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// Copyright 2010 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 textproto
import (
"bufio"
"bytes"
"fmt"
"io"
"strconv"
"strings"
"sync"
)
// A Reader implements convenience methods for reading requests
// or responses from a text protocol network connection.
type Reader struct {
R *bufio.Reader
dot *dotReader
buf []byte // a re-usable buffer for readContinuedLineSlice
}
// NewReader returns a new Reader reading from r.
//
// To avoid denial of service attacks, the provided bufio.Reader
// should be reading from an io.LimitReader or similar Reader to bound
// the size of responses.
func NewReader(r *bufio.Reader) *Reader {
return &Reader{R: r}
}
// ReadLine reads a single line from r,
// eliding the final \n or \r\n from the returned string.
func (r *Reader) ReadLine() (string, error) {
line, err := r.readLineSlice()
return string(line), err
}
// ReadLineBytes is like ReadLine but returns a []byte instead of a string.
func (r *Reader) ReadLineBytes() ([]byte, error) {
line, err := r.readLineSlice()
if line != nil {
buf := make([]byte, len(line))
copy(buf, line)
line = buf
}
return line, err
}
func (r *Reader) readLineSlice() ([]byte, error) {
r.closeDot()
var line []byte
for {
l, more, err := r.R.ReadLine()
if err != nil {
return nil, err
}
// Avoid the copy if the first call produced a full line.
if line == nil && !more {
return l, nil
}
line = append(line, l...)
if !more {
break
}
}
return line, nil
}
// ReadContinuedLine reads a possibly continued line from r,
// eliding the final trailing ASCII white space.
// Lines after the first are considered continuations if they
// begin with a space or tab character. In the returned data,
// continuation lines are separated from the previous line
// only by a single space: the newline and leading white space
// are removed.
//
// For example, consider this input:
//
// Line 1
// continued...
// Line 2
//
// The first call to ReadContinuedLine will return "Line 1 continued..."
// and the second will return "Line 2".
//
// Empty lines are never continued.
func (r *Reader) ReadContinuedLine() (string, error) {
line, err := r.readContinuedLineSlice(noValidation)
return string(line), err
}
// trim returns s with leading and trailing spaces and tabs removed.
// It does not assume Unicode or UTF-8.
func trim(s []byte) []byte {
i := 0
for i < len(s) && (s[i] == ' ' || s[i] == '\t') {
i++
}
n := len(s)
for n > i && (s[n-1] == ' ' || s[n-1] == '\t') {
n--
}
return s[i:n]
}
// ReadContinuedLineBytes is like ReadContinuedLine but
// returns a []byte instead of a string.
func (r *Reader) ReadContinuedLineBytes() ([]byte, error) {
line, err := r.readContinuedLineSlice(noValidation)
if line != nil {
buf := make([]byte, len(line))
copy(buf, line)
line = buf
}
return line, err
}
// readContinuedLineSlice reads continued lines from the reader buffer,
// returning a byte slice with all lines. The validateFirstLine function
// is run on the first read line, and if it returns an error then this
// error is returned from readContinuedLineSlice.
func (r *Reader) readContinuedLineSlice(validateFirstLine func([]byte) error) ([]byte, error) {
if validateFirstLine == nil {
return nil, fmt.Errorf("missing validateFirstLine func")
}
// Read the first line.
line, err := r.readLineSlice()
if err != nil {
return nil, err
}
if len(line) == 0 { // blank line - no continuation
return line, nil
}
if err := validateFirstLine(line); err != nil {
return nil, err
}
// Optimistically assume that we have started to buffer the next line
// and it starts with an ASCII letter (the next header key), or a blank
// line, so we can avoid copying that buffered data around in memory
// and skipping over non-existent whitespace.
if r.R.Buffered() > 1 {
peek, _ := r.R.Peek(2)
if len(peek) > 0 && (isASCIILetter(peek[0]) || peek[0] == '\n') ||
len(peek) == 2 && peek[0] == '\r' && peek[1] == '\n' {
return trim(line), nil
}
}
// ReadByte or the next readLineSlice will flush the read buffer;
// copy the slice into buf.
r.buf = append(r.buf[:0], trim(line)...)
