Add Templates with Parsing

+ Changes NewComposer to return error.
+ Add lib to handle templates using "text/template".
+ Add -T option to following commands
    - compose.
    - reply
    - forward
+ Quoted replies using templates.
+ Forwards as body using templates
+ Default templates are installed similar to filters.
+ Templates Config in aerc.conf.
    - Required templates are parsed while loading config.
+ Add aerc-templates.7 manual for using template data.

Makefile

@@ -35,7 +35,8 @@ DOCS := \
 	aerc-sendmail.5 \
 	aerc-notmuch.5 \
 	aerc-smtp.5 \
-	aerc-tutorial.7
+	aerc-tutorial.7 \
+	aerc-templates.7
 
 .1.scd.1:
 	scdoc < $< > $@
@@ -58,7 +59,7 @@ clean:
 
 install: all
 	mkdir -p $(BINDIR) $(MANDIR)/man1 $(MANDIR)/man5 $(MANDIR)/man7 \
-		$(SHAREDIR) $(SHAREDIR)/filters
+		$(SHAREDIR) $(SHAREDIR)/filters $(SHAREDIR)/templates
 	install -m755 aerc $(BINDIR)/aerc
 	install -m644 aerc.1 $(MANDIR)/man1/aerc.1
 	install -m644 aerc-search.1 $(MANDIR)/man1/aerc-search.1
@@ -75,6 +76,8 @@ install: all
 	install -m755 filters/hldiff $(SHAREDIR)/filters/hldiff
 	install -m755 filters/html $(SHAREDIR)/filters/html
 	install -m755 filters/plaintext $(SHAREDIR)/filters/plaintext
+	install -m644 templates/quoted_reply $(SHAREDIR)/templates/quoted_reply
+	install -m644 templates/forward_as_body $(SHAREDIR)/templates/forward_as_body
 
 RMDIR_IF_EMPTY:=sh -c '\
 if test -d $$0 && ! ls -1qA $$0 | grep -q . ; then \

commands/account/compose.go

@@ -24,13 +24,17 @@ func (Compose) Complete(aerc *widgets.Aerc, args []string) []string {
 }
 
 func (Compose) Execute(aerc *widgets.Aerc, args []string) error {
-	body, err := buildBody(args)
+	body, template, err := buildBody(args)
 	if err != nil {
 		return err
 	}
 	acct := aerc.SelectedAccount()
-	composer := widgets.NewComposer(aerc,
+
-		aerc.Config(), acct.AccountConfig(), acct.Worker(), nil)
+	composer, err := widgets.NewComposer(aerc,
+		aerc.Config(), acct.AccountConfig(), acct.Worker(), template, nil)
+	if err != nil {
+		return err
+	}
 	tab := aerc.NewTab(composer, "New email")
 	composer.OnHeaderChange("Subject", func(subject string) {
 		if subject == "" {
@@ -44,11 +48,11 @@ func (Compose) Execute(aerc *widgets.Aerc, args []string) error {
 	return nil
 }
 
-func buildBody(args []string) (string, error) {
+func buildBody(args []string) (string, string, error) {
-	var body, headers string
+	var body, template, headers string
-	opts, optind, err := getopt.Getopts(args, "H:")
+	opts, optind, err := getopt.Getopts(args, "H:T:")
 	if err != nil {
-		return "", err
+		return "", "", err
 	}
 	for _, opt := range opts {
 		switch opt.Option {
@@ -60,11 +64,13 @@ func buildBody(args []string) (string, error) {
 			} else {
 				headers += opt.Value + ":\n"
 			}
+		case 'T':
+			template = opt.Value
 		}
 	}
 	posargs := args[optind:]
 	if len(posargs) > 1 {
-		return "", errors.New("Usage: compose [-H] [body]")
+		return "", template, errors.New("Usage: compose [-H] [body]")
 	}
 	if len(posargs) == 1 {
 		body = posargs[0]
@@ -76,5 +82,5 @@ func buildBody(args []string) (string, error) {
 			body = headers + "\n\n"
 		}
 	}
-	return body, nil
+	return body, template, nil
 }

