compose: ensure signature uses standard delimiter

Since it has recently been a topic on IRC, and to guide users new to
"raw" email, add a note on how signatures are detected and what they
should look like.

Prepend signature-file and signature-cmd with the standard delimiter if
missing.

Signed-off-by: Moritz Poldrack <git@moritz.sh>
Signed-off-by: Robin Jarry <robin@jarry.cc>

3 files changed, 24 insertions, 0 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 450465e2..ccd714bd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -20,6 +20,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
   `PATH` has been modified to include all variations of the `libexec` subdirs.
 - The built-in `colorize` filter theme is now configured in styleset files into
   the `[viewer]` section.
+- The standard Usenet signature delimiter `"-- "` is now prepended to
+  `signature-file` and `signature-cmd` if not already present.
 
 ### Deprecated
 
diff --git a/doc/aerc-accounts.5.scd b/doc/aerc-accounts.5.scd
index a078e4bf..fdf10b76 100644
--- a/doc/aerc-accounts.5.scd
+++ b/doc/aerc-accounts.5.scd
@@ -160,6 +160,11 @@ Note that many of these configuration options are written for you, such as
 	Specifies the file to read in order to obtain the signature to be added
 	to emails sent from this account.
 
+	Please note that by convention the Usenet signature style of two dashes,
+	followed by a space ("-- ") should be placed at the top of the signature
+	to separate content and signature. Aerc will add that delimiter if it is
+	not already present.
+
 *signature-cmd* = _<command>_
 	Specifies the command to execute with _sh -c_ in order to obtain the
 	signature to be added to emails sent from this account. If the command
diff --git a/widgets/compose.go b/widgets/compose.go
index 94fd79d5..7311de7a 100644
--- a/widgets/compose.go
+++ b/widgets/compose.go
@@ -1,6 +1,7 @@
 package widgets
 
 import (
+	"bufio"
 	"bytes"
 	"fmt"
 	"io"
@@ -550,6 +551,7 @@ func (c *Composer) AddSignature() {
 	} else {
 		signature = c.readSignatureFromFile()
 	}
+	signature = ensureSignatureDelimiter(signature)
 	c.AppendContents(bytes.NewReader(signature))
 }
 
@@ -581,6 +583,21 @@ func (c *Composer) readSignatureFromFile() []byte {
 	return signature
 }
 
+func ensureSignatureDelimiter(signature []byte) []byte {
+	buf := bytes.NewBuffer(signature)
+	scanner := bufio.NewScanner(buf)
+	for scanner.Scan() {
+		line := scanner.Text()
+		if line == "-- " {
+			// signature contains standard delimiter, we're good
+			return signature
+		}
+	}
+	// signature does not contain standard delimiter, prepend one
+	sig := "\n\n-- \n" + strings.TrimLeft(string(signature), " \t\r\n")
+	return []byte(sig)
+}
+
 func (c *Composer) FocusTerminal() *Composer {
 	c.Lock()
 	defer c.Unlock()