Telnet Protocol Implementation Analysis

CircleMUD (C)

Files

/Users/thiagobelem/tmp/mud-analysis/CircleMUD/src/telnet.h - Standard telnet header
/Users/thiagobelem/tmp/mud-analysis/CircleMUD/src/comm.c - Communication/network layer

Telnet Options Supported

Standard telnet options defined in telnet.h (lines 82-122):

TELOPT_BINARY (0) - 8-bit data path
TELOPT_ECHO (1) - Echo control
TELOPT_SGA (3) - Suppress Go Ahead
TELOPT_NAWS (31) - Negotiate About Window Size
TELOPT_TTYPE (24) - Terminal Type
TELOPT_LINEMODE (34) - Linemode option
TELOPT_LFLOW (33) - Remote flow control
TELOPT_TSPEED (32) - Terminal speed
TELOPT_AUTHENTICATION (37)
TELOPT_ENCRYPT (38)
TELOPT_NEW_ENVIRON (39)
And 33+ other standard telnet options

MUD-Specific Protocol Support

NONE - No evidence of GMCP, MSDP, MSSP, MCCP, MXP, or ATCP support

Implementation Details

Uses standard BSD telnet header definitions (lines 42-72 of telnet.h)
Manual telnet negotiation with IAC (Interpret As Command) codes
Echo control functions: echo_off() and echo_on() in comm.c (lines 955-983)
Simple DO/WILL/WONT negotiation
No compression, no out-of-band protocols

Approach

Minimal telnet implementation (bootstrap approach)
Focuses on basic echo control for password entry
All protocol handling manual/hardcoded in comm.c
No subcommand negotiation for advanced features

DikuMUD2 (C)

Files

/Users/thiagobelem/tmp/mud-analysis/DikuMUD2/dm-dist-ii/protocol.h - Protocol definitions
/Users/thiagobelem/tmp/mud-analysis/DikuMUD2/dm-dist-ii/protocol.c - Protocol implementation
/Users/thiagobelem/tmp/mud-analysis/DikuMUD2/dm-dist-ii/comm.c - Network layer

Telnet Options Supported

Custom protocol.h defines custom terminal control scheme:

TERM_DUMB, TERM_TTY, TERM_ANSI, TERM_VT100, TERM_INTERNAL
Width/height negotiation
Echo control (CONTROL_ECHO_OFF, CONTROL_ECHO_ON)
Custom color codes using escape sequences
Terminal type tracking

MUD-Specific Protocol Support

NONE - No GMCP, MSDP, MSSP, MCCP, MXP, or ATCP support

Implementation Details

Custom protocol wrapper around basic telnet
struct terminal_setup_type tracks client capabilities (lines 46-54)
Custom color mapping system (CONTROL_FG_, CONTROL_BG_)
Multi-connection protocol support with unique frame markers
Protocol messages for setup, text, host info, etc.

Approach

Custom protocol layer on top of telnet (not standard telnet negotiation)
Proprietary client required for full feature support
Terminal type detection built-in
No compression or advanced OOB protocols

Evennia (Python)

Files

/Users/thiagobelem/tmp/mud-analysis/Evennia/evennia/server/portal/telnet.py - Main telnet protocol
/Users/thiagobelem/tmp/mud-analysis/Evennia/evennia/server/portal/telnet_oob.py - Out-of-band protocols
/Users/thiagobelem/tmp/mud-analysis/Evennia/evennia/server/portal/mccp.py - MCCP v2 compression
/Users/thiagobelem/tmp/mud-analysis/Evennia/evennia/server/portal/mssp.py - Server status protocol
/Users/thiagobelem/tmp/mud-analysis/Evennia/evennia/server/portal/mxp.py - MUD eXtension Protocol
/Users/thiagobelem/tmp/mud-analysis/Evennia/evennia/server/portal/naws.py - Window size negotiation
/Users/thiagobelem/tmp/mud-analysis/Evennia/evennia/server/portal/ttype.py - Terminal type detection

Standard Telnet Options Supported

From telnet.py imports and usage:

ECHO (line 14) - Echo control
GA (line 15) - Go Ahead
IAC (line 16) - Interpret As Command
LINEMODE (lines 17-20) with MODE_EDIT, LINEMODE_TRAPSIG
WILL/WONT (lines 23-24)
NULL (line 22)
NOP (line 21)
NAWS (line 34, naws.py line 18) - Negotiate About Window Size
TTYPE (line 31, ttype.py line 18) - Terminal Type

