cososo-ltd · DavidCozens · Jul 29, 2026 · Jul 29, 2026
diff --git a/README.md b/README.md
@@ -10,19 +10,15 @@ It builds on a baseline that simulates the sort of device you might be adding th
 measures itself: see [docs/baseline.md](docs/baseline.md) for what the baseline is, how the
 figures are made, and how to run it.
 
-## This stage — Buffered
+## This stage — TCP
 
-A circular buffer in front of the sender, and a service task that drains it. `Log` now enqueues and
-returns instead of sending, so the logging task is no longer held up by the network, and a mutex
-makes the two sides safe on different tasks — which means logging can now happen from any task, not
-just this one.
-
-Most of the cost is the ring and the service seam's stack — the send moved onto that task, so that
-is where the depth moved too.
+The sender is a TCP stream to the collector on 5601 instead of a UDP datagram, with records framed
+by octet count as a receiver on a stream expects. A record the network drops is retransmitted
+rather than lost, and a send to a collector that is not there fails instead of quietly succeeding.
 
 <!-- STAGE-COST:START (generated by scripts/gen-cost-table.py — do not edit by hand) -->
 
-**Cost above baseline: Flash +6,788 B, RAM +5,676 B.**
+**Cost above baseline: Flash +7,320 B, RAM +5,856 B.**
 
 <!-- STAGE-COST:END -->
 
@@ -44,6 +40,7 @@ committed as [`run-report.md`](run-report.md), and rewritten by every stage.
 | Sequence numbers | every record numbered, so a gap in the sequence is visible | +6,032 | +436 |
 | Message cap | a bounded record size, so a long message truncates instead of being dropped | +6,032 | +1,956 |
 | Buffered | logging that returns immediately, with the send moved off the logging task | +6,788 | +5,676 |
+| TCP | records the network retransmits instead of dropping, and a send that fails when the collector is gone | +7,320 | +5,856 |
 
 *Deltas are bytes above the baseline, which is itself Flash 350,308 B, RAM 111,192 B.*
 

diff --git a/app/syslog/Syslog.c b/app/syslog/Syslog.c
@@ -1,6 +1,6 @@
 /* See Syslog.h.
  *
- * A UDP sender over lwIP behind a circular buffer: Log enqueues and returns, and
+ * A TCP stream over lwIP behind a circular buffer: Log enqueues and returns, and
  * the service task drains and sends. The mutex is what makes those two sides
  * safe on different tasks.
  *
@@ -15,17 +15,20 @@
 #include "SolidSyslogEndpointHost.h"
 #include "SolidSyslogFreeRtosMutex.h"
 #include "SolidSyslogLwipRawAddress.h"
-#include "SolidSyslogLwipRawDatagram.h"
 #include "SolidSyslogLwipRawMarshal.h"
 #include "SolidSyslogLwipRawResolver.h"
+#include "SolidSyslogLwipRawTcpStream.h"
 #include "SolidSyslogMetaSd.h"
 #include "SolidSyslogNullStore.h"
 #include "SolidSyslogStdAtomicCounter.h"
-#include "SolidSyslogUdpSender.h"
+#include "SolidSyslogStreamSender.h"
 #include "SyslogFields.h"
 
 #include "lwip/tcpip.h"
 
+#include "FreeRTOS.h"
+#include "task.h"
+
 #include <stddef.h>
 #include <stdint.h>
 #include <string.h>
@@ -34,7 +37,7 @@
  * the resolver numeric-only — no DNS, so no LWIP_DNS and no DNS resolver
  * component to compile. */
 #define SYSLOG_COLLECTOR_HOST "10.0.2.2"
-#define SYSLOG_COLLECTOR_PORT ((uint16_t) 5514U)
+#define SYSLOG_COLLECTOR_PORT ((uint16_t) 5601U)
 
 /* Depth enough to absorb a burst while the sender is busy, without sizing for a
  * backlog the store is there to hold. */
@@ -46,7 +49,13 @@ static uint8_t s_ring[SOLIDSYSLOG_CIRCULAR_BUFFER_RING_BYTES(SYSLOG_BUFFER_RECOR
 /* The logger reads these on every record, so they outlive Syslog_Start. */
 static struct SolidSyslogStructuredData* s_sd[1];
 
-/* Every lwIP Raw call the datagram makes has to happen on the thread that owns
+/* Bounds the connect spin so it yields instead of busy-waiting. */
+static void SyslogSleep(int milliseconds)
+{
+    vTaskDelay(pdMS_TO_TICKS(milliseconds));
+}
+
+/* Every lwIP Raw call the stream makes has to happen on the thread that owns
  * the lwIP core. lwipopts.h sets LWIP_TCPIP_CORE_LOCKING, so taking the core
  * lock in the caller's own task is simpler and cheaper than posting to the tcpip
  * mailbox — and unconditionally synchronous, which the marshal contract
@@ -73,16 +82,17 @@ void Syslog_Start(void)
 {
     SolidSyslogLwipRaw_SetMarshal(LwipCoreLockMarshal);
 
-    /* A numeric resolver to parse the literal, a datagram for the socket, and an
-     * address slot for the resolver to write into. No EndpointVersion — this
-     * collector never moves, so the sender resolves once and pins it. */
-    struct SolidSyslogUdpSenderConfig senderConfig = {
+    struct SolidSyslogLwipRawTcpStreamConfig tcpConfig = {.Sleep = SyslogSleep};
+
+    /* No EndpointVersion — this collector never moves, so the sender resolves
+     * once and pins it. */
+    struct SolidSyslogStreamSenderConfig senderConfig = {
         .Resolver = SolidSyslogLwipRawResolver_Create(),
-        .Datagram = SolidSyslogLwipRawDatagram_Create(),
+        .Stream = SolidSyslogLwipRawTcpStream_Create(&tcpConfig),
         .Address = SolidSyslogLwipRawAddress_Create(),
         .Endpoint = CollectorEndpoint,
     };
-    struct SolidSyslogSender* sender = SolidSyslogUdpSender_Create(&senderConfig);
+    struct SolidSyslogSender* sender = SolidSyslogStreamSender_Create(&senderConfig);
 