commands/msg/forward.go

@@ -1,20 +1,21 @@
 package msg
 
 import (
-	"bufio"
+	"bytes"
 	"errors"
 	"fmt"
-	"git.sr.ht/~sircmpwn/aerc/lib"
-	"git.sr.ht/~sircmpwn/aerc/models"
-	"git.sr.ht/~sircmpwn/aerc/widgets"
-	"git.sr.ht/~sircmpwn/getopt"
-	"github.com/emersion/go-message"
-	"github.com/emersion/go-message/mail"
 	"io"
 	"io/ioutil"
 	"os"
 	"path"
 	"strings"
+
+	"github.com/emersion/go-message"
+	"github.com/emersion/go-message/mail"
+
+	"git.sr.ht/~sircmpwn/aerc/models"
+	"git.sr.ht/~sircmpwn/aerc/widgets"
+	"git.sr.ht/~sircmpwn/getopt"
 )
 
 type forward struct{}
@@ -32,15 +33,18 @@ func (forward) Complete(aerc *widgets.Aerc, args []string) []string {
 }
 
 func (forward) Execute(aerc *widgets.Aerc, args []string) error {
-	opts, optind, err := getopt.Getopts(args, "A")
+	opts, optind, err := getopt.Getopts(args, "AT:")
 	if err != nil {
 		return err
 	}
 	attach := false
+	template := ""
 	for _, opt := range opts {
 		switch opt.Option {
 		case 'A':
 			attach = true
+		case 'T':
+			template = opt.Value
 		}
 	}
 
@@ -69,10 +73,20 @@ func (forward) Execute(aerc *widgets.Aerc, args []string) error {
 		"To":      to,
 		"Subject": subject,
 	}
-	composer := widgets.NewComposer(aerc, aerc.Config(), acct.AccountConfig(),
-		acct.Worker(), defaults)
 
-	addTab := func() {
+	addTab := func() (*widgets.Composer, error) {
+		if template != "" {
+			defaults["OriginalFrom"] = models.FormatAddresses(msg.Envelope.From)
+			defaults["OriginalDate"] = msg.Envelope.Date.Format("Mon Jan 2, 2006 at 3:04 PM")
+		}
+
+		composer, err := widgets.NewComposer(aerc, aerc.Config(), acct.AccountConfig(),
+			acct.Worker(), template, defaults)
+		if err != nil {
+			aerc.PushError("Error: " + err.Error())
+			return nil, err
+		}
+
 		tab := aerc.NewTab(composer, subject)
 		if to == "" {
 			composer.FocusRecipient()
@@ -87,28 +101,17 @@ func (forward) Execute(aerc *widgets.Aerc, args []string) error {
 			}
 			tab.Content.Invalidate()
 		})
+		return composer, nil
 	}
 
 	if attach {
-		forwardAttach(store, composer, msg, addTab)
-	} else {
-		forwardBodyPart(store, composer, msg, addTab)
-	}
-	return nil
-}
-
-func forwardAttach(store *lib.MessageStore, composer *widgets.Composer,
-	msg *models.MessageInfo, addTab func()) {
-
-	store.FetchFull([]uint32{msg.Uid}, func(reader io.Reader) {
 		tmpDir, err := ioutil.TempDir("", "aerc-tmp-attachment")
 		if err != nil {
-			// TODO: Do something with the error
+			return err
-			addTab()
-			return
 		}
 		tmpFileName := path.Join(tmpDir,
 			strings.ReplaceAll(fmt.Sprintf("%s.eml", msg.Envelope.Subject), "/", "-"))
+		store.FetchFull([]uint32{msg.Uid}, func(reader io.Reader) {
 			tmpFile, err := os.Create(tmpFileName)
 			if err != nil {
 				println(err)
@@ -119,16 +122,20 @@ func forwardAttach(store *lib.MessageStore, composer *widgets.Composer,
 
 			defer tmpFile.Close()
 			io.Copy(tmpFile, reader)
+			composer, err := addTab()
+			if err != nil {
+				return
+			}
 			composer.AddAttachment(tmpFileName)
 			composer.OnClose(func(composer *widgets.Composer) {
 				os.RemoveAll(tmpDir)
 			})
-		addTab()
 		})
-}
+	} else {
+		if template == "" {
+			template = aerc.Config().Templates.Forwards
+		}
 
