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+// 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.
+
+// Code to parse a template.
+
+package template
+
+import (
+ "fmt"
+ "io"
+ "io/ioutil"
+ "os"
+ "reflect"
+ "strconv"
+ "strings"
+ "unicode"
+ "utf8"
+)
+
+// Errors returned during parsing and execution. Users may extract the information and reformat
+// if they desire.
+type Error struct {
+ Line int
+ Msg string
+}
+
+func (e *Error) String() string { return fmt.Sprintf("line %d: %s", e.Line, e.Msg) }
+
+// checkError is a deferred function to turn a panic with type *Error into a plain error return.
+// Other panics are unexpected and so are re-enabled.
+func checkError(error *os.Error) {
+ if v := recover(); v != nil {
+ if e, ok := v.(*Error); ok {
+ *error = e
+ } else {
+ // runtime errors should crash
+ panic(v)
+ }
+ }
+}
+
+// Most of the literals are aces.
+var lbrace = []byte{'{'}
+var rbrace = []byte{'}'}
+var space = []byte{' '}
+var tab = []byte{'\t'}
+
+// The various types of "tokens", which are plain text or (usually) brace-delimited descriptors
+const (
+ tokAlternates = iota
+ tokComment
+ tokEnd
+ tokLiteral
+ tokOr
+ tokRepeated
+ tokSection
+ tokText
+ tokVariable
+)
+
+// FormatterMap is the type describing the mapping from formatter
+// names to the functions that implement them.
+type FormatterMap map[string]func(io.Writer, string, ...interface{})
+
+// Built-in formatters.
+var builtins = FormatterMap{
+ "html": HTMLFormatter,
+ "str": StringFormatter,
+ "": StringFormatter,
+}
+
+// The parsed state of a template is a vector of xxxElement structs.
+// Sections have line numbers so errors can be reported better during execution.
+
+// Plain text.
+type textElement struct {
+ text []byte
+}
+
+// A literal such as .meta-left or .meta-right
+type literalElement struct {
+ text []byte
+}
+
+// A variable invocation to be evaluated
+type variableElement struct {
+ linenum int
+ args []interface{} // The fields and literals in the invocation.
+ fmts []string // Names of formatters to apply. len(fmts) > 0
+}
+
+// A variableElement arg to be evaluated as a field name
+type fieldName string
+
+// A .section block, possibly with a .or
+type sectionElement struct {
+ linenum int // of .section itself
+ field string // cursor field for this block
+ start int // first element
+ or int // first element of .or block
+ end int // one beyond last element
+}
+
+// A .repeated block, possibly with a .or and a .alternates
+type repeatedElement struct {
+ sectionElement // It has the same structure...
+ altstart int // ... except for alternates
+ altend int
+}
+
+// Template is the type that represents a template definition.
+// It is unchanged after parsing.
+type Template struct {
+ fmap FormatterMap // formatters for variables
+ // Used during parsing:
+ ldelim, rdelim []byte // delimiters; default {}
+ buf []byte // input text to process
+ p int // position in buf
+ linenum int // position in input
+ // Parsed results:
+ elems []interface{}
+}
+
+// New creates a new template with the specified formatter map (which
+// may be nil) to define auxiliary functions for formatting variables.
+func New(fmap FormatterMap) *Template {
+ t := new(Template)
+ t.fmap = fmap
+ t.ldelim = lbrace
+ t.rdelim = rbrace
+ t.elems = make([]interface{}, 0, 16)
+ return t
+}
+
+// Report error and stop executing. The line number must be provided explicitly.
+func (t *Template) execError(st *state, line int, err string, args ...interface{}) {
+ panic(&Error{line, fmt.Sprintf(err, args...)})
+}
+
+// Report error, panic to terminate parsing.
+// The line number comes from the template state.
+func (t *Template) parseError(err string, args ...interface{}) {
+ panic(&Error{t.linenum, fmt.Sprintf(err, args...)})
+}
+
+// Is this an exported - upper case - name?
+func isExported(name string) bool {
+ rune, _ := utf8.DecodeRuneInString(name)
+ return unicode.IsUpper(rune)
+}
+
+// -- Lexical analysis
+
+// Is c a space character?
+func isSpace(c uint8) bool { return c == ' ' || c == '\t' || c == '\r' || c == '\n' }
+
+// Safely, does s[n:n+len(t)] == t?
