fix(j2mod): do not declare serverFileRecord; FC20 two-sub-request self-test

RELEASE.md

@@ -21,6 +21,28 @@ manual workflow and no releases (`own/go-modbus/README.md`).
 
 ---
 
+## v0.4.1
+
+**Date:** 2026-11-09
+
+**Previous release:** v0.4.0
+
+## Summary
+
+j2mod declares `serverFileRecord` false, and the self-tests read two FC20 sub-requests at once.
+
+## Changes
+
+### Fixed
+
+- **`j2mod` declared `serverFileRecord` although j2mod 3.4.0 answers the second of two FC20 sub-requests with the wrong records** (FIXTURES.md rule 10; Modbus Application Protocol V1.1b3, 6.14): `140e0600010000000206000200000002` is answered `140c0506000b0506000100020000`, not `140c0506000b01a4050600010002`. The go-modbus interop suite found it. The server still answers FC20 and FC21 (`serverFunctions`), but the pairings that need `serverFileRecord` now skip the j2mod server.
+
+### Added
+
+- **Self-test** `values.fc20.two-sub-requests`: an FC20 with two sub-requests, sent with `raw`, must return the records of both from the fixture.
+
+---
+
 ## v0.4.0
 
 **Date:** 2026-11-08

adapters/j2mod/README.md

@@ -152,6 +152,7 @@ both are `connection-lost`.
 | `diagnostics` with other than two data bytes | `ReadSerialDiagnosticsRequest` has exactly one data word. Usage error, nothing sent. |
 | file numbers 10000 and above | `SimpleProcessImage.getFileByNumber` refuses them (exception 2). |
 | `serverIllegalFunction` | Over TCP an unknown function code closes the connection instead of exception 1: `IllegalFunctionRequest.readData` skips the MBAP length rather than the data length and reads past the frame (finding 1). Over UDP the library answers `c101` correctly, but the feature is declared for the adapter. |
+| `serverFileRecord` | FC20 with two sub-requests answers the second one with the wrong records: `ReadFileRecordResponse.getMessage` advances the offset wrongly (finding 5; FIXTURES.md rule 10, spec 6.14). FC20 and FC21 are still answered by the library, with the adapter's checks in front. The self-tests send two sub-requests (`values.fc20.two-sub-requests`). |
 
 ## Findings about the library (3.4.0)
 

adapters/j2mod/src/main/java/org/otfabric/modbusinterop/j2mod/Main.java

@@ -155,7 +155,10 @@ private static JsonObject capabilities() {
         // FC08 and FC17 request classes answer exception 1 on the server side.
         features.addProperty("serverDiagnostics", false);
         features.addProperty("serverReportServerId", false);
-        features.addProperty("serverFileRecord", true);
+        // FC20 with two sub-requests answers the second with the wrong
+        // records (README, finding 5; FIXTURES.md rule 10). FC20 and FC21
+        // are still answered by the library (serverFunctions).
+        features.addProperty("serverFileRecord", false);
         features.addProperty("serverFifoQueue", true);
         features.addProperty("clientDiagnostics", true);
         features.addProperty("clientReportServerId", true);

docs/COMPATIBILITY.md

@@ -61,7 +61,7 @@ also build and pass on the release before (v3.1.12 and 3.15.0).
 | `clientUnitIdCheck` | **no** | yes | **no** | yes | yes | **no** | **no** | **no** | yes |
 | `serverDiagnostics` | **no** | yes | **no** | yes ² | **no** | **no** | **no** | **no** | **no** |
 | `serverReportServerId` | **no** ³ | yes | **no** | **no** | **no** ⁴ | **no** | **no** | **no** | yes |
-| `serverFileRecord` | **no** | yes | **no** | **no** | **no** | yes | **no** | **no** | **no** |
+| `serverFileRecord` | **no** | yes | **no** | **no** | **no** | **no** | **no** | **no** | **no** |
 | `serverFifoQueue` | **no** | yes | **no** | **no** | **no** | yes | **no** | **no** | **no** |
 | `clientDiagnostics` | **no** | yes | **no** | **no** | **no** | yes | **no** | **no** | **no** |
 | `clientReportServerId` | yes | yes | **no** | **no** | yes | yes | **no** | **no** | yes |
@@ -266,8 +266,10 @@ every response. Details and hex in `adapters/j2mod/README.md`.
 - FC20 with two sub-requests (spec 6.14): `140e0600010000000206000200000002`
   is answered `140c0506000b0506000100020000`, expected
   `140c0506000b01a4050600010002` (`ReadFileRecordResponse.getMessage`
-  advances the offset wrongly). Not in the self-tests, which read one
-  sub-request.
+  advances the offset wrongly). Found by the go-modbus interop suite after
+  v0.4.0, which declared `serverFileRecord` true; it is false since v0.4.1,
+  and the self-tests now send two sub-requests
+  (`values.fc20.two-sub-requests`).
 - Over UDP, FC24 and FC20 responses are framed by a data length that is never
   updated: FC24 `1804de` is answered one byte short, the empty queue carries
   3 stale bytes, FC20 is answered with MBAP length 0 and no PDU.

scripts/interop.sh

@@ -383,6 +383,17 @@ for server in "${ADAPTERS[@]}"; do
 2 0 4 1
 FILES
         else skip "${pair}: FC20 values"; fi
+        # Two sub-requests in one FC20 (FIXTURES.md rule 10): records 0..1 of
+        # file 1 and of file 2. Only raw sends more than one.
+        at values.fc20.two-sub-requests
+        if supported "${client}" "${server}" "server:serverFileRecord,client:clientRaw,client:clientRawAnyResponse"; then
+            got=$(run_client "${client}" raw --function 20 --data 0e0600010000000206000200000002 --host "${name}" | jq -r '.response.data')
+            # Byte count 0x0c, then per sub-response: length 5, reference type 6, two registers.
+            want="0c$(jq -r '[.fileRecords[0].records[0:2], .fileRecords[1].records[0:2]][] | map(tostring) | join(" ")' "${FIXTURE}" \
+                | while read -r r0 r1; do printf '0506%04x%04x' "${r0}" "${r1}"; done)"
+            if [[ "${got}" == "${want}" ]]; then ok "${pair}: FC20 with two sub-requests returns the records of both"
+            else fail "${pair}: FC20 with two sub-requests returns ${got}, want ${want}"; fi
+        else skip "${pair}: FC20 with two sub-requests (needs server:serverFileRecord,client:clientRaw,client:clientRawAnyResponse)"; fi
         at values.fc24
         if supported "${client}" "${server}" "server:serverFifoQueue,client:clientFifoQueue"; then
             for index in 0 1 2; do

versions.yaml

@@ -3,7 +3,7 @@
 # The Dockerfiles are the source of truth for a build:
 # scripts/check-versions.sh fails when this file disagrees with them.
 
-interop_version: "0.4.0"
+interop_version: "0.4.1"
 contract_version: "1.2"        # docs/CONTAINER_CONTRACT.md, schemaVersion of every document
 fixture_schema: "1.1"          # fixtures/schema/modbus-fixture.schema.json