-func forwardBodyPart(store *lib.MessageStore, composer *widgets.Composer,
-	msg *models.MessageInfo, addTab func()) {
 		// TODO: something more intelligent than fetching the 1st part
 		// TODO: add attachments!
 		store.FetchBodyPart(msg.Uid, []int{1}, func(reader io.Reader) {
@@ -151,19 +158,11 @@ func forwardBodyPart(store *lib.MessageStore, composer *widgets.Composer,
 				addTab()
 				return
 			}
-
+			buf := new(bytes.Buffer)
-		pipeout, pipein := io.Pipe()
+			buf.ReadFrom(part.Body)
-		scanner := bufio.NewScanner(part.Body)
+			defaults["Original"] = buf.String()
-		go composer.PrependContents(pipeout)
-		// TODO: Let user customize the date format used here
-		io.WriteString(pipein, fmt.Sprintf("Forwarded message from %s on %s:\n\n",
-			msg.Envelope.From[0].Name,
-			msg.Envelope.Date.Format("Mon Jan 2, 2006 at 3:04 PM")))
-		for scanner.Scan() {
-			io.WriteString(pipein, fmt.Sprintf("%s\n", scanner.Text()))
-		}
-		pipein.Close()
-		pipeout.Close()
 			addTab()
 		})
+	}
+	return nil
 }

commands/msg/reply.go

@@ -1,7 +1,7 @@
 package msg
 
 import (
-	"bufio"
+	"bytes"
 	"errors"
 	"fmt"
 	"io"
@@ -32,16 +32,17 @@ func (reply) Complete(aerc *widgets.Aerc, args []string) []string {
 }
 
 func (reply) Execute(aerc *widgets.Aerc, args []string) error {
-	opts, optind, err := getopt.Getopts(args, "aq")
+	opts, optind, err := getopt.Getopts(args, "aqT:")
 	if err != nil {
 		return err
 	}
 	if optind != len(args) {
-		return errors.New("Usage: reply [-aq]")
+		return errors.New("Usage: reply [-aq -T <template>]")
 	}
 	var (
 		quote    bool
 		replyAll bool
+		template string
 	)
 	for _, opt := range opts {
 		switch opt.Option {
@@ -49,11 +50,14 @@ func (reply) Execute(aerc *widgets.Aerc, args []string) error {
 			replyAll = true
 		case 'q':
 			quote = true
+		case 'T':
+			template = opt.Value
 		}
 	}
 
 	widget := aerc.SelectedTab().(widgets.ProvidesMessage)
 	acct := widget.SelectedAccount()
+
 	if acct == nil {
 		return errors.New("No account selected")
 	}
@@ -116,14 +120,23 @@ func (reply) Execute(aerc *widgets.Aerc, args []string) error {
 		"In-Reply-To": msg.Envelope.MessageId,
 	}
 
-	composer := widgets.NewComposer(aerc, aerc.Config(),
+	addTab := func() error {
-		acct.AccountConfig(), acct.Worker(), defaults)
+		if template != "" {
+			defaults["OriginalFrom"] = models.FormatAddresses(msg.Envelope.From)
+			defaults["OriginalDate"] = msg.Envelope.Date.Format("Mon Jan 2, 2006 at 3:04 PM")
+		}
+
+		composer, err := widgets.NewComposer(aerc, aerc.Config(),
+			acct.AccountConfig(), acct.Worker(), template, defaults)
+		if err != nil {
+			aerc.PushError("Error: " + err.Error())
+			return err
+		}
 
 		if args[0] == "reply" {
 			composer.FocusTerminal()
 		}
 
-	addTab := func() {
 		tab := aerc.NewTab(composer, subject)
 		composer.OnHeaderChange("Subject", func(subject string) {
 			if subject == "" {
@@ -133,27 +146,21 @@ func (reply) Execute(aerc *widgets.Aerc, args []string) error {
 			}
 			tab.Content.Invalidate()
 		})
+
+		return nil
 	}
 
 	if quote {
-		var (
+		if template == "" {
-			path []int
+			template = aerc.Config().Templates.QuotedReply
-			part *models.BodyStructure
-		)
-		if len(msg.BodyStructure.Parts) != 0 {
-			part, path = findPlaintext(msg.BodyStructure, path)
-		}
-		if part == nil {
-			part = msg.BodyStructure
-			path = []int{1}
 		}
 
