Protocol Version 1

If the client and the server agree on protocol version 1 after negotiation, the client starts communicating using that protocol. First, the client selects the method and requests it from the server. Then the server accepts the request and continues the communication.

Selecting the Method

• The client starts by sending the method code in a single byte (ex: if the method code is 1, the client sends \x01). The method code can be 1, 2, 3, 4, 5, or 125. Refer to the Supported Methods section for more information about the methods.
• Upon receiving the method request, the server responds with a single byte denoting the method status code for that request. If the method request is accepted, the server and the client will continue communication. Refer to the Supported Methods section for more information about the structure of the remaining part of the communication.
• If the method request is not accepted or there is no more communication to happen, the client and the server will close the connection.

Method Codes

The supported method codes and their names.

Method code	Method name
1	Get Text
2	Send Text
3	Get Files
4	Send File
5	Get Image/Screenshot
125	Info

Method Status Codes

When the server receives a method request from the client, it will respond to the client with one of the following status codes. The status code will be sent to the client as a single byte. For example, if the status code is 1, the server sends the byte \x01.

The supported method status codes and their descriptions.

Status code value	Status code name	Description
1	OK	The method is accepted. If this method is to send data to the server, the client can now start sending data. If this method is to get data from the server, the server will now start sending data.
2	NO_DATA	This status occurs only for methods that get data from the server (ex: get_text, get_files). This status implies that the method is valid and accepted, but the server has no data to send (possibly because there is no text or files copied into the clipboard of the server device). Therefore, the communication ends at this point, and the connection can be closed now.
3	UNKNOWN_METHOD	This status code is sent when the client requests an invalid method request code. The request is rejected, and the communication ends at this point. Therefore, the server and the client can close the connection.
4	METHOD_NOT_IMPLEMENTED	This status code implies that the method request code is valid. However, the server does not implement that method. Therefore, the request has to be rejected. The communication ends at this point, and the connection can be closed now.

Supported Methods

The following methods are supported in this protocol version.

Notes:

• All numeric values (ex: lengths and number of files) are sent/received as 64-bit signed integers in big-endian format.
• All the lengths of strings and file sizes are measured in bytes, and they are sent/received as numeric values as specified above.
• All the texts sent/received are UTF-8 encoded and do not contain a terminating null byte or any other prefixes or suffixes. The length of a text is calculated after encoding in this way.
• All the files sent/received are considered binary files. Therefore, the Unix/Windows style line endings or other platform-specific things in the file content are not changed. Also, the file content is considered a sequence of bytes, which is not modified (compressed or encoded) during transmission. The names of the files are considered as text and thus sent/received as specified above.
• Optional: Strings having line breaks should prefer LF ("\n") over CRLF ("\r\n") as the line separator.

Get Text

This method is used to get the copied text from the server to the client. Once the client requests this method code from the server and the server acknowledges the client with the status OK, the server will send the length of the copied text followed by the copied text to the client. Once the copied text is transmitted, the communication ends, and the connection can be closed. The client may copy the received text to the clipboard of the client device.

• The length is the number of bytes in the text sent after this. It should be less than 4 MiB in size. The length is encoded and sent, as specified above in the notes.
• The copied text is the text that is copied to the clipboard of the server device. It is encoded as specified above in the notes.

Send Text

This method is used to send the copied text from the client to the server. Once the client requests this method code from the server and the server acknowledges the client with the status OK, the client will send the length of the copied text followed by the copied text to the server. Once the copied text is transmitted, the communication ends, and the connection can be closed. The server may copy the received text to the clipboard of the server device.

• The length is the number of bytes in the text sent after this. It should be less than 4 MiB in size. The length is encoded and sent, as specified above in the notes.
• The copied text is the text that is copied to the clipboard of the client device. It is encoded as specified above in the notes.

Get Files

This method is used to get the copied files from the server to the client. This method only supports sending regular files (i.e., directories, links, or other types are not supported). Once the client requests this method code from the server and the server acknowledges the client with the status OK, the server will send the number of files encoded as a numeric value as specified above in the notes. After sending the number of files, each file is sent sequentially, as follows.

• First, the length of the file name is sent. A file name can have at most 1024 bytes after encoding. It is encoded as specified above in the notes.
• Then, the file name is sent. It is a text encoded as specified above in the notes. The file name cannot contain the characters '/' (forward-slash) or '\' (back-slash).
• Next, the size of the file is sent. File size can be at most 64 GiB. It is encoded as a numeric value, as specified above in the notes.
• Then, the file content is sent as a stream of bytes, as specified above in the notes.

Once all the files are transmitted, the communication ends, and the connection can be closed.

Send File

This method is used to send a file from the client to the server. This method only supports sending a single regular file at a time (i.e., directories, links, or other types are not supported). Once the client requests this method code from the server and the server acknowledges the client with the status OK, the client will send the file to the server as follows.

• First, the length of the file name is sent. A file name can have at most 1024 bytes after encoding. It is encoded as specified above in the notes.
• Then, the file name is sent. It is a text encoded as specified above in the notes. The file name cannot contain the characters '/' (forward-slash) or '\' (back-slash).
• Next, the size of the file is sent. File size can be at most 64 GiB. It is encoded as a numeric value, as specified above in the notes.
• Then, the file content is sent as a stream of bytes, as specified above in the notes.

Once the file is transmitted, the communication ends, and the connection can be closed.

Get Image/Screenshot

This method is used to get a copied image or a screenshot from the server to the client. If the server device has an image copied to the clipboard, it will be sent. Otherwise, a screenshot of the server device will be sent as an image. The image gets encoded as a PNG image. Once the client requests this method code from the server, and if the server can get the image, the server acknowledges the client with the status OK. Then, the server will send the image as follows.

• First, the size of the image in bytes is sent. The image can be at most 1 GiB in size. It is encoded as a numeric value, as specified above in the notes.
• Then, the image is sent as a stream of bytes, as specified above in the notes.

Once the image is transmitted, the communication ends, and the connection can be closed. Note that there is no file name for the image. The client should create a file name if it needs to save this image as a file. If the server fails to get the image, it will send the status NO_DATA for the client's request instead of the status OK and terminate the connection without sending any further data.

Info

This method is used to get the name of the server. Once the client requests this method code from the server, and the server acknowledges the client with the status OK, the server will send the length of the name, followed by the server's name, "clip_share", to the client. Once the name is transmitted, the communication ends, and the connection can be closed.

• The length is the number of bytes in the name sent after this. It is encoded and sent, as specified above in the notes.
• The server's name is encoded as a text, as specified above in the notes.