eric-wang-1990 opened a new pull request, #3578:
URL: https://github.com/apache/arrow-adbc/pull/3578
## Summary
Reordered HTTP delegating handlers in DatabricksConnection to ensure
RetryHttpHandler processes responses before ThriftErrorMessageHandler throws
exceptions. This fixes a bug where 503 Service Unavailable responses with
Retry-After headers (e.g., during cluster auto-start) were not being retried.
## Problem
Previously, the handler chain had ThriftErrorMessageHandler as the innermost
handler:
```
ThriftErrorMessageHandler (inner) → RetryHttpHandler (outer) → Network
```
This caused ThriftErrorMessageHandler to process error responses first and
throw exceptions immediately, preventing RetryHttpHandler from retrying 503
responses during cluster auto-start scenarios.
## Solution
Reordered the chain so RetryHttpHandler is inside ThriftErrorMessageHandler:
```
RetryHttpHandler (inner) → ThriftErrorMessageHandler (outer) → Network
```
Now responses flow: Network → RetryHttpHandler → ThriftErrorMessageHandler
With this order:
1. RetryHttpHandler processes 503 responses first and retries them according
to Retry-After headers
2. Only after all retries are exhausted does ThriftErrorMessageHandler throw
exceptions with Thrift error messages
## Changes
- Reordered handlers in `DatabricksConnection.CreateHttpHandler()`
- Added comprehensive documentation explaining handler chain execution order
and why it matters
- Added cross-references in `RetryHttpHandlerTest` and
`ThriftErrorMessageHandlerTest` pointing to the production code
## Test Plan
- ✅ All existing unit tests pass:
- `ThriftErrorMessageHandlerTest`: 11/11 tests pass
- `RetryHttpHandlerTest`: 14/14 tests pass
- The fix will be validated in E2E tests when connecting to Databricks
clusters that need auto-start
## Related Issues
Fixes cluster auto-start retry issues where 503 responses with Retry-After
headers were not being retried.
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