Add an opt-in text clipboard packet by Wouze · Pull Request #155 · moonlight-stream/moonlight-common-c

Wouze · 2026-09-23T14:42:23Z

Summary

Add LiSendClipboardText() so a client can send UTF-8 clipboard text to the host. A zero-length send subscribes to host updates and does not change the host clipboard.
Add host-to-client control message 0x5505. Clients that do not implement the new callback ignore it.
Allow encrypted control messages larger than the old 256-byte stack buffer, which is required for a paragraph of clipboard text. Text is capped at 32,755 bytes.

This is the protocol piece for Sunshine and Moonlight Qt pull requests that use the same commit.

Test plan

Linux Moonlight client with Sync clipboard enabled, against a Sunshine host built with this commit, copies text both ways
A stock Moonlight client still connects; it does not receive clipboard text it did not subscribe for
Mac and Windows clients are not run yet; they share this library once their Moonlight Qt build includes it

Wouze · 2026-10-02T19:23:19Z

Hi. I merged current master into this branch, including the extended-key modifier. Sunshine and Moonlight Qt are both waiting on this protocol change. Could you review it when you have time?

Wouze · 2026-10-07T13:35:50Z

Hi @cgutman

ReenigneArcher approved this on October 3 and Sunshine and the Moonlight Qt setting are waiting on it. Could you take a look when you have time?

Thanks

Wouze · 2026-10-15T13:13:51Z

Hello

cgutman · 2026-10-19T06:26:55Z

+    }
+
+    // The unencrypted input path encrypts into a 128-byte stack buffer.
+    if (!isControlStreamEncrypted()) {


We need to check IS_SUNSHINE() here too.

cgutman · 2026-10-19T06:27:21Z

+    token ^= token << 5;
+    if (token == 0) {
+        token = 1;
+    }


What is the purpose of the token?

cgutman · 2026-10-19T06:28:17Z

+        char stackBuffer[256];
+        char* plainBuffer = stackBuffer;
+
+        if (paylen < 0 || paylen > 65535) {


You can drop these changes. We encrypt in place now.

cgutman · 2026-10-19T06:29:24Z

+        packet = (PNVCTL_ENET_PACKET_HEADER_V2)plainBuffer;
        packet->type = ptype;
-        packet->payloadLength = paylen;
+        packet->payloadLength = (unsigned short)paylen;


This is an unsafe truncating cast.

cgutman · 2026-10-19T06:31:37Z

+
+    // The unencrypted input path encrypts into a 128-byte stack buffer.
+    if (!isControlStreamEncrypted()) {
+        return -1;


LI_ERR_UNSUPPORTED

cgutman · 2026-10-19T06:32:10Z

 int LiSendUtf8TextEvent(const char *text, unsigned int length);

+// Send clipboard text to a Sunshine host. length 0 subscribes to host clipboard
+// updates and does not change the host clipboard. Requires an encrypted control stream.


Client authors don't know what an encrypted control stream is. I would just remove that detail.

cgutman · 2026-10-19T06:32:53Z

+        return -1;
+    }
+
+    holder->channelId = 0;


Use a new channel ID for this. You can take 0x6 which used to be for UTF-8 data.

cgutman · 2026-10-19T06:33:50Z

            break;
+        case IDX_CLIPBOARD_TEXT:
+            if (ListenerCallbacks.clipboardText != NULL) {
+                ListenerCallbacks.clipboardText(queuedCb->data.clipboardText.token,


Null check is not necessary, since the callback infrastructure ensures all callback pointers are populated

Clipboard sends are Sunshine-only on channel 0x6, and the unused echo token is gone. The control stream keeps master's in-place encryption.

Wouze · 2026-10-23T18:48:10Z

@cgutman the notes are in f197f1d. Clipboard sends are Sunshine-only on channel 0x6, the echo token is gone, and the control stream uses the current in-place encryption. Could you take another look?

Thanks

cgutman · 2026-11-01T21:14:21Z

I think the 32KB limit might be a problem in practice, so I introduced a new jumbo control message for you in 4853e70. Your Sunshine PR will need to be updated to add support for parsing this new header, but that should be pretty easy.

Can you adapt your changes to increase the limit clipboard data on to something larger like a few MB?

Wouze · 2026-11-01T21:18:51Z

Yes i agree with you, i initially gave it a small limit for testing

What size do you think would be sufficient? Also should we do images and other files? Personally I use copy/paste images all the time but idk if it fits this thing without hacky workarounds

cgutman · 2026-11-01T21:29:00Z

I think we could model something after the SDL3 clipboard API with a bidirectional protocol with 3 message types:

Clipboard offer message with all of the MIME types of what resides in our clipboard which we send when the clipboard changes
Clipboard payload request message with the specific MIME type they want the data for
Clipboard payload response message with the MIME type and the data itself

We would likely need some sort of chunking scheme for cases where the clipboard data is larger than 32 MB (the default ENet packet size limit).

Edit: I can take a stab at a protocol design later.

Either side offers the MIME types on its clipboard when it changes. The other side requests the types it wants and receives each one as data, tied to the offer by a sequence number. Data over 4 MB is sent in chunks of jumbo control messages, up to 64 MB. An offer with no types subscribes to host clipboard changes. This replaces the text-only clipboard messages.

Wouze · 2026-11-11T20:11:09Z

@cgutman reworked this based on your offer/request payload idea:

Each side sends an offer with the MIME types it has, the other side requests what it wants and gets the data back, matched by a sequence number
Anything over 4 MB gets chunked over your jumbo control messages, capped at 64 MB
Removed the old text-only messages. An empty offer now just subscribes to host clipboard changes

Other side of it:

Sunshine (feat(linux): add opt-in text clipboard sync SunshineStream/Sunshine#5782) does text and PNG/JPEG on Linux
Moonlight (Add an opt-in Sync clipboard setting moonlight-qt#2019) is text only for now since Qt's clipboard doesn't update during a stream, images can come later with SDL3

Tested 6 MB both ways between a Mac client and a Linux host, fully working

Can you take another look when you get a chance?

This was referenced Sep 23, 2026

feat(linux): add opt-in text clipboard sync SunshineStream/Sunshine#5782

Draft

Add an opt-in Sync clipboard setting moonlight-stream/moonlight-qt#2019

Open

Add an opt-in text clipboard packet between client and host.

d22d24c

Wouze force-pushed the clipboard-sync branch from 6152af4 to d22d24c Compare September 23, 2026 14:47

Merge branch 'master' into clipboard-sync

cfd6610

ReenigneArcher approved these changes Oct 3, 2026

View reviewed changes

tillbob approved these changes Oct 10, 2026

View reviewed changes

cgutman requested changes Oct 19, 2026

View reviewed changes

Merge branch 'master' into clipboard-sync

f197f1d

Clipboard sends are Sunshine-only on channel 0x6, and the unused echo token is gone. The control stream keeps master's in-place encryption.

Wouze requested a review from cgutman October 31, 2026 22:55

Wouze added 3 commits November 4, 2026 16:14

Merge master for jumbo control messages

0b4f597

Merge remote-tracking branch 'origin/master' into clipboard-sync

8968961

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Wouze commented Sep 23, 2026 •

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