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/fs"
    11  	"os"
    12  	"path"
    13  	"path/filepath"
    14  	"sync"
    15  	"text/template"
    16  	"text/template/parse"
    17  )
    18  
    19  // Template is a specialized Template from "text/template" that produces a safe
    20  // HTML document fragment.
    21  type Template struct {
    22  	// Sticky error if escaping fails, or escapeOK if succeeded.
    23  	escapeErr error
    24  	// We could embed the text/template field, but it's safer not to because
    25  	// we need to keep our version of the name space and the underlying
    26  	// template's in sync.
    27  	text *template.Template
    28  	// The underlying template's parse tree, updated to be HTML-safe.
    29  	Tree       *parse.Tree
    30  	*nameSpace // common to all associated templates
    31  }
    32  
    33  // escapeOK is a sentinel value used to indicate valid escaping.
    34  var escapeOK = fmt.Errorf("template escaped correctly")
    35  
    36  // nameSpace is the data structure shared by all templates in an association.
    37  type nameSpace struct {
    38  	mu      sync.Mutex
    39  	set     map[string]*Template
    40  	escaped bool
    41  	esc     escaper
    42  }
    43  
    44  // Templates returns a slice of the templates associated with t, including t
    45  // itself.
    46  func (t *Template) Templates() []*Template {
    47  	ns := t.nameSpace
    48  	ns.mu.Lock()
    49  	defer ns.mu.Unlock()
    50  	// Return a slice so we don't expose the map.
    51  	m := make([]*Template, 0, len(ns.set))
    52  	for _, v := range ns.set {
    53  		m = append(m, v)
    54  	}
    55  	return m
    56  }
    57  
    58  // Option sets options for the template. Options are described by
    59  // strings, either a simple string or "key=value". There can be at
    60  // most one equals sign in an option string. If the option string
    61  // is unrecognized or otherwise invalid, Option panics.
    62  //
    63  // Known options:
    64  //
    65  // missingkey: Control the behavior during execution if a map is
    66  // indexed with a key that is not present in the map.
    67  //	"missingkey=default" or "missingkey=invalid"
    68  //		The default behavior: Do nothing and continue execution.
    69  //		If printed, the result of the index operation is the string
    70  //		"<no value>".
    71  //	"missingkey=zero"
    72  //		The operation returns the zero value for the map type's element.
    73  //	"missingkey=error"
    74  //		Execution stops immediately with an error.
    75  //
    76  func (t *Template) Option(opt ...string) *Template {
    77  	t.text.Option(opt...)
    78  	return t
    79  }
    80  
    81  // checkCanParse checks whether it is OK to parse templates.
    82  // If not, it returns an error.
    83  func (t *Template) checkCanParse() error {
    84  	if t == nil {
    85  		return nil
    86  	}
    87  	t.nameSpace.mu.Lock()
    88  	defer t.nameSpace.mu.Unlock()
    89  	if t.nameSpace.escaped {
    90  		return fmt.Errorf("html/template: cannot Parse after Execute")
    91  	}
    92  	return nil
    93  }
    94  
    95  // escape escapes all associated templates.
    96  func (t *Template) escape() error {
    97  	t.nameSpace.mu.Lock()
    98  	defer t.nameSpace.mu.Unlock()
    99  	t.nameSpace.escaped = true
   100  	if t.escapeErr == nil {
   101  		if t.Tree == nil {
   102  			return fmt.Errorf("template: %q is an incomplete or empty template", t.Name())
   103  		}
   104  		if err := escapeTemplate(t, t.text.Root, t.Name()); err != nil {
   105  			return err
   106  		}
   107  	} else if t.escapeErr != escapeOK {
   108  		return t.escapeErr
   109  	}
   110  	return nil
   111  }
   112  
   113  // Execute applies a parsed template to the specified data object,
   114  // writing the output to wr.
   115  // If an error occurs executing the template or writing its output,
   116  // execution stops, but partial results may already have been written to
   117  // the output writer.
   118  // A template may be executed safely in parallel, although if parallel
   119  // executions share a Writer the output may be interleaved.
