rfc822.cpp

著名的加密软件的应用于电子邮件中

/*
 *  Functions to aide manipulation of MIME RFC822 headers.
 *
 *  Filename: RFC822.cpp
 *
 *  Last Edited: July 15, 1996
 *
 *  Author: Scott Manjourides
 *
 *  Portions adopted from code originally written by Stever Dorner.
 *  Copyright 1995, 1996 QUALCOMM Inc.
 *
 *  Send comments and questions to <[e-mail]>
 */

#include <stdlib.h>
#include <malloc.h>
#include <string.h>

#include <istream.h> // ifstream class
#include <fstream.h> // ofstream class

#include "rfc822.h"

/* ========================================================================= */

const char *kRFC822_MustBeQuoted = "()<>@,;:\\\"/[]?= ";
const char *kRFC822_MustBeEscaped = "\\\"";
const char *kRFC822_EOL = "\r\n";

/* ========================================================================= */

#define safefree(p) { if (p) { free(p); (p) = NULL; } }

/* ========================================================================= */

/*
 *  Find next RFC822 token in given string, copying it into a newly created
 *  string. Advance pointer past token and any following whitespace.
 *   
 *  NOTE: The user of this function is responsible for freeing returned
 *        string.
 *
 *  Args:
 *   cpp [IN/OUT] Handle (pointer-to-pointer) of RFC822 string to extract from
 *
 *  Returns: String containing next token, NULL if error.
 *         Moves cpp to first non-whitespace character AFTER extracted token
 */
char *rfc822_extract_token(char **cpp)
{
	char *start, *cp = *cpp;

	cp = rfc822_skipws(cp); // Skip white space
	start = cp;

	cp = rfc822_skipword(cp); // Skip word

	if (cp > start)
	{
		const int len = cp - start;
		char *buf = (char *) malloc(len + 1);

		if (buf)
		{
			rfc822_unquote_strcpy(buf, start, len);
			*cpp = rfc822_skipws(cp);

			return (buf);
		}
	}

	return (NULL); // No token to extract
}

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

/*
 *  Advances to next non-whitespace character in string. This includes
 *  ignoring RFC822 comments.
 *   
 *  Args:
 *   cp [IN] RFC822 string
 *
 *  Returns: Pointer to next non-whitespace character.
 */
char *rfc822_skipws(char *cp)
{
	do {
		while (*cp == ' ') // Skip spaces
			cp++;

		if (*cp == '(') // A comment?
		{
			int nested = 1;

			while ((*++cp) && (nested)) // Find end of comment
			{
				switch (*cp)
				{
					case '(': nested++;
					break;

					case ')': nested--;
					break;

					case '\\': // Escape character
						if ((*(cp+1)) != '\0') // Check for end-of-string
							cp++;
					break;

					case '\"': // Quote inside comment
						while ((*cp) && (*++cp != '\"')) // Go 'til end of quote
							if ((*cp == '\\') && ((*(cp+1)) != '\0'))
								cp++; // Escaped character inside quote -- inside comment (eeek!)
					break;
				}
			}
		}
	} while (*cp == ' ');

	return cp;
}

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

/*
 *  Advances to next character in string directly after the current token.
 *  The first character must be the beginning of a valid token or end of
 *  string (ie. all whitespace must be skipped BEFORE calling this function).
 *
 *  Args:
 *   cp [IN] RFC822 string
 *
 *  Returns: Pointer to next valid whitespace character.
 */
char *rfc822_skipword(char *cp)
{
	int bInQuotes = 0;

	// First character must be a quote to be valid double-quoted string
	if (*cp == '\"')
	{
		bInQuotes = 1;
		cp++;
	}
	
	while (*cp)
	{
		if (strchr(kRFC822_MustBeQuoted, *cp))
		{
			if (!bInQuotes) // Found a character that should be double-quoted, but is not
				return (cp);

			// Now we know we are inside a double-quoted string

			switch (*cp)
			{
				case '\"': return (cp+1); // End double-quote
					break;
				case '\\': cp++; // Escape character, skip next
					break;
				default: // nothing
					break;
			}
		}

		cp++;
	}

	return (cp);
}

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

/*
 *  Calculates the length of the given text string if it were converted
 *  to an RFC822 string.
 *
 *  Args:
 *   cp [IN] Text string
 *
 *  Returns: Equivalent RFC822 length of given text.
 */
unsigned int rfc822_quoted_strlen(char *cp)
{
	unsigned int len = 0, bQuoted = 0;

	while (*cp)
	{
		len++;

		if ((!bQuoted) && (strchr(kRFC822_MustBeQuoted, *cp) != NULL))
			bQuoted = 1;

		if (strchr(kRFC822_MustBeEscaped, *cp) != NULL)
			len++, bQuoted = 1;

		cp++;
	}

	if (bQuoted)
		len += 2; // Quotes

	return (len);
}

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

/*
 *  Copies and converts the source text string to a destination
 *  RFC822 string. The source must be NULL terminated, and the
 *  destination will be NULL terminated.
 *
 *  Args:
 *   dst [OUT] RFC822 string
 *   src [IN]  Text string
 *
 *  Returns: Pointer to destination NULL termination.
 */
char *rfc822_quote_strcpy(char *dst, const char *src)
{
	const unsigned int bQuoted = ( strpbrk(src, kRFC822_MustBeQuoted) ? 1 : 0 );

	if (bQuoted)
		*dst++ = '\"';

	while (*src)
	{
		if (strchr(kRFC822_MustBeEscaped, *src) != NULL)
			*dst++ = '\\';

