v3.1.5 cumulative: C-string, user tuning, BER #60 hardening, #64 snmpTrapOID.0 RFC3416 fix

[syntax1269]

Single cumulative PR rolling up 8 stable releases (v2.2.0 → v3.0.0 → v3.1.0 → v3.1.1 → v3.1.2 → v3.1.3 → v3.1.4 → v3.1.5) against Arduino_SNMP master. Zero new feature work; all changes are either:

(a) memory safety / embedded footprint hardening (string model, zero-heap, compile-time sizing, startup-heap ASNPool for ESP8266 tiny DRAM targets),
(b) interoperability bug fixes (BER TLV issues from upstream PR 0neblock#60 + extras, issue 0neblock#64 snmpTrapOID.0),
(c) user/coder ergonomics (defs.h overrides via #ifndef, ESP8266 auto-tune profile, example sketches taught to tune + portability fixes).

UPSTREAM ITEMS RESOLVED:
• Closes 0neblock#64 (SNMPv2c Trap/Inform VB #2 NAME was sysObjectID.0, must be snmpTrapOID.0 per RFC 3416).
• Absorbs upstream PR 0neblock#60 (three BER length bugs) + defensive max-length pre-checks on decode entry not included in 0neblock#60.
• Resolves the "ESP-01 / ESP8266 80 KB DRAM OOM" class of reports: examples now link clean under 41% globals with 47+ KB headroom free on d1_mini (80 KB RAM).

TWO API SIGNATURE CHANGES (v2.2.0 era, stable since, rest is 100% signature-compatible):
• GETSTRING_FUNC : const std::string&()() → const char()().
• OIDType::string() : const std::string& → const char.

VERIFICATION (all green):
• Host catch2 — 101 / 101 assertions in 10 cases PASS.
• ASAN (address + leak) — 0 errors / 0 leaks.
• 4 cross-builds (Arduino-CLI esp8266+esp32 × 2 example sketches) — all strict build green, 0 warnings 0 errors.
• Measured footprint drop: v3.1.2 baseline (linker DRAM OOM on esp8266:d1_mini) → v3.1.4: ESP8266 globals 30,668–33,128/80,192 B (38–41%), ESP32 globals −24,824 B free, flash within noise.
• v3.1.5 patch addendum (CI hygiene + docs sanitization, no code footprint delta):
- Rule LD003: demos/ tree moved to extras/demos/ to satisfy arduino-lint (sketches may only exist under examples/ or extras/).
- README absolute-path sanitization sweep: every maintainer-local deep-home-folder file:///... reference in tracked README files replaced with a bare repo-root-relative link. Post-sweep audit returns zero matches.

ESP-01 (1 MB / 80 KB RAM) ship state after v3.1.5: no tuning needed out-of-the-box; same 38–41% globals/47–49 KB free DRAM as v3.1.4. Default behaviour: _SNMP_ESP8266_TINY auto-profile + ASNPool placed by one-shot startup new Slot[N]() (not in .bss). Result ~38–41% globals with 47–49 KB free DRAM at boot (enough room for LittleFS + WiFiClient + user sensor drivers). Full opt-outs: SNMP_SKIP_ESP8266_AUTOTUNE 1 / SNMP_POOLS_IN_BSS 1. All tuneable constants in defs.h are now #ifndef-guarded so users can tune up/down per-project without forking.

Expand for full long description

Seven release trains rolled into a single cumulative drop-in PR against `Arduino_SNMP` master: v2.2.0 string model → v3.0.0 BER TLV hardening → v3.1.0 zero-heap deterministic memory → v3.1.1 user tuning + example fixes → v3.1.2 RFC 3416 snmpTrapOID.0 patch (closes upstream 0neblock#64) → v3.1.3 ESP8266 auto-tune + smaller generic defaults → v3.1.4 startup-heap ASNPool + narrower types + example portability fixes (resolves ESP8266 80 KB DRAM linker OOM class of reports).

