Further reduce spam score by adding encoding info.

A lot of spam filters are more likely to flag email without an encoding
in the Content-Type headers as spam.  Netdata is technically not locale
aware, but the email message is sent from a bash script, and bash is
locale aware, so the message will be encoded in whatever the environment
dictated character encoding is (which is usually UTF-8) these days.

It turns out that my assessment in the previous commit was incorrect,
and it actually is trivial to get a MIME compatible encoding name from a
shell script, so lets try to make sure the encoding is set
automatically.

When not explicitly set by the user, we first try to determine the
system encoding using the `locale` command.  If this fails and the user
has not explicitly set an encoding, then it defaults to UTF-8, which is
the de-facto standard on all modern Linux distributions and thus should
be correct most of the time.

Users can override the detection by setting EMAIL_CHARSET in
health_alarm_notify.conf.

For English speaking users, this should result in no change.  For
non-English speaking users, this may fix display of non-punycode encoded
hostnames.

1 files changed, 11 insertions, 2 deletions

diff --git a/plugins.d/alarm-notify.sh b/plugins.d/alarm-notify.sh
index 1c0c1d548b..ddfae68ddf 100755
--- a/plugins.d/alarm-notify.sh
+++ b/plugins.d/alarm-notify.sh
@@ -290,6 +290,7 @@ declare -A role_recipients_custom=()
 # email configs
 EMAIL_SENDER=""
 DEFAULT_RECIPIENT_EMAIL="root"
+EMAIL_CHARSET=$(locale charmap 2>/dev/null)
 declare -A role_recipients_email=()
 
 # load the user configuration
@@ -301,6 +302,14 @@ else
     error "Cannot find file ${NETDATA_CONFIG_DIR}/health_alarm_notify.conf. Using internal defaults."
 fi
 
+# If we didn't autodetect the character set for e-mail and it wasn't
+# set by the user, we need to set it to a reasonable default.  UTF-8
+# should be correct for almost all modern UNIX systems.
+if [ -z ${EMAIL_CHARSET} ]
+    then
+    EMAIL_CHARSET="UTF-8"
+fi
+
 # -----------------------------------------------------------------------------
 # filter a recipient based on alarm event severity
 
@@ -1401,7 +1410,7 @@ Content-Type: multipart/alternative; boundary="multipart-boundary"
 This is a MIME-encoded multipart message
 
 --multipart-boundary
-Content-Type: text/plain
+Content-Type: text/plain; encoding=${EMAIL_CHARSET}
 Content-Disposition: inline
 Content-Transfer-Encoding: 8bit
 
@@ -1419,7 +1428,7 @@ Date    : ${date}
 Notification generated on ${this_host}
 
 --multipart-boundary
-Content-Type: text/html
+Content-Type: text/html; encoding=${EMAIL_CHARSET}
 Content-Disposition: inline
 Content-Transfer-Encoding: 8bit