WhitespaceReader.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / Net / System / Net / Mail / WhitespaceReader.cs / 1305376 / WhitespaceReader.cs
                        

                        
                            //------------------------------------------------------------------------------ 
// 
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// 
//----------------------------------------------------------------------------- 

namespace System.Net.Mail 
{ 
    using System;
    using System.Text; 
    using System.Net.Mime;
    using System.Globalization;
    using System.Collections;
    using System.Diagnostics; 

    // FWS, CFWS, and Comments are defined in RFC 2822 section 3.2.3. 
    // 
    // FWS is a Folding White Space, or a series of spaces and tabs that may also contain a CRLF.
    // 
    // CFWS is a FWS that also allows for nested comments enclosed in parenthesis.  (comment (nested))
    //
    // Valid values for these are declared in MailBnfHelper.cs and are explained in MailBNF.cs.
    // 
    internal static class WhitespaceReader
    { 
        // 
        // This skips all folding and whitespace characters
        // 
        // Preconditions:
        // - The data string must not be null or empty.
        // - The index must be within the upper bounds of the data string.
        // 
        // Return value:
        // - The index of the next character that is NOT a whitespace character. 
        // - -1 if the beginning of the data string is reached. 
        //
        // A FormatException will be thrown if a CR or LF is found NOT in the sequence CRLF. 
        internal static int ReadFwsReverse(string data, int index)
        {
            Debug.Assert(!String.IsNullOrEmpty(data), "data was null or empty");
            Debug.Assert(index < data.Length, "index was outside the bounds of the string"); 
            bool expectCR = false;
 
            for ( ; index >= 0; index--) 
            {
                // Check for a valid CRLF pair 
                if (data[index] == MailBnfHelper.CR && expectCR)
                {
                    expectCR = false; // valid pair
                } 
                // LF without CR, or CR without LF, invalid
                else if (data[index] == MailBnfHelper.CR || expectCR) 
                { 
                    throw new FormatException(SR.GetString(SR.MailAddressInvalidFormat));
                } 
                // LF is only valid if preceded by a CR.
                // Skip both if they're found together.
                else if (data[index] == MailBnfHelper.LF)
                { 
                    expectCR = true;
                } 
                // Skip whitespace 
                else if (data[index] == MailBnfHelper.Space || data[index] == MailBnfHelper.Tab)
                { 
                    // No-op
                }
                else
                { 
                    // Neither check hit so we must be on something that is not whitespace
                    break; 
                } 
            }
 
            if (expectCR)
            {
                // We found a LF without an immediately preceding CR, invalid.
                throw new FormatException(SR.GetString(SR.MailAddressInvalidFormat)); 
            }
            return index; 
        } 

        // This method functions similarly to ReadFwsReverse but will also skip any comments. 
        //
        // Comments are text within '(' and ')' and may be nested. There may also be consecutive comments.  Unicode is
        // allowed, as the comments are not transmitted.
        // 
        // This method was explicitly written in a non-recursive fashion to avoid malicious or accidental
        // stack-overflows from user input. 
        // 
        // Preconditions:
        // - The data string must not be null or empty 
        // - The index must be within the upper bounds of the data string.
        //
        // Return value:
        // - The given index if it data[index] was not a ')' or white space 
        // - The index of the next non comment or white space character
        //   e.g. " d ( ( c o mment) )" returns index 1 
        // - -1 if skipping the comments and/or whitespace moves you to the beginning of the data string. 
        //   e.g. " (comment) " returns -1
        // 
        // Throws a FormatException for mismatched '(' and ')', or for unescaped characters not allowed in comments.
        internal static int ReadCfwsReverse(string data, int index)
        {
            Debug.Assert(!String.IsNullOrEmpty(data), "data was null or empty"); 
            Debug.Assert(index < data.Length, "index was outside the bounds of the string");
 
            int commentDepth = 0; 

            // Check for valid whitespace 
            index = ReadFwsReverse(data, index);

            while (index >= 0)
            { 
                // Check for escaped characters.  They must be within comments.
                int quotedCharCount = QuotedPairReader.CountQuotedChars(data, index, true); 
                if (commentDepth > 0 && quotedCharCount > 0) 
                {
                    index = index - quotedCharCount; 
                }
                // Start a new comment
                else if (data[index] == MailBnfHelper.EndComment)
                { 
                    commentDepth++;
                    index--; 
                } 
                // Finish a comment
                else if (data[index] == MailBnfHelper.StartComment) 
                {
                    commentDepth--;
                    if (commentDepth < 0)
                    { 
                        // Mismatched '('
                        throw new FormatException(SR.GetString(SR.MailHeaderFieldInvalidCharacter, 
                            MailBnfHelper.StartComment)); 
                    }
                    index--; 
                }
                // Check for valid characters within comments.  Allow Unicode, as we won't transmit any comments.
                else if (commentDepth > 0
                    && (data[index] > MailBnfHelper.Ascii7bitMaxValue || MailBnfHelper.Ctext[data[index]])) 
                {
                    index--; 
                } 
                // If we're still in a comment, this must be an invalid char
                else if (commentDepth > 0) 
                {
                    throw new FormatException(SR.GetString(SR.MailHeaderFieldInvalidCharacter, data[index]));
                }
                // We must no longer be in a comment, and this is not a whitespace char, return 
                else
                { 
                    break; 
                }
 
                // Check for valid whitespace
                index = ReadFwsReverse(data, index);
            }
 
            if (commentDepth > 0)
            { 
                // Mismatched ')', throw 
                throw new FormatException(SR.GetString(SR.MailHeaderFieldInvalidCharacter, MailBnfHelper.EndComment));
            } 

            return index;
        }
    } 
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.

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