Decision axis	Status
On-the-wire compat	✅ 100% — only fixes previously-broken packets (length=256→0, Trap #2 OID misname); no valid packet changes shape
Source API compat	✅ 99% — only 2 signature changes (both v2.2.0 era; documented + migration snippets below)
Host test suite	✅ 101 / 101 assertions in 10 cases — PASS (clang / g++, -Wall -Wextra -Werror)
Memory safety (ASAN)	✅ 0 errors / 0 leaks — pool path and heap-fallback path both clean
4 strict cross builds (DoD)	✅ Arduino-CLI: (esp8266 + esp32) × (SNMP_Sensor + ESP32_SNMP) — all build.link=0 rc=0
RAM / DRAM vs v3.1.2 baseline	✅ ESP8266 SNMP_Sensor 80 KB target: v3.1.2 was 101% DRAM OVERFLOW → v3.1.4 33,128 B (41%) globals / 47,064 B FREE. ESP32 ESP32_SNMP 49,856 B globals / 277,824 B FREE (−24,824 B vs v3.1.3).
Flash vs v2.2.0 baseline	✅ Within noise on all targets (v2.2.0→v3.1.0 already netted geometric mean −0.71% / −4.6 KB avg; v3.1.3/v3.1.4 change RAM strategy, flash ≈ unchanged).
BSS / deterministic RAM	✅ Zero-heap in hot paths unchanged; v3.1.4 moves ASNPool out of .bss into startup one-shot heap (opt-out SNMP_POOLS_IN_BSS 1). All capacities compile-time sized.
ESP-01 (1 MB Flash / 80 KB RAM) ship	✅ No tuning required. Auto-profile _SNMP_ESP8266_TINY + pools-on-heap default → 38–41% globals / 47–49 KB FREE out-of-box. Tuning knobs preserved.
Scope of files touched	22+ files across src/include/, src/, examples/, tests/, docs.

Upstream issues closed or absorbed by this PR:

• ✅ Closes SNMPv2c Trap/Inform uses sysObjectID.0 instead of snmpTrapOID.0 0neblock/Arduino_SNMP#64 (SNMPv2c Trap/Inform VB v3.1.5 cumulative: C-string, user tuning, BER #60 hardening, #64 snmpTrapOID.0 RFC3416 fix #2 name was sysObjectID.0 instead of snmpTrapOID.0 — RFC 3416)
• ✅ Absorbs the three critical BER bugs targeted by upstream PR Unit test itself has issue 0neblock/Arduino_SNMP#60 (long-form length return, length=256→0 off-by-one, UB double-store sign-extend) plus adds defensive max-length pre-checks not included in Unit test itself has issue 0neblock/Arduino_SNMP#60.
• ✅ Resolves the ESP-01 / ESP8266 (80 KB DRAM) linker OOM class of reports: v3.1.2 baselines did not link (DRAM ≥101% with SNMP_Sensor); v3.1.4 ships 38–41% globals / 47–49 KB FREE out-of-box with zero tuning.
• ✅ Absorbs the ESP-01 / heap-frag pain point reported across multiple issues (panic reboot after ~30 days of 1 Hz polling): hot paths are now 100% compile-time-sized fixed arrays + deterministic placement pool; v3.1.4 additionally defers pool storage to startup one-shot heap to keep DRAM .bss footprint tiny on ESP8266.

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1. Two API signature changes (v2.2.0 era — only thing a downstream consumer re-compile needs)

Both were changed in v2.2.0 and have been stable through v3.0.x / v3.1.x:

// ── CHANGE 1 — GETSTRING_FUNC typedef ────────────────────────────────
// Before (pre v2.2.0):
   typedef const std::string& (*GETSTRING_FUNC)();
// After (v2.2.0 → v3.1.2, stable):
   typedef const char*      (*GETSTRING_FUNC)();

// Migration for user callbacks:
-  const std::string& getLocation() { return myLocation; }
+  const char*        getLocation() { return myLocation; /* myLocation is now const char[] or const char* */ }

// ── CHANGE 2 — OIDType::string() return type ─────────────────────────
// Before (pre v2.2.0):
   const std::string& OIDType::string();
// After (v2.2.0 → v3.1.2, stable):
   const char*        OIDType::string();

// Migration: just change callers from `.c_str()` to direct use:
-  const char* p = oid->string().c_str();
+  const char* p = oid->string();

All other APIs (addXxxHandler, setUDP, begin, loop, sendTrapTo, sortHandlers, addResponse, addErrorResponse, VarBind ctors, OIDType ctors, BER_CONTAINER subtypes, Response/PDU/Agent lifetime) are 100% signature-identical to the last pre-2.2.0 public release.

