From 4a92c26fbc739734ce5227c1be8efd440306cebf Mon Sep 17 00:00:00 2001
From: Jordan <me@jordan.im>
Date: Sat, 15 Jan 2022 10:09:56 -0700
Subject: keep, archive: normalize URLs (RFC 3986), improve logging

---
 urlesc/urlesc.go | 180 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 180 insertions(+)
 create mode 100644 urlesc/urlesc.go

(limited to 'urlesc/urlesc.go')

diff --git a/urlesc/urlesc.go b/urlesc/urlesc.go
new file mode 100644
index 0000000..1b84624
--- /dev/null
+++ b/urlesc/urlesc.go
@@ -0,0 +1,180 @@
+// 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 urlesc implements query escaping as per RFC 3986.
+// It contains some parts of the net/url package, modified so as to allow
+// some reserved characters incorrectly escaped by net/url.
+// See https://github.com/golang/go/issues/5684
+package urlesc
+
+import (
+	"bytes"
+	"net/url"
+	"strings"
+)
+
+type encoding int
+
+const (
+	encodePath encoding = 1 + iota
+	encodeUserPassword
+	encodeQueryComponent
+	encodeFragment
+)
+
+// Return true if the specified character should be escaped when
+// appearing in a URL string, according to RFC 3986.
+func shouldEscape(c byte, mode encoding) bool {
+	// §2.3 Unreserved characters (alphanum)
+	if 'A' <= c && c <= 'Z' || 'a' <= c && c <= 'z' || '0' <= c && c <= '9' {
+		return false
+	}
+
+	switch c {
+	case '-', '.', '_', '~': // §2.3 Unreserved characters (mark)
+		return false
+
+	// §2.2 Reserved characters (reserved)
+	case ':', '/', '?', '#', '[', ']', '@', // gen-delims
+		'!', '$', '&', '\'', '(', ')', '*', '+', ',', ';', '=': // sub-delims
+		// Different sections of the URL allow a few of
+		// the reserved characters to appear unescaped.
+		switch mode {
+		case encodePath: // §3.3
+			// The RFC allows sub-delims and : @.
+			// '/', '[' and ']' can be used to assign meaning to individual path
+			// segments.  This package only manipulates the path as a whole,
+			// so we allow those as well.  That leaves only ? and # to escape.
+			return c == '?' || c == '#'
+
+		case encodeUserPassword: // §3.2.1
+			// The RFC allows : and sub-delims in
+			// userinfo.  The parsing of userinfo treats ':' as special so we must escape
+			// all the gen-delims.
+			return c == ':' || c == '/' || c == '?' || c == '#' || c == '[' || c == ']' || c == '@'
+
+		case encodeQueryComponent: // §3.4
+			// The RFC allows / and ?.
+			return c != '/' && c != '?'
+
+		case encodeFragment: // §4.1
+			// The RFC text is silent but the grammar allows
+			// everything, so escape nothing but #
+			return c == '#'
+		}
+	}
+
+	// Everything else must be escaped.
+	return true
+}
+
+// QueryEscape escapes the string so it can be safely placed
+// inside a URL query.
+func QueryEscape(s string) string {
+	return escape(s, encodeQueryComponent)
+}
+
+func escape(s string, mode encoding) string {
+	spaceCount, hexCount := 0, 0
+	for i := 0; i < len(s); i++ {
+		c := s[i]
+		if shouldEscape(c, mode) {
+			if c == ' ' && mode == encodeQueryComponent {
+				spaceCount++
+			} else {
+				hexCount++
+			}
+		}
+	}
+
+	if spaceCount == 0 && hexCount == 0 {
+		return s
+	}
+
+	t := make([]byte, len(s)+2*hexCount)
+	j := 0
+	for i := 0; i < len(s); i++ {
+		switch c := s[i]; {
+		case c == ' ' && mode == encodeQueryComponent:
+			t[j] = '+'
+			j++
+		case shouldEscape(c, mode):
+			t[j] = '%'
+			t[j+1] = "0123456789ABCDEF"[c>>4]
+			t[j+2] = "0123456789ABCDEF"[c&15]
+			j += 3
+		default:
+			t[j] = s[i]
+			j++
+		}
+	}
+	return string(t)
+}
+
+var uiReplacer = strings.NewReplacer(
+	"%21", "!",
+	"%27", "'",
+	"%28", "(",
+	"%29", ")",
+	"%2A", "*",
+)
+
+// unescapeUserinfo unescapes some characters that need not to be escaped as per RFC3986.
+func unescapeUserinfo(s string) string {
+	return uiReplacer.Replace(s)
+}
+
+// Escape reassembles the URL into a valid URL string.
+// The general form of the result is one of:
+//
+//	scheme:opaque
+//	scheme://userinfo@host/path?query#fragment
+//
+// If u.Opaque is non-empty, String uses the first form;
+// otherwise it uses the second form.
+//
+// In the second form, the following rules apply:
+//	- if u.Scheme is empty, scheme: is omitted.
+//	- if u.User is nil, userinfo@ is omitted.
+//	- if u.Host is empty, host/ is omitted.
+//	- if u.Scheme and u.Host are empty and u.User is nil,
+//	   the entire scheme://userinfo@host/ is omitted.
+//	- if u.Host is non-empty and u.Path begins with a /,
+//	   the form host/path does not add its own /.
+//	- if u.RawQuery is empty, ?query is omitted.
+//	- if u.Fragment is empty, #fragment is omitted.
+func Escape(u *url.URL) string {
+	var buf bytes.Buffer
+	if u.Scheme != "" {
+		buf.WriteString(u.Scheme)
+		buf.WriteByte(':')
+	}
+	if u.Opaque != "" {
+		buf.WriteString(u.Opaque)
+	} else {
+		if u.Scheme != "" || u.Host != "" || u.User != nil {
+			buf.WriteString("//")
+			if ui := u.User; ui != nil {
+				buf.WriteString(unescapeUserinfo(ui.String()))
+				buf.WriteByte('@')
+			}
+			if h := u.Host; h != "" {
+				buf.WriteString(h)
+			}
+		}
+		if u.Path != "" && u.Path[0] != '/' && u.Host != "" {
+			buf.WriteByte('/')
+		}
+		buf.WriteString(escape(u.Path, encodePath))
+	}
+	if u.RawQuery != "" {
+		buf.WriteByte('?')
+		buf.WriteString(u.RawQuery)
+	}
+	if u.Fragment != "" {
+		buf.WriteByte('#')
+		buf.WriteString(escape(u.Fragment, encodeFragment))
+	}
+	return buf.String()
+}
-- 
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