   120  func (t *Template) Execute(wr io.Writer, data interface{}) error {
   121  	if err := t.escape(); err != nil {
   122  		return err
   123  	}
   124  	return t.text.Execute(wr, data)
   125  }
   126  
   127  // ExecuteTemplate applies the template associated with t that has the given
   128  // name to the specified data object and writes the output to wr.
   129  // If an error occurs executing the template or writing its output,
   130  // execution stops, but partial results may already have been written to
   131  // the output writer.
   132  // A template may be executed safely in parallel, although if parallel
   133  // executions share a Writer the output may be interleaved.
   134  func (t *Template) ExecuteTemplate(wr io.Writer, name string, data interface{}) error {
   135  	tmpl, err := t.lookupAndEscapeTemplate(name)
   136  	if err != nil {
   137  		return err
   138  	}
   139  	return tmpl.text.Execute(wr, data)
   140  }
   141  
   142  // lookupAndEscapeTemplate guarantees that the template with the given name
   143  // is escaped, or returns an error if it cannot be. It returns the named
   144  // template.
   145  func (t *Template) lookupAndEscapeTemplate(name string) (tmpl *Template, err error) {
   146  	t.nameSpace.mu.Lock()
   147  	defer t.nameSpace.mu.Unlock()
   148  	t.nameSpace.escaped = true
   149  	tmpl = t.set[name]
   150  	if tmpl == nil {
   151  		return nil, fmt.Errorf("html/template: %q is undefined", name)
   152  	}
   153  	if tmpl.escapeErr != nil && tmpl.escapeErr != escapeOK {
   154  		return nil, tmpl.escapeErr
   155  	}
   156  	if tmpl.text.Tree == nil || tmpl.text.Root == nil {
   157  		return nil, fmt.Errorf("html/template: %q is an incomplete template", name)
   158  	}
   159  	if t.text.Lookup(name) == nil {
   160  		panic("html/template internal error: template escaping out of sync")
   161  	}
   162  	if tmpl.escapeErr == nil {
   163  		err = escapeTemplate(tmpl, tmpl.text.Root, name)
   164  	}
   165  	return tmpl, err
   166  }
   167  
   168  // DefinedTemplates returns a string listing the defined templates,
   169  // prefixed by the string "; defined templates are: ". If there are none,
   170  // it returns the empty string. Used to generate an error message.
   171  func (t *Template) DefinedTemplates() string {
   172  	return t.text.DefinedTemplates()
   173  }
   174  
   175  // Parse parses text as a template body for t.
   176  // Named template definitions ({{define ...}} or {{block ...}} statements) in text
   177  // define additional templates associated with t and are removed from the
   178  // definition of t itself.
   179  //
   180  // Templates can be redefined in successive calls to Parse,
   181  // before the first use of Execute on t or any associated template.
   182  // A template definition with a body containing only white space and comments
   183  // is considered empty and will not replace an existing template's body.
   184  // This allows using Parse to add new named template definitions without
   185  // overwriting the main template body.
   186  func (t *Template) Parse(text string) (*Template, error) {
   187  	if err := t.checkCanParse(); err != nil {
   188  		return nil, err
   189  	}
   190  
   191  	ret, err := t.text.Parse(text)
   192  	if err != nil {
   193  		return nil, err
   194  	}
   195  
   196  	// In general, all the named templates might have changed underfoot.
   197  	// Regardless, some new ones may have been defined.
   198  	// The template.Template set has been updated; update ours.
   199  	t.nameSpace.mu.Lock()
   200  	defer t.nameSpace.mu.Unlock()
   201  	for _, v := range ret.Templates() {
   202  		name := v.Name()
   203  		tmpl := t.set[name]
   204  		if tmpl == nil {
   205  			tmpl = t.new(name)
   206  		}
   207  		tmpl.text = v
   208  		tmpl.Tree = v.Tree
   209  	}
   210  	return t, nil
   211  }
   212  
   213  // AddParseTree creates a new template with the name and parse tree
   214  // and associates it with t.
   215  //
   216  // It returns an error if t or any associated template has already been executed.
