From a7d31e61566f0d2e6cb0821fcdaf74ccfc1f8f64 Mon Sep 17 00:00:00 2001 From: Guus Sliepen Date: Fri, 3 Apr 2020 00:15:29 +0200 Subject: [PATCH] Add IPv4 style fragments for UDP style channels. Add a More Fragments (MF) bit to the ctl field in the header, and reuse the wnd field for the fragment offset. We only handle fragments that are received in-order. But this allows an application to not care about the maximum segment size. --- utcp.c | 89 ++++++++++++++++++++++++++++++++++++++++++++--------- utcp_priv.h | 2 ++ 2 files changed, 76 insertions(+), 15 deletions(-) diff --git a/utcp.c b/utcp.c index f2caab7..383e27f 100644 --- a/utcp.c +++ b/utcp.c @@ -145,12 +145,13 @@ static void print_packet(struct utcp_connection *c, const char *dir, const void *p = 0; - debug(c, "%s: len %lu src %u dst %u seq %u ack %u wnd %u aux %x ctl %s%s%s%s data %s\n", + debug(c, "%s: len %lu src %u dst %u seq %u ack %u wnd %u aux %x ctl %s%s%s%s%s data %s\n", dir, (unsigned long)len, hdr.src, hdr.dst, hdr.seq, hdr.ack, hdr.wnd, hdr.aux, hdr.ctl & SYN ? "SYN" : "", hdr.ctl & RST ? "RST" : "", hdr.ctl & FIN ? "FIN" : "", hdr.ctl & ACK ? "ACK" : "", + hdr.ctl & MF ? "MF" : "", str ); } @@ -368,12 +369,22 @@ static ssize_t buffer_discard(struct buffer *buf, size_t len) { buf->offset -= buf->size; } - buf->offset += len; + if(buf->used == len) { + buf->offset = 0; + } else { + buf->offset += len; + } + buf->used -= len; return len; } +static void buffer_clear(struct buffer *buf) { + buf->used = 0; + buf->offset = 0; +} + static bool buffer_set_size(struct buffer *buf, uint32_t minsize, uint32_t maxsize) { if(maxsize < minsize) { maxsize = minsize; @@ -644,7 +655,7 @@ void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) { static void ack(struct utcp_connection *c, bool sendatleastone) { int32_t left = seqdiff(c->snd.last, c->snd.nxt); - int32_t cwndleft = min(c->snd.cwnd, c->snd.wnd) - seqdiff(c->snd.nxt, c->snd.una); + int32_t cwndleft = is_reliable(c) ? min(c->snd.cwnd, c->snd.wnd) - seqdiff(c->snd.nxt, c->snd.una) : MAX_UNRELIABLE_SIZE; assert(left >= 0); @@ -672,7 +683,7 @@ static void ack(struct utcp_connection *c, bool sendatleastone) { pkt->hdr.src = c->src; pkt->hdr.dst = c->dst; pkt->hdr.ack = c->rcv.nxt; - pkt->hdr.wnd = c->rcvbuf.maxsize; + pkt->hdr.wnd = is_reliable(c) ? c->rcvbuf.maxsize : 0; pkt->hdr.ctl = ACK; pkt->hdr.aux = 0; @@ -685,6 +696,14 @@ static void ack(struct utcp_connection *c, bool sendatleastone) { c->snd.nxt += seglen; left -= seglen; + if(!is_reliable(c)) { + if(left) { + pkt->hdr.ctl |= MF; + } else { + pkt->hdr.ctl &= ~MF; + } + } + if(seglen && fin_wanted(c, c->snd.nxt)) { seglen--; pkt->hdr.ctl |= FIN; @@ -699,6 +718,10 @@ static void ack(struct utcp_connection *c, bool sendatleastone) { print_packet(c, "send", pkt, sizeof(pkt->hdr) + seglen); c->utcp->send(c->utcp, pkt, sizeof(pkt->hdr) + seglen); + + if(left && !is_reliable(c)) { + pkt->hdr.wnd += seglen; + } } while(left); } @@ -759,8 +782,13 @@ ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) { // Add data to send buffer. - if(is_reliable(c) || (c->state != SYN_SENT && c->state != SYN_RECEIVED)) { + if(is_reliable(c)) { len = buffer_put(&c->sndbuf, data, len); + } else if(c->state != SYN_SENT && c->state != SYN_RECEIVED) { + if(len > MAX_UNRELIABLE_SIZE || buffer_put(&c->sndbuf, data, len) != (ssize_t)len) { + errno = EMSGSIZE; + return -1; + } } else { return 0; } @@ -1095,15 +1123,50 @@ static void handle_in_order(struct utcp_connection *c, const void *data, size_t c->rcv.nxt += len; } +static void handle_unreliable(struct utcp_connection *c, const struct hdr *hdr, const void *data, size_t len) { + // Fast path for unfragmented packets + if(!hdr->wnd && !(hdr->ctl & MF)) { + c->recv(c, data, len); + c->rcv.nxt = hdr->seq + len; + return; + } -static void handle_incoming_data(struct utcp_connection *c, uint32_t seq, const void *data, size_t len) { + // Ensure reassembled packet are not larger than 64 kiB + if(hdr->wnd >= MAX_UNRELIABLE_SIZE || hdr->wnd + len > MAX_UNRELIABLE_SIZE) { + return; + } + + // Don't accept out of order fragments + if(hdr->wnd && hdr->seq != c->rcv.nxt) { + return; + } + + // Reset the receive buffer for the first fragment + if(!hdr->wnd) { + buffer_clear(&c->rcvbuf); + } + + ssize_t rxd = buffer_put_at(&c->rcvbuf, hdr->wnd, data, len); + + if(rxd != (ssize_t)len) { + return; + } + + // Send the packet if it's the final fragment + if(!(hdr->ctl & MF)) { + buffer_call(&c->rcvbuf, c->recv, c, 0, hdr->wnd + len); + } + + c->rcv.nxt = hdr->seq + len; +} + +static void handle_incoming_data(struct utcp_connection *c, const struct hdr *hdr, const void *data, size_t len) { if(!is_reliable(c)) { - c->recv(c, data, len); - c->rcv.nxt = seq + len; + handle_unreliable(c, hdr, data, len); return; } - uint32_t offset = seqdiff(seq, c->rcv.nxt); + uint32_t offset = seqdiff(hdr->seq, c->rcv.nxt); if(offset + len > c->rcvbuf.maxsize) { abort(); @@ -1160,7 +1223,7 @@ ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) { // Drop packets with an unknown CTL flag - if(hdr.ctl & ~(SYN | ACK | RST | FIN)) { + if(hdr.ctl & ~(SYN | ACK | RST | FIN | MF)) { print_packet(NULL, "recv", data, len); errno = EBADMSG; return -1; @@ -1374,10 +1437,6 @@ synack: debug(c, "packet out of order, offset %u bytes", rcv_offset); } - if(rcv_offset >= 0) { - c->rcv.nxt = hdr.seq + len; - } - #endif } @@ -1733,7 +1792,7 @@ skip_ack: return 0; } - handle_incoming_data(c, hdr.seq, ptr, len); + handle_incoming_data(c, &hdr, ptr, len); } // 7. Process FIN stuff diff --git a/utcp_priv.h b/utcp_priv.h index fe3fa6d..5672f06 100644 --- a/utcp_priv.h +++ b/utcp_priv.h @@ -29,6 +29,7 @@ #define ACK 2 #define FIN 4 #define RST 8 +#define MF 16 #define AUX_INIT 1 #define AUX_FRAME 2 @@ -41,6 +42,7 @@ #define DEFAULT_RCVBUFSIZE 0 #define DEFAULT_MAXRCVBUFSIZE 131072 +#define MAX_UNRELIABLE_SIZE 65536 #define DEFAULT_MTU 1000 #define USEC_PER_SEC 1000000L -- 2.39.2