private static void ProcessOperators(Stack <LicenseExpressionToken> operatorStack, Stack <Tuple <bool, object> > operandStack)
{
var op = operatorStack.Pop();
var rightOperand = PopIfNotEmpty(operandStack);
var leftOperand = PopIfNotEmpty(operandStack);
if (op.TokenType == LicenseTokenType.WITH)
{
if (!(rightOperand.Item1 == leftOperand.Item1 == true))
{
throw new NuGetLicenseExpressionParsingException(string.Format(CultureInfo.CurrentCulture, Strings.NuGetLicenseExpression_InvalidExpression));
}
var right = rightOperand.Item2 as LicenseExpressionToken;
var left = leftOperand.Item2 as LicenseExpressionToken;
var withNode = new WithOperator(NuGetLicense.ParseIdentifier(left.Value), NuGetLicenseException.ParseIdentifier(right.Value));
operandStack.Push(new Tuple <bool, object>(false, withNode));
}
else
{
var logicalOperator = op.TokenType == LicenseTokenType.AND ? LogicalOperatorType.And : LogicalOperatorType.Or;
var right = rightOperand.Item1 ?
NuGetLicense.ParseIdentifier(((LicenseExpressionToken)rightOperand.Item2).Value) :
(NuGetLicenseExpression)rightOperand.Item2;
var left = leftOperand.Item1 ?
NuGetLicense.ParseIdentifier(((LicenseExpressionToken)leftOperand.Item2).Value) :
(NuGetLicenseExpression)leftOperand.Item2;
var newExpression = new LogicalOperator(logicalOperator, left, right);
operandStack.Push(new Tuple <bool, object>(false, newExpression));
}
}
/// <summary>
/// Parses a License Expression if valid.
/// The expression would be parsed correct, even if non-standard exceptions are encountered. The non-standard Licenses/Exceptions have metadata on them with which the caller can make decisions.
/// Based on the Shunting Yard algorithm. <see href="https://en.wikipedia.org/wiki/Shunting-yard_algorithm"/>
/// This method first creates an postfix expression by separating the operators and operands.
/// Later the postfix expression is evaluated into an object model that represents the expression. Note that brackets are dropped in this conversion and this is not round-trippable.
/// The token precedence helps make sure that the expression is a valid infix one.
/// </summary>
/// <param name="expression">The expression to be parsed.</param>
/// <returns>Parsed NuGet License Expression model.</returns>
/// <exception cref="NuGetLicenseExpressionParsingException">If the expression is empty or null.</exception>
/// <exception cref="NuGetLicenseExpressionParsingException">If the expression has invalid characters</exception>
/// <exception cref="NuGetLicenseExpressionParsingException">If the expression itself is invalid. Example: MIT OR OR Apache-2.0, or the MIT or Apache-2.0, because the expressions are case sensitive.</exception>
/// <exception cref="NuGetLicenseExpressionParsingException">If the expression's brackets are mismatched.</exception>
/// <exception cref="NuGetLicenseExpressionParsingException">If the licenseIdentifier is deprecated.</exception>
/// <exception cref="NuGetLicenseExpressionParsingException">If the exception identifier is deprecated.</exception>
internal static NuGetLicenseExpression Parse(string expression)
{
try
{
var tokens = GetTokens(expression);
var operatorStack = new Stack <LicenseExpressionToken>();
// The operand stack can contain both unprocessed value and complex expressions such as MIT OR Apache-2.0.
// Complex expressions are valid operands for the logical operators. The first value represents whether it's value or an expression.