   217  func (t *Template) AddParseTree(name string, tree *parse.Tree) (*Template, error) {
   218  	if err := t.checkCanParse(); err != nil {
   219  		return nil, err
   220  	}
   221  
   222  	t.nameSpace.mu.Lock()
   223  	defer t.nameSpace.mu.Unlock()
   224  	text, err := t.text.AddParseTree(name, tree)
   225  	if err != nil {
   226  		return nil, err
   227  	}
   228  	ret := &Template{
   229  		nil,
   230  		text,
   231  		text.Tree,
   232  		t.nameSpace,
   233  	}
   234  	t.set[name] = ret
   235  	return ret, nil
   236  }
   237  
   238  // Clone returns a duplicate of the template, including all associated
   239  // templates. The actual representation is not copied, but the name space of
   240  // associated templates is, so further calls to Parse in the copy will add
   241  // templates to the copy but not to the original. Clone can be used to prepare
   242  // common templates and use them with variant definitions for other templates
   243  // by adding the variants after the clone is made.
   244  //
   245  // It returns an error if t has already been executed.
   246  func (t *Template) Clone() (*Template, error) {
   247  	t.nameSpace.mu.Lock()
   248  	defer t.nameSpace.mu.Unlock()
   249  	if t.escapeErr != nil {
   250  		return nil, fmt.Errorf("html/template: cannot Clone %q after it has executed", t.Name())
   251  	}
   252  	textClone, err := t.text.Clone()
   253  	if err != nil {
   254  		return nil, err
   255  	}
   256  	ns := &nameSpace{set: make(map[string]*Template)}
   257  	ns.esc = makeEscaper(ns)
   258  	ret := &Template{
   259  		nil,
   260  		textClone,
   261  		textClone.Tree,
   262  		ns,
   263  	}
   264  	ret.set[ret.Name()] = ret
   265  	for _, x := range textClone.Templates() {
   266  		name := x.Name()
   267  		src := t.set[name]
   268  		if src == nil || src.escapeErr != nil {
   269  			return nil, fmt.Errorf("html/template: cannot Clone %q after it has executed", t.Name())
   270  		}
   271  		x.Tree = x.Tree.Copy()
   272  		ret.set[name] = &Template{
   273  			nil,
   274  			x,
   275  			x.Tree,
   276  			ret.nameSpace,
   277  		}
   278  	}
   279  	// Return the template associated with the name of this template.
   280  	return ret.set[ret.Name()], nil
   281  }
   282  
   283  // New allocates a new HTML template with the given name.
   284  func New(name string) *Template {
   285  	ns := &nameSpace{set: make(map[string]*Template)}
   286  	ns.esc = makeEscaper(ns)
   287  	tmpl := &Template{
   288  		nil,
   289  		template.New(name),
   290  		nil,
   291  		ns,
   292  	}
   293  	tmpl.set[name] = tmpl
   294  	return tmpl
   295  }
   296  
   297  // New allocates a new HTML template associated with the given one
   298  // and with the same delimiters. The association, which is transitive,
   299  // allows one template to invoke another with a {{template}} action.
   300  //
   301  // If a template with the given name already exists, the new HTML template
   302  // will replace it. The existing template will be reset and disassociated with
   303  // t.
   304  func (t *Template) New(name string) *Template {
   305  	t.nameSpace.mu.Lock()
   306  	defer t.nameSpace.mu.Unlock()
   307  	return t.new(name)
   308  }
   309  
   310  // new is the implementation of New, without the lock.
   311  func (t *Template) new(name string) *Template {
   312  	tmpl := &Template{
   313  		nil,
   314  		t.text.New(name),
   315  		nil,
   316  		t.nameSpace,
   317  	}
   318  	if existing, ok := tmpl.set[name]; ok {
   319  		emptyTmpl := New(existing.Name())
   320  		*existing = *emptyTmpl
   321  	}
   322  	tmpl.set[name] = tmpl
   323  	return tmpl
   324  }
   325  
   326  // Name returns the name of the template.
   327  func (t *Template) Name() string {
   328  	return t.text.Name()
   329  }
   330  
   331  // FuncMap is the type of the map defining the mapping from names to
   332  // functions. Each function must have either a single return value, or two
   333  // return values of which the second has type error. In that case, if the
   334  // second (error) argument evaluates to non-nil during execution, execution
   335  // terminates and Execute returns that error. FuncMap has the same base type
   336  // as FuncMap in "text/template", copied here so clients need not import
   337  // "text/template".
   338  type FuncMap map[string]interface{}
   339  
   340  // Funcs adds the elements of the argument map to the template's function map.
