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Phase 3 PR 43 — followup commit: validate pymodbus simulator end-to-end + fix three real bugs surfaced by running it. winget-installed Python 3.12.10 + pip-installed pymodbus[simulator]==3.13.0 on the dev box; both profiles boot cleanly, the integration-suite smoke test passes against either profile.

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Three substantive issues caught + fixed during the validation pass:
1. pymodbus rejects unknown keys at device-list / setup level. My PR 43 commit had `_layout_note`, `_uint16_layout`, `_bits_layout`, `_write_note` device-level JSON-comment fields that crashed pymodbus startup with `INVALID key in setup`. Removed all device-level _* fields. Inline `_quirk` keys WITHIN individual register entries are tolerated by pymodbus 3.13.0 — kept those in dl205.json since they document the byte math per quirk and the README + git history aren't enough context for a hand-author reading raw integer values. Documented the constraint in the top-level _comment of each profile.
2. pymodbus rejects sweeping `write` ranges that include any cell not assigned a type. My initial standard.json had `write: [[0, 2047]]` but only seeded HR[0..31] + HR[100] + HR[200..209] + bits[1024..1109] — pymodbus blew up on cell 32 (gap between HR[31] and HR[100]). Fixed by listing per-block write ranges that exactly mirror the seeded ranges. Same fix in dl205.json (was `[[0, 16383]]`).
3. pymodbus simulator stores all 4 standard Modbus tables in ONE underlying cell array — each cell can only be typed once (BITS or UINT16, not both). My initial standard.json had `bits[0..31]` AND `uint16[0..31]` overlapping at the same addresses; pymodbus crashed with `ERROR "uint16" <Cell> used`. Fixed by relocating coils to address 1024+, well clear of the uint16 entries at 0..209. Documented the layout constraint in the standard.json top-level _comment.
Substantive driver bug fixed: ModbusTcpTransport.ConnectAsync was using `new TcpClient()` (default constructor — dual-stack, IPv6 first) then `ConnectAsync(host, port)` with the user's hostname. .NET's TcpClient default-resolves "localhost" to ::1 first, fails to connect to pymodbus (which binds 0.0.0.0 IPv4-only), and only then retries IPv4 — the failure surfaces as the entire ConnectAsync timeout (2s by default) before the IPv4 attempt even starts. PR 30's smoke test silently SKIPPED because the fixture's TCP probe hit the same dual-stack ordering and timed out. Both fixed: ModbusSimulatorFixture probe now resolves Dns.GetHostAddresses, prefers AddressFamily.InterNetwork, dials IPv4 explicitly. ModbusTcpTransport does the same — resolves first, prefers IPv4, falls back to whatever Dns returns (handles IPv6-only hosts in the future). This is a real production-readiness fix because most Modbus PLCs are IPv4-only — a generic dual-stack TcpClient would burn the entire connect timeout against any IPv4-only PLC, masquerading as a connection failure when the PLC is actually fine.
Smoke-test address shifted HR[100] -> HR[200]. Standard.json's HR[100] is the auto-incrementing register that drives subscribe-and-receive tests, so write-then-read against it would race the increment. HR[200] is the first cell of a writable scratch range present in BOTH simulator profiles. DL205Profile.cs xml-doc updated to explain the shift; tag name "DL205_Smoke_HReg100" -> "Smoke_HReg200" + smoke test references updated. dl205.json gains a matching scratch HR[200..209] range so the smoke test runs identically against either profile.
Validation matrix:
- standard.json boot: clean (TCP 5020 listening within ~3s of pymodbus.simulator launch).
- dl205.json boot: clean.
- pymodbus client direct FC06 to HR[200]=1234 + FC03 read: round-trip OK.
- raw-bytes PowerShell TcpClient FC06 + 12-byte response: matches FC06 spec (echo of address + value).
- DL205SmokeTest against standard.json: 1/1 pass (was failing as 'BadInternalError' due to the dual-stack timeout + tag-name typo — both fixed).
- DL205SmokeTest against dl205.json: 1/1 pass.
- Modbus.Tests Unit suite: 52/52 pass — dual-stack transport fix is non-breaking.
- Solution build clean.
Memory + future-PR setup: pymodbus install + activation pattern is now bullet-pointed at the top of Pymodbus/README.md so future PRs (the per-quirk DL205_<behavior> tests in PR 44+) don't have to repeat the trial-and-error of getting the simulator + integration tests cooperating. The three bugs above are documented inline in the JSON profiles + ModbusTcpTransport so they don't bite again.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Joseph Doherty
2026-04-18 21:14:02 -04:00
parent a05b84858d
commit 02fccbc762
6 changed files with 110 additions and 50 deletions
Download Patch File Download Diff File Expand all files Collapse all files

