Initial commit: extracted from impostor-bbs gems/bbs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/bbs/telnet.rb

@@ -0,0 +1,98 @@
+# frozen_string_literal: true
+
+module BBS
+  module Telnet
+    IAC  = 255
+    WILL = 251
+    WONT = 252
+    DO   = 253
+    DONT = 254
+    SB   = 250
+    SE   = 240
+
+    ECHO_OPT = 1
+    SGA_OPT  = 3
+
+    def negotiate
+      send_raw [IAC, WILL, SGA_OPT].pack('C*')
+      send_raw [IAC, WILL, ECHO_OPT].pack('C*')
+      send_raw [IAC, DO,   SGA_OPT].pack('C*')
+    end
+
+    def readline
+      line    = +""
+      last_cr = false
+
+      loop do
+        raw  = @client.read(1)
+        return nil if raw.nil?
+        byte = raw.ord
+
+        if byte == IAC
+          absorb_iac
+          last_cr = false
+          next
+        end
+
+        if byte == 13
+          last_cr = true
+          next
+        end
+
+        if byte == 10 || (byte == 0 && last_cr)
+          write "\r\n"
+          return line
+        end
+
+        last_cr = false
+        next if byte == 0
+
+        if byte == 8 || byte == 127
+          unless line.empty?
+            line.chop!
+            write "\b \b"
+          end
+          next
+        end
+
+        next if byte < 32
+
+        line << raw
+        write raw
+      end
+    end
+
+    def write(data)
+      @client.write(data)
+    rescue StandardError
+      nil
+    end
+
+    private
+
+    def absorb_iac
+      cmd = @client.read(1)
+      return if cmd.nil?
+
+      case cmd.ord
+      when SB
+        loop do
+          b = @client.read(1)
+          break if b.nil?
+          if b.ord == IAC
+            s = @client.read(1)
+            break if s.nil? || s.ord == SE
+          end
+        end
+      when WILL, WONT, DO, DONT
+        @client.read(1)
+      end
+    end
+
+    def send_raw(data)
+      @client.write(data)
+    rescue StandardError
+      nil
+    end
+  end
+end