private void BuildFallbackBlock(TagHelperAttributeList attributes, DefaultTagHelperContent builder)
{
EnsureGlobbingUrlBuilder();
var fallbackSrcs = GlobbingUrlBuilder.BuildUrlList(FallbackSrc, FallbackSrcInclude, FallbackSrcExclude);
if (fallbackSrcs.Any())
{
// Build the <script> tag that checks the test method and if it fails, renders the extra script.
builder.Append(Environment.NewLine)
.Append("<script>(")
.Append(FallbackTestExpression)
.Append("||document.write(\"");
// May have no "src" attribute in the dictionary e.g. if Src and SrcInclude were not bound.
if (!attributes.ContainsName(SrcAttributeName))
{
// Need this entry to place each fallback source.
attributes.Add(new TagHelperAttribute(SrcAttributeName, value: null));
}
foreach (var src in fallbackSrcs)
{
// Fallback "src" values come from bound attributes and globbing. Must always be non-null.
Debug.Assert(src != null);
builder.Append("<script");
foreach (var attribute in attributes)
{
if (!attribute.Name.Equals(SrcAttributeName, StringComparison.OrdinalIgnoreCase))
{
var encodedKey = JavaScriptEncoder.JavaScriptStringEncode(attribute.Name);
var attributeValue = attribute.Value.ToString();
var encodedValue = JavaScriptEncoder.JavaScriptStringEncode(attributeValue);
AppendAttribute(builder, encodedKey, encodedValue, escapeQuotes: true);
}
else
{
// Ignore attribute.Value; use src instead.
var attributeValue = src;
if (AppendVersion == true)
{
attributeValue = _fileVersionProvider.AddFileVersionToPath(attributeValue);
}
// attribute.Key ("src") does not need to be JavaScript-encoded.
var encodedValue = JavaScriptEncoder.JavaScriptStringEncode(attributeValue);
AppendAttribute(builder, attribute.Name, encodedValue, escapeQuotes: true);
}
}
builder.Append("><\\/script>");
}
builder.Append("\"));</script>");
}
}
private void BuildFallbackBlock(TagHelperContent builder)
{
EnsureGlobbingUrlBuilder();
var fallbackHrefs =
GlobbingUrlBuilder.BuildUrlList(FallbackHref, FallbackHrefInclude, FallbackHrefExclude).ToArray();
if (fallbackHrefs.Length > 0)
{
if (AppendVersion == true)
{
for (var i = 0; i < fallbackHrefs.Length; i++)
{
// fallbackHrefs come from bound attributes and globbing. Must always be non-null.
Debug.Assert(fallbackHrefs[i] != null);
fallbackHrefs[i] = _fileVersionProvider.AddFileVersionToPath(fallbackHrefs[i]);
}
}
builder.Append(HtmlString.NewLine);
// Build the <meta /> tag that's used to test for the presence of the stylesheet
builder
.AppendEncoded("<meta name=\"x-stylesheet-fallback-test\" class=\"")
.Append(FallbackTestClass)
.AppendEncoded("\" />");
// Build the <script /> tag that checks the effective style of <meta /> tag above and renders the extra
// <link /> tag to load the fallback stylesheet if the test CSS property value is found to be false,
// indicating that the primary stylesheet failed to load.
builder
.AppendEncoded("<script>")
.AppendEncoded(
string.Format(
CultureInfo.InvariantCulture,
JavaScriptResources.GetEmbeddedJavaScript(FallbackJavaScriptResourceName),
JavaScriptEncoder.JavaScriptStringEncode(FallbackTestProperty),
JavaScriptEncoder.JavaScriptStringEncode(FallbackTestValue),
JavaScriptStringArrayEncoder.Encode(JavaScriptEncoder, fallbackHrefs)))
.AppendEncoded("</script>");
}
}