-		store.FetchBodyPart(msg.Uid, path, func(reader io.Reader) {
+		store.FetchBodyPart(msg.Uid, []int{1}, func(reader io.Reader) {
 			header := message.Header{}
 			header.SetText(
-				"Content-Transfer-Encoding", part.Encoding)
+				"Content-Transfer-Encoding", msg.BodyStructure.Encoding)
-			header.SetContentType(part.MIMEType, part.Params)
+			header.SetContentType(msg.BodyStructure.MIMEType, msg.BodyStructure.Params)
-			header.SetText("Content-Description", part.Description)
+			header.SetText("Content-Description", msg.BodyStructure.Description)
 			entity, err := message.New(header, reader)
 			if err != nil {
 				// TODO: Do something with the error
@@ -168,25 +175,15 @@ func (reply) Execute(aerc *widgets.Aerc, args []string) error {
 				return
 			}
 
-			pipeout, pipein := io.Pipe()
+			buf := new(bytes.Buffer)
-			scanner := bufio.NewScanner(part.Body)
+			buf.ReadFrom(part.Body)
-			go composer.PrependContents(pipeout)
+			defaults["Original"] = buf.String()
-			// TODO: Let user customize the date format used here
-			io.WriteString(pipein, fmt.Sprintf("On %s %s wrote:\n",
-				msg.Envelope.Date.Format("Mon Jan 2, 2006 at 3:04 PM"),
-				msg.Envelope.From[0].Name))
-			for scanner.Scan() {
-				io.WriteString(pipein, fmt.Sprintf("> %s\n", scanner.Text()))
-			}
-			pipein.Close()
-			pipeout.Close()
 			addTab()
 		})
-	} else {
-		addTab()
-	}
-
 		return nil
+	} else {
+		return addTab()
+	}
 }
 
 func findPlaintext(bs *models.BodyStructure,

commands/msg/unsubscribe.go

@@ -87,13 +87,17 @@ func unsubscribeMailto(aerc *widgets.Aerc, u *url.URL) error {
 		"To":      u.Opaque,
 		"Subject": u.Query().Get("subject"),
 	}
-	composer := widgets.NewComposer(
+	composer, err := widgets.NewComposer(
 		aerc,
 		aerc.Config(),
 		acct.AccountConfig(),
 		acct.Worker(),
+		"",
 		defaults,
 	)
+	if err != nil {
+		return err
+	}
 	composer.SetContents(strings.NewReader(u.Query().Get("body")))
 	tab := aerc.NewTab(composer, "unsubscribe")
 	composer.OnHeaderChange("Subject", func(subject string) {

config/aerc.conf.in

@@ -139,3 +139,23 @@ text/*=awk -f @SHAREDIR@/filters/plaintext
 #
 # Executed when a new email arrives in the selected folder
 new-email=
+
+[templates]
+# Templates are used to populate email bodies automatically.
+#
+
+# The directories where the templates are stored. It takes a colon-separated
+# list of directories.
+#
+# default: @SHAREDIR@/templates/
+template-dirs=@SHAREDIR@/templates/
+
+# The template to be used for quoted replies.
+#
+# default: quoted_reply
+quoted-reply=quoted_reply
+
+# The template to be used for forward as body.
+#
+# default: forward_as_body
+forwards=forward_as_body

config/config.go

@@ -16,6 +16,8 @@ import (
 	"github.com/gdamore/tcell"
 	"github.com/go-ini/ini"
 	"github.com/kyoh86/xdg"
+
+	"git.sr.ht/~sircmpwn/aerc/lib/templates"
 )
 
 type GeneralConfig struct {
@@ -98,6 +100,12 @@ type TriggersConfig struct {
 	ExecuteCommand func(command []string) error
 }
 
+type TemplateConfig struct {
+	TemplateDirs []string
+	QuotedReply  string `ini:"quoted-reply"`
+	Forwards     string `ini:"forwards"`
+}
+
 type AercConfig struct {
 	Bindings  BindingConfig
 	Compose   ComposeConfig
@@ -108,6 +116,7 @@ type AercConfig struct {
 	Triggers  TriggersConfig  `ini:"-"`
 	Ui        UIConfig
 	General   GeneralConfig
+	Templates TemplateConfig
 }
 
