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Source file src/html/template/template.go

     1	// Copyright 2011 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	package template
     6	
     7	import (
     8		"fmt"
     9		"io"
    10		"io/ioutil"
    11		"path/filepath"
    12		"sync"
    13		"text/template"
    14		"text/template/parse"
    15	)
    16	
    17	// Template is a specialized Template from "text/template" that produces a safe
    18	// HTML document fragment.
    19	type Template struct {
    20		// Sticky error if escaping fails.
    21		escapeErr error
    22		// We could embed the text/template field, but it's safer not to because
    23		// we need to keep our version of the name space and the underlying
    24		// template's in sync.
    25		text *template.Template
    26		// The underlying template's parse tree, updated to be HTML-safe.
    27		Tree       *parse.Tree
    28		*nameSpace // common to all associated templates
    29	}
    30	
    31	// escapeOK is a sentinel value used to indicate valid escaping.
    32	var escapeOK = fmt.Errorf("template escaped correctly")
    33	
    34	// nameSpace is the data structure shared by all templates in an association.
    35	type nameSpace struct {
    36		mu  sync.Mutex
    37		set map[string]*Template
    38	}
    39	
    40	// Templates returns a slice of the templates associated with t, including t
    41	// itself.
    42	func (t *Template) Templates() []*Template {
    43		ns := t.nameSpace
    44		ns.mu.Lock()
    45		defer ns.mu.Unlock()
    46		// Return a slice so we don't expose the map.
    47		m := make([]*Template, 0, len(ns.set))
    48		for _, v := range ns.set {
    49			m = append(m, v)
    50		}
    51		return m
    52	}
    53	
    54	// Option sets options for the template. Options are described by
    55	// strings, either a simple string or "key=value". There can be at
    56	// most one equals sign in an option string. If the option string
    57	// is unrecognized or otherwise invalid, Option panics.
    58	//
    59	// Known options:
    60	//
    61	// missingkey: Control the behavior during execution if a map is
    62	// indexed with a key that is not present in the map.
    63	//	"missingkey=default" or "missingkey=invalid"
    64	//		The default behavior: Do nothing and continue execution.
    65	//		If printed, the result of the index operation is the string
    66	//		"<no value>".
    67	//	"missingkey=zero"
    68	//		The operation returns the zero value for the map type's element.
    69	//	"missingkey=error"
    70	//		Execution stops immediately with an error.
    71	//
    72	func (t *Template) Option(opt ...string) *Template {
    73		t.text.Option(opt...)
    74		return t
    75	}
    76	
    77	// escape escapes all associated templates.
    78	func (t *Template) escape() error {
    79		t.nameSpace.mu.Lock()
    80		defer t.nameSpace.mu.Unlock()
    81		if t.escapeErr == nil {
    82			if t.Tree == nil {
    83				return fmt.Errorf("template: %q is an incomplete or empty template%s", t.Name(), t.text.DefinedTemplates())
    84			}
    85			if err := escapeTemplate(t, t.text.Root, t.Name()); err != nil {
    86				return err
    87			}
    88		} else if t.escapeErr != escapeOK {
    89			return t.escapeErr
    90		}
    91		return nil
    92	}
    93	
    94	// Execute applies a parsed template to the specified data object,
    95	// writing the output to wr.
    96	// If an error occurs executing the template or writing its output,
    97	// execution stops, but partial results may already have been written to
    98	// the output writer.
    99	// A template may be executed safely in parallel.
   100	func (t *Template) Execute(wr io.Writer, data interface{}) error {
   101		if err := t.escape(); err != nil {
   102			return err
   103		}
   104		return t.text.Execute(wr, data)
   105	}
   106	
   107	// ExecuteTemplate applies the template associated with t that has the given
   108	// name to the specified data object and writes the output to wr.
   109	// If an error occurs executing the template or writing its output,
   110	// execution stops, but partial results may already have been written to
   111	// the output writer.
   112	// A template may be executed safely in parallel.