// Read continuation lines.
for r.skipSpace() > 0 {
line, err := r.readLineSlice()
if err != nil {
break
}
r.buf = append(r.buf, ' ')
r.buf = append(r.buf, trim(line)...)
}
return r.buf, nil
}
// skipSpace skips R over all spaces and returns the number of bytes skipped.
func (r *Reader) skipSpace() int {
n := 0
for {
c, err := r.R.ReadByte()
if err != nil {
// Bufio will keep err until next read.
break
}
if c != ' ' && c != '\t' {
r.R.UnreadByte()
break
}
n++
}
return n
}
func (r *Reader) readCodeLine(expectCode int) (code int, continued bool, message string, err error) {
line, err := r.ReadLine()
if err != nil {
return
}
return parseCodeLine(line, expectCode)
}
func parseCodeLine(line string, expectCode int) (code int, continued bool, message string, err error) {
if len(line) < 4 || line[3] != ' ' && line[3] != '-' {
err = ProtocolError("short response: " + line)
return
}
continued = line[3] == '-'
code, err = strconv.Atoi(line[0:3])
if err != nil || code < 100 {
err = ProtocolError("invalid response code: " + line)
return
}
message = line[4:]
if 1 <= expectCode && expectCode < 10 && code/100 != expectCode ||
10 <= expectCode && expectCode < 100 && code/10 != expectCode ||
100 <= expectCode && expectCode < 1000 && code != expectCode {
err = &Error{code, message}
}
return
}
// ReadCodeLine reads a response code line of the form
//
// code message
//
// where code is a three-digit status code and the message
// extends to the rest of the line. An example of such a line is:
//
// 220 plan9.bell-labs.com ESMTP
//
// If the prefix of the status does not match the digits in expectCode,
// ReadCodeLine returns with err set to &Error{code, message}.
// For example, if expectCode is 31, an error will be returned if
// the status is not in the range [310,319].
//
// If the response is multi-line, ReadCodeLine returns an error.
//
// An expectCode <= 0 disables the check of the status code.
func (r *Reader) ReadCodeLine(expectCode int) (code int, message string, err error) {
code, continued, message, err := r.readCodeLine(expectCode)
if err == nil && continued {
err = ProtocolError("unexpected multi-line response: " + message)
}
return
}
// ReadResponse reads a multi-line response of the form:
//
// code-message line 1
// code-message line 2
// ...
// code message line n
//
// where code is a three-digit status code. The first line starts with the
// code and a hyphen. The response is terminated by a line that starts
// with the same code followed by a space. Each line in message is
// separated by a newline (\n).
//
// See page 36 of RFC 959 (https://www.ietf.org/rfc/rfc959.txt) for
// details of another form of response accepted:
//
// code-message line 1
// message line 2
// ...
// code message line n
//
// If the prefix of the status does not match the digits in expectCode,
// ReadResponse returns with err set to &Error{code, message}.
// For example, if expectCode is 31, an error will be returned if
// the status is not in the range [310,319].
//
// An expectCode <= 0 disables the check of the status code.
func (r *Reader) ReadResponse(expectCode int) (code int, message string, err error) {
code, continued, message, err := r.readCodeLine(expectCode)
multi := continued
for continued {
line, err := r.ReadLine()
if err != nil {
return 0, "", err
}
var code2 int
var moreMessage string
code2, continued, moreMessage, err = parseCodeLine(line, 0)
if err != nil || code2 != code {
message += "\n" + strings.TrimRight(line, "\r\n")
continued = true
continue
}
message += "\n" + moreMessage
}
if err != nil && multi && message != "" {
// replace one line error message with all lines (full message)
err = &Error{code, message}
}
return
}
// DotReader returns a new Reader that satisfies Reads using the
// decoded text of a dot-encoded block read from r.
// The returned Reader is only valid until the next call
// to a method on r.
