1 files changed, 316 insertions, 0 deletions
diff --git a/src/encoding/pem/pem.go b/src/encoding/pem/pem.go
new file mode 100644
index 0000000..d26e4c8
--- /dev/null
+++ b/src/encoding/pem/pem.go
@@ -0,0 +1,316 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package pem implements the PEM data encoding, which originated in Privacy
+// Enhanced Mail. The most common use of PEM encoding today is in TLS keys and
+// certificates. See RFC 1421.
+package pem
+
+import (
+	"bytes"
+	"encoding/base64"
+	"errors"
+	"io"
+	"sort"
+	"strings"
+)
+
+// A Block represents a PEM encoded structure.
+//
+// The encoded form is:
+//
+//	-----BEGIN Type-----
+//	Headers
+//	base64-encoded Bytes
+//	-----END Type-----
+//
+// where Headers is a possibly empty sequence of Key: Value lines.
+type Block struct {
+	Type    string            // The type, taken from the preamble (i.e. "RSA PRIVATE KEY").
+	Headers map[string]string // Optional headers.
+	Bytes   []byte            // The decoded bytes of the contents. Typically a DER encoded ASN.1 structure.
+}
+
+// getLine results the first \r\n or \n delineated line from the given byte
+// array. The line does not include trailing whitespace or the trailing new
+// line bytes. The remainder of the byte array (also not including the new line
+// bytes) is also returned and this will always be smaller than the original
+// argument.
+func getLine(data []byte) (line, rest []byte) {
+	i := bytes.IndexByte(data, '\n')
+	var j int
+	if i < 0 {
+		i = len(data)
+		j = i
+	} else {
+		j = i + 1
+		if i > 0 && data[i-1] == '\r' {
+			i--
+		}
+	}
+	return bytes.TrimRight(data[0:i], " \t"), data[j:]
+}
+
+// removeSpacesAndTabs returns a copy of its input with all spaces and tabs
+// removed, if there were any. Otherwise, the input is returned unchanged.
+//
+// The base64 decoder already skips newline characters, so we don't need to
+// filter them out here.
+func removeSpacesAndTabs(data []byte) []byte {
+	if !bytes.ContainsAny(data, " \t") {
+		// Fast path; most base64 data within PEM contains newlines, but
+		// no spaces nor tabs. Skip the extra alloc and work.
+		return data
+	}
+	result := make([]byte, len(data))
+	n := 0
+
+	for _, b := range data {
+		if b == ' ' || b == '\t' {
+			continue
+		}
+		result[n] = b
+		n++
+	}
+
+	return result[0:n]
+}
+
+var pemStart = []byte("\n-----BEGIN ")
+var pemEnd = []byte("\n-----END ")
+var pemEndOfLine = []byte("-----")
+var colon = []byte(":")
+
+// Decode will find the next PEM formatted block (certificate, private key
+// etc) in the input. It returns that block and the remainder of the input. If
+// no PEM data is found, p is nil and the whole of the input is returned in
+// rest.
+func Decode(data []byte) (p *Block, rest []byte) {
+	// pemStart begins with a newline. However, at the very beginning of
+	// the byte array, we'll accept the start string without it.
+	rest = data
+	for {
+		if bytes.HasPrefix(rest, pemStart[1:]) {
+			rest = rest[len(pemStart)-1:]
+		} else if _, after, ok := bytes.Cut(rest, pemStart); ok {
+			rest = after
+		} else {
+			return nil, data
+		}
+
+		var typeLine []byte
+		typeLine, rest = getLine(rest)
+		if !bytes.HasSuffix(typeLine, pemEndOfLine) {
+			continue
+		}
+		typeLine = typeLine[0 : len(typeLine)-len(pemEndOfLine)]
+
+		p = &Block{
+			Headers: make(map[string]string),
+			Type:    string(typeLine),
+		}
+
+		for {
+			// This loop terminates because getLine's second result is
+			// always smaller than its argument.
+			if len(rest) == 0 {
+				return nil, data
+			}
+			line, next := getLine(rest)
+
+			key, val, ok := bytes.Cut(line, colon)
+			if !ok {
+				break
+			}
+
+			// TODO(agl): need to cope with values that spread across lines.
+			key = bytes.TrimSpace(key)
+			val = bytes.TrimSpace(val)
+			p.Headers[string(key)] = string(val)
+			rest = next
+		}
+
+		var endIndex, endTrailerIndex int
+
+		// If there were no headers, the END line might occur
+		// immediately, without a leading newline.
