Add support for line mode, NAWS, Status (#10)

* Add initial support for line mode

* Formatting and more SLC code

* Add initial tests for linemode code

* Document Line Mode constants properly

* Correct mistaken comment

* Add character-at-a-time mode

* Formatting

* Fix formatting, finish forward mask code and change from Into to From

* Fix Mode and Unknown encoding in Line Mode and add tests for de- and encoding

* Restore documentation of ECHO

src/constants.rs

@@ -13,7 +13,7 @@ pub const IAC: u8 = 255;
 // Subnegotiation Begin
 pub const SB: u8 = 250;
 
-// Negotiate About Window Size
+// Negotiate About Window Size <https://datatracker.ietf.org/doc/rfc1073/>
 pub const NAWS: u8 = 31;
 
 // Subnegotiation End
@@ -39,10 +39,16 @@ pub const CRLF: &[u8] = b"\r\n";
 
 // Linemode - <https://datatracker.ietf.org/doc/html/rfc1116#section-2.1>
 pub const LINEMODE: u8 = 34;
+// `<https://tools.ietf.org/search/rfc1116>` 2.2 LINEMODE suboption MODE
+pub const MODE: u8 = 1; // Indicates the suboption code for the LINEMODE MODE. This is used to negotiate the mode of line processing between the Telnet client and server, allowing for a more flexible and efficient handling of line-oriented data.
 
-// Linemode subnegotiation options -
-// <https://datatracker.ietf.org/doc/html/rfc1184#section-2>
-pub const MODE: u8 = 1; //
+/// Defines the suboption code for the LINEMODE SLC (Special Character) function. This is used in Telnet communications to negotiate the handling of special characters that control various terminal functions, such as interrupt, flush, and suspend actions.
+/// The SLC suboption allows for the configuration and manipulation of these special characters, enhancing the control over the terminal behavior in a Telnet session.
+pub const LINEMODE_SLC: u8 = 3;
+
+/// Represents a mask used in LINEMODE negotiations to indicate the forwarding of linemode options. When set, this mask signals that the client wishes to forward linemode options to the server, thereby enabling the server to configure linemode settings.
+/// This capability is part of the LINEMODE suboptions negotiation, allowing for dynamic and flexible configuration of line processing behaviors based on the client's requirements and capabilities.
+pub const LINEMODE_FORWARD_MASK: u8 = 2;
 
 // When set, the client side of the connection should process all input lines,
 // performing any editing function, and only send completed lines to the remote
@@ -77,6 +83,15 @@ pub const DONT: u8 = 254;
 // End of Record negotiation
 pub const TELOPT_EOR: u8 = 25;
 
+/// STATUS - Verify the current status of options - https://www.rfc-editor.org/rfc/rfc859.html
+pub const STATUS: u8 = 5;
+
+/// TIMING MARK - Verify that requested information has been used - https://datatracker.ietf.org/doc/rfc860/
+pub const TIMING_MARK: u8 = 6;
+
+/// Remote flow control - https://datatracker.ietf.org/doc/rfc1372/
+pub const REMOTE_FLOW_CONTROL: u8 = 33;
+
 // End of Record - <https://tintin.mudhalla.net/protocols/eor/>
 pub const EOR: u8 = 239;
 
