Make ZipHeaderInputStream read sub 5 byte entries correctly

Closes gh-13525

spring-boot-tools/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/JarWriter.java

@@ -357,15 +357,15 @@ public class JarWriter implements LoaderClassesWriter {
 		public int read(byte[] b, int off, int len) throws IOException {
 			int read = (this.headerStream != null ? this.headerStream.read(b, off, len)
 					: -1);
-			if (read > 0) {
-				this.position += read;
-			}
-			else {
-				read = 0;
+			if (read <= 0) {
+				return readRemainder(b, off, len);
 			}
-			if (read < len) {
-				read += super.read(b, off + read, len - read);
 			this.position += read;
+			if (read < len) {
+				int remainderRead = readRemainder(b, off + read, len - read);
+				if (remainderRead > 0) {
+					read += remainderRead;
+				}
 			}
 			if (this.position >= this.headerLength) {
 				this.headerStream = null;
@@ -377,6 +377,14 @@ public class JarWriter implements LoaderClassesWriter {
 			return Arrays.equals(this.header, ZIP_HEADER);
 		}
 
+		private int readRemainder(byte[] b, int off, int len) throws IOException {
+			int read = super.read(b, off, len);
+			if (read > 0) {
+				this.position += read;
+			}
+			return read;
+		}
+
 	}
 
 	/**

spring-boot-tools/spring-boot-loader-tools/src/test/java/org/springframework/boot/loader/tools/ZipHeaderPeekInputStreamTests.java

@@ -142,4 +142,56 @@ public class ZipHeaderPeekInputStreamTests {
 		}
 	}
 
+	@Test
+	public void readMoreThanEntireStreamWhenStreamLengthIsLessThanZipHeaderLength()
+			throws IOException {
+		ZipHeaderPeekInputStream in = null;
+		try {
+			in = new ZipHeaderPeekInputStream(
+					new ByteArrayInputStream(new byte[] { 10 }));
+			byte[] bytes = new byte[8];
+			assertThat(in.read(bytes)).isEqualTo(1);
+			assertThat(bytes).containsExactly(10, 0, 0, 0, 0, 0, 0, 0);
+		}
+		finally {
+			if (in != null) {
+				in.close();
+			}
+		}
+	}
+
+	@Test
+	public void readMoreThanEntireStreamWhenStreamLengthIsSameAsHeaderLength()
+			throws IOException {
+		ZipHeaderPeekInputStream in = null;
+		try {
+			in = new ZipHeaderPeekInputStream(
+					new ByteArrayInputStream(new byte[] { 1, 2, 3, 4 }));
+			byte[] bytes = new byte[8];
+			assertThat(in.read(bytes)).isEqualTo(4);
+			assertThat(bytes).containsExactly(1, 2, 3, 4, 0, 0, 0, 0);
+		}
+		finally {
+			if (in != null) {
+				in.close();
+			}
+		}
+	}
+
+	@Test
+	public void readMoreThanEntireStreamWhenStreamLengthIsZero() throws IOException {
+		ZipHeaderPeekInputStream in = null;
+		try {
+			in = new ZipHeaderPeekInputStream(new ByteArrayInputStream(new byte[0]));
+			byte[] bytes = new byte[8];
+			assertThat(in.read(bytes)).isEqualTo(-1);
+			assertThat(bytes).containsExactly(0, 0, 0, 0, 0, 0, 0, 0);
+		}
+		finally {
+			if (in != null) {
+				in.close();
+			}
+		}
+	}
+
 }