//
// Dot encoding is a common framing used for data blocks
// in text protocols such as SMTP. The data consists of a sequence
// of lines, each of which ends in "\r\n". The sequence itself
// ends at a line containing just a dot: ".\r\n". Lines beginning
// with a dot are escaped with an additional dot to avoid
// looking like the end of the sequence.
//
// The decoded form returned by the Reader's Read method
// rewrites the "\r\n" line endings into the simpler "\n",
// removes leading dot escapes if present, and stops with error io.EOF
// after consuming (and discarding) the end-of-sequence line.
func (r *Reader) DotReader() io.Reader {
r.closeDot()
r.dot = &dotReader{r: r}
return r.dot
}
type dotReader struct {
r *Reader
state int
}
// Read satisfies reads by decoding dot-encoded data read from d.r.
func (d *dotReader) Read(b []byte) (n int, err error) {
// Run data through a simple state machine to
// elide leading dots, rewrite trailing \r\n into \n,
// and detect ending .\r\n line.
const (
stateBeginLine = iota // beginning of line; initial state; must be zero
stateDot // read . at beginning of line
stateDotCR // read .\r at beginning of line
stateCR // read \r (possibly at end of line)
stateData // reading data in middle of line
stateEOF // reached .\r\n end marker line
)
br := d.r.R
for n < len(b) && d.state != stateEOF {
var c byte
c, err = br.ReadByte()
if err != nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
break
}
switch d.state {
case stateBeginLine:
if c == '.' {
d.state = stateDot
continue
}
if c == '\r' {
d.state = stateCR
continue
}
d.state = stateData
case stateDot:
if c == '\r' {
d.state = stateDotCR
continue
}
if c == '\n' {
d.state = stateEOF
continue
}
d.state = stateData
case stateDotCR:
if c == '\n' {
d.state = stateEOF
continue
}
// Not part of .\r\n.
// Consume leading dot and emit saved \r.
br.UnreadByte()
c = '\r'
d.state = stateData
case stateCR:
if c == '\n' {
d.state = stateBeginLine
break
}
// Not part of \r\n. Emit saved \r
br.UnreadByte()
c = '\r'
d.state = stateData
case stateData:
if c == '\r' {
d.state = stateCR
continue
}
if c == '\n' {
d.state = stateBeginLine
}
}
b[n] = c
n++
}
if err == nil && d.state == stateEOF {
err = io.EOF
}
if err != nil && d.r.dot == d {
d.r.dot = nil
}
return
}
// closeDot drains the current DotReader if any,
// making sure that it reads until the ending dot line.
func (r *Reader) closeDot() {
if r.dot == nil {
return
}
buf := make([]byte, 128)
for r.dot != nil {
// When Read reaches EOF or an error,
// it will set r.dot == nil.
r.dot.Read(buf)
}
}
// ReadDotBytes reads a dot-encoding and returns the decoded data.
//
// See the documentation for the DotReader method for details about dot-encoding.
func (r *Reader) ReadDotBytes() ([]byte, error) {
return io.ReadAll(r.DotReader())
}
// ReadDotLines reads a dot-encoding and returns a slice
// containing the decoded lines, with the final \r\n or \n elided from each.
//
// See the documentation for the DotReader method for details about dot-encoding.
func (r *Reader) ReadDotLines() ([]string, error) {
// We could use ReadDotBytes and then Split it,
// but reading a line at a time avoids needing a
// large contiguous block of memory and is simpler.
var v []string
var err error
for {
var line string
line, err = r.ReadLine()
if err != nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
break
}
// Dot by itself marks end; otherwise cut one dot.
if len(line) > 0 && line[0] == '.' {
if len(line) == 1 {
break
}
line = line[1:]
}
v = append(v, line)
}
return v, err
}
var colon = []byte(":")
// ReadMIMEHeader reads a MIME-style header from r.
// The header is a sequence of possibly continued Key: Value lines
// ending in a blank line.
