update_oai-pmh Improve HTTP request headers

Motivation:

The `User-Agent` request header was not being sent due to a bug.

The havester lacks support for the `From` request header.

Both HTTP request headers are recommented by the Harvester's guidelines:

https://www.openarchives.org/OAI/2.0/guidelines-harvester.htm

Modification:

Fix bug with `User-Agent` header.  Add support for `From` header.

The `From` header takes an email address as an argument.  Rather than
requiring a configuration file, the code looks for likely places where
the user may have already configured their email address.

Result:

The OAI-PMH harvester more closely followes the corresponding
guidelines.

scripts/update_oai-pmh.rb

@@ -17,12 +17,11 @@ class OaiPmhClient
 
     persistent_connection_adapter
 
-    headers {"User-Agent" => "LEAPS-WG3-client/0.1"}
+    headers 'User-Agent' => 'LEAPS-WG3-client/0.1'
 
     def initialize(oai_pmh_endpoint, from_id=nil)
         self.class.base_uri oai_pmh_endpoint
-
-        # TODO add from_id support as 'From' request header
+        self.class.headers "From" => from_id if from_id
 
         # WORK_AROUND: The connection adapter is persistent across multiple
         # URLs (which is good), but the adapter+connection-caching somehow
@@ -233,6 +232,27 @@ class SeriesStatistics
     end
 end
 
+# Try to discover someone's email address by looking in various likely
+# configuration files.  Returns the email address if it's unambiguous.
+def find_email_address
+    candidate_emails = []
+
+    # Look in Zoom
+    zoomConfig = File.expand_path("~/.config/zoomus.conf")
+    if File.file?(zoomConfig)
+        File.open( zoomConfig ).each do |line|
+            if line =~ /^userEmailAddress=(.*?)$/
+                candidate_emails.append($1)
+            end
+        end
+    end
+
+    # TODO Look in Thunderbird
+    #find ~.thunderbird -name prefs.js | xargs sed -n 's/user_pref."mail.identity.id1.useremail", "\([^"]*\)".*/\1/p'
+
+    #  Return email address if there is no ambiguity.
+    return candidate_emails.uniq.count == 1 ? candidate_emails[0] : nil
+end
 
 def check_oai_pmh_endpoint(endpoint_url)
     queryIdentify_url = endpoint_url + "?verb=Identify"
@@ -423,6 +443,13 @@ up_to_date = true
 file_path = '_data/facilities.yml'
 facilities = YAML.safe_load(File.read(file_path), permitted_classes: [Date])
 
+email_address = find_email_address
+if email_address
+    puts "INFO: identifying OAI-PMH activity as from <#{email_address}>"
+else
+    puts "WARNING: unable to discover your email address.  Carrying on under a cloak of anonymity."
+end
+
 facilities.each do |facility|
     odr = facility['odr']
     next unless odr && odr.key?('oai-pmh-endpoint')
@@ -433,7 +460,7 @@ facilities.each do |facility|
     oai_pmh_endpoint = oai_pmh['link']
     next unless oai_pmh_endpoint
 
-    $client = OaiPmhClient.new(oai_pmh_endpoint)
+    $client = OaiPmhClient.new(oai_pmh_endpoint, email_address)
 
     expected_status = oai_pmh['status']