/*
* Copyright (C) 2012-2015 DataStax Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.datastax.driver.core;
import java.util.*;
/**
* A very simple json parser.
* The only reason we need to read json in the driver is because for
* historical reason Cassandra encodes a few properties using json in
* the schema and we need to decode them.
* <p/>
* We however don't need a full-blown JSON library because:
* 1) we know we only need to decode string lists and string maps
* 2) we can basically assume the input is valid, we don't particularly
* have to bother about decoding exactly JSON as long as we at least
* decode what we need.
* 3) we don't really care much about performance, none of this is done
* in performance sensitive parts.
* <p/>
* So instead of pulling a new dependency, we roll out our own very dumb
* parser. We should obviously not expose this publicly.
*/
class SimpleJSONParser {
private final String input;
private int idx;
private SimpleJSONParser(String input) {
this.input = input;
}
public static List<String> parseStringList(String input) {
if (input == null || input.isEmpty())
return Collections.<String>emptyList();
List<String> output = new ArrayList<String>();
SimpleJSONParser parser = new SimpleJSONParser(input);
if (parser.nextCharSkipSpaces() != '[')
throw new IllegalArgumentException("Not a JSON list: " + input);
char c = parser.nextCharSkipSpaces();
if (c == ']')
return output;
while (true) {
assert c == '"';
output.add(parser.nextString());
c = parser.nextCharSkipSpaces();
if (c == ']')
return output;
assert c == ',';
c = parser.nextCharSkipSpaces();
}
}
public static Map<String, String> parseStringMap(String input) {
if (input == null || input.isEmpty())
return Collections.<String, String>emptyMap();
Map<String, String> output = new HashMap<String, String>();
SimpleJSONParser parser = new SimpleJSONParser(input);
if (parser.nextCharSkipSpaces() != '{')
throw new IllegalArgumentException("Not a JSON map: " + input);
char c = parser.nextCharSkipSpaces();
if (c == '}')
return output;
while (true) {
assert c == '"';
String key = parser.nextString();
c = parser.nextCharSkipSpaces();
assert c == ':';
c = parser.nextCharSkipSpaces();
assert c == '"';
String value = parser.nextString();
output.put(key, value);
c = parser.nextCharSkipSpaces();
if (c == '}')
return output;
assert c == ',';
c = parser.nextCharSkipSpaces();
}
}
/**
* Read the next char, the one at position idx, and advance ix.
*/
private char nextChar() {
if (idx >= input.length())
throw new IllegalArgumentException("Invalid json input: " + input);
return input.charAt(idx++);
}
/**
* Same as nextChar, except that it skips space characters (' ', '\t' and '\n').
*/
private char nextCharSkipSpaces() {
char c = nextChar();
while (c == ' ' || c == '\t' || c == '\n')
c = nextChar();
return c;
}
/**
* Reads a String, assuming idx is on the first character of the string (i.e. the
* one after the opening double-quote character).
* After the string has been read, idx will be on the first character after
* the closing double-quote.
*/
private String nextString() {
assert input.charAt(idx - 1) == '"' : "Char is '" + input.charAt(idx - 1) + '\'';
StringBuilder sb = new StringBuilder();
while (true) {
char c = nextChar();
switch (c) {
case '\n':
case '\r':
throw new IllegalArgumentException("Unterminated string");
case '\\':
c = nextChar();
switch (c) {
case 'b':
sb.append('\b');
break;
case 't':
sb.append('\t');
break;
case 'n':
sb.append('\n');
break;
case 'f':
sb.append('\f');
break;
case 'r':
sb.append('\r');
break;
case 'u':
sb.append((char) Integer.parseInt(input.substring(idx, idx + 4), 16));
idx += 4;
break;
case '"':
case '\'':
case '\\':
case '/':
sb.append(c);
break;
default:
throw new IllegalArgumentException("Illegal escape");
}
break;
default:
if (c == '"')
return sb.toString();
sb.append(c);
}
}
}
}