sub2api/backend/internal/service/openai_compact_fallback.go

package service

import (
	"errors"
	"net/http"
	"strings"

	"github.com/gin-gonic/gin"
	"github.com/tidwall/gjson"
)

type openAICompactFallbackSignal struct {
	payload []byte
	message string
}

func (e *openAICompactFallbackSignal) Error() string {
	if e == nil || strings.TrimSpace(e.message) == "" {
		return "upstream compact request failed"
	}
	return e.message
}

func asOpenAICompactFallbackSignal(err error) (*openAICompactFallbackSignal, bool) {
	var signal *openAICompactFallbackSignal
	return signal, errors.As(err, &signal) && signal != nil
}

func isExplicitOpenAICompactContext(c *gin.Context) bool {
	return isOpenAIResponsesCompactPath(c) || isOpenAINativeCompactionV2(c)
}

func newOpenAICompactFallbackSignal(c *gin.Context, payload []byte, message string) error {
	if !isExplicitOpenAICompactContext(c) ||
		!isOpenAICompactModelFailure(http.StatusBadRequest, message, payload) {
		return nil
	}
	return &openAICompactFallbackSignal{
		payload: append([]byte(nil), payload...),
		message: sanitizeUpstreamErrorMessage(strings.TrimSpace(message)),
	}
}

func isExplicitOpenAICompactRequest(c *gin.Context, body []byte) bool {
	return isOpenAIResponsesCompactPath(c) || HasCompactionTriggerInInput(body)
}

// resolveOpenAICompactFallbackModel prefers the account's compact-only rule
// for the client-visible model. The process-wide fallback is used only when
// that account has no matching compact rule.
func (s *OpenAIGatewayService) resolveOpenAICompactFallbackModel(account *Account, requestedModel string) string {
	requestedModel = strings.TrimSpace(requestedModel)
	if account != nil {
		if mapped, matched := account.ResolveCompactMappedModel(requestedModel); matched {
			if mapped = strings.TrimSpace(mapped); mapped != "" {
				return mapped
			}
		}
	}
	if s == nil || s.cfg == nil {
		return ""
	}
	fallback := strings.TrimSpace(s.cfg.Gateway.OpenAICompactModel)
	if fallback == "" {
		return ""
	}
	return strings.TrimSpace(resolveOpenAIAccountUpstreamModelForRequest(account, fallback, false))
}

func isOpenAICompactModelFailure(statusCode int, upstreamMsg string, upstreamBody []byte) bool {
	if isOpenAIContextWindowError(upstreamMsg, upstreamBody) {
		return true
	}
	if statusCode != http.StatusBadRequest && statusCode != http.StatusNotFound {
		return false
	}

	values := []string{
		extractUpstreamErrorCode(upstreamBody),
		upstreamMsg,
		gjson.GetBytes(upstreamBody, "error.type").String(),
		gjson.GetBytes(upstreamBody, "response.error.code").String(),
		gjson.GetBytes(upstreamBody, "response.error.type").String(),
	}
	for _, value := range values {
		value = strings.ToLower(strings.TrimSpace(value))
		switch value {
		case "model_not_found", "model_not_available", "unsupported_model", "invalid_model":
			return true
		}
		if strings.Contains(value, "model") && (strings.Contains(value, "not found") ||
			strings.Contains(value, "does not exist") ||
			strings.Contains(value, "unavailable") ||
			strings.Contains(value, "unsupported") ||
			strings.Contains(value, "not supported")) {
			return true
		}
	}
	// Some compact providers return only a failed response shell. It is safe to
	// retry that shape for an explicit compact request, but a populated error is
	// left untouched so business and policy failures keep their original wire.
	if strings.EqualFold(strings.TrimSpace(gjson.GetBytes(upstreamBody, "response.status").String()), "failed") ||
		strings.EqualFold(strings.TrimSpace(gjson.GetBytes(upstreamBody, "status").String()), "failed") {
		for _, path := range []string{
			"error.message", "error.code", "error.type",
			"response.error.message", "response.error.code", "response.error.type",
		} {
			if strings.TrimSpace(gjson.GetBytes(upstreamBody, path).String()) != "" {
				return false
			}
		}
		return strings.TrimSpace(upstreamMsg) == ""
	}
	return false
}

// prepareOpenAICompactFallbackRetry returns a body for one safe, same-account
// retry. Callers invoke it only before any downstream response has been
// written; it changes the model and deliberately leaves path, trigger, and
// native-v2 context state untouched.
func (s *OpenAIGatewayService) prepareOpenAICompactFallbackRetry(
	c *gin.Context,
	account *Account,
	requestedModel string,
	currentBody []byte,
	statusCode int,
	upstreamMsg string,
	upstreamBody []byte,
	alreadyRetried bool,
) ([]byte, string, bool) {
	if alreadyRetried || !isExplicitOpenAICompactRequest(c, currentBody) ||
		!isOpenAICompactModelFailure(statusCode, upstreamMsg, upstreamBody) {
		return currentBody, "", false
	}
	fallbackModel := s.resolveOpenAICompactFallbackModel(account, requestedModel)
	currentModel := strings.TrimSpace(gjson.GetBytes(currentBody, "model").String())
	if fallbackModel == "" || strings.EqualFold(fallbackModel, currentModel) {
		return currentBody, "", false
	}
	retryBody := ReplaceModelInBody(currentBody, fallbackModel)
	if strings.EqualFold(strings.TrimSpace(gjson.GetBytes(retryBody, "model").String()), currentModel) {
		return currentBody, "", false
	}
	return retryBody, fallbackModel, true
}