// The returned map m maps CanonicalMIMEHeaderKey(key) to a
// sequence of values in the same order encountered in the input.
//
// For example, consider this input:
//
// My-Key: Value 1
// Long-Key: Even
// Longer Value
// My-Key: Value 2
//
// Given that input, ReadMIMEHeader returns the map:
//
// map[string][]string{
// "My-Key": {"Value 1", "Value 2"},
// "Long-Key": {"Even Longer Value"},
// }
func (r *Reader) ReadMIMEHeader() (MIMEHeader, error) {
// Avoid lots of small slice allocations later by allocating one
// large one ahead of time which we'll cut up into smaller
// slices. If this isn't big enough later, we allocate small ones.
var strs []string
hint := r.upcomingHeaderNewlines()
if hint > 0 {
strs = make([]string, hint)
}
m := make(MIMEHeader, hint)
// The first line cannot start with a leading space.
if buf, err := r.R.Peek(1); err == nil && (buf[0] == ' ' || buf[0] == '\t') {
line, err := r.readLineSlice()
if err != nil {
return m, err
}
return m, ProtocolError("malformed MIME header initial line: " + string(line))
}
for {
kv, err := r.readContinuedLineSlice(mustHaveFieldNameColon)
if len(kv) == 0 {
return m, err
}
// Key ends at first colon.
k, v, ok := bytes.Cut(kv, colon)
if !ok {
return m, ProtocolError("malformed MIME header line: " + string(kv))
}
key := canonicalMIMEHeaderKey(k)
// As per RFC 7230 field-name is a token, tokens consist of one or more chars.
// We could return a ProtocolError here, but better to be liberal in what we
// accept, so if we get an empty key, skip it.
if key == "" {
continue
}
// Skip initial spaces in value.
value := strings.TrimLeft(string(v), " \t")
vv := m[key]
if vv == nil && len(strs) > 0 {
// More than likely this will be a single-element key.
// Most headers aren't multi-valued.
// Set the capacity on strs[0] to 1, so any future append
// won't extend the slice into the other strings.
vv, strs = strs[:1:1], strs[1:]
vv[0] = value
m[key] = vv
} else {
m[key] = append(vv, value)
}
if err != nil {
return m, err
}
}
}
// noValidation is a no-op validation func for readContinuedLineSlice
// that permits any lines.
func noValidation(_ []byte) error { return nil }
// mustHaveFieldNameColon ensures that, per RFC 7230, the
// field-name is on a single line, so the first line must
// contain a colon.
func mustHaveFieldNameColon(line []byte) error {
if bytes.IndexByte(line, ':') < 0 {
return ProtocolError(fmt.Sprintf("malformed MIME header: missing colon: %q", line))
}
return nil
}
var nl = []byte("\n")
// upcomingHeaderNewlines returns an approximation of the number of newlines
// that will be in this header. If it gets confused, it returns 0.
func (r *Reader) upcomingHeaderNewlines() (n int) {
// Try to determine the 'hint' size.
r.R.Peek(1) // force a buffer load if empty
s := r.R.Buffered()
if s == 0 {
return
}
peek, _ := r.R.Peek(s)
return bytes.Count(peek, nl)
}
// CanonicalMIMEHeaderKey returns the canonical format of the
// MIME header key s. The canonicalization converts the first
// letter and any letter following a hyphen to upper case;
// the rest are converted to lowercase. For example, the
// canonical key for "accept-encoding" is "Accept-Encoding".
// MIME header keys are assumed to be ASCII only.
