Add openai codex support

internal/util/provider.go

@@ -0,0 +1,24 @@
+// Package util provides utility functions used across the CLIProxyAPI application.
+// These functions handle common tasks such as determining AI service providers
+// from model names and managing HTTP proxies.
+package util
+
+import (
+	"strings"
+)
+
+// GetProviderName determines the AI service provider based on the model name.
+// It analyzes the model name string to identify which service provider it belongs to.
+//
+// Supported providers:
+// - "gemini" for Google's Gemini models
+// - "gpt" for OpenAI's GPT models
+// - "unknow" for unrecognized model names
+func GetProviderName(modelName string) string {
+	if strings.Contains(modelName, "gemini") {
+		return "gemini"
+	} else if strings.Contains(modelName, "gpt") {
+		return "gpt"
+	}
+	return "unknow"
+}