// true => LicenseExpressionToken, false => NuGetLicenseExpression
var operandStack = new Stack <Tuple <bool, object> >();
var lastTokenType = LicenseTokenType.IDENTIFIER;
var firstPass = true;
foreach (var token in tokens)
{
var currentTokenType = token.TokenType;
switch (token.TokenType)
{
case LicenseTokenType.IDENTIFIER:
if (!firstPass && !token.TokenType.IsValidPrecedingToken(lastTokenType))
{
throw new NuGetLicenseExpressionParsingException(string.Format(CultureInfo.CurrentCulture, Strings.NuGetLicenseExpression_InvalidToken, token.Value));
}
// Add it to the operandstack. Only add it to the expression when you meet an operator
operandStack.Push(new Tuple <bool, object>(true, token));
break;
case LicenseTokenType.OPENING_BRACKET:
if (!firstPass && !token.TokenType.IsValidPrecedingToken(lastTokenType))
{
throw new NuGetLicenseExpressionParsingException(string.Format(CultureInfo.CurrentCulture, Strings.NuGetLicenseExpression_InvalidToken, token.Value));
}
operatorStack.Push(token);
break;
case LicenseTokenType.CLOSING_BRACKET:
if (firstPass || !token.TokenType.IsValidPrecedingToken(lastTokenType))
{
throw new NuGetLicenseExpressionParsingException(string.Format(CultureInfo.CurrentCulture, Strings.NuGetLicenseExpression_InvalidToken, token.Value));
}
// pop until we hit the opening bracket
while (operatorStack.Count > 0 && operatorStack.Peek().TokenType != LicenseTokenType.OPENING_BRACKET)
{
ProcessOperators(operatorStack, operandStack);
}
if (operatorStack.Count > 0)
{
// pop the bracket
operatorStack.Pop();
}
else
{
throw new NuGetLicenseExpressionParsingException(string.Format(CultureInfo.CurrentCulture, Strings.NuGetLicenseExpression_MismatchedParentheses));
}
break;
case LicenseTokenType.WITH:
case LicenseTokenType.AND:
case LicenseTokenType.OR:
if (firstPass && !token.TokenType.IsValidPrecedingToken(lastTokenType))
{
throw new NuGetLicenseExpressionParsingException(string.Format(CultureInfo.CurrentCulture, Strings.NuGetLicenseExpression_InvalidToken, token.Value));
}
if (operatorStack.Count == 0 || // The operator stack is empty
operatorStack.Peek().TokenType == LicenseTokenType.OPENING_BRACKET || // The last token is an opening bracket (treat it the same as empty
token.TokenType < operatorStack.Peek().TokenType) // An operator that has higher priority than the operator on the stack
{
operatorStack.Push(token);
}
// An operator that has lower/same priority than the operator on the stack
else if (token.TokenType >= operatorStack.Peek().TokenType)
{
ProcessOperators(operatorStack, operandStack);
operatorStack.Push(token);
}
break;
default:
throw new NuGetLicenseExpressionParsingException("Should not happen. File a bug with repro steps on NuGet/Home if seen.");
}
lastTokenType = currentTokenType;
firstPass = false;
}
while (operatorStack.Count > 0)
{
if (operatorStack.Peek().TokenType != LicenseTokenType.OPENING_BRACKET)
{
ProcessOperators(operatorStack, operandStack);
}
else
{
throw new NuGetLicenseExpressionParsingException(string.Format(CultureInfo.CurrentCulture, Strings.NuGetLicenseExpression_MismatchedParentheses));
}
}
// This handles the no operators scenario. This check could be simpler, but it's dangerous to assume all scenarios have been handled by the above logic.
// As written and as tested, you would never have more than 1 operand on the stack
if (operandStack.Count != 1)
{
throw new NuGetLicenseExpressionParsingException(string.Format(CultureInfo.CurrentCulture, Strings.NuGetLicenseExpression_InvalidExpression));
}
else
{
var value = operandStack.Pop();
return(value.Item1 ? NuGetLicense.ParseIdentifier(((LicenseExpressionToken)value.Item2).Value, allowUnlicensed: true) : (NuGetLicenseExpression)value.Item2);
}
}
catch (NuGetLicenseExpressionParsingException)
{
throw;
}
catch (Exception e)
{
throw new NuGetLicenseExpressionParsingException(e.Message, e);
}
}