feat: size the message cap to this device's records

CMakeLists.txt

@@ -41,6 +41,10 @@ set(LWIP_CONTRIB_FREERTOS_DIR "${LWIP_DIR}/contrib/ports/freertos")
 # Pinned to a commit until there is a release tag to pin to.
 set(SOLIDSYSLOG_PLATFORMS "LwipRaw;Atomics" CACHE STRING "" FORCE)
 
+# Compile-time limits. Every tunable is #ifndef-guarded, so this file only needs
+# the ones this device wants changed.
+set(SOLIDSYSLOG_USER_TUNABLES_FILE "${APP_DIR}/config/solid_syslog_tunables.h")
+
 include(FetchContent)
 FetchContent_Declare(SolidSyslog
     GIT_REPOSITORY https://github.com/cososo-ltd/solid-syslog.git

README.md

@@ -10,16 +10,18 @@ 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 — Sequence numbers
+## This stage — Message cap
 
-Every record carries `[meta sequenceId="N"]`. The counter increments once per record *formatted*,
-not per record delivered, so a record that never arrives leaves a gap rather than no trace at all.
+The longest record this device will emit is capped at 256 bytes, down from the library's default of
+2048. Anything longer is truncated rather than dropped, and 256 sits well inside what RFC 5426
+guarantees a UDP receiver will accept.
 
-That earns its place from the next stage on, where a full buffer can start dropping records.
+The cost is not in flash — it is RAM, because the record is built on the stack of whichever task
+logs, and that seam had been sitting at the FreeRTOS minimum.
 
 <!-- STAGE-COST:START (generated by scripts/gen-cost-table.py — do not edit by hand) -->
 
-**Cost above baseline: Flash +6,032 B, RAM +436 B.**
+**Cost above baseline: Flash +6,032 B, RAM +1,956 B.**
 
 <!-- STAGE-COST:END -->
 
@@ -39,6 +41,7 @@ committed as [`run-report.md`](run-report.md), and rewritten by every stage.
 | First record | a valid RFC 5424 record on the wire, over UDP | +4,716 | +372 |
 | Header fields | a timestamped record naming the device, instead of nil values | +5,100 | +372 |
 | 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 |
 
 *Deltas are bytes above the baseline, which is itself Flash 350,308 B, RAM 111,192 B.*
 

app/AppConfig.h

@@ -10,10 +10,11 @@
 /* CMSDK UART0 on the mps2-an385, surfaced by QEMU over -serial stdio. */
 #define DEVICE_UART0_BASE ((uintptr_t) 0x40004000U)
 
-/* Both seams are idle, so both get the FreeRTOS floor — twice what an idle seam
- * measures is well below it. Whatever deepens one grows it there. The reported
- * figure is high-water usage, which does not depend on the allocation. */
-#define LOG_TASK_STACK_WORDS (configMINIMAL_STACK_SIZE)
+/* Twice the measured high-water mark, or the FreeRTOS floor where that is below
+ * it — as the service seam still is, being idle. Whatever deepens a seam grows
+ * it here and is charged for it. The reported figure is high-water usage, which
+ * does not depend on the allocation. */
+#define LOG_TASK_STACK_WORDS (configMINIMAL_STACK_SIZE * 4U)
 #define SERVICE_TASK_STACK_WORDS (configMINIMAL_STACK_SIZE)
 #define LOG_TASK_PRIORITY (tskIDLE_PRIORITY + 1U)
 #define SERVICE_TASK_PRIORITY (tskIDLE_PRIORITY + 1U)

app/config/solid_syslog_tunables.h

@@ -0,0 +1,18 @@
+/* SolidSyslog compile-time overrides for this device. Reached via
+ * SOLIDSYSLOG_USER_TUNABLES_FILE; anything not set here keeps the library
+ * default from SolidSyslogTunablesDefaults.h. */
+#ifndef SOLID_SYSLOG_TUNABLES_H
+#define SOLID_SYSLOG_TUNABLES_H
+
+/* The longest record this device will emit. The library defaults to 2048, the
+ * size RFC 5424 section 6.1 says a receiver should accept; over UDP, RFC 5426
+ * section 3.2 guarantees only that 480 will be accepted. This device's records are
+ * far shorter, so 256 stays well inside every guarantee and anything longer is
+ * truncated rather than dropped. */
+#define SOLIDSYSLOG_MAX_MESSAGE_SIZE 256U
+
+/* One sender, so one destination address. The default of 3 suits a device
+ * running UDP, plain TCP and TLS at once. */
+#define SOLIDSYSLOG_ADDRESS_POOL_SIZE 1U
+
+#endif /* SOLID_SYSLOG_TUNABLES_H */