   113	func (t *Template) ExecuteTemplate(wr io.Writer, name string, data interface{}) error {
   114		tmpl, err := t.lookupAndEscapeTemplate(name)
   115		if err != nil {
   116			return err
   117		}
   118		return tmpl.text.Execute(wr, data)
   119	}
   120	
   121	// lookupAndEscapeTemplate guarantees that the template with the given name
   122	// is escaped, or returns an error if it cannot be. It returns the named
   123	// template.
   124	func (t *Template) lookupAndEscapeTemplate(name string) (tmpl *Template, err error) {
   125		t.nameSpace.mu.Lock()
   126		defer t.nameSpace.mu.Unlock()
   127		tmpl = t.set[name]
   128		if tmpl == nil {
   129			return nil, fmt.Errorf("html/template: %q is undefined", name)
   130		}
   131		if tmpl.escapeErr != nil && tmpl.escapeErr != escapeOK {
   132			return nil, tmpl.escapeErr
   133		}
   134		if tmpl.text.Tree == nil || tmpl.text.Root == nil {
   135			return nil, fmt.Errorf("html/template: %q is an incomplete template", name)
   136		}
   137		if t.text.Lookup(name) == nil {
   138			panic("html/template internal error: template escaping out of sync")
   139		}
   140		if tmpl.escapeErr == nil {
   141			err = escapeTemplate(tmpl, tmpl.text.Root, name)
   142		}
   143		return tmpl, err
   144	}
   145	
   146	// Parse parses a string into a template. Nested template definitions
   147	// will be associated with the top-level template t. Parse may be
   148	// called multiple times to parse definitions of templates to associate
   149	// with t. It is an error if a resulting template is non-empty (contains
   150	// content other than template definitions) and would replace a
   151	// non-empty template with the same name.  (In multiple calls to Parse
   152	// with the same receiver template, only one call can contain text
   153	// other than space, comments, and template definitions.)
   154	func (t *Template) Parse(src string) (*Template, error) {
   155		t.nameSpace.mu.Lock()
   156		t.escapeErr = nil
   157		t.nameSpace.mu.Unlock()
   158		ret, err := t.text.Parse(src)
   159		if err != nil {
   160			return nil, err
   161		}
   162		// In general, all the named templates might have changed underfoot.
   163		// Regardless, some new ones may have been defined.
   164		// The template.Template set has been updated; update ours.
   165		t.nameSpace.mu.Lock()
   166		defer t.nameSpace.mu.Unlock()
   167		for _, v := range ret.Templates() {
   168			name := v.Name()
   169			tmpl := t.set[name]
   170			if tmpl == nil {
   171				tmpl = t.new(name)
   172			}
   173			// Restore our record of this text/template to its unescaped original state.
   174			tmpl.escapeErr = nil
   175			tmpl.text = v
   176			tmpl.Tree = v.Tree
   177		}
   178		return t, nil
   179	}
   180	
   181	// AddParseTree creates a new template with the name and parse tree
   182	// and associates it with t.
   183	//
   184	// It returns an error if t has already been executed.
   185	func (t *Template) AddParseTree(name string, tree *parse.Tree) (*Template, error) {
   186		t.nameSpace.mu.Lock()
   187		defer t.nameSpace.mu.Unlock()
   188		if t.escapeErr != nil {
   189			return nil, fmt.Errorf("html/template: cannot AddParseTree to %q after it has executed", t.Name())
   190		}
   191		text, err := t.text.AddParseTree(name, tree)
   192		if err != nil {
   193			return nil, err
   194		}
   195		ret := &Template{
   196			nil,
   197			text,
   198			text.Tree,
   199			t.nameSpace,
   200		}
   201		t.set[name] = ret
   202		return ret, nil
   203	}
   204	
   205	// Clone returns a duplicate of the template, including all associated
   206	// templates. The actual representation is not copied, but the name space of
   207	// associated templates is, so further calls to Parse in the copy will add
   208	// templates to the copy but not to the original. Clone can be used to prepare
   209	// common templates and use them with variant definitions for other templates
   210	// by adding the variants after the clone is made.