 // Input: TimestampFormat
@@ -305,6 +314,23 @@ func (config *AercConfig) LoadConfig(file *ini.File) error {
 			return err
 		}
 	}
+	if templatesSec, err := file.GetSection("templates"); err == nil {
+		if err := templatesSec.MapTo(&config.Templates); err != nil {
+			return err
+		}
+		templateDirs := templatesSec.Key("template-dirs").String()
+		config.Templates.TemplateDirs = strings.Split(templateDirs, ":")
+		for key, val := range templatesSec.KeysHash() {
+			if key == "template-dirs" {
+				continue
+			}
+			_, err := templates.ParseTemplateFromFile(
+				val, config.Templates.TemplateDirs, templates.TestTemplateData())
+			if err != nil {
+				return err
+			}
+		}
+	}
 	return nil
 }
 

doc/aerc-config.5.scd

@@ -240,6 +240,31 @@ They are configured in the *[triggers]* section of aerc.conf.
 	Format specifiers from *index-format* are expanded with respect to the new
 	message.
 
+## Templates
+
+Templates are used to populate the body of an email. The compose, reply
+and forward commands can be called with the -T flag with the name of the
+template name.
+
+aerc ships with some default templates installed in the share directory (usually
+_/usr/share/aerc/templates_).
+
+*template-dirs*
+	The directory where the templates are stored. The config takes a
+	colon-separated list of dirs.
+
+	Default: "/usr/share/aerc/templates"
+
+*quoted-reply*
+	The template to be used for quoted replies.
+
+	Default: "quoted_reply"
+
+*forwards*
+	The template to be used for forward as body.
+
+	Default: "forward_as_body"
+
 # ACCOUNTS.CONF
 
 This file is used for configuring each mail account used for aerc. Each section

doc/aerc-templates.7.scd

@@ -0,0 +1,89 @@
+aerc-templates(7)
+
+# NAME
+
+aerc-templates - template file specification for *aerc*(1)
+
+# SYNOPSIS
+
+aerc uses the go "text/template" package for the template parsing
+which supports basic go lang operations.
+
+# MESSAGE DATA
+
+The following data can be used in templates. Though they are not all
+available always.
+
+*Addresses*
+	An array of mail.Address. That can be used to add sender or recipient
+	names to the template.
+
+	- From: List of senders.
+	- To: List of To recipients. Not always Available.
+	- Cc: List of Cc recipients. Not always Available.
+	- Bcc: List of Cc recipients. Not always Available.
+	- OriginalFrom: List of senders of the original message.
+	  Available for quoted reply and forward.
+
+	Example:
+
+	Get the name of the first sender.
+	```
+	{{(index .From 0).Name}}
+	```
+
+	Get the email address of the first sender
+	```
+	{{(index .From 0).Address}}
+	```
+
+*Date and Time*
+	The date and time information is always available and can be easily
+	formated.
+
+	- Date: Date and Time information when the compose window is opened.
+	- OriginalDate: Date and Time when the original message of received.
+	  Available for quoted reply and forward.
+
+	The _dateFormat_ function can be used to format the date and time.
+
+	Example:
+
+	Format the date to go's time package format options.
+	```
+	{{dateFormat .Date "Mon Jan 2 15:04:05 -0700 MST 2006"}}
+	```
+
+*Subject*
+	The subject of the email is available for quoted reply and forward.
+
+	Example:
+	{{.Subject}}
+
+*Original Message*
+	When using quoted reply or forward, the original message is available.
+	It can be used using two functions that are available to templates.
+
+	Example:
+
+	_wrapText_ function can be used to wrap the original text to a number
+	of characters per line.
+	```
+	{{wrapText .OriginalText 72}}
+	```
+
+	_quote_ function prepends each line with "> " and wraps the text to
+	72 characters pre line.
+	```
+	{{quote .OriginalText}}
+	```
+
+# SEE ALSO
+
+*aerc*(1) *aerc-config*(5)
+
+# AUTHORS
+
+Maintained by Drew DeVault <sir@cmpwn.com>, who is assisted by other open
+source contributors. For more information about aerc development, see
+https://git.sr.ht/~sircmpwn/aerc.