14
src/ZB.MOM.WW.OtOpcUa.Driver.Modbus/ModbusTcpTransport.cs
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@@ -28,10 +28,20 @@ public sealed class ModbusTcpTransport : IModbusTransport
public async Task ConnectAsync(CancellationToken ct)
{
_client = new TcpClient();
// Resolve the host explicitly + prefer IPv4. .NET's TcpClient default-constructor is
// dual-stack (IPv6 first, fallback to IPv4) — but most Modbus TCP devices (PLCs and
// simulators like pymodbus) bind 0.0.0.0 only, so the IPv6 attempt times out and we
// burn the entire ConnectAsync budget before even trying IPv4. Resolving first +
// dialing the IPv4 address directly sidesteps that.
var addresses = await System.Net.Dns.GetHostAddressesAsync(_host, ct).ConfigureAwait(false);
var ipv4 = System.Linq.Enumerable.FirstOrDefault(addresses,
a => a.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork);
var target = ipv4 ?? (addresses.Length > 0 ? addresses[0] : System.Net.IPAddress.Loopback);
_client = new TcpClient(target.AddressFamily);
using var cts = CancellationTokenSource.CreateLinkedTokenSource(ct);
cts.CancelAfter(_timeout);
await _client.ConnectAsync(_host, _port, cts.Token).ConfigureAwait(false);
await _client.ConnectAsync(target, _port, cts.Token).ConfigureAwait(false);
_stream = _client.GetStream();
}

18
tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/DL205/DL205Profile.cs
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@@ -14,13 +14,17 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests.DL205;
/// </remarks>
public static class DL205Profile
{
/// <summary>Holding register the smoke test reads. Address 100 sidesteps the DL205
/// register-zero quirk (pending confirmation) — see modbus-test-plan.md.</summary>
public const ushort SmokeHoldingRegister = 100;
/// <summary>
/// Holding register the smoke test writes + reads. Address 200 is the first cell of the
/// scratch HR range in both <c>Pymodbus/standard.json</c> (HR[200..209] = 0) and
/// <c>Pymodbus/dl205.json</c> (HR[4096..4103] added in PR 43 for the same purpose), so
/// the smoke test runs identically against either simulator profile. Originally
/// targeted HR[100] — moved to HR[200] when the standard profile claimed HR[100] as
/// the auto-incrementing register that drives subscribe-and-receive tests.
/// </summary>
public const ushort SmokeHoldingRegister = 200;
/// <summary>Expected value the pymodbus profile seeds into register 100. When running
/// against a real DL205 (or a pymodbus profile where this register is writable), the smoke
/// test seeds this value first, then reads it back.</summary>
/// <summary>Value the smoke test writes then reads back to assert round-trip integrity.</summary>
public const short SmokeHoldingValue = 1234;
public static ModbusDriverOptions BuildOptions(string host, int port) => new()
@@ -32,7 +36,7 @@ public static class DL205Profile
Tags =
[
new ModbusTagDefinition(
Name: "DL205_Smoke_HReg100",
Name: "Smoke_HReg200",
Region: ModbusRegion.HoldingRegisters,
Address: SmokeHoldingRegister,
DataType: ModbusDataType.Int16,

