What causes "No start tag found" in Tencent/matrix?

Verify the power-profile XML resource exists and has a valid root element (e.g. or ).

Tencent/matrix · error · XmlPullParserException

No start tag found

Error message

No start tag found

What it means

PowerProfile's XML parsing helper advances the XmlPullParser to the first START_TAG and throws XmlPullParserException("No start tag found") if it reaches END_DOCUMENT first — i.e. the power-profile XML resource is empty or contains only text/comments. This mirrors AOSP's PowerProfile parser and guards against malformed power profile files.

Solutions

Verify the power-profile XML resource exists and has a valid root element (e.g. <powerprofile> or <device>).
Re-check the resource id/parser passed to the PowerProfile constructor; ensure it resolves to the intended XML.
Wrap PowerProfile construction in try-catch for XmlPullParserException and fall back to a bundled default profile.

Example fix

// before
XmlPullParser p = res.getXml(R.xml.maybe_empty_profile);
PowerProfile profile = new PowerProfile(p, "device"); // throws if empty

// after
XmlPullParser p = res.getXml(R.xml.power_profile);
try {
    PowerProfile profile = new PowerProfile(p, "device");
} catch (XmlPullParserException e) {
    PowerProfile profile = new PowerProfile(res.getXml(R.xml.default_profile), "device");
}

Defensive patterns

Strategy: try-catch

Validate before calling

// Verify the resource parses before constructing PowerProfile
XmlPullParser p = res.getXml(R.xml.power_profile);
int t;
while ((t = p.next()) != XmlPullParser.START_TAG && t != XmlPullParser.END_DOCUMENT) {}
if (t == XmlPullParser.END_DOCUMENT) {
    // empty resource: use default profile instead
}

Try / catch

try {
    PowerProfile profile = new PowerProfile(parser, firstElementName);
} catch (XmlPullParserException | IOException e) {
    PowerProfile profile = loadDefaultProfile();
}

Prevention

Validate custom power-profile XML files with an XML linter before shipping.
Ensure the resource id passed to the parser points at a well-formed XML file.
Test profile loading on the target devices/ROMs where empty streams may occur.

When it happens

Trigger: Constructing a PowerProfile over a power-profile XML (custom com.android.internal.R.xml.power_profile override or a test fixture) whose stream is empty or has no root element, so the parser hits END_DOCUMENT before any START_TAG.

Common situations: Providing a truncated or blank custom power_profile.xml in tests; resource resolution returning an empty stream on certain OEM ROMs; misconfigured XmlResourceParser pointing at a non-XML resource.

Understand the failure class

Background: "failed to read file", EACCES, ENOENT and "could not read <path>" errors: when a program can't read a file from disk — this error's family across 49 libraries.

Related errors

AI-assisted analysis of Tencent/matrix@3b8293bd65 (2026-09-08). Data as JSON: /api/errors/d37a598938538efe. Report an issue: GitHub.

Appendix: source

Thrown at matrix/matrix-android/matrix-battery-canary/src/main/java/com/tencent/matrix/batterycanary/utils/PowerProfile.java:661

        } else {
            return 0;
        }
    }

    public double getBatteryCapacity() {
        return getAveragePower(POWER_BATTERY_CAPACITY);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    static class XmlUtils {
        public static void beginDocument(XmlPullParser parser, String firstElementName) throws XmlPullParserException, IOException {
            int type;
            while ((type = parser.next()) != parser.START_TAG
                    && type != parser.END_DOCUMENT) {
            }

            if (type != parser.START_TAG) {
                throw new XmlPullParserException("No start tag found");
            }

            if (!parser.getName().equals(firstElementName)) {
                throw new XmlPullParserException("Unexpected start tag: found " + parser.getName() +
                        ", expected " + firstElementName);
            }
        }

        public static void nextElement(XmlPullParser parser) throws XmlPullParserException, IOException {
            int type;
            while ((type = parser.next()) != parser.START_TAG
                    && type != parser.END_DOCUMENT) {
            }
        }
    }
}

View on GitHub (pinned to 3b8293bd65)