fix: reset decoder state after decode errors

[jarvis9443]

This fixes a decoder state leak after simdjson on-demand parsing errors.

When simdjson_ffi_next() hit an error while walking nested arrays or objects, it returned the error but left state.frames intact. Reusing the same parser for a later valid JSON body could then continue from stale iterator frames and eventually report simdjson: error: trailing content found.

The fix resets decoder state before starting a new parse and also resets it in the parse/next error paths. This keeps parser reuse safe after failed decodes, which matches the documented usage pattern of reusing a parser instance across multiple decode() calls.

A regression case was added for the failure sequence:

1. decode a nested string error: {"model":["\\uD800"]}
2. decode valid OpenAI-compatible JSON
3. decode another valid OpenAI-compatible JSON

Before this fix, the later valid decode failed with trailing content found.

Validation:

PATH=/usr/local/openresty/nginx/sbin:$PATH prove -v t/02-decode.t
PATH=/usr/local/openresty/nginx/sbin:$PATH make test

Summary by CodeRabbit

• Bug Fixes

  • Parser now fully resets its internal decode state after encountering a decoding error, preventing leftover state from affecting subsequent parses.

• Tests

  • Added a test to verify recovery from a nested string decoding failure and successful reuse of the same parser for later valid payloads.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 62c59a94-958a-49c2-a844-f104c03b81ad

📥 Commits

Reviewing files that changed from the base of the PR and between d5439cc and 979e314.

📒 Files selected for processing (1)

• t/02-decode.t

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📝 Walkthrough

Walkthrough

New decoder-state reset helper clears opcode counter and frame stack; the helper is called before parse initialization and in parse/next error paths. A test is added to verify the parser recovers after a nested string decode error and can decode subsequent valid payloads.

Changes

Decoder State Recovery on Parse Errors

Layer / File(s)	Summary
Decoder state reset helper src/simdjson_ffi.cpp	New static helper simdjson_ffi_reset_decoder_state() zeroes the opcode batch counter and clears the decoder frames stack.
Parser integration of state reset src/simdjson_ffi.cpp	Helper called before state->document initialization in simdjson_ffi_parse(), and added to error handlers in simdjson_ffi_parse() and simdjson_ffi_next() to clear state on failure.
Test coverage for parser recovery t/02-decode.t	Adds TEST 12: parser recovers after nested string decode error that asserts an initial decode error returns nil and STRING_ERROR, then reuses the same parser to decode valid payloads; also updates nearby test numbering.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Suggested reviewers

• nic-6443

🚥 Pre-merge checks | ✅ 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'fix: reset decoder state after decode errors' accurately and concisely describes the main change across both files: implementing decoder state reset logic in error paths and before parsing.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
E2e Test Quality Review	✅ Passed	Real E2E test using Nginx/Lua server and simdjson library validates parser recovery after nested errors; all assertions clear, no dependencies, perfect PR alignment.
Security Check	✅ Passed	PR is a JSON parser bugfix (state reset) with no logging/credential/auth/TLS/DB code. All 7 security categories show no vulnerabilities.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/fix-decode-error-state

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[membphis]

LGTM

[coderabbitai]

Actionable comments posted: 0