compose: use a proper header instead of a string map

Prior to this commit, the composer was based on a map[string]string.
While this approach was very versatile, it lead to a constant encoding / decoding
of addresses and other headers.

This commit switches to a different model, where the composer is based on a header.
Commands which want to interact with it can simply set some defaults they would
like to have. Users can overwrite them however they like.

In order to get access to the functions generating / getting the msgid go-message
was upgraded.

14 files changed, 318 insertions, 217 deletions

diff --git a/commands/compose/header.go b/commands/compose/header.go
index 5188a8a2..dd0adee9 100644
--- a/commands/compose/header.go
+++ b/commands/compose/header.go
@@ -57,18 +57,17 @@ func (Header) Execute(aerc *widgets.Aerc, args []string) error {
 	composer, _ := aerc.SelectedTab().(*widgets.Composer)
 
 	if !force {
-		headers, _, err := composer.PrepareHeader()
+		headers, err := composer.PrepareHeader()
 		if err != nil {
 			return err
 		}
 
-		if headers.Has(strings.Title(args[optind])) {
+		if headers.Has(args[optind]) {
 			return fmt.Errorf("Header %s already exists", args[optind])
 		}
 	}
 
-	composer.AddEditor(strings.Title(args[optind]),
-		strings.Join(args[optind+1:], " "), false)
+	composer.AddEditor(args[optind], strings.Join(args[optind+1:], " "), false)
 
 	return nil
 }
diff --git a/commands/compose/postpone.go b/commands/compose/postpone.go
index 60c9df1a..365b683f 100644
--- a/commands/compose/postpone.go
+++ b/commands/compose/postpone.go
@@ -40,7 +40,7 @@ func (Postpone) Execute(aerc *widgets.Aerc, args []string) error {
 
 	aerc.Logger().Println("Postponing mail")
 
-	header, _, err := composer.PrepareHeader()
+	header, err := composer.PrepareHeader()
 	if err != nil {
 		return errors.Wrap(err, "PrepareHeader")
 	}
diff --git a/commands/compose/send.go b/commands/compose/send.go
index abbcb544..70446dab 100644
--- a/commands/compose/send.go
+++ b/commands/compose/send.go
@@ -4,7 +4,6 @@ import (
 	"crypto/tls"
 	"fmt"
 	"io"
-	"net/mail"
 	"net/url"
 	"os/exec"
 	"strings"
@@ -17,9 +16,11 @@ import (
 	"github.com/pkg/errors"
 
 	"git.sr.ht/~sircmpwn/aerc/lib"
+	"git.sr.ht/~sircmpwn/aerc/lib/format"
 	"git.sr.ht/~sircmpwn/aerc/models"
 	"git.sr.ht/~sircmpwn/aerc/widgets"
 	"git.sr.ht/~sircmpwn/aerc/worker/types"
+	"github.com/emersion/go-message/mail"
 	"golang.org/x/oauth2"
 )
 
@@ -71,15 +72,19 @@ func (Send) Execute(aerc *widgets.Aerc, args []string) error {
 		}
 	}
 
-	header, rcpts, err := composer.PrepareHeader()
+	header, err := composer.PrepareHeader()
 	if err != nil {
 		return errors.Wrap(err, "PrepareHeader")
 	}
+	rcpts, err := listRecipients(header)
+	if err != nil {
+		return errors.Wrap(err, "listRecipients")
+	}
 
 	if config.From == "" {
 		return errors.New("No 'From' configured for this account")
 	}
-	from, err := mail.ParseAddress(config.From)
+	from, err := format.ParseAddress(config.From)
 	if err != nil {
 		return errors.Wrap(err, "ParseAddress(config.From)")
 	}
@@ -288,7 +293,12 @@ func (Send) Execute(aerc *widgets.Aerc, args []string) error {
 					composer.Close()
 				}
 			})
-			header, _, _ := composer.PrepareHeader()
+			header, err := composer.PrepareHeader()
+			if err != nil {
+				aerc.PushError(" " + err.Error())
+				w.Close()
+				return
+			}
 			composer.WriteMessage(header, w)
 			w.Close()
 		} else {
@@ -299,3 +309,17 @@ func (Send) Execute(aerc *widgets.Aerc, args []string) error {
 	}()
 	return nil
 }
+
+func listRecipients(h *mail.Header) ([]string, error) {
+	var rcpts []string
+	for _, key := range []string{"to", "cc", "bcc"} {
+		list, err := h.AddressList(key)
+		if err != nil {
+			return nil, err
+		}
+		for _, addr := range list {
+			rcpts = append(rcpts, addr.Address)
+		}
+	}
+	return rcpts, nil
+}
diff --git a/commands/msg/forward.go b/commands/msg/forward.go
index b17482f9..475d6805 100644
--- a/commands/msg/forward.go
+++ b/commands/msg/forward.go
@@ -15,6 +15,7 @@ import (
 	"git.sr.ht/~sircmpwn/aerc/models"
 	"git.sr.ht/~sircmpwn/aerc/widgets"
 	"git.sr.ht/~sircmpwn/aerc/worker/types"
+	"github.com/emersion/go-message/mail"
 
 	"git.sr.ht/~sircmpwn/getopt"
 )
@@ -49,11 +50,6 @@ func (forward) Execute(aerc *widgets.Aerc, args []string) error {
 		}
 	}
 
