Add signatures

This adds the ability for per-account signatures in the accounts.conf
config file. The signature is added to emails in the editor at the
bottom of the email. This includes when forwarding, replying to, and
composing emails.

There are two config options: signature-file and signature-cmd. The
former allows a signature to be read from a file and the latter allows
an arbitrary command to be executed to return the signature.

The config options have been documented in aerc-config

2 files changed, 66 insertions, 2 deletions

diff --git a/widgets/aerc.go b/widgets/aerc.go
index fe3c1e2..8671c87 100644
--- a/widgets/aerc.go
+++ b/widgets/aerc.go
@@ -430,7 +430,7 @@ func (aerc *Aerc) Mailto(addr *url.URL) error {
 			defaults[header] = strings.Join(vals, ",")
 		}
 	}
-	composer := NewComposer(aerc.Config(),
+	composer := NewComposer(aerc, aerc.Config(),
 		acct.AccountConfig(), acct.Worker(), defaults)
 	composer.FocusSubject()
 	title := "New email"
diff --git a/widgets/compose.go b/widgets/compose.go
index 0e7f09e..22c58da 100644
--- a/widgets/compose.go
+++ b/widgets/compose.go
@@ -2,6 +2,8 @@ package widgets
 
 import (
 	"bufio"
+	"bytes"
+	"fmt"
 	"io"
 	"io/ioutil"
 	"mime"
@@ -17,6 +19,7 @@ import (
 	"github.com/emersion/go-message/mail"
 	"github.com/gdamore/tcell"
 	"github.com/mattn/go-runewidth"
+	"github.com/mitchellh/go-homedir"
 	"github.com/pkg/errors"
 
 	"git.sr.ht/~sircmpwn/aerc/config"
@@ -29,6 +32,7 @@ type Composer struct {
 
 	acct   *config.AccountConfig
 	config *config.AercConfig
+	aerc   *Aerc
 
 	defaults    map[string]string
 	editor      *Terminal
@@ -48,7 +52,7 @@ type Composer struct {
 	width int
 }
 
-func NewComposer(conf *config.AercConfig,
+func NewComposer(aerc *Aerc, conf *config.AercConfig,
 	acct *config.AccountConfig, worker *types.Worker, defaults map[string]string) *Composer {
 
 	if defaults == nil {
@@ -68,6 +72,7 @@ func NewComposer(conf *config.AercConfig,
 	}
 
 	c := &Composer{
+		aerc:     aerc,
 		editors:  editors,
 		acct:     acct,
 		config:   conf,
@@ -80,6 +85,8 @@ func NewComposer(conf *config.AercConfig,
 		focusable: focusable,
 	}
 
+	c.AddSignature()
+
 	c.updateGrid()
 	c.ShowTerminal()
 
@@ -140,6 +147,63 @@ func (c *Composer) SetContents(reader io.Reader) *Composer {
 	return c
 }
 
+func (c *Composer) PrependContents(reader io.Reader) {
+	buf := bytes.NewBuffer(nil)
+	c.email.Seek(0, io.SeekStart)
+	io.Copy(buf, c.email)
+	c.email.Seek(0, io.SeekStart)
+	io.Copy(c.email, reader)
+	io.Copy(c.email, buf)
+	c.email.Sync()
+}
+
+func (c *Composer) AppendContents(reader io.Reader) {
+	c.email.Seek(0, io.SeekEnd)
+	io.Copy(c.email, reader)
+	c.email.Sync()
+}
+
+func (c *Composer) AddSignature() {
+	var signature []byte
+	if c.acct.SignatureCmd != "" {
+		var err error
+		signature, err = c.readSignatureFromCmd()
+		if err != nil {
+			signature = c.readSignatureFromFile()
+		}
+	} else {
+		signature = c.readSignatureFromFile()
+	}
+	c.AppendContents(bytes.NewReader(signature))
+}
+
+func (c *Composer) readSignatureFromCmd() ([]byte, error) {
+	sigCmd := c.acct.SignatureCmd
+	cmd := exec.Command("sh", "-c", sigCmd)
+	signature, err := cmd.Output()
+	if err != nil {
+		return nil, err
+	}
+	return signature, nil
+}
+
+func (c *Composer) readSignatureFromFile() []byte {
+	sigFile := c.acct.SignatureFile
+	if sigFile == "" {
+		return nil
+	}
+	sigFile, err := homedir.Expand(sigFile)
+	if err != nil {
+		return nil
+	}
+	signature, err := ioutil.ReadFile(sigFile)
+	if err != nil {
+		c.aerc.PushError(fmt.Sprintf(" Error loading signature from file: %v", sigFile))
+		return nil
+	}
+	return signature
+}
+
 func (c *Composer) FocusTerminal() *Composer {
 	if c.editor == nil {
 		return c