feat: install the SolidSyslog error handler

Nothing in the library fails loudly. A _Create that cannot succeed returns a Null
object and carries on, so a logger that has silently stopped looks exactly like
one with nothing to say. The handler is what tells them apart, and it goes in
before the first _Create rather than after something looks wrong.

  Flash  +404 B
  RAM      +8 B

The handler prints to the same console as everything else, so a fault lands in
the run report next to the rest of what the device did. It names the four
lifecycle categories a misconfigured integration raises and prints the rest
numerically — a device reacting to those would switch on the range, not the text.

That is 404 bytes for something this device may never use. It buys the
difference between a silent failure and a sentence, which is worth more than the
bytes on anything that has to be trusted to report.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: DavidCozens

CMakeLists.txt

@@ -130,6 +130,7 @@ add_executable(baseline
     ${APP_DIR}/net/EthernetIf.c
     ${APP_DIR}/storage/diskio.c
     ${APP_DIR}/storage/SemihostingDisk.c
+    ${APP_DIR}/syslog/SyslogErrorHandler.c
     $<TARGET_OBJECTS:baseline_upstream>
 )
 
@@ -150,6 +151,7 @@ target_include_directories(baseline PRIVATE
     ${APP_DIR}/net/smsc9220
     ${APP_DIR}/platform                      # CmsdkUart.h, SemihostingExit.h, SemihostingIo.h
     ${APP_DIR}/storage                       # SemihostingDisk.h
+    ${APP_DIR}/syslog                        # SyslogErrorHandler.h
     ${FREERTOS_KERNEL_PATH}/include
     ${FREERTOS_PORT_DIR}
     ${LWIP_DIR}/src/include

README.md

@@ -10,14 +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 — Linked
+## This stage — Error handler
 
-SolidSyslog is in the build with the lwIP platform selected: the core library, plus the components
-that integrate lwIP in raw mode. Nothing calls it yet, so the linker strips it all back out.
+The device installs its own handler on SolidSyslog's error slot, before creating anything. A
+`_Create` that cannot succeed returns a Null object rather than failing, so without this a
+mis-wired logger and a quiet one look identical.
 
 <!-- STAGE-COST:START (generated by scripts/gen-cost-table.py — do not edit by hand) -->
 
-**Cost above baseline: Flash +0 B, RAM +0 B.**
+**Cost above baseline: Flash +404 B, RAM +8 B.**
 
 <!-- STAGE-COST:END -->
 
@@ -32,6 +33,7 @@ committed as [`run-report.md`](run-report.md), and rewritten by every stage.
 |---|---|---|---|
 | Baseline | a device that already networks, stores, and holds an mTLS session — before any syslog | — | — |
 | Linked | the core library and lwIP raw-mode networking, linked but not yet called | +0 | +0 |
+| Error handler | a fault inside the logger reaches the console instead of being silent | +404 | +8 |
 
 *Deltas are bytes above the baseline, which is itself Flash 350,308 B, RAM 111,192 B.*
 

app/main.c

@@ -9,6 +9,7 @@
 #include "SemihostingExit.h"
 #include "ServiceTask.h"
 #include "SimulatedExistingApp.h"
+#include "SyslogErrorHandler.h"
 
 #include "lwip/tcpip.h"
 
@@ -93,6 +94,9 @@ int main(void)
     CmsdkUart_Init(&UART_ACCESS, DEVICE_UART0_BASE);
     (void) printf("[device] solid-syslog-example (FreeRTOS + lwIP + mbedTLS + FatFs)\n");
 
+    /* Before the first _Create — see SyslogErrorHandler.h for why that matters. */
+    SyslogErrorHandler_Install();
+
     /* lwIP tcpip thread + core-lock mutex + mbox. Pre-scheduler safe. */
     tcpip_init(NULL, NULL);
 

app/syslog/SyslogErrorHandler.c

@@ -0,0 +1,89 @@
+/* See SyslogErrorHandler.h. Prints to the same console as the rest of the
+ * device, so a fault shows up in the run report next to everything else. */
+
+#include "SyslogErrorHandler.h"
+
+#include "SolidSyslogError.h"
+#include "SolidSyslogErrorCategory.h"
+#include "SolidSyslogPrival.h"
+
+#include <stdint.h>
+#include <stdio.h>
+
+static const char* SeverityName(enum SolidSyslogSeverity severity)
+{
+    switch (severity)
+    {
+        case SOLIDSYSLOG_SEVERITY_EMERGENCY:
+            return "EMERGENCY";
+        case SOLIDSYSLOG_SEVERITY_ALERT:
+            return "ALERT";
+        case SOLIDSYSLOG_SEVERITY_CRITICAL:
+            return "CRITICAL";
+        case SOLIDSYSLOG_SEVERITY_ERROR:
+            return "ERROR";
+        case SOLIDSYSLOG_SEVERITY_WARNING:
+            return "WARNING";
+        case SOLIDSYSLOG_SEVERITY_NOTICE:
+            return "NOTICE";
+        case SOLIDSYSLOG_SEVERITY_INFORMATIONAL:
+            return "INFO";
+        case SOLIDSYSLOG_SEVERITY_DEBUG:
+            return "DEBUG";
+    }
+    return "?";
+}
+
+/* The four a misconfigured integration raises. Role-specific categories sit in
+ * ranges above 0x0100 and print numerically. */
+static const char* CategoryName(uint16_t category)
+{
+    switch (category)
+    {
+        case SOLIDSYSLOG_CAT_BAD_CONFIG:
+            return "bad-config";
+        case SOLIDSYSLOG_CAT_BAD_ARGUMENT:
+            return "bad-argument";
+        case SOLIDSYSLOG_CAT_POOL_EXHAUSTED:
+            return "pool-exhausted";
+        case SOLIDSYSLOG_CAT_UNKNOWN_DESTROY:
+            return "unknown-destroy";
+        default:
+            return NULL;
+    }
+}
+
+static void OnSyslogError(void* context, const struct SolidSyslogErrorEvent* event)
+{
+    (void) context;
+
+    if (event == NULL)
+    {
+        return;
+    }
+
+    /* Sources are matched by pointer identity — Name is only ever a label, which
+     * is all it is used for here. */
+    const char* source = ((event->Source != NULL) && (event->Source->Name != NULL)) ? event->Source->Name : "?";
+    const char* category = CategoryName(event->Category);
+
+    if (category != NULL)
+    {
+        (void) printf("[syslog] %s %s %s (detail %ld)\n", SeverityName(event->Severity), source, category, (long) event->Detail);
+    }
+    else
+    {
+        (void) printf(
+            "[syslog] %s %s category 0x%04X (detail %ld)\n",
+            SeverityName(event->Severity),
+            source,
+            (unsigned int) event->Category,
+            (long) event->Detail
+        );
+    }
+}
+
+void SyslogErrorHandler_Install(void)
+{
+    SolidSyslog_SetErrorHandler(OnSyslogError, NULL);
+}

