code review 4185053: http: introduce Header type, implement with net/textproto

src/pkg/net/textproto/header.go

+// 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 = CanonicalMIMEHeaderKey(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[CanonicalMIMEHeaderKey(key)] = []string{value}
+}
+
+// Get gets the first value associated with the given key.
+// If there are no values associated with the key, Get returns "".
+// Get is a convenience method.  For more complex queries,
+// access the map directly.
+func (h MIMEHeader) Get(key string) string {
+        if h == nil {
+                return ""
+        }
+        v := h[CanonicalMIMEHeaderKey(key)]
+        if len(v) == 0 {
+                return ""
+        }
+        return v[0]
+}
+
+// Del deletes the values associated with key.
+func (h MIMEHeader) Del(key string) {
+        h[CanonicalMIMEHeaderKey(key)] = nil, false
+}