+func equal(s []byte, n int, t []byte) bool {
+ b := s[n:]
+ if len(t) > len(b) { // not enough space left for a match.
+ return false
+ }
+ for i, c := range t {
+ if c != b[i] {
+ return false
+ }
+ }
+ return true
+}
+
+// isQuote returns true if c is a string- or character-delimiting quote character.
+func isQuote(c byte) bool {
+ return c == '"' || c == '`' || c == '\''
+}
+
+// endQuote returns the end quote index for the quoted string that
+// starts at n, or -1 if no matching end quote is found before the end
+// of the line.
+func endQuote(s []byte, n int) int {
+ quote := s[n]
+ for n++; n < len(s); n++ {
+ switch s[n] {
+ case '\\':
+ if quote == '"' || quote == '\'' {
+ n++
+ }
+ case '\n':
+ return -1
+ case quote:
+ return n
+ }
+ }
+ return -1
+}
+
+// nextItem returns the next item from the input buffer. If the returned
+// item is empty, we are at EOF. The item will be either a
+// delimited string or a non-empty string between delimited
+// strings. Tokens stop at (but include, if plain text) a newline.
+// Action tokens on a line by themselves drop any space on
+// either side, up to and including the newline.
+func (t *Template) nextItem() []byte {
+ startOfLine := t.p == 0 || t.buf[t.p-1] == '\n'
+ start := t.p
+ var i int
+ newline := func() {
+ t.linenum++
+ i++
+ }
+ // Leading space up to but not including newline
+ for i = start; i < len(t.buf); i++ {
+ if t.buf[i] == '\n' || !isSpace(t.buf[i]) {
+ break
+ }
+ }
+ leadingSpace := i > start
+ // What's left is nothing, newline, delimited string, or plain text
+ switch {
+ case i == len(t.buf):
+ // EOF; nothing to do
+ case t.buf[i] == '\n':
+ newline()
+ case equal(t.buf, i, t.ldelim):
+ left := i // Start of left delimiter.
+ right := -1 // Will be (immediately after) right delimiter.
+ haveText := false // Delimiters contain text.
+ i += len(t.ldelim)
+ // Find the end of the action.
+ for ; i < len(t.buf); i++ {
+ if t.buf[i] == '\n' {
+ break
+ }
+ if isQuote(t.buf[i]) {
+ i = endQuote(t.buf, i)
+ if i == -1 {
+ t.parseError("unmatched quote")
+ return nil
+ }
+ continue
+ }
+ if equal(t.buf, i, t.rdelim) {
+ i += len(t.rdelim)
+ right = i
+ break
+ }
+ haveText = true
+ }
+ if right < 0 {
+ t.parseError("unmatched opening delimiter")
+ return nil
+ }
+ // Is this a special action (starts with '.' or '#') and the only thing on the line?
+ if startOfLine && haveText {
+ firstChar := t.buf[left+len(t.ldelim)]
+ if firstChar == '.' || firstChar == '#' {
+ // It's special and the first thing on the line. Is it the last?
+ for j := right; j < len(t.buf) && isSpace(t.buf[j]); j++ {
+ if t.buf[j] == '\n' {
+ // Yes it is. Drop the surrounding space and return the {.foo}
+ t.linenum++
+ t.p = j + 1
+ return t.buf[left:right]
+ }
+ }
+ }
+ }
+ // No it's not. If there's leading space, return that.
+ if leadingSpace {
+ // not trimming space: return leading space if there is some.
+ t.p = left
+ return t.buf[start:left]
+ }
+ // Return the word, leave the trailing space.
+ start = left
+ break
+ default:
+ for ; i < len(t.buf); i++ {
+ if t.buf[i] == '\n' {
+ newline()
+ break
+ }
+ if equal(t.buf, i, t.ldelim) {
+ break
+ }
+ }
+ }
+ item := t.buf[start:i]
+ t.p = i
+ return item
+}
+
+// Turn a byte array into a space-split array of strings,
+// taking into account quoted strings.
+func words(buf []byte) []string {
+ s := make([]string, 0, 5)
+ for i := 0; i < len(buf); {
+ // One word per loop
+ for i < len(buf) && isSpace(buf[i]) {
+ i++
+ }
+ if i == len(buf) {
+ break
+ }
+ // Got a word
+ start := i
+ if isQuote(buf[i]) {
+ i = endQuote(buf, i)
+ if i < 0 {
+ i = len(buf)
+ } else {
+ i++
+ }
+ }
+ // Even with quotes, break on space only. This handles input
+ // such as {""|} and catches quoting mistakes.
