SftpFileSystem: Open Modes & FileChannel locks #389
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As pointed out in apache#283, FileSystemProvider.newFileChannel(...) uses READ as default not only when no options are given, but always when neither WRITE nor APPEND are present. Also tighten some other rules, and fail if write modes are specified in newInputStream(...). Bug: apache#383
SSH_FXP_BLOCK is available only in SFTPv6. It was introduced in draft 08. Throw an UnsupportedOperationException if the negotiated SFTP version is lower. Respect the contract of FileChannel.lock(): a shared lock can be requested only if the channel was opened for reading, and an exclusive lock only if the channel is writable. Check this, and throw appropriate exceptions if the condition is violated. Pass on the correct lock flags to the server. At the server, repeat the version check, and respect the flags passed. Since Java does not have delete locks we map them to write locks. The draft RFC[1] is silent on what to do if no flags are passed at all: we use an exclusive write lock if the handle was opened for writing, and a shared read lock otherwise. We cannot throw an exception since we must be able to support old Apache MINA sshd clients that sent zero as lock flags. [1] https://www.ietf.org/archive/id/draft-ietf-secsh-filexfer-13.txt Bug: apache#384
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Two commits:
StandardOpenOptions when creating file channels or input/output streams. Fixes SftpFileSystemProvider.newFileChannel() uses wrong default mode #383.FileChannel.lock(...). Fixes FileChannel.lock() doesn't work for read-only channels from SftpFileSystemProvider.newFileChannel() #384.