encoding/pem: add marshalling support.

R=rsc
CC=golang-dev
https://golang.org/cl/203043

src/pkg/encoding/pem/pem.go

@@ -10,6 +10,8 @@ package pem
 import (
 	"bytes"
 	"encoding/base64"
+	"io"
+	"os"
 	"strings"
 )
 
@@ -159,3 +161,99 @@ Error:
 	}
 	return
 }
+
+const pemLineLength = 64
+
+type lineBreaker struct {
+	line [pemLineLength]byte
+	used int
+	out  io.Writer
+}
+
+func (l *lineBreaker) Write(b []byte) (n int, err os.Error) {
+	if l.used+len(b) < pemLineLength {
+		copy(l.line[l.used:], b)
+		l.used += len(b)
+		return len(b), nil
+	}
+
+	n, err = l.out.Write(l.line[0:l.used])
+	if err != nil {
+		return
+	}
+	excess := pemLineLength - l.used
+	l.used = 0
+
+	n, err = l.out.Write(b[0:excess])
+	if err != nil {
+		return
+	}
+
+	n, err = l.out.Write([]byte{'\n'})
+	if err != nil {
+		return
+	}
+
+	return l.Write(b[excess:])
+}
+
+func (l *lineBreaker) Close() (err os.Error) {
+	if l.used > 0 {
+		_, err = l.out.Write(l.line[0:l.used])
+		if err != nil {
+			return
+		}
+		_, err = l.out.Write([]byte{'\n'})
+	}
+
+	return
+}
+
+func Encode(out io.Writer, b *Block) (err os.Error) {
+	_, err = out.Write(pemStart[1:])
+	if err != nil {
+		return
+	}
+	_, err = out.Write(strings.Bytes(b.Type + "-----\n"))
+	if err != nil {
+		return
+	}
+
+	for k, v := range b.Headers {
+		_, err = out.Write(strings.Bytes(k + ": " + v + "\n"))
+		if err != nil {
+			return
+		}
+	}
+
+	if len(b.Headers) > 1 {
+		_, err = out.Write([]byte{'\n'})
+		if err != nil {
+			return
+		}
+	}
+
+	var breaker lineBreaker
+	breaker.out = out
+
+	b64 := base64.NewEncoder(base64.StdEncoding, &breaker)
+	_, err = b64.Write(b.Bytes)
+	if err != nil {
+		return
+	}
+	b64.Close()
+	breaker.Close()
+
+	_, err = out.Write(pemEnd[1:])
+	if err != nil {
+		return
+	}
+	_, err = out.Write(strings.Bytes(b.Type + "-----\n"))
+	return
+}
+
+func EncodeToMemory(b *Block) []byte {
+	buf := bytes.NewBuffer(nil)
+	Encode(buf, b)
+	return buf.Bytes()
+}

src/pkg/encoding/pem/pem_test.go

@@ -5,9 +5,10 @@
 package pem
 
 import (
-	"testing"
-	"strings"
+	"bytes"
 	"reflect"
+	"strings"
+	"testing"
 )
 
 type GetLineTest struct {
@@ -49,6 +50,73 @@ func TestDecode(t *testing.T) {
 	}
 }
 
+func TestEncode(t *testing.T) {
+	r := EncodeToMemory(privateKey2)
+	if string(r) != pemPrivateKey {
+		t.Errorf("got:%s want:%s", r, pemPrivateKey)
+	}
+}
+
+type lineBreakerTest struct {
+	in, out string
+}
+
+const sixtyFourCharString = "0123456789012345678901234567890123456789012345678901234567890123"
+
+var lineBreakerTests = []lineBreakerTest{
+	lineBreakerTest{"", ""},
+	lineBreakerTest{"a", "a\n"},
+	lineBreakerTest{"ab", "ab\n"},
+	lineBreakerTest{sixtyFourCharString, sixtyFourCharString + "\n"},
+	lineBreakerTest{sixtyFourCharString + "X", sixtyFourCharString + "\nX\n"},
+	lineBreakerTest{sixtyFourCharString + sixtyFourCharString, sixtyFourCharString + "\n" + sixtyFourCharString + "\n"},
+}
+
+func TestLineBreaker(t *testing.T) {
+	for i, test := range lineBreakerTests {
+		buf := bytes.NewBuffer(nil)
+		var breaker lineBreaker
+		breaker.out = buf
+		_, err := breaker.Write(strings.Bytes(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 string(buf.Bytes()) != test.out {
+			t.Errorf("#%d: got:%s want:%s", i, string(buf.Bytes()), test.out)
+		}
+	}
+
+	for i, test := range lineBreakerTests {
+		buf := bytes.NewBuffer(nil)
+		var breaker lineBreaker
+		breaker.out = buf
+
+		for i := 0; i < len(test.in); i++ {
+			_, err := breaker.Write(strings.Bytes(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 string(buf.Bytes()) != test.out {
+			t.Errorf("#%d: (byte by byte) got:%s want:%s", i, string(buf.Bytes()), test.out)
+		}
+	}
+}
+
 var pemData = `verify return:0
 -----BEGIN CERTIFICATE-----
 sdlfkjskldfj