lib/templates/template.go

@@ -0,0 +1,160 @@
+package templates
+
+import (
+	"bytes"
+	"errors"
+	"net/mail"
+	"os"
+	"path"
+	"strings"
+	"text/template"
+	"time"
+
+	"github.com/mitchellh/go-homedir"
+)
+
+type TemplateData struct {
+	To      []*mail.Address
+	Cc      []*mail.Address
+	Bcc     []*mail.Address
+	From    []*mail.Address
+	Date    time.Time
+	Subject string
+	// Only available when replying with a quote
+	OriginalText string
+	OriginalFrom []*mail.Address
+	OriginalDate time.Time
+}
+
+func TestTemplateData() TemplateData {
+	defaults := map[string]string{
+		"To":           "John Doe <john@example.com>",
+		"Cc":           "Josh Doe <josh@example.com>",
+		"From":         "Jane Smith <jane@example.com>",
+		"Subject":      "This is only a test",
+		"OriginalText": "This is only a test text",
+		"OriginalFrom": "John Doe <john@example.com>",
+		"OriginalDate": time.Now().Format("Mon Jan 2, 2006 at 3:04 PM"),
+	}
+
+	return ParseTemplateData(defaults)
+}
+
+func ParseTemplateData(defaults map[string]string) TemplateData {
+	originalDate, _ := time.Parse("Mon Jan 2, 2006 at 3:04 PM", defaults["OriginalDate"])
+	td := TemplateData{
+		To:           parseAddressList(defaults["To"]),
+		Cc:           parseAddressList(defaults["Cc"]),
+		Bcc:          parseAddressList(defaults["Bcc"]),
+		From:         parseAddressList(defaults["From"]),
+		Date:         time.Now(),
+		Subject:      defaults["Subject"],
+		OriginalText: defaults["Original"],
+		OriginalFrom: parseAddressList(defaults["OriginalFrom"]),
+		OriginalDate: originalDate,
+	}
+	return td
+}
+
+func parseAddressList(list string) []*mail.Address {
+	addrs, err := mail.ParseAddressList(list)
+	if err != nil {
+		return nil
+	}
+
+	return addrs
+}
+
+func wrapLine(text string, lineWidth int) string {
+	words := strings.Fields(text)
+	if len(words) == 0 {
+		return text
+	}
+	wrapped := words[0]
+	spaceLeft := lineWidth - len(wrapped)
+	for _, word := range words[1:] {
+		if len(word)+1 > spaceLeft {
+			wrapped += "\n" + word
+			spaceLeft = lineWidth - len(word)
+		} else {
+			wrapped += " " + word
+			spaceLeft -= 1 + len(word)
+		}
+	}
+
+	return wrapped
+}
+
+func wrapText(text string, lineWidth int) string {
+	text = strings.ReplaceAll(text, "\r\n", "\n")
+	lines := strings.Split(text, "\n")
+	var wrapped string
+
+	for _, line := range lines {
+		wrapped += wrapLine(line, lineWidth) + "\n"
+	}
+	return wrapped
+}
+
+// Wraping lines at 70 so that with the "> " of the quote it is under 72
+func quote(text string) string {
+	text = strings.ReplaceAll(text, "\r\n", "\n")
+
+	quoted := "> " + wrapText(text, 70)
+	quoted = strings.ReplaceAll(quoted, "\n", "\n> ")
+	return quoted
+}
+
+var templateFuncs = template.FuncMap{
+	"quote":      quote,
+	"wrapText":   wrapText,
+	"dateFormat": time.Time.Format,
+}
+
+func findTemplate(templateName string, templateDirs []string) (string, error) {
+	for _, dir := range templateDirs {
+		templateFile, err := homedir.Expand(path.Join(dir, templateName))
+		if err != nil {
+			return "", err
+		}
+
+		if _, err := os.Stat(templateFile); os.IsNotExist(err) {
+			continue
+		}
+		return templateFile, nil
+	}
+
+	return "", errors.New("Can't find template - " + templateName)
+}
+
+func ParseTemplateFromFile(templateName string, templateDirs []string, data interface{}) ([]byte, error) {
+	templateFile, err := findTemplate(templateName, templateDirs)
+	if err != nil {
+		return nil, err
+	}
+	emailTemplate, err :=
+		template.New(templateName).Funcs(templateFuncs).ParseFiles(templateFile)
+	if err != nil {
+		return nil, err
+	}
+
+	var outString bytes.Buffer
+	if err := emailTemplate.Execute(&outString, data); err != nil {
+		return nil, err
+	}
+	return outString.Bytes(), nil
+}
+
+func ParseTemplate(templateText string, data interface{}) ([]byte, error) {
+	emailTemplate, err :=
+		template.New("email_template").Funcs(templateFuncs).Parse(templateText)
+	if err != nil {
+		return nil, err
+	}
+
+	var outString bytes.Buffer
+	if err := emailTemplate.Execute(&outString, data); err != nil {
+		return nil, err
+	}
+	return outString.Bytes(), nil
+}