+		if len(p.Headers) == 0 && bytes.HasPrefix(rest, pemEnd[1:]) {
+			endIndex = 0
+			endTrailerIndex = len(pemEnd) - 1
+		} else {
+			endIndex = bytes.Index(rest, pemEnd)
+			endTrailerIndex = endIndex + len(pemEnd)
+		}
+
+		if endIndex < 0 {
+			continue
+		}
+
+		// After the "-----" of the ending line, there should be the same type
+		// and then a final five dashes.
+		endTrailer := rest[endTrailerIndex:]
+		endTrailerLen := len(typeLine) + len(pemEndOfLine)
+		if len(endTrailer) < endTrailerLen {
+			continue
+		}
+
+		restOfEndLine := endTrailer[endTrailerLen:]
+		endTrailer = endTrailer[:endTrailerLen]
+		if !bytes.HasPrefix(endTrailer, typeLine) ||
+			!bytes.HasSuffix(endTrailer, pemEndOfLine) {
+			continue
+		}
+
+		// The line must end with only whitespace.
+		if s, _ := getLine(restOfEndLine); len(s) != 0 {
+			continue
+		}
+
+		base64Data := removeSpacesAndTabs(rest[:endIndex])
+		p.Bytes = make([]byte, base64.StdEncoding.DecodedLen(len(base64Data)))
+		n, err := base64.StdEncoding.Decode(p.Bytes, base64Data)
+		if err != nil {
+			continue
+		}
+		p.Bytes = p.Bytes[:n]
+
+		// the -1 is because we might have only matched pemEnd without the
+		// leading newline if the PEM block was empty.
+		_, rest = getLine(rest[endIndex+len(pemEnd)-1:])
+		return p, rest
+	}
+}
+
+const pemLineLength = 64
+
+type lineBreaker struct {
+	line [pemLineLength]byte
+	used int
+	out  io.Writer
+}
+
+var nl = []byte{'\n'}
+
+func (l *lineBreaker) Write(b []byte) (n int, err 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(nl)
+	if err != nil {
+		return
+	}
+
+	return l.Write(b[excess:])
+}
+
+func (l *lineBreaker) Close() (err error) {
+	if l.used > 0 {
+		_, err = l.out.Write(l.line[0:l.used])
+		if err != nil {
+			return
+		}
+		_, err = l.out.Write(nl)
+	}
+
+	return
+}
+
+func writeHeader(out io.Writer, k, v string) error {
+	_, err := out.Write([]byte(k + ": " + v + "\n"))
+	return err
+}
+
+// Encode writes the PEM encoding of b to out.
+func Encode(out io.Writer, b *Block) error {
+	// Check for invalid block before writing any output.
+	for k := range b.Headers {
+		if strings.Contains(k, ":") {
+			return errors.New("pem: cannot encode a header key that contains a colon")
+		}
+	}
+
+	// All errors below are relayed from underlying io.Writer,
+	// so it is now safe to write data.
+
+	if _, err := out.Write(pemStart[1:]); err != nil {
+		return err
+	}
+	if _, err := out.Write([]byte(b.Type + "-----\n")); err != nil {
+		return err
+	}
+
+	if len(b.Headers) > 0 {
+		const procType = "Proc-Type"
+		h := make([]string, 0, len(b.Headers))
+		hasProcType := false
+		for k := range b.Headers {
+			if k == procType {
+				hasProcType = true
+				continue
+			}
+			h = append(h, k)
+		}
+		// The Proc-Type header must be written first.
+		// See RFC 1421, section 4.6.1.1
+		if hasProcType {
+			if err := writeHeader(out, procType, b.Headers[procType]); err != nil {
+				return err
+			}
+		}
+		// For consistency of output, write other headers sorted by key.
+		sort.Strings(h)
+		for _, k := range h {
+			if err := writeHeader(out, k, b.Headers[k]); err != nil {
+				return err
+			}
+		}
+		if _, err := out.Write(nl); err != nil {
+			return err
+		}
+	}
+
+	var breaker lineBreaker
+	breaker.out = out
+
+	b64 := base64.NewEncoder(base64.StdEncoding, &breaker)
+	if _, err := b64.Write(b.Bytes); err != nil {
+		return err
+	}
+	b64.Close()
+	breaker.Close()
+
+	if _, err := out.Write(pemEnd[1:]); err != nil {
+		return err
+	}
+	_, err := out.Write([]byte(b.Type + "-----\n"))
+	return err
+}
+
+// EncodeToMemory returns the PEM encoding of b.
+//
+// If b has invalid headers and cannot be encoded,
+// EncodeToMemory returns nil. If it is important to
+// report details about this error case, use Encode instead.
+func EncodeToMemory(b *Block) []byte {
+	var buf bytes.Buffer
+	if err := Encode(&buf, b); err != nil {
+		return nil
+	}
+	return buf.Bytes()
+}