		*dst++ = *src++;
	}

	if (bQuoted)
		*dst++ = '\"';

	*dst = '\0';

	return (dst);
}

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

/*
 *  Copies and converts the source RFC822 string to a destination
 *  text string. The source must be NULL terminated, and the
 *  destination will be NULL terminated.
 *
 *  Args:
 *   dst [OUT] Text string
 *   src [IN]  RFC822 string
 *   len [IN]  Maximum charcters to copy; Zero implies whole string
 *
 *  Returns: Pointer to destination NULL termination.
 */
char *rfc822_unquote_strcpy(char *dst, const char *src, unsigned int len)
{
	// If 'len' is provided (ie. >0) then only len chars will be copied
	// Otherwise, copy 'til end-of-string
	char *end;
	unsigned int bEscaped = 0;

	end = strchr(src, '\0');

	if ((len > 0) && ((src + len) < end))
		end = (char *) src + len;

	while (src < end)
	{
		if (bEscaped)
			bEscaped = 0;
		else
		{
			switch (*src)
			{
				case '\\':	bEscaped = 1;
				case '\"':	src++;
							continue;
				break;
			}
		}

		*dst++ = *src++;
	}

	*dst = '\0';

	return dst;
}

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

/*
 *  Finds and extracts a header line from a full multi-lined header. All
 *  unfolding (removing newlines) is done before header line is returned.
 *
 *  NOTE: The user of this function is responsible for freeing the
 *        returned string.
 *
 *  Args:
 *   pFullHeader [IN] Pointer to a full RFC822 header, including newlines
 *   pLinePrefix [IN] Prefix of header line to extract
 *
 *  Returns: Extracted header line string; dynamically allocated.
 */
char *rfc822_extract_header(const char *pFullHeader, const char *pLinePrefix)
{
	const char *kNewline = "\r\n";
	const unsigned int kNewlineLen = (2);
	const unsigned int nPreLen = strlen(pLinePrefix);

	char *pStart, *pEnd, *pBuf, *pPos, *pRetBuf;

	if (nPreLen < 1)
		return (NULL);

	pStart = (char *) pFullHeader;

	/* Find first 'line' which matches prefix */
	while ((pStart) && (strnicmp(pStart, pLinePrefix, nPreLen) != 0))
		if (pStart = strstr(pStart, kNewline))
			pStart += kNewlineLen;

	if (!pStart)
		return (NULL); /* Not found */

	/* Find the end of this header line */
	for (pEnd = strstr(pStart, kNewline); (pEnd != NULL); pEnd = strstr(pEnd, kNewline))
	{
		pPos = pEnd + kNewlineLen;

		/* Does header line continue on next line? */
		if ((*pPos == ' ') || (*pPos == '\t'))
			pEnd = pPos;
		else
			break;
	}

	/* If we ran off the end of the string, then the end is the last char in the string */
	if (pEnd == NULL)
		pEnd = strchr(pStart, '\0');
	
	pBuf = pRetBuf = (char *) malloc(pEnd - pStart + 1); /* Max length of output string */

	for (pPos = pStart; pPos < pEnd; pPos++)
	{
		if (strncmp(pPos, kNewline, kNewlineLen) == 0) /* We're at a newline */
			pPos += kNewlineLen; /* Skip over newline */

		*pBuf++ = *pPos;
	}

	*pBuf = '\0';

	return (pRetBuf);
}

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

/*
 *  Reads and returns the RFC822 header from input file. This is defined
 *  here as reading until the first blank line from current file
 *  position. The blank line is discarded.
 *
 *  NOTE: The user of this function is responsible for freeing the
 *        returned string.
 *
 *  Args:
 *   inFile [IN] Input file stream; already open
 *
 *  Returns: Complete multi-lined RFC822 header; dynamically allocated.
 *     The file pointer is left immediately after the first read blank line.
 */
char *rfc822_read_header(ifstream& inFile)
{
	// We don't know how big the header is, but we know each line
	// must be less than 1024 chars. We use 'kBlockSize' to
	// increase the memory of the header while ensuring that
	// there is at least kBlockSize available for each read.
	const unsigned int kBlockSize = 1024;

	char *pBuf, *pPos, *cp;
	unsigned int nBufSize, nStrLen;

	if ((!inFile.good()) || (inFile.eof()))
		return NULL;

	nStrLen = nBufSize = 0;
	pBuf = NULL;

	while ((inFile.good()) && (!inFile.eof()))
	{
		if ((nBufSize - nStrLen) < (kBlockSize + 1))
		{
			nBufSize += kBlockSize;
			if ((cp = (char *) realloc(pBuf, nBufSize)) == NULL)
			{
				safefree(pBuf);
				return (NULL); // Out of memory?
			}

			pPos = (pBuf = cp) + nStrLen;
		}

		// Get next line
		cp = pPos;
		while ((inFile.good()) && (!inFile.eof()))
			if ((*cp++ = inFile.get()) == '\n')
			{
				*cp = '\0';
				break;
			}

		/* inFile.getline(pPos, kBlockSize); */
		/* getline() strips '\n' chars! Yuck! */

		if (strcmp(pPos, kRFC822_EOL) == 0) /* Empty line */
			break;

		pPos = strchr(pPos, '\0');
		nStrLen = pPos - pBuf;
	}

	// Null terminate the header string
	*pPos = '\0';

	// Chop off any excess allocated memory
	if (cp = (char *) realloc(pBuf, strlen(pBuf) + 1))
		pBuf = cp;
	
	return (pBuf);
}