filters: make it explicit that encoding is UTF-8

Document filter input charset
Add w3m filter example to default config
Adapt html and html-unsafe filters

Fixes: https://todo.sr.ht/~rjarry/aerc/65
Signed-off-by: q3cpma <q3cpma@posteo.net>
Acked-by: Robin Jarry <robin@jarry.cc>

config/aerc.conf

@@ -292,6 +292,7 @@ reply-to-self=true
 #subject,~^\[PATCH=colordiff
 text/plain=sed 's/^>\+.*/\x1b[36m&\x1b[0m/'
 #text/html=pandoc -f html -t plain
+#text/html=w3m -dump -I UTF-8 -T text/html
 #image/*=catimg -w $(tput cols) -
 
 [triggers]

doc/aerc-config.5.scd

@@ -497,6 +497,9 @@ aerc ships with some default filters installed in the share directory (usually
 _/usr/share/aerc/filters_). Note that these may have additional dependencies
 that aerc does not have alone.
 
+Note that said email body is converted into UTF-8 before being passed to
+filters.
+
 ## TRIGGERS
 
 Triggers specify commands to execute when certain events occur.

filters/html

@@ -3,6 +3,7 @@
 # any phoning home by rendered emails
 export SOCKS_SERVER="127.0.0.1:1"
 exec socksify w3m \
+	-I UTF-8 \
 	-T text/html \
 	-cols $(tput cols) \
 	-dump \

filters/html-unsafe

@@ -9,6 +9,7 @@ else
 	PRE_CMD=""
 fi
 exec $PRE_CMD w3m \
+	-I UTF-8 \
 	-T text/html \
 	-cols $(tput cols) \
 	-dump \