feat(ai): support configurable request JSON library

[nic-6443]

This adds an APISIX-level JSON library selector for request body parsing used by core.request.get_request_body_table, and reuses the same selector for AI upstream request body encoding.

The supported values are cjson, simdjson, and qjson. The default is simdjson. qjson is available as an experimental option for users who explicitly opt in after evaluating compatibility. The config schema owns the enum/default validation, and request_json caches the validated value from local_conf. The selected decode/encode behavior is fixed by the configured value: cjson uses cjson decode and encode, simdjson uses simdjson decode and cjson encode, and qjson uses qjson decode and encode. qjson decode results are materialized before returning from core.request so existing table consumers such as JSONPath matching can keep using normal Lua table traversal.

lua-qjson and api7-lua-resty-simdjson are installed through LuaRocks dependencies. The simdjson package keeps cjson array metadata for decoded arrays, so empty arrays still round-trip as arrays when encoded by cjson. The Rust toolchain bootstrap logic is shared by CI and install-dependencies to keep the minimum rustc/rustup setup in one place. Docker build paths that run make deps also install or carry the Rust/helper prerequisites needed to build simdjson.

Docs include benchmark data for cjson, simdjson, and qjson on large AI request bodies.

Tests added/updated:

• t/core/request.t covers selector behavior, qjson materialization, simdjson empty-array round-trip behavior, and AI transport encoding
• t/core/config-default.t covers the default value

Checks run:

• luacheck apisix/core/request_json.lua apisix/core/request.lua apisix/plugins/ai-transport/http.lua apisix/plugins/ai-transport/auth-aws.lua
• perl -I. -c t/core/request.t
• bash -n ci/common.sh utils/install-dependencies.sh utils/install-rust-toolchain.sh ci/linux_apisix_current_luarocks_runner.sh
• git diff --check
• request_json qjson smoke test via resty
• qjson LuaRocks install smoke test
• lua-qjson LuaRocks install with Makefile Rust/Cargo home selection
• api7-lua-resty-simdjson LuaRocks install smoke test
• request_json simdjson empty-array round-trip smoke test via resty

[Copilot]

Pull request overview

Adds an APISIX-level setting apisix.request_body_json_lib (default qjson, options cjson/simdjson/qjson) controlling the JSON library used by core.request.get_request_body_table and by AI transport upstream body encoding. Introduces a new module apisix.core.request_json that lazily loads the selected library, plus rockspec dependencies on lua-qjson and lua-resty-simdjson.

Changes:

• New module apisix/core/request_json.lua selecting between cjson/qjson/simdjson based on local config, wired into apisix/core/request.lua and AI transport encoders (ai-transport/http.lua, ai-transport/auth-aws.lua).
• Schema + default config additions for request_body_json_lib, and new rockspec deps lua-qjson and lua-resty-simdjson.
• Docs (en/zh) and tests covering selector behavior, AI encoder routing, and the new default in config-default.t.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
apisix/core/request_json.lua	New selector module with lazy load of qjson/simdjson and cjson fallback.
apisix/core/request.lua	Replaces core.json.decode with request_json.decode for request body parsing.
apisix/plugins/ai-transport/http.lua	Switches upstream body encode to request_json.encode.
apisix/plugins/ai-transport/auth-aws.lua	Switches SigV4 body encode to request_json.encode; drops unused core import.
apisix/cli/schema.lua	Adds enum schema for request_body_json_lib.
apisix/cli/config.lua	Adds default request_body_json_lib = "qjson".
conf/config.yaml.example	Documents new option in example config.
apisix-master-0.rockspec	Adds lua-qjson and lua-resty-simdjson dependencies.
docs/en/latest/plugins/ai-proxy.md	English docs for the new option.
docs/zh/latest/plugins/ai-proxy.md	Chinese docs for the new option.
t/core/request.t	Adds tests for selector behavior and AI transport encoder routing.
t/core/config-default.t	Adds assertion on the new default value.

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[moonming]

why we need rust？