MUD-Specific Protocol Support

MCCP (v2) - Mud Client Compression Protocol
- File: mccp.py, line 22: MCCP = bytes([86])
- Zlib-based compression (lines 26-39)
- Reduces bandwidth by 70-90%
- Negotiated via WILL/WONT (line 64)
MSSP - Mud Server Status Protocol
- File: mssp.py, line 20: MSSP = bytes([70])
- Server metadata: NAME, PLAYERS, UPTIME, PORT, CODEBASE (lines 88-113)
- Includes: ANSI, GMCP, MCCP, MSDP, MXP, SSL, UTF-8, VT100, XTERM256 support flags
- Designed for web crawlers and listing portals
GMCP - Generic Mud Communication Protocol
- File: telnet_oob.py, line 47: GMCP = bytes([201])
- Supports all core GMCP commands (lines 106-150 of CMProtocols)
- Commands: core., char., room., comm., client.*, etc.
- Uses JSON for structured data (line 27)
MSDP - Mud Server Data Protocol
- File: telnet_oob.py, lines 37-44: MSDP = bytes([69])
- MSDP_VAR, MSDP_VAL, MSDP_TABLE_OPEN/CLOSE, MSDP_ARRAY_OPEN/CLOSE
- Structured variable-value protocol
MXP - Mud eXtension Protocol
- File: mxp.py, line 26: MXP = bytes([91])
- Partial implementation (SEND tag only, line 8)
- Supports MXP_TEMPSECURE mode (line 28)
- SEND and URL parsing (lines 22-23)
- Configurable via MXP_ENABLED setting (line 67)
TTYPE - Terminal Type Detection (MTTS)
- File: ttype.py, line 18: TTYPE = bytes([24])
- MTTS bitstring capabilities (lines 23-36)
- Supports: ANSI, VT100, UTF-8, XTERM256, TRUECOLOR, PROXY, SCREENREADER, etc.
- Multi-step negotiation (lines 107-199)
- Client fingerprinting (Mudlet, CMUD, Mushclient, etc.)

Implementation Details

Uses Twisted framework's telnet support as base (line 13)
Protocol flags dictionary tracks negotiated capabilities
Callback system for feature negotiation (addCallbacks pattern)
Negotiation map for protocol-specific handlers
Silent flag propagation system
OOB protocols check handshake_done() gates

Approach

Modular protocol system with separate classes per feature
Modern Python with async/await via Twisted
Configuration-driven feature enablement
Extensible protocol_flags dictionary
Proper RFC/standard compliance

CoffeeMud (Java)

Files

/Users/thiagobelem/tmp/mud-analysis/CoffeeMud/com/planet_ink/coffee_mud/Libraries/CMProtocols.java - Protocol library
/Users/thiagobelem/tmp/mud-analysis/CoffeeMud/com/planet_ink/coffee_mud/Libraries/interfaces/TelnetFilter.java - Telnet filtering

Standard Telnet Options Supported

Not explicitly documented in visible source, but filtering suggests standard telnet with:

Color code handling
MXP tag support
MSP (Mud Sound Protocol) support (line 77)
Text filtering and word wrapping
Escape sequence handling

MUD-Specific Protocol Support

GMCP - Generic Mud Communication Protocol
- File: CMProtocols.java, line 106: enum GMCPCommand
- Core 50+ commands including:
  - core_hello, core_supports_*, core_keepalive, core_ping, core_goodbye
  - char_login, char_vitals, char_statusvars, char_status, char_base, char_maxstats, char_worth
  - char_items_*, char_skills_get, char_effects_get
  - room_info, room_exits, room_items_*, room_mobiles, room_players
  - comm_channel, comm_channel_players
  - group, request_*, maplevel, client, external_discord_hello
- Full enum definition (lines 106-151)
MXP - Mud eXtension Protocol
- File: CMProtocols.java: mxp() method (lines 75-82)
- Image support with getHashedMXPImage, getDefaultMXPImage
- MXP image path configuration (MXPIMAGEPATH setting)
- Can be disabled via CMSecurity flags (line 77)
MSP - Mud Sound Protocol
- File: CMProtocols.java, line 75: msp() method
- Format: !!SOUND(soundName V=volume P=priority U=url)
- Configurable sound path (MSPPATH setting, line 79)
- Volume and priority support
MCP - Multi-User Dungeon Client Protocol
- File: CMProtocols.java: MCP parsing (lines 85-300+)
- Full state machine parser: McpParseStartState enum
- Key-value pair parsing with quoted values
- Multi-line command support
- Star-tag support for extensibility

