Add upstream model list fetching and a Codex-specific model section

internal/chatcmpl/client.go

@@ -42,6 +42,33 @@ func (c *Client) endpoint() string {
 	return c.BaseURL + "/chat/completions"
 }
 
+// ListModels fetches the upstream model catalog. Not every provider
+// implements it; callers should treat an error as "list unavailable"
+// and fall back to manual entry.
+func (c *Client) ListModels(ctx context.Context) (*ModelList, error) {
+	httpReq, err := http.NewRequestWithContext(ctx, http.MethodGet, c.BaseURL+"/models", nil)
+	if err != nil {
+		return nil, err
+	}
+	httpReq.Header.Set("Accept", "application/json")
+	if c.APIKey != "" {
+		httpReq.Header.Set("Authorization", "Bearer "+c.APIKey)
+	}
+	resp, err := c.HTTP.Do(httpReq)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		return nil, &UpstreamError{StatusCode: resp.StatusCode, Message: readErrorBody(resp)}
+	}
+	var out ModelList
+	if err := json.NewDecoder(io.LimitReader(resp.Body, 8<<20)).Decode(&out); err != nil {
+		return nil, fmt.Errorf("decode upstream model list: %w", err)
+	}
+	return &out, nil
+}
+
 func (c *Client) do(ctx context.Context, req *Request) (*http.Response, error) {
 	body, err := json.Marshal(req)
 	if err != nil {

internal/chatcmpl/client_test.go

@@ -73,6 +73,49 @@ func TestCreateStreamRejectsNon2xx(t *testing.T) {
 	}
 }
 
+func TestListModels(t *testing.T) {
+	var gotPath, gotAuth string
+	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotPath = r.URL.Path
+		gotAuth = r.Header.Get("Authorization")
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{"object":"list","data":[{"id":"deepseek-chat","object":"model","owned_by":"deepseek"},{"id":"deepseek-reasoner"}]}`))
+	}))
+	defer upstream.Close()
+
+	client := NewClient(upstream.URL, "sk-up")
+	list, err := client.ListModels(context.Background())
+	if err != nil {
+		t.Fatalf("ListModels: %v", err)
+	}
+	if gotPath != "/models" {
+		t.Errorf("path = %q, want /models", gotPath)
+	}
+	if gotAuth != "Bearer sk-up" {
+		t.Errorf("authorization = %q", gotAuth)
+	}
+	if len(list.Data) != 2 || list.Data[0].ID != "deepseek-chat" {
+		t.Fatalf("models = %+v", list.Data)
+	}
+}
+
+func TestListModelsUpstreamError(t *testing.T) {
+	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusUnauthorized)
+		_, _ = w.Write([]byte(`{"error":{"message":"bad key"}}`))
+	}))
+	defer upstream.Close()
+
+	_, err := NewClient(upstream.URL, "sk-bad").ListModels(context.Background())
+	var ue *UpstreamError
+	if !errors.As(err, &ue) {
+		t.Fatalf("error = %v, want *UpstreamError", err)
+	}
+	if ue.StatusCode != http.StatusUnauthorized || ue.Message != "bad key" {
+		t.Errorf("upstream error = %+v", ue)
+	}
+}
+
 func TestStreamNext(t *testing.T) {
 	sse := strings.Join([]string{
 		`data: {"id":"1","choices":[{"index":0,"delta":{"content":"Hel"}}]}`,

internal/chatcmpl/types.go

@@ -102,6 +102,18 @@ type Error struct {
 	Code    any    `json:"code,omitempty"`
 }
 
+// ModelInfo is one entry of an upstream model catalog.
+type ModelInfo struct {
+	ID      string `json:"id"`
+	Object  string `json:"object,omitempty"`
+	OwnedBy string `json:"owned_by,omitempty"`
+}
+
+// ModelList is the upstream /models response body.
+type ModelList struct {
+	Data []ModelInfo `json:"data"`
+}
+
 // StreamChunk is one SSE data payload of a streaming response.
 type StreamChunk struct {
 	ID      string        `json:"id"`

internal/gateway/gateway_test.go

@@ -23,6 +23,11 @@ type fakeUpstream struct {
 }
 
 func (f *fakeUpstream) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if r.Method == http.MethodGet && r.URL.Path == "/models" {
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = io.WriteString(w, `{"object":"list","data":[{"id":"ds-chat"},{"id":"ds-haiku"}]}`)
+		return
+	}
 	if r.URL.Path != "/chat/completions" {
 		w.WriteHeader(http.StatusNotFound)
 		return
@@ -683,6 +688,61 @@ func TestApplyRejectsWrongTarget(t *testing.T) {
 	}
 }
 
