// Return (as a DateTimeOffset) the value corresponding to the query string parameter "startTime".
// queryString is expected to be "a=b&c=d&...", without leading question mark.
static DateTimeOffset ExtractStartDate(ReadOnlySpan <byte> queryString)
{
byte[] scratch = ArrayPool <byte> .Shared.Rent(64); // worst case scenario for decoding
try
{
foreach (var segment in Utf8.Split(queryString, '&'))
{
// segment reads "a=b"
int index = segment.IndexOf((byte)'='); // Span<T>.IndexOf extension method
if (index < 9 /* "startTime".Length */)
{
// no '=' found, or key can't possibly be "startTime"
continue;
}
var urlEncodedKeyNameAsUtf8 = segment.Slice(0, index);
var decodeStatus = UrlEncoder.Default.Decode(urlEncodedKeyNameAsUtf8, scratch, out var bytesConsumed, out var bytesWritten, isQueryString: true);
if (decodeStatus != OperationStatus.Done)
{
continue; // bad key name - skip
}
var urlDecodedKeyNameAsUtf8 = scratch.AsSpan(0, bytesWritten);
if (!Utf8.AreEqual(urlDecodedKeyNameAsUtf8, utf8 "startTime", stringComparison: StringComparison.OrdinalIgnoreCase))
{
continue; // incorrect key name - skip
}
// At this point we're done with the scratch buffer so can reuse it.
decodeStatus = UrlEncoder.Default.Decode(segment.Slice(index + 1), scratch, out bytesConsumed, out bytesWritten, isQueryString: true);
if (decodeStatus != OperationStatus.Done)
{
continue; // bad value - skip
}
var urlDecodedValueAsUtf8 = scratch.AsSpan(0, bytesWritten);
if (Utf8Parser.TryParse(urlDecodedValueAsUtf8, out DateTimeOffset value, out bytesConsumed) && bytesConsumed == urlDecodedValueAsUtf8.Length)
{
return(value); // success!
}
}
throw new Exception("Couldn't extract start date."); // or return sentinel value indicating failure
}
finally
{
ArrayPool <byte> .Shared.Return(scratch);
}
}