-	to := ""
-	if len(args) != 1 {
-		to = strings.Join(args[optind:], ", ")
-	}
-
 	widget := aerc.SelectedTab().(widgets.ProvidesMessage)
 	acct := widget.SelectedAccount()
 	if acct == nil {
@@ -69,11 +65,19 @@ func (forward) Execute(aerc *widgets.Aerc, args []string) error {
 	}
 	acct.Logger().Println("Forwarding email " + msg.Envelope.MessageId)
 
+	h := &mail.Header{}
 	subject := "Fwd: " + msg.Envelope.Subject
-	defaults := map[string]string{
-		"To":      to,
-		"Subject": subject,
+	h.SetSubject(subject)
+
+	if len(args) != 1 {
+		to := strings.Join(args[optind:], ", ")
+		tolist, err := mail.ParseAddressList(to)
+		if err != nil {
+			return fmt.Errorf("invalid to address(es): %v", err)
+		}
+		h.SetAddressList("to", tolist)
 	}
+
 	original := models.OriginalMail{
 		From:          format.FormatAddresses(msg.Envelope.From),
 		Date:          msg.Envelope.Date,
@@ -81,15 +85,15 @@ func (forward) Execute(aerc *widgets.Aerc, args []string) error {
 	}
 
 	addTab := func() (*widgets.Composer, error) {
-		composer, err := widgets.NewComposer(aerc, acct, aerc.Config(), acct.AccountConfig(),
-			acct.Worker(), template, defaults, original)
+		composer, err := widgets.NewComposer(aerc, acct, aerc.Config(),
+			acct.AccountConfig(), acct.Worker(), template, h, original)
 		if err != nil {
 			aerc.PushError("Error: " + err.Error())
 			return nil, err
 		}
 
 		tab := aerc.NewTab(composer, subject)
-		if to == "" {
+		if !h.Has("to") {
 			composer.FocusRecipient()
 		} else {
 			composer.FocusTerminal()
diff --git a/commands/msg/recall.go b/commands/msg/recall.go
index 5212041e..b6c7f65d 100644
--- a/commands/msg/recall.go
+++ b/commands/msg/recall.go
@@ -53,15 +53,9 @@ func (Recall) Execute(aerc *widgets.Aerc, args []string) error {
 	}
 	acct.Logger().Println("Recalling message " + msgInfo.Envelope.MessageId)
 
-	// copy the headers to the defaults map for addition to the composition
-	defaults := make(map[string]string)
-	headerFields := msgInfo.RFC822Headers.Fields()
-	for headerFields.Next() {
-		defaults[headerFields.Key()] = headerFields.Value()
-	}
-
 	composer, err := widgets.NewComposer(aerc, acct, aerc.Config(),
-		acct.AccountConfig(), acct.Worker(), "", defaults, models.OriginalMail{})
+		acct.AccountConfig(), acct.Worker(), "", msgInfo.RFC822Headers,
+		models.OriginalMail{})
 	if err != nil {
 		return errors.Wrap(err, "Cannot open a new composer")
 	}
diff --git a/commands/msg/reply.go b/commands/msg/reply.go
index 0298ac20..863c7d25 100644
--- a/commands/msg/reply.go
+++ b/commands/msg/reply.go
@@ -145,22 +145,22 @@ func (reply) Execute(aerc *widgets.Aerc, args []string) error {
 		subject = msg.Envelope.Subject
 	}
 
-	defaults := map[string]string{
-		"To":          format.FormatAddresses(to),
-		"Cc":          format.FormatAddresses(cc),
-		"From":        format.AddressForHumans(from),
-		"Subject":     subject,
-		"In-Reply-To": msg.Envelope.MessageId,
-	}
+	h := &mail.Header{}
+	h.SetAddressList("to", to)
+	h.SetAddressList("cc", cc)
+	h.SetAddressList("from", []*mail.Address{from})
+	h.SetSubject(subject)
+	h.SetMsgIDList("in-reply-to", []string{msg.Envelope.MessageId})
+	//TODO: references header
 	original := models.OriginalMail{
-		From: format.FormatAddresses(msg.Envelope.From),
-		Date: msg.Envelope.Date,
+		From:          format.FormatAddresses(msg.Envelope.From),
+		Date:          msg.Envelope.Date,
 		RFC822Headers: msg.RFC822Headers,
 	}
 
 	addTab := func() error {
 		composer, err := widgets.NewComposer(aerc, acct, aerc.Config(),
-			acct.AccountConfig(), acct.Worker(), template, defaults, original)
+			acct.AccountConfig(), acct.Worker(), template, h, original)
 		if err != nil {
 			aerc.PushError("Error: " + err.Error())
 			return err
diff --git a/commands/msg/unsubscribe.go b/commands/msg/unsubscribe.go
index dec90d5e..205a255d 100644
--- a/commands/msg/unsubscribe.go
+++ b/commands/msg/unsubscribe.go
@@ -9,6 +9,7 @@ import (
 	"git.sr.ht/~sircmpwn/aerc/lib"
 	"git.sr.ht/~sircmpwn/aerc/models"
 	"git.sr.ht/~sircmpwn/aerc/widgets"
+	"github.com/emersion/go-message/mail"
 )
 