   211	//
   212	// It returns an error if t has already been executed.
   213	func (t *Template) Clone() (*Template, error) {
   214		t.nameSpace.mu.Lock()
   215		defer t.nameSpace.mu.Unlock()
   216		if t.escapeErr != nil {
   217			return nil, fmt.Errorf("html/template: cannot Clone %q after it has executed", t.Name())
   218		}
   219		textClone, err := t.text.Clone()
   220		if err != nil {
   221			return nil, err
   222		}
   223		ret := &Template{
   224			nil,
   225			textClone,
   226			textClone.Tree,
   227			&nameSpace{
   228				set: make(map[string]*Template),
   229			},
   230		}
   231		for _, x := range textClone.Templates() {
   232			name := x.Name()
   233			src := t.set[name]
   234			if src == nil || src.escapeErr != nil {
   235				return nil, fmt.Errorf("html/template: cannot Clone %q after it has executed", t.Name())
   236			}
   237			x.Tree = x.Tree.Copy()
   238			ret.set[name] = &Template{
   239				nil,
   240				x,
   241				x.Tree,
   242				ret.nameSpace,
   243			}
   244		}
   245		return ret, nil
   246	}
   247	
   248	// New allocates a new HTML template with the given name.
   249	func New(name string) *Template {
   250		tmpl := &Template{
   251			nil,
   252			template.New(name),
   253			nil,
   254			&nameSpace{
   255				set: make(map[string]*Template),
   256			},
   257		}
   258		tmpl.set[name] = tmpl
   259		return tmpl
   260	}
   261	
   262	// New allocates a new HTML template associated with the given one
   263	// and with the same delimiters. The association, which is transitive,
   264	// allows one template to invoke another with a {{template}} action.
   265	func (t *Template) New(name string) *Template {
   266		t.nameSpace.mu.Lock()
   267		defer t.nameSpace.mu.Unlock()
   268		return t.new(name)
   269	}
   270	
   271	// new is the implementation of New, without the lock.
   272	func (t *Template) new(name string) *Template {
   273		tmpl := &Template{
   274			nil,
   275			t.text.New(name),
   276			nil,
   277			t.nameSpace,
   278		}
   279		tmpl.set[name] = tmpl
   280		return tmpl
   281	}
   282	
   283	// Name returns the name of the template.
   284	func (t *Template) Name() string {
   285		return t.text.Name()
   286	}
   287	
   288	// FuncMap is the type of the map defining the mapping from names to
   289	// functions. Each function must have either a single return value, or two
   290	// return values of which the second has type error. In that case, if the
   291	// second (error) argument evaluates to non-nil during execution, execution
   292	// terminates and Execute returns that error. FuncMap has the same base type
   293	// as FuncMap in "text/template", copied here so clients need not import
   294	// "text/template".
   295	type FuncMap map[string]interface{}
   296	
   297	// Funcs adds the elements of the argument map to the template's function map.
   298	// It panics if a value in the map is not a function with appropriate return
   299	// type. However, it is legal to overwrite elements of the map. The return
   300	// value is the template, so calls can be chained.
   301	func (t *Template) Funcs(funcMap FuncMap) *Template {
   302		t.text.Funcs(template.FuncMap(funcMap))
   303		return t
   304	}
   305	
   306	// Delims sets the action delimiters to the specified strings, to be used in
   307	// subsequent calls to Parse, ParseFiles, or ParseGlob. Nested template
   308	// definitions will inherit the settings. An empty delimiter stands for the
   309	// corresponding default: {{ or }}.
   310	// The return value is the template, so calls can be chained.
   311	func (t *Template) Delims(left, right string) *Template {
   312		t.text.Delims(left, right)
   313		return t
   314	}
   315	
   316	// Lookup returns the template with the given name that is associated with t,
   317	// or nil if there is no such template.
