compose: warn before sending without attachment

Prevent the embarrassing forgotten attachment scenario by warning the
user before sending a message that may need an attachment but does not
have one. Whether a message needs an attachment is determined by testing
a configurable regex against the message body.

Signed-off-by: Jason Cox <dev@jasoncarloscox.com>
Acked-by: Robin Jarry <robin@jarry.cc>

7 files changed, 106 insertions, 6 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 107f8dfc..6554f61f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,6 +22,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Support for attaching files with `mailto:`-links
 - Filter commands now have the `AERC_MIME_TYPE` and `AERC_FILENAME` variables
   defined in their environment.
+- Warn before sending emails that may need an attachment with
+  `no-attachment-warning` in `aerc.conf`.
 
 ### Changed
 
diff --git a/commands/compose/send.go b/commands/compose/send.go
index 3786721b..ccfe7886 100644
--- a/commands/compose/send.go
+++ b/commands/compose/send.go
@@ -100,6 +100,40 @@ func (Send) Execute(aerc *widgets.Aerc, args []string) error {
 		rcpts:    rcpts,
 	}
 
+	warn, err := composer.ShouldWarnAttachment()
+	if err != nil || warn {
+		msg := "You may have forgotten an attachment."
+		if err != nil {
+			logging.Warnf("failed to check for a forgotten attachment: %v", err)
+			msg = "Failed to check for a forgotten attachment."
+		}
+
+		prompt := widgets.NewPrompt(aerc.Config(),
+			msg+" Abort send? [Y/n] ",
+			func(text string) {
+				if text == "n" || text == "N" {
+					send(aerc, composer, ctx, header, tabName)
+				}
+			}, func(cmd string) ([]string, string) {
+				if cmd == "" {
+					return []string{"y", "n"}, ""
+				}
+
+				return nil, ""
+			},
+		)
+
+		aerc.PushPrompt(prompt)
+	} else {
+		send(aerc, composer, ctx, header, tabName)
+	}
+
+	return nil
+}
+
+func send(aerc *widgets.Aerc, composer *widgets.Composer, ctx sendCtx,
+	header *mail.Header, tabName string,
+) {
 	// we don't want to block the UI thread while we are sending
 	// so we do everything in a goroutine and hide the composer from the user
 	aerc.RemoveTab(composer)
@@ -109,6 +143,7 @@ func (Send) Execute(aerc *widgets.Aerc, args []string) error {
 	mode.NoQuit()
 
 	var copyBuf bytes.Buffer // for the Sent folder content if CopyTo is set
+	config := composer.Config()
 
 	failCh := make(chan error)
 	// writer
@@ -116,6 +151,7 @@ func (Send) Execute(aerc *widgets.Aerc, args []string) error {
 		defer logging.PanicHandler()
 
 		var sender io.WriteCloser
+		var err error
 		switch ctx.scheme {
 		case "smtp":
 			fallthrough
@@ -151,7 +187,7 @@ func (Send) Execute(aerc *widgets.Aerc, args []string) error {
 		// leave no-quit mode
 		defer mode.NoQuitDone()
 
-		err = <-failCh
+		err := <-failCh
 		if err != nil {
 			aerc.PushError(strings.ReplaceAll(err.Error(), "\n", " "))
 			aerc.NewTab(composer, tabName)
@@ -176,7 +212,6 @@ func (Send) Execute(aerc *widgets.Aerc, args []string) error {
 		composer.SetSent()
 		composer.Close()
 	}()
-	return nil
 }
 
 func listRecipients(h *mail.Header) ([]*mail.Address, error) {
diff --git a/config/aerc.conf b/config/aerc.conf
index a980c70e..384a0db3 100644
--- a/config/aerc.conf
+++ b/config/aerc.conf
@@ -297,6 +297,18 @@ address-book-cmd=
 # Default: true
 reply-to-self=true
 
