Simple readline algorithm for Networking

Are there any simple standardized way of reading a full line from a socket that mallocs the memory for you? If so, what are they? If not, is there a way to do it in approximately O(1) time (obviously not including the time for the memory allocation).

FILE* f;
char buffa[LINE_MAX];

f = fdopen(socket, "r+");
fgets(buffa, sizeof(buffa), f);