lib: Send and receive window updates

This adds sending and receiving window updates for flow control. I
used the 8 pad bits as part of the window update field, so it's 24
bits, allowing for ~16 million packets in flight.

Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks>
Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>

4 files changed, 41 insertions, 12 deletions

diff --git a/include/ouroboros/fccntl.h b/include/ouroboros/fccntl.h
index ccd74b6c..0ebc90f3 100644
--- a/include/ouroboros/fccntl.h
+++ b/include/ouroboros/fccntl.h
@@ -46,9 +46,9 @@
 #define FLOWFINVALID  (FLOWFWRONLY | FLOWFRDWR)
 
 /* FRCT flags */
-#define FRCTFRESCNTRL 00000001 /* Feedback from receiver */
-#define FRCTFRTX      00000002 /* Reliable flow          */
-#define FRCTFLINGER   00000004 /* Sent unsent data       */
+#define FRCTFRTX      00000001 /* Reliable flow          */
+#define FRCTFRESCNTL  00000002 /* Feedback from receiver */
+#define FRCTFLINGER   00000004 /* Send unsent data       */
 
 /* Flow operations */
 #define FLOWSRCVTIMEO 00000001 /* Set read timeout       */
diff --git a/src/lib/CMakeLists.txt b/src/lib/CMakeLists.txt
index 5e60e375..02fca2d9 100644
--- a/src/lib/CMakeLists.txt
+++ b/src/lib/CMakeLists.txt
@@ -196,6 +196,8 @@ set(DELTA_T_ACK_DELAY 10 CACHE STRING
   "Maximum time to wait before acknowledging a packet (ms)")
 set(FRCT_REORDER_QUEUE_SIZE 256 CACHE STRING
   "Size of the reordering queue, must be a power of 2")
+set(FRCT_START_WINDOW 64 CACHE STRING
+  "Start window, must be a power of 2")
 set(FRCT_RTO_MIN 250 CACHE STRING
   "Minimum Retransmission Timeout (RTO) for FRCT (us)")
 set(FRCT_TICK_TIME 500 CACHE STRING
diff --git a/src/lib/config.h.in b/src/lib/config.h.in
index 38c364c6..36221b8c 100644
--- a/src/lib/config.h.in
+++ b/src/lib/config.h.in
@@ -75,6 +75,7 @@
 #define DELT_ACK            (@DELTA_T_ACK_DELAY@ * MILLION)  /* ns */
 
 #define RQ_SIZE             (@FRCT_REORDER_QUEUE_SIZE@)
+#define START_WINDOW        (@FRCT_START_WINDOW@)
 #define RTO_MIN             (@FRCT_RTO_MIN@ * 1000)
 
 #define TICTIME             (@FRCT_TICK_TIME@ * 1000)        /* ns */
diff --git a/src/lib/frct.c b/src/lib/frct.c
index 6ead72af..7f2d8fd3 100644
--- a/src/lib/frct.c
+++ b/src/lib/frct.c
@@ -67,8 +67,7 @@ enum frct_flags {
 struct frct_pci {
         uint8_t  flags;
 
-        uint8_t  pad;
-
+        uint8_t  pad;    /* 24 bit window! */
         uint16_t window;
 
         uint32_t seqno;
@@ -205,6 +204,10 @@ static struct frcti * frcti_create(int fd)
                 frcti->rcv_cr.cflags |= FRCTFRTX;
         }
 
+        frcti->snd_cr.cflags |= FRCTFRESCNTL;
+
+        frcti->snd_cr.rwe = START_WINDOW;
+
         frcti->snd_cr.inact  = (3 * mpl + a + r) / BILLION + 1; /* s */
         frcti->snd_cr.act.tv_sec = now.tv_sec - (frcti->snd_cr.inact + 1);
 
@@ -244,13 +247,13 @@ static uint16_t frcti_getflags(struct frcti * frcti)
 static void frcti_setflags(struct frcti * frcti,
                            uint16_t       flags)
 {
-        flags |= FRCTFRESCNTRL | FRCTFRTX; /* Should not be set by command */
+        flags |= FRCTFRTX; /* Should not be set by command */
 
         assert(frcti);
 
         pthread_rwlock_wrlock(&frcti->lock);
 
-        frcti->snd_cr.cflags &= FRCTFRESCNTRL | FRCTFRTX; /* Zero other flags */
+        frcti->snd_cr.cflags &= FRCTFRTX; /* Zero other flags */
 
         frcti->snd_cr.cflags &= flags;
 