+#
+# Warn before sending an email that matches the specified regexp but does not
+# have any attachments. Leave empty to disable this feature.
+#
+# Uses Go's regexp syntax, documented at https://golang.org/s/re2syntax. The
+# "(?im)" flags are set by default (case-insensitive and multi-line).
+#
+# Example:
+# no-attachment-warning=^[^>]*attach(ed|ment)
+#
+no-attachment-warning=
+
 [filters]
 #
 # Filters allow you to pipe an email body through a shell command to render
diff --git a/config/config.go b/config/config.go
index e40d964a..0de1780c 100644
--- a/config/config.go
+++ b/config/config.go
@@ -203,10 +203,11 @@ type BindingConfigContext struct {
 }
 
 type ComposeConfig struct {
-	Editor         string     `ini:"editor"`
-	HeaderLayout   [][]string `ini:"-"`
-	AddressBookCmd string     `ini:"address-book-cmd"`
-	ReplyToSelf    bool       `ini:"reply-to-self"`
+	Editor              string         `ini:"editor"`
+	HeaderLayout        [][]string     `ini:"-"`
+	AddressBookCmd      string         `ini:"address-book-cmd"`
+	ReplyToSelf         bool           `ini:"reply-to-self"`
+	NoAttachmentWarning *regexp.Regexp `ini:"-"`
 }
 
 type FilterConfig struct {
@@ -523,6 +524,18 @@ func (config *AercConfig) LoadConfig(file *ini.File) error {
 			if key == "header-layout" {
 				config.Compose.HeaderLayout = parseLayout(val)
 			}
+
+			if key == "no-attachment-warning" && len(val) > 0 {
+				re, err := regexp.Compile("(?im)" + val)
+				if err != nil {
+					return fmt.Errorf(
+						"Invalid no-attachment-warning '%s': %w",
+						val, err,
+					)
+				}
+
+				config.Compose.NoAttachmentWarning = re
+			}
 		}
 	}
 
diff --git a/doc/aerc-config.5.scd b/doc/aerc-config.5.scd
index 2c5f809d..21472e6e 100644
--- a/doc/aerc-config.5.scd
+++ b/doc/aerc-config.5.scd
@@ -493,6 +493,20 @@ These options are configured in the *[compose]* section of aerc.conf.
 
 	Default: true
 
+*no-attachment-warning*
+	Specifies a regular expression against which an email's body should be
+	tested before sending an email with no attachment. If the regexp
+	matches, aerc will warn you before sending the message. Leave empty to
+	disable this feature.
+
+	Uses Go's regexp syntax, documented at https://golang.org/s/re2syntax.
+	The "(?im)" flags are set by default (case-insensitive and multi-line).
+
+	Example:
+		no-attachment-warning=^[^>]\*attach(ed|ment)
+
+	Default: none
+
 ## FILTERS
 
 Filters allow you to pipe an email body through a shell command to render
diff --git a/widgets/aerc.go b/widgets/aerc.go
index 35c32fe3..81d07474 100644
--- a/widgets/aerc.go
+++ b/widgets/aerc.go
@@ -598,6 +598,10 @@ func (aerc *Aerc) BeginExCommand(cmd string) {
 	aerc.focus(exline)
 }
 
+func (aerc *Aerc) PushPrompt(prompt *ExLine) {
+	aerc.prompts.Push(prompt)
+}
+
 func (aerc *Aerc) RegisterPrompt(prompt string, cmd []string) {
 	p := NewPrompt(aerc.conf, prompt, func(text string) {
 		if text != "" {
diff --git a/widgets/compose.go b/widgets/compose.go
index dc0c21aa..6e34365a 100644
--- a/widgets/compose.go
+++ b/widgets/compose.go
@@ -776,6 +776,26 @@ func (c *Composer) WriteMessage(header *mail.Header, writer io.Writer) error {
 	}
 }
 
+func (c *Composer) ShouldWarnAttachment() (bool, error) {
+	regex := c.config.Compose.NoAttachmentWarning
+
+	if regex == nil || len(c.attachments) > 0 {
+		return false, nil
+	}
+
+	err := c.reloadEmail()
+	if err != nil {
+		return false, errors.Wrap(err, "reloadEmail")
+	}
+
+	body, err := io.ReadAll(c.email)
+	if err != nil {
+		return false, errors.Wrap(err, "io.ReadAll")
+	}
+
+	return regex.Match(body), nil
+}
+
 func writeMsgImpl(c *Composer, header *mail.Header, writer io.Writer) error {
 	if len(c.attachments) == 0 && len(c.textParts) == 0 {
 		// no attachments