in runner-core/src/main/java/org/apache/apisix/plugin/runner/handler/PayloadDecoder.java [124:133]
private int bytes2Int(byte[] b, int start, int len) {
int sum = 0;
int end = start + len;
for (int i = start; i < end; i++) {
int n = b[i] & 0xff;
n <<= (--len) * 8;
sum += n;
}
return sum;
}