   318	func (t *Template) Lookup(name string) *Template {
   319		t.nameSpace.mu.Lock()
   320		defer t.nameSpace.mu.Unlock()
   321		return t.set[name]
   322	}
   323	
   324	// Must is a helper that wraps a call to a function returning (*Template, error)
   325	// and panics if the error is non-nil. It is intended for use in variable initializations
   326	// such as
   327	//	var t = template.Must(template.New("name").Parse("html"))
   328	func Must(t *Template, err error) *Template {
   329		if err != nil {
   330			panic(err)
   331		}
   332		return t
   333	}
   334	
   335	// ParseFiles creates a new Template and parses the template definitions from
   336	// the named files. The returned template's name will have the (base) name and
   337	// (parsed) contents of the first file. There must be at least one file.
   338	// If an error occurs, parsing stops and the returned *Template is nil.
   339	func ParseFiles(filenames ...string) (*Template, error) {
   340		return parseFiles(nil, filenames...)
   341	}
   342	
   343	// ParseFiles parses the named files and associates the resulting templates with
   344	// t. If an error occurs, parsing stops and the returned template is nil;
   345	// otherwise it is t. There must be at least one file.
   346	func (t *Template) ParseFiles(filenames ...string) (*Template, error) {
   347		return parseFiles(t, filenames...)
   348	}
   349	
   350	// parseFiles is the helper for the method and function. If the argument
   351	// template is nil, it is created from the first file.
   352	func parseFiles(t *Template, filenames ...string) (*Template, error) {
   353		if len(filenames) == 0 {
   354			// Not really a problem, but be consistent.
   355			return nil, fmt.Errorf("html/template: no files named in call to ParseFiles")
   356		}
   357		for _, filename := range filenames {
   358			b, err := ioutil.ReadFile(filename)
   359			if err != nil {
   360				return nil, err
   361			}
   362			s := string(b)
   363			name := filepath.Base(filename)
   364			// First template becomes return value if not already defined,
   365			// and we use that one for subsequent New calls to associate
   366			// all the templates together. Also, if this file has the same name
   367			// as t, this file becomes the contents of t, so
   368			//  t, err := New(name).Funcs(xxx).ParseFiles(name)
   369			// works. Otherwise we create a new template associated with t.
   370			var tmpl *Template
   371			if t == nil {
   372				t = New(name)
   373			}
   374			if name == t.Name() {
   375				tmpl = t
   376			} else {
   377				tmpl = t.New(name)
   378			}
   379			_, err = tmpl.Parse(s)
   380			if err != nil {
   381				return nil, err
   382			}
   383		}
   384		return t, nil
   385	}
   386	
   387	// ParseGlob creates a new Template and parses the template definitions from the
   388	// files identified by the pattern, which must match at least one file. The
   389	// returned template will have the (base) name and (parsed) contents of the
   390	// first file matched by the pattern. ParseGlob is equivalent to calling
   391	// ParseFiles with the list of files matched by the pattern.
   392	func ParseGlob(pattern string) (*Template, error) {
   393		return parseGlob(nil, pattern)
   394	}
   395	
   396	// ParseGlob parses the template definitions in the files identified by the
   397	// pattern and associates the resulting templates with t. The pattern is
   398	// processed by filepath.Glob and must match at least one file. ParseGlob is
   399	// equivalent to calling t.ParseFiles with the list of files matched by the
   400	// pattern.
   401	func (t *Template) ParseGlob(pattern string) (*Template, error) {
   402		return parseGlob(t, pattern)
   403	}
   404	
   405	// parseGlob is the implementation of the function and method ParseGlob.
   406	func parseGlob(t *Template, pattern string) (*Template, error) {
   407		filenames, err := filepath.Glob(pattern)
   408		if err != nil {
   409			return nil, err
   410		}
   411		if len(filenames) == 0 {
   412			return nil, fmt.Errorf("html/template: pattern matches no files: %#q", pattern)
   413		}
   414		return parseFiles(t, filenames...)
   415	}
   416	

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