@@ -287,6 +290,7 @@ static ssize_t __frcti_queued_pdu(struct frcti * frcti)
         idx = frcti->rq[pos];
         if (idx != -1) {
                 ++frcti->rcv_cr.lwe;
+                ++frcti->rcv_cr.rwe;
                 frcti->rq[pos] = -1;
         }
 
@@ -390,12 +394,18 @@ static int __frcti_snd(struct frcti *       frcti,
                 /* There are no unacknowledged packets. */
                 assert(snd_cr->seqno == snd_cr->lwe);
                 random_buffer(&snd_cr->seqno, sizeof(snd_cr->seqno));
-                frcti->snd_cr.lwe = snd_cr->seqno - 1;
+                snd_cr->lwe = snd_cr->seqno - 1;
+                snd_cr->rwe = snd_cr->lwe + START_WINDOW;
         }
 
         seqno = snd_cr->seqno;
         pci->seqno = hton32(seqno);
 
+        if (now.tv_sec - rcv_cr->act.tv_sec < rcv_cr->inact) {
+                pci->flags |= FRCT_FC;
+                *((uint32_t *) pci) |= hton32(rcv_cr->rwe & 0x00FFFFFF);
+        }
+
         if (!rtx) {
                 snd_cr->lwe++;
         } else {
@@ -405,7 +415,7 @@ static int __frcti_snd(struct frcti *       frcti,
                         frcti->probe   = true;
                 }
 
-                if (now.tv_sec - rcv_cr->act.tv_sec <= rcv_cr->inact) {
+                if (now.tv_sec - rcv_cr->act.tv_sec <= frcti->a) {
                         pci->flags |= FRCT_ACK;
                         pci->ackno = hton32(rcv_cr->lwe);
                         rcv_cr->seqno = rcv_cr->lwe;
@@ -457,6 +467,7 @@ static void __frcti_rcv(struct frcti *       frcti,
         struct frct_pci * pci;
         struct timespec   now;
         struct frct_cr *  rcv_cr;
+        struct frct_cr *  snd_cr;
         uint32_t          seqno;
         uint32_t          ackno;
         int               fd = -1;
@@ -464,6 +475,7 @@ static void __frcti_rcv(struct frcti *       frcti,
         assert(frcti);
 
         rcv_cr = &frcti->rcv_cr;
+        snd_cr = &frcti->snd_cr;
 
         clock_gettime(PTHREAD_COND_CLOCK, &now);
 
@@ -476,10 +488,12 @@ static void __frcti_rcv(struct frcti *       frcti,
         pthread_rwlock_wrlock(&frcti->lock);
 
         if (now.tv_sec - rcv_cr->act.tv_sec > rcv_cr->inact) {
-                if (pci->flags & FRCT_DRF) /* New run. */
+                if (pci->flags & FRCT_DRF)  { /* New run. */
                         rcv_cr->lwe = seqno;
-                else
+                        rcv_cr->rwe = seqno + RQ_SIZE;
+                } else {
                         goto drop_packet;
+                }
         }
 
         if (pci->flags & FRCT_ACK) {
@@ -493,6 +507,14 @@ static void __frcti_rcv(struct frcti *       frcti,
                 }
         }
 
+        if (pci->flags & FRCT_FC) {
+                uint32_t rwe = ntoh32(*((uint32_t *)pci) & hton32(0x00FFFFFF));
+                if (before(rwe, snd_cr->lwe & 0x00FFFFFF))
+                        snd_cr->rwe += 0x01000000;
+
+                snd_cr->rwe = (snd_cr->rwe & 0xFF000000) + rwe;
+        }
+
         if (!(pci->flags & FRCT_DATA))
                 goto drop_packet;
 
@@ -502,7 +524,11 @@ static void __frcti_rcv(struct frcti *       frcti,
         }
 
         if (rcv_cr->cflags & FRCTFRTX) {
-                if ((seqno - rcv_cr->lwe) >= RQ_SIZE)
+
+                if (!before(seqno, rcv_cr->rwe)) /* Out of window */
+                        goto drop_packet;
+
+                if (!before(seqno, rcv_cr->lwe + RQ_SIZE))
                         goto drop_packet; /* Out of rq. */
 
                 if (frcti->rq[pos] != -1)