= tokens.size())
error_parser("unexpected end in input");
return tokens[idx].type == t;
}

void Parser::must_match(TokenType t, const std::string& err) {
if (!is_match(t)) error_parser(err);
void Parser::must_match(TokenType t, const std::string &err)
{
if (!is_match(t))
error_parser(err);
}

void Parser::next() {
void Parser::next()
{
idx++;
if (idx >= tokens.size()) error_parser("unexpected end in input");
if (idx >= tokens.size())
error_parser("unexpected end in input");
}

// search for keyword in "map", returns index in map or -1 if not found
int Parser::search(const std::string& s) {
int Parser::search(const std::string &s)
{
int p = -1;
for (int i = 0; i < keymap->size(); i++)
if (dict < (*keymap)[i].size() && (*keymap)[i][dict] == s) {
if (dict < (*keymap)[i].size() && (*keymap)[i][dict] == s)
{
p = i;
break;
}
return p;
}

Value Parser::parse_value(std::shared_ptr<JSON> o) {
Value Parser::parse_value(std::shared_ptr<JSON> o)
{
Value v = Value();
v.setNull();
switch (tokens[idx].type) {
switch (tokens[idx].type)
{
case TokenType::Integer:
v.setInt(Util::Parse::Integer(tokens[idx].text));
break;
Expand Down Expand Up @@ -230,10 +299,12 @@ namespace JSON {

next();

while (!is_match(TokenType::RightBracket)) {
while (!is_match(TokenType::RightBracket))
{
o->arrays.back()->push_back(parse_value(o));
next();
if (!is_match(TokenType::Comma)) break;
if (!is_match(TokenType::Comma))
break;
next();
if (is_match(TokenType::RightBracket))
error_parser("comma cannot be followed by ']'");
Expand All @@ -253,15 +324,18 @@ namespace JSON {
return v;
}

std::shared_ptr<JSON> Parser::parse_core() {
std::shared_ptr<JSON> Parser::parse_core()
{
std::shared_ptr<JSON> o = std::shared_ptr<JSON>(new JSON());

must_match(TokenType::LeftBrace, "expected '{'");
next();

while (is_match(TokenType::String)) {
while (is_match(TokenType::String))
{
int p = search(tokens[idx].text);
if (p < 0) {
if (p < 0)
{
if (!skipUnknownKeys)
error_parser("\"" + tokens[idx].text + "\" is not an allowed \"key\"");
}
Expand All @@ -273,7 +347,8 @@ namespace JSON {
o->Add(p, parse_value(o));
next();

if (!is_match(TokenType::Comma)) break;
if (!is_match(TokenType::Comma))
break;
next();
if (!is_match(TokenType::String))
error_parser("comma needs to be followed by property");
Expand All @@ -282,7 +357,8 @@ namespace JSON {
must_match(TokenType::RightBrace, "expected '}'");
return o;
}
std::shared_ptr<JSON> Parser::parse(const std::string& j) {
std::shared_ptr<JSON> Parser::parse(const std::string &j)
{
json = j;
idx = 0;
tokenizer();
Expand Down
2 changes: 1 addition & 1 deletion Library/NMEA.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -438,7 +438,7 @@ namespace AIS {
}
}
catch (std::exception const& e) {
std::cout << "NMEA model: " << e.what() ;
Error() << "NMEA model: " << e.what() ;
}
}
}
Expand Down

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