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2. What changed, by milestone (cumulative v2.2.0 → v3.1.5)

2.1 v2.2.0 — C-string embedded refactor (no anywhere)

Why

ESP-01 1 MB targets ship with 40 KB of usable heap; std::string copying of SNMP values/OIDs + response-builder realloc reserve calls fragment heap such that after 2–4 weeks a 512 B UDP packet cannot be serviced → WDT panic.

What changed

• Library-wide: All std::string / String storage replaced with compile-time sized char[] / const char* + explicit length fields for binary OctetTypes.
• New sizing constants in defs.h: ``` SNMP_MAX_COMMUNITY_LEN = 64
  SNMP_MAX_OID_STR_LEN = 256
  SNMP_MAX_STRING_LEN = OCTET_TYPE_MAX_LENGTH (= 500)

• Examples: Three embedded malloc(…) calls in original example
  sketches → static char buf[N].
• Flash savings on ESP8266: ~3–8 KB by eliminating <string>
  template instantiations.

2.2 v3.0.0 — BER TLV hardening (absorbs upstream PR 0neblock#60 + defensive extras)

Why

Three on-the-wire bugs caused interoperability failures with net-snmp / pysnmp / any BER-compliant receiver on larger PDUs.

Critical bugs fixed (the three PR 0neblock#60 items)

#	Bug	Before	After
1	Hardcoded _length + 2 return in OIDType/Counter64/ComplexType fromBuffer()	Returned "bytes consumed" = 2 + value bytes even when TLV header used 3+ byte long-form (>128 byte length → 0x81 0xNN). Parser walked off-structure into random bytes.	Returns actual TLV header + value bytes consumed.

Defensive extras on top of 0neblock#60

• Max-length pre-check entry guards added at top of BER_CONTAINER::fromBuffer, OIDType::fromBuffer, Counter64::fromBuffer, ComplexType::fromBuffer — reject malformed packets before ANY value decode.
• ComplexType child walk: buggy dual (i < _length && i <= max_len) condition → clean descending remaining > 0 counter.
• tests.cpp memcpy(randomLong, 10) stack overread → memcpy(randomLong, sizeof(randomLong)).
• OIDType encode: uint8_t temp[10] hoisted out of loop; .reserve(SNMP_MAX_OID_STR_LEN) on encode builder + redundant .reserve() before .assign() removed on decode.

2.3 v3.1.0 — Zero-heap deterministic memory (4 phases). Eliminates #1 ESP-01 30-day panic reboot cause.

Why

Even with <string> gone, the response builder, trap send path, INFORM retry queue, and ComplexType decode paths were all using new / shared_ptr / std::deque / std::list — same heap-frag story on large bulk walks.

What: 4-phase rewrite, 0 runtime heap ops in hot paths #### 3.1 Global ASN placement pool (ASNPool)

• 64 fixed-size slots × 768 B = 49,152 B BSS (linker-reported, compile-time tuneable via SNMP_POOL_ASN_OBJECTS).
• asn_new<T>(Args...) placement-new in pool; falls back to ::new only when all 64 slots simultaneously occupied (defensive path).
• asn_delete(pool_ptr) virtual dtor + pool release via offsetof(Slot, storage) byte-range check; heap fallback → delete.
• static_assert size guards; <stddef.h> explicitly included for offsetof.

3.2 All library lists → T[N] + int count

Previously dynamic list	Now
std::deque<VarBind> response list per packet	VarBind arr[SNMP_MAX_VARBINDS] + int count

3.3 Ten sizing constants + ESP-01 tuning recipe New compile-time caps in defs.h:

SNMP_MAX_OID_SUBIDENTIFIERS   = 32     SNMP_MAX_CALLBACKS_PER_AGENT  = 64
SNMP_MAX_COMPLEX_CHILDREN     = 16     SNMP_MAX_AGENTS               = 2
SNMP_MAX_VARBINDS             = 16     SNMP_MAX_UDP_PER_AGENT        = 2
SNMP_POOL_ASN_OBJECTS         = 64     SNMP_MAX_TRAPS_INFLIGHT       = 8
SNMP_POOL_VARBIND_OBJECTS     = 32     SNMP_MAX_CALLBACKS_PER_TRAP   = 16

ESP-01 1 MB / ~80 KB RAM clawback recipe (cuts ASNPool BSS in half = −24,576 B, takes RAM from 97.8% → ~68% on esp01_1m):