app/syslog/SyslogErrorHandler.h

@@ -0,0 +1,15 @@
+/* The device's reaction to a SolidSyslog internal fault.
+ *
+ * Nothing in the library fails loudly — a _Create that cannot succeed returns a
+ * Null object instead — so a logger that has silently stopped looks exactly like
+ * one with nothing to say. This is the only thing that tells them apart, which
+ * is why it goes in before the first _Create and not after something looks
+ * wrong. */
+#ifndef SYSLOG_ERROR_HANDLER_H
+#define SYSLOG_ERROR_HANDLER_H
+
+/** Install the handler on the library's single global slot. Call once, at
+ *  startup, before any SolidSyslog object is created. */
+void SyslogErrorHandler_Install(void);
+
+#endif /* SYSLOG_ERROR_HANDLER_H */

measurements/error-handler.csv

@@ -0,0 +1,13 @@
+# error-handler 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,350392
+flash_data,320
+static_bss,110880
+heap_used,4440
+mbedtls_peak,21336
+mbedtls_free,11432
+lwip_mem_free,7576
+lwip_pbufs_free,14
+stack_log,120
+stack_service,52
+stack_harness,2840

measurements/stages.tsv

@@ -11,3 +11,4 @@
 # after it, and this history has already had one inserted.
 Baseline	Baseline	a device that already networks, stores, and holds an mTLS session — before any syslog
 linked	Linked	the core library and lwIP raw-mode networking, linked but not yet called
+error-handler	Error handler	a fault inside the logger reaches the console instead of being silent

run-report.md

@@ -1,4 +1,4 @@
-# solid-syslog-example — run (linked)
+# solid-syslog-example — run (error-handler)
 
 ## Device (self-measured)
 
@@ -9,14 +9,14 @@
 [device]   sim app (lwIP up, FatFs mounted, broker session held over mTLS): ready
 [report] --- SolidSyslog cost above baseline (simulated existing application) ---
 [report] key,current,baseline,used_above_baseline
-[report] flash_text,349992,349992,0
-[report] flash_data,316,316,0
-[report] static_bss,110876,110876,0
+[report] flash_text,350392,349992,400
+[report] flash_data,320,316,4
+[report] static_bss,110880,110876,4
 [report] heap_used,4440,4440,0
-[report] mbedtls_peak,21328,21332,-4
-[report] mbedtls_free,11440,11436,4
+[report] mbedtls_peak,21208,21332,-124
+[report] mbedtls_free,11560,11436,124
 [report] lwip_mem_free,7576,7576,0
-[report] lwip_pbufs_free,14,14,0
+[report] lwip_pbufs_free,13,14,-1
 [report] stack_log,120,120,0
 [report] stack_service,52,52,0
 [report] stack_harness,2840,2840,0
@@ -28,7 +28,7 @@
 
 ```text
    text	   data	    bss	    dec	    hex	filename
- 349984	    324	 110876	 461184	  70980	/w/build/baseline-cross/baseline.elf
+ 350384	    328	 110880	 461592	  70b18	/w/build/baseline-cross/baseline.elf
 ```
 
 ## Listeners (proved before the device ran)
@@ -49,17 +49,17 @@
 (nothing — this device sends no records yet)
 ```
 
-## Self-check (vs measurements/linked.csv)
+## Self-check (vs measurements/error-handler.csv)
 
 ```text
-  OK    flash_text: 349992 (expected 349992, Δ0)
-  OK    flash_data: 316 (expected 316, Δ0)
-  OK    static_bss: 110876 (expected 110876, Δ0)
+  OK    flash_text: 350392 (expected 350392, Δ0)
+  OK    flash_data: 320 (expected 320, Δ0)
+  OK    static_bss: 110880 (expected 110880, Δ0)
   OK    heap_used: 4440 (expected 4440, Δ0)
-  OK    mbedtls_peak: 21328 (expected 21332, Δ4)
-  OK    mbedtls_free: 11440 (expected 11436, Δ4)
+  OK    mbedtls_peak: 21208 (expected 21336, Δ128)
+  OK    mbedtls_free: 11560 (expected 11432, Δ128)
   OK    lwip_mem_free: 7576 (expected 7576, Δ0)
-  OK    lwip_pbufs_free: 14 (expected 14, Δ0)
+  OK    lwip_pbufs_free: 13 (expected 14, Δ1)
   OK    stack_log: 120 (expected 120, Δ0)
   OK    stack_service: 52 (expected 52, Δ0)
   OK    stack_harness: 2840 (expected 2840, Δ0)