+ for i < len(buf) && !isSpace(buf[i]) {
+ i++
+ }
+ s = append(s, string(buf[start:i]))
+ }
+ return s
+}
+
+// Analyze an item and return its token type and, if it's an action item, an array of
+// its constituent words.
+func (t *Template) analyze(item []byte) (tok int, w []string) {
+ // item is known to be non-empty
+ if !equal(item, 0, t.ldelim) { // doesn't start with left delimiter
+ tok = tokText
+ return
+ }
+ if !equal(item, len(item)-len(t.rdelim), t.rdelim) { // doesn't end with right delimiter
+ t.parseError("internal error: unmatched opening delimiter") // lexing should prevent this
+ return
+ }
+ if len(item) <= len(t.ldelim)+len(t.rdelim) { // no contents
+ t.parseError("empty directive")
+ return
+ }
+ // Comment
+ if item[len(t.ldelim)] == '#' {
+ tok = tokComment
+ return
+ }
+ // Split into words
+ w = words(item[len(t.ldelim) : len(item)-len(t.rdelim)]) // drop final delimiter
+ if len(w) == 0 {
+ t.parseError("empty directive")
+ return
+ }
+ first := w[0]
+ if first[0] != '.' {
+ tok = tokVariable
+ return
+ }
+ if len(first) > 1 && first[1] >= '0' && first[1] <= '9' {
+ // Must be a float.
+ tok = tokVariable
+ return
+ }
+ switch first {
+ case ".meta-left", ".meta-right", ".space", ".tab":
+ tok = tokLiteral
+ return
+ case ".or":
+ tok = tokOr
+ return
+ case ".end":
+ tok = tokEnd
+ return
+ case ".section":
+ if len(w) != 2 {
+ t.parseError("incorrect fields for .section: %s", item)
+ return
+ }
+ tok = tokSection
+ return
+ case ".repeated":
+ if len(w) != 3 || w[1] != "section" {
+ t.parseError("incorrect fields for .repeated: %s", item)
+ return
+ }
+ tok = tokRepeated
+ return
+ case ".alternates":
+ if len(w) != 2 || w[1] != "with" {
+ t.parseError("incorrect fields for .alternates: %s", item)
+ return
+ }
+ tok = tokAlternates
+ return
+ }
+ t.parseError("bad directive: %s", item)
+ return
+}
+
+// formatter returns the Formatter with the given name in the Template, or nil if none exists.
+func (t *Template) formatter(name string) func(io.Writer, string, ...interface{}) {
+ if t.fmap != nil {
+ if fn := t.fmap[name]; fn != nil {
+ return fn
+ }
+ }
+ return builtins[name]
+}
+
+// -- Parsing
+
+// newVariable allocates a new variable-evaluation element.
+func (t *Template) newVariable(words []string) *variableElement {
+ formatters := extractFormatters(words)
+ args := make([]interface{}, len(words))
+
+ // Build argument list, processing any literals
+ for i, word := range words {
+ var lerr os.Error
+ switch word[0] {
+ case '"', '`', '\'':
+ v, err := strconv.Unquote(word)
+ if err == nil && word[0] == '\'' {
+ args[i] = []int(v)[0]
+ } else {
+ args[i], lerr = v, err
+ }
+
+ case '.', '+', '-', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
+ v, err := strconv.Btoi64(word, 0)
+ if err == nil {
+ args[i] = v
+ } else {
+ v, err := strconv.Atof64(word)
+ args[i], lerr = v, err
+ }
+
+ default:
+ args[i] = fieldName(word)
+ }
+ if lerr != nil {
+ t.parseError("invalid literal: %q: %s", word, lerr)
+ }
+ }
+
+ // We could remember the function address here and avoid the lookup later,
+ // but it's more dynamic to let the user change the map contents underfoot.
+ // We do require the name to be present, though.
+
+ // Is it in user-supplied map?
+ for _, f := range formatters {
+ if t.formatter(f) == nil {
+ t.parseError("unknown formatter: %q", f)
+ }
+ }
+
+ return &variableElement{t.linenum, args, formatters}
+}
+
+// extractFormatters extracts a list of formatters from words.
+// After the final space-separated argument in a variable, formatters may be
+// specified separated by pipe symbols. For example: {a b c|d|e}
+// The words parameter still has the formatters joined by '|' in the last word.
