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This article is about how to share with you the analysis of the spice agent clipboard sharing mechanism, the editor thinks it is very practical, so I share it with you to learn. I hope you can get something after reading this article.

The spice protocol defines a set of two-way communication channels for communication between spice clients and spice agent. Spice provides only one communication channel, and the specific content of the transmitted data is opaque to the protocol. This channel can be used for a variety of purposes, such as clipboard sharing between clients and clients, resolution settings, and so on.

The data transfer process of clipboard data sharing in spice is the same. Take the win32-vd_agent source code as an example: when a party, such as the client, performs a copy operation, it will send GRAB data to spice agent, and this function will be called when spice agent receives the GRAB data from the client:

Bool VDAgent::handle_clipboard_grab (VDAgentClipboardGrab* clipboard_grab, uint32_t size) {std::set grab_formats; _ grab_types.clear (); for (uint32_t I = 0; I

Types [0]); iTunes +) {vd_printf ("grab type% u", clipboard_grab- > types [I]); uint32_t format = get_clipboard_format (clipboard_grab- > types [I]); / / On first supported type, open and empty the clipboard if (format & & grab_formats.empty ()) {if (! OpenClipboard (_ hwnd)) {return false } EmptyClipboard ();} / For all supported type set delayed rendering if (format) {_ grab_types.insert (clipboard_grab- > types [I]); if (grab_formats.insert (format) .second) {SetClipboardData (format, NULL) } if (grab_formats.empty ()) {vd_printf ("No supported clipboard types in client grab"); return true;} CloseClipboard (); set_clipboard_owner (owner_client); return true;}

This function empties the clipboard of guest and passes set_clipboard_owner (owner_client); sets the owner of the clipboard to client.

When the client (guest) side performs the paste operation, spice agent calls the on_clipboard_request (UINT format) function to send REQUEST data to the client.

When the client side receives the REQUEST data, it will send the CLIPBOARD data to the agent on the client, that is, encapsulate the clipboard data into the VDAgentClipboard. After receiving the data, spice agent calls the handle_clipboard () function to parse the data and write it to the client's clipboard.

Bool VDAgent::handle_clipboard (VDAgentClipboard* clipboard, uint32_t size) {HANDLE clip_data; UINT format; bool ret = false; if (_ clipboard_owner! = owner_client) {vd_printf ("Received clipboard data from client while clipboard is not owned by client"); goto fin;} if (clipboard- > type = = VD_AGENT_CLIPBOARD_NONE) {goto fin } switch (clipboard- > type) {case VD_AGENT_CLIPBOARD_UTF8_TEXT: clip_data = utf8_alloc ((LPCSTR) clipboard- > data, size); break; case VD_AGENT_CLIPBOARD_IMAGE_PNG: case VD_AGENT_CLIPBOARD_IMAGE_BMP: {DWORD cximage_format = get_cximage_format (clipboard- > type); ASSERT (cximage_format); CxImage image (clipboard- > data, size, cximage_format) Clip_data = image.CopyToHandle (); break;} default: vd_printf ("Unsupported clipboard type% u", clipboard- > type); goto fin;} format = get_clipboard_format (clipboard- > type); if (format = = 0) {vd_printf ("Unknown clipboard format, type% u", clipboard- > type); goto fin;} ret =! SetClipboardData (format, clip_data) If (! ret) {DWORD err = GetLastError (); if (err = = ERROR_NOT_ENOUGH_MEMORY) {vd_printf ("Not enough memory to set clipboard data, size% u bytes", size);} else {vd_printf ("SetClipboardData failed:% lu", err);} fin: set_control_event (CONTROL_CLIPBOARD); return ret;}

The clipboard data sharing process is shown in figure 1.1. The agent on the client and the clipboard data processing flow on the client are symmetrical. So the same is true when the Guest machine copies, first sets the clipboard owner to guest, and sends GRAB data to the client. When receiving the REQUEST data request from the client, the CLIPBOARD data is sent to the client.

Figure 1.1 client-guest clipboard data transfer

The above is how to analyze the spice agent clipboard sharing mechanism. The editor believes that there are some knowledge points that we may see or use in our daily work. I hope you can learn more from this article. For more details, please follow the industry information channel.

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