/// <summary>
/// Opens a stream for writing an archive.
/// </summary>
/// <param name="archiveNumber">The 0-based index of the archive within
/// the chain.</param>
/// <param name="archiveName">The name of the archive that was returned
/// by <see cref="GetArchiveName"/>.</param>
/// <param name="truncate">True if the stream should be truncated when
/// opened (if it already exists); false if an existing stream is being
/// re-opened for writing additional data.</param>
/// <param name="compressionEngine">Instance of the compression engine
/// doing the operations.</param>
/// <returns>A writable Stream where the compressed archive bytes will be
/// written, or null to cancel the archive creation.</returns>
/// <remarks>
/// This method opens the file from the <see cref="ArchiveFiles"/> list
/// with the specified index. If the archive number is outside the bounds
/// of the list, this method returns null.
/// <para>If the <see cref="EnableOffsetOpen"/> flag is set, this method
/// will seek to the start of any existing archive in the file, or to the
/// end of the file if the existing file is not an archive.</para>
/// </remarks>
public virtual Stream OpenArchiveWriteStream(
int archiveNumber,
string archiveName,
bool truncate,
CompressionEngine compressionEngine)
{
if (archiveNumber >= this.archiveFiles.Count)
{
return null;
}
if (string.IsNullOrWhiteSpace(archiveName))
{
throw new ArgumentNullException("archiveName");
}
// All archives must be in the same directory,
// so always use the directory from the first archive.
string archiveFile = Path.Combine(
Path.GetDirectoryName(this.archiveFiles[0]), archiveName);
Stream stream = File.Open(
archiveFile,
(truncate ? FileMode.OpenOrCreate : FileMode.Open),
FileAccess.ReadWrite);
if (this.enableOffsetOpen)
{
if (compressionEngine == null) {
throw new ArgumentNullException("compressionEngine");
}
long offset = compressionEngine.FindArchiveOffset(
new DuplicateStream(stream));
// If this is not an archive file, append the archive to it.
if (offset < 0)
{
offset = stream.Length;
}
if (offset > 0)
{
stream = new OffsetStream(stream, offset);
}
stream.Seek(0, SeekOrigin.Begin);
}
if (truncate)
{
// Truncate the stream, in case a larger old archive starts here.
stream.SetLength(0);
}
return stream;
}
/// <summary>
/// Opens the archive stream for reading. Returns a DuplicateStream instance,
/// so the stream may be virtually opened multiple times.
/// </summary>
/// <param name="archiveNumber">The archive number to open (ignored; 0 is assumed).</param>
/// <param name="archiveName">The name of the archive being opened.</param>
/// <param name="compressionEngine">Instance of the compression engine doing the operations.</param>
/// <returns>A stream from which archive bytes are read.</returns>
public Stream OpenArchiveReadStream(int archiveNumber, string archiveName, CompressionEngine compressionEngine)
{
return new DuplicateStream(this.archiveStream);
}
/// <summary>
/// Opens the archive stream for reading.
/// </summary>
/// <param name="archiveNumber">The zero-based index of the archive to
/// open.</param>
/// <param name="archiveName">The name of the archive being opened.</param>
/// <param name="compressionEngine">Instance of the compression engine
/// doing the operations.</param>
/// <returns>A stream from which archive bytes are read, or null to cancel
/// extraction of the archive.</returns>
/// <remarks>
/// This method opens the file from the <see cref="ArchiveFiles"/> list with
/// the specified index. If the archive number is outside the bounds of the
/// list, this method returns null.
/// <para>If the <see cref="EnableOffsetOpen"/> flag is set, this method will
/// seek to the start of any existing archive in the file, or to the end of
/// the file if the existing file is not an archive.</para>
/// </remarks>
public virtual Stream OpenArchiveReadStream(
int archiveNumber, string archiveName, CompressionEngine compressionEngine)
{
if (archiveNumber >= this.archiveFiles.Count)
{
return null;
}
string archiveFile = this.archiveFiles[archiveNumber];
Stream stream = File.Open(
archiveFile, FileMode.Open, FileAccess.Read, FileShare.Read);
if (this.enableOffsetOpen)
{
if (compressionEngine == null) {
throw new ArgumentNullException("compressionEngine");
}
long offset = compressionEngine.FindArchiveOffset(
new DuplicateStream(stream));
if (offset > 0)
{
stream = new OffsetStream(stream, offset);
}
else
{
stream.Seek(0, SeekOrigin.Begin);
}
}
return stream;
}