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Source file src/html/template/url.go

  // Copyright 2011 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 template
  
  import (
  	"bytes"
  	"fmt"
  	"strings"
  )
  
  // urlFilter returns its input unless it contains an unsafe protocol in which
  // case it defangs the entire URL.
  func urlFilter(args ...interface{}) string {
  	s, t := stringify(args...)
  	if t == contentTypeURL {
  		return s
  	}
  	if i := strings.IndexRune(s, ':'); i >= 0 && !strings.ContainsRune(s[:i], '/') {
  		protocol := strings.ToLower(s[:i])
  		if protocol != "http" && protocol != "https" && protocol != "mailto" {
  			return "#" + filterFailsafe
  		}
  	}
  	return s
  }
  
  // urlEscaper produces an output that can be embedded in a URL query.
  // The output can be embedded in an HTML attribute without further escaping.
  func urlEscaper(args ...interface{}) string {
  	return urlProcessor(false, args...)
  }
  
  // urlNormalizer normalizes URL content so it can be embedded in a quote-delimited
  // string or parenthesis delimited url(...).
  // The normalizer does not encode all HTML specials. Specifically, it does not
  // encode '&' so correct embedding in an HTML attribute requires escaping of
  // '&' to '&'.
  func urlNormalizer(args ...interface{}) string {
  	return urlProcessor(true, args...)
  }
  
  // urlProcessor normalizes (when norm is true) or escapes its input to produce
  // a valid hierarchical or opaque URL part.
  func urlProcessor(norm bool, args ...interface{}) string {
  	s, t := stringify(args...)
  	if t == contentTypeURL {
  		norm = true
  	}
  	var b bytes.Buffer
  	written := 0
  	// The byte loop below assumes that all URLs use UTF-8 as the
  	// content-encoding. This is similar to the URI to IRI encoding scheme
  	// defined in section 3.1 of  RFC 3987, and behaves the same as the
  	// EcmaScript builtin encodeURIComponent.
  	// It should not cause any misencoding of URLs in pages with
  	// Content-type: text/html;charset=UTF-8.
  	for i, n := 0, len(s); i < n; i++ {
  		c := s[i]
  		switch c {
  		// Single quote and parens are sub-delims in RFC 3986, but we
  		// escape them so the output can be embedded in single
  		// quoted attributes and unquoted CSS url(...) constructs.
  		// Single quotes are reserved in URLs, but are only used in
  		// the obsolete "mark" rule in an appendix in RFC 3986
  		// so can be safely encoded.
  		case '!', '#', '$', '&', '*', '+', ',', '/', ':', ';', '=', '?', '@', '[', ']':
  			if norm {
  				continue
  			}
  		// Unreserved according to RFC 3986 sec 2.3
  		// "For consistency, percent-encoded octets in the ranges of
  		// ALPHA (%41-%5A and %61-%7A), DIGIT (%30-%39), hyphen (%2D),
  		// period (%2E), underscore (%5F), or tilde (%7E) should not be
  		// created by URI producers
  		case '-', '.', '_', '~':
  			continue
  		case '%':
  			// When normalizing do not re-encode valid escapes.
  			if norm && i+2 < len(s) && isHex(s[i+1]) && isHex(s[i+2]) {
  				continue
  			}
  		default:
  			// Unreserved according to RFC 3986 sec 2.3
  			if 'a' <= c && c <= 'z' {
  				continue
  			}
  			if 'A' <= c && c <= 'Z' {
  				continue
  			}
  			if '0' <= c && c <= '9' {
  				continue
  			}
  		}
  		b.WriteString(s[written:i])
  		fmt.Fprintf(&b, "%%%02x", c)
  		written = i + 1
  	}
  	if written == 0 {
  		return s
  	}
  	b.WriteString(s[written:])
  	return b.String()
  }
  

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