 // Unsubscribe helps people unsubscribe from mailing lists by way of the
@@ -84,10 +85,13 @@ func parseUnsubscribeMethods(header string) (methods []*url.URL) {
 func unsubscribeMailto(aerc *widgets.Aerc, u *url.URL) error {
 	widget := aerc.SelectedTab().(widgets.ProvidesMessage)
 	acct := widget.SelectedAccount()
-	defaults := map[string]string{
-		"To":      u.Opaque,
-		"Subject": u.Query().Get("subject"),
+
+	h := &mail.Header{}
+	h.SetSubject(u.Query().Get("subject"))
+	if to, err := mail.ParseAddressList(u.Opaque); err == nil {
+		h.SetAddressList("to", to)
 	}
+
 	composer, err := widgets.NewComposer(
 		aerc,
 		acct,
@@ -95,7 +99,7 @@ func unsubscribeMailto(aerc *widgets.Aerc, u *url.URL) error {
 		acct.AccountConfig(),
 		acct.Worker(),
 		"",
-		defaults,
+		h,
 		models.OriginalMail{},
 	)
 	if err != nil {
diff --git a/config/config.go b/config/config.go
index 87d183a4..51982d26 100644
--- a/config/config.go
+++ b/config/config.go
@@ -413,8 +413,10 @@ func (config *AercConfig) LoadConfig(file *ini.File) error {
 			if key == "template-dirs" {
 				continue
 			}
+			// we want to fail during startup if the templates are not ok
+			// hence we do a dummy execute here
 			_, err := templates.ParseTemplateFromFile(
-				val, config.Templates.TemplateDirs, templates.TestTemplateData())
+				val, config.Templates.TemplateDirs, templates.DummyData())
 			if err != nil {
 				return err
 			}
diff --git a/go.mod b/go.mod
index 380b7a1a..2a5be540 100644
--- a/go.mod
+++ b/go.mod
@@ -11,7 +11,7 @@ require (
 	github.com/emersion/go-imap-idle v0.0.0-20190519112320-2704abd7050e
 	github.com/emersion/go-imap-sortthread v1.1.1-0.20201009054724-d020d96306b3
 	github.com/emersion/go-maildir v0.2.0
-	github.com/emersion/go-message v0.12.1-0.20200824204225-9094bd0b8bc0
+	github.com/emersion/go-message v0.13.1-0.20201112194930-f77964fe28bd
 	github.com/emersion/go-pgpmail v0.0.0-20200303213726-db035a3a4139
 	github.com/emersion/go-sasl v0.0.0-20200509203442-7bfe0ed36a21
 	github.com/emersion/go-smtp v0.12.1
@@ -39,7 +39,6 @@ require (
 	golang.org/x/net v0.0.0-20200301022130-244492dfa37a // indirect
 	golang.org/x/oauth2 v0.0.0-20200107190931-bf48bf16ab8d
 	golang.org/x/sys v0.0.0-20200302150141-5c8b2ff67527 // indirect
-	golang.org/x/text v0.3.3 // indirect
 	google.golang.org/appengine v1.6.5 // indirect
 	gopkg.in/ini.v1 v1.44.0 // indirect
 	gopkg.in/yaml.v2 v2.2.8 // indirect
diff --git a/go.sum b/go.sum
index f4f418fb..cefdaac7 100644
--- a/go.sum
+++ b/go.sum
@@ -26,8 +26,8 @@ github.com/emersion/go-maildir v0.2.0 h1:fC4+UVGl8GcQGbFF7AWab2JMf4VbKz+bMNv07xx
 github.com/emersion/go-maildir v0.2.0/go.mod h1:I2j27lND/SRLgxROe50Vam81MSaqPFvJ0OHNnDZ7n84=
 github.com/emersion/go-message v0.10.4-0.20190609165112-592ace5bc1ca/go.mod h1:3h+HsGTCFHmk4ngJ2IV/YPhdlaOcR6hcgqM3yca9v7c=
 github.com/emersion/go-message v0.11.1/go.mod h1:C4jnca5HOTo4bGN9YdqNQM9sITuT3Y0K6bSUw9RklvY=
-github.com/emersion/go-message v0.12.1-0.20200824204225-9094bd0b8bc0 h1:G2VV/Wp2opDvR0ecue3UY/IX1/8OlTmMKKi+ENe1nG0=
-github.com/emersion/go-message v0.12.1-0.20200824204225-9094bd0b8bc0/go.mod h1:C4jnca5HOTo4bGN9YdqNQM9sITuT3Y0K6bSUw9RklvY=
+github.com/emersion/go-message v0.13.1-0.20201112194930-f77964fe28bd h1:6CXxdoOzAyQForkd2U/JNceVyNpmg92alCU2R+4dwIY=