4
tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/DL205/DL205SmokeTests.cs
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@@ -38,13 +38,13 @@ public sealed class DL205SmokeTests(ModbusSimulatorFixture sim)
// zeroed at simulator start, and tests must not depend on prior-test state per the
// test-plan conventions.
var writeResults = await driver.WriteAsync(
[new(FullReference: "DL205_Smoke_HReg100", Value: (short)DL205Profile.SmokeHoldingValue)],
[new(FullReference: "Smoke_HReg200", Value: (short)DL205Profile.SmokeHoldingValue)],
TestContext.Current.CancellationToken);
writeResults.Count.ShouldBe(1);
writeResults[0].StatusCode.ShouldBe(0u, "write must succeed against the ModbusPal DL205 profile");
var readResults = await driver.ReadAsync(
["DL205_Smoke_HReg100"],
["Smoke_HReg200"],
TestContext.Current.CancellationToken);
readResults.Count.ShouldBe(1);
readResults[0].StatusCode.ShouldBe(0u);

14
tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/ModbusSimulatorFixture.cs
View File

@@ -46,8 +46,18 @@ public sealed class ModbusSimulatorFixture : IAsyncDisposable
try
{
using var client = new TcpClient();
var task = client.ConnectAsync(Host, Port);
// Force IPv4 family on the probe — pymodbus's TCP server binds 0.0.0.0 (IPv4 only)
// while .NET's TcpClient default-resolves "localhost" → IPv6 ::1 first, fails to
// connect, and only then tries IPv4. Under .NET 10 the IPv6 fail surfaces as a
// 2s timeout (no graceful fallback by default), so the C# probe times out even
// though a PowerShell probe of the same endpoint succeeds. Resolving + dialing
// explicit IPv4 sidesteps the dual-stack ordering.
using var client = new TcpClient(System.Net.Sockets.AddressFamily.InterNetwork);
var task = client.ConnectAsync(
System.Net.Dns.GetHostAddresses(Host)
.FirstOrDefault(a => a.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork)
?? System.Net.IPAddress.Loopback,
Port);
if (!task.Wait(TimeSpan.FromSeconds(2)) || !client.Connected)
{
SkipReason = $"Modbus simulator at {Host}:{Port} did not accept a TCP connection within 2s. " +