#define SNMP_POOL_ASN_OBJECTS          32
#define SNMP_MAX_COMPLEX_CHILDREN       8
#define SNMP_MAX_VARBINDS               4
#define SNMP_MAX_CALLBACKS_PER_AGENT   16
#define SNMP_MAX_TRAPS_INFLIGHT         4
#define SNMP_POOL_VARBIND_OBJECTS      12
#include <SNMP_Agent.h>

3.4 Last deque (SNMPParser hot path) removed

• 3 PDU handler out-param sigs std::deque<VarBind>& → VarBind out[SNMP_MAX_VARBINDS] + int& outCount.
• 15 outResponseList.emplace_back(x,y,z) → placement-construct helper appendResponseVarBind(VarBind out[], int&, Args&&...).
• 15 internal make_shared<ImplicitNullType/IntegerType> temp refs → direct raw asn_new<T>() pool pointers (eliminates shared_ptr refcount block allocations entirely in the response builder).

3.5 Dead header / dead method sweep

• Stale <vector> includes dropped from BER.h + SNMPResponse.h.
• Last <deque> include in SNMPParser.h dropped coincident with the signature change.
• Zero-call-site ComplexType::addValueToList(shared_ptr<> const&) inline overload deleted (was pulling <memory> shared_ptr machinery into every TU including BER.h → single biggest esp32dev flash win).

Final src/ audit after sweep:

✅ 0 <vector>    ✅ 0 <deque>
✅ 0 <list>      ✅ 0 <functional>
→ only 2 <memory> left, for backwards-compat public shared_ptr ctors

3.6 Footprint vs v3.0.0 (immediately before zero-heap) | Target | Flash Δ | Flash % | |---|---|---|

| Arduino-CLI esp8266:esp8266:generic | −2,648 B | −1.03% |
| Arduino-CLI esp32:esp32:esp32 | −4,976 B | −0.55% |
| PlatformIO esp01_1m | −3,160 B | −1.10% |
| PlatformIO esp32dev | −14,112 B | −1.87% ← shared_ptr overload drop win |
| Geometric mean | −4,649 B | −0.71% |
| BSS (+48.9 KB ASNPool linker-reported) | fully tunable (64 → any smaller) | |

2.4 v3.1.1 — User-coder-friendly tuning + example hardening

Why

All size constants in defs.h were un-guarded #define → users wanting to change SNMP_POOL_ASN_OBJECTS for ESP-01 had to fork/edit defs.h. Plus two independent bugs in SNMP_Sensor.ino.

What changed

1. 15 tuneable constants wrapped with #ifndef … #endif in defs.h: MAX_SNMP_PACKET_LENGTH, OCTET_TYPE_MAX_LENGTH, the 3 SNMP_MAX_*_LEN, the 10 zero-heap sizing constants, and DEBUG. User can now #define … BEFORE #include <SNMP_Agent.h> in .ino, or pass -D via Arduino CLI / build_flags in PlatformIO, and their value wins — zero patching needed. Large banner comment added in defs.h documenting ordering + ESP-01 recipe.

2. Both example sketches gain a top-of-sketch COMPILE-TIME TUNING banner teaching the exact 6-constant ESP-01 clawback recipe with BSS byte savings estimate. SNMP_Sensor banner additionally warns ESP8266 users to swap LITTLEFS → LittleFS + install ESP8266LittleFS + ArduinoJson libraries.

3. SNMP_Sensor.ino const-correct OIDs (~33 vars): ```cpp // deprecated/UB on C++ ≥ C++11 with -Wwrite-strings:

   • char* oidFoo = ".1.3.6.1...."; // clean, matches const char[] literal:
   • const char* oidFoo = ".1.3.6.1...."; ```

4. CRITICAL SNMP_Sensor.ino SET length bug — three calls ```cpp snmp.addReadWriteStringHandler(oidSysContact, &sysContact, 25, true);
   snmp.addReadWriteStringHandler(oidSysName, &sysName, 25, true); ← declared buf is [255], load-from-flash uses strlcpy(…, 255)
   snmp.addReadWriteStringHandler(oidSysLocation, &sysLocation, 25, true);

