From 12230a96de179655036fa214320dd6810a17cac8 Mon Sep 17 00:00:00 2001
From: Lars Bahner <lars.bahner@gmail.com>
Date: Thu, 9 May 2024 18:53:02 +0200
Subject: [PATCH] Add content_type parsing

---
 msg/errors.go  |  3 +--
 msg/message.go |  6 ++---
 msg/mime.go    | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++
 msg/reply.go   |  2 +-
 4 files changed, 71 insertions(+), 6 deletions(-)
 create mode 100644 msg/mime.go

diff --git a/msg/errors.go b/msg/errors.go
index 929a9b3..3975265 100644
--- a/msg/errors.go
+++ b/msg/errors.go
@@ -14,8 +14,7 @@ var (
 	ErrFetchDoc              = fmt.Errorf("failed to fetch entity document")
 	ErrInvalidMessageType    = fmt.Errorf("invalid Message type")
 	ErrInvalidRecipient      = fmt.Errorf("invalid recipient")
-	ErrMissingContentType    = fmt.Errorf("empty ContentType")
-	ErrMissingContent        = fmt.Errorf("empty ContentType")
+	ErrMissingContent        = fmt.Errorf("empty Content")
 	ErrMissingFrom           = fmt.Errorf("mmissing From sender")
 	ErrMissinSignature       = fmt.Errorf("mmissing signature")
 	ErrNilMessage            = fmt.Errorf("nil Message provided")
diff --git a/msg/message.go b/msg/message.go
index f211e92..5fdda31 100644
--- a/msg/message.go
+++ b/msg/message.go
@@ -12,9 +12,9 @@ import (
 )
 
 const (
-	PREFIX               = "/ma/"
-	MESSAGE              = PREFIX + ma.VERSION
-	MESSAGE_CONTENT_TYPE = "application/x.ma"
+	PREFIX       = "/ma/"
+	MESSAGE      = PREFIX + ma.VERSION
+	CONTENT_TYPE = "application/x.ma"
 )
 
 // This struct mimicks the Message format, but it's *not* Message.
diff --git a/msg/mime.go b/msg/mime.go
new file mode 100644
index 0000000..a09b634
--- /dev/null
+++ b/msg/mime.go
@@ -0,0 +1,66 @@
+package msg
+
+import (
+	"fmt"
+	"mime"
+	"strings"
+)
+
+var (
+	ErrInvalidContentType = fmt.Errorf("invalid Message ContentType")
+	ErrMissingContentType = fmt.Errorf("empty ContentType")
+	ErrMissingSerialiser  = fmt.Errorf("missing serialiser")
+)
+
+// Returns the message type as defined in the contenttype, not the message as such
+func (m *Message) MessageType() (string, error) {
+
+	_, params, err := m.ParseContentType()
+	if err != nil {
+		return "", ErrInvalidContentType
+	}
+
+	for k, v := range params {
+		if k == "type" {
+			return v, nil
+		}
+	}
+
+	return "", ErrInvalidContentType
+}
+
+// Returns the message type as defined in the contenttype, not the message as such
+func (m *Message) MessageSerialiser() (string, error) {
+
+	contentType, _, err := m.ParseContentType()
+	if err != nil {
+		return "", ErrInvalidContentType
+	}
+
+	elements := strings.Split(contentType, "+")
+	if len(elements) == 1 {
+		return contentType, fmt.Errorf("%s: %w", contentType, ErrMissingSerialiser)
+	}
+
+	return elements[1], nil
+}
+
+// A parser which add a little specific functionality to the standard mime.ParseMediaType
+// Use this instead.
+func (m *Message) ParseContentType() (string, map[string]string, error) {
+
+	contentType, params, err := mime.ParseMediaType(m.ContentType)
+	if err != nil {
+		return contentType, params, fmt.Errorf("msg_parse_content_type: %w", err)
+	}
+
+	if contentType == "" {
+		return contentType, params, ErrMissingContentType
+	}
+
+	if contentType != CONTENT_TYPE {
+		return contentType, params, fmt.Errorf("%s: %w", contentType, ErrInvalidContentType)
+	}
+
+	return contentType, params, nil
+}
diff --git a/msg/reply.go b/msg/reply.go
index e62ce8c..ea2e5d3 100644
--- a/msg/reply.go
+++ b/msg/reply.go
@@ -43,7 +43,7 @@ func (m *Message) Reply(ctx context.Context, replyBytes []byte, privKey ed25519.
 		return err
 	}
 
-	mimeType := MESSAGE_CONTENT_TYPE + "+" + REPLY_SERIALIZATION
+	mimeType := CONTENT_TYPE + "+" + REPLY_SERIALIZATION
 	contentType := mime.FormatMediaType(mimeType, REPLY_CONTENT_TYPE_PARAMS)
 
 	reply := &Message{