40
tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/Pymodbus/dl205.json
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@@ -1,5 +1,5 @@
{
"_comment": "DL205.json — AutomationDirect DirectLOGIC DL205/DL260 quirk simulator. Models each behavior in docs/v2/dl205.md as concrete register values so DL205_<behavior> integration tests can assert against this profile WITHOUT a live PLC. Loaded by `pymodbus.simulator`. See ../README.md. Per-quirk address layout matches the table in dl205.md exactly. `shared blocks: true` matches DL series behavior — coils/HR overlay the same word address space (a Y-output is both a discrete bit AND part of a system V-memory register).",
"_comment": "DL205.json — DirectLOGIC DL205/DL260 quirk simulator. Models docs/v2/dl205.md as concrete register values. NOTE: pymodbus rejects unknown keys at device-list / setup level; explanatory comments live at top-level _comment + in README + git. Inline _quirk keys WITHIN individual register entries are accepted by pymodbus 3.13.0 (it only validates addr / value / action / parameters per entry). Each quirky uint16 is a pre-computed raw 16-bit value; pymodbus serves it verbatim. shared blocks=true matches DL series memory model. write list mirrors each seeded block — pymodbus rejects sweeping write ranges that include undefined cells.",
"server_list": {
"srv": {
@@ -27,15 +27,37 @@
},
"invalid": [],
"write": [
[0, 16383]
[0, 0],
[200, 209],
[1024, 1024],
[1040, 1042],
[1056, 1057],
[1072, 1072],
[1280, 1282],
[1343, 1343],
[1407, 1407],
[2048, 2050],
[3072, 3074],
[4000, 4007],
[8448, 8448]
],
"_comment_uint16": "Holding-register seeds. Every quirky value is a raw uint16 with the byte math worked out in dl205.md so the simulator serves it verbatim — pymodbus does NOT decode strings, BCD, or float-CDAB on its own; that's the driver's job.",
"uint16": [
{"_quirk": "V0 marker. HR[0] = 0xCAFE proves register 0 is valid on DL205/DL260 (rejects-register-0 was a DL05/DL06 relative-mode artefact). 0xCAFE = 51966.",
{"_quirk": "V0 marker. HR[0]=0xCAFE proves register 0 is valid on DL205/DL260 (rejects-register-0 was a DL05/DL06 relative-mode artefact). 0xCAFE = 51966.",
"addr": 0, "value": 51966},
{"_quirk": "Scratch HR range 200..209 — mirrors the standard.json scratch range so the smoke test (DL205Profile.SmokeHoldingRegister=200) round-trips identically against either profile.",
"addr": 200, "value": 0},
{"addr": 201, "value": 0},
{"addr": 202, "value": 0},
{"addr": 203, "value": 0},
{"addr": 204, "value": 0},
{"addr": 205, "value": 0},
{"addr": 206, "value": 0},
{"addr": 207, "value": 0},
{"addr": 208, "value": 0},
{"addr": 209, "value": 0},
{"_quirk": "V2000 marker. V2000 octal = decimal 1024 = PDU 0x0400. Marker 0x2000 = 8192.",
"addr": 1024, "value": 8192},
@@ -57,16 +79,14 @@
{"_quirk": "BCD register. Decimal 1234 stored as BCD nibbles 0x1234 = 4660. NOT binary 1234 (= 0x04D2).",
"addr": 1072, "value": 4660},
{"_quirk": "FC03 cap test. Real DL205/DL260 FC03 caps at 128 registers (above spec's 125). HR[1280..1407] is 128 contiguous registers; rest of block defaults to 0.",
{"_quirk": "FC03 cap test marker — first cell of a 128-register span the FC03 cap test reads. Other cells in the span aren't seeded explicitly, so reads of HR[1283..1342] / 1344..1406 return the default 0; the seeded markers at 1280, 1281, 1282, 1343, 1407 prove the span boundaries.",
"addr": 1280, "value": 0},
{"addr": 1281, "value": 1},
{"addr": 1282, "value": 2},
{"addr": 1343, "value": 63, "_marker": "FC03Block_mid"},
{"addr": 1407, "value": 127, "_marker": "FC03Block_last"}
{"addr": 1343, "value": 63},
{"addr": 1407, "value": 127}
],
"_comment_bits": "Coils — Y outputs at 2048+, C relays at 3072+, scratch C at 4000-4007 for write tests. DL260 X inputs would be at discrete-input addresses 0..511 but pymodbus's shared-blocks mode + same-table-as-coils means those would conflict with HR seeds; FC02 tests against this profile use a separate discrete-input block instead — that's why `di size` is large but the X-input markers live in `bits` only when `shared blocks=false`. Document trade-off in README.",
"bits": [
{"_quirk": "Y0 marker. DL260 maps Y0 to coil 2048 (0-based). Coil 2048 = ON proves the mapping.",
"addr": 2048, "value": 1},

70
tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/Pymodbus/standard.json
View File

