Gopher Protocol

Gopher Protocol Guide

Understanding the Gopher protocol and how it's implemented in the MCP server.

What is Gopher?

The Gopher protocol is a TCP-based document retrieval protocol designed in 1991 at the University of Minnesota. It predates the World Wide Web and provides a simple, hierarchical menu-based interface for accessing documents and services.

Protocol Basics

Connection

• Protocol: TCP
• Default Port: 70
• Encryption: None (standard Gopher)

Request Format

<selector><TAB><search><CR><LF>

• Selector: Path to the resource
• Search: Optional search query (for type 7)
• CR LF: Carriage return and line feed

Response Format

Gopher servers return raw data without headers. The format depends on the item type.

Gopher Item Types

Type	Description	Example
0	Text file	Plain text documents
1	Directory/Menu	Hierarchical menus
2	CSO phone book	Name server
3	Error	Error message
4	BinHex file	Macintosh file
5	DOS binary	PC binary file
6	UUEncoded file	Unix file
7	Search server	Full-text search
8	Telnet session	Telnet link
9	Binary file	Generic binary
g	GIF image	GIF file
I	Image file	Other image
h	HTML file	HTML document
i	Info line	Non-selectable text
s	Sound file	Audio file

Menu Format

Gopher menus (type 1) use a specific line format:

<type><display text><TAB><selector><TAB><host><TAB><port><CR><LF>

Example:

0Welcome Text /welcome.txt gopher.example.com 70
1Subdirectory /subdir gopher.example.com 70
iInformation line fake null 0

URL Format

Gopher URLs follow this format:

gopher://<host>[:<port>]/<type><selector>[?<search>]

Examples:

gopher://gopher.floodgap.com/1/
gopher://gopher.floodgap.com:70/0/gopher/welcome
gopher://gopher.floodgap.com/7/v2/vs?python

Implementation in MCP Server

Supported Features

• Menu Browsing (type 1): Full menu parsing and navigation
• Text Files (type 0): Complete text file retrieval
• Search (type 7): Search server support with queries
• Binary Metadata (types 4, 5, 6, 9, g, I): Metadata without download

URL Parsing

The server parses Gopher URLs into components:

{
    "host": "gopher.floodgap.com",
    "port": 70,
    "gopher_type": "1",
    "selector": "/",
    "search": None
}

Response Processing

Menu Response (Type 1)

Returns structured menu items:

{
  "kind": "menu",
  "items": [
    {
      "type": "1",
      "title": "Directory Name",
      "selector": "/path",
      "host": "gopher.example.com",
      "port": 70,
      "nextUrl": "gopher://gopher.example.com:70/1/path"
    }
  ]
}

Text Response (Type 0)

Returns text content:

{
  "kind": "text",
  "content": "File content here...",
  "metadata": {
    "size": 1234,
    "encoding": "utf-8"
  }
}

Binary Response (Types 4, 5, 6, 9, g, I)

Returns metadata only:

{
  "kind": "binary",
  "metadata": {
    "type": "9",
    "size": 5678,
    "description": "Binary file"
  }
}

Security Considerations

Input Validation

• URL format validation
• Selector length limits (max 1024 characters)
• Search query length limits (max 256 characters)
• Host allowlist support

Resource Limits

• Maximum response size (default 1MB)
• Connection timeout (default 30 seconds)
• Read timeout enforcement

Binary File Protection

Binary files return metadata only to prevent:

• Memory exhaustion
• Malicious file downloads
• Unnecessary bandwidth usage

Popular Gopher Servers

Floodgap Systems

gopher://gopher.floodgap.com/1/

The most well-known Gopher server, maintained by Cameron Kaiser. Contains extensive Gopher resources and information.

Quux.org

gopher://quux.org/1/

Long-running Gopher server with various content.

Gopher Lawn

gopher://gopherlawn.net/1/

Community Gopher server with user-contributed content.

Best Practices

For Users

1. Start with main menus (type 1)
2. Follow menu structure hierarchically
3. Use search (type 7) for finding content
4. Be patient with slow servers

For Developers

1. Always validate URLs before requests
2. Implement proper timeout handling
3. Parse menu items carefully
4. Handle errors gracefully
5. Respect server resources

Common Issues

Empty Menus

Some servers return empty menus for certain paths. This is normal behavior.

Slow Responses

Gopher servers may be slow or intermittent. Use appropriate timeouts.

Character Encoding

Gopher predates Unicode. Most content is ASCII or ISO-8859-1.

Further Reading

• RFC 1436 - The Gopher Protocol
• Gopher Wikipedia
• Floodgap Gopher

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Made with ❤️ by Cameron Rye