# Lua Adapter API

> **中文**: [lua-adapters.md](./lua-adapters.md)

Every upstream source is mounted with a `.lua` adapter that **transforms** the unified
OpenAI-format request into the upstream's native format, and converts upstream
responses / stream chunks back into the unified format. The Go layer only handles
scheduling, concurrency and pass-through — so **adding an adapter or adapting a new
protocol never requires recompiling Go**.

Adapters live in two equivalent places:
- Bundled: `internal/lua/adapters/<name>.lua` (embedded at build time)
- Override: a same-named script in the configured `adapter_dir` (takes precedence)

> **When are they loaded?** All adapters are loaded once at startup by
> `lua.NewVM(adapter_dir)`. Adapters uploaded via the WebUI
> (`Core.UploadAdapter` → `vm.LoadAdapter`) and sources edited online take
> effect immediately, without a restart. Directly editing a `.lua` file under
> `adapter_dir` requires a process restart to reload.

## Table of Contents

1. [Script Structure](#1-script-structure)
2. [Static Fields](#2-static-fields)
3. [Transform Hooks](#3-transform-hooks)
4. [Optional Hooks](#4-optional-hooks)
5. [Built-in Helper Functions](#5-built-in-helper-functions)
6. [meta Contract](#6-meta-contract)
7. [A Complete Minimal Adapter](#7-a-complete-minimal-adapter)
8. [Multimodal & disable_thinking](#8-multimodal--disable_thinking)

---

## 1. Script Structure

A script is a Lua file that returns a table — it **must** `return` a table:

```lua
local adapter = {}
adapter.name = "mysrc"
adapter.version = "1.0.0"
-- ... fields and functions ...
return adapter
```

Scripts are executed by LuaJIT (via golua bindings, cgo). Each adapter owns an
**independent VM + worker pool**; adapters never interfere with each other. No mutable
state may be shared across workers (`log` to stdout is the only side effect).

## 2. Static Fields

| Field | Type | Required | Description |
|-------|------|----------|-------------|
| `name` | string | yes | Adapter name, shown in the WebUI |
| `version` | string | no | Version, shown in the WebUI |
| `endpoint` | string | no | Upstream path, default `/chat/completions`; overridable by `source.endpoint` / `source.image_endpoint` |
| `headers` | table | no | Static default request headers; used as fallback when no `build_headers` hook is defined |

These fields are extracted statically at load time (compile-once); reading them never
occupies a pooled worker.

## 3. Transform Hooks

### `transform_request(raw_body) -> string`

Input: the unified OpenAI-format JSON string built by the Go layer (the
`/v1/chat/completions` request body).
Output: the request body string to send upstream.

```lua
function adapter.transform_request(raw_body)
    local ok, req = pcall(json.decode, raw_body)
    if not ok then return raw_body end
    req.model = "upstream-model-name"      -- rewrite the model name
    req.stream = req.stream or false
    return json.encode(req)
end
```

Contract:
- The returned string is POSTed verbatim to `base_url + (source.endpoint or adapter.endpoint)`.
- Internal gateway fields such as `disable_thinking` and `extra_body` should be cleaned
  up by the transform (`openai.lua` deletes both).

### `transform_response(raw_body) -> string`

Input: the raw JSON string of a non-streaming upstream response.
Output: a JSON string in the unified format.

Unified format fields:

| Field | Type | Description |
|-------|------|-------------|
| `content` | string | Response text |
| `finish_reason` | string | `stop` / `length` / `tool_calls` etc. |
| `reasoning_content` | string (optional) | Reasoning text (DeepSeek etc.) |
| `token_usage` | table | `{ prompt, completion, total }` (tokens) |
| `tool_calls` | array (optional) | Tool calls: `{ id, type, name, arguments }`; `arguments` is a **decoded** table |

```lua
function adapter.transform_response(raw_body)
    local ok, resp = pcall(json.decode, raw_body)
    if not ok or resp == nil then return raw_body end
    local unified = {
        content = "",
        finish_reason = "",
        token_usage = { prompt = 0, completion = 0, total = 0 }
    }
    if type(resp.choices) == "table" and #resp.choices > 0 then
        local ch = resp.choices[1]
        unified.content = ch.message.content or ""
        unified.finish_reason = ch.finish_reason or ""
        if ch.message.reasoning_content then
            unified.reasoning_content = ch.message.reasoning_content
        end
    end
    return json.encode(unified)
end
```

### `transform_stream_chunk(raw_chunk) -> string`

Input: the raw JSON string of each `data:` line in the SSE stream (without the
`data:` prefix).
Output: a unified chunk JSON string; **returning `""` skips that chunk**.

