Sub2API v1.0 - AI API 网关（二开初始版本，基于上游 Wei-Shaw/sub2api）

backend/internal/service/upstream_response_model.go

@@ -0,0 +1,203 @@
+package service
+
+import (
+	"strings"
+
+	"github.com/gin-gonic/gin"
+	"github.com/tidwall/gjson"
+)
+
+const (
+	upstreamResponseModelObserverContextKey = "upstream_response_model_observer"
+	upstreamResponseModelMaxLength          = 200
+)
+
+// upstreamResponseModelObserver tracks one forwarding attempt (or one WS turn).
+// A terminal declaration wins over an earlier declaration; otherwise the first
+// declaration is retained. Observation never affects the forwarding path.
+//
+// Billing normally ignores the observed model as well; the only exception is a
+// channel explicitly configured with billing_model_source = response_model,
+// where a conflict flag makes billing fall back to the baseline model
+// (see responseModelBillingDeclaration).
+type upstreamResponseModelObserver struct {
+	first    string
+	terminal string
+	conflict bool
+}
+
+func (o *upstreamResponseModelObserver) Observe(model string, terminal bool) {
+	model = normalizeObservedUpstreamResponseModel(model)
+	if model == "" {
+		return
+	}
+	current := o.Model()
+	if current != "" && !strings.EqualFold(current, model) {
+		o.conflict = true
+	}
+	if terminal {
+		o.terminal = model
+		return
+	}
+	if o.first == "" {
+		o.first = model
+	}
+}
+
+func normalizeObservedUpstreamResponseModel(model string) string {
+	model = strings.TrimSpace(model)
+	if model == "" {
+		return ""
+	}
+	runes := []rune(model)
+	if len(runes) > upstreamResponseModelMaxLength {
+		model = string(runes[:upstreamResponseModelMaxLength])
+	}
+	return model
+}
+
+func (o *upstreamResponseModelObserver) ObserveOpenAI(payload []byte, eventType string) {
+	model := firstValidTrimmedGJSONModel(payload, "response.model", "model")
+	o.Observe(model, isUpstreamResponseModelTerminalEvent(eventType))
+}
+
+func (o *upstreamResponseModelObserver) ObserveAnthropic(payload []byte) {
+	model := firstValidTrimmedGJSONModel(payload, "message.model", "model")
+	o.Observe(model, false)
+}
+
+func (o *upstreamResponseModelObserver) ObserveGemini(payload []byte) {
+	model := firstValidTrimmedGJSONModel(
+		payload,
+		"modelVersion",
+		"response.modelVersion",
+		"response.response.modelVersion",
+	)
+	// Gemini streaming has no universal terminal event carrying modelVersion;
+	// treating each declaration as terminal retains the latest chunk.
+	o.Observe(model, true)
+}
+
+func (o *upstreamResponseModelObserver) Model() string {
+	if o == nil {
+		return ""
+	}
+	if o.terminal != "" {
+		return o.terminal
+	}
+	return o.first
+}
+
+func (o *upstreamResponseModelObserver) Conflict() bool {
+	return o != nil && o.conflict
+}
+
+func beginUpstreamResponseModelObservation(c *gin.Context) *upstreamResponseModelObserver {
+	observer := &upstreamResponseModelObserver{}
+	if c != nil {
+		c.Set(upstreamResponseModelObserverContextKey, observer)
+	}
+	return observer
+}
+
+func upstreamResponseModelObserverFromContext(c *gin.Context) *upstreamResponseModelObserver {
+	if c == nil {
+		return nil
+	}
+	value, ok := c.Get(upstreamResponseModelObserverContextKey)
+	if !ok {
+		return nil
+	}
+	observer, _ := value.(*upstreamResponseModelObserver)
+	return observer
+}
+
+func observedUpstreamResponseModel(c *gin.Context) string {
+	return upstreamResponseModelObserverFromContext(c).Model()
+}
+
+func observedUpstreamResponseModelConflict(c *gin.Context) bool {
+	return upstreamResponseModelObserverFromContext(c).Conflict()
+}
+
+func observeOpenAISSEBody(observer *upstreamResponseModelObserver, body string) {
+	if observer == nil || strings.TrimSpace(body) == "" {
+		return
+	}
+	forEachOpenAISSEDataPayload(body, func(payload []byte) {
+		eventType := strings.TrimSpace(gjson.GetBytes(payload, "type").String())
+		observer.ObserveOpenAI(payload, eventType)
+	})
+}
+
+func firstValidTrimmedGJSONModel(payload []byte, paths ...string) string {
+	if len(payload) == 0 {
+		return ""
+	}
+	for _, path := range paths {
+		value := gjson.GetBytes(payload, path)
+		if !value.Exists() || value.Type != gjson.String {
+			continue
+		}
+		if model := strings.TrimSpace(value.String()); model != "" {
+			// Validate only after finding a candidate. This avoids a full validation
+			// pass on the common model-free delta path while still rejecting malformed
+			// payloads that appear to declare a model.
+			if !gjson.ValidBytes(payload) {
+				return ""
+			}
+			return model
+		}
+	}
+	return ""
+}
+
+func isUpstreamResponseModelTerminalEvent(eventType string) bool {
+	switch strings.TrimSpace(eventType) {
+	case "response.completed", "response.done", "response.failed", "response.incomplete", "response.cancelled", "response.canceled":
+		return true
+	default:
+		return false
+	}
+}
+
+func upstreamModelMismatch(sentModel, responseModel string) *bool {
+	responseModel = strings.TrimSpace(responseModel)
+	if responseModel == "" {
+		return nil
+	}
+	sentModel = strings.TrimSpace(sentModel)
+	mismatch := sentModel == "" || !upstreamModelsMatchForAudit(sentModel, responseModel)
+	return &mismatch
+}
+
+func upstreamModelsMatchForAudit(sentModel, responseModel string) bool {
+	if strings.EqualFold(sentModel, responseModel) {
+		return true
+	}
+
+	// xAI reports the runtime build ID for these supported public aliases.
+	// Canonicalize only for mismatch auditing; keep the raw response model for
+	// observability and for the separate response-model billing safeguards.
+	sentGrokModel := canonicalGrokBuildRuntimeModel(sentModel)
+	return sentGrokModel != "" && sentGrokModel == canonicalGrokBuildRuntimeModel(responseModel)
+}
+
+func canonicalGrokBuildRuntimeModel(model string) string {
+	switch strings.ToLower(strings.TrimSpace(model)) {
+	case "grok-4.5", "grok-4.5-latest", "grok-4.5-build":
+		return "grok-4.5-build"
+	case "grok-4.6", "grok-4.6-latest", "grok-4.6-build":
+		return "grok-4.6-build"
+	default:
+		return ""
+	}
+}
+
+func upstreamSentModel(requestedModel, upstreamModel string) string {
+	sentModel := strings.TrimSpace(upstreamModel)
+	if sentModel == "" {
+		sentModel = strings.TrimSpace(requestedModel)
+	}
+	return sentModel
+}