Add JsonWriter

src/main/java/net/fabricmc/mappingio/MappingWriter.java

@@ -23,6 +23,7 @@
 import java.nio.file.Path;
 
 import net.fabricmc.mappingio.format.EnigmaWriter;
+import net.fabricmc.mappingio.format.JsonWriter;
 import net.fabricmc.mappingio.format.MappingFormat;
 import net.fabricmc.mappingio.format.Tiny1Writer;
 import net.fabricmc.mappingio.format.Tiny2Writer;
@@ -45,6 +46,7 @@ static MappingWriter create(Writer writer, MappingFormat format) throws IOExcept
 		switch (format) {
 		case TINY: return new Tiny1Writer(writer);
 		case TINY_2: return new Tiny2Writer(writer, false);
+		case JSON: return new JsonWriter(writer);
 		default: throw new UnsupportedOperationException("format "+format+" is not implemented");
 		}
 	}

src/main/java/net/fabricmc/mappingio/format/JsonUtil.java

@@ -0,0 +1,81 @@
+/*
+ * Copyright (c) 2021 FabricMC
+ *
+ * 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 net.fabricmc.mappingio.format;
+
+import java.io.IOException;
+import java.io.Writer;
+
+final class JsonUtil {
+	public static boolean needEscape(String s) {
+		for (int pos = 0, len = s.length(); pos < len; pos++) {
+			char c = s.charAt(pos);
+			if (toEscape.indexOf(c) >= 0) return true;
+		}
+
+		return false;
+	}
+
+	public static void writeEscaped(String s, Writer out) throws IOException {
+		final int len = s.length();
+		int start = 0;
+
+		for (int pos = 0; pos < len; pos++) {
+			char c = s.charAt(pos);
+			int idx = toEscape.indexOf(c);
+
+			if (idx >= 0) {
+				out.write(s, start, pos - start);
+				out.write('\\');
+				out.write(escaped.charAt(idx));
+				start = pos + 1;
+			}
+		}
+
+		out.write(s, start, len - start);
+	}
+
+	public static String unescape(String str) {
+		int pos = str.indexOf('\\');
+		if (pos < 0) return str;
+
+		StringBuilder ret = new StringBuilder(str.length() - 1);
+		int start = 0;
+
+		do {
+			ret.append(str, start, pos);
+			pos++;
+			int type;
+
+			if (pos >= str.length()) {
+				throw new RuntimeException("incomplete escape sequence at the end");
+			} else if ((type = escaped.indexOf(str.charAt(pos))) < 0) {
+				throw new RuntimeException("invalid escape character: \\"+str.charAt(pos));
+			} else {
+				ret.append(toEscape.charAt(type));
+			}
+
+			start = pos + 1;
+		} while ((pos = str.indexOf('\\', start)) >= 0);
+
+		ret.append(str, start, str.length());
+
+		return ret.toString();
+	}
+
+	private static final String toEscape = "\"\\\b\f\n\r\t";
+	private static final String escaped = "\"\\bfnrt";
+}