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reader.go
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reader.go
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// Copyright 2013 The Go-IMAP Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the go-imap.LICENSE file.
package imap
import (
"bytes"
"fmt"
"io"
"strconv"
)
// ParserError indicates a problem with the server response format. This could
// be the result of an unsupported extension or nonstandard server behavior.
type ParserError struct {
Info string // Short message explaining the problem
Line []byte // Full or partial response line, starting with the tag
Offset int // Parser offset, starting at 0
}
func (err *ParserError) Error() string {
if err.Line == nil {
return "imap: " + err.Info
}
line, ellipsis := err.Line, ""
if len(line) > rawLimit {
line, ellipsis = line[:rawLimit], "..."
}
return fmt.Sprintf("imap: %s at offset %d of %+q%s",
err.Info, err.Offset, line, ellipsis)
}
// readerInput is the interface for reading all parts of a response. This
// interface is implemented by transport.
type readerInput interface {
io.Reader
ReadLine() (line []byte, err error)
}
// reader creates rawResponse structs and provides additional lines and literals
// to the parser when requested.
type reader struct {
readerInput
LiteralReader
tagid []byte // Tag prefix expected in command completion responses ([A-Z]+)
order int64 // Response order counter
}
// rawResponse is an intermediate response form used to construct full Response
// objects. The struct returned by reader.Next() contains the start of the next
// response up to the first literal string, if there is one. The parser reads
// literals and additional lines as needed via reader.More(), which appends new
// bytes to line and tail. The current parser position can be calculated as
// len(raw.line) - len(raw.tail).
type rawResponse struct {
*Response
*reader
line []byte // Full response line without literals or CRLFs
tail []byte // Unconsumed line ending (parser state)
}
// newReader returns a reader configured to accept tagged responses beginning
// with tagid.
func newReader(in readerInput, lr LiteralReader, tagid string) *reader {
if in == nil || lr == nil || len(tagid) == 0 {
panic("imap: bad arguments to newReader")
}
for _, c := range tagid {
if c < 'A' || c > 'Z' {
panic("imap: bad tagid format")
}
}
return &reader{in, lr, []byte(tagid), 0}
}
// Next returns the next unparsed server response, or any data read prior to an
// error. If an error is returned and rsp != nil, the connection should be
// terminated because the client and server are no longer synchronized.
func (r *reader) Next() (raw *rawResponse, err error) {
raw = &rawResponse{reader: r}
if raw.line, err = r.ReadLine(); err != nil {
if len(raw.line) == 0 {
raw = nil
}
} else if tag := r.tag(raw.line); tag != "" {
r.order++
raw.Response = &Response{Order: r.order, Raw: raw.line, Tag: tag}
raw.tail = raw.line[len(tag)+1:]
} else {
err = &ProtocolError{"bad response tag", raw.line}
}
return
}
// More returns the next literal string and reads one more line from the server.
func (r *reader) More(raw *rawResponse, i LiteralInfo) (l Literal, err error) {
src := io.LimitedReader{R: r, N: int64(i.Len)}
if l, err = r.ReadLiteral(&src, i); l != nil {
raw.Literals = append(raw.Literals, l)
if err == nil {
var line []byte
if line, err = r.ReadLine(); len(line) > 0 { // ok if err != nil
pos := raw.pos()
raw.line = append(raw.line, line...)
raw.tail = raw.line[pos:]
raw.Raw = raw.line
}
}
} else if err == nil {
// Sanity check for user-provided ReadLiteral implementations
panic("imap: ReadLiteral returned (nil, nil)")
}
return
}
// tag verifies that line is a valid start of a new server response and returns
// the full response tag. Valid tags are "*" (untagged status/data), "+"
// (continuation request), and strings in the format "{r.tagid}[0-9]+" (command
// completion). The tag must be followed by a space.
func (r *reader) tag(line []byte) string {
if n := bytes.IndexByte(line, ' '); n == 1 {
if c := line[0]; c == '*' || c == '+' {
return string(c)
}
} else if i := len(r.tagid); i < n && bytes.Equal(line[:i], r.tagid) {
for _, c := range line[i:n] {
if c < '0' || c > '9' {
return ""
}
}
return string(line[:n])
}
return ""
}
// Error returned by parseCondition to indicate that rsp.Type != Status.
