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332 lines (305 loc) · 10.2 KB
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package com.babelqueue;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
/**
* A minimal, dependency-free JSON reader/writer — just enough for the BabelQueue
* wire envelope. It keeps the Java core free of Jackson/Gson so it never forces a
* JSON library on consumers.
*
* <p>Parsing yields {@link LinkedHashMap} (objects, insertion order preserved),
* {@link ArrayList} (arrays), {@link String}, {@link Boolean}, {@code null}, and
* {@link Long}/{@link BigInteger}/{@link Double} (numbers). Writing emits compact
* JSON with slashes and non-ASCII left unescaped, matching the other SDK cores.
*/
final class Json {
private Json() {}
// ---- Writer ---------------------------------------------------------------
static String write(Object value) {
StringBuilder sb = new StringBuilder();
writeValue(sb, value);
return sb.toString();
}
private static void writeValue(StringBuilder sb, Object v) {
if (v == null) {
sb.append("null");
} else if (v instanceof String s) {
writeString(sb, s);
} else if (v instanceof Boolean b) {
sb.append(b ? "true" : "false");
} else if (v instanceof Map<?, ?> m) {
writeObject(sb, m);
} else if (v instanceof Iterable<?> it) {
writeArray(sb, it);
} else if (v instanceof Number n) {
writeNumber(sb, n);
} else {
writeString(sb, v.toString());
}
}
private static void writeObject(StringBuilder sb, Map<?, ?> m) {
sb.append('{');
boolean first = true;
for (Map.Entry<?, ?> e : m.entrySet()) {
if (!first) {
sb.append(',');
}
first = false;
writeString(sb, String.valueOf(e.getKey()));
sb.append(':');
writeValue(sb, e.getValue());
}
sb.append('}');
}
private static void writeArray(StringBuilder sb, Iterable<?> it) {
sb.append('[');
boolean first = true;
for (Object o : it) {
if (!first) {
sb.append(',');
}
first = false;
writeValue(sb, o);
}
sb.append(']');
}
private static void writeNumber(StringBuilder sb, Number n) {
if (n instanceof Double || n instanceof Float) {
double d = n.doubleValue();
if (Double.isNaN(d) || Double.isInfinite(d)) {
throw new BabelQueueException("Cannot encode non-finite number: " + n);
}
sb.append(Double.toString(d));
} else {
sb.append(n.toString());
}
}
private static void writeString(StringBuilder sb, String s) {
sb.append('"');
for (int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
switch (c) {
case '"' -> sb.append("\\\"");
case '\\' -> sb.append("\\\\");
case '\b' -> sb.append("\\b");
case '\f' -> sb.append("\\f");
case '\n' -> sb.append("\\n");
case '\r' -> sb.append("\\r");
case '\t' -> sb.append("\\t");
default -> {
if (c < 0x20) {
sb.append(String.format("\\u%04x", (int) c));
} else {
// Slashes, non-ASCII (UTF-8), <, >, & are all left literal.
sb.append(c);
}
}
}
}
sb.append('"');
}
// ---- Parser ---------------------------------------------------------------
static Object parse(String raw) {
Parser p = new Parser(raw);
p.skipWhitespace();
Object value = p.parseValue();
p.skipWhitespace();
if (!p.atEnd()) {
throw new BabelQueueException("Trailing content after JSON value at index " + p.index());
}
return value;
}
private static final class Parser {
private final String s;
private int i;
Parser(String s) {
this.s = s;
}
int index() {
return i;
}
boolean atEnd() {
return i >= s.length();
}
void skipWhitespace() {
while (i < s.length()) {
char c = s.charAt(i);
if (c == ' ' || c == '\t' || c == '\n' || c == '\r') {
i++;
} else {
break;
}
}
}
private char peek() {
if (i >= s.length()) {
throw error("unexpected end of input");
}
return s.charAt(i);
}
private char next() {
if (i >= s.length()) {
throw error("unexpected end of input");
}
return s.charAt(i++);
}
private BabelQueueException error(String message) {
return new BabelQueueException("JSON parse error at index " + i + ": " + message);
}
Object parseValue() {
skipWhitespace();
char c = peek();
return switch (c) {
case '{' -> parseObject();
case '[' -> parseArray();
case '"' -> parseString();
case 't', 'f' -> parseBoolean();
case 'n' -> parseNull();
default -> {
if (c == '-' || (c >= '0' && c <= '9')) {
yield parseNumber();
}
throw error("unexpected character '" + c + "'");
}
};
}
private Map<String, Object> parseObject() {
Map<String, Object> map = new LinkedHashMap<>();
next(); // consume '{'
skipWhitespace();
if (peek() == '}') {
next();
return map;
}
while (true) {
skipWhitespace();
if (peek() != '"') {
throw error("expected string key");
}
String key = parseString();
skipWhitespace();
if (next() != ':') {
throw error("expected ':'");
}
map.put(key, parseValue());
skipWhitespace();
char c = next();
if (c == '}') {
return map;
}
if (c != ',') {
throw error("expected ',' or '}'");
}
}
}
private List<Object> parseArray() {
List<Object> list = new ArrayList<>();
next(); // consume '['
skipWhitespace();
if (peek() == ']') {
next();
return list;
}
while (true) {
list.add(parseValue());
skipWhitespace();
char c = next();
if (c == ']') {
return list;
}
if (c != ',') {
throw error("expected ',' or ']'");
}
}
}
private String parseString() {
next(); // consume opening '"'
StringBuilder sb = new StringBuilder();
while (true) {
char c = next();
if (c == '"') {
return sb.toString();
}
if (c == '\\') {
char e = next();
switch (e) {
case '"' -> sb.append('"');
case '\\' -> sb.append('\\');
case '/' -> sb.append('/');
case 'b' -> sb.append('\b');
case 'f' -> sb.append('\f');
case 'n' -> sb.append('\n');
case 'r' -> sb.append('\r');
case 't' -> sb.append('\t');
case 'u' -> {
if (i + 4 > s.length()) {
throw error("invalid \\u escape");
}
sb.append((char) Integer.parseInt(s.substring(i, i + 4), 16));
i += 4;
}
default -> throw error("invalid escape '\\" + e + "'");
}
} else {
sb.append(c);
}
}
}
private Boolean parseBoolean() {
if (s.startsWith("true", i)) {
i += 4;
return Boolean.TRUE;
}
if (s.startsWith("false", i)) {
i += 5;
return Boolean.FALSE;
}
throw error("invalid literal");
}
private Object parseNull() {
if (s.startsWith("null", i)) {
i += 4;
return null;
}
throw error("invalid literal");
}
private Number parseNumber() {
int start = i;
if (peek() == '-') {
next();
}
while (!atEnd() && Character.isDigit(peek())) {
next();
}
boolean isDouble = false;
if (!atEnd() && peek() == '.') {
isDouble = true;
next();
while (!atEnd() && Character.isDigit(peek())) {
next();
}
}
if (!atEnd() && (peek() == 'e' || peek() == 'E')) {
isDouble = true;
next();
if (!atEnd() && (peek() == '+' || peek() == '-')) {
next();
}
while (!atEnd() && Character.isDigit(peek())) {
next();
}
}
String token = s.substring(start, i);
if (isDouble) {
return Double.valueOf(token);
}
try {
return Long.valueOf(token);
} catch (NumberFormatException ex) {
return new BigInteger(token);
}
}
}
}