fix: allow async SMB read responses

[suyanhanx]

Closes #165

Summary

• allow File::read_block to accept async SMB2 responses
• reuse the existing pending-response handling instead of rejecting the read immediately

Why

This fixes a real downstream problem in OpenDAL's new SMB backend draft PR: apache/opendal#7374.

That OpenDAL branch is intentionally not carrying a local smb-rs fork. With crates.io smb = 0.11.1, a real Samba behavior run still hits read-path failures like:

IO Error: Invalid argument: Async command is not allowed in this context.

OpenDAL only passes today because its retry layer reconnects and retries those reads. In other words, the downstream behavior suite is green, but only because retries are masking this smb-rs bug.

This change makes read_block consistent with the existing write path, which already calls with_allow_async(true).

Public downstream reproduction

The downstream reproduction is public now:

• OpenDAL draft PR: apache/opendal#7374
• OpenDAL commit: 41faefd11f0f76253136e6aaa610bf360342d0a2

To reproduce the bug without this fix:

git clone https://github.com/apache/opendal.git
cd opendal
git fetch https://github.com/suyanhanx/opendal.git feat/smb-service
git checkout 41faefd11f0f76253136e6aaa610bf360342d0a2
cd core
RUST_LOG=debug \
OPENDAL_TEST=smb \
OPENDAL_SMB_ENDPOINT=127.0.0.1:1445 \
OPENDAL_SMB_SHARE=MyShare \
OPENDAL_SMB_ROOT=/ \
OPENDAL_SMB_USER=alice \
OPENDAL_SMB_PASSWORD=alipass \
cargo test -p opendal --features tests,services-smb behavior -- --nocapture

Observed downstream behavior with crates.io smb = 0.11.1:

• final result is still 92 passed; 0 failed
• debug logs show many async pending responses
• some large reads also log Async command is not allowed in this context
• OpenDAL retry logs then show the same read being retried successfully

Representative downstream log lines:

IO Error: Invalid argument: Async command is not allowed in this context.
will retry after 1s because: Unexpected (temporary) at read ... Async command is not allowed in this context.

Validation

• cargo check -p smb

To validate this change against the public downstream repro above, temporarily point the OpenDAL checkout to this PR branch and rerun the same behavior command. For example:

[patch.crates-io]
smb = { git = "https://github.com/suyanhanx/smb-rs", branch = "fix/allow-async-read-response" }

Expected result with this PR applied:

• the same OpenDAL behavior command still finishes 92 passed; 0 failed
• async pending responses are still observed in debug logs
• the previous Async command is not allowed in this context read failures disappear
• OpenDAL no longer needs retry to recover those reads

[coderabbitai]

Walkthrough

Updated File::read_block to permit async SMB2 responses by changing the receive options from ReceiveOptions::new() to ReceiveOptions::new().with_allow_async(true), enabling proper handling of asynchronous server responses during file read operations.

Changes

Cohort / File(s)	Summary
SMB File Read Async Support crates/smb/src/resource/file.rs	Modified read_block to enable async response handling by adding with_allow_async(true) to ReceiveOptions, allowing the method to transparently handle async SMB2 status responses from servers like TrueNAS SCALE.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Poem

🐰 A rabbit reads files through async skies,
No longer blocked by server replies,
One tiny flag makes the session flow free,
Async responses now work—hooray! ✨📖

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'fix: allow async SMB read responses' accurately describes the main change: enabling async SMB2 response handling in the read_block method.
Linked Issues check	✅ Passed	The PR implements the exact fix suggested in issue #165: enabling allow_async for read_block by adding .with_allow_async(true) to ReceiveOptions, addressing the primary objective.
Out of Scope Changes check	✅ Passed	The change is narrowly focused on enabling async handling for read_block only; no unrelated modifications or scope creep detected beyond the stated objective.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[suyanhanx]

Opened the downstream OpenDAL draft PR that depends on this fix: apache/opendal#7374

That PR intentionally avoids carrying a local smb-rs fork. With crates.io smb = 0.11.1, OpenDAL's real Samba behavior run still logs Async command is not allowed in this context on some large reads and only passes because the retry layer reconnects and retries. Once this PR lands upstream, I can update the OpenDAL PR notes to point at the released fix instead of the retry-masked dependency bug.

[afiffon]

I finally got to properly release v0.11.2, which rolls out this patch to crates.io!