Reverting merge from trunk

[official-gcc.git] / libgo / go / net / textproto / reader.go

// 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"
        "io"
        "io/ioutil"
        "strconv"
        "strings"
)

// BUG(rsc): To let callers manage exposure to denial of service
// attacks, Reader should allow them to set and reset a limit on
// the number of bytes read from the connection.

// 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.
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".
//
// A line consisting of only white space is never continued.
//
func (r *Reader) ReadContinuedLine() (string, error) {
        line, err := r.readContinuedLineSlice()
        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()
        if line != nil {
                buf := make([]byte, len(line))
                copy(buf, line)
                line = buf
        }
        return line, err
}

func (r *Reader) readContinuedLineSlice() ([]byte, error) {
        // 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
        }

        // Optimistically assume that we have started to buffer the next line
        // and it starts with an ASCII letter (the next header key), so we can
        // avoid copying that buffered data around in memory and skipping over
        // non-existent whitespace.
        if r.R.Buffered() > 1 {
                peek, err := r.R.Peek(1)
                if err == nil && isASCIILetter(peek[0]) {
                        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, 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 (http://www.ietf.org/rfc/rfc959.txt) for
// details.
//
// 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)
        for err == nil && continued {
                line, err := r.ReadLine()
                if err != nil {
                        return 0, "", err
                }

                var code2 int
                var moreMessage string
                code2, continued, moreMessage, err = parseCodeLine(line, expectCode)
                if err != nil || code2 != code {
                        message += "\n" + strings.TrimRight(line, "\r\n")
                        continued = true
                        continue
                }
                message += "\n" + moreMessage
        }
        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 ioutil.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
}

// 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)
        for {
                kv, err := r.readContinuedLineSlice()
                if len(kv) == 0 {
                        return m, err
                }

                // Key ends at first colon; should not have spaces but
                // they appear in the wild, violating specs, so we
                // remove them if present.
                i := bytes.IndexByte(kv, ':')
                if i < 0 {
                        return m, ProtocolError("malformed MIME header line: " + string(kv))
                }
                endKey := i
                for endKey > 0 && kv[endKey-1] == ' ' {
                        endKey--
                }
                key := canonicalMIMEHeaderKey(kv[:endKey])

                // Skip initial spaces in value.
                i++ // skip colon
                for i < len(kv) && (kv[i] == ' ' || kv[i] == '\t') {
                        i++
                }
                value := string(kv[i:])

                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
                }
        }
}

// 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)
        for len(peek) > 0 {
                i := bytes.IndexByte(peek, '\n')
                if i < 3 {
                        // Not present (-1) or found within the next few bytes,
                        // implying we're at the end ("\r\n\r\n" or "\n\n")
                        return
                }
                n++
                peek = peek[i+1:]
        }
        return
}

// 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.
func CanonicalMIMEHeaderKey(s string) string {
        // Quick check for canonical encoding.
        upper := true
        for i := 0; i < len(s); i++ {
                c := s[i]
                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'

// canonicalMIMEHeaderKey is like CanonicalMIMEHeaderKey but is
// allowed to mutate the provided byte slice before returning the
// string.
func canonicalMIMEHeaderKey(a []byte) string {
        // Look for it in commonHeaders , so that we can avoid an
        // allocation by sharing the strings among all users
        // of textproto. If we don't find it, a has been canonicalized
        // so just return string(a).
        upper := true
        lo := 0
        hi := len(commonHeaders)
        for i := 0; i < len(a); i++ {
                // 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 a[i] == ' ' {
                        a[i] = '-'
                        upper = true
                        continue
                }
                c := a[i]
                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

                if lo < hi {
                        for lo < hi && (len(commonHeaders[lo]) <= i || commonHeaders[lo][i] < c) {
                                lo++
                        }
                        for hi > lo && commonHeaders[hi-1][i] > c {
                                hi--
                        }
                }
        }
        if lo < hi && len(commonHeaders[lo]) == len(a) {
                return commonHeaders[lo]
        }
        return string(a)
}

var commonHeaders = []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",
}