feat: migrate backend from rust to go

This commit replaces the Axum/Rust backend with a Gin/Go implementation. The original Rust code has been archived in the 'rust' branch.

internal/providers/openai.go

@@ -0,0 +1,113 @@
+package providers
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"strings"
+
+	"llm-proxy/internal/config"
+	"llm-proxy/internal/models"
+	"github.com/go-resty/resty/v2"
+)
+
+type OpenAIProvider struct {
+	client  *resty.Client
+	config  config.OpenAIConfig
+	apiKey  string
+}
+
+func NewOpenAIProvider(cfg config.OpenAIConfig, apiKey string) *OpenAIProvider {
+	return &OpenAIProvider{
+		client:  resty.New(),
+		config:  cfg,
+		apiKey: apiKey,
+	}
+}
+
+func (p *OpenAIProvider) Name() string {
+	return "openai"
+}
+
+func (p *OpenAIProvider) ChatCompletion(ctx context.Context, req *models.UnifiedRequest) (*models.ChatCompletionResponse, error) {
+	messagesJSON, err := MessagesToOpenAIJSON(req.Messages)
+	if err != nil {
+		return nil, fmt.Errorf("failed to convert messages: %w", err)
+	}
+
+	body := BuildOpenAIBody(req, messagesJSON, false)
+
+	// Transition: Newer models require max_completion_tokens
+	if strings.HasPrefix(req.Model, "o1-") || strings.HasPrefix(req.Model, "o3-") || strings.Contains(req.Model, "gpt-5") {
+		if maxTokens, ok := body["max_tokens"]; ok {
+			delete(body, "max_tokens")
+			body["max_completion_tokens"] = maxTokens
+		}
+	}
+
+	resp, err := p.client.R().
+		SetContext(ctx).
+		SetHeader("Authorization", "Bearer "+p.apiKey).
+		SetBody(body).
+		Post(fmt.Sprintf("%s/chat/completions", p.config.BaseURL))
+
+	if err != nil {
+		return nil, fmt.Errorf("request failed: %w", err)
+	}
+
+	if !resp.IsSuccess() {
+		return nil, fmt.Errorf("OpenAI API error (%d): %s", resp.StatusCode(), resp.String())
+	}
+
+	var respJSON map[string]interface{}
+	if err := json.Unmarshal(resp.Body(), &respJSON); err != nil {
+		return nil, fmt.Errorf("failed to parse response: %w", err)
+	}
+
+	return ParseOpenAIResponse(respJSON, req.Model)
+}
+
+func (p *OpenAIProvider) ChatCompletionStream(ctx context.Context, req *models.UnifiedRequest) (<-chan *models.ChatCompletionStreamResponse, error) {
+	messagesJSON, err := MessagesToOpenAIJSON(req.Messages)
+	if err != nil {
+		return nil, fmt.Errorf("failed to convert messages: %w", err)
+	}
+
+	body := BuildOpenAIBody(req, messagesJSON, true)
+
+	// Transition: Newer models require max_completion_tokens
+	if strings.HasPrefix(req.Model, "o1-") || strings.HasPrefix(req.Model, "o3-") || strings.Contains(req.Model, "gpt-5") {
+		if maxTokens, ok := body["max_tokens"]; ok {
+			delete(body, "max_tokens")
+			body["max_completion_tokens"] = maxTokens
+		}
+	}
+
+	resp, err := p.client.R().
+		SetContext(ctx).
+		SetHeader("Authorization", "Bearer "+p.apiKey).
+		SetBody(body).
+		SetDoNotParseResponse(true).
+		Post(fmt.Sprintf("%s/chat/completions", p.config.BaseURL))
+
+	if err != nil {
+		return nil, fmt.Errorf("request failed: %w", err)
+	}
+
+	if !resp.IsSuccess() {
+		return nil, fmt.Errorf("OpenAI API error (%d): %s", resp.StatusCode(), resp.String())
+	}
+
+	ch := make(chan *models.ChatCompletionStreamResponse)
+	
+	go func() {
+		defer close(ch)
+		err := StreamOpenAI(resp.RawBody(), ch)
+		if err != nil {
+			// In a real app, you might want to send an error chunk or log it
+			fmt.Printf("Stream error: %v\n", err)
+		}
+	}()
+
+	return ch, nil
+}