MuntashirAkon/AppManager · error · IOException

Failed to read Paxheader. Encountered a non-number while…

Error message

Failed to read Paxheader. Encountered a non-number while reading length

What it means

Thrown by TarUtils.parsePaxHeaders while parsing the decimal length prefix of a PAX record when a byte that is not an ASCII digit is found (COMPRESS-530 fix). The PAX format requires records to start with a decimal byte count; anything else is malformed input, previously causing silent bad parses.

Solutions

1. Verify the archive is valid and not corrupted (checksum, tar -tvf test)
2. Ensure the stream is positioned at the actual PAX header record, not elsewhere
3. Re-transfer in binary mode if the file passed through text-mode transfer (line-ending mangling)
4. Catch IOException and reject the archive

// sanity-check the file starts like a tar before parsing
byte[] h = new byte[512];
if (!Magic.isTarHeader(h)) throw new IOException("Not a valid tar archive");

try {
    // read tar
} catch (IOException e) {
    if (e.getMessage().contains("non-number while reading length")) {
        throw new CorruptArchiveException("PAX record length prefix is not numeric", e);
    }
    throw e;
}

When it happens

Trigger: Reading a stream positioned at data that is not a valid PAX record length: corrupt archive, wrong stream offset, or a non-PAX header misinterpreted as PAX data.

Common situations: Mixing archive formats (reading a ustar/oldgnu header as pax), corruption from FTP ASCII-mode transfers, or fuzzed files.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• Failed to read Paxheader.GNU.sparse.offset is expected…
• Failed to read Paxheader.Value should end with a newline
• Error detected parsing the pax header
• Failed to read Paxheader. Expected
• Paxheader value size

AI-assisted analysis of MuntashirAkon/AppManager@0152f468fc (2026-09-12). Data as JSON: /api/errors/a1bd9b199fc8f4d7. Report an issue: GitHub.

Appendix: source

Thrown at app/src/main/java/org/apache/commons/compress/archivers/tar/TarUtils.java:760

                                if (keyword.equals("GNU.sparse.numbytes")) {
                                    if (offset == null) {
                                        throw new IOException("Failed to read Paxheader." +
                                                "GNU.sparse.offset is expected before GNU.sparse.numbytes shows up.");
                                    }
                                    sparseHeaders.add(new TarArchiveStructSparse(offset, Long.parseLong(value)));
                                    offset = null;
                                }
                            }
                            break;
                        }
                        coll.write((byte) ch);
                    }
                    break; // Processed single header
                }

                // COMPRESS-530 : throw if we encounter a non-number while reading length
                if (ch < '0' || ch > '9') {
                    throw new IOException("Failed to read Paxheader. Encountered a non-number while reading length");
                }

                len *= 10;
                len += ch - '0';
            }
            if (ch == -1){ // EOF
                break;
            }
        }
        if (offset != null) {
            // offset but no numBytes
            sparseHeaders.add(new TarArchiveStructSparse(offset, 0));
        }
        return headers;
    }

    /**
     * For PAX Format 0.1, the sparse headers are stored in a single variable : GNU.sparse.map

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