Dell: partition attributes into PATCH and POST groups with POST-based drift detection

[atd9876]

Description

Dell iDRACs use two distinct write patterns: PATCH for DellAttributes and POST for actions like certificate import. This sub-task implements attribute partitioning and idempotent POST handling with drift detection.

Changes

1. partitionAttributes in redfish_dell.go — splits the incoming SettingsAttributes map into two groups:

   • PATCH group: keys that map to DellAttributes endpoints (standard key-value pairs)
   • POST group: keys with the 3-field format "POST <action-url> <check-collection-url>" indicating an action that creates/replaces a collection member

2. 3-field POST key format — "POST /redfish/v1/.../ImportCertificate /redfish/v1/.../Certificates":

   • Field 1: literal POST
   • Field 2: the action URL to POST to
   • Field 3: the collection URL to check for existing members (drift detection)

3. buildPostKey(actionURL, collectionURL) — constructs the 3-field key from components.

4. hashRequestBody(body) — SHA-256 hash of the POST request body, stored as the ETag equivalent for POST operations (since POST responses from Dell don't return ETags).

5. POST drift detection — before issuing a POST, check if the target collection already has a member whose body hash matches. If it does, the operation is a no-op (idempotent). This prevents duplicate certificate imports.

6. Dell SetBMCAttributesImmediately — orchestrates both groups: PATCH attributes via httpBasedUpdateBMCAttributes, POST attributes via action URL, returns unified map[string]ApplyResult.

7. Dell GetBMCAttributeValues — wires through to detectSettingsDrift for PATCH attributes; for POST attributes, checks collection member existence.

Tests

• TestBuildPostKey — key construction and parsing
• TestHashRequestBody — deterministic hash
• TestPartitionAttributes — correct grouping of PATCH vs POST keys
• POST idempotency: duplicate POST detected via body hash → no re-POST

Files

• bmc/redfish_dell.go (partition logic, POST orchestration, drift detection)
• bmc/oem_helpers.go (buildPostKey, hashRequestBody, POST handling in update path)
• bmc/oem_helpers_test.go (tests for this PR's scope)

Acceptance Criteria

• Attributes with POST prefix are routed to action URL, not PATCH
• Duplicate POST is detected via body hash — no redundant certificate import
• PATCH attributes still use ETag-based drift detection from sub-task 4
• make test green

[coderabbitai]

🔗 Related PRs

#579 - Improve Dell hardware support with enhanced firmware updates and BMC configuration [merged]
#834 - Override some of the default redfish attribute for dell registry stru… [merged]
#844 - Fix dell fetch BMC attribute method [merged]
#849 - Improved handling of BMC attribute values by consulting registry type definitions [merged]
#902 - BMC Settings Spec to support display names for enum typed settings attributes for Dell [merged]

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