templates/forward_as_body

@@ -0,0 +1,2 @@
+Forwarded message from {{(index .OriginalFrom 0).Name}} on {{dateFormat .OriginalDate "Mon Jan 2, 2006 at 3:04 PM"}}:
+{{wrapText .OriginalText 72}}

templates/quoted_reply

@@ -0,0 +1,2 @@
+on {{dateFormat .OriginalDate "Mon Jan 2, 2006 at 3:04 PM"}}, {{(index .OriginalFrom 0).Name}} wrote:
+{{quote .OriginalText}}

widgets/aerc.go

@@ -431,8 +431,11 @@ func (aerc *Aerc) Mailto(addr *url.URL) error {
 			defaults[header] = strings.Join(vals, ",")
 		}
 	}
-	composer := NewComposer(aerc, aerc.Config(),
+	composer, err := NewComposer(aerc, aerc.Config(),
-		acct.AccountConfig(), acct.Worker(), defaults)
+		acct.AccountConfig(), acct.Worker(), "", defaults)
+	if err != nil {
+		return nil
+	}
 	composer.FocusSubject()
 	title := "New email"
 	if subj, ok := defaults["Subject"]; ok {

widgets/compose.go

@@ -23,6 +23,7 @@ import (
 	"github.com/pkg/errors"
 
 	"git.sr.ht/~sircmpwn/aerc/config"
+	"git.sr.ht/~sircmpwn/aerc/lib/templates"
 	"git.sr.ht/~sircmpwn/aerc/lib/ui"
 	"git.sr.ht/~sircmpwn/aerc/worker/types"
 )
@@ -53,7 +54,7 @@ type Composer struct {
 }
 
 func NewComposer(aerc *Aerc, conf *config.AercConfig,
-	acct *config.AccountConfig, worker *types.Worker, defaults map[string]string) *Composer {
+	acct *config.AccountConfig, worker *types.Worker, template string, defaults map[string]string) (*Composer, error) {
 
 	if defaults == nil {
 		defaults = make(map[string]string)
@@ -62,13 +63,14 @@ func NewComposer(aerc *Aerc, conf *config.AercConfig,
 		defaults["From"] = acct.From
 	}
 
+	templateData := templates.ParseTemplateData(defaults)
 	layout, editors, focusable := buildComposeHeader(
 		conf.Compose.HeaderLayout, defaults)
 
 	email, err := ioutil.TempFile("", "aerc-compose-*.eml")
 	if err != nil {
 		// TODO: handle this better
-		return nil
+		return nil, err
 	}
 
 	c := &Composer{
@@ -86,11 +88,14 @@ func NewComposer(aerc *Aerc, conf *config.AercConfig,
 	}
 
 	c.AddSignature()
+	if err := c.AddTemplate(template, templateData); err != nil {
+		return nil, err
+	}
 
 	c.updateGrid()
 	c.ShowTerminal()
 
-	return c
+	return c, nil
 }
 
 func buildComposeHeader(layout HeaderLayout, defaults map[string]string) (
@@ -163,6 +168,32 @@ func (c *Composer) AppendContents(reader io.Reader) {
 	c.email.Sync()
 }
 
+func (c *Composer) AddTemplate(template string, data interface{}) error {
+	if template == "" {
+		return nil
+	}
+
+	templateText, err := templates.ParseTemplateFromFile(template, c.config.Templates.TemplateDirs, data)
+	if err != nil {
+		return err
+	}
+	c.PrependContents(bytes.NewReader(templateText))
+	return nil
+}
+
+func (c *Composer) AddTemplateFromString(template string, data interface{}) error {
+	if template == "" {
+		return nil
+	}
+
+	templateText, err := templates.ParseTemplate(template, data)
+	if err != nil {
+		return err
+	}
+	c.PrependContents(bytes.NewReader(templateText))
+	return nil
+}
+
 func (c *Composer) AddSignature() {
 	var signature []byte
 	if c.acct.SignatureCmd != "" {