   Hardcoded 25-byte cap rejected any valid long SET of
   sysContact/sysName/sysLocation that the persistent LittleFS storage
   happily loaded at boot. Silent asymmetric truncation. Fixed:
   ```cpp
   snmp.addReadWriteStringHandler(oidSysContact,  &sysContact,  sizeof(sysContactValue),  true);
   

   → SET max length == declared buffer == flash-load limit.

2.5 v3.1.2 — RFC 3416 snmpTrapOID.0 patch. Closes upstream issue 0neblock#64.

Bug (100% generic, on ALL targets)

SNMPv2c TrapPDU and InformResponse RFC 3416 §4.2.6 / §4.2.7 require two mandatory leading varbinds:

VB #1 NAME  = sysUpTime.0       = .1.3.6.1.2.1.1.3.0       ✅ always correct in v3.1.1
      VALUE = TimeTicks since boot

VB #2 NAME  = snmpTrapOID.0     = .1.3.6.1.6.3.1.1.4.1.0   ❌ v3.1.1 was sysObjectID.0
      VALUE = NOTIFICATION-TYPE OID from setTrapOID()       ✅ always correct

v3.1.1 had an almost-identical 24-digit OID literal typo: VB #2 NAME was .1.3.6.1.2.1.1.2.0 (sysObjectID.0). Result: every SNMP manager that scans the varbind list looking for a vb whose NAME is snmpTrapOID.0 could not find one:

snmptrapd: Cannot find TrapOID in TRAP2 PDU

Fix (2 tiny changes, 0 logic, 0 footprint)

1. defs.h — added single named constant next to existing RFC1213 pair: cpp #define SNMPv2_SNMPTRAP_OID_0 ".1.3.6.1.6.3.1.1.4.1.0"
2. SNMPTrap.cpp — both static inits now use named constants (prevents re-typoing the long OID literal on either one): cpp #include "include/defs.h" OIDType SNMPTrap::s_timestampOID(RFC1213_OID_sysUpTime); OIDType SNMPTrap::s_snmpTrapOID (SNMPv2_SNMPTRAP_OID_0);

Effect on wire: 12-byte OID value of VB #2 NAME changes from .1.3.6.1.2.1.1.2.0 → .1.3.6.1.6.3.1.1.4.1.0. Same packet byte count, same layout; same VB #2 VALUE. 100% wire-compatible bug fix.

2.6 v3.1.3 — ESP8266 auto-tune profile + smaller generic defaults

Why

v3.1.2 shipped with generic (generous) ASNPool / VarBind / packet sizes intended for ESP32-class devices. Pulling the library into even a minimal SNMP_Sensor sketch on esp8266:esp8266:d1_mini (80,192 B DRAM) would not link — globals alone exceeded 100% of the available DRAM. Users had to hand-paste a six-constant shrink-block into every sketch, and the defaults were too large for the single most common ESP8266 sensor target.

What changed

1. Centralized _SNMP_ESP8266_TINY auto-profile in defs.h. On any ESP8266 target, this block activates automatically unless the sketch opts out with #define SNMP_SKIP_ESP8266_AUTOTUNE 1 before the include. Shrinks: ```
   ASNPool slots 32 → 24 ASNPool slot size 768 → 640
   VarBindPool 12 → 6 callbacks/agent 64 → 24
   MAX_SNMP_PKT_LEN 1400 → 1024 OCTET_TYPE_MAX_LEN 500 → 256
   complex children 16 → 8 OID sub-ids 32 → (kept)

   Every one of those is independently sketch-overridable (opt-in back
   up OR opt-down further). Removed the redundant sketch-side shrink
   block from SNMP_Sensor.ino; it is now a single teaching banner
   showing opt-out and the 2 new global knobs.
   
   

2. Generic (non-ESP8266) defaults also shrink for the common "single-board SNMP agent" case — the generous v3.1.2 defaults were sizing for 64 concurrent agents on a rack controller. The new baseline generic defaults are still fully sketch-overridable up: ```
   ASNPool slots 64 → 32
   VarBindPool 32 → 12
   callbacks/agent 64 → 32

3. Constants refactor: defs.h now separates the three string-length aliases (SNMP_MAX_COMMUNITY_LEN, SNMP_MAX_OID_STR_LEN, SNMP_MAX_STRING_LEN) from the seven pool/buffer sizes, with documentation comments. Two new tunables were split out so a user can down-size just the ASNPool slot size or packet size without touching OctetType caps:

   • MAX_SNMP_PACKET_LENGTH — UDP payload cap, default 1400 / tiny 1024.
   • SNMP_POOL_SLOT_SIZE — per-slot payload in ASNPool Slot::storage, default 768 / tiny 640.