+// extractFormatters splits formatters, replaces the last word with the content
+// found before the first '|' within it, and returns the formatters obtained.
+// If no formatters are found in words, the default formatter is returned.
+func extractFormatters(words []string) (formatters []string) {
+ // "" is the default formatter.
+ formatters = []string{""}
+ if len(words) == 0 {
+ return
+ }
+ var bar int
+ lastWord := words[len(words)-1]
+ if isQuote(lastWord[0]) {
+ end := endQuote([]byte(lastWord), 0)
+ if end < 0 || end+1 == len(lastWord) || lastWord[end+1] != '|' {
+ return
+ }
+ bar = end + 1
+ } else {
+ bar = strings.IndexRune(lastWord, '|')
+ if bar < 0 {
+ return
+ }
+ }
+ words[len(words)-1] = lastWord[0:bar]
+ formatters = strings.Split(lastWord[bar+1:], "|")
+ return
+}
+
+// Grab the next item. If it's simple, just append it to the template.
+// Otherwise return its details.
+func (t *Template) parseSimple(item []byte) (done bool, tok int, w []string) {
+ tok, w = t.analyze(item)
+ done = true // assume for simplicity
+ switch tok {
+ case tokComment:
+ return
+ case tokText:
+ t.elems = append(t.elems, &textElement{item})
+ return
+ case tokLiteral:
+ switch w[0] {
+ case ".meta-left":
+ t.elems = append(t.elems, &literalElement{t.ldelim})
+ case ".meta-right":
+ t.elems = append(t.elems, &literalElement{t.rdelim})
+ case ".space":
+ t.elems = append(t.elems, &literalElement{space})
+ case ".tab":
+ t.elems = append(t.elems, &literalElement{tab})
+ default:
+ t.parseError("internal error: unknown literal: %s", w[0])
+ }
+ return
+ case tokVariable:
+ t.elems = append(t.elems, t.newVariable(w))
+ return
+ }
+ return false, tok, w
+}
+
+// parseRepeated and parseSection are mutually recursive
+
+func (t *Template) parseRepeated(words []string) *repeatedElement {
+ r := new(repeatedElement)
+ t.elems = append(t.elems, r)
+ r.linenum = t.linenum
+ r.field = words[2]
+ // Scan section, collecting true and false (.or) blocks.
+ r.start = len(t.elems)
+ r.or = -1
+ r.altstart = -1
+ r.altend = -1
+Loop:
+ for {
+ item := t.nextItem()
+ if len(item) == 0 {
+ t.parseError("missing .end for .repeated section")
+ break
+ }
+ done, tok, w := t.parseSimple(item)
+ if done {
+ continue
+ }
+ switch tok {
+ case tokEnd:
+ break Loop
+ case tokOr:
+ if r.or >= 0 {
+ t.parseError("extra .or in .repeated section")
+ break Loop
+ }
+ r.altend = len(t.elems)
+ r.or = len(t.elems)
+ case tokSection:
+ t.parseSection(w)
+ case tokRepeated:
+ t.parseRepeated(w)
+ case tokAlternates:
+ if r.altstart >= 0 {
+ t.parseError("extra .alternates in .repeated section")
+ break Loop
+ }
+ if r.or >= 0 {
+ t.parseError(".alternates inside .or block in .repeated section")
+ break Loop
+ }
+ r.altstart = len(t.elems)
+ default:
+ t.parseError("internal error: unknown repeated section item: %s", item)
+ break Loop
+ }
+ }
+ if r.altend < 0 {
+ r.altend = len(t.elems)
+ }
+ r.end = len(t.elems)
+ return r
+}
+
+func (t *Template) parseSection(words []string) *sectionElement {
+ s := new(sectionElement)
+ t.elems = append(t.elems, s)
+ s.linenum = t.linenum
+ s.field = words[1]
+ // Scan section, collecting true and false (.or) blocks.
