How are WAV files validated?

[jordanpadams]

Per #1425:

I have read through the background information associated with ticket #662 and the subsequent tickets and it is not entirely clear what makes a valid WAV file. The WAV files in question can be played without issue in applications like VLC and Apple Music.

[jordanpadams]

The fix for validating WAV files was implemented as part of a fix here: #1390

The software now validates WAV files by directly inspecting their binary file headers. Specifically, the validation logic reads the file to confirm the presence and placement of required WAV signature strings and structural elements:

• It checks for the 'RIFF' chunk ID at the very start of the file, which is required for all WAV files.
• It reads the size field in the header and compares it to the file’s actual size as a consistency check; a mismatch issues a warning.
• It checks for the 'WAVE' format marker immediately after the size header.
• It ensures that the 'fmt ' sub-chunk identifier follows, which is necessary for valid WAV files.

If any of these structural validations fail (such as missing 'RIFF', 'WAVE', or 'fmt ' headers, or reading errors), specific error messages are triggered indicating the file is not a valid WAV.
This implementation is handled in the checkWavHeader method within the AudioVideo class and is invoked during validation when the document type is identified as 'WAV'. The associated errors and warnings are recorded using standard problem reporting mechanisms within the application.

You can review the main validation logic for WAV files in the source here:

validate/src/main/java/gov/nasa/pds/tools/validate/content/AudioVideo.java

Lines 44 to 121 in c74b9bb

	}
	}
	content.close();
	if (a != audio) {
	this.listener.addProblem(new ValidationProblem(
	new ProblemDefinition(ExceptionType.ERROR, ProblemType.NOT_MP4_FILE,
	"Does not look like an MP4/M4A because expected audio but found none: " + urlRef.toString()),
	target));
	}
	if (v != video) {
	this.listener.addProblem(new ValidationProblem(
	new ProblemDefinition(ExceptionType.ERROR, ProblemType.NOT_MP4_FILE,
	"Does not look like an MP4/M4A because expected video but found none: " + urlRef.toString()),
	target));
	}
	} catch (Exception e) {
	ProblemDefinition def =
	new ProblemDefinition(ExceptionType.ERROR, ProblemType.INTERNAL_ERROR,
	"Error occurred while processing MP4/M4A file content for "
	+ FilenameUtils.getName(urlRef.toString()) + ": " + e.getMessage());
	this.listener.addProblem(new ValidationProblem(def, this.target));
	}
	}
	public boolean checkWavHeader() {
	File file = FileUtils.toFile(this.urlRef);
	try (RandomAccessFile raf = new RandomAccessFile(file, "r")) {
	// Check RIFF chunk ID ("RIFF")
	byte[] riff = new byte[4];
	raf.readFully(riff);
	if (!new String(riff).equals("RIFF")) {
	this.listener.addProblem(new ValidationProblem(
	new ProblemDefinition(ExceptionType.ERROR, ProblemType.NOT_WAV_FILE,
	"Does not look like a WAV because did not find expected 'RIFF' in header: " + urlRef.toString()),
	target));
	return false;
	}
	// Skip file size
	byte[] sz = new byte[4];
	raf.readFully(sz);
	/* RIFF requires the chunk size to be 8 bytes less than the file size reported by the OS */
	int size = ByteBuffer.wrap(sz).order(ByteOrder.LITTLE_ENDIAN).getInt() + 8;
	if (size != file.length()) {
	this.listener.addProblem(new ValidationProblem(
	new ProblemDefinition(ExceptionType.WARNING, ProblemType.NON_WAV_FILE,
	String.format("Does not look like a valid WAV because the file length %d does not match the size in the header %d: %s", file.length(), size, urlRef.toString())),
	target));
	}
	// Check WAVE format ("WAVE")
	byte[] wave = new byte[4];
	raf.readFully(wave);
	if (!new String(wave).equals("WAVE")) {
	this.listener.addProblem(new ValidationProblem(
	new ProblemDefinition(ExceptionType.ERROR, ProblemType.NOT_WAV_FILE,
	"Does not look like a WAV because did not find expected 'WAVE' in header: " + urlRef.toString()),
	target));
	return false;
	}
	// Check 'fmt ' sub-chunk ("fmt ")
	byte[] fmt = new byte[4];
	raf.readFully(fmt);
	if (!new String(fmt).equals("fmt ")) {
	this.listener.addProblem(new ValidationProblem(
	new ProblemDefinition(ExceptionType.ERROR, ProblemType.NOT_WAV_FILE,
	"Does not look like a WAV because did not find expected 'fmt ' in header: " + urlRef.toString()),
	target));
	return false;
	}
	} catch (IOException e) {
	this.listener.addProblem(new ValidationProblem(
	new ProblemDefinition(ExceptionType.ERROR, ProblemType.NOT_WAV_FILE,
	"Does not look like a WAV because cannot read from it: " + urlRef.toString()),
	target));
	return false;
	}
	return true;
	}
	}

This ensures proper structural validation of WAV files, rather than misidentifying them as other audio formats and improves robustness per the referenced PR.