Add sendPayload API

plugins/webapi/message/sendPayload.go

+package message
+
+import (
+	"net/http"
+
+	"github.com/iotaledger/goshimmer/packages/binary/messagelayer/payload"
+	"github.com/iotaledger/goshimmer/plugins/issuer"
+	"github.com/labstack/echo"
+)
+
+// sendPayload creates a message of the given payload and
+// broadcasts it to the node's neighbors. It returns the message ID if successful.
+func sendPayload(c echo.Context) error {
+	var request MessageRequest
+	if err := c.Bind(&request); err != nil {
+		log.Info(err.Error())
+		return c.JSON(http.StatusBadRequest, MessageResponse{Error: err.Error()})
+	}
+
+	//TODO: to check max payload size allowed, if exceeding return an error
+
+	parsedPayload, _, err := payload.FromBytes(request.Payload)
+	if err != nil {
+		return c.JSON(http.StatusBadRequest, MessageResponse{Error: "not a valid payload"})
+	}
+
+	msg, err := issuer.IssuePayload(parsedPayload)
+	if err != nil {
+		return c.JSON(http.StatusBadRequest, MessageResponse{Error: err.Error()})
+	}
+
+	return c.JSON(http.StatusOK, MessageResponse{ID: msg.Id().String()})
+}
+
+// MessageResponse contains the ID of the message sent.
+type MessageResponse struct {
+	ID    string `json:"id,omitempty"`
+	Error string `json:"error,omitempty"`
+}
+
+// MessageRequest contains the message to send.
+type MessageRequest struct {
+	Payload []byte `json:"payload"`
+}