// If s contains a space or invalid header field bytes, it is
// returned without modifications.
func CanonicalMIMEHeaderKey(s string) string {
// Quick check for canonical encoding.
upper := true
for i := 0; i < len(s); i++ {
c := s[i]
if !validHeaderFieldByte(c) {
return s
}
if upper && 'a' <= c && c <= 'z' {
return canonicalMIMEHeaderKey([]byte(s))
}
if !upper && 'A' <= c && c <= 'Z' {
return canonicalMIMEHeaderKey([]byte(s))
}
upper = c == '-'
}
return s
}
const toLower = 'a' - 'A'
// validHeaderFieldByte reports whether b is a valid byte in a header
// field name. RFC 7230 says:
//
// header-field = field-name ":" OWS field-value OWS
// field-name = token
// tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
// "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
// token = 1*tchar
func validHeaderFieldByte(b byte) bool {
return int(b) < len(isTokenTable) && isTokenTable[b]
}
// canonicalMIMEHeaderKey is like CanonicalMIMEHeaderKey but is
// allowed to mutate the provided byte slice before returning the
// string.
//
// For invalid inputs (if a contains spaces or non-token bytes), a
// is unchanged and a string copy is returned.
func canonicalMIMEHeaderKey(a []byte) string {
// See if a looks like a header key. If not, return it unchanged.
for _, c := range a {
if validHeaderFieldByte(c) {
continue
}
// Don't canonicalize.
return string(a)
}
upper := true
for i, c := range a {
// Canonicalize: first letter upper case
// and upper case after each dash.
// (Host, User-Agent, If-Modified-Since).
// MIME headers are ASCII only, so no Unicode issues.
if upper && 'a' <= c && c <= 'z' {
c -= toLower
} else if !upper && 'A' <= c && c <= 'Z' {
c += toLower
}
a[i] = c
upper = c == '-' // for next time
}
commonHeaderOnce.Do(initCommonHeader)
// The compiler recognizes m[string(byteSlice)] as a special
// case, so a copy of a's bytes into a new string does not
// happen in this map lookup:
if v := commonHeader[string(a)]; v != "" {
return v
}
return string(a)
}
// commonHeader interns common header strings.
var commonHeader map[string]string
var commonHeaderOnce sync.Once
func initCommonHeader() {
commonHeader = make(map[string]string)
for _, v := range []string{
"Accept",
"Accept-Charset",
"Accept-Encoding",
"Accept-Language",
"Accept-Ranges",
"Cache-Control",
"Cc",
"Connection",
"Content-Id",
"Content-Language",
"Content-Length",
"Content-Transfer-Encoding",
"Content-Type",
"Cookie",
"Date",
"Dkim-Signature",
"Etag",
"Expires",
"From",
"Host",
"If-Modified-Since",
"If-None-Match",
"In-Reply-To",
"Last-Modified",
"Location",
"Message-Id",
"Mime-Version",
"Pragma",
"Received",
"Return-Path",
"Server",
"Set-Cookie",
"Subject",
"To",
"User-Agent",
"Via",
"X-Forwarded-For",
"X-Imforwards",
"X-Powered-By",
} {
commonHeader[v] = v
}
}
// isTokenTable is a copy of net/http/lex.go's isTokenTable.
// See https://httpwg.github.io/specs/rfc7230.html#rule.token.separators
var isTokenTable = [127]bool{
'!': true,
'#': true,
'$': true,
'%': true,
'&': true,
'\'': true,
'*': true,
'+': true,
'-': true,
'.': true,
'0': true,
'1': true,
'2': true,
'3': true,
'4': true,
'5': true,
'6': true,
'7': true,
'8': true,
'9': true,
'A': true,
'B': true,
'C': true,
'D': true,
'E': true,
'F': true,
'G': true,
'H': true,
'I': true,
'J': true,
'K': true,
'L': true,
'M': true,
'N': true,
'O': true,
'P': true,
'Q': true,
'R': true,
'S': true,
'T': true,
'U': true,
'W': true,
'V': true,
'X': true,
'Y': true,
'Z': true,
'^': true,
'_': true,
'`': true,
'a': true,
'b': true,
'c': true,
'd': true,
'e': true,
'f': true,
'g': true,
'h': true,
'i': true,
'j': true,
'k': true,
'l': true,
'm': true,
'n': true,
'o': true,
'p': true,
'q': true,
'r': true,
's': true,
't': true,
'u': true,
'v': true,
'w': true,
'x': true,
'y': true,
'z': true,
'|': true,
'~': true,
}