lib: intro the sendmail module

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>

diff --git a/lib/sendmail.nit b/lib/sendmail.nit
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+# This file is part of NIT ( http://www.nitlanguage.org ).
+#
+# Copyright 2014 Alexis Laferrière <alexis.laf@xymus.net>
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Send emails using the `sendmail` program
+#
+# Usage example:
+# ~~~~
+# if sendmail_is_available then
+#     var mail = new Mail("from@example.com", "Title", "Content")
+#     mail.to.add "to@example.org"
+#     mail.send
+# else print "please install sendmail"
+# ~~~~
+module sendmail
+
+import base64
+
+# Can we find the external program `sendmail`?
+fun sendmail_is_available: Bool do return "sendmail".program_is_in_path
+
+# An email to be sent using `sendmail`
+class Mail
+
+       # Sender of this email
+       var from: String is writable
+
+       # Recipients of the message
+       var to = new Array[String]
+
+       # Recipients of a carbon copy of the message
+       var cc = new Array[String]
+
+       # Recipients of a blind carbon copy of the message
+       var bcc = new Array[String]
+
+       # Subject of this mail
+       var subject: String is writable
+
+       # Content of this mail
+       var content: String is writable
+
+       # Metadata in the header of this mail
+       var header = new HashMap[String, String]
+
+       # Should the content of this email be encrypted using base64?
+       #
+       # This will also set the header `Content-Transfer-Encoding` to base64.
+       # By default, the encoding is 8bit.
+       var encrypt_with_base64 = false
+
+       # Send this mail using the `sendmail` command
+       #
+       # require: `sendmail_is_available`
+       fun send: Bool
+       do
+               assert sendmail_is_available
+
+               # All recipients
+               var all = new Array[String]
+               all.add_all to
+               all.add_all cc
+               all.add_all bcc
+
+               var proc = new OProcess("sendmail", all.join(","))
+               if proc.is_writable then proc.write to_s
+               proc.close
+               proc.wait
+               var status = proc.status
+               return status == 0
+       end
+
+       redef fun to_s
+       do
+               # Set encoding (and encode if needed)
+               var content = content
+               var encoding
+               if encrypt_with_base64 then
+                       content = content.encode_base64
+                       encoding = "base64"
+               else
+                       encoding = "8bit"
+               end
+               header["Content-Transfer-Encoding"] = encoding
+
+               # Generate expected format
+               return """
+From: {{{from}}}\r
+To: {{{to.join(",")}}}\r
+CC: {{{cc.join(",")}}}\r
+BCC: {{{bcc.join(",")}}}\r
+Subject: {{{subject}}}\r
+{{{header.join("\r\n", ": ")}}}\r
+{{{content}}}"""
+       end
+end