+ s.start = len(t.elems)
+ s.or = -1
+Loop:
+ for {
+ item := t.nextItem()
+ if len(item) == 0 {
+ t.parseError("missing .end for .section")
+ break
+ }
+ done, tok, w := t.parseSimple(item)
+ if done {
+ continue
+ }
+ switch tok {
+ case tokEnd:
+ break Loop
+ case tokOr:
+ if s.or >= 0 {
+ t.parseError("extra .or in .section")
+ break Loop
+ }
+ s.or = len(t.elems)
+ case tokSection:
+ t.parseSection(w)
+ case tokRepeated:
+ t.parseRepeated(w)
+ case tokAlternates:
+ t.parseError(".alternates not in .repeated")
+ default:
+ t.parseError("internal error: unknown section item: %s", item)
+ }
+ }
+ s.end = len(t.elems)
+ return s
+}
+
+func (t *Template) parse() {
+ for {
+ item := t.nextItem()
+ if len(item) == 0 {
+ break
+ }
+ done, tok, w := t.parseSimple(item)
+ if done {
+ continue
+ }
+ switch tok {
+ case tokOr, tokEnd, tokAlternates:
+ t.parseError("unexpected %s", w[0])
+ case tokSection:
+ t.parseSection(w)
+ case tokRepeated:
+ t.parseRepeated(w)
+ default:
+ t.parseError("internal error: bad directive in parse: %s", item)
+ }
+ }
+}
+
+// -- Execution
+
+// -- Public interface
+
+// Parse initializes a Template by parsing its definition. The string
+// s contains the template text. If any errors occur, Parse returns
+// the error.
+func (t *Template) Parse(s string) (err os.Error) {
+ if t.elems == nil {
+ return &Error{1, "template not allocated with New"}
+ }
+ if !validDelim(t.ldelim) || !validDelim(t.rdelim) {
+ return &Error{1, fmt.Sprintf("bad delimiter strings %q %q", t.ldelim, t.rdelim)}
+ }
+ defer checkError(&err)
+ t.buf = []byte(s)
+ t.p = 0
+ t.linenum = 1
+ t.parse()
+ return nil
+}
+
+// ParseFile is like Parse but reads the template definition from the
+// named file.
+func (t *Template) ParseFile(filename string) (err os.Error) {
+ b, err := ioutil.ReadFile(filename)
+ if err != nil {
+ return err
+ }
+ return t.Parse(string(b))
+}
+
+// Execute applies a parsed template to the specified data object,
+// generating output to wr.
+func (t *Template) Execute(wr io.Writer, data interface{}) (err os.Error) {
+ // Extract the driver data.
+ val := reflect.ValueOf(data)
+ defer checkError(&err)
+ t.p = 0
+ t.execute(0, len(t.elems), &state{parent: nil, data: val, wr: wr})
+ return nil
+}
+
+// SetDelims sets the left and right delimiters for operations in the
+// template. They are validated during parsing. They could be
+// validated here but it's better to keep the routine simple. The
+// delimiters are very rarely invalid and Parse has the necessary
+// error-handling interface already.
+func (t *Template) SetDelims(left, right string) {
+ t.ldelim = []byte(left)
+ t.rdelim = []byte(right)
+}
+
+// Parse creates a Template with default parameters (such as {} for
+// metacharacters). The string s contains the template text while
+// the formatter map fmap, which may be nil, defines auxiliary functions
+// for formatting variables. The template is returned. If any errors
+// occur, err will be non-nil.
+func Parse(s string, fmap FormatterMap) (t *Template, err os.Error) {
+ t = New(fmap)
+ err = t.Parse(s)
+ if err != nil {
+ t = nil
+ }
+ return
+}
+
+// ParseFile is a wrapper function that creates a Template with default
+// parameters (such as {} for metacharacters). The filename identifies
+// a file containing the template text, while the formatter map fmap, which
+// may be nil, defines auxiliary functions for formatting variables.
+// The template is returned. If any errors occur, err will be non-nil.
+func ParseFile(filename string, fmap FormatterMap) (t *Template, err os.Error) {
+ b, err := ioutil.ReadFile(filename)
+ if err != nil {
+ return nil, err
+ }
+ return Parse(string(b), fmap)
+}
+
+// MustParse is like Parse but panics if the template cannot be parsed.
+func MustParse(s string, fmap FormatterMap) *Template {
+ t, err := Parse(s, fmap)
+ if err != nil {
+ panic("template.MustParse error: " + err.String())
+ }
+ return t
+}
+
+// MustParseFile is like ParseFile but panics if the file cannot be read
+// or the template cannot be parsed.
+func MustParseFile(filename string, fmap FormatterMap) *Template {
+ b, err := ioutil.ReadFile(filename)
+ if err != nil {
+ panic("template.MustParseFile error: " + err.String())
+ }
+ return MustParse(string(b), fmap)
+}
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