   341  // It must be called before the template is parsed.
   342  // It panics if a value in the map is not a function with appropriate return
   343  // type. However, it is legal to overwrite elements of the map. The return
   344  // value is the template, so calls can be chained.
   345  func (t *Template) Funcs(funcMap FuncMap) *Template {
   346  	t.text.Funcs(template.FuncMap(funcMap))
   347  	return t
   348  }
   349  
   350  // Delims sets the action delimiters to the specified strings, to be used in
   351  // subsequent calls to Parse, ParseFiles, or ParseGlob. Nested template
   352  // definitions will inherit the settings. An empty delimiter stands for the
   353  // corresponding default: {{ or }}.
   354  // The return value is the template, so calls can be chained.
   355  func (t *Template) Delims(left, right string) *Template {
   356  	t.text.Delims(left, right)
   357  	return t
   358  }
   359  
   360  // Lookup returns the template with the given name that is associated with t,
   361  // or nil if there is no such template.
   362  func (t *Template) Lookup(name string) *Template {
   363  	t.nameSpace.mu.Lock()
   364  	defer t.nameSpace.mu.Unlock()
   365  	return t.set[name]
   366  }
   367  
   368  // Must is a helper that wraps a call to a function returning (*Template, error)
   369  // and panics if the error is non-nil. It is intended for use in variable initializations
   370  // such as
   371  //	var t = template.Must(template.New("name").Parse("html"))
   372  func Must(t *Template, err error) *Template {
   373  	if err != nil {
   374  		panic(err)
   375  	}
   376  	return t
   377  }
   378  
   379  // ParseFiles creates a new Template and parses the template definitions from
   380  // the named files. The returned template's name will have the (base) name and
   381  // (parsed) contents of the first file. There must be at least one file.
   382  // If an error occurs, parsing stops and the returned *Template is nil.
   383  //
   384  // When parsing multiple files with the same name in different directories,
   385  // the last one mentioned will be the one that results.
   386  // For instance, ParseFiles("a/foo", "b/foo") stores "b/foo" as the template
   387  // named "foo", while "a/foo" is unavailable.
   388  func ParseFiles(filenames ...string) (*Template, error) {
   389  	return parseFiles(nil, readFileOS, filenames...)
   390  }
   391  
   392  // ParseFiles parses the named files and associates the resulting templates with
   393  // t. If an error occurs, parsing stops and the returned template is nil;
   394  // otherwise it is t. There must be at least one file.
   395  //
   396  // When parsing multiple files with the same name in different directories,
   397  // the last one mentioned will be the one that results.
   398  //
   399  // ParseFiles returns an error if t or any associated template has already been executed.
   400  func (t *Template) ParseFiles(filenames ...string) (*Template, error) {
   401  	return parseFiles(t, readFileOS, filenames...)
   402  }
   403  
   404  // parseFiles is the helper for the method and function. If the argument
   405  // template is nil, it is created from the first file.
   406  func parseFiles(t *Template, readFile func(string) (string, []byte, error), filenames ...string) (*Template, error) {
   407  	if err := t.checkCanParse(); err != nil {
   408  		return nil, err
   409  	}
   410  
   411  	if len(filenames) == 0 {
   412  		// Not really a problem, but be consistent.
   413  		return nil, fmt.Errorf("html/template: no files named in call to ParseFiles")
   414  	}
   415  	for _, filename := range filenames {
   416  		name, b, err := readFile(filename)
   417  		if err != nil {
   418  			return nil, err
   419  		}
   420  		s := string(b)
   421  		// First template becomes return value if not already defined,
   422  		// and we use that one for subsequent New calls to associate
   423  		// all the templates together. Also, if this file has the same name
   424  		// as t, this file becomes the contents of t, so
   425  		//  t, err := New(name).Funcs(xxx).ParseFiles(name)
   426  		// works. Otherwise we create a new template associated with t.
   427  		var tmpl *Template
   428  		if t == nil {
   429  			t = New(name)
   430  		}
   431  		if name == t.Name() {
   432  			tmpl = t
   433  		} else {
   434  			tmpl = t.New(name)
   435  		}
   436  		_, err = tmpl.Parse(s)
   437  		if err != nil {
   438  			return nil, err
   439  		}
   440  	}
   441  	return t, nil
   442  }
   443  
   444  // ParseGlob creates a new Template and parses the template definitions from
   445  // the files identified by the pattern. The files are matched according to the
   446  // semantics of filepath.Match, and the pattern must match at least one file.
