internal static RouteTable Create(Dictionary <object, string[]> templatesByHandler)
{
var routes = new List <RouteEntry>();
foreach (var keyValuePair in templatesByHandler)
{
var parsedTemplates = keyValuePair.Value.Select(v => TemplateParser.ParseTemplate(v)).ToArray();
var allRouteParameterNames = parsedTemplates
.SelectMany(GetParameterNames)
.Distinct(StringComparer.OrdinalIgnoreCase)
.ToArray();
foreach (var parsedTemplate in parsedTemplates)
{
var unusedRouteParameterNames = allRouteParameterNames
.Except(GetParameterNames(parsedTemplate), StringComparer.OrdinalIgnoreCase)
.ToArray();
var entry = new RouteEntry(parsedTemplate, keyValuePair.Key, unusedRouteParameterNames);
routes.Add(entry);
}
}
return(new RouteTable(routes.OrderBy(id => id, RoutePrecedence).ToArray()));
}
/// <summary>
/// Route precedence algorithm.
/// We collect all the routes and sort them from most specific to
/// less specific. The specificity of a route is given by the specificity
/// of its segments and the position of those segments in the route.
/// * A literal segment is more specific than a parameter segment.
/// * A parameter segment with more constraints is more specific than one with fewer constraints
/// * Segment earlier in the route are evaluated before segments later in the route.
/// For example:
/// /Literal is more specific than /Parameter
/// /Route/With/{parameter} is more specific than /{multiple}/With/{parameters}
/// /Product/{id:int} is more specific than /Product/{id}
///
/// Routes can be ambiguous if:
/// They are composed of literals and those literals have the same values (case insensitive)
/// They are composed of a mix of literals and parameters, in the same relative order and the
/// literals have the same values.
/// For example:
/// * /literal and /Literal
/// /{parameter}/literal and /{something}/literal
/// /{parameter:constraint}/literal and /{something:constraint}/literal
///
/// To calculate the precedence we sort the list of routes as follows:
/// * Shorter routes go first.
/// * A literal wins over a parameter in precedence.
/// * For literals with different values (case insensitive) we choose the lexical order
/// * For parameters with different numbers of constraints, the one with more wins
/// If we get to the end of the comparison routing we've detected an ambiguous pair of routes.
/// </summary>
internal static int RouteComparison(RouteEntry x, RouteEntry y)
{
if (ReferenceEquals(x, y))
{
return(0);
}
var xTemplate = x.Template;
var yTemplate = y.Template;
if (xTemplate.Segments.Length != y.Template.Segments.Length)
{
return(xTemplate.Segments.Length < y.Template.Segments.Length ? -1 : 1);
}
else
{
for (var i = 0; i < xTemplate.Segments.Length; i++)
{
var xSegment = xTemplate.Segments[i];
var ySegment = yTemplate.Segments[i];
if (!xSegment.IsParameter && ySegment.IsParameter)
{
return(-1);
}
if (xSegment.IsParameter && !ySegment.IsParameter)
{
return(1);
}
if (xSegment.IsParameter)
{
// Always favor non-optional parameters over optional ones
if (!xSegment.IsOptional && ySegment.IsOptional)
{
return(-1);
}
if (xSegment.IsOptional && !ySegment.IsOptional)
{
return(1);
}
if (xSegment.Constraints.Length > ySegment.Constraints.Length)
{
return(-1);
}
else if (xSegment.Constraints.Length < ySegment.Constraints.Length)
{
return(1);
}
}
else
{
var comparison = string.Compare(xSegment.Value, ySegment.Value, StringComparison.OrdinalIgnoreCase);
if (comparison != 0)
{
return(comparison);
}
}
}
throw new InvalidOperationException($@"The following routes are ambiguous:
'{x.Template.TemplateText}' in '{x.Handler}'
'{y.Template.TemplateText}' in '{y.Handler}'
");
}
}