     /* One counter Increment per record formatted, so a record that never reaches
      * the collector leaves a gap in the sequence rather than no trace at all. */

diff --git a/measurements/stages.tsv b/measurements/stages.tsv
@@ -18,3 +18,4 @@ header-fields	Header fields	a timestamped record naming the device, instead of n
 sequence-id	Sequence numbers	every record numbered, so a gap in the sequence is visible
 message-cap	Message cap	a bounded record size, so a long message truncates instead of being dropped
 buffered	Buffered	logging that returns immediately, with the send moved off the logging task
+tcp	TCP	records the network retransmits instead of dropping, and a send that fails when the collector is gone
diff --git a/measurements/tcp.csv b/measurements/tcp.csv
@@ -0,0 +1,13 @@
+# tcp figures (bytes) — captured by scripts/run.sh (CAPTURE=1).
+# The device reads measurements/Baseline.csv as its frozen baseline and reports current-minus-Baseline.
+flash_text,357140
+flash_data,488
+static_bss,116560
+heap_used,4440
+mbedtls_peak,21328
+mbedtls_free,11440
+lwip_mem_free,7576
+lwip_pbufs_free,13
+stack_log,568
+stack_service,724
+stack_harness,2848
diff --git a/run-report.md b/run-report.md
@@ -1,4 +1,4 @@
-# solid-syslog-example — run (buffered)
+# solid-syslog-example — run (tcp)
 
 ## Device (self-measured)
 
@@ -10,16 +10,16 @@
 [device]   first record logged: yes
 [report] --- SolidSyslog cost above baseline (simulated existing application) ---
 [report] key,current,baseline,used_above_baseline
-[report] flash_text,356608,349992,6616
+[report] flash_text,357140,349992,7148
 [report] flash_data,488,316,172
-[report] static_bss,116380,110876,5504
+[report] static_bss,116560,110876,5684
 [report] heap_used,4440,4440,0
-[report] mbedtls_peak,21200,21332,-132
-[report] mbedtls_free,11568,11436,132
+[report] mbedtls_peak,21328,21332,-4
+[report] mbedtls_free,11440,11436,4
 [report] lwip_mem_free,7576,7576,0
 [report] lwip_pbufs_free,13,14,-1
 [report] stack_log,568,120,448
-[report] stack_service,780,52,728
+[report] stack_service,724,52,672
 [report] stack_harness,2848,2840,8
 [report] --- end ---
 [device] ready
@@ -29,7 +29,7 @@
 
 ```text
    text	   data	    bss	    dec	    hex	filename
- 356600	    496	 116380	 473476	  73984	/w/build/baseline-cross/baseline.elf
+ 357132	    496	 116560	 474188	  73c4c	/w/build/baseline-cross/baseline.elf
 ```
 
 ## Listeners (proved before the device ran)
@@ -47,23 +47,23 @@
 ## Collector (syslog-ng) received
 
 ```text
-wire   <134>1 2026-07-29T07:17:47.410000Z 10.0.2.15 solid-syslog-example - BOOT [meta sequenceId="1"] device started
-parsed PRIORITY=134 TIMESTAMP=2026-07-29T07:17:47+00:00 HOSTNAME=10.0.2.15 APP_NAME=solid-syslog-example PROCID= MSGID=BOOT STRUCTURED_DATA=[meta sequenceId="1"] MSG=device started
+wire   <134>1 2026-07-29T07:30:26.440000Z 10.0.2.15 solid-syslog-example - BOOT [meta sequenceId="1"] device started
+parsed PRIORITY=134 TIMESTAMP=2026-07-29T07:30:26+00:00 HOSTNAME=10.0.2.15 APP_NAME=solid-syslog-example PROCID= MSGID=BOOT STRUCTURED_DATA=[meta sequenceId="1"] MSG=device started
 ```
 
-## Self-check (vs measurements/buffered.csv)
+## Self-check (vs measurements/tcp.csv)
 
 ```text
-  OK    flash_text: 356608 (expected 356608, Δ0)
+  OK    flash_text: 357140 (expected 357140, Δ0)
   OK    flash_data: 488 (expected 488, Δ0)
-  OK    static_bss: 116380 (expected 116380, Δ0)
+  OK    static_bss: 116560 (expected 116560, Δ0)
   OK    heap_used: 4440 (expected 4440, Δ0)
-  OK    mbedtls_peak: 21200 (expected 21316, Δ116)
-  OK    mbedtls_free: 11568 (expected 11452, Δ116)
+  OK    mbedtls_peak: 21328 (expected 21328, Δ0)
+  OK    mbedtls_free: 11440 (expected 11440, Δ0)
   OK    lwip_mem_free: 7576 (expected 7576, Δ0)
   OK    lwip_pbufs_free: 13 (expected 13, Δ0)
   OK    stack_log: 568 (expected 568, Δ0)
-  OK    stack_service: 780 (expected 780, Δ0)
+  OK    stack_service: 724 (expected 724, Δ0)
   OK    stack_harness: 2848 (expected 2848, Δ0)
 ```