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Source file src/net/http/internal/chunked.go

Documentation: net/http/internal

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // The wire protocol for HTTP's "chunked" Transfer-Encoding.
     6  
     7  // Package internal contains HTTP internals shared by net/http and
     8  // net/http/httputil.
     9  package internal
    10  
    11  import (
    12  	"bufio"
    13  	"bytes"
    14  	"errors"
    15  	"fmt"
    16  	"io"
    17  )
    18  
    19  const maxLineLength = 4096 // assumed <= bufio.defaultBufSize
    20  
    21  var ErrLineTooLong = errors.New("header line too long")
    22  
    23  // NewChunkedReader returns a new chunkedReader that translates the data read from r
    24  // out of HTTP "chunked" format before returning it.
    25  // The chunkedReader returns io.EOF when the final 0-length chunk is read.
    26  //
    27  // NewChunkedReader is not needed by normal applications. The http package
    28  // automatically decodes chunking when reading response bodies.
    29  func NewChunkedReader(r io.Reader) io.Reader {
    30  	br, ok := r.(*bufio.Reader)
    31  	if !ok {
    32  		br = bufio.NewReader(r)
    33  	}
    34  	return &chunkedReader{r: br}
    35  }
    36  
    37  type chunkedReader struct {
    38  	r        *bufio.Reader
    39  	n        uint64 // unread bytes in chunk
    40  	err      error
    41  	buf      [2]byte
    42  	checkEnd bool // whether need to check for \r\n chunk footer
    43  }
    44  
    45  func (cr *chunkedReader) beginChunk() {
    46  	// chunk-size CRLF
    47  	var line []byte
    48  	line, cr.err = readChunkLine(cr.r)
    49  	if cr.err != nil {
    50  		return
    51  	}
    52  	cr.n, cr.err = parseHexUint(line)
    53  	if cr.err != nil {
    54  		return
    55  	}
    56  	if cr.n == 0 {
    57  		cr.err = io.EOF
    58  	}
    59  }
    60  
    61  func (cr *chunkedReader) chunkHeaderAvailable() bool {
    62  	n := cr.r.Buffered()
    63  	if n > 0 {
    64  		peek, _ := cr.r.Peek(n)
    65  		return bytes.IndexByte(peek, '\n') >= 0
    66  	}
    67  	return false
    68  }
    69  
    70  func (cr *chunkedReader) Read(b []uint8) (n int, err error) {
    71  	for cr.err == nil {
    72  		if cr.checkEnd {
    73  			if n > 0 && cr.r.Buffered() < 2 {
    74  				// We have some data. Return early (per the io.Reader
    75  				// contract) instead of potentially blocking while
    76  				// reading more.
    77  				break
    78  			}
    79  			if _, cr.err = io.ReadFull(cr.r, cr.buf[:2]); cr.err == nil {
    80  				if string(cr.buf[:]) != "\r\n" {
    81  					cr.err = errors.New("malformed chunked encoding")
    82  					break
    83  				}
    84  			}
    85  			cr.checkEnd = false
    86  		}
    87  		if cr.n == 0 {
    88  			if n > 0 && !cr.chunkHeaderAvailable() {
    89  				// We've read enough. Don't potentially block
    90  				// reading a new chunk header.
    91  				break
    92  			}
    93  			cr.beginChunk()
    94  			continue
    95  		}
    96  		if len(b) == 0 {
    97  			break
    98  		}
    99  		rbuf := b
   100  		if uint64(len(rbuf)) > cr.n {
   101  			rbuf = rbuf[:cr.n]
   102  		}
   103  		var n0 int
   104  		n0, cr.err = cr.r.Read(rbuf)
   105  		n += n0
   106  		b = b[n0:]
   107  		cr.n -= uint64(n0)
   108  		// If we're at the end of a chunk, read the next two
   109  		// bytes to verify they are "\r\n".
   110  		if cr.n == 0 && cr.err == nil {
   111  			cr.checkEnd = true
   112  		}
   113  	}
   114  	return n, cr.err
   115  }
   116  
   117  // Read a line of bytes (up to \n) from b.
   118  // Give up if the line exceeds maxLineLength.
   119  // The returned bytes are owned by the bufio.Reader
   120  // so they are only valid until the next bufio read.
   121  func readChunkLine(b *bufio.Reader) ([]byte, error) {
   122  	p, err := b.ReadSlice('\n')
   123  	if err != nil {
   124  		// We always know when EOF is coming.
   125  		// If the caller asked for a line, there should be a line.
   126  		if err == io.EOF {
   127  			err = io.ErrUnexpectedEOF
   128  		} else if err == bufio.ErrBufferFull {
   129  			err = ErrLineTooLong
   130  		}
   131  		return nil, err
   132  	}
   133  	if len(p) >= maxLineLength {
   134  		return nil, ErrLineTooLong
   135  	}
   136  	p = trimTrailingWhitespace(p)