var errNotStatus error = &ParserError{Info: "not a status response"}
// Parse converts rawResponse into a full Response object by calling parseX
// methods, which gradually consume raw.tail.
func (raw *rawResponse) Parse() (rsp *Response, err error) {
if raw.Response == nil {
return nil, &ParserError{"unparsable response", raw.line, 0}
}
switch rsp = raw.Response; rsp.Tag {
case "*":
if err = raw.parseCondition(OK | NO | BAD | PREAUTH | BYE); err == nil {
rsp.Type = Status
err = raw.parseStatus()
} else if err == errNotStatus {
rsp.Type = Data
rsp.Fields, err = raw.parseFields(nul)
if len(rsp.Fields) == 0 && err == nil {
err = raw.error("empty data response", 0)
}
}
case "+":
rsp.Type = Continue
raw.parseContinue()
default:
if err = raw.parseCondition(OK | NO | BAD); err == nil {
rsp.Type = Done
err = raw.parseStatus()
} else if err == errNotStatus {
err = &ParserError{"unknown response type", raw.line, 0}
}
}
if len(raw.tail) > 0 && err == nil {
err = raw.unexpected(0)
}
raw.Response = nil
return
}
// pos returns the current parser position in raw.line.
func (raw *rawResponse) pos() int {
return len(raw.line) - len(raw.tail)
}
// error returns a ParserError to indicate a problem with the response at the
// specified offset. The offset is relative to raw.tail.
func (raw *rawResponse) error(info string, off int) error {
return &ParserError{info, raw.line, raw.pos() + off}
}
// unexpected returns a ParserError to indicate an unexpected byte at the
// specified offset. The offset is relative to raw.tail.
func (raw *rawResponse) unexpected(off int) error {
c := raw.line[raw.pos()+off]
return raw.error(fmt.Sprintf("unexpected %+q", c), off)
}
// missing returns a ParserError to indicate the absence of a required character
// or section at the specified offset. The offset is relative to raw.tail.
func (raw *rawResponse) missing(v interface{}, off int) error {
if _, ok := v.(byte); ok {
return raw.error(fmt.Sprintf("missing %+q", v), off)
}
return raw.error(fmt.Sprintf("missing %v", v), off)
}
// Valid status conditions.
var bStatus = []struct {
b []byte
s RespStatus
}{
{[]byte("OK"), OK},
{[]byte("NO"), NO},
{[]byte("BAD"), BAD},
{[]byte("PREAUTH"), PREAUTH},
{[]byte("BYE"), BYE},
}
// parseCondition extracts the status condition if raw is a status response
// (ABNF: resp-cond-*). errNotStatus is returned for all other response types.
func (raw *rawResponse) parseCondition(accept RespStatus) error {
outer:
for _, v := range bStatus {
if n := len(v.b); n <= len(raw.tail) {
for i, c := range v.b {
if raw.tail[i]&0xDF != c { // &0xDF converts [a-z] to upper case
continue outer
}
}
if n == len(raw.tail) {
return raw.missing("SP", n)
} else if raw.tail[n] == ' ' {
if accept&v.s == 0 {
return raw.error("unacceptable status condition", 0)
}
raw.Status = v.s
raw.tail = raw.tail[n+1:]
return nil
}
// Assume data response with a matching prefix (e.g. "* NOT STATUS")
break
}
}
return errNotStatus
}
// parseStatus extracts the optional response code and required text after the
// status condition (ABNF: resp-text).
func (raw *rawResponse) parseStatus() error {
if len(raw.tail) > 0 && raw.tail[0] == '[' {
var err error
raw.tail = raw.tail[1:]
if raw.Fields, err = raw.parseFields(']'); err != nil {
return err
} else if len(raw.Fields) == 0 {
return raw.error("empty response code", -1)
} else if len(raw.tail) == 0 {
// Some servers do not send any text after the response code
// (e.g. "* OK [UNSEEN 1]"). This is not allowed, according to RFC
// 3501 ABNF, but we accept it for compatibility with other clients.
