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read.go
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read.go
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// Copyright 2012 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 build
import (
"bufio"
"errors"
"io"
)
type importReader struct {
b *bufio.Reader
buf []byte
peek byte
err error
eof bool
nerr int
}
func isIdent(c byte) bool {
return 'A' <= c && c <= 'Z' || 'a' <= c && c <= 'z' || '0' <= c && c <= '9' || c == '_' || c >= 0x80
}
var (
errSyntax = errors.New("syntax error")
errNUL = errors.New("unexpected NUL in input")
)
// syntaxError records a syntax error, but only if an I/O error has not already been recorded.
func (r *importReader) syntaxError() {
if r.err == nil {
r.err = errSyntax
}
}
// readByte reads the next byte from the input, saves it in buf, and returns it.
// If an error occurs, readByte records the error in r.err and returns 0.
func (r *importReader) readByte() byte {
c, err := r.b.ReadByte()
if err == nil {
r.buf = append(r.buf, c)
if c == 0 {
err = errNUL
}
}
if err != nil {
if err == io.EOF {
r.eof = true
} else if r.err == nil {
r.err = err
}
c = 0
}
return c
}
// peekByte returns the next byte from the input reader but does not advance beyond it.
// If skipSpace is set, peekByte skips leading spaces and comments.
func (r *importReader) peekByte(skipSpace bool) byte {
if r.err != nil {
if r.nerr++; r.nerr > 10000 {
panic("go/build: import reader looping")
}
return 0
}
// Use r.peek as first input byte.
// Don't just return r.peek here: it might have been left by peekByte(false)
// and this might be peekByte(true).
c := r.peek
if c == 0 {
c = r.readByte()
}
for r.err == nil && !r.eof {
if skipSpace {
// For the purposes of this reader, semicolons are never necessary to
// understand the input and are treated as spaces.
switch c {
case ' ', '\f', '\t', '\r', '\n', ';':
c = r.readByte()
continue
case '/':
c = r.readByte()
if c == '/' {
for c != '\n' && r.err == nil && !r.eof {
c = r.readByte()
}
} else if c == '*' {
var c1 byte
for (c != '*' || c1 != '/') && r.err == nil {
if r.eof {
r.syntaxError()
}
c, c1 = c1, r.readByte()
}
} else {
r.syntaxError()
}
c = r.readByte()
continue
}
}
break
}
r.peek = c
return r.peek
}
// nextByte is like peekByte but advances beyond the returned byte.
func (r *importReader) nextByte(skipSpace bool) byte {
c := r.peekByte(skipSpace)
r.peek = 0
return c
}
// readKeyword reads the given keyword from the input.
// If the keyword is not present, readKeyword records a syntax error.
func (r *importReader) readKeyword(kw string) {
r.peekByte(true)
for i := 0; i < len(kw); i++ {
if r.nextByte(false) != kw[i] {
r.syntaxError()
return
}
}
if isIdent(r.peekByte(false)) {
r.syntaxError()
}
}
// readIdent reads an identifier from the input.
// If an identifier is not present, readIdent records a syntax error.
func (r *importReader) readIdent() {
c := r.peekByte(true)
if !isIdent(c) {
r.syntaxError()
return
}
for isIdent(r.peekByte(false)) {
r.peek = 0
}
}
// readString reads a quoted string literal from the input.
// If an identifier is not present, readString records a syntax error.
func (r *importReader) readString(save *[]string) {
switch r.nextByte(true) {
case '`':
start := len(r.buf) - 1
for r.err == nil {
if r.nextByte(false) == '`' {
if save != nil {
*save = append(*save, string(r.buf[start:]))
}
break
}
if r.eof {
r.syntaxError()
}
}
case '"':
start := len(r.buf) - 1
for r.err == nil {
c := r.nextByte(false)
if c == '"' {
if save != nil {
*save = append(*save, string(r.buf[start:]))
}
break
}
if r.eof || c == '\n' {
r.syntaxError()
}
if c == '\\' {
r.nextByte(false)
}
}
default:
r.syntaxError()
}
}
// readImport reads an import clause - optional identifier followed by quoted string -
// from the input.
func (r *importReader) readImport(imports *[]string) {
c := r.peekByte(true)
if c == '.' {
r.peek = 0
} else if isIdent(c) {
r.readIdent()
}
r.readString(imports)
}
// readComments is like ioutil.ReadAll, except that it only reads the leading
// block of comments in the file.
func readComments(f io.Reader) ([]byte, error) {
r := &importReader{b: bufio.NewReader(f)}
r.peekByte(true)
if r.err == nil && !r.eof {
// Didn't reach EOF, so must have found a non-space byte. Remove it.
r.buf = r.buf[:len(r.buf)-1]
}
return r.buf, r.err
}
// readImports is like ioutil.ReadAll, except that it expects a Go file as input
// and stops reading the input once the imports have completed.
func readImports(f io.Reader, reportSyntaxError bool, imports *[]string) ([]byte, error) {
r := &importReader{b: bufio.NewReader(f)}
r.readKeyword("package")
r.readIdent()
for r.peekByte(true) == 'i' {
r.readKeyword("import")
if r.peekByte(true) == '(' {
r.nextByte(false)
for r.peekByte(true) != ')' && r.err == nil {
r.readImport(imports)
}
r.nextByte(false)
} else {
r.readImport(imports)
}
}
// If we stopped successfully before EOF, we read a byte that told us we were done.
// Return all but that last byte, which would cause a syntax error if we let it through.
if r.err == nil && !r.eof {
return r.buf[:len(r.buf)-1], nil
}
// If we stopped for a syntax error, consume the whole file so that
// we are sure we don't change the errors that go/parser returns.
if r.err == errSyntax && !reportSyntaxError {
r.err = nil
for r.err == nil && !r.eof {
r.readByte()
}
}
return r.buf, r.err
}