从零准备 Redis：启动隔离实例并读写第一个键

import java.nio.charset.StandardCharsets;
import java.util.Arrays;
public class Main {
  record Result(boolean complete, byte[] payload, int consumed) {}
  static Result parse(byte[] data, int limit) {
    if (data == null || limit < 0) throw new IllegalArgumentException();
    if (data.length == 0) return new Result(false, null, 0);
    if (data[0] != '$') throw new IllegalArgumentException();
    int end = -1;
    for (int i=1; i+1<data.length; i++) {
      if (data[i]=='\r' && data[i+1]=='\n') { end=i; break; }
    }
    if (end < 0) return new Result(false, null, 0);
    String text = new String(data, 1, end-1, StandardCharsets.US_ASCII);
    if (!text.matches("-1|[0-9]+")) throw new IllegalArgumentException();
    long length;
    try { length=Long.parseLong(text); }
    catch (NumberFormatException e) { throw new IllegalArgumentException(e); }
    int start=end+2; // 头部结束后才开始计算载荷边界
    if (length == -1) return new Result(true, null, start);
    if (length > limit) throw new IllegalArgumentException();
    long needed=(long)start+length+2; // 相加不能溢出 int
    if (needed > data.length) return new Result(false, null, 0);
    int tail=start+(int)length;
    if (data[tail]!='\r' || data[tail+1]!='\n') throw new IllegalArgumentException();
    return new Result(true, Arrays.copyOfRange(data,start,tail), tail+2);
  }
  static byte[] bytes(String s) { return s.getBytes(StandardCharsets.UTF_8); }
  static void check(boolean condition) { if (!condition) throw new AssertionError(); }
  static void reject(String wire, int limit) {
    try { parse(bytes(wire),limit); throw new AssertionError("应拒绝"); }
    catch (IllegalArgumentException expected) { /* 期望的格式错误 */ }
  }
  public static void main(String[] args) {
    // 固定期望覆盖正常、空值和错误边界，失败立即中断验证
    Result one=parse(bytes("$5\r\nhello\r\nextra"),100);
    check(one.complete && one.consumed==11 && Arrays.equals(one.payload,bytes("hello")));
    Result empty=parse(bytes("$0\r\n\r\n"),100); check(empty.complete && empty.payload.length==0);
    Result absent=parse(bytes("$-1\r\n"),100); check(absent.complete && absent.payload==null);
    check(!parse(bytes("$5\r\nhe"),100).complete);
    check(!parse(new byte[0],100).complete);
    check(Arrays.equals(parse(bytes("$6\r\n中文\r\n"),100).payload,bytes("中文")));
    reject("$3\r\nabcXX",100);
    reject("$1000\r\n",10);
    reject("$-2\r\n",100);
    System.out.println("PASS 9 RESP tests");
  }
}