Stream the waveform compute so large uploads no longer buffer the whole file (Wave 2 OOM)

DeepDrftContent/Processors/AudioProcessor.cs

@@ -288,6 +288,105 @@ public class AudioProcessor
         return new PcmData(pcm, metadata.Channels, metadata.SampleRate, metadata.BitsPerSample);
     }
 
+    /// <summary>
+    /// Reads only the WAV header region from <paramref name="stream"/> (a bounded window, never the
+    /// audio body) and returns where the PCM data region begins, how long it is, and the format
+    /// parameters needed to decode it — the streaming counterpart of <see cref="TryExtractPcm"/>. The
+    /// data length is clamped against <paramref name="totalFileLength"/> (the true backing-file size),
+    /// so the caller streams exactly the present PCM. Returns null for the same inputs
+    /// <see cref="TryExtractPcm"/> rejects — non-WAV bytes (mp3/flac), float, and padded-container
+    /// EXTENSIBLE — so the caller treats null as "no profile computable" and continues gracefully.
+    ///
+    /// <paramref name="stream"/> must be positioned at the start; on return its position is past the
+    /// header window (the caller seeks to <c>DataStart</c> before streaming the body). No whole-file
+    /// buffer is allocated — peak memory is the bounded header window.
+    /// </summary>
+    public async Task<WavPcmStreamInfo?> TryReadPcmStreamInfoAsync(
+        Stream stream, long totalFileLength, CancellationToken cancellationToken = default)
+    {
+        var window = await ReadWavHeaderWindowAsync(stream, cancellationToken);
+        if (window is null)
+        {
+            return null;
+        }
+
+        var validation = ValidateWavStructure(window);
+        if (!validation.IsValid || validation.IsFloat)
+        {
+            return null;
+        }
+
+        WavMetadata metadata;
+        try
+        {
+            metadata = ParseWavMetadata(window, validation);
+            ValidateAudioParameters(metadata);
+            if (metadata.IsPaddedContainer)
+            {
+                return null;
+            }
+        }
+        catch
+        {
+            return null;
+        }
+
+        long dataStart = validation.DataChunkPos + 8;
+        if (dataStart > totalFileLength)
+        {
+            return null;
+        }
+
+        var available = totalFileLength - dataStart;
+        var dataLength = Math.Min((long)metadata.DataSize, available);
+        if (dataLength <= 0)
+        {
+            return null;
+        }
+
+        return new WavPcmStreamInfo(
+            dataStart, dataLength, metadata.Channels, metadata.SampleRate, metadata.BitsPerSample);
+    }
+
+    /// <summary>
+    /// Reads enough of <paramref name="stream"/> to contain the fmt chunk and the data chunk's 8-byte
+    /// header, growing in 64 KB steps until the data chunk is locatable or EOF / the
+    /// <see cref="HeaderWindowCap"/> is reached. Bails after the first read when the bytes are not a
+    /// RIFF/WAVE container, so a non-WAV stream (mp3/flac) costs one read, not the full cap. Returns
+    /// null only when nothing could be read.
+    /// </summary>
+    private static async Task<byte[]?> ReadWavHeaderWindowAsync(Stream stream, CancellationToken ct)
+    {
+        using var ms = new MemoryStream();
+        var buffer = new byte[HeaderWindowStep];
+        while (ms.Length < HeaderWindowCap)
+        {
+            var read = await stream.ReadAsync(buffer, ct);
+            if (read == 0)
+                break;
+            ms.Write(buffer, 0, read);
+
+            var soFar = ms.ToArray();
+
+            // Early-out for non-WAV input: once at least the 12-byte RIFF/WAVE preamble is in hand,
+            // a missing signature means this will never be a WAV — stop rather than read to the cap.
+            if (soFar.Length >= 12 && !HasRiffWaveSignature(soFar))
+                return soFar;
+
+            // FindChunk returns -1 until the data chunk header is fully in the window; on a normal
+            // file it sits within the first 64 KB so this loop runs exactly once.
+            if (FindChunk(soFar, "data") >= 0)
+                return soFar;
+        }
+
+        return ms.Length > 0 ? ms.ToArray() : null;
+    }
+
+    private static bool HasRiffWaveSignature(byte[] buffer) =>
+        buffer.Length >= 12
+        && System.Text.Encoding.ASCII.GetString(buffer, 0, 4) == "RIFF"
+        && System.Text.Encoding.ASCII.GetString(buffer, 8, 4) == "WAVE";
+
     /// <summary>
     /// Extracts metadata from WAV file buffer with comprehensive validation
     /// </summary>
@@ -698,4 +797,21 @@ public readonly record struct PcmData(
     ReadOnlyMemory<byte> Pcm,
     int Channels,
     int SampleRate,
+    int BitsPerSample);
+
+/// <summary>
+/// Where a WAV's PCM data region lives and how to decode it, without the bytes themselves — the
+/// streaming counterpart of <see cref="PcmData"/>. The caller seeks to <see cref="DataStart"/> and
+/// streams exactly <see cref="DataLength"/> bytes through a loudness accumulator.
+/// </summary>
+/// <param name="DataStart">Absolute byte offset of the first PCM sample (past the data chunk header).</param>
+/// <param name="DataLength">PCM region length in bytes, clamped to what the backing file actually holds.</param>
+/// <param name="Channels">Number of interleaved channels.</param>
+/// <param name="SampleRate">Samples per second.</param>
+/// <param name="BitsPerSample">Bit depth per sample (8, 16, 24, or 32).</param>
+public readonly record struct WavPcmStreamInfo(
+    long DataStart,
+    long DataLength,
+    int Channels,
+    int SampleRate,
     int BitsPerSample);