From 11f9d440bf72589253b5f19e376f3be516f676be Mon Sep 17 00:00:00 2001
From: Solderpunk <solderpunk@sdf.org>
Date: Tue, 29 Oct 2019 19:45:36 +0200
Subject: [PATCH] Initial implementation.

---
 LICENSE        |   2 +-
 README.md      |  43 ++++++++++++++++-
 gemini-demo.go | 123 +++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 166 insertions(+), 2 deletions(-)
 create mode 100644 gemini-demo.go

diff --git a/LICENSE b/LICENSE
index c2e480e..3547482 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,4 +1,4 @@
-Copyright (c) <year> <owner> . All rights reserved.
+Copyright (c) <2019> <solderpunk@sdf.org> . All rights reserved.
 
 Redistribution and use in source and binary forms, with or without modification,
 are permitted provided that the following conditions are met:
diff --git a/README.md b/README.md
index ec087fb..b566200 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,44 @@
 # gemini-demo-3
 
-Minimal but usable interactive Gemini client in almost < 100 LOC of Go
\ No newline at end of file
+Minimal but usable interactive Gemini client in not quite < 100 LOC
+of Go.
+
+## Rationale
+
+One of the original design criteria for the Gemini protocol was that
+"a basic but usable (not ultra-spartan) client should fit comfortably
+within 50 or so lines of code in a modern high-level language.
+Certainly not more than 100".  This client was written to gauge how
+close to (or far from!) that goal the initial rough specification is.
+
+## Capabilities
+
+This crude but functional client:
+
+* Has a minimal interactive interface for "Gemini maps"
+* Will print plain text in UTF-8
+* Will NOT prompt for user input
+* Will NOT follow redirects
+* Will report errors
+* Does NOT DO ANY validation of TLS certificates
+
+Non-text files are not yet handled.
+
+This is less functional than the Python demo (gemini-demo-1) or Lua
+demo (gemini-demo-2).  Further, it's the only one of these demo
+clients which is not currently below 100 lines.  This may be as much
+due to my inexperience with Go as with the language's unavoidable
+verbosity.  Improvements welcome.
+
+## Usage
+
+Run the client and you'll get a prompt.  Type a Gemini URL (the scheme
+is implied, so simply entering e.g. `gemini.conman.org` will work) to
+visit a Gemini location.
+
+If a Gemini menu is visited, you'll see numeric indices for links, ala
+VF-1 or AV-98.  Type a number to visit that link.
+
+There is very crude history: you can type `b` to go "back".
+
+Type `q` to quit.
diff --git a/gemini-demo.go b/gemini-demo.go
new file mode 100644
index 0000000..2c2dd4f
--- /dev/null
+++ b/gemini-demo.go
@@ -0,0 +1,123 @@
+package main
+
+import (
+	"bufio"
+	"crypto/tls"
+	"fmt"
+	"io/ioutil"
+	"net/url"
+	"os"
+	"strconv"
+	"strings"
+)
+
+func main() {
+	stdinReader := bufio.NewReader(os.Stdin)
+	var u string // URL
+	links := make([]string, 0, 100)
+	history := make([]string, 0, 100)
+	for {
+		fmt.Print("> ")
+		cmd, _ := stdinReader.ReadString('\n')
+		cmd = strings.TrimSpace(cmd)
+		// Command dispatch
+		switch strings.ToLower(cmd) {
+		case "": // Nothing
+			continue
+		case "q": // Quit
+			fmt.Println("Bye!")
+			os.Exit(0)
+		case "b": // Back
+			if len(history) < 2 {
+				fmt.Println("No history yet!")
+				continue
+			}
+			u = history[len(history)-2]
+			history = history[0 : len(history)-2]
+		default:
+			index, err := strconv.Atoi(cmd)
+			if err != nil {
+				// Treat this as a URL
+				u = cmd
+				if !strings.HasPrefix(u, "gemini://") {
+					u = "gemini://" + u
+				}
+			} else {
+				// Treat this as a menu lookup
+				u = links[index-1]
+			}
+		}
+		// Parse URL
+		parsed, err := url.Parse(u)
+		if err != nil {
+			fmt.Println("Error parsing URL!")
+			continue
+		}
+		// Connect to server
+		conn, err := tls.Dial("tcp", parsed.Host+":1965", &tls.Config{InsecureSkipVerify: true})
+		if err != nil {
+			fmt.Println("Failed to connect: " + err.Error())
+			continue
+		}
+		defer conn.Close()
+		// Send request
+		conn.Write([]byte(u + "\r\n"))
+		// Receive and parse response header
+		reader := bufio.NewReader(conn)
+		responseHeader, err := reader.ReadString('\n')
+		parts := strings.Fields(responseHeader)
+		status, err := strconv.Atoi(parts[0][0:1])
+		meta := parts[1]
+		// Switch on status code
+		switch status {
+		case 1, 3, 6:
+			// No input, redirects or client certs
+			fmt.Println("Unsupported feature!")
+		case 2:
+			// Successful transaction
+			// text/* content only
+			if !strings.HasPrefix(meta, "text/") {
+				fmt.Println("Unsupported type " + meta)
+				continue
+			}
+			// Read everything
+			bodyBytes, err := ioutil.ReadAll(reader)
+			if err != nil {
+				fmt.Println("Error reading body")
+				continue
+			}
+			body := string(bodyBytes)
+			if meta == "text/gemini" {
+				// Handle Gemini map
+				links = make([]string, 0, 100)
+				for _, line := range strings.Split(body, "\n") {
+					if strings.HasPrefix(line, "=>") {
+						line = line[2:]
+						bits := strings.Fields(line)
+						parsedLink, err := url.Parse(bits[0])
+						if err != nil {
+							continue
+						}
+						link := parsed.ResolveReference(parsedLink).String()
+						var label string
+						if len(bits) == 1 {
+							label = link
+						} else {
+							label = strings.Join(bits[1:], " ")
+						}
+						links = append(links, link)
+						fmt.Printf("[%d] %s\n", len(links), label)
+					} else {
+						fmt.Println(line)
+					}
+				}
+			} else {
+				// Just print any other kind of text
+				fmt.Print(body)
+			}
+			history = append(history, u)
+		case 4, 5:
+			fmt.Println("ERROR: " + meta)
+		}
+	}
+}