add customer followup

src/main/java/com/imyeyu/api/util/JavaCV.java

@@ -16,10 +16,18 @@ import java.io.InputStream;
 /// @since 2025-10-23 17:05
 public class JavaCV {
 
+	/// 单次跳转分片上限
+	///
+	/// 任何真实文件的当前位置加该值都不会溢出 long
+	private static final long SKIP_PIECE = 1L << 40;
+
 	/// 从视频流顺序解码并提取指定时间附近的一帧 PNG 图片
 	///
 	/// 不执行时间定位，避免为了取实时缩略图而把整个视频复制到临时文件
 	///
+	/// moov 原子位于文件尾部的视频（非 faststart）仍会触发 FFmpeg 回调 AVSEEK_SIZE 探测文件大小，
+	/// 依赖底层流的 skip/reset 语义正确，因此必须配合 `SkipSafeInputStream` 规避 GridFS 的溢出缺陷
+	///
 	/// @param stream        视频输入流
 	/// @param targetSeconds 目标时间，单位为秒
 	/// @return PNG 图片字节流
@@ -27,7 +35,7 @@ public class JavaCV {
 	public static ByteArrayOutputStream captureThumbnail(InputStream stream, double targetSeconds) throws Exception {
 		long targetMicros = toMicros(targetSeconds);
 		ByteArrayOutputStream firstFrame = new ByteArrayOutputStream();
-		try (FFmpegFrameGrabber grabber = new FFmpegFrameGrabber(stream)) {
+		try (FFmpegFrameGrabber grabber = new FFmpegFrameGrabber(new SkipSafeInputStream(stream))) {
 			grabber.start();
 			try (Java2DFrameConverter converter = new Java2DFrameConverter()) {
 				Frame frame;
@@ -61,4 +69,73 @@ public class JavaCV {
 		}
 		return new ByteArrayOutputStream();
 	}
+
+	/// 分片跳转流包装
+	///
+	/// GridFSDownloadStreamImpl 的 skip 以 `currentPosition + n` 计算目标位置且不防护 long 溢出，
+	/// 当 javacv 的 SeekCallback 以 `skip(Long.MAX_VALUE)` 探测流结尾时，位于流末尾的第二次调用
+	/// 会因溢出落入正常分支，返回未实际跳过的 `Long.MAX_VALUE` 并污染内部位置，
+	/// 导致 `avformat_open_input` 在 `while (true)` 内 100% CPU 死循环
+	///
+	/// 此包装将大额跳转拆分为不超过 {@link #SKIP_PIECE} 的分片，保证每次调用的目标位置不溢出
+	private static class SkipSafeInputStream extends InputStream {
+
+		private final InputStream stream;
+
+		private SkipSafeInputStream(InputStream stream) {
+			this.stream = stream;
+		}
+
+		@Override
+		public int read() throws IOException {
+			return stream.read();
+		}
+
+		@Override
+		public int read(byte[] b, int off, int len) throws IOException {
+			return stream.read(b, off, len);
+		}
+
+		@Override
+		public long skip(long n) throws IOException {
+			if (n <= 0) {
+				return 0;
+			}
+			long total = 0;
+			while (0 < n) {
+				long skipped = stream.skip(Math.min(n, SKIP_PIECE));
+				if (skipped <= 0) {
+					break;
+				}
+				total += skipped;
+				n -= skipped;
+			}
+			return total;
+		}
+
+		@Override
+		public int available() throws IOException {
+			return stream.available();
+		}
+
+		@Override
+		public void close() throws IOException {
+			stream.close();
+		}
+
+		@Override
+		public synchronized void mark(int readlimit) {
+			stream.mark(readlimit);
+		}
+
+		@Override
+		public synchronized void reset() throws IOException {
+			stream.reset();
+		}
+
+		@Override
+		public boolean markSupported() {
+			return stream.markSupported();
+		}
+	}
 }