Add backend package: common LLM interface for ollama and OpenAI-compatible APIs
Defines a Backend interface with shared Message/Tool/ToolCall types. OllamaBackend wraps /api/chat; OpenAIBackend covers OpenAI, OpenRouter, and any compatible API. Factory reads OLLIE_BACKEND, OLLIE_API_URL, OLLIE_API_KEY. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Levi Neely
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// Package backend defines the Backend interface and shared types for LLM
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// providers. All backends speak the same canonical types; provider-specific
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// wire formats are handled inside each implementation.
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package backend
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import (
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"context"
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"encoding/json"
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)
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// Message is a single conversation turn.
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type Message struct {
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Role string `json:"role"` // "system" | "user" | "assistant" | "tool"
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Content string `json:"content"`
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ToolCalls []ToolCall `json:"tool_calls,omitempty"` // set by assistant when calling tools
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ToolCallID string `json:"tool_call_id,omitempty"` // set on role=tool replies (required by OpenAI)
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}
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// Tool describes a callable function exposed to the model.
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type Tool struct {
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Name string `json:"name"`
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Description string `json:"description"`
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Parameters json.RawMessage `json:"parameters"` // JSON Schema object
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}
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// ToolCall is the model's request to invoke a function.
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type ToolCall struct {
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ID string `json:"id,omitempty"` // provider-assigned; may be empty (Ollama)
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Name string `json:"name"`
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Arguments json.RawMessage `json:"arguments"` // always a JSON object
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}
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// Response is the model's reply for one Chat call.
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type Response struct {
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Message Message
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StopReason string // "stop" | "tool_calls" | "length" | ...
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}
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// Backend is the interface all LLM providers must implement.
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type Backend interface {
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// Chat sends messages to the model and returns its response.
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// tools may be nil for plain completion requests.
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Chat(ctx context.Context, model string, messages []Message, tools []Tool) (*Response, error)
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}
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package backend
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import (
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"fmt"
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"os"
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)
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// New constructs a Backend from environment variables.
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//
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// OLLIE_BACKEND ollama | openai | openrouter (default: ollama)
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// OLLIE_API_URL override base URL for the selected backend
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// OLLIE_API_KEY API key (required for openai / openrouter)
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func New() (Backend, error) {
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which := os.Getenv("OLLIE_BACKEND")
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if which == "" {
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which = "ollama"
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}
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apiURL := os.Getenv("OLLIE_API_URL")
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apiKey := os.Getenv("OLLIE_API_KEY")
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switch which {
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case "ollama":
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return NewOllama(apiURL), nil
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case "openai":
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return NewOpenAI(apiURL, apiKey), nil
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case "openrouter":
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url := apiURL
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if url == "" {
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url = "https://openrouter.ai/api"
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}
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return NewOpenAI(url, apiKey), nil
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default:
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return nil, fmt.Errorf("unknown OLLIE_BACKEND %q (supported: ollama, openai, openrouter)", which)
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}
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}
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package backend
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import (
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"bytes"
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"context"
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"encoding/json"
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"fmt"
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"io"
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"net/http"
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)
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// OllamaBackend speaks the Ollama /api/chat wire format.
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type OllamaBackend struct {
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baseURL string
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client *http.Client
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}
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func NewOllama(baseURL string) *OllamaBackend {
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if baseURL == "" {
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baseURL = "http://localhost:11434"
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}
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return &OllamaBackend{baseURL: baseURL, client: &http.Client{}}
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}
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// -- wire types --
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type ollamaMessage struct {
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Role string `json:"role"`
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Content string `json:"content"`
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ToolCalls []ollamaToolCall `json:"tool_calls,omitempty"`
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}
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type ollamaToolCall struct {
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Function ollamaFunction `json:"function"`
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}
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type ollamaFunction struct {
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Name string `json:"name"`
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Arguments json.RawMessage `json:"arguments"`
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}
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type ollamaTool struct {
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Type string `json:"type"`
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Function ollamaToolFunction `json:"function"`
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}
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type ollamaToolFunction struct {
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Name string `json:"name"`
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Description string `json:"description"`
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Parameters json.RawMessage `json:"parameters"`
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}
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type ollamaChatRequest struct {
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Model string `json:"model"`
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Messages []ollamaMessage `json:"messages"`
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Tools []ollamaTool `json:"tools,omitempty"`
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Stream bool `json:"stream"`
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}
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type ollamaChatResponse struct {
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Message ollamaMessage `json:"message"`
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Done bool `json:"done"`
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}
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// -- implementation --
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func (b *OllamaBackend) Chat(ctx context.Context, model string, messages []Message, tools []Tool) (*Response, error) {
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wireMessages := make([]ollamaMessage, len(messages))
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for i, m := range messages {
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wireMessages[i] = ollamaMessage{Role: m.Role, Content: m.Content}
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for _, tc := range m.ToolCalls {
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wireMessages[i].ToolCalls = append(wireMessages[i].ToolCalls, ollamaToolCall{
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Function: ollamaFunction{Name: tc.Name, Arguments: tc.Arguments},
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})
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}
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}
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var wireTools []ollamaTool
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for _, t := range tools {
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wireTools = append(wireTools, ollamaTool{
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Type: "function",
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Function: ollamaToolFunction{
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Name: t.Name,
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Description: t.Description,
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Parameters: t.Parameters,
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},
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})
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}
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req := ollamaChatRequest{
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Model: model,
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Messages: wireMessages,
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Tools: wireTools,
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Stream: false,
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}
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data, err := json.Marshal(req)
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if err != nil {
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return nil, err
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}
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httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, b.baseURL+"/api/chat", bytes.NewReader(data))
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if err != nil {
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return nil, err
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}
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httpReq.Header.Set("Content-Type", "application/json")
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resp, err := b.client.Do(httpReq)
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if err != nil {
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return nil, err
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}
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defer resp.Body.Close()
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if resp.StatusCode != http.StatusOK {
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body, _ := io.ReadAll(resp.Body)
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return nil, fmt.Errorf("ollama HTTP %d: %s", resp.StatusCode, body)
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}
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var wire ollamaChatResponse
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if err := json.NewDecoder(resp.Body).Decode(&wire); err != nil {
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return nil, err
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}
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msg := Message{Role: wire.Message.Role, Content: wire.Message.Content}
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for _, tc := range wire.Message.ToolCalls {
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msg.ToolCalls = append(msg.ToolCalls, ToolCall{
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Name: tc.Function.Name,
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Arguments: tc.Function.Arguments,
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})
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}
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stopReason := "stop"
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if len(msg.ToolCalls) > 0 {
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stopReason = "tool_calls"
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}
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return &Response{Message: msg, StopReason: stopReason}, nil
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}
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@ -0,0 +1,162 @@
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package backend
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import (
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"bytes"
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"context"
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"encoding/json"
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"fmt"
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"io"
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"net/http"
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)
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// OpenAIBackend speaks the OpenAI /v1/chat/completions wire format.
