upgrade deps; rewrite smtp session

vendor/github.com/jhillyerd/enmime/internal/textproto/header.go

@@ -0,0 +1,56 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package textproto
+
+// A MIMEHeader represents a MIME-style header mapping
+// keys to sets of values.
+type MIMEHeader map[string][]string
+
+// Add adds the key, value pair to the header.
+// It appends to any existing values associated with key.
+func (h MIMEHeader) Add(key, value string) {
+	key = CanonicalEmailMIMEHeaderKey(key)
+	h[key] = append(h[key], value)
+}
+
+// Set sets the header entries associated with key to
+// the single element value. It replaces any existing
+// values associated with key.
+func (h MIMEHeader) Set(key, value string) {
+	h[CanonicalEmailMIMEHeaderKey(key)] = []string{value}
+}
+
+// Get gets the first value associated with the given key.
+// It is case insensitive; CanonicalMIMEHeaderKey is used
+// to canonicalize the provided key.
+// If there are no values associated with the key, Get returns "".
+// To use non-canonical keys, access the map directly.
+func (h MIMEHeader) Get(key string) string {
+	if h == nil {
+		return ""
+	}
+	v := h[CanonicalEmailMIMEHeaderKey(key)]
+	if len(v) == 0 {
+		return ""
+	}
+	return v[0]
+}
+
+// Values returns all values associated with the given key.
+// It is case insensitive; CanonicalMIMEHeaderKey is
+// used to canonicalize the provided key. To use non-canonical
+// keys, access the map directly.
+// The returned slice is not a copy.
+func (h MIMEHeader) Values(key string) []string {
+	if h == nil {
+		return nil
+	}
+	return h[CanonicalEmailMIMEHeaderKey(key)]
+}
+
+// Del deletes the values associated with key.
+func (h MIMEHeader) Del(key string) {
+	delete(h, CanonicalEmailMIMEHeaderKey(key))
+}