fix: propagate QR output failures

auth.go

@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"io"
 	"net/http"
 	"net/url"
 	"os"
@@ -251,6 +252,19 @@ type longPollData struct {
 
 type stringOrNumber string
 
+type recordingWriter struct {
+	w   io.Writer
+	err error
+}
+
+func (writer *recordingWriter) Write(payload []byte) (int, error) {
+	written, err := writer.w.Write(payload)
+	if err != nil && writer.err == nil {
+		writer.err = err
+	}
+	return written, err
+}
+
 func (value *stringOrNumber) UnmarshalJSON(payload []byte) error {
 	decoded, err := decodeStringOrNumber(payload)
 	if err != nil {
@@ -282,10 +296,18 @@ func (client *Client) Login(ctx context.Context) (AuthData, error) {
 		if _, err := qr.Encode(loginData.LoginURL, qr.L); err != nil {
 			return AuthData{}, fmt.Errorf("encode login QR code: %w", err)
 		}
-		fmt.Fprintf(client.qrWriter, "请使用米家APP扫描下方二维码\n%s\n", loginData.LoginURL)
+		writer := &recordingWriter{w: client.qrWriter}
-		qrterminal.GenerateHalfBlock(loginData.LoginURL, qrterminal.L, client.qrWriter)
+		if _, err := fmt.Fprintf(writer, "请使用米家APP扫描下方二维码\n%s\n", loginData.LoginURL); err != nil {
+			return AuthData{}, fmt.Errorf("write QR login output: %w", err)
+		}
+		qrterminal.GenerateHalfBlock(loginData.LoginURL, qrterminal.L, writer)
+		if writer.err != nil {
+			return AuthData{}, fmt.Errorf("write QR login output: %w", writer.err)
+		}
 		if loginData.QR != "" {
-			fmt.Fprintf(client.qrWriter, "二维码图片: %s\n", loginData.QR)
+			if _, err := fmt.Fprintf(writer, "二维码图片: %s\n", loginData.QR); err != nil {
+				return AuthData{}, fmt.Errorf("write QR login output: %w", err)
+			}
 		}
 	}
 	return client.completeQRLogin(ctx, loginData)

auth_test.go

@@ -12,10 +12,19 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"sync/atomic"
 	"testing"
 	"time"
 )
 
+var errQRWriterFailed = errors.New("QR writer failed")
+
+type failingQRWriter struct{}
+
+func (failingQRWriter) Write([]byte) (int, error) {
+	return 0, errQRWriterFailed
+}
+
 func TestParseServiceResponse(t *testing.T) {
 	var result struct {
 		Code int `json:"code"`
@@ -244,6 +253,40 @@ func TestLoginQRCoreFlow(t *testing.T) {
 	}
 }
 
+func TestLoginReturnsQROutputErrorBeforeLongPoll(t *testing.T) {
+	var longPollRequests atomic.Int32
+	var server *httptest.Server
+	server = httptest.NewServer(http.HandlerFunc(func(writer http.ResponseWriter, request *http.Request) {
+		switch request.URL.Path {
+		case "/serviceLogin":
+			_, _ = io.WriteString(writer, `&&&START&&&{"code":70016,"location":"`+server.URL+`/prepare"}`)
+		case "/loginUrl":
+			_, _ = io.WriteString(writer, `&&&START&&&{"code":0,"loginUrl":"https://qr.example/login","qr":"https://qr.example/image","lp":"`+server.URL+`/lp"}`)
+		case "/lp":
+			longPollRequests.Add(1)
+			_, _ = io.WriteString(writer, `&&&START&&&{"code":70016}`)
+		default:
+			http.NotFound(writer, request)
+		}
+	}))
+	defer server.Close()
+
+	client, err := NewClient(t.TempDir(), WithHTTPClient(server.Client()), WithQRWriter(failingQRWriter{}))
+	if err != nil {
+		t.Fatal(err)
+	}
+	client.serviceLoginURL = server.URL + "/serviceLogin"
+	client.loginURL = server.URL + "/loginUrl"
+
+	_, err = client.Login(context.Background())
+	if !errors.Is(err, errQRWriterFailed) {
+		t.Fatalf("Login() error = %v, want %v", err, errQRWriterFailed)
+	}
+	if requests := longPollRequests.Load(); requests != 0 {
+		t.Fatalf("long-poll requests = %d, want 0", requests)
+	}
+}
+
 func TestQRLoginRejectsIncompleteCallbackWithoutSaving(t *testing.T) {
 	var server *httptest.Server
 	server = httptest.NewServer(http.HandlerFunc(func(writer http.ResponseWriter, request *http.Request) {