Add a content type or override an existing one #

Content type is MIME type, that specifies how the data is encoded in the message payload. Content types supported by go-asyncapi out-of-the-box are listed in features page.

Unknown content types, that are not built-in not added as described below, are treated as application/json.

Content type-related code is generated inside Marshal<Protocol> and Unmarshal<Protocol> methods of the message types. So it should marshal and unmarshal the message payload to/from method’s parameter.

The following example shows how to add the code for content type text/plain.

For that define two following templates and put them to any file, say my_templates/content_types.tmpl:

{{ define "code/proto/mime/messageDecoder/text/plain" }}
    var b {{ goPkgExt "strings" }}Builder
    if _, err := {{ goPkgExt "io" }}Copy(&b, r); err != nil {
        return {{ goPkgExt "fmt" }}Errorf("read message: %w", err)
    }
    m.payload = {{goPkg .PayloadType}}{{.PayloadType | goID}}(b.String())
{{- end }}

{{ define "code/proto/mime/messageEncoder/text/plain" }}
    r := {{ goPkgExt "strings" }}NewReader(string(m.Payload))
    if _, err := {{ goPkgExt "io" }}Copy(w, r); err != nil {
        return {{ goPkgExt "fmt" }}Errorf("write message: %w", err)
    }
{{- end }}

Then specify the template directory when generating the code:

go-asyncapi code -T my_templates my_asyncapi.yaml

Couple of notes:

• Template functions goPkgExt and goPkg are used to correctly import a package (or package where a type is defined) and get the imported prefix. For more details see templating guide.
• Replacing the existing content type is done the same way.