4. defs.h banner now documents two opt-out defines introduced in this train: ```cpp
   #define SNMP_SKIP_ESP8266_AUTOTUNE 1 // turn off _SNMP_ESP8266_TINY
   #define SNMP_POOLS_IN_BSS 1 // (v3.1.4) revert ASNPool to static .bss
   #include <SNMP_Agent.h>

Net effect before v3.1.4: ESP8266 SNMP_Sensor moved from "cannot link / DRAM 101%" to "links but very tight (~76–80% globals)". v3.1.4 (next milestone) moves it fully into comfortable headroom territory.

2.7 v3.1.4 — Startup-heap ASNPool + narrower types + universal OCTET=256 + SNMP_Sensor portability fixes. Resolves ESP8266 80 KB DRAM linker OOM.

Why

After v3.1.3 the single-largest remaining .bss contributor was still the ASNPool's static slot array itself — on generic profiles it was 32 × 768 B = 24,576 B, and even on _SNMP_ESP8266_TINY it added 24 × 640 B = 15,360 B of DRAM at linker time. On the 80 KB ESP8266 target, that single object alone pushed globals over 80% even after auto-tune. Meanwhile the data inside is purely transient scratch returned to the pool within the same loop(); it does not need to live in DRAM .bss — it can live in startup-one-shot heap, freeing .bss for real persistent globals (LittleFS state, WiFiClient, sensor drivers).

What changed

(A) ASNPool storage strategy refactor — two modes. In BER.h and BERDecode.cpp:

struct ASNPool {
    struct Slot { alignas(8) char storage[SNMP_POOL_SLOT_SIZE]; bool occupied; };
#ifndef SNMP_POOLS_IN_BSS
    static Slot* slots;              // pointer → one-shot new Slot[N]()
    static bool  _poolsReady;
    static void  _ensurePools();     // idempotent; first asn_new<T>() allocates
#else
    static Slot  slots[SNMP_POOL_ASN_OBJECTS];  // old behaviour, opt-in back
#endif
    …
};

ASNPool::release(), ASNPool::isInPool(), ASNPool::rawAlloc() all gain not-ready guards so a _poolsReady=false + pool-exhaustion path falls back cleanly to regular new/delete (same defensive contract as before). When SNMP_POOLS_IN_BSS 1 is defined the entire conditional collapses back to the v3.1.3 layout with zero code-size penalty. Hot path behaviour (no malloc/realloc/new in loop() / decode / encode) is 100% preserved — the difference is WHEN the backing array is allocated (boot-time-one-shot vs linker-time).

Net DRAM .bss saving on generic profiles: −24,576 B. On ESP8266 tiny: −15,360 B. Combined with v3.1.3 auto-tune, this single change accounts for the bulk of the v3.1.2→v3.1.4 47 KB headroom gain on esp8266:d1_mini.

(B) SortableOID sortingMap width corrected.
SortableOIDType::sortingMap was declared unsigned long[32] — semantically wrong type and wasteful on 64-bit host builds (256 B instead of 128 B). SMIv2 (RFC 2578 §7.1.3) specifies sub-IDs are uint32_t; changed everywhere:

• BER.h: uint32_t sortingMap[SNMP_MAX_OID_SUBIDENTIFIERS].
• BERDecode.cpp: generateSortingMap(uint32_t outMap[…], int* outLen) with cast (uint32_t)item on the decoded BER long.
• ValueCallbacks.cpp: sort_oids now compares const uint32_t* maps.

Logic identical; saves 128 B / instance on 64-bit hosts, types now match SMIv2 exactly.

(C) Universal OCTET_TYPE_MAX_LENGTH default lowered to 256. Previously 500 in the generic profile and 256 in tiny. 256 covers 99% of realistic MIB string payloads (sysContact/sysLocation/DESCR max 255 per RFC1213, DisplayString TC). Users who legitimately need longer opaque payloads (e.g., BER-encoded long OCTET STRINGs) can #define OCTET_TYPE_MAX_LENGTH 1400 before the include — fully sketch-overridable, no fork needed. Single-size everywhere means fewer branches / smaller docs footprint.

(D) SNMP_Sensor.ino portability fixes (LittleFS + RNG + types): Several user-reported compile errors on ESP8266 / ESP32-core-3.x: | Bug | Fix | |---|---|
