Merge pull request #2 from spi-ca/ISSUE-1

Issue 1 - fixes Short writes in strutil.LineBreaker

strutil/chunk.go

@@ -7,6 +7,7 @@ import (
 const pemLineLength = 64
 
 // LineBreaker is an io.Writer that advances a newline if one line exceeds 64 bytes.
+// this source originally comes from the url(https://cs.opensource.google/go/go/+/refs/tags/go1.24.0:src/encoding/pem/pem.go;l=89)
 type LineBreaker struct {
 	// Out os
 	Out  io.Writer
@@ -28,24 +29,32 @@ func (l *LineBreaker) Write(b []byte) (n int, err error) {
 		return len(b), nil
 	}
 
-	n, err = l.Out.Write(l.line[0:l.used])
+	_, err = l.Out.Write(l.line[0:l.used:l.used])
 	if err != nil {
 		return
 	}
-	excess := pemLineLength - l.used
-	l.used = 0
+	brk := pemLineLength - l.used
 
-	n, err = l.Out.Write(b[0:excess])
-	if err != nil {
-		return
+	var nn int
+	for len(b) >= brk {
+		nn, err = l.Out.Write(b[0:brk:brk])
+		n += nn
+		if err != nil {
+			return
+		}
+
+		_, err = l.Out.Write(nl)
+		if err != nil {
+			return
+		}
+		b = b[brk:]
+		brk = pemLineLength
 	}
 
-	n, err = l.Out.Write(nl)
-	if err != nil {
-		return
-	}
-
-	return l.Out.Write(b[excess:])
+	l.used = len(b)
+	copy(l.line[:], b)
+	n += len(b)
+	return
 }
 
 // Close flushes any pending output from the writer.

strutil/chunk_test.go

@@ -0,0 +1,95 @@
+package strutil
+
+import (
+	"io"
+	"strings"
+	"testing"
+)
+
+type lineBreakerTest struct {
+	in, out string
+}
+
+const sixtyFourCharString = "0123456789012345678901234567890123456789012345678901234567890123"
+
+var lineBreakerTests = []lineBreakerTest{
+	{"", ""},
+	{"a", "a\n"},
+	{"ab", "ab\n"},
+	{sixtyFourCharString, sixtyFourCharString + "\n"},
+	{sixtyFourCharString + "X", sixtyFourCharString + "\nX\n"},
+	{sixtyFourCharString + sixtyFourCharString, sixtyFourCharString + "\n" + sixtyFourCharString + "\n"},
+}
+
+func TestLineBreaker(t *testing.T) {
+	for i, test := range lineBreakerTests {
+		buf := new(strings.Builder)
+		var breaker LineBreaker
+		breaker.Out = buf
+		_, err := breaker.Write([]byte(test.in))
+		if err != nil {
+			t.Errorf("#%d: error from Write: %s", i, err)
+			continue
+		}
+		err = breaker.Close()
+		if err != nil {
+			t.Errorf("#%d: error from Close: %s", i, err)
+			continue
+		}
+
+		if got := buf.String(); got != test.out {
+			t.Errorf("#%d: got:%s want:%s", i, got, test.out)
+		}
+	}
+
+	for i, test := range lineBreakerTests {
+		buf := new(strings.Builder)
+		var breaker LineBreaker
+		breaker.Out = buf
+
+		for i := 0; i < len(test.in); i++ {
+			_, err := breaker.Write([]byte(test.in[i : i+1]))
+			if err != nil {
+				t.Errorf("#%d: error from Write (byte by byte): %s", i, err)
+				continue
+			}
+		}
+		err := breaker.Close()
+		if err != nil {
+			t.Errorf("#%d: error from Close (byte by byte): %s", i, err)
+			continue
+		}
+
+		if got := buf.String(); got != test.out {
+			t.Errorf("#%d: (byte by byte) got:%s want:%s", i, got, test.out)
+		}
+	}
+}
+
+func FuzzLineBreaker(f *testing.F) {
+	for _, test := range lineBreakerTests {
+		f.Add(test.in, len(test.in))
+		f.Add(test.in, 1)
+	}
+
+	f.Fuzz(func(t *testing.T, in string, chunkSize int) {
+		if chunkSize <= 0 || chunkSize > len(in)+1 {
+			return
+		}
+		var out strings.Builder
+		var l LineBreaker
+		l.Out = &out
+		chunk := make([]byte, chunkSize)
+		n, err := io.CopyBuffer(&l, strings.NewReader(in), chunk)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if n != int64(len(in)) {
+			t.Errorf("invalid written count: got %d, expected %d", n, len(in))
+		}
+		l.Close()
+		if len(in) > 0 && out.Len() != len(in)+1+(len(in)-1)/pemLineLength {
+			t.Fatalf("invalid final size: got %d, expected %d", out.Len(), len(in)+1+(len(in)-1)/pemLineLength)
+		}
+	})
+}