LSA校验和计算(java源码)

最近在写一个路由模拟工具，由于没有找到java的相关代码，jpcap又没有提供路由协议包解析的类，所以在git开了一个基于jpcap的路由工具包的工程，链接如下：点击打开链接

今天在写这个工具与路由器交互动作时发现lsa的校验和算法找不到java的源码，于是花了一晚上把quagga的校验和计算代码改成了java的。亲测可用，源码如下：

public class lsaChecksum {public static shortospf_lsa_checksum (byte[] data){  /* Skip the AGE field */  int len = data.length;   /* Checksum offset starts from "options" field, not the beginning of the     lsa_header struct. The offset is 14, rather than 16. */  int checksum_offset = 14;  return fletcher_checksum(data, len, checksum_offset);}/* Fletcher Checksum -- Refer to RFC1008. */private static final int MODX=4102;   /* 5802 should be fine */private static final int FLETCHER_CHECKSUM_VALIDATE=0xffff;/* To be consistent, offset is 0-based index, rather than the 1-based    index required in the specification ISO 8473, Annex C.1 *//* calling with offset == FLETCHER_CHECKSUM_VALIDATE will validate the checksum   without modifying the buffer; a valid checksum returns 0 */public static shortfletcher_checksum(byte[] buffer, int len, int offset){  byte[] p;  int x, y, c0, c1;  short checksum;  int partial_len, i, left = len;    checksum = 0;  p = buffer;  c0 = 0;  c1 = 0;  while (left != 0)    {      partial_len =left<MODX?left:MODX;// MIN(left, MODX);      for (i = 0; i < partial_len; i++){  c0 = c0 + (p[i]&0xff);  c1 += c0;}      c0 = c0 % 255;      c1 = c1 % 255;      left -= partial_len;    }  /* The cast is important, to ensure the mod is taken as a signed value. */  x = (int)((len - offset - 1) * c0 - c1) % 255;  if (x <= 0)    x += 255;  y = 510 - c0 - x;  if (y > 255)      y -= 255;  if (offset == FLETCHER_CHECKSUM_VALIDATE)    {      checksum = (short) ((c1 << 8) + c0);    }  else    {      /*       * Now we write this to the packet.       * We could skip this step too, since the checksum returned would       * be stored into the checksum field by the caller.       */      buffer[offset] = (byte) x;      buffer[offset + 1] = (byte) y;      for(int ii=0;ii<len;ii++){      System.out.printf("%x ",buffer[ii]);      }      /* Take care of the endian issue */      checksum = (short) ((x << 8) | (y & 0xFF));    }  return checksum;}}

单元测试代码如下：

public class lsaChecksumTest {@Beforepublic void setUp() throws Exception {}@Testpublic void testOspf_lsa_checksum() {byte[] data={0x22,0x02,0x01,0x01,0x03,0x02,0x01,0x01,0x03,0x02,(byte) 0x80,0x00,0x00,0x01,0x00,0x00,0x00,0x20,(byte) 0xff,(byte) 0xff,(byte) 0xff,0x00,0x01,0x01,0x03,0x02,0x01,0x01,0x03,0x01};short result=lsaChecksum.ospf_lsa_checksum(data);if(result!=(short)0xa975)fail("wrong checksum");}}