SIM 808 TCP connection (Arduino library) - c++

Question

I AM WORKING WITH SIM808 for tcp connection, below is what my code looks like it is pretty much the basic tcp connection and i keep get fetch over and I can tell that is a problem with my content lenght but i feel if i have a better understanding that will be fine.
#include <DFRobot_sim808.h>
#include <SoftwareSerial.h>
//#define PIN_TX 10
//#define PIN_RX 11
//SoftwareSerial mySerial(PIN_TX,PIN_RX);
//DFRobot_SIM808 sim808(&mySerial);//Connect RX,TX,PWR,
DFRobot_SIM808 sim808(&Serial);
char http_cmd[] = "GET /media/uploads/mbed_official/hello.txt HTTP/1.0\r\n\r\n";
char buffer[512];
void setup(){
//mySerial.begin(9600);
Serial.begin(9600);
//******** Initialize sim808 module *************
while(!sim808.init()) {
delay(1000);
Serial.print("Sim808 init error\r\n");
}
delay(3000);
//*********** Attempt DHCP *******************
while(!sim808.join(F("cmnet"))) {
Serial.println("Sim808 join network error");
delay(2000);
}
//************ Successful DHCP ****************
Serial.print("IP Address is ");
Serial.println(sim808.getIPAddress());
//*********** Establish a TCP connection ************
if(!sim808.connect(TCP,"mbed.org", 80)) {
Serial.println("Connect error");
}else{
Serial.println("Connect mbed.org success");
}
//*********** Send a GET request *****************
Serial.println("waiting to fetch...");
sim808.send(http_cmd, sizeof(http_cmd)-1);
while (true) {
int ret = sim808.recv(buffer, sizeof(buffer)-1);
if (ret <= 0){
Serial.println("fetch over...");
break;
}
buffer[ret] = '\0';
Serial.print("Recv: ");
Serial.print(ret);
Serial.print(" bytes: ");
Serial.println(buffer);
break;
}
//************* Close TCP or UDP connections **********
sim808.close();
//*** Disconnect wireless connection, Close Moving Scene *******
sim808.disconnect();
}
void loop(){
}
but i dont seem to understand what goes on at a point of the code, what does the part below, mean in the code
while (true) {
int ret = sim808.recv(buffer, sizeof(buffer)-1);
if (ret <= 0){
Serial.println("fetch over...");
break;
}
buffer[ret] = '\0';
Serial.print("Recv: ");
Serial.print(ret);
Serial.print(" bytes: ");
Serial.println(buffer);
break;
}
with emphasis on int ret = sim808.recv(buffer, sizeof(buffer)-1); how is the value of ret gotten?

Answer 1

If you just open up the .h file in the library you will find that it is pretty well documented. Have a look at the declaration for the function you are asking about:
/** read data from socket
* #param socket socket
* #param buf buffer that will store the data read from socket
* #param len string length need to read from socket
* #returns bytes that actually read
*/
int recv(char* buf, int len);
It details exactly what each parameter is and what the return value is. Looks like it returns the number of bytes read.