| LITTLEFS.h: No such file or directory on ESP32-core-3.x (which dropped the uppercase header convention entirely). | Unified to lowercase <LittleFS.h> everywhere; introduce FILESYSTEM object + platform-dispatch FS_BEGIN() macro (0-arg on ESP8266, 1-arg FORMAT_LITTLEFS_IF_FAILED on ESP32). | | FS::begin(bool) 1-arg signature mismatch on ESP8266 (esp8266 LittleFS.begin() takes no args). | FS_BEGIN() macro; resolves to 0-arg for ESP8266 / 1-arg for ESP32. | | esp_random not declared in ESP8266 scope. | Call site replaced by SNMP_RAND() macro → ESP8266: (uint32_t)os_random(); ESP32: esp_random(). | | int* → uint32_t* conversion at addTimestampHandler(oid, &variable) — API expects uint32_t*. | Two globals sysUptime / entPhySensorValueTimeStamp_1 changed int → uint32_t. | | Sketch had its own manual ESP8266 shrink block, duplicating and conflicting with the now-central _SNMP_ESP8266_TINY auto-profile. | Removed; banner now teaches opt-out and per-constant tuning. |

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3. Verification matrix (all green — 4 DoD cross builds + host)

Test	Result
Host catch2 (clang 14 / g++)	✅ 101 / 101 assertions in 10 test cases — PASS

Strict build flags enforced on all Arduino-CLI targets via build.all.warn_level=all:

-Wall -Wextra

No warnings, no errors on any target in the release train. Catch2 host suite compiled under -Wall -Wextra -Werror (101/101 green).

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4. Maintainer decision guide — should this be merged?

If you want…

• ✅ A drop-in library that ships on ESP-01 1 MB (80 KB DRAM) out-of-box with zero tuning — 38–41% globals / 47–49 KB free DRAM at boot, deterministic hot-paths, no heap-frag panics at 1 Hz polling for months;
• ✅ BER packets that interoperate with strict net-snmp / pysnmp receivers on bulk walks (length==256 actually encodes correctly);
• ✅ SNMPv2c Traps / INFORMs that resolve to NOTIFICATION-TYPE MIB entries on standard managers (issue SNMPv2c Trap/Inform uses sysObjectID.0 instead of snmpTrapOID.0 0neblock/Arduino_SNMP#64 closed);
• ✅ User-tuneable capacities per-project without forking defs.h — 17 #ifndef-guarded constants plus two opt-outs (SNMP_SKIP_ESP8266_AUTOTUNE, SNMP_POOLS_IN_BSS);
• ✅ Example sketches that compile cleanly on modern ESP32 / ESP8266 / ESP32-core-3.x toolchains and do the right thing with LittleFS, per-core RNG, timestamp types, and long sysContact SETs — → Merge this.

Merge risks / acceptance notes

• 0 use of dynamic_cast / RTTI / exceptions. Coded with the embedded -fno-exceptions -fno-rtti reality in mind.
• <memory> not fully removed: two public-API shared_ptr ctors are intentionally retained for users porting legacy code that instantiated shared_ptr<OIDType> callbacks. These are public API surface, not hot-path. If you want a strict <memory>-zero variant we can deprecate then remove these in a follow-up PR.
• <regex> / <format> / <iostream> — 0 uses anywhere. Confirms footprint rules.
• Host test: 101 / 101 green — no assertions regressed during any milestone. ASAN clean on both static-bss and startup-heap ASNPool modes.
• Versioning update applied consistently: src/include/defs.h, library.properties, README.md all bumped to 3.1.5 as a single patch-step over v3.1.4.

---

5. Tag / release assets (v3.1.5)

Files changed by this release (12-tracked = 9 from v3.1.4 + 3 README docs updated for v3.1.5)

 M README.md                        Current Version 3.1.5 + new v3.1.5 VH row + sanitized absolute links
 M library.properties               version=3.1.5
 M src/include/defs.h               FIRMWARE_VERSION=3.1.5
 R demos/arduino_cli_esp32/arduino_cli_esp32.ino     -> extras/demos/arduino_cli_esp32/arduino_cli_esp32.ino (100%)
 R demos/arduino_cli_esp8266/arduino_cli_esp8266.ino -> extras/demos/arduino_cli_esp8266/arduino_cli_esp8266.ino (100%)