TelnetFilter Features

From TelnetFilter.java:

fullOutFilter - Complete output processing (MXP, MSP, word wrap, colors)
simpleOutFilter - Minimal processing (escapes only)
colorOnlyFilter - Color codes with MXP
mxpSafetyFilter - MXP tag safety
wrapOnlyFilter - Word wrap only
simpleInFilter/fullInFilter - Input safety filtering

Implementation Details

CMProtocols extends StdLibrary (line 61)
Modular filtering system for input/output
Pronoun tag substitution system
Comprehensive MXP image management
MCP parser with full state machine (McpParseStartState)
GMCP command enum for type-safe handling

Approach

Comprehensive MUD protocol support (MXP, MSP, MCP, GMCP)
Java-based with strong typing and enums
Modular filter system for text processing
Configuration-driven feature enablement
Professional-grade implementation

Comparative Summary

Protocol Support Matrix

Protocol	CircleMUD	DikuMUD2	Evennia	CoffeeMud
ECHO	YES	NO	YES	YES (implicit)
SGA	YES	NO	YES	YES (implicit)
NAWS	YES (defined)	Custom	YES	NO
TTYPE	YES (defined)	Custom	YES	NO
GMCP	NO	NO	YES	YES
MSDP	NO	NO	YES	Partial (GMCP only)
MSSP	NO	NO	YES	NO
MCCP	NO	NO	YES	NO
MXP	NO	NO	YES	YES
MSP	NO	NO	NO	YES
MCP	NO	NO	NO	YES
Compression	NO	NO	YES (zlib)	NO

Implementation Approach Comparison

CircleMUD: Minimal, bootstrap implementation

Defines all standard telnet options but doesn't implement most
Only uses ECHO negotiation in practice
No MUD-specific protocols
Hardcoded manual negotiation

DikuMUD2: Custom proprietary protocol

Replaces standard telnet with custom wire protocol
Terminal type tracking built-in
Color mapping system
Requires custom client implementation
No standard telnet negotiation

Evennia: Modern, comprehensive, modular

Full RFC compliance for all supported protocols
Modular architecture: separate class per protocol
Configuration-driven enablement
Strong encapsulation with negotiation gates
Uses modern async (Twisted) framework
Best for standardized client support

CoffeeMud: Professional, feature-rich

Comprehensive MUD protocol ecosystem (MCP, GMCP, MXP, MSP)
Type-safe enum-based approach
State machine parser for complex protocols
Integrated filtering system
Best for rich client features and extensibility

Key Findings for Ruby Implementation

Standard Telnet is Minimal: CircleMUD shows that true telnet negotiation is simple - just ECHO control needed for basics
OOB Protocols are Essential: Evennia demonstrates that modern MUDs rely on out-of-band protocols (GMCP, MSDP, MSSP, MCCP) for advanced features
Modularity is Important: Evennia's separate protocol classes vs CoffeeMud's monolithic approach shows that separation of concerns aids maintainability
Configuration Matters: Both Evennia and CoffeeMud use settings/config for feature enablement, reducing coupling
Compression is Valuable: MCCP (zlib compression) is the only standard protocol that significantly improves bandwidth efficiency
Protocol Negotiation Pattern: All use similar pattern:
- Server sends WILL/DO offer
- Client responds with WILL/WONT or DO/DONT
- Subnegotiation (SB/SE) for detailed options
- Callback system for async handling
Best Practices:
- Use weakref for protocol references (Evennia pattern)
- Protocol flags dictionary for capability tracking
- Separate modules for each protocol
- Configuration-driven enablement
- Callback-based negotiation (not blocking)
- Proper RFC compliance

TiuTalk/telnet_protocols_research.md

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Telnet Protocol Implementation Analysis

CircleMUD (C)

Files

Telnet Options Supported

MUD-Specific Protocol Support

Implementation Details

Approach

DikuMUD2 (C)

Files

Telnet Options Supported

MUD-Specific Protocol Support

Implementation Details

Approach

Evennia (Python)

Files

Standard Telnet Options Supported

MUD-Specific Protocol Support

Implementation Details

Approach

CoffeeMud (Java)

Files

Standard Telnet Options Supported

MUD-Specific Protocol Support

TelnetFilter Features

Implementation Details

Approach

Comparative Summary

Protocol Support Matrix

Implementation Approach Comparison

Key Findings for Ruby Implementation