CDS XMLAdapter Plugin

This plugin for the SAP Cloud Application Programming Model (CAP) extends the default REST adapter to support XML payloads. It parses incoming XML data, converts it to JSON, and ensures compatibility with CAP's processing logic.

Features

• Parses incoming XML payloads into JSON.
• Converts Content-Type from application/xml to application/json for CAP compatibility.
• Removes XML namespaces and attributes to create a clean JSON structure.
• Converts boolean values correctly ("true" → true, "false" → false).
• Returns appropriate error messages for invalid XML or unsupported content types.

Installation

To install the plugin, add it to your CAP project.

npm install cds-xmladapter-plugin

Usage

1. Add the XMLAdapter to Your CAP Project

   Extend your CAP server to use the XMLAdapter.

   const cds = require("@sap/cds");
   const XMLAdapter = require("cds-xmladapter-plugin");
   
   cds.on("bootstrap", (app) => {
       app.use(new XMLAdapter().router);
   });
   
   module.exports = cds.server;

2. Send XML Requests

   Use tools like Postman or custom clients to send requests with XML payloads. Ensure the Content-Type header is set to application/xml.

   Example XML payload:

   <ExchangeRate>
       <ID>123</ID>
       <Rate>10.5</Rate>
       <FromCurrency>EUR</FromCurrency>
       <ToCurrency>USD</ToCurrency>
       <IsValid>true</IsValid>
   </ExchangeRate>

3. Handle XML Data in CAP

   The plugin automatically converts the XML to JSON, which can be processed by your CAP service logic.

How It Works

The plugin integrates with CAP's middleware pipeline and processes incoming requests as follows:

1. Checks if the Content-Type is application/xml.
2. Parses the XML payload into JSON using xml2js.
3. Removes XML namespaces and attributes.
4. Converts boolean values ("true" → true, "false" → false).
5. Updates the Content-Type to application/json for compatibility with CAP services.
6. Passes the parsed data to the next middleware in the chain.

If the Content-Type is not application/xml, it returns a 415 Unsupported Media Type error. For invalid XML payloads, it returns a 400 Bad Request error.

const cds = require("@sap/cds");
const { parseStringPromise } = require("xml2js");
const HttpAdapter = require("@sap/cds/lib/srv/protocols/http");

class XMLAdapter extends HttpAdapter {
    get router() {
        const router = super.router;

        router.use((req, res, next) => {
            if (req.method in { POST: 1, PUT: 1, PATCH: 1 } && req.headers["content-type"]) {
                if (!req.headers["content-type"].includes("application/xml")) {
                    res.status(415).json({ error: "Invalid content type. Expected 'application/xml'." });
                    return;
                }
            }
            next();
        });

        router.use((req, res, next) => {
            if (req.headers["content-type"] && req.headers["content-type"].includes("application/xml")) {
                let xmlBody = "";
                req.on("data", (chunk) => {
                    xmlBody += chunk.toString();
                });

                req.on("end", async () => {
                    try {
                        const jsonBody = await parseStringPromise(xmlBody, {
                            explicitArray: false,
                            ignoreAttrs: true,
                            tagNameProcessors: [(name) => name.replace(/^.*:/, "")],
                            valueProcessors: [
                                (value) => {
                                    if (value === "true") return true;
                                    if (value === "false") return false;
                                    return value;
                                },
                            ]
                        });

                        req.body = jsonBody;
                        req.headers["content-type"] = "application/json";
                        next();
                    } catch (err) {
                        res.status(400).json({ error: "Invalid XML format." });
                    }
                });
            } else {
                next();
            }
        });

        return router;
    }
}

module.exports = XMLAdapter;

License

This project is licensed under the MIT License - see the LICENSE file for details.

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

Acknowledgments

Thanks to the SAP CAP community for their support and contributions.