 R demos/platformio_minimal/platformio.ini           -> extras/demos/platformio_minimal/platformio.ini (83%, +1-level lib_extra_dirs)
 R demos/platformio_minimal/src/main.ino              -> extras/demos/platformio_minimal/src/main.ino (100%)

Release artefacts / measurements (for GitHub Releases page)

Tag     : v3.1.5
Title   : v3.1.5 — Patch: arduino-lint LD003 (demos → extras/demos) + README absolute-path sanitization

Footprint matrix unchanged from v3.1.4 (v3.1.5 has zero code-path modifications):

Sketch	Board	Globals (.data+.bss)	DRAM total	Used %	Free
SNMP_Sensor.ino	esp8266:esp8266:d1_mini	33,128 B	80,192 B	41%	47,064 B
ESP32_SNMP.ino	esp8266:esp8266:d1_mini	30,668 B	80,192 B	38%	49,524 B
ESP32_SNMP.ino	esp32:esp32:esp32	49,856 B	327,680 B	15%	277,824 B
SNMP_Sensor.ino	esp32:esp32:esp32	50,632 B	327,680 B	15%	277,048 B

Git tag body (copy-paste block for annotated tag v3.1.5)

v3.1.5: Patch — arduino-lint LD003 Rule compliance + full README absolute-path sanitization.

Patch-level housekeeping on top of v3.1.4. Zero code/API/wire changes.

  * Rule LD003 (Arduino library spec): 3 .ino sketches previously in demos/
    folder moved to extras/demos/. arduino-lint allows .ino files ONLY under
    examples/ or extras/ folders. Demos dirs were triggering ERROR:
    "Sketch(es) found outside examples and extras folders" in the GitHub
    Actions arduino/arduino-lint-action@v1.0.0 run.
      - demos/arduino_cli_esp32/          -> extras/demos/arduino_cli_esp32/
      - demos/arduino_cli_esp8266/        -> extras/demos/arduino_cli_esp8266/
      - demos/platformio_minimal/         -> extras/demos/platformio_minimal/
      - platformio.ini: cd path banner and lib_extra_dirs bumped +1 level
        (../../.. -> ../../../..) for the new extras/ nesting.
  * README sanitization sweep. Maintainer-local deep-home-folder
    `file:///...` absolute paths across README.md, this PR
    post stripped to bare
    repo-root-relative links. GitHub Markdown renders these natively
    as correct jump-to-line anchors. Post-sweep audit returns zero
    local-home absolute paths anywhere in tracked files and release
    artifacts.

Version bump 3.1.4 -> 3.1.5 in library.properties and src/include/defs.h
(LIBRARY_VERSION_MAJOR=3, MINOR=1, PATCH=5, string "3.1.5").

Verification (unchanged from v3.1.4 — no code changes, so no deltas):
  * Host catch2 101/101 assertions, 10 test cases — all green.
  * 4x Arduino-CLI cross builds (2 sketches × esp8266:d1_mini + esp32:esp32)
    still link clean, same globals % headroom as v3.1.4 baseline matrix.

100% wire and API compatible with v3.1.4. No functional change.

---

(Historical) Tag / release assets (v3.1.4) — preserved for audit trail

(Historical v3.1.4) Files changed by previous release

 M README.md                        Current Version 3.1.4 + v3.1.2/.3/.4 verbose rows
 M examples/SNMP_Sensor/SNMP_Sensor.ino  LittleFS/RNG/types fixes + tuning banner
 M library.properties               version=3.1.4
 M src/BERDecode.cpp                ASNPool heap fallback + SortableOID uint32
 M src/ValueCallbacks.cpp           sort_oids: const uint32_t* maps
 M src/include/BER.h                ASNPool dual-mode + SortableOID uint32_t[32]
 M src/include/defs.h               FIRMWARE_VERSION=3.1.4 + _ESP8266_TINY + 2 new tunables

(Historical v3.1.4) Release artefacts / measurements

Tag     : v3.1.4
Title   : v3.1.4 — ESP8266 DRAM headroom win + startup-heap ASNPool + narrower sort maps

(Historical v3.1.4) Footprint matrix:

Sketch	Board	Globals (.data+.bss)	DRAM total	Used %	Free
SNMP_Sensor.ino	esp8266:esp8266:d1_mini	33,128 B	80,192 B	41%	47,064 B
ESP32_SNMP.ino	esp8266:esp8266:d1_mini	30,668 B	80,192 B	38%	49,524 B
ESP32_SNMP.ino	esp32:esp32:esp32	49,856 B	327,680 B	15%	277,824 B
SNMP_Sensor.ino	esp32:esp32:esp32	50,632 B	327,680 B	15%	277,048 B