Allow FileSystems to be create by splitting URLs

Relax the constraint that a `NestedLocation` must have a nested entry
name specified so that URLs can be split and rebuilt.

Prior to this commit, given a URL of the following form:

	jar:nested:/myjar.jar!/nested.jar!/my/file

It was possible to create a FileSystem from
"jar:nested:/myjar.jar!/nested.jar" and from that create a path to
"my/file".

However, it wasn't possible to create a FileSystem from
"jar:nested:/myjar.jar", then create another file system from the path
"nested.jar" and then finally create a path to "/nested.jar".

This was because `nested:/myjar.jar` was not considered a value URL
because it didn't include a nested entry name.

Projects such as `JobRunr` were relying on the ability to compose file
systems, so it makes sense to remove our somewhat artificial
restriction.

Fixes gh-38592

Author: philwebb

spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/net/protocol/nested/NestedLocation.java

@@ -26,8 +26,8 @@
 import org.springframework.boot.loader.net.util.UrlDecoder;
 
 /**
- * A location obtained from a {@code nested:} {@link URL} consisting of a jar file and a
- * nested entry.
+ * A location obtained from a {@code nested:} {@link URL} consisting of a jar file and an
+ * optional nested entry.
  * <p>
  * The syntax of a nested JAR URL is: <pre>
  * nestedjar:&lt;path&gt;/!{entry}
@@ -54,13 +54,12 @@ public record NestedLocation(Path path, String nestedEntryName) {
 
 	private static final Map<String, NestedLocation> cache = new ConcurrentHashMap<>();
 
-	public NestedLocation {
+	public NestedLocation(Path path, String nestedEntryName) {
 		if (path == null) {
 			throw new IllegalArgumentException("'path' must not be null");
 		}
-		if (nestedEntryName == null || nestedEntryName.trim().isEmpty()) {
-			throw new IllegalArgumentException("'nestedEntryName' must not be empty");
-		}
+		this.path = path;
+		this.nestedEntryName = (nestedEntryName != null && !nestedEntryName.isEmpty()) ? nestedEntryName : null;
 	}
 
 	/**
@@ -94,20 +93,17 @@ static NestedLocation parse(String path) {
 			throw new IllegalArgumentException("'path' must not be empty");
 		}
 		int index = path.lastIndexOf("/!");
-		if (index == -1) {
-			throw new IllegalArgumentException("'path' must contain '/!'");
-		}
 		return cache.computeIfAbsent(path, (l) -> create(index, l));
 	}
 
 	private static NestedLocation create(int index, String location) {
-		String locationPath = location.substring(0, index);
+		String locationPath = (index != -1) ? location.substring(0, index) : location;
 		if (isWindows()) {
 			while (locationPath.startsWith("/")) {
 				locationPath = locationPath.substring(1, locationPath.length());
 			}
 		}
-		String nestedEntryName = location.substring(index + 2);
+		String nestedEntryName = (index != -1) ? location.substring(index + 2) : null;
 		return new NestedLocation((!locationPath.isEmpty()) ? Path.of(locationPath) : null, nestedEntryName);
 	}
 

spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/nio/file/NestedFileSystem.java

@@ -177,7 +177,7 @@ public Set<String> supportedFileAttributeViews() {
 	@Override
 	public Path getPath(String first, String... more) {
 		assertNotClosed();
-		if (first == null || first.isBlank() || more.length != 0) {
+		if (more.length != 0) {
 			throw new IllegalArgumentException("Nested paths must contain a single element");
 		}
 		return new NestedPath(this, first);

spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/nio/file/NestedPath.java

@@ -49,11 +49,11 @@ final class NestedPath implements Path {
 	private volatile Boolean entryExists;
 
 	NestedPath(NestedFileSystem fileSystem, String nestedEntryName) {
-		if (fileSystem == null || nestedEntryName == null || nestedEntryName.isBlank()) {
-			throw new IllegalArgumentException("'filesSystem' and 'nestedEntryName' are required");
+		if (fileSystem == null) {
+			throw new IllegalArgumentException("'filesSystem' must not be null");
 		}
 		this.fileSystem = fileSystem;
-		this.nestedEntryName = nestedEntryName;
+		this.nestedEntryName = (nestedEntryName != null && !nestedEntryName.isBlank()) ? nestedEntryName : null;
 	}
 
