fix(admin): allow bidirectional format conversion for upstream.nodes in PATCH requests

[janiussyafiq]

Description

Fixes asymmetric PATCH behavior when converting upstream.nodes between array and hash table formats.

Problem Statement

The Admin API exhibits inconsistent behavior when patching a route's upstream.nodes field:

• Converting from array → hash table works
• Converting from hash table → array fails with validation error:
  {"error_msg":"invalid configuration: property \"upstream\" validation failed: property \"nodes\" validation failed: object matches none of the required"}

This happens despite both formats being officially supported by the schema.

Root Cause

The merge() function in apisix/core/table.lua only checks if the origin value is an array before deciding whether to replace or recursively merge:

if _M.nkeys(origin[k]) ~= #origin[k] then
  merge(origin[k] or {}, extend[k] or {})  -- Merge if origin is hash
else
  origin[k] = v  -- Replace if origin is array
end

When patching from hash table → array:

• Origin is hash table, so it tries to merge
• This creates an invalid mixed structure with both string keys (from hash) and numeric indexes (from array)
• Validation fails because it's neither a valid hash nor a valid array

Solution

Modified the merge logic to check both the origin and incoming values:

• If either is an array → replace (prevents invalid mixed structures)
• If both are hash tables → merge (safe to combine)

Which issue(s) this PR fixes:

Fixes #13045

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)

[Copilot]

Pull request overview

This PR fixes asymmetric Admin API PATCH behavior when upstream.nodes changes between array and hash-table formats by adjusting the deep-merge logic to avoid creating mixed array/hash tables during patch merges.

Changes:

• Update core.table.merge() to replace (not recursively merge) when either the existing value or incoming value is an array.
• Add an Admin API test that exercises PATCH conversions between array and hash-table upstream.nodes formats.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
apisix/core/table.lua	Adjusts merge behavior to prevent invalid mixed table structures when patching between array/hash formats.
t/admin/routes-array-nodes.t	Adds a regression test for PATCHing upstream.nodes across both supported representations.

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[Copilot]

This test performs multiple admin calls (PUT, then PATCH array→hash, then PATCH hash→array) but only asserts the final call’s result. If the intermediate PATCH fails, the test can still pass because later calls overwrite code/body. Add checks after each call (e.g., if code >= 300 then ... return end) so the test fails as soon as any step fails, and so it actually verifies both conversions.

[janiussyafiq]

fixed

[Baoyuantop]

It is recommended to use table.isarray

[janiussyafiq]

fixed