Add support for chunking of served files

This removes the limitation that a file served from FLASH memory
needs to be smaller than the TCP buffer size. Now we serve up to
the TCP buffer size in the first go and then remember what parts
still need to be sent. As soon as the previous package has been
acked, the next chunk of data is copied from flash into the
TCP transmit buffer and gets sent. We take care only to send
the current TCP window size so no further fragmentation needs to
happen, thus optimizing transmission of the remainder.

Author: logicog

httpd/httpd.c

@@ -33,6 +33,8 @@ __xdata uint16_t slen;
 __xdata uint16_t o_idx;
 __xdata uint16_t mpos;
 __xdata uint16_t len_left;
+__xdata uint16_t cont_len;
+__xdata uint32_t cont_addr;
 
 // HTTP header properties
 __xdata uint8_t boundary[72];
@@ -386,12 +388,22 @@ void httpd_appcall(void)
 		if (slen > uip_mss()) {
 			print_string("Sending A: "); print_short(slen); write_char('\n');
 			uip_send(outbuf + o_idx, uip_mss());
-			print_string("Sending A done\n");
 			s->tstate = TSTATE_TX;
 		} else if (slen > 0) {
 			print_string("Sending B: "); print_short(slen); write_char('\n');
 			uip_send(outbuf + o_idx, slen);
-			print_string("Sending B done\n");
+			s->tstate = TSTATE_TX;
+		} else if (cont_len) {
+			print_string("CONT cont_len: "); print_short(cont_len);
+			slen = cont_len > uip_mss() ? uip_mss() : cont_len;
+			if (slen > TCP_OUTBUF_SIZE)
+				slen = TCP_OUTBUF_SIZE;
+			flash_region.addr = cont_addr;
+			flash_region.len = slen;
+			flash_read_bulk(outbuf);
+			uip_send(outbuf, slen);
+			cont_len -= slen;
+			cont_addr += slen;
 			s->tstate = TSTATE_TX;
 		}
 	} else if (uip_newdata() && s->tstate == TSTATE_POST) {
@@ -452,7 +464,11 @@ void httpd_appcall(void)
 			slen += strtox(outbuf + slen, mime_strings[f_data[entry].mime]);
 			slen += strtox(outbuf + slen, "\r\nCache-Control: max-age=2592000\r\n\r\n");
 			len_left = f_data[entry].len;
-
+			if (len_left > (TCP_OUTBUF_SIZE - slen)) {
+				cont_len = len_left - (TCP_OUTBUF_SIZE - slen);
+				len_left = TCP_OUTBUF_SIZE - slen;
+				cont_addr = f_data[entry].start + len_left;
+			}
 			print_string("MIME: "); print_string(mime_strings[f_data[entry].mime]); write_char('\n');
 			flash_region.addr = f_data[entry].start;
 			flash_region.len = len_left;