Unified chunk format:

| Field | Type | Description |
|-------|------|-------------|
| `content` | string | Incremental text for this chunk (may be `""`) |
| `done` | boolean (optional) | `true` ends the stream (when `finish_reason` appears) |

```lua
function adapter.transform_stream_chunk(raw_chunk)
    local ok, chunk = pcall(json.decode, raw_chunk)
    if not ok then return "" end
    if not chunk.choices or #chunk.choices == 0 then return "" end
    local delta = chunk.choices[1].delta or {}
    local fr = chunk.choices[1].finish_reason
    return json.encode({
        content = delta.content or "",
        done = (fr ~= nil)
    })
end
```

## 4. Optional Hooks

### `build_headers(meta) -> table<string,string>`

Dynamically generate / sign request headers (e.g. KimiCode's HMAC signature). If the
script does not define this function, the Go layer falls back to the static
`adapter.headers` (or `source.headers`).

```lua
function adapter.build_headers(meta)
    local msg = meta.method .. meta.url .. meta.body
    return {
        ["X-App-Sign"] = hmac_sha256_hex(meta.source.meta.app_secret, msg),
        ["X-Timestamp"] = meta.timestamp,
    }
end
```

Returning a non-table errors; returning `{}` means no custom headers (no fallback to
static headers).

## 5. Built-in Helper Functions

Global functions shared by all adapters (injected by Go):

| Function | Description |
|----------|-------------|
| `json.encode(v)` | Lua value → JSON string; returns `"null"` on failure |
| `json.decode(s)` | JSON string → Lua value; returns `nil` on failure |
| `hmac_sha256_hex(key, data)` | HMAC-SHA256, lowercase hex string |
| `sha256_hex(data)` | SHA-256, lowercase hex string |
| `base64_encode(s)` | Standard Base64 encoding |
| `tohex(s)` | Bytes → lowercase hex string |
| `log(level, msg)` | Prints `[adapter/<name>] <msg>` to stdout |

Note: scripts run under LuaJIT with the full standard library (`string`/`table`/`pcall`
etc.); `os`/`io` are not exposed (sandbox semantics).

## 6. meta Contract

The meta structure shared by `build_headers(meta)` and the request transforms:

| Field | Description |
|-------|-------------|
| `meta.url` | Full request URL |
| `meta.method` | HTTP method (usually `POST`) |
| `meta.body` | Request body string |
| `meta.api_key` | The source's `api_key` |
| `meta.timestamp` | Request timestamp |
| `meta.source` | table: `{ name, meta = { ... } }` — the source's `meta` field (e.g. `app_secret`) |

## 7. A Complete Minimal Adapter

```lua
local adapter = {}

adapter.name = "mysrc"
adapter.version = "1.0.0"
adapter.endpoint = "/chat/completions"
adapter.headers = { ["X-Tenant"] = "prod" }

function adapter.transform_request(raw_body)
    local ok, req = pcall(json.decode, raw_body)
    if not ok then return raw_body end
    req.disable_thinking = nil
    req.extra_body = nil
    return json.encode(req)
end

function adapter.transform_response(raw_body)
    local ok, resp = pcall(json.decode, raw_body)
    if not ok or resp == nil then return raw_body end
    local unified = {
        content = "",
        finish_reason = "",
        token_usage = { prompt = 0, completion = 0, total = 0 }
    }
    if type(resp.choices) == "table" and #resp.choices > 0 then
        local ch = resp.choices[1]
        unified.content = ch.message.content or ""
        unified.finish_reason = ch.finish_reason or ""
    end
    return json.encode(unified)
end

function adapter.transform_stream_chunk(raw_chunk)
    local ok, chunk = pcall(json.decode, raw_chunk)
    if not ok then return "" end
    if not chunk.choices or #chunk.choices == 0 then return "" end
    return json.encode({
        content = (chunk.choices[1].delta or {}).content or "",
        done = (chunk.choices[1].finish_reason ~= nil)
    })
end

return adapter
```

Corresponding `config.yaml` source:

```yaml
sources:
  - name: mysrc
    base_url: https://upstream.example.com
    api_key: sk-xxx
    adapter: mysrc           # or omit = bundled adapter with the same name
    endpoint: /chat/completions
    models:
      - id: my-model
        priority: 50
        kind: chat
```

## 8. Multimodal & disable_thinking

- **Multimodal**: if the request `content` is an array
  (`[{type:"text"...},{type:"image_url"...}]`), the Go layer passes it through
  verbatim to the adapter. Sources whose protocol doesn't support it (Anthropic /
  Gemini / Ollama) must convert inside `transform_request`; the bundled
  `anthropic.lua` / `gemini.lua` / `ollama.lua` already do.
- **disable_thinking**: the gateway passes `disable_thinking:true` from the request
  body into `transform_request`. The DeepSeek adapter maps it to
  `extra_body.thinking = { type = "disabled" }` and cleans up its own field; other
  adapters handle it per their protocol (implement or ignore as needed).