raw.tail = nil
return nil
} else if raw.tail[0] != ' ' {
return raw.missing("SP", 0)
}
raw.tail = raw.tail[1:]
}
if len(raw.tail) == 0 {
return raw.missing("status text", 0)
}
raw.Info = string(raw.tail)
raw.tail = nil
return nil
}
// parseContinue extracts the text or Base64 data from a continuation request
// (ABNF: continue-req). Base64 data is saved in its original form to raw.Info,
// and decoded as []byte into raw.Fields[0].
func (raw *rawResponse) parseContinue() {
if n := len(raw.tail); n == 0 {
raw.Label = "BASE64"
raw.Fields = []Field{[]byte(nil)}
} else if n&3 == 0 {
if b, err := b64dec(raw.tail); err == nil {
raw.Label = "BASE64"
raw.Fields = []Field{b}
}
}
// ABNF uses resp-text, but section 7.5 states "The remainder of this
// response is a line of text." Assume that response codes are not allowed.
raw.Info = string(raw.tail)
raw.tail = nil
}
// parseFields extracts as many data fields from raw.tail as possible until it
// finds the stop byte in a delimiter position. An error is returned if the stop
// byte is not found. NUL stop causes all of raw.tail to be consumed (NUL does
// not appear anywhere in raw.line - checked by transport).
func (raw *rawResponse) parseFields(stop byte) (fields []Field, err error) {
if len(raw.tail) > 0 && raw.tail[0] == stop {
// Empty parenthesized list, BODY[] and friends, or an error
raw.tail = raw.tail[1:]
return
}
for len(raw.tail) > 0 && err == nil {
var f Field
switch raw.next() {
case QuotedString:
f, err = raw.parseQuotedString()
case LiteralString:
f, err = raw.parseLiteralString()
case List:
raw.tail = raw.tail[1:]
f, err = raw.parseFields(')')
default:
f, err = raw.parseAtom(raw.Type == Data && stop != ']')
}
if err == nil || f != nil {
fields = append(fields, f)
}
// Delimiter
if len(raw.tail) > 0 && err == nil {
switch raw.tail[0] {
case ' ':
if len(raw.tail) > 1 {
raw.tail = raw.tail[1:]
} else {
err = raw.unexpected(0)
}
case stop:
raw.tail = raw.tail[1:]
return
case '(':
// body-type-mpart is 1*body without a space in between
if len(raw.tail) == 1 {
err = raw.unexpected(0)
}
default:
err = raw.unexpected(0)
}
}
}
if stop != nul && err == nil {
err = raw.missing(stop, 0)
}
return
}
// next returns the type of the next response field. The default type is Atom,
// which includes atoms, numbers, and NILs.
func (raw *rawResponse) next() FieldType {
switch raw.tail[0] {
case '"':
return QuotedString
case '{':
return LiteralString
case '(':
return List
// RFC 5738 utf8-quoted
case '*':
if len(raw.tail) >= 2 && raw.tail[1] == '"' {
return QuotedString
}
// RFC 3516 literal8
case '~':
if len(raw.tail) >= 2 && raw.tail[1] == '{' {
return LiteralString
}
}
return Atom
}
// parseQuotedString returns the next quoted string. The string stays quoted,
// but validation is performed to ensure that subsequent calls to Unquote() are
// successful.
func (raw *rawResponse) parseQuotedString() (f Field, err error) {
start := 1
if raw.tail[0] == '*' {
start++
}
escaped := false
for n, c := range raw.tail[start:] {
if escaped {
escaped = false
} else if c == '\\' {
escaped = true
} else if c == '"' {
n += start + 1
if _, ok := UnquoteBytes(raw.tail[:n]); ok {
f = string(raw.tail[:n])
raw.tail = raw.tail[n:]
return
}
break
}
}
err = raw.error("bad quoted string", 0)
return
}
// parseLiteralString returns the next literal string. The octet count should be
// the last field in raw.tail. An additional line of text will be appended to
// raw.line and raw.tail after the literal is received.