@@ -1,5 +1,5 @@
{
"_comment": "Standard.json — generic Modbus TCP server for the integration suite. Loaded by `pymodbus.simulator`. See ../README.md for the launch command. Holding registers 0..31 are seeded with their address as value (HR[5]=5) for easy mental-map diagnostics. HR[100] auto-increments via pymodbus's built-in `increment` action so subscribe-and-receive integration tests have a register that ticks without a write. HR[200..209] is a scratch range left at 0 for write-roundtrip tests. Coils 0..31 alternate on/off (even=on); coils 100..109 scratch.",
"_comment": "Standard.json — generic Modbus TCP server for the integration suite. See ../README.md. NOTE: pymodbus rejects unknown keys at device-list / setup level; explanatory comments live in the README + git history. Layout: HR[0..31]=address-as-value, HR[100]=auto-increment, HR[200..209]=scratch, coils 1024..1055=alternating, coils 1100..1109=scratch. Coils live at 1024+ because pymodbus stores all 4 standard tables in ONE underlying cell array — bits and uint16 at the same address conflict (each cell can only be typed once).",
"server_list": {
"srv": {
@@ -14,11 +14,11 @@
"device_list": {
"dev": {
"setup": {
"co size": 1024,
"di size": 1024,
"hr size": 1024,
"ir size": 1024,
"shared blocks": false,
"co size": 2048,
"di size": 2048,
"hr size": 2048,
"ir size": 2048,
"shared blocks": true,
"type exception": false,
"defaults": {
"value": {"bits": 0, "uint16": 0, "uint32": 0, "float32": 0.0, "string": " "},
@@ -27,26 +27,11 @@
},
"invalid": [],
"write": [
[0, 1023]
],
"bits": [
{"addr": 0, "value": 1}, {"addr": 1, "value": 0},
{"addr": 2, "value": 1}, {"addr": 3, "value": 0},
{"addr": 4, "value": 1}, {"addr": 5, "value": 0},
{"addr": 6, "value": 1}, {"addr": 7, "value": 0},
{"addr": 8, "value": 1}, {"addr": 9, "value": 0},
{"addr": 10, "value": 1}, {"addr": 11, "value": 0},
{"addr": 12, "value": 1}, {"addr": 13, "value": 0},
{"addr": 14, "value": 1}, {"addr": 15, "value": 0},
{"addr": 16, "value": 1}, {"addr": 17, "value": 0},
{"addr": 18, "value": 1}, {"addr": 19, "value": 0},
{"addr": 20, "value": 1}, {"addr": 21, "value": 0},
{"addr": 22, "value": 1}, {"addr": 23, "value": 0},
{"addr": 24, "value": 1}, {"addr": 25, "value": 0},
{"addr": 26, "value": 1}, {"addr": 27, "value": 0},
{"addr": 28, "value": 1}, {"addr": 29, "value": 0},
{"addr": 30, "value": 1}, {"addr": 31, "value": 0}
[0, 31],
[100, 100],
[200, 209],
[1024, 1055],
[1100, 1109]
],
"uint16": [
@@ -69,7 +54,38 @@
{"addr": 100, "value": 0,
"action": "increment",
"parameters": {"minval": 0, "maxval": 65535}}
"parameters": {"minval": 0, "maxval": 65535}},
{"addr": 200, "value": 0}, {"addr": 201, "value": 0},
{"addr": 202, "value": 0}, {"addr": 203, "value": 0},
{"addr": 204, "value": 0}, {"addr": 205, "value": 0},
{"addr": 206, "value": 0}, {"addr": 207, "value": 0},
{"addr": 208, "value": 0}, {"addr": 209, "value": 0}
],
"bits": [
{"addr": 1024, "value": 1}, {"addr": 1025, "value": 0},
{"addr": 1026, "value": 1}, {"addr": 1027, "value": 0},
{"addr": 1028, "value": 1}, {"addr": 1029, "value": 0},
{"addr": 1030, "value": 1}, {"addr": 1031, "value": 0},
{"addr": 1032, "value": 1}, {"addr": 1033, "value": 0},
{"addr": 1034, "value": 1}, {"addr": 1035, "value": 0},
{"addr": 1036, "value": 1}, {"addr": 1037, "value": 0},
{"addr": 1038, "value": 1}, {"addr": 1039, "value": 0},
{"addr": 1040, "value": 1}, {"addr": 1041, "value": 0},
{"addr": 1042, "value": 1}, {"addr": 1043, "value": 0},
{"addr": 1044, "value": 1}, {"addr": 1045, "value": 0},
{"addr": 1046, "value": 1}, {"addr": 1047, "value": 0},
{"addr": 1048, "value": 1}, {"addr": 1049, "value": 0},
{"addr": 1050, "value": 1}, {"addr": 1051, "value": 0},
{"addr": 1052, "value": 1}, {"addr": 1053, "value": 0},
{"addr": 1054, "value": 1}, {"addr": 1055, "value": 0},
{"addr": 1100, "value": 0}, {"addr": 1101, "value": 0},
{"addr": 1102, "value": 0}, {"addr": 1103, "value": 0},
{"addr": 1104, "value": 0}, {"addr": 1105, "value": 0},
{"addr": 1106, "value": 0}, {"addr": 1107, "value": 0},
{"addr": 1108, "value": 0}, {"addr": 1109, "value": 0}
],
"uint32": [],