netwerk/base/nsReadLine.h

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
   2  *
   3  * This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef nsReadLine_h__
   8 #define nsReadLine_h__
   9
  10 #include "nsIInputStream.h"
  11 #include "mozilla/Likely.h"
  12
  13 /**
  14  * @file
  15  * Functions to read complete lines from an input stream.
  16  *
  17  * To properly use the helper function in here (NS_ReadLine) the caller should
  18  * create a nsLineBuffer<T> with new, and pass it to NS_ReadLine every time it
  19  * wants a line out.
  20  *
  21  * When done, the object should be deleted.
  22  */
  23
  24 /**
  25  * @internal
  26  * Buffer size. This many bytes will be buffered. If a line is longer than this,
  27  * the partial line will be appended to the out parameter of NS_ReadLine and the
  28  * buffer will be emptied.
  29  * Note: if you change this constant, please update the regression test in
  30  * netwerk/test/unit/test_readline.js accordingly (bug 397850).
  31  */
  32 #define kLineBufferSize 4096
  33
  34 /**
  35  * @internal
  36  * Line buffer structure, buffers data from an input stream.
  37  * The buffer is empty when |start| == |end|.
  38  * Invariant: |start| <= |end|
  39  */
  40 template <typename CharT>
  41 class nsLineBuffer {
  42  public:
  43   nsLineBuffer() : start(buf), end(buf) {}
  44
  45   CharT buf[kLineBufferSize + 1];
  46   CharT* start;
  47   CharT* end;
  48 };
  49
  50 /**
  51  * Read a line from an input stream. Lines are separated by '\r' (0x0D) or '\n'
  52  * (0x0A), or "\r\n" or "\n\r".
  53  *
  54  * @param aStream
  55  *        The stream to read from
  56  * @param aBuffer
  57  *        The line buffer to use.  A single line buffer must not be used with
  58  *        different input streams.
  59  * @param aLine [out]
  60  *        The string where the line will be stored.
  61  * @param more [out]
  62  *        Whether more data is available in the buffer. If true, NS_ReadLine may
  63  *        be called again to read further lines. Otherwise, further calls to
  64  *        NS_ReadLine will return an error.
  65  *
  66  * @retval NS_OK
  67  *         Read successful
  68  * @retval error
  69  *         Input stream returned an error upon read. See
  70  *         nsIInputStream::read.
  71  */
  72 template <typename CharT, class StreamType, class StringType>
  73 nsresult NS_ReadLine(StreamType* aStream, nsLineBuffer<CharT>* aBuffer,
  74                      StringType& aLine, bool* more) {
  75   CharT eolchar = 0;  // the first eol char or 1 after \r\n or \n\r is found
  76
  77   aLine.Truncate();
  78
  79   while (true) {  // will be returning out of this loop on eol or eof
  80     if (aBuffer->start == aBuffer->end) {  // buffer is empty.  Read into it.
  81       uint32_t bytesRead;
  82       nsresult rv = aStream->Read(aBuffer->buf, kLineBufferSize, &bytesRead);
  83       if (NS_FAILED(rv) || MOZ_UNLIKELY(bytesRead == 0)) {
  84         *more = false;
  85         return rv;
  86       }
  87       aBuffer->start = aBuffer->buf;
  88       aBuffer->end = aBuffer->buf + bytesRead;
  89       *(aBuffer->end) = '\0';
  90     }
  91
  92     /*
  93      * Walk the buffer looking for an end-of-line.
  94      * There are 3 cases to consider:
  95      *  1. the eol char is the last char in the buffer
  96      *  2. the eol char + one more char at the end of the buffer
  97      *  3. the eol char + two or more chars at the end of the buffer
  98      * we need at least one char after the first eol char to determine if
  99      * it's a \r\n or \n\r sequence (and skip over it), and we need one
 100      * more char after the end-of-line to set |more| correctly.
 101      */
 102     CharT* current = aBuffer->start;
 103     if (MOZ_LIKELY(eolchar == 0)) {
 104       for (; current < aBuffer->end; ++current) {
 105         if (*current == '\n' || *current == '\r') {
 106           eolchar = *current;
 107           *current++ = '\0';
 108           aLine.Append(aBuffer->start);
 109           break;
 110         }
 111       }
 112     }
 113     if (MOZ_LIKELY(eolchar != 0)) {
 114       for (; current < aBuffer->end; ++current) {
 115         if ((eolchar == '\r' && *current == '\n') ||
 116             (eolchar == '\n' && *current == '\r')) {
 117           eolchar = 1;
 118           continue;
 119         }
 120         aBuffer->start = current;
 121         *more = true;
 122         return NS_OK;
 123       }
 124     }
 125
 126     if (eolchar == 0) aLine.Append(aBuffer->start);
 127     aBuffer->start = aBuffer->end;  // mark the buffer empty
 128   }
 129 }
 130
 131 #endif  // nsReadLine_h__