static Multipart from(String boundary, Publisher<? extends HttpData> contents) {
        return from(boundary, contents, ByteBufAllocator.DEFAULT);
    }
Returns a decoded {@link Multipart} from the specified {@code boundary} and
{@link Publisher} of {@link HttpData}.
For instance, {@link Multipart} could be decoded from the specified {@link HttpResponse}
in the following way:
<pre>{@code
HttpResponse response = ...;
SplitHttpResponse splitResponse = response.split();
ResponseHeaders responseHeaders = splitResponse.headers().join();
ByteStreamMessage responseContents = splitResponse.body();
MediaType contentType = responseHeaders.contentType();
if (contentType != null && contentType.isMultipart()) {
    String boundary = Multiparts.getBoundary(contentType);
    Multipart multipart = Multipart.from(boundary, responseContents);
    ...
} else {
    handleNonMultipartResponse(responseHeaders, responseContents);
}
}</pre>
core/src/main/java/com/linecorp/armeria/common/multipart/Multipart.java