198 lines
7.2 KiB
Go
198 lines
7.2 KiB
Go
// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package template
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import (
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"fmt"
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)
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// Error describes a problem encountered during template Escaping.
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type Error struct {
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// ErrorCode describes the kind of error.
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ErrorCode ErrorCode
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// Name is the name of the template in which the error was encountered.
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Name string
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// Line is the line number of the error in the template source or 0.
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Line int
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// Description is a human-readable description of the problem.
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Description string
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}
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// ErrorCode is a code for a kind of error.
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type ErrorCode int
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// We define codes for each error that manifests while escaping templates, but
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// escaped templates may also fail at runtime.
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//
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// Output: "ZgotmplZ"
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// Example:
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// <img src="{{.X}}">
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// where {{.X}} evaluates to `javascript:...`
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// Discussion:
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// "ZgotmplZ" is a special value that indicates that unsafe content reached a
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// CSS or URL context at runtime. The output of the example will be
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// <img src="#ZgotmplZ">
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// If the data comes from a trusted source, use content types to exempt it
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// from filtering: URL(`javascript:...`).
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const (
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// OK indicates the lack of an error.
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OK ErrorCode = iota
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// ErrAmbigContext: "... appears in an ambiguous URL context"
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// Example:
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// <a href="
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// {{if .C}}
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// /path/
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// {{else}}
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// /search?q=
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// {{end}}
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// {{.X}}
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// ">
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// Discussion:
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// {{.X}} is in an ambiguous URL context since, depending on {{.C}},
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// it may be either a URL suffix or a query parameter.
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// Moving {{.X}} into the condition removes the ambiguity:
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// <a href="{{if .C}}/path/{{.X}}{{else}}/search?q={{.X}}">
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ErrAmbigContext
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// ErrBadHTML: "expected space, attr name, or end of tag, but got ...",
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// "... in unquoted attr", "... in attribute name"
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// Example:
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// <a href = /search?q=foo>
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// <href=foo>
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// <form na<e=...>
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// <option selected<
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// Discussion:
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// This is often due to a typo in an HTML element, but some runes
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// are banned in tag names, attribute names, and unquoted attribute
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// values because they can tickle parser ambiguities.
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// Quoting all attributes is the best policy.
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ErrBadHTML
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// ErrBranchEnd: "{{if}} branches end in different contexts"
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// Example:
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// {{if .C}}<a href="{{end}}{{.X}}
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// Discussion:
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// Package html/template statically examines each path through an
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// {{if}}, {{range}}, or {{with}} to escape any following pipelines.
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// The example is ambiguous since {{.X}} might be an HTML text node,
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// or a URL prefix in an HTML attribute. The context of {{.X}} is
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// used to figure out how to escape it, but that context depends on
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// the run-time value of {{.C}} which is not statically known.
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//
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// The problem is usually something like missing quotes or angle
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// brackets, or can be avoided by refactoring to put the two contexts
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// into different branches of an if, range or with. If the problem
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// is in a {{range}} over a collection that should never be empty,
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// adding a dummy {{else}} can help.
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ErrBranchEnd
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// ErrEndContext: "... ends in a non-text context: ..."
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// Examples:
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// <div
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// <div title="no close quote>
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// <script>f()
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// Discussion:
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// Executed templates should produce a DocumentFragment of HTML.
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// Templates that end without closing tags will trigger this error.
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// Templates that should not be used in an HTML context or that
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// produce incomplete Fragments should not be executed directly.
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//
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// {{define "main"}} <script>{{template "helper"}}</script> {{end}}
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// {{define "helper"}} document.write(' <div title=" ') {{end}}
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//
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// "helper" does not produce a valid document fragment, so should
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// not be Executed directly.
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ErrEndContext
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// ErrNoSuchTemplate: "no such template ..."
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// Examples:
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// {{define "main"}}<div {{template "attrs"}}>{{end}}
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// {{define "attrs"}}href="{{.URL}}"{{end}}
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// Discussion:
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// Package html/template looks through template calls to compute the
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// context.
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// Here the {{.URL}} in "attrs" must be treated as a URL when called
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// from "main", but you will get this error if "attrs" is not defined
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// when "main" is parsed.
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ErrNoSuchTemplate
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// ErrOutputContext: "cannot compute output context for template ..."
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// Examples:
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// {{define "t"}}{{if .T}}{{template "t" .T}}{{end}}{{.H}}",{{end}}
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// Discussion:
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// A recursive template does not end in the same context in which it
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// starts, and a reliable output context cannot be computed.
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// Look for typos in the named template.
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// If the template should not be called in the named start context,
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// look for calls to that template in unexpected contexts.
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// Maybe refactor recursive templates to not be recursive.
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ErrOutputContext
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// ErrPartialCharset: "unfinished JS regexp charset in ..."
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// Example:
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// <script>var pattern = /foo[{{.Chars}}]/</script>
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// Discussion:
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// Package html/template does not support interpolation into regular
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// expression literal character sets.
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ErrPartialCharset
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// ErrPartialEscape: "unfinished escape sequence in ..."
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// Example:
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// <script>alert("\{{.X}}")</script>
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// Discussion:
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// Package html/template does not support actions following a
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// backslash.
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// This is usually an error and there are better solutions; for
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// example
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// <script>alert("{{.X}}")</script>
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// should work, and if {{.X}} is a partial escape sequence such as
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// "xA0", mark the whole sequence as safe content: JSStr(`\xA0`)
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ErrPartialEscape
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// ErrRangeLoopReentry: "on range loop re-entry: ..."
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// Example:
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// <script>var x = [{{range .}}'{{.}},{{end}}]</script>
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// Discussion:
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// If an iteration through a range would cause it to end in a
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// different context than an earlier pass, there is no single context.
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// In the example, there is missing a quote, so it is not clear
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// whether {{.}} is meant to be inside a JS string or in a JS value
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// context. The second iteration would produce something like
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//
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// <script>var x = ['firstValue,'secondValue]</script>
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ErrRangeLoopReentry
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// ErrSlashAmbig: '/' could start a division or regexp.
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// Example:
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// <script>
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// {{if .C}}var x = 1{{end}}
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// /-{{.N}}/i.test(x) ? doThis : doThat();
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// </script>
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// Discussion:
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// The example above could produce `var x = 1/-2/i.test(s)...`
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// in which the first '/' is a mathematical division operator or it
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// could produce `/-2/i.test(s)` in which the first '/' starts a
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// regexp literal.
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// Look for missing semicolons inside branches, and maybe add
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// parentheses to make it clear which interpretation you intend.
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ErrSlashAmbig
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)
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func (e *Error) Error() string {
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if e.Line != 0 {
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return fmt.Sprintf("html/template:%s:%d: %s", e.Name, e.Line, e.Description)
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} else if e.Name != "" {
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return fmt.Sprintf("html/template:%s: %s", e.Name, e.Description)
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}
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return "html/template: " + e.Description
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}
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// errorf creates an error given a format string f and args.
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// The template Name still needs to be supplied.
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func errorf(k ErrorCode, line int, f string, args ...interface{}) *Error {
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return &Error{k, "", line, fmt.Sprintf(f, args...)}
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}
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