feat: Basic attachment support

src/awk/attach.awk

@@ -0,0 +1,35 @@
+## src/awk/attach.awk
+## Prepend attachment to iCalendar file.
+##
+## @assign file: Path to base64-encoded content
+## @assign mime: Mime
+## @assign filename: Original filename
+
+# Functions
+
+# Write attachment
+#
+# @local variables: line, aline
+function write_attachment(    line, aline, fl) {
+  line = "ATTACH;ENCODING=BASE64;VALUE=BINARY;FMTTYPE="mime";FILENAME="filename":"
+  fl = 1
+  while (getline aline <file) {
+    line = line aline
+    if (fl && length(line) >= 73) {
+      print substr(line, 1, 73)
+      line = substr(line, 74)
+      fl = 0
+    }
+    while (length(line) >= 72) {
+      print " "substr(line, 1, 72)
+      line = substr(line, 73)
+    }
+  }
+  if (line)
+    print " "line
+}
+
+# AWK program
+
+/^END:VEVENT$/ { write_attachment() }
+{ print }