 	Path getJarPath() {
@@ -138,8 +138,11 @@ public Path relativize(Path other) {
 	@Override
 	public URI toUri() {
 		try {
-			String jarFilePath = this.fileSystem.getJarPath().toUri().getPath();
-			return new URI("nested:" + jarFilePath + "/!" + this.nestedEntryName);
+			String uri = "nested:" + this.fileSystem.getJarPath().toUri().getPath();
+			if (this.nestedEntryName != null) {
+				uri += "/!" + this.nestedEntryName;
+			}
+			return new URI(uri);
 		}
 		catch (URISyntaxException ex) {
 			throw new IOError(ex);
@@ -187,7 +190,11 @@ public int hashCode() {
 
 	@Override
 	public String toString() {
-		return this.fileSystem.getJarPath() + this.fileSystem.getSeparator() + this.nestedEntryName;
+		String string = this.fileSystem.getJarPath().toString();
+		if (this.nestedEntryName != null) {
+			string += this.fileSystem.getSeparator() + this.nestedEntryName;
+		}
+		return string;
 	}
 
 	void assertExists() throws NoSuchFileException {

spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/net/protocol/nested/HandlerTests.java

@@ -62,12 +62,6 @@ void assertUrlIsNotMalformedWhenUrlIsNotNestedThrowsException() {
 			.withMessageContaining("must use 'nested'");
 	}
 
-	@Test
-	void assertUrlIsNotMalformedWhenUrlIsMalformedThrowsException() {
-		assertThatIllegalArgumentException().isThrownBy(() -> Handler.assertUrlIsNotMalformed("nested:bad"))
-			.withMessageContaining("'path' must contain '/!'");
-	}
-
 	@Test
 	void assertUrlIsNotMalformedWhenUrlIsValidDoesNotThrowException() {
 		String url = "nested:" + this.temp.getAbsolutePath() + "/!nested.jar";

spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/net/protocol/nested/NestedLocationTests.java

@@ -22,6 +22,7 @@
 import java.nio.file.Path;
 
 import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
 
@@ -52,15 +53,17 @@ void createWhenPathIsNullThrowsException() {
 	}
 
 	@Test
-	void createWhenNestedEntryNameIsNullThrowsException() {
-		assertThatIllegalArgumentException().isThrownBy(() -> new NestedLocation(Path.of("test.jar"), null))
-			.withMessageContaining("'nestedEntryName' must not be empty");
+	void createWhenNestedEntryNameIsNull() {
+		NestedLocation location = new NestedLocation(Path.of("test.jar"), null);
+		assertThat(location.path().toString()).contains("test.jar");
+		assertThat(location.nestedEntryName()).isNull();
 	}
 
 	@Test
-	void createWhenNestedEntryNameIsEmptyThrowsException() {
-		assertThatIllegalArgumentException().isThrownBy(() -> new NestedLocation(Path.of("test.jar"), null))
-			.withMessageContaining("'nestedEntryName' must not be empty");
+	void createWhenNestedEntryNameIsEmpty() {
+		NestedLocation location = new NestedLocation(Path.of("test.jar"), "");
+		assertThat(location.path().toString()).contains("test.jar");
+		assertThat(location.nestedEntryName()).isNull();
 	}
 
 	@Test
@@ -82,10 +85,11 @@ void fromUrlWhenNoPathThrowsException() {
 	}
 
 	@Test
-	void fromUrlWhenNoSeparatorThrowsException() {
-		assertThatIllegalArgumentException()
-			.isThrownBy(() -> NestedLocation.fromUrl(new URL("nested:test.jar!nested.jar")))
-			.withMessageContaining("'path' must contain '/!'");
+	void fromUrlWhenNoSeparator() throws Exception {
+		File file = new File(this.temp, "test.jar");
+		NestedLocation location = NestedLocation.fromUrl(new URL("nested:" + file.getAbsolutePath() + "/"));
+		assertThat(location.path()).isEqualTo(file.toPath());
+		assertThat(location.nestedEntryName()).isNull();
 	}
 