+github.com/emersion/go-message v0.13.1-0.20201112194930-f77964fe28bd/go.mod h1:SXSs/8KamlsyxjpHL1Q3yf5Jrv7QG5icuvPK1SMcnzw=
 github.com/emersion/go-pgpmail v0.0.0-20200303213726-db035a3a4139 h1:JTUbkRuQFtDrl5KHWR2jrh9SUeSDEEEjUcHJkXdAE2Q=
 github.com/emersion/go-pgpmail v0.0.0-20200303213726-db035a3a4139/go.mod h1:+Ovy1VQCUKPdjWkOiWvFoiFaWXkqn1PA793VvfEYWQU=
 github.com/emersion/go-sasl v0.0.0-20190520160400-47d427600317/go.mod h1:G/dpzLu16WtQpBfQ/z3LYiYJn3ZhKSGWn83fyoyQe/k=
@@ -40,6 +40,8 @@ github.com/emersion/go-smtp v0.12.1 h1:1R8BDqrR2HhlGwgFYcOi+BVTvK1bMjAB65QcVpJ5s
 github.com/emersion/go-smtp v0.12.1/go.mod h1:SD9V/xa4ndMw77lR3Mf7htkp8RBNYuPh9UeuBs9tpUQ=
 github.com/emersion/go-textwrapper v0.0.0-20160606182133-d0e65e56babe h1:40SWqY0zE3qCi6ZrtTf5OUdNm5lDnGnjRSq9GgmeTrg=
 github.com/emersion/go-textwrapper v0.0.0-20160606182133-d0e65e56babe/go.mod h1:aqO8z8wPrjkscevZJFVE1wXJrLpC5LtJG7fqLOsPb2U=
+github.com/emersion/go-textwrapper v0.0.0-20200911093747-65d896831594 h1:IbFBtwoTQyw0fIM5xv1HF+Y+3ZijDR839WMulgxCcUY=
+github.com/emersion/go-textwrapper v0.0.0-20200911093747-65d896831594/go.mod h1:aqO8z8wPrjkscevZJFVE1wXJrLpC5LtJG7fqLOsPb2U=
 github.com/fsnotify/fsnotify v1.4.7 h1:IXs+QLmnXW2CcXuY+8Mzv/fWEsPGWxqefPtCP5CnV9I=
 github.com/fsnotify/fsnotify v1.4.7/go.mod h1:jwhsz4b93w/PPRr/qN1Yymfu8t87LnFCMoQvtojpjFo=
 github.com/gdamore/encoding v1.0.0 h1:+7OoQ1Bc6eTm5niUzBa0Ctsh6JbMW6Ra+YNuAtDBdko=
@@ -67,6 +69,8 @@ github.com/lucasb-eyer/go-colorful v1.0.3/go.mod h1:R4dSotOR9KMtayYi1e77YzuveK+i
 github.com/martinlindhe/base36 v0.0.0-20190418230009-7c6542dfbb41/go.mod h1:+AtEs8xrBpCeYgSLoY/aJ6Wf37jtBuR0s35750M27+8=
 github.com/martinlindhe/base36 v1.0.0 h1:eYsumTah144C0A8P1T/AVSUk5ZoLnhfYFM3OGQxB52A=
 github.com/martinlindhe/base36 v1.0.0/go.mod h1:+AtEs8xrBpCeYgSLoY/aJ6Wf37jtBuR0s35750M27+8=
+github.com/martinlindhe/base36 v1.1.0 h1:cIwvvwYse/0+1CkUPYH5ZvVIYG3JrILmQEIbLuar02Y=
+github.com/martinlindhe/base36 v1.1.0/go.mod h1:+AtEs8xrBpCeYgSLoY/aJ6Wf37jtBuR0s35750M27+8=
 github.com/mattn/go-isatty v0.0.12 h1:wuysRhFDzyxgEmMf5xjvJ2M9dZoWAXNNr5LSBS7uHXY=
 github.com/mattn/go-isatty v0.0.12/go.mod h1:cbi8OIDigv2wuxKPP5vlRcQ1OAZbq2CE4Kysco4FUpU=
 github.com/mattn/go-pointer v0.0.0-20180825124634-49522c3f3791/go.mod h1:2zXcozF6qYGgmsG+SeTZz3oAbFLdD3OWqnUbNvJZAlc=
@@ -114,8 +118,8 @@ golang.org/x/sys v0.0.0-20200302150141-5c8b2ff67527 h1:uYVVQ9WP/Ds2ROhcaGPeIdVq0
 golang.org/x/sys v0.0.0-20200302150141-5c8b2ff67527/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.2/go.mod h1:bEr9sfX3Q8Zfm5fL9x+3itogRgK3+ptLWKqgva+5dAk=
-golang.org/x/text v0.3.3 h1:cokOdA+Jmi5PJGXLlLllQSgYigAEfHXJAERHVMaCc2k=
-golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
+golang.org/x/text v0.3.4-0.20201021145329-22f1617af38e h1:0kyKOEC0chG7FKmnf/1uNwvDLc3NtNTRip2rXAN9nwI=
+golang.org/x/text v0.3.4-0.20201021145329-22f1617af38e/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20190328211700-ab21143f2384/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
 google.golang.org/appengine v1.4.0/go.mod h1:xpcJRLb0r/rnEns0DIKYYv+WjYCduHsrkT7/EB5XEv4=
diff --git a/lib/format/format.go b/lib/format/format.go
index e19ca319..2ba4d646 100644
--- a/lib/format/format.go
+++ b/lib/format/format.go
@@ -61,6 +61,7 @@ func AddressForHumans(a *mail.Address) string {
 
