system/dbus: print incomplete string in buffer

Not sure if this will ever be reached, but nice to have nonetheless.

Signed-off-by: Ophestra <cat@gensokyo.uk>

system/dbus.go

@@ -7,7 +7,6 @@ import (
 	"fmt"
 	"log"
 	"reflect"
-	"strconv"
 	"strings"
 	"sync"
 	"syscall"
@@ -170,9 +169,11 @@ func (s *linePrefixWriter) write(p []byte, a int) (int, error) {
 		return a + n, nil
 	} else {
 		n, _ := s.buf.Write(p[:i])
+		s.n += n + 1
 
 		v := s.buf.String()
 		if strings.HasPrefix(v, "init: ") {
+			s.n -= len(v) + 1
 			// pass through container init messages
 			s.println(s.prefix + v)
 		} else {
@@ -180,22 +181,20 @@ func (s *linePrefixWriter) write(p []byte, a int) (int, error) {
 		}
 
 		s.buf.Reset()
-		s.n += n + 1
 		return s.write(p[i+1:], a+n+1)
 	}
 }
 
 func (s *linePrefixWriter) Dump() {
 	s.mu.RLock()
-	// the final write might go past the threshold,
-	// and the buffer might still contain data
-	var n int
 	for _, m := range s.msg {
-		n += len(m)
 		s.println(s.prefix + m)
 	}
-	if s.n > lpwSizeThreshold {
+	if s.buf != nil && s.buf.Len() != 0 {
-		s.println(s.prefix + "dropped " + strconv.Itoa(s.n-n) + " bytes of output")
+		s.println("*" + s.prefix + s.buf.String())
+	}
+	if s.n >= lpwSizeThreshold {
+		s.println("+" + s.prefix + "write threshold reached, output may be incomplete")
 	}
 	s.mu.RUnlock()
 }

system/dbus_test.go

@@ -392,10 +392,11 @@ func TestLinePrefixWriter(t *testing.T) {
 	}{
 		{"nop", "(nop) ", func(func(string)) {}, nil, nil, nil, nil, ""},
 
-		{"partial", "(break) ", func(w func(string)) {
+		{"partial", "(partial) ", func(w func(string)) {
 			w("C-65533: -> ")
-		}, nil, nil, nil, nil,
+		}, nil, nil, nil, []string{
-			"C-65533: -> "},
+			"*(partial) C-65533: -> ",
+		}, "C-65533: -> "},
 
 		{"break", "(break) ", func(w func(string)) {
 			w("C-65533: -> ")
@@ -414,8 +415,10 @@ func TestLinePrefixWriter(t *testing.T) {
 		{"threshold", "(threshold) ", func(w func(s string)) {
 			w(string(make([]byte, lpwSizeThreshold)))
 			w("\n")
-		}, []error{nil, syscall.ENOMEM}, nil, nil, nil,
+		}, []error{nil, syscall.ENOMEM}, nil, nil, []string{
-			string(make([]byte, lpwSizeThreshold))},
+			"*(threshold) " + string(make([]byte, lpwSizeThreshold)),
+			"+(threshold) write threshold reached, output may be incomplete",
+		}, string(make([]byte, lpwSizeThreshold))},
 
 		{"threshold multi", "(threshold multi) ", func(w func(s string)) {
 			w(":3\n")
@@ -423,15 +426,20 @@ func TestLinePrefixWriter(t *testing.T) {
 			w("\n")
 		}, []error{nil, nil, syscall.ENOMEM}, nil, []string{
 			":3",
-		}, nil, string(make([]byte, lpwSizeThreshold-3))},
+		}, []string{
+			"*(threshold multi) " + string(make([]byte, lpwSizeThreshold-3)),
+			"+(threshold multi) write threshold reached, output may be incomplete",
+		}, string(make([]byte, lpwSizeThreshold-3))},
 
 		{"threshold multi partial", "(threshold multi partial) ", func(w func(s string)) {
 			w(":3\n")
 			w(string(make([]byte, lpwSizeThreshold-2)))
-		}, []error{nil, syscall.ENOMEM}, nil, []string{
+			w("dropped\n")
+		}, []error{nil, nil, syscall.ENOMEM}, nil, []string{
 			":3",
 		}, []string{
-			"dropped 16777215 bytes of output",
+			"*(threshold multi partial) " + string(make([]byte, lpwSizeThreshold-2)),
+			"+(threshold multi partial) write threshold reached, output may be incomplete",
 		}, string(make([]byte, lpwSizeThreshold-2))},
 
 		{"threshold exact", "(threshold exact) ", func(w func(s string)) {
@@ -439,7 +447,9 @@ func TestLinePrefixWriter(t *testing.T) {
 			w("\n")
 		}, nil, nil, []string{
 			string(make([]byte, lpwSizeThreshold-1)),
-		}, nil, ""},
+		}, []string{
+			"+(threshold exact) write threshold reached, output may be incomplete",
+		}, ""},
 
 		{"sample", "(dbus) ", func(w func(s string)) {
 			w("init: received setup parameters\n")
@@ -595,16 +605,15 @@ func TestLinePrefixWriter(t *testing.T) {
 
 			var pos int
 			tc.f(func(s string) {
-				if _, err := out.Write([]byte(s)); err != nil {
+				_, err := out.Write([]byte(s))
 				if tc.wantErr != nil {
 					if !reflect.DeepEqual(err, tc.wantErr[pos]) {
 						t.Fatalf("Write: error = %v, want %v", err, tc.wantErr[pos])
 					}
-					} else {
+				} else if err != nil {
 					t.Fatalf("Write: unexpected error: %v", err)
 					return
 				}
-				}
 				pos++
 			})
 
@@ -629,7 +638,7 @@ func TestLinePrefixWriter(t *testing.T) {
 				wantDump[i] = tc.prefix + m
 			}
 			for i, m := range tc.wantExt {
-				wantDump[len(tc.want)+i] = tc.prefix + m
+				wantDump[len(tc.want)+i] = m
 			}
 			t.Run("dump", func(t *testing.T) {
 				got := make([]string, 0, len(wantDump))