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// Compatible with OpenRouter, OpenAI, and any other OpenAI-compatible API.
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type OpenAIBackend struct {
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baseURL string
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apiKey string
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client *http.Client
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}
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func NewOpenAI(baseURL, apiKey string) *OpenAIBackend {
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if baseURL == "" {
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baseURL = "https://api.openai.com"
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}
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return &OpenAIBackend{baseURL: baseURL, apiKey: apiKey, client: &http.Client{}}
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}
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// -- wire types --
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type openAIMessage struct {
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Role string `json:"role"`
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Content string `json:"content,omitempty"`
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ToolCalls []openAIToolCall `json:"tool_calls,omitempty"`
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ToolCallID string `json:"tool_call_id,omitempty"`
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}
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type openAIToolCall struct {
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ID string `json:"id"`
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Type string `json:"type"`
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Function openAIFunctionCall `json:"function"`
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}
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type openAIFunctionCall struct {
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Name string `json:"name"`
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Arguments string `json:"arguments"` // JSON string, not object
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}
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type openAITool struct {
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Type string `json:"type"`
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Function openAIToolFunction `json:"function"`
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}
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type openAIToolFunction struct {
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Name string `json:"name"`
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Description string `json:"description"`
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Parameters json.RawMessage `json:"parameters"`
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}
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type openAIChatRequest struct {
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Model string `json:"model"`
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Messages []openAIMessage `json:"messages"`
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Tools []openAITool `json:"tools,omitempty"`
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Stream bool `json:"stream"`
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}
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type openAIChatResponse struct {
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Choices []openAIChoice `json:"choices"`
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}
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type openAIChoice struct {
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Message openAIMessage `json:"message"`
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FinishReason string `json:"finish_reason"`
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}
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// -- implementation --
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func (b *OpenAIBackend) Chat(ctx context.Context, model string, messages []Message, tools []Tool) (*Response, error) {
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wireMessages := make([]openAIMessage, len(messages))
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for i, m := range messages {
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wireMessages[i] = openAIMessage{
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Role: m.Role,
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Content: m.Content,
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ToolCallID: m.ToolCallID,
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}
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for _, tc := range m.ToolCalls {
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wireMessages[i].ToolCalls = append(wireMessages[i].ToolCalls, openAIToolCall{
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ID: tc.ID,
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Type: "function",
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Function: openAIFunctionCall{
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Name: tc.Name,
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Arguments: string(tc.Arguments),
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},
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})
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}
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}
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var wireTools []openAITool
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for _, t := range tools {
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wireTools = append(wireTools, openAITool{
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Type: "function",
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Function: openAIToolFunction{
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Name: t.Name,
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Description: t.Description,
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Parameters: t.Parameters,
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},
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})
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}
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req := openAIChatRequest{
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Model: model,
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Messages: wireMessages,
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Tools: wireTools,
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Stream: false,
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}
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data, err := json.Marshal(req)
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if err != nil {
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return nil, err
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}
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httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, b.baseURL+"/v1/chat/completions", bytes.NewReader(data))
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if err != nil {
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return nil, err
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}
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httpReq.Header.Set("Content-Type", "application/json")
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if b.apiKey != "" {
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httpReq.Header.Set("Authorization", "Bearer "+b.apiKey)
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}
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resp, err := b.client.Do(httpReq)
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if err != nil {
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return nil, err
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}
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defer resp.Body.Close()
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if resp.StatusCode != http.StatusOK {
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body, _ := io.ReadAll(resp.Body)
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return nil, fmt.Errorf("openai HTTP %d: %s", resp.StatusCode, body)
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}
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var wire openAIChatResponse
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if err := json.NewDecoder(resp.Body).Decode(&wire); err != nil {
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return nil, err
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}
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if len(wire.Choices) == 0 {
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return nil, fmt.Errorf("openai: empty choices in response")
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}
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choice := wire.Choices[0]
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msg := Message{Role: choice.Message.Role, Content: choice.Message.Content}
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for _, tc := range choice.Message.ToolCalls {
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// Arguments arrive as a JSON string; convert to RawMessage.
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args := json.RawMessage(tc.Function.Arguments)
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msg.ToolCalls = append(msg.ToolCalls, ToolCall{
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ID: tc.ID,
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Name: tc.Function.Name,
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Arguments: args,
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})
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}
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return &Response{Message: msg, StopReason: choice.FinishReason}, nil
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}
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