 var atom *regexp.Regexp = regexp.MustCompile("^[a-z0-9!#$%7'*+-/=?^_`{}|~ ]+$")
 
+// FormatAddresses formats a list of addresses into a human readable string
 func FormatAddresses(l []*mail.Address) string {
 	formatted := make([]string, len(l))
 	for i, a := range l {
diff --git a/lib/templates/template.go b/lib/templates/template.go
index f979ba23..197f159f 100644
--- a/lib/templates/template.go
+++ b/lib/templates/template.go
@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"fmt"
 	"io"
-	"net/mail"
 	"os"
 	"os/exec"
 	"path"
@@ -12,6 +11,8 @@ import (
 	"text/template"
 	"time"
 
+	"github.com/emersion/go-message/mail"
+
 	"git.sr.ht/~sircmpwn/aerc/models"
 	"github.com/mitchellh/go-homedir"
 )
@@ -37,47 +38,34 @@ type TemplateData struct {
 	OriginalMIMEType string
 }
 
-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",
-	}
-
-	original := models.OriginalMail{
-		Date:     time.Now(),
-		From:     "John Doe <john@example.com>",
-		Text:     "This is only a test text",
-		MIMEType: "text/plain",
+func ParseTemplateData(h *mail.Header, original models.OriginalMail) TemplateData {
+	// we ignore errors as this shouldn't fail the sending / replying even if
+	// something is wrong with the message we reply to
+	to, _ := h.AddressList("to")
+	cc, _ := h.AddressList("cc")
+	bcc, _ := h.AddressList("bcc")
+	from, _ := h.AddressList("from")
+	subject, err := h.Text("subject")
+	if err != nil {
+		subject = h.Get("subject")
 	}
 
-	return ParseTemplateData(defaults, original)
-}
-
-func ParseTemplateData(defaults map[string]string, original models.OriginalMail) TemplateData {
 	td := TemplateData{
-		To:               parseAddressList(defaults["To"]),
-		Cc:               parseAddressList(defaults["Cc"]),
-		Bcc:              parseAddressList(defaults["Bcc"]),
-		From:             parseAddressList(defaults["From"]),
+		To:               to,
+		Cc:               cc,
+		Bcc:              bcc,
+		From:             from,
 		Date:             time.Now(),
-		Subject:          defaults["Subject"],
+		Subject:          subject,
 		OriginalText:     original.Text,
-		OriginalFrom:     parseAddressList(original.From),
 		OriginalDate:     original.Date,
 		OriginalMIMEType: original.MIMEType,
 	}
-	return td
-}
-
-func parseAddressList(list string) []*mail.Address {
-	addrs, err := mail.ParseAddressList(list)
-	if err != nil {
-		return nil
+	if original.RFC822Headers != nil {
+		origFrom, _ := original.RFC822Headers.AddressList("from")
+		td.OriginalFrom = origFrom
 	}
-
-	return addrs
+	return td
 }
 
 // wrap allows to chain wrapText
@@ -194,6 +182,34 @@ func findTemplate(templateName string, templateDirs []string) (string, error) {
 		"Can't find template %q in any of %v ", templateName, templateDirs)
 }
 
+//DummyData provides dummy data to test template validity
+func DummyData() interface{} {
+	from := &mail.Address{
+		Name:    "John Doe",
+		Address: "john@example.com",
+	}
+	to := &mail.Address{
+		Name:    "Alice Doe",
+		Address: "alice@example.com",
+	}
+	h := &mail.Header{}
+	h.SetAddressList("from", []*mail.Address{from})
+	h.SetAddressList("to", []*mail.Address{to})
+
+	oh := &mail.Header{}
+	oh.SetAddressList("from", []*mail.Address{to})
+	oh.SetAddressList("to", []*mail.Address{from})
+
+	original := models.OriginalMail{
+		Date:          time.Now(),
+		From:          from.String(),
+		Text:          "This is only a test text",
+		MIMEType:      "text/plain",
+		RFC822Headers: oh,
+	}
+	return ParseTemplateData(h, original)
+}
+
 func ParseTemplateFromFile(templateName string, templateDirs []string, data interface{}) (io.Reader, error) {
 	templateFile, err := findTemplate(templateName, templateDirs)
 	if err != nil {
diff --git a/widgets/aerc.go b/widgets/aerc.go
index acdd8b4a..b4b4e28f 100644
--- a/widgets/aerc.go
+++ b/widgets/aerc.go
@@ -9,6 +9,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/emersion/go-message/mail"
 	"github.com/gdamore/tcell"
 	"github.com/google/shlex"
 	"golang.org/x/crypto/openpgp"
@@ -496,27 +497,38 @@ func (aerc *Aerc) Mailto(addr *url.URL) error {
 	if acct == nil {
 		return errors.New("No account selected")
 	}
-	defaults := make(map[string]string)
-	defaults["To"] = addr.Opaque
-	headerMap := map[string]string{
-		"cc":          "Cc",
-		"in-reply-to": "In-Reply-To",
-		"subject":     "Subject",
-	}
+
+	var subject string
+	h := &mail.Header{}
+	h.SetAddressList("to", []*mail.Address{&mail.Address{Address: addr.Opaque}})
 	for key, vals := range addr.Query() {
-		if header, ok := headerMap[strings.ToLower(key)]; ok {
-			defaults[header] = strings.Join(vals, ",")
+		switch strings.ToLower(key) {
+		case "cc":
+			list, err := mail.ParseAddressList(strings.Join(vals, ","))
+			if err != nil {
+				break
+			}
+			h.SetAddressList("Cc", list)
+		case "in-reply-to":
+			h.SetMsgIDList("In-Reply-To", vals)
+		case "subject":
+			subject = strings.Join(vals, ",")
+			h.SetText("Subject", subject)
+		default:
+			// any other header gets ignored on purpose to avoid control headers
+			// being injected
 		}
 	}
+
 	composer, err := NewComposer(aerc, acct, aerc.Config(),
-		acct.AccountConfig(), acct.Worker(), "", defaults, models.OriginalMail{})
+		acct.AccountConfig(), acct.Worker(), "", h, models.OriginalMail{})
 	if err != nil {
 		return nil
 	}
 	composer.FocusSubject()
 	title := "New email"
-	if subj, ok := defaults["Subject"]; ok {
-		title = subj
+	if subject != "" {
+		title = subject
 		composer.FocusTerminal()
 	}
 	tab := aerc.NewTab(composer, title)
diff --git a/widgets/compose.go b/widgets/compose.go
index 522146ab..73ebcb3e 100644
--- a/widgets/compose.go
+++ b/widgets/compose.go
@@ -8,7 +8,7 @@ import (
 	"io/ioutil"
 	"mime"
 	"net/http"
-	gomail "net/mail"
+	"net/textproto"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -23,6 +23,7 @@ import (
 
