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• Have you included sample input, output, error, and expected output?
• Have you checked if you are using correct configuration?
• Did you try online tool?

Description

XMLBuilder outputs empty line at the start of output, which breaks some XML processors.

According to: https://www.stat.auckland.ac.nz/~paul/ItDT/HTML/node46.html#:~:text=The%20first%20line%20of%20an,encoding%20used%20in%20the%20file.

The first line of an XML document should be a declaration that this is an XML document, including the version of XML being used.

Specifically first line, not second line. Even if first line is empty string.

"fast-xml-parser": "^4.0.6"

Input

<?xml version="1.0" encoding="UTF-8"?>
<testsuites>
</testsuites>

Code

import { XMLParser, XMLBuilder, XMLValidator } from "fast-xml-parser";
import fs from "fs";

const parser = new XMLParser({
  ignoreAttributes: false,
  preserveOrder: true,
  cdataPropName: "__cdata",
});
console.info("Parsing junit.xml ...");
const origXml = fs.readFileSync("junit.xml");
const jObj = parser.parse(origXml);
console.debug("Original XML:", origXml.toString("utf8"));
console.info("Parsed.");

// ...

const builder = new XMLBuilder({
  ignoreAttributes: false,
  preserveOrder: true,
  cdataPropName: "__cdata",
  format: true,
});
// console.log(builder.build(jObj));
console.debug(builder.build(jObj));
console.info("Saving to junit.xml ...");
fs.writeFileSync("junit.xml", builder.build(jObj), { encoding: "utf8" });
console.info("Saved.");

Output (buggy)

<?xml   version="1.0" encoding="UTF-8"?>
<testsuites>
</testsuites>

• note the first empty line
• not an issue, but not pretty, is that <?xml version="1.0" has too much space

expected output

<?xml version="1.0" encoding="UTF-8"?>
<testsuites>
</testsuites>

workaround

use String.trimStart()

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• Yes
• No

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