   137  	p, err = removeChunkExtension(p)
   138  	if err != nil {
   139  		return nil, err
   140  	}
   141  	return p, nil
   142  }
   143  
   144  func trimTrailingWhitespace(b []byte) []byte {
   145  	for len(b) > 0 && isASCIISpace(b[len(b)-1]) {
   146  		b = b[:len(b)-1]
   147  	}
   148  	return b
   149  }
   150  
   151  func isASCIISpace(b byte) bool {
   152  	return b == ' ' || b == '\t' || b == '\n' || b == '\r'
   153  }
   154  
   155  // removeChunkExtension removes any chunk-extension from p.
   156  // For example,
   157  //     "0" => "0"
   158  //     "0;token" => "0"
   159  //     "0;token=val" => "0"
   160  //     `0;token="quoted string"` => "0"
   161  func removeChunkExtension(p []byte) ([]byte, error) {
   162  	semi := bytes.IndexByte(p, ';')
   163  	if semi == -1 {
   164  		return p, nil
   165  	}
   166  	// TODO: care about exact syntax of chunk extensions? We're
   167  	// ignoring and stripping them anyway. For now just never
   168  	// return an error.
   169  	return p[:semi], nil
   170  }
   171  
   172  // NewChunkedWriter returns a new chunkedWriter that translates writes into HTTP
   173  // "chunked" format before writing them to w. Closing the returned chunkedWriter
   174  // sends the final 0-length chunk that marks the end of the stream but does
   175  // not send the final CRLF that appears after trailers; trailers and the last
   176  // CRLF must be written separately.
   177  //
   178  // NewChunkedWriter is not needed by normal applications. The http
   179  // package adds chunking automatically if handlers don't set a
   180  // Content-Length header. Using newChunkedWriter inside a handler
   181  // would result in double chunking or chunking with a Content-Length
   182  // length, both of which are wrong.
   183  func NewChunkedWriter(w io.Writer) io.WriteCloser {
   184  	return &chunkedWriter{w}
   185  }
   186  
   187  // Writing to chunkedWriter translates to writing in HTTP chunked Transfer
   188  // Encoding wire format to the underlying Wire chunkedWriter.
   189  type chunkedWriter struct {
   190  	Wire io.Writer
   191  }
   192  
   193  // Write the contents of data as one chunk to Wire.
   194  // NOTE: Note that the corresponding chunk-writing procedure in Conn.Write has
   195  // a bug since it does not check for success of io.WriteString
   196  func (cw *chunkedWriter) Write(data []byte) (n int, err error) {
   197  
   198  	// Don't send 0-length data. It looks like EOF for chunked encoding.
   199  	if len(data) == 0 {
   200  		return 0, nil
   201  	}
   202  
   203  	if _, err = fmt.Fprintf(cw.Wire, "%x\r\n", len(data)); err != nil {
   204  		return 0, err
   205  	}
   206  	if n, err = cw.Wire.Write(data); err != nil {
   207  		return
   208  	}
   209  	if n != len(data) {
   210  		err = io.ErrShortWrite
   211  		return
   212  	}
   213  	if _, err = io.WriteString(cw.Wire, "\r\n"); err != nil {
   214  		return
   215  	}
   216  	if bw, ok := cw.Wire.(*FlushAfterChunkWriter); ok {
   217  		err = bw.Flush()
   218  	}
   219  	return
   220  }
   221  
   222  func (cw *chunkedWriter) Close() error {
   223  	_, err := io.WriteString(cw.Wire, "0\r\n")
   224  	return err
   225  }
   226  
   227  // FlushAfterChunkWriter signals from the caller of NewChunkedWriter
   228  // that each chunk should be followed by a flush. It is used by the
   229  // http.Transport code to keep the buffering behavior for headers and
   230  // trailers, but flush out chunks aggressively in the middle for
   231  // request bodies which may be generated slowly. See Issue 6574.
   232  type FlushAfterChunkWriter struct {
   233  	*bufio.Writer
   234  }
   235  
   236  func parseHexUint(v []byte) (n uint64, err error) {
   237  	for i, b := range v {
   238  		switch {
   239  		case '0' <= b && b <= '9':
   240  			b = b - '0'
   241  		case 'a' <= b && b <= 'f':
   242  			b = b - 'a' + 10
   243  		case 'A' <= b && b <= 'F':
   244  			b = b - 'A' + 10
   245  		default:
   246  			return 0, errors.New("invalid byte in chunk length")
   247  		}
   248  		if i == 16 {
   249  			return 0, errors.New("http chunk length too large")
   250  		}
   251  		n <<= 4
   252  		n |= uint64(b)
   253  	}
   254  	return
   255  }
   256  

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