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162 lines
5.5 KiB
Markdown
162 lines
5.5 KiB
Markdown
# clipboard
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Copy files and text through network.
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Main lowlevel logic from [FreeRDP](https://github.com/FreeRDP/FreeRDP).
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To enjoy file copy and paste feature on Linux/OSX,
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please build with `unix-file-copy-paste` feature.
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TODO: Move this lib to a separate project.
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## How it works
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Terminalogies:
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- cliprdr: this module
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- local: the endpoint which initiates a file copy events
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- remote: the endpoint which paste the file copied from `local`
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The main algorithm of copying and pasting files is from
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[Remote Desktop Protocol: Clipboard Virtual Channel Extension](https://winprotocoldoc.blob.core.windows.net/productionwindowsarchives/MS-RDPECLIP/%5bMS-RDPECLIP%5d.pdf),
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and could be concluded as:
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0. local and remote notify each other that it's ready.
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1. local subscribes/listening to the system's clipboard for file copy
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2. local once got file copy event, notice the remote
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3. remote confirms receive and try pulls the file list
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4. local updates its file-list, the remote flushes pulled file list to the clipboard
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5. remote OS or desktop manager initiates a paste, making other programs reading
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clipboard files. Convert those reading requests to RPCs
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- on Windows, all file reading will go through the stream file API
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- on Linux/OSX, FUSE is used for converting reading requests to RPCs
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- in case of local clipboard been transferred back
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and leading to a dead loop,
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all file copy event pointing at the FUSE directory will be ignored
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6. finishing pasting all files one by one.
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In a perspective of network data transferring:
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```mermaid
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sequenceDiagram
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participant l as Local
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participant r as Remote
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note over l, r: Initialize
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l ->> r: Monitor Ready
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r ->> l: Monitor Ready
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loop Get clipboard update
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l ->> r: Format List (I got update)
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r ->> l: Format List Response (notified)
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r ->> l: Format Data Request (requests file list)
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activate l
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note left of l: Retrive file list from system clipboard
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l ->> r: Format Data Response (containing file list)
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deactivate l
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note over r: Update system clipboard with received file list
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end
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loop Some application requests copied files
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note right of r: application reads file from x to x+y
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note over r: the file is the a-th file on list
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r ->> l: File Contents Request (read file a offset x size y)
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activate l
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note left of l: Find a-th file on list, read from x to x+y
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l ->> r: File Contents Response (contents of file a offset x size y)
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deactivate l
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end
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```
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Note: In actual implementation, both sides could play send clipboard update
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and request file contents.
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There is no such limitation that only local can update clipboard
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and copy files to remote.
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## impl
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### windows
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The protocol was originally designed as an extension of the Windows RDP,
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so the specific message packages fits windows well.
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When starting cliprdr, a thread is spawn to create a invisible window
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and to subscribe to OLE clipboard events.
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The window's callback (see `cliprdr_proc` in `src/windows/wf_cliprdr.c`) was
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set to handle a variaty of events.
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Detailed implementation is shown in pictures above.
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### Linux/OSX
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The Cliprdr Server implementation has mainly 3 parts:
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- Clipboard Client
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- Local File list
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- FUSE server
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#### Clipboard Client
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The clipboard client has a thread polling for file urls on clipboard.
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If the client found any updates of file urls,
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after filtering out those pointing to our FUSE directory or duplicated,
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send format list directly to remote.
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The cliprdr server also uses clipboard client for setting clipboard,
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or retrive paths from system.
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#### Local File List
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The local file list is a temperary list of file metadata.
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When receiving file contents PDU from peer, the server picks
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out the file requested and open it for reading if necessary.
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Also when receiving Format Data Request PDU from remote asking for file list,
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the local file list should be rebuilt from file list retrieved from Clipboard Client.
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Some caching and preloading could done on it since applications are likely to read
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on the list sequentially.
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#### FUSE server
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The FUSE server could convert POSIX file reading request to File Contents
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Request/Response RPCs.
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When received file list from remote,
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the FUSE server will figure out the file system tree and rearrange its content.
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#### Groceries
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- The protocol was originally implemented for windows,
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so paths in PDU will all be converted to DOS formats in UTF-16 LE encoding,
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and datetimes will be converted to LDAP timestamp instead of
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unix timestamp
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```text
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UNIX
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/usr/bin/rustdesk
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->
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DOS
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\usr\bin\rustdesk
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```
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- To better fit for preserving permissions on unix-like platforms,
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a reserved area of FileDescriptor PDU
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- you may notice
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the mountpoint is still occupied after the application quits.
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That's because the FUSE server was not mounted with `AUTO_UNMOUNT`.
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- It's hard to implement gressful shutdown for a multi-processed program
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- `AUTO_UNMOUNT` was not enabled by default and requires enable
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`user_allow_other` in configure. Letting users edit such global
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configuration to use this feature might not be a good idea.
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- use [`umount()`](https://man7.org/linux/man-pages/man2/umount.2.html)
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syscall to unmount will also require that option.
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- we currently directly call [`umount`](https://man7.org/linux/man-pages/man8/umount.8.html)
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program to unmount dangling FUSE server. It worked perfectly for now.
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