Golang - Socket Read Operation is taking long time - sockets

Question

I'm trying to read the response from a socket using the tcp connection type and net package in go.
func main() {
start := time.Now()
con, _ := net.Dial("tcp", "prodserver:6778")
defer con.Close()
b := make([]byte, 0, 512)
k := 0
for {
if len(b) == cap(b) {
b = append(b, 0)[:len(b)]
}
readStart := time.Now()
n, err := con.Read(b[len(b):cap(b)])
readEnd := time.Since(readStart)
fmt.Print("Start Iteraton #" + strconv.Itoa(k) + " ")
fmt.Print(readEnd)
fmt.Println(" End Iteraton #" + strconv.Itoa(k) + " byte size: " + strconv.Itoa(len(b)) + " ")
b = b[:len(b)+n]
if err != nil {
if err == io.EOF {
err = nil
}
// return b, err
break
}
k++
}
}
So I have tried calculate the duration taken for each read and printed to the console. And the results were interesting, all the read operations were very fast it took around a micro or milli seconds to complete except for the last read, it took around 1 minute.
Output:
Start Iteraton #0 551.32278ms End Iteraton #0 byte size: 0
Start Iteraton #1 11.577µs End Iteraton #1 byte size: 512
Start Iteraton #2 10.333µs End Iteraton #2 byte size: 896
Start Iteraton #3 5.204µs End Iteraton #3 byte size: 1408
Start Iteraton #4 6.605µs End Iteraton #4 byte size: 2048
Start Iteraton #5 6.452µs End Iteraton #5 byte size: 3072
//
// so on for the rest of iteration the time taken was very similar to above
//
Start Iteraton #238 37.747µs End Iteraton #238 byte size: 340285
Start Iteraton #239 23.235µs End Iteraton #239 byte size: 341630
Start Iteraton #240 58.041µs End Iteraton #240 byte size: 342975
Start Iteraton #241 34.192µs End Iteraton #241 byte size: 344320
Start Iteraton #242 101.094µs End Iteraton #242 byte size: 345665
Start Iteraton #243 1m0.307097139s End Iteraton #243 byte size: 346430
Any idea on why the last read operation is taking long time to complete? Is there any timeout we need to set.