unbridled-41 opened a new pull request, #5424:
URL: https://github.com/apache/rocketmq-dashboard/pull/5424
## Problem / Evidence
`GET /api/dlq/export-excel` returns HTTP 502 for the entire group when any
single dead-letter message has a decoded body longer than 32,767 characters,
instead of producing a workbook.
- `instance/dlq/DLQMessageExcelRow.java:70` copied the full body into the
`Body` cell.
- `provider/apache/RocketMQDLQProvider.java:404` puts the whole decoded body
into the VO (`toUtf8Text(message.getBody())`), and `:357-366` wraps any write
failure as `throw new BusinessException(502, "Failed to export DLQ messages as
Excel: ...")`.
- EasyExcel 3.3.4 → POI 4.1.2 rejects cell text beyond
`SpreadsheetVersion.getMaxTextLength()`. Reproduced in a unit test:
```
WARN RocketMQDLQProvider -- Failed to build Excel export for group group-a:
The maximum length of cell contents (text) is 32767 characters
BusinessException: Failed to export DLQ messages as Excel: The maximum
length of cell contents (text) is 32767 characters
```
RocketMQ allows message bodies far larger than one spreadsheet cell, so a
single unlucky dead letter makes the whole group's export unusable.
## Root cause / Fix
The `Body` cell was written unbounded while every other cell is naturally
short. Clamp it to the spreadsheet limit with a visible `...[truncated]`
marker, backing off one character when the cut would land between a surrogate
pair so the cell never contains an unpaired half.
## Priority & scoring
PRIORITY 57 = 影响 20 (the export of a whole group fails, and the operator
cannot tell which message caused it) + 波及 6 (DLQ Excel export endpoint) + 可复现
20 (deterministic for a body over 32,767 chars) + 维护价值 11 (restores the
documented export contract).
FIX_CONFIDENCE 92: bounded clamp in one row mapper, with the exact POI
failure reproduced before the fix and the neighbouring row asserted intact
after.
## Tests
```
cd server && mvn -o test -Dtest=RocketMQDLQProviderTest
```
- Red before the fix: the new test errors with `BusinessException: Failed to
export DLQ messages as Excel: The maximum length of cell contents (text) is
32767 characters`.
- Green after: `Tests run: 46, Failures: 0, Errors: 0, Skipped: 0` (also
`-Dtest='org.apache.rocketmq.studio.instance.dlq.*Test'` → 44 passed).
- The regression test drives a real EasyExcel workbook read back and asserts
the oversized cell is clamped, ends with the marker, contains no unpaired
surrogate, and that the following row still exports its body intact.
- `mvn -o checkstyle:check` passes.
## Risk
Low. Only the `Body` cell content changes, and only when it exceeds a limit
that previously aborted the request. Exported bodies that fit are
byte-identical.
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