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libssh2-1.6.0
docs/TODO
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Daniel Stenberg
docs: move INSTALL, AUTHORS, HACKING and TODO to docs/
07 мар 2015, 13:42
07 мар 2015, 13:42
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Things TODO =========== * Fix the numerous malloc+copy operations for sending data, see "Buffering Improvements" below for details * make sure the windowing code adapts better to slow situations so that it doesn't then use as much memory as today. Possibly by an app-controllable "Window mode"? * Decrease the number of mallocs. Everywhere. Will get easier once the buffering improvements have been done. * Use SO_NOSIGPIPE for Mac OS/BSD systems where MSG_NOSIGNAL doesn't exist/work * Extend the test suite to actually test lots of aspects of libssh2 * Fix all compiler warnings (some can't be done without API changes) * Expose error messages sent by the server * select() is troublesome with libssh2 when using multiple channels over the same session. See "New Transport API" below for more details. At next SONAME bump =================== * stop using #defined macros as part of the official API. The macros should either be turned into real functions or discarded from the API. * fix the parts of the API where object pointers and function pointers are mixed like libssh2_session_callback_set() * remove the following functions from the API/ABI libssh2_base64_decode() libssh2_session_flag() libssh2_channel_handle_extended_data() libssh2_channel_receive_window_adjust() libssh2_poll() libssh2_poll_channel_read() libssh2_session_startup() (libssh2_session_handshake() is the replacement) libssh2_banner_set() (libssh2_session_banner_set() is the repacement) * Rename a few function: libssh2_hostkey_hash => libssh2_session_hostkey_hash libssh2_banner_set => libssh2_session_banner_set * change 'int' to 'libssh2_socket_t' in the public API for sockets. * Use 'size_t' for string lengths in all functions. * Add a comment field to struct libssh2_knownhost. * remove the existing libssh2_knownhost_add() function and rename libssh2_knownhost_addc to become the new libssh2_knownhost_add instead * remove the existing libssh2_scp_send_ex() function and rename libssh2_scp_send64 to become the new libssh2_scp_send instead. * remove the existing libssh2_knownhost_check() functin and rename libssh2_knownhost_checkp() to become the new libssh2_knownhost_check instead Buffering Improvements ====================== transport_write - If this function gets called with a total packet size that is larger than 32K, it should create more than one SSH packet so that it keeps the largest one below 32K sftp_write - should not copy/allocate anything for the data, only create a header chunk and pass on the payload data to channel_write "pointed to" New Transport API ================= THE PROBLEM The problem in a nutshell is that when an application opens up multiple channels over a single session, those are all using the same socket. If the application is then using select() to wait for traffic (like any sensible app does) and wants to act on the data when select() tells there is something to for example read, what does an application do? With our current API, you have to loop over all the channels and read from them to see if they have data. This effectively makes blocking reads impossible. If the app has many channels in a setup like this, it even becomes slow. (The original API had the libssh2_poll_channel_read() and libssh2_poll() to somewhat overcome this hurdle, but they too have pretty much the same problems plus a few others.) Traffic in the other direction is similarly limited: the app has to try sending to all channels, even though some of them may very well not accept any data at that point. A SOLUTION I suggest we introduce two new helper functions: libssh2_transport_read() - Read "a bunch" of data from the given socket and returns information to the app about what channels that are now readable (ie they will not block when read from). The function can be called over and over and it will repeatedly return info about what channels that are readable at that moment. libssh2_transport_write() - Returns information about what channels that are writable, in the sense that they have windows set from the remote side that allows data to get sent. Writing to one of those channels will not block. Of course, the underlying socket may only accept a certain amount of data, so at the first short return, nothing more should be attempted to get sent until select() (or equivalent) has been used on the master socket again. I haven't yet figured out a sensible API for how these functions should return that info, but if we agree on the general principles I guess we can work that out. VOLUNTARY I wanted to mention that these two helper functions would not be mandatory in any way. They would just be there for those who want them, and existing programs can remain using the old functions only if they prefer to. New SFTP API ============ PURPOSE Provide API functions that explicitly tells at once that a (full) SFTP file transfer is wanted, to allow libssh2 to leverage on that knowledge to speed up things internally. It can for example do read ahead, buffer writes (merge small writes into larger chunks), better tune the SSH window and more. This sort of API is already provided for SCP transfers. API New functions: LIBSSH2_SFTP_HANDLE *libssh2_sftp_send(SFTP_SESSION *sftp, uint64_t filesize, char *remote_path, size_t remote_path_len, long mode); Tell libssh2 that a local file with a given size is about to get sent to the SFTP server. LIBSSH2_SFTP_HANDLE *libssh2_sftp_recv(); Tell libssh2 that a remote file is requested to get downloaded from the SFTP server. Only the setup of the file transfer is different from an application's point of view. Depending on direction of the transfer(s), the following already existing functions should then be used until the transfer is complete: libssh2_sftp_read() libssh2_sftp_write() HOW TO USE 1. Setup the transfer using one of the two new functions. 2. Loop through the reading or writing of data. 3. Cleanup the transfer