 	"git.sr.ht/~sircmpwn/aerc/completer"
 	"git.sr.ht/~sircmpwn/aerc/config"
+	"git.sr.ht/~sircmpwn/aerc/lib/format"
 	"git.sr.ht/~sircmpwn/aerc/lib/templates"
 	"git.sr.ht/~sircmpwn/aerc/lib/ui"
 	"git.sr.ht/~sircmpwn/aerc/models"
@@ -30,7 +31,9 @@ import (
 )
 
 type Composer struct {
-	editors map[string]*headerEditor
+	editors map[string]*headerEditor // indexes in lower case (from / cc / bcc)
+	header  *mail.Header
+	parent  models.OriginalMail // parent of current message, only set if reply
 
 	acctConfig *config.AccountConfig
 	config     *config.AercConfig
@@ -38,13 +41,10 @@ type Composer struct {
 	aerc       *Aerc
 
 	attachments []string
-	date        time.Time
-	defaults    map[string]string
 	editor      *Terminal
 	email       *os.File
 	grid        *ui.Grid
 	heditors    *ui.Grid // from, to, cc display a user can jump to
-	msgId       string
 	review      *reviewMessage
 	worker      *types.Worker
 	completer   *completer.Completer
@@ -61,22 +61,29 @@ type Composer struct {
 
 func NewComposer(aerc *Aerc, acct *AccountView, conf *config.AercConfig,
 	acctConfig *config.AccountConfig, worker *types.Worker, template string,
-	defaults map[string]string, original models.OriginalMail) (*Composer, error) {
+	h *mail.Header, orig models.OriginalMail) (*Composer, error) {
 
-	if defaults == nil {
-		defaults = make(map[string]string)
+	if h == nil {
+		h = new(mail.Header)
 	}
-	if from := defaults["From"]; from == "" {
-		defaults["From"] = acctConfig.From
+	if fl, err := h.AddressList("from"); err != nil || fl == nil {
+		fl, err = mail.ParseAddressList(acctConfig.From)
+		// realistically this blows up way before us during the config loading
+		if err != nil {
+			return nil, err
+		}
+		if fl != nil {
+			h.SetAddressList("from", fl)
+
+		}
 	}
 
-	templateData := templates.ParseTemplateData(defaults, original)
+	templateData := templates.ParseTemplateData(h, orig)
 	cmpl := completer.New(conf.Compose.AddressBookCmd, func(err error) {
 		aerc.PushError(
 			fmt.Sprintf("could not complete header: %v", err))
 		worker.Logger.Printf("could not complete header: %v", err)
 	}, aerc.Logger())
-	layout, editors, focusable := buildComposeHeader(aerc, cmpl, defaults)
 
 	email, err := ioutil.TempFile("", "aerc-compose-*.eml")
 	if err != nil {
@@ -89,18 +96,15 @@ func NewComposer(aerc *Aerc, acct *AccountView, conf *config.AercConfig,
 		acctConfig: acctConfig,
 		aerc:       aerc,
 		config:     conf,
-		date:       time.Now(),
-		defaults:   defaults,
-		editors:    editors,
+		header:     h,
+		parent:     orig,
 		email:      email,
-		layout:     layout,
-		msgId:      mail.GenerateMessageID(),
 		worker:     worker,
 		// You have to backtab to get to "From", since you usually don't edit it
 		focused:   1,
-		focusable: focusable,
 		completer: cmpl,
 	}
+	c.buildComposeHeader(aerc, cmpl)
 
 	if err := c.AddTemplate(template, templateData); err != nil {
 		return nil, err
@@ -113,56 +117,51 @@ func NewComposer(aerc *Aerc, acct *AccountView, conf *config.AercConfig,
 	return c, nil
 }
 
-func buildComposeHeader(aerc *Aerc, cmpl *completer.Completer,
-	defaults map[string]string) (
-	newLayout HeaderLayout,
-	editors map[string]*headerEditor,
-	focusable []ui.MouseableDrawableInteractive,
-) {
-	layout := aerc.conf.Compose.HeaderLayout
-	editors = make(map[string]*headerEditor)
-	focusable = make([]ui.MouseableDrawableInteractive, 0)
+func (c *Composer) buildComposeHeader(aerc *Aerc, cmpl *completer.Completer) {
+
+	c.layout = aerc.conf.Compose.HeaderLayout
+	c.editors = make(map[string]*headerEditor)
+	c.focusable = make([]ui.MouseableDrawableInteractive, 0)
 
