Arduino - SD.h / Ethernet.h - Buffered file read / write

SD-Ethernet-Buffered-Read-Write.c

int bufferSize = 64; // buffer size you want to use
while(file.available()) // file you previously pointed at
{
    char buffer[bufferSize];
    memset(buffer, '\n', bufferSize); // don't forget to fill the buffer with \n to prevent errors on last buffer read
    file.read(&buffer, bufferSize); // read from file
    client->write(buffer, bufferSize); // write to client
}