1 files changed, 135 insertions, 0 deletions
diff --git a/libgo/go/golang.org/x/mod/sumdb/tlog/note.go b/libgo/go/golang.org/x/mod/sumdb/tlog/note.go
new file mode 100644
index 00000000000..ce5353e0feb
--- /dev/null
+++ b/libgo/go/golang.org/x/mod/sumdb/tlog/note.go
@@ -0,0 +1,135 @@
+// Copyright 2019 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 tlog
+
+import (
+	"bytes"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"strconv"
+	"strings"
+	"unicode/utf8"
+)
+
+// A Tree is a tree description, to be signed by a go.sum database server.
+type Tree struct {
+	N    int64
+	Hash Hash
+}
+
+// FormatTree formats a tree description for inclusion in a note.
+//
+// The encoded form is three lines, each ending in a newline (U+000A):
+//
+//	go.sum database tree
+//	N
+//	Hash
+//
+// where N is in decimal and Hash is in base64.
+//
+// A future backwards-compatible encoding may add additional lines,
+// which the parser can ignore.
+// A future backwards-incompatible encoding would use a different
+// first line (for example, "go.sum database tree v2").
+func FormatTree(tree Tree) []byte {
+	return []byte(fmt.Sprintf("go.sum database tree\n%d\n%s\n", tree.N, tree.Hash))
+}
+
+var errMalformedTree = errors.New("malformed tree note")
+var treePrefix = []byte("go.sum database tree\n")
+
+// ParseTree parses a formatted tree root description.
+func ParseTree(text []byte) (tree Tree, err error) {
+	// The message looks like:
+	//
+	//	go.sum database tree
+	//	2
+	//	nND/nri/U0xuHUrYSy0HtMeal2vzD9V4k/BO79C+QeI=
+	//
+	// For forwards compatibility, extra text lines after the encoding are ignored.
+	if !bytes.HasPrefix(text, treePrefix) || bytes.Count(text, []byte("\n")) < 3 || len(text) > 1e6 {
+		return Tree{}, errMalformedTree
+	}
+
+	lines := strings.SplitN(string(text), "\n", 4)
+	n, err := strconv.ParseInt(lines[1], 10, 64)
+	if err != nil || n < 0 || lines[1] != strconv.FormatInt(n, 10) {
+		return Tree{}, errMalformedTree
+	}
+
+	h, err := base64.StdEncoding.DecodeString(lines[2])
+	if err != nil || len(h) != HashSize {
+		return Tree{}, errMalformedTree
+	}
+
+	var hash Hash
+	copy(hash[:], h)
+	return Tree{n, hash}, nil
+}
+
+var errMalformedRecord = errors.New("malformed record data")
+
+// FormatRecord formats a record for serving to a client
+// in a lookup response or data tile.
+//
+// The encoded form is the record ID as a single number,
+// then the text of the record, and then a terminating blank line.
+// Record text must be valid UTF-8 and must not contain any ASCII control
+// characters (those below U+0020) other than newline (U+000A).
+// It must end in a terminating newline and not contain any blank lines.
+func FormatRecord(id int64, text []byte) (msg []byte, err error) {
+	if !isValidRecordText(text) {
+		return nil, errMalformedRecord
+	}
+	msg = []byte(fmt.Sprintf("%d\n", id))
+	msg = append(msg, text...)
+	msg = append(msg, '\n')
+	return msg, nil
+}
+
+// isValidRecordText reports whether text is syntactically valid record text.
+func isValidRecordText(text []byte) bool {
+	var last rune
+	for i := 0; i < len(text); {
+		r, size := utf8.DecodeRune(text[i:])
+		if r < 0x20 && r != '\n' || r == utf8.RuneError && size == 1 || last == '\n' && r == '\n' {
+			return false
+		}
+		i += size
+		last = r
+	}
+	if last != '\n' {
+		return false
+	}
+	return true
+}
+
+// ParseRecord parses a record description at the start of text,
+// stopping immediately after the terminating blank line.
+// It returns the record id, the record text, and the remainder of text.
+func ParseRecord(msg []byte) (id int64, text, rest []byte, err error) {
+	// Leading record id.
+	i := bytes.IndexByte(msg, '\n')
+	if i < 0 {
+		return 0, nil, nil, errMalformedRecord
+	}
+	id, err = strconv.ParseInt(string(msg[:i]), 10, 64)
+	if err != nil {
+		return 0, nil, nil, errMalformedRecord
+	}
+	msg = msg[i+1:]
+
+	// Record text.
+	i = bytes.Index(msg, []byte("\n\n"))
+	if i < 0 {
+		return 0, nil, nil, errMalformedRecord
+	}
+	text, rest = msg[:i+1], msg[i+2:]
+	if !isValidRecordText(text) {
+		return 0, nil, nil, errMalformedRecord
+	}
+	return id, text, rest, nil
+}