2 files changed, 82 insertions, 0 deletions
diff --git a/internal/server.go b/internal/server.go
index 46b95ef..3ae9be2 100644
--- a/internal/server.go
+++ b/internal/server.go
@@ -2,7 +2,9 @@ package internal
 
 import (
 	"context"
+	"fmt"
 	"net"
+	"runtime/debug"
 	"strings"
 	"sync"
 
@@ -84,6 +86,7 @@ func (s *Server) Serve() error {
 		go func() {
 			defer s.Wg.Done()
 			defer func() { _ = conn.Close() }()
+			defer s.recoverPanic("connection", "remote", conn.RemoteAddr().String())
 			s.HandleConn(conn)
 		}()
 	}
@@ -129,12 +132,25 @@ func (s *Server) propagateClose() {
 	s.Wg.Add(1)
 	go func() {
 		defer s.Wg.Done()
+		defer s.recoverPanic("close propagation")
 
 		<-s.Ctx.Done()
 		_ = s.Listener.Close()
 	}()
 }
 
+func (s *Server) recoverPanic(goroutine string, keyvals ...any) {
+	if r := recover(); r != nil {
+		keyvals = append([]any{
+			"msg", "panic in server goroutine",
+			"goroutine", goroutine,
+			"panic", fmt.Sprintf("%v", r),
+			"stack", string(debug.Stack()),
+		}, keyvals...)
+		_ = s.ErrorLog.Log(keyvals...)
+	}
+}
+
 // JoinDefaultPort appends ":<port>" iff the address does not already contain a port.
 func JoinDefaultPort(address string, port string) string {
 	if len(address) > 0 && address[0] == '[' {
diff --git a/internal/server_test.go b/internal/server_test.go
new file mode 100644
index 0000000..62d8681
--- /dev/null
+++ b/internal/server_test.go
@@ -0,0 +1,66 @@
+package internal_test
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"tildegit.org/tjp/sliderule/internal"
+)
+
+type captureLogger struct {
+	mu   sync.Mutex
+	logs []string
+}
+
+func (cl *captureLogger) Log(keyvals ...any) error {
+	cl.mu.Lock()
+	defer cl.mu.Unlock()
+
+	for _, val := range keyvals {
+		cl.logs = append(cl.logs, fmt.Sprint(val))
+	}
+	return nil
+}
+
+func (cl *captureLogger) String() string {
+	cl.mu.Lock()
+	defer cl.mu.Unlock()
+
+	return strings.Join(cl.logs, " ")
+}
+
+func TestServerRecoversConnectionPanic(t *testing.T) {
+	var logs captureLogger
+	server, err := internal.NewServer(
+		context.Background(),
+		"localhost",
+		"tcp",
+		"127.0.0.1:0",
+		&logs,
+		func(net.Conn) { panic("boom") },
+	)
+	require.Nil(t, err)
+
+	done := make(chan error, 1)
+	go func() { done <- server.Serve() }()
+
+	conn, err := net.Dial(server.Network(), server.Address())
+	require.Nil(t, err)
+	_ = conn.Close()
+
+	require.Eventually(t, func() bool {
+		return strings.Contains(logs.String(), "panic in server goroutine")
+	}, time.Second, 10*time.Millisecond)
+
+	server.Close()
+	assert.Nil(t, <-done)
+	assert.Contains(t, logs.String(), "boom")
+}