Set checksum for SSH host public key. Use same syntax with --checksum
option. TYPE is hash type. The supported hash type is sha-1 or
md5. DIGEST is hex digest. For example:
sha-1=b030503d4de4539dc7885e6f0f5e256704edf4c3. This option can be
used to validate server's public key when SFTP is used. If this
option is not set, which is default, no validation takes place.
This commits implements basic downloading feature for sftp URI. This
includes segmented downloads, and connection (sftp session) pooling.
Download via HTTP proxy has not been implemented yet.
We use libssh2 to implement sftp feature. SSHSession is closely
designed to TLSSession, but it differs in several aspects. In this
code, we only implements read part of sftp, since aria2 won't offer
uploading feature. Adding SSH/sftp to SocketCore is a bit bloat. But
by doing this we can reuse DownloadCommand, without mostly no
modification. We can just create SSHDownloadCommand by inheriting it,
just like existing ftp.
Tatsuhiro Tsujikawa