-	for _, row := range layout {
-		for _, h := range row {
-			e := newHeaderEditor(h, "", aerc.SelectedAccount().UiConfig())
+	for i, row := range c.layout {
+		for j, h := range row {
+			h = strings.ToLower(h)
+			c.layout[i][j] = h // normalize to lowercase
+			e := newHeaderEditor(h, c.header, aerc.SelectedAccount().UiConfig())
 			if aerc.conf.Ui.CompletionPopovers {
-				e.input.TabComplete(cmpl.ForHeader(h), aerc.SelectedAccount().UiConfig().CompletionDelay)
+				e.input.TabComplete(cmpl.ForHeader(h),
+					aerc.SelectedAccount().UiConfig().CompletionDelay)
 			}
-			editors[h] = e
+			c.editors[h] = e
 			switch h {
-			case "From":
+			case "from":
 				// Prepend From to support backtab
-				focusable = append([]ui.MouseableDrawableInteractive{e}, focusable...)
+				c.focusable = append([]ui.MouseableDrawableInteractive{e}, c.focusable...)
 			default:
-				focusable = append(focusable, e)
+				c.focusable = append(c.focusable, e)
 			}
 		}
 	}
 
-	// Add Cc/Bcc editors to layout if in defaults and not already visible
-	for _, h := range []string{"Cc", "Bcc"} {
-		if val, ok := defaults[h]; ok && val != "" {
-			if _, ok := editors[h]; !ok {
-				e := newHeaderEditor(h, "", aerc.SelectedAccount().UiConfig())
+	// Add Cc/Bcc editors to layout if present in header and not already visible
+	for _, h := range []string{"cc", "bcc"} {
+		if c.header.Has(h) {
+			if _, ok := c.editors[h]; !ok {
+				e := newHeaderEditor(h, c.header, aerc.SelectedAccount().UiConfig())
 				if aerc.conf.Ui.CompletionPopovers {
 					e.input.TabComplete(cmpl.ForHeader(h), aerc.SelectedAccount().UiConfig().CompletionDelay)
 				}
-				editors[h] = e
-				focusable = append(focusable, e)
-				layout = append(layout, []string{h})
+				c.editors[h] = e
+				c.focusable = append(c.focusable, e)
+				c.layout = append(c.layout, []string{h})
 			}
 		}
 	}
 
-	// Set default values for all editors
-	for key := range editors {
-		if val, ok := defaults[key]; ok {
-			editors[key].input.Set(val)
-			delete(defaults, key)
-		}
+	// load current header values into all editors
+	for _, e := range c.editors {
+		e.loadValue()
 	}
-	return layout, editors, focusable
 }
 
 func (c *Composer) SetSent() {
@@ -205,15 +204,10 @@ func (c *Composer) AddTemplate(template string, data interface{}) error {
 		return fmt.Errorf("Template loading failed: %v", err)
 	}
 
-	// add the headers contained in the template to the default headers
+	// copy the headers contained in the template to the compose headers
 	hf := mr.Header.Fields()
 	for hf.Next() {
-		var val string
-		var err error
-		if val, err = hf.Text(); err != nil {
-			val = hf.Value()
-		}
-		c.defaults[hf.Key()] = val
+		c.header.Set(hf.Key(), hf.Value())
 	}
 
 	part, err := mr.NextPart()
@@ -293,7 +287,7 @@ func (c *Composer) FocusRecipient() *Composer {
 
 // OnHeaderChange registers an OnChange callback for the specified header.
 func (c *Composer) OnHeaderChange(header string, fn func(subject string)) {
-	if editor, ok := c.editors[header]; ok {
+	if editor, ok := c.editors[strings.ToLower(header)]; ok {
 		editor.OnChange(func() {
 			fn(editor.input.String())
 		})
@@ -378,49 +372,24 @@ func (c *Composer) Worker() *types.Worker {
 	return c.worker
 }
 
-func (c *Composer) PrepareHeader() (*mail.Header, []string, error) {
-	header := &mail.Header{}
-	for h, val := range c.defaults {
-		if val == "" {
-			continue
-		}
-		header.SetText(h, val)
-	}
-	header.SetText("Message-Id", c.msgId)
-	header.SetDate(c.date)
-
-	headerKeys := make([]string, 0, len(c.editors))
-	for key := range c.editors {
-		headerKeys = append(headerKeys, key)
+//PrepareHeader finalizes the header, adding the value from the editors
+func (c *Composer) PrepareHeader() (*mail.Header, error) {
+	for _, editor := range c.editors {
+		editor.storeValue()
 	}
 
-	var rcpts []string
-	for h, editor := range c.editors {
-		val := editor.input.String()
-		if val == "" {
-			continue
-		}
-		switch h {
-		case "From", "To", "Cc", "Bcc": // Address headers
-			hdrRcpts, err := gomail.ParseAddressList(val)
-			if err != nil {
-				return nil, nil, errors.Wrapf(err, "ParseAddressList(%s)", val)
-			}
-			edRcpts := make([]*mail.Address, len(hdrRcpts))
-			for i, addr := range hdrRcpts {
-				edRcpts[i] = (*mail.Address)(addr)
-			}
-			header.SetAddressList(h, edRcpts)
-			if h != "From" {
-				for _, addr := range edRcpts {
-					rcpts = append(rcpts, addr.Address)
-				}
-			}
-		default:
-			header.SetText(h, val)
+	// control headers not normally set by the user
+	// repeated calls to PrepareHeader should be a noop
+	if !c.header.Has("Message-Id") {
+		err := c.header.GenerateMessageID()
+		if err != nil {
+			return nil, err
 		}
 	}
-	return header, rcpts, nil
+	if !c.header.Has("Date") {
+		c.header.SetDate(time.Now())
+	}
+	return c.header, nil
 }
 
 func (c *Composer) WriteMessage(header *mail.Header, writer io.Writer) error {
@@ -639,39 +608,51 @@ func (c *Composer) FocusEditor(editor *headerEditor) {
 
