public async Task <MimePartSpan> ReadStructureAsync(Stream mailStream, CancellationToken cancellationToken)
{
using (UnencodedStreamReader reader = new UnencodedStreamReader(mailStream, leaveOpen: true))
{
MimePartBuilder topLevelBuilder = new MimePartBuilder();
var currentBuilder = topLevelBuilder;
StringBuilder currentHeader = new StringBuilder();
while ((await ReadLine(reader, cancellationToken)).TryGet(out Memory <byte> line))
{
long position = reader.BytePositition;
if (currentBuilder.Parent != null &&
currentBuilder.Parent.EndBoundary.Span.SequenceEqual(line.Span))
{
currentBuilder = currentBuilder.Parent;
continue;
}
if (currentBuilder.Parent != null &&
currentBuilder.Parent.Boundary.Span.SequenceEqual(line.Span))
{
currentBuilder = new MimePartBuilder(currentBuilder.Parent, position);
continue;
}
if (!currentBuilder.Boundary.IsEmpty &&
currentBuilder.Children == null &&
currentBuilder.Boundary.Span.SequenceEqual(line.Span))
{
currentBuilder.Children = new List <MimePartBuilder>();
currentBuilder = new MimePartBuilder(currentBuilder, position);
continue;
}
currentBuilder.End = position;
if (!currentBuilder.HeaderComplete)
{
void ProcessPendingHeader()
{
if (currentHeader.Length == 0)
{
return;
}
string headerString = currentHeader.ToString();
currentHeader.Clear();
if (TestRegex(ContentTypeRegex, headerString, out var match))
{
string type = match.Groups["type"].Value;
if (type == "multipart")
{
CaptureCollection paramCaptures = match.Groups["param"].Captures;
CaptureCollection valueCaptures = match.Groups["value"].Captures;
for (int i = 0; i < paramCaptures.Count; i++)
{
switch (paramCaptures[i].Value.ToLowerInvariant())
{
case "charset":
break;
case "boundary":
ReadOnlySpan <char> value = valueCaptures[i].Value.AsSpan();
if (value.Length > 1 &&
value[0] == '"' &&
value[value.Length - 1] == '"')
{
value = value.Slice(1, value.Length - 2);
if (value.Contains("\\", StringComparison.Ordinal))
{
value = Regex.Replace(value.ToString(), @"\\.", m => m.Value[1].ToString());
}
}
currentBuilder.EndBoundary =
Encoding.ASCII.GetBytes("--" + value.ToString() + "--");
break;
}
}
}
}
}
if (line.Length == 0)
{
// header's over, process pending ones
ProcessPendingHeader();
currentBuilder.ContentStart = position;
continue;
}
if (IsImportantHeader(line))
{
currentHeader.Append(Encoding.ASCII.GetString(line.Span));
continue;
}
if (currentHeader.Length > 0)
{
byte first = line.Span[0];
if (first == ' ' || first == '\t')
{
currentHeader.Append(Encoding.ASCII.GetString(line.Span));
continue;
}
// We found another header, process the current one.
ProcessPendingHeader();
if (IsImportantHeader(line))
{
currentHeader.Append(Encoding.ASCII.GetString(line.Span));
}
}
}
}
currentBuilder.End = reader.BytePositition;
return(topLevelBuilder.ToMimePart());
}
}
public MimePartBuilder(MimePartBuilder parent, long position)
{
Parent = parent;
Start = position;
parent?.Children.Add(this);
}