   447  // The returned template will have the (base) name and (parsed) contents of the
   448  // first file matched by the pattern. ParseGlob is equivalent to calling
   449  // ParseFiles with the list of files matched by the pattern.
   450  //
   451  // When parsing multiple files with the same name in different directories,
   452  // the last one mentioned will be the one that results.
   453  func ParseGlob(pattern string) (*Template, error) {
   454  	return parseGlob(nil, pattern)
   455  }
   456  
   457  // ParseGlob parses the template definitions in the files identified by the
   458  // pattern and associates the resulting templates with t. The files are matched
   459  // according to the semantics of filepath.Match, and the pattern must match at
   460  // least one file. ParseGlob is equivalent to calling t.ParseFiles with the
   461  // list of files matched by the pattern.
   462  //
   463  // When parsing multiple files with the same name in different directories,
   464  // the last one mentioned will be the one that results.
   465  //
   466  // ParseGlob returns an error if t or any associated template has already been executed.
   467  func (t *Template) ParseGlob(pattern string) (*Template, error) {
   468  	return parseGlob(t, pattern)
   469  }
   470  
   471  // parseGlob is the implementation of the function and method ParseGlob.
   472  func parseGlob(t *Template, pattern string) (*Template, error) {
   473  	if err := t.checkCanParse(); err != nil {
   474  		return nil, err
   475  	}
   476  	filenames, err := filepath.Glob(pattern)
   477  	if err != nil {
   478  		return nil, err
   479  	}
   480  	if len(filenames) == 0 {
   481  		return nil, fmt.Errorf("html/template: pattern matches no files: %#q", pattern)
   482  	}
   483  	return parseFiles(t, readFileOS, filenames...)
   484  }
   485  
   486  // IsTrue reports whether the value is 'true', in the sense of not the zero of its type,
   487  // and whether the value has a meaningful truth value. This is the definition of
   488  // truth used by if and other such actions.
   489  func IsTrue(val interface{}) (truth, ok bool) {
   490  	return template.IsTrue(val)
   491  }
   492  
   493  // ParseFS is like ParseFiles or ParseGlob but reads from the file system fs
   494  // instead of the host operating system's file system.
   495  // It accepts a list of glob patterns.
   496  // (Note that most file names serve as glob patterns matching only themselves.)
   497  func ParseFS(fs fs.FS, patterns ...string) (*Template, error) {
   498  	return parseFS(nil, fs, patterns)
   499  }
   500  
   501  // ParseFS is like ParseFiles or ParseGlob but reads from the file system fs
   502  // instead of the host operating system's file system.
   503  // It accepts a list of glob patterns.
   504  // (Note that most file names serve as glob patterns matching only themselves.)
   505  func (t *Template) ParseFS(fs fs.FS, patterns ...string) (*Template, error) {
   506  	return parseFS(t, fs, patterns)
   507  }
   508  
   509  func parseFS(t *Template, fsys fs.FS, patterns []string) (*Template, error) {
   510  	var filenames []string
   511  	for _, pattern := range patterns {
   512  		list, err := fs.Glob(fsys, pattern)
   513  		if err != nil {
   514  			return nil, err
   515  		}
   516  		if len(list) == 0 {
   517  			return nil, fmt.Errorf("template: pattern matches no files: %#q", pattern)
   518  		}
   519  		filenames = append(filenames, list...)
   520  	}
   521  	return parseFiles(t, readFileFS(fsys), filenames...)
   522  }
   523  
   524  func readFileOS(file string) (name string, b []byte, err error) {
   525  	name = filepath.Base(file)
   526  	b, err = os.ReadFile(file)
   527  	return
   528  }
   529  
   530  func readFileFS(fsys fs.FS) func(string) (string, []byte, error) {
   531  	return func(file string) (name string, b []byte, err error) {
   532  		name = path.Base(file)
   533  		b, err = fs.ReadFile(fsys, file)
   534  		return
   535  	}
   536  }
   537  

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