 // AddEditor appends a new header editor to the compose window.
 func (c *Composer) AddEditor(header string, value string, appendHeader bool) {
-	if _, ok := c.editors[header]; ok {
-		if appendHeader {
-			header := c.editors[header].input.String()
-			value = strings.TrimSpace(header) + ", " + value
+	var editor *headerEditor
+	header = strings.ToLower(header)
+	if e, ok := c.editors[header]; ok {
+		e.storeValue() // flush modifications from the user to the header
+		editor = e
+	} else {
+		e := newHeaderEditor(header, c.header,
+			c.aerc.SelectedAccount().UiConfig())
+		if c.config.Ui.CompletionPopovers {
+			e.input.TabComplete(c.completer.ForHeader(header),
+				c.config.Ui.CompletionDelay)
 		}
-		c.editors[header].input.Set(value)
-		if value == "" {
-			c.FocusEditor(c.editors[header])
+		c.editors[header] = e
+		c.layout = append(c.layout, []string{header})
+		// Insert focus of new editor before terminal editor
+		c.focusable = append(
+			c.focusable[:len(c.focusable)-1],
+			e,
+			c.focusable[len(c.focusable)-1],
+		)
+		editor = e
+	}
+
+	if appendHeader {
+		currVal := editor.input.String()
+		if currVal != "" {
+			value = strings.TrimSpace(currVal) + ", " + value
 		}
-		return
 	}
-	e := newHeaderEditor(header, value, c.aerc.SelectedAccount().UiConfig())
-	if c.config.Ui.CompletionPopovers {
-		e.input.TabComplete(c.completer.ForHeader(header), c.config.Ui.CompletionDelay)
-	}
-	c.editors[header] = e
-	c.layout = append(c.layout, []string{header})
-	// Insert focus of new editor before terminal editor
-	c.focusable = append(
-		c.focusable[:len(c.focusable)-1],
-		e,
-		c.focusable[len(c.focusable)-1],
-	)
-	c.updateGrid()
+	if value != "" || appendHeader {
+		c.editors[header].input.Set(value)
+		editor.storeValue()
+	}
 	if value == "" {
 		c.FocusEditor(c.editors[header])
 	}
+	c.updateGrid()
 }
 
 // updateGrid should be called when the underlying header layout is changed.
 func (c *Composer) updateGrid() {
 	heditors, height := c.layout.grid(
-		func(h string) ui.Drawable { return c.editors[h] },
+		func(h string) ui.Drawable {
+			return c.editors[h]
+		},
 	)
 
 	if c.grid == nil {
@@ -707,21 +688,82 @@ func (c *Composer) reloadEmail() error {
 
 type headerEditor struct {
 	name     string
+	header   *mail.Header
 	focused  bool
 	input    *ui.TextInput
 	uiConfig config.UIConfig
 }
 
-func newHeaderEditor(name string, value string, uiConfig config.UIConfig) *headerEditor {
-	return &headerEditor{
-		input:    ui.NewTextInput(value, uiConfig),
+func newHeaderEditor(name string, h *mail.Header,
+	uiConfig config.UIConfig) *headerEditor {
+	he := &headerEditor{
+		input:    ui.NewTextInput("", uiConfig),
 		name:     name,
+		header:   h,
 		uiConfig: uiConfig,
 	}
+	he.loadValue()
+	return he
+}
+
+//extractHumanHeaderValue extracts the human readable string for key from the
+//header. If a parsing error occurs the raw value is returned
+func extractHumanHeaderValue(key string, h *mail.Header) string {
+	var val string
+	var err error
+	switch strings.ToLower(key) {
+	case "to", "from", "cc", "bcc":
+		var list []*mail.Address
+		list, err = h.AddressList(key)
+		val = format.FormatAddresses(list)
+	default:
+		val, err = h.Text(key)
+	}
+	if err != nil {
+		// if we can't parse it, show it raw
+		val = h.Get(key)
+	}
+	return val
+}
+
+//loadValue loads the value of he.name form the underlying header
+//the value is decoded and meant for human consumption.
+//decoding issues are ignored and return their raw values
+func (he *headerEditor) loadValue() {
+	he.input.Set(extractHumanHeaderValue(he.name, he.header))
+	he.input.Invalidate()
+}
+
+//storeValue writes the current state back to the underlying header.
+//errors are ignored
+func (he *headerEditor) storeValue() {
+	val := he.input.String()
+	switch strings.ToLower(he.name) {
+	case "to", "from", "cc", "bcc":
+		list, err := mail.ParseAddressList(val)
+		if err == nil {
+			he.header.SetAddressList(he.name, list)
+		} else {
+			// garbage, but it'll blow up upon sending and the user can
+			// fix the issue
+			he.header.SetText(he.name, val)
+		}
+		val = format.FormatAddresses(list)
+	default:
+		he.header.SetText(he.name, val)
+	}
+}
+
+//setValue overwrites the current value of the header editor and flushes it
+//to the underlying header
+func (he *headerEditor) setValue(val string) {
+	he.input.Set(val)
+	he.storeValue()
 }
 
 func (he *headerEditor) Draw(ctx *ui.Context) {
-	name := he.name + " "
+	normalized := textproto.CanonicalMIMEHeaderKey(he.name)
+	name := normalized + " "
 	size := runewidth.StringWidth(name)
 	defaultStyle := he.uiConfig.GetStyle(config.STYLE_DEFAULT)
 	headerStyle := he.uiConfig.GetStyle(config.STYLE_HEADER)