measurements/message-cap.csv

@@ -0,0 +1,13 @@
+# message-cap 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,355868
+flash_data,472
+static_bss,112676
+heap_used,4440
+mbedtls_peak,21228
+mbedtls_free,11540
+lwip_mem_free,7576
+lwip_pbufs_free,13
+stack_log,800
+stack_service,52
+stack_harness,2848

measurements/stages.tsv

@@ -16,3 +16,4 @@ logger	Logger created	the logger object, reporting exactly what is still missing
 udp	First record	a valid RFC 5424 record on the wire, over UDP
 header-fields	Header fields	a timestamped record naming the device, instead of nil values
 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

run-report.md

@@ -1,4 +1,4 @@
-# solid-syslog-example — run (sequence-id)
+# solid-syslog-example — run (message-cap)
 
 ## Device (self-measured)
 
@@ -12,13 +12,13 @@
 [report] key,current,baseline,used_above_baseline
 [report] flash_text,355868,349992,5876
 [report] flash_data,472,316,156
-[report] static_bss,111156,110876,280
+[report] static_bss,112676,110876,1800
 [report] heap_used,4440,4440,0
-[report] mbedtls_peak,21332,21332,0
-[report] mbedtls_free,11436,11436,0
+[report] mbedtls_peak,21288,21332,-44
+[report] mbedtls_free,11480,11436,44
 [report] lwip_mem_free,7576,7576,0
 [report] lwip_pbufs_free,13,14,-1
-[report] stack_log,136,120,16
+[report] stack_log,800,120,680
 [report] stack_service,52,52,0
 [report] stack_harness,2848,2840,8
 [report] --- end ---
@@ -29,7 +29,7 @@
 
 ```text
    text	   data	    bss	    dec	    hex	filename
- 355860	    480	 111156	 467496	  72228	/w/build/baseline-cross/baseline.elf
+ 355860	    480	 112676	 469016	  72818	/w/build/baseline-cross/baseline.elf
 ```
 
 ## Listeners (proved before the device ran)
@@ -47,22 +47,22 @@
 ## Collector (syslog-ng) received
 
 ```text
-wire   <134>1 2026-07-29T07:15:27.620000Z 10.0.2.15 solid-syslog-example - BOOT [meta sequenceId="1"] device started
-parsed PRIORITY=134 TIMESTAMP=2026-07-29T07:15:27+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 2026-07-29T07:16:37.410000Z 10.0.2.15 solid-syslog-example - BOOT [meta sequenceId="1"] device started
+parsed PRIORITY=134 TIMESTAMP=2026-07-29T07:16:37+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/sequence-id.csv)
+## Self-check (vs measurements/message-cap.csv)
 
 ```text
   OK    flash_text: 355868 (expected 355868, Δ0)
   OK    flash_data: 472 (expected 472, Δ0)
-  OK    static_bss: 111156 (expected 111156, Δ0)
+  OK    static_bss: 112676 (expected 112676, Δ0)
   OK    heap_used: 4440 (expected 4440, Δ0)
-  OK    mbedtls_peak: 21332 (expected 21344, Δ12)
-  OK    mbedtls_free: 11436 (expected 11424, Δ12)
+  OK    mbedtls_peak: 21288 (expected 21228, Δ60)
+  OK    mbedtls_free: 11480 (expected 11540, Δ60)
   OK    lwip_mem_free: 7576 (expected 7576, Δ0)
   OK    lwip_pbufs_free: 13 (expected 13, Δ0)
-  OK    stack_log: 136 (expected 136, Δ0)
+  OK    stack_log: 800 (expected 800, Δ0)
   OK    stack_service: 52 (expected 52, Δ0)
   OK    stack_harness: 2848 (expected 2848, Δ0)
 ```