@@ -107,3 +122,123 @@ pub const CHARSET_TTABLE_IS: u8 = 4;
 pub const CHARSET_TTABLE_REJECTED: u8 = 5;
 pub const CHARSET_TTABLE_ACK: u8 = 6;
 pub const CHARSET_TTABLE_NAK: u8 = 7;
+
+/// Constants representing different levels and functionalities associated with
+/// Telnet's Special Linemode Characters (SLC).
+
+/// `SLC_DEFAULT`: Represents the default state of a linemode option. This level indicates
+/// that the default action should be taken for a particular SLC function.
+/// It is typically used when no specific action or value is assigned to an SLC function.
+pub const SLC_DEFAULT: u8 = 3;
+
+/// `SLC_VALUE`: Signifies that a specific value is associated with an SLC function. This
+/// level is used when a particular SLC function is configured with a specific,
+/// non-default value that must be recognized and acted upon.
+pub const SLC_VALUE: u8 = 2;
+
+/// `SLC_CANTCHANGE`: Indicates that the current SLC function's setting cannot be modified.
+/// This level is used for SLC functions that are essential for the operation
+/// or for which the ability to change the setting would result in undesired behavior.
+pub const SLC_CANTCHANGE: u8 = 1;
+
+/// `SLC_NOSUPPORT`: Represents the lack of support for a particular SLC function. This
+/// level is used when a Telnet client or server does not recognize or cannot
+/// implement the specific SLC function being queried or set.
+pub const SLC_NOSUPPORT: u8 = 0;
+
+/// `SLC_LEVELBITS`: A mask used to isolate the level bits in an SLC function definition.
+/// This constant is used in operations that require identifying the specific
+/// level associated with an SLC function.
+pub const SLC_LEVELBITS: u8 = 3;
+
+/// `SLC_ACK`: A flag used to acknowledge the receipt or acceptance of an SLC function
+/// setting. This acknowledgment can be part of a negotiation process where
+/// one side proposes a setting and the other side acknowledges it.
+pub const SLC_ACK: u8 = 128;
+
+/// `SLC_FLUSHIN`: A flag indicating that all incoming data should be flushed (i.e., discarded).
+/// This is used in situations where it is necessary to clear the input buffer,
+/// such as when the mode of operation changes or in response to certain error conditions.
+pub const SLC_FLUSHIN: u8 = 64;
+
+/// `SLC_FLUSHOUT`: Similar to `SLC_FLUSHIN`, but for outgoing data. This flag indicates that
+/// all data queued for output should be flushed. This can be useful in situations
+/// where an immediate response is needed, or when clearing the output buffer
+/// is required to maintain the correct sequence of data or commands.
+pub const SLC_FLUSHOUT: u8 = 32;
+
+/// Telnet Special Linemode Characters (SLC) Functions as Constants
+
+// SLC Function Names
+/// SLC_SYNCH: Synchronize
+pub const SLC_SYNCH: u8 = 1;
+/// SLC_BRK: Break
+pub const SLC_BRK: u8 = 2;
+/// SLC_IP: Interrupt Process
+pub const SLC_IP: u8 = 3;
+/// SLC_AO: Abort Output
+pub const SLC_AO: u8 = 4;
+/// SLC_AYT: Are You There
+pub const SLC_AYT: u8 = 5;
+/// SLC_EOR: End of Record
+pub const SLC_EOR: u8 = 6;
+/// SLC_ABORT: Abort
+pub const SLC_ABORT: u8 = 7;
+/// SLC_EOF: End of File
+pub const SLC_EOF: u8 = 8;
+/// SLC_SUSP: Suspend Process
+pub const SLC_SUSP: u8 = 9;
+/// SLC_EC: Erase Character
+pub const SLC_EC: u8 = 10;
+/// SLC_EL: Erase Line
+pub const SLC_EL: u8 = 11;
+/// SLC_EW: Erase Word
+pub const SLC_EW: u8 = 12;
+/// SLC_RP: Repaint
+pub const SLC_RP: u8 = 13;
+/// SLC_LNEXT: Literal Next
+pub const SLC_LNEXT: u8 = 14;
+/// SLC_XON: Resume Transmission
+pub const SLC_XON: u8 = 15;
+/// SLC_XOFF: Stop Transmission
+pub const SLC_XOFF: u8 = 16;
+/// SLC_FORW1: Forward Character
+pub const SLC_FORW1: u8 = 17;
+/// SLC_FORW2: Forward Line
+pub const SLC_FORW2: u8 = 18;
+/// SLC_MCL: Move Cursor Left
+pub const SLC_MCL: u8 = 19;
+/// SLC_MCR: Move Cursor Right
+pub const SLC_MCR: u8 = 20;
+/// SLC_MCWL: Move Cursor Word Left
+pub const SLC_MCWL: u8 = 21;
+/// SLC_MCWR: Move Cursor Word Right
+pub const SLC_MCWR: u8 = 22;
+/// SLC_MCUB: Move Cursor Up One Line
+pub const SLC_MCUB: u8 = 23;
+/// SLC_MCUF: Move Cursor Down One Line
+pub const SLC_MCUF: u8 = 24;
+/// SLC_LP: Local Print
+pub const SLC_LP: u8 = 25;
+/// SLC_XONC: XON Character
+pub const SLC_XONC: u8 = 26;
+/// SLC_XOFFC: XOFF Character
+pub const SLC_XOFFC: u8 = 27;
+/// SLC_EXIT: Exit
+pub const SLC_EXIT: u8 = 28;
+/// SLC_SUSPC: Suspend Current Process
+pub const SLC_SUSPC: u8 = 29;
+/// SLC_DSUSPC: Delayed Suspend Current Process
+pub const SLC_DSUSPC: u8 = 30;
+/// SLC_REPRINT: Reprint Unread Input
+pub const SLC_REPRINT: u8 = 31;
+/// SLC_ABORTC: Abort Output Character
+pub const SLC_ABORTC: u8 = 32;
+/// SLC_EOFCHAR: End of File Character
+pub const SLC_EOFCHAR: u8 = 33;
+/// SLC_SUSPCHAR: Suspend Process Character
+pub const SLC_SUSPCHAR: u8 = 34;
+/// SLC_BRKC: Break Character
+pub const SLC_BRKC: u8 = 35;
+/// SLC_EORC: End of Record Character
+pub const SLC_EORC: u8 = 36;