Method DecodeFromBase64

xmpsdk/src/XMPUtils.cpp:1549–1663

class static */

// bad input is rejected.

/* class static */ void
XMPUtils::DecodeFromBase64 ( XMP_StringPtr	 encodedStr,
							 XMP_StringLen	 encodedLen,
							 XMP_StringPtr * rawStr,
							 XMP_StringLen * rawLen )
{
	if ( (encodedStr == 0) && (encodedLen != 0) ) XMP_Throw ( "Null encoded data buffer", kXMPErr_BadParam );
	if ( encodedLen == 0 ) {
		*rawStr = 0;
		*rawLen = 0;
		return;
	}

	unsigned char	ch, rawChunk[3];
	unsigned long	inStr, inChunk, inLimit, merge, padding;

	XMP_StringLen	outputSize	= (encodedLen / 4) * 3; // Only a close approximation.

	sBase64Str->erase();
	sBase64Str->reserve ( outputSize );


	// ----------------------------------------------------------------------------------------
	// Each 8 bits of input produces 6 bits of output, so 4 input bytes become 3 output bytes.
	// Process all but the last 4 data bytes first, then deal with the final chunk. Whitespace
	// in the input must be ignored. The first loop finds where the last 4 data bytes start and
	// counts the number of padding equal signs.

	padding = 0;
	for ( inStr = 0, inLimit = encodedLen; (inStr < 4) && (inLimit > 0); ) {
		inLimit -= 1;	// ! Don't do in the loop control, the decr/test order is wrong.
		ch = encodedStr[inLimit];
		if ( ch == '=' ) {
			padding += 1;	// The equal sign padding is a data byte.
		} else if ( DecodeBase64Char(ch) == 0xFF ) {
			continue;	// Ignore whitespace, don't increment inStr.
		} else {
			inStr += 1;
		}
	}

	// ! Be careful to count whitespace that is immediately before the final data. Otherwise
	// ! middle portion will absorb the final data and mess up the final chunk processing.

	while ( (inLimit > 0) && (DecodeBase64Char(encodedStr[inLimit-1]) == 0xFF) ) --inLimit;

	if ( inStr == 0 ) return;	// Nothing but whitespace.
	if ( padding > 2 ) XMP_Throw ( "Invalid encoded string", kXMPErr_BadParam );

	// -------------------------------------------------------------------------------------------
	// Now process all but the last chunk. The limit ensures that we have at least 4 data bytes
	// left when entering the output loop, so the inner loop will succeed without overrunning the
	// end of the data. At the end of the outer loop we might be past inLimit though.

	inStr = 0;
	while ( inStr < inLimit ) {

		merge = 0;