func (raw *rawResponse) parseLiteralString() (f Field, err error) {
var info LiteralInfo
start := 1
if raw.tail[0] == '~' {
info.Bin = true
start++
}
n := len(raw.tail) - 1
if n-start < 1 || raw.tail[n] != '}' {
err = raw.unexpected(0)
return
}
oc, err := strconv.ParseUint(string(raw.tail[start:n]), 10, 32)
if err != nil {
err = raw.error("bad literal octet count", start)
return
}
info.Len = uint32(oc)
if f, err = raw.More(raw, info); err == nil {
raw.tail = raw.tail[n+1:]
}
return
}
// atomSpecials identifies ASCII characters that either may not appear in atoms
// or require special handling (ABNF: ATOM-CHAR).
var atomSpecials [char]bool
func init() {
// atom-specials + '[' to provide special handling for BODY[...]
s := []byte{'(', ')', '{', ' ', '%', '*', '"', '[', '\\', ']', '\x7F'}
for c := byte(0); c < char; c++ {
atomSpecials[c] = c < ctl || bytes.IndexByte(s, c) >= 0
}
}
// parseAtom returns the next atom, number, or NIL. The syntax rules are relaxed
// to treat sequences such as "BODY[...]<...>" as a single atom. Numbers are
// converted to uint32, NIL is converted to nil, everything else becomes a
// string. Flags (e.g. "\Seen") are converted to title case, other strings are
// left in their original form.
func (raw *rawResponse) parseAtom(astring bool) (f Field, err error) {
n, flag := 0, false
for end := len(raw.tail); n < end; n++ {
if c := raw.tail[n]; c >= char || atomSpecials[c] {
switch c {
case '\\':
if n == 0 {
flag = true
astring = false
continue // ABNF: flag (e.g. `\Seen`)
}
case '*':
if n == 1 && flag {
n++ // ABNF: flag-perm (`\*`), end of atom
}
case '[':
if n == 4 && bytes.EqualFold(raw.tail[:4], []byte("BODY")) {
pos := raw.pos()
raw.tail = raw.tail[n+1:] // Temporary shift for parseFields
// TODO: Literals between '[' and ']' are handled correctly,
// but only the octet count will make it into the returned
// atom. Would any server actually send a literal here, and
// is it a problem to discard it since the client already
// knows what was requested?
if _, err = raw.parseFields(']'); err != nil {
return
}
n = raw.pos() - pos - 1
raw.tail = raw.line[pos:] // Undo temporary shift
end = len(raw.tail)
astring = false
}
continue // ABNF: fetch-att ("BODY[...]<...>"), atom, or astring
case ']':
if astring {
continue // ABNF: ASTRING-CHAR
}
}
break // raw.tail[n] is a delimiter or an unexpected byte
}
}
// Atom must have at least one character, two if it starts with a backslash
if n < 2 && (n == 0 || flag) {
err = raw.unexpected(0)
return
}
// Take whatever was found, let parseFields report delimiter errors
atom := raw.tail[:n]
if norm := normalize(atom); flag {
f = norm
} else if norm != "NIL" {
if c := norm[0]; '0' <= c && c <= '9' {
if ui, err := strconv.ParseUint(norm, 10, 32); err == nil {
f = uint32(ui)
}
}
if f == nil {
if raw.Label == "" {
raw.Label = norm
}
f = string(atom)
}
}
raw.tail = raw.tail[n:]
return
}
// normalize returns a normalized string copy of an atom. Non-flag atoms are
// converted to upper case. Flags are converted to title case (e.g. `\Seen`).
func normalize(atom []byte) string {
norm := []byte(nil)
want := byte(0) // Want upper case
for i, c := range atom {
have := c & 0x20
if c &= 0xDF; 'A' <= c && c <= 'Z' && have != want {
norm = make([]byte, len(atom))
break
} else if i == 1 && atom[0] == '\\' {
want = 0x20 // Want lower case starting at i == 2
}
}
if norm == nil {
return string(atom) // Fast path: no changes
}
want = 0
for i, c := range atom {
if c &= 0xDF; 'A' <= c && c <= 'Z' {
norm[i] = c | want
} else {
norm[i] = atom[i]
}
if i == 1 && atom[0] == '\\' {
want = 0x20
}
}
return string(norm)
}