Why doesn't data return when I use Sim808 http request
One problem I can see is the while loop has a break statement in it that "exits" the while loop before printing the data. Removing that break and printing the data out where the break "was" may help. Here's an example of what I'm trying to say:

void setup(){
  Serial.begin(9600);  
}

void loop(){

  while(true){
    int ret = 0;
    if(ret &lt;= 0){
      Serial.println("fetch over...");
      // Print out the received data here...
      Serial.print("Recv: ");
      Serial.print(ret);
      break;
    }
  }

}