+func TestFetchModels(t *testing.T) {
+	env := newTestEnv(t)
+	resp := env.post(t, "/api/fetch-models", map[string]any{
+		"base_url": env.upstreamURL,
+		"api_key":  "up-key",
+	}, "")
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf("status = %d", resp.StatusCode)
+	}
+	var out struct {
+		Items []struct {
+			ID string `json:"id"`
+		} `json:"items"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&out); err != nil {
+		t.Fatalf("decode: %v", err)
+	}
+	if len(out.Items) != 2 || out.Items[0].ID != "ds-chat" {
+		t.Errorf("items = %+v", out.Items)
+	}
+}
+
+func TestFetchModelsRejectsBadInput(t *testing.T) {
+	env := newTestEnv(t)
+	for _, body := range []map[string]any{
+		{"base_url": env.upstreamURL},
+		{"api_key": "up-key"},
+		{"base_url": "ftp://x", "api_key": "k"},
+	} {
+		resp := env.post(t, "/api/fetch-models", body, "")
+		resp.Body.Close()
+		if resp.StatusCode != http.StatusBadRequest {
+			t.Errorf("body %v status = %d, want 400", body, resp.StatusCode)
+		}
+	}
+}
+
+func TestFetchModelsUpstreamFailure(t *testing.T) {
+	env := newTestEnv(t)
+	broken := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusUnauthorized)
+		_, _ = io.WriteString(w, `{"error":{"message":"bad key"}}`)
+	}))
+	defer broken.Close()
+	resp := env.post(t, "/api/fetch-models", map[string]any{
+		"base_url": broken.URL,
+		"api_key":  "sk-bad",
+	}, "")
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusBadGateway {
+		t.Errorf("status = %d, want 502", resp.StatusCode)
+	}
+}
+
 func TestListProvidersFiltersByTarget(t *testing.T) {
 	env := newCodexTestEnv(t)
 	codexItems := env.get(t, "/api/providers?target=codex")["items"].([]any)

internal/gateway/handlers.go

@@ -1,10 +1,15 @@
 package gateway
 
 import (
+	"context"
+	"errors"
 	"fmt"
 	"net/http"
+	"net/url"
+	"strings"
 	"time"
 
+	"gitea.rutua.cn/kate522/CrossRelay/internal/chatcmpl"
 	"gitea.rutua.cn/kate522/CrossRelay/internal/claudecfg"
 	"gitea.rutua.cn/kate522/CrossRelay/internal/codexcfg"
 	"gitea.rutua.cn/kate522/CrossRelay/internal/config"
@@ -71,6 +76,48 @@ func (s *Server) handleListProviders(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, map[string]any{"items": items})
 }
 
+type fetchModelsInput struct {
+	BaseURL string `json:"base_url"`
+	APIKey  string `json:"api_key"`
+}
+
+// handleFetchModels proxies the upstream model catalog so the UI can
+// offer a picker without talking to the provider directly.
+func (s *Server) handleFetchModels(w http.ResponseWriter, r *http.Request) {
+	var in fetchModelsInput
+	if err := decodeJSON(r, &in, 1<<20); err != nil {
+		writeAPIError(w, http.StatusBadRequest, "invalid request body: "+err.Error())
+		return
+	}
+	in.BaseURL = strings.TrimSpace(in.BaseURL)
+	in.APIKey = strings.TrimSpace(in.APIKey)
+	if in.BaseURL == "" || in.APIKey == "" {
+		writeAPIError(w, http.StatusBadRequest, "base URL and API key are required")
+		return
+	}
+	if u, err := url.Parse(in.BaseURL); err != nil || (u.Scheme != "http" && u.Scheme != "https") || u.Host == "" {
+		writeAPIError(w, http.StatusBadRequest, "base URL must be an http(s) URL")
+		return
+	}
+	ctx, cancel := context.WithTimeout(r.Context(), 20*time.Second)
+	defer cancel()
+	list, err := chatcmpl.NewClient(in.BaseURL, in.APIKey).ListModels(ctx)
+	if err != nil {
+		var ue *chatcmpl.UpstreamError
+		if errors.As(err, &ue) {
+			writeAPIError(w, http.StatusBadGateway, fmt.Sprintf("upstream %d: %s", ue.StatusCode, ue.Message))
+			return
+		}
+		writeAPIError(w, http.StatusBadGateway, fmt.Sprintf("upstream request failed: %v", err))
+		return
+	}
+	items := []chatcmpl.ModelInfo{}
+	if list != nil {
+		items = list.Data
+	}
+	writeJSON(w, http.StatusOK, map[string]any{"items": items})
+}
+
 func (s *Server) handleCreateProvider(w http.ResponseWriter, r *http.Request) {
 	var in providerInput
 	if err := decodeJSON(r, &in, 1<<20); err != nil {

internal/gateway/server.go

@@ -75,6 +75,7 @@ func (s *Server) Handler() http.Handler {
 	mux.HandleFunc("POST /v1/messages/count_tokens", s.withAuth(s.handleCountTokens))
 	mux.HandleFunc("POST /v1/responses", s.withAuth(s.handleResponses))
 	mux.HandleFunc("GET /api/status", s.handleStatus)
+	mux.HandleFunc("POST /api/fetch-models", s.handleFetchModels)
 	mux.HandleFunc("GET /api/providers", s.handleListProviders)
 	mux.HandleFunc("POST /api/providers", s.handleCreateProvider)
 	mux.HandleFunc("PUT /api/providers/{id}", s.handleUpdateProvider)