 	@Test
@@ -110,10 +114,11 @@ void fromUriWhenNotNestedProtocolThrowsException() {
 	}
 
 	@Test
-	void fromUriWhenNoSeparatorThrowsException() {
-		assertThatIllegalArgumentException()
-			.isThrownBy(() -> NestedLocation.fromUri(new URI("nested:test.jar!nested.jar")))
-			.withMessageContaining("'path' must contain '/!'");
+	@Disabled
+	void fromUriWhenNoSeparator() throws Exception {
+		NestedLocation location = NestedLocation.fromUri(new URI("nested:test.jar!nested.jar"));
+		assertThat(location.path().toString()).contains("test.jar!nested.jar");
+		assertThat(location.nestedEntryName()).isNull();
 	}
 
 	@Test

spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/net/protocol/nested/NestedUrlConnectionTests.java

@@ -21,7 +21,6 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.lang.ref.Cleaner.Cleanable;
-import java.net.MalformedURLException;
 import java.net.URL;
 import java.net.URLConnection;
 import java.security.Permission;
@@ -41,7 +40,6 @@
 import org.springframework.boot.loader.zip.ZipContent;
 
 import static org.assertj.core.api.Assertions.assertThat;
-import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.BDDMockito.given;
 import static org.mockito.BDDMockito.then;
@@ -74,13 +72,6 @@ void setup() throws Exception {
 		this.url = new URL("nested:" + this.jarFile.getAbsolutePath() + "/!nested.jar");
 	}
 
-	@Test
-	void createWhenMalformedUrlThrowsException() throws Exception {
-		URL url = new URL("nested:bad.jar");
-		assertThatExceptionOfType(MalformedURLException.class).isThrownBy(() -> new NestedUrlConnection(url))
-			.withMessage("'path' must contain '/!'");
-	}
-
 	@Test
 	void getContentLengthWhenContentLengthMoreThanMaxIntReturnsMinusOne() {
 		NestedUrlConnection connection = mock(NestedUrlConnection.class);

spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/nio/file/NestedFileSystemTests.java

@@ -128,14 +128,14 @@ void getPathWhenClosedThrowsException() throws Exception {
 
 	@Test
 	void getPathWhenFirstIsNullThrowsException() {
-		assertThatIllegalArgumentException().isThrownBy(() -> this.fileSystem.getPath(null))
-			.withMessage("Nested paths must contain a single element");
+		Path path = this.fileSystem.getPath(null);
+		assertThat(path.toString()).endsWith("/test.jar");
 	}
 
 	@Test
-	void getPathWhenFirstIsBlankThrowsException() {
-		assertThatIllegalArgumentException().isThrownBy(() -> this.fileSystem.getPath(""))
-			.withMessage("Nested paths must contain a single element");
+	void getPathWhenFirstIsBlank() {
+		Path path = this.fileSystem.getPath("");
+		assertThat(path.toString()).endsWith("/test.jar");
 	}
 
 	@Test

spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/nio/file/NestedFileSystemZipFileSystemIntegrationTests.java

@@ -23,6 +23,7 @@
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.Collections;
+import java.util.List;
 
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
@@ -74,4 +75,22 @@ void nestedZipWithoutNewFileSystem() throws Exception {
 		assertThat(Files.readAllBytes(path)).containsExactly(0x3);
 	}
 
+	@Test // gh-38592
+	void nestedZipSplitAndRestore() throws Exception {
+		File file = new File(this.temp, "test.jar");
+		TestJar.create(file);
+		URI uri = JarUrl.create(file, "nested.jar", "3.dat").toURI();
+		String[] components = uri.toString().split("!");
+		System.out.println(List.of(components));
+		try (FileSystem rootFs = FileSystems.newFileSystem(URI.create(components[0]), Collections.emptyMap())) {
+			Path childPath = rootFs.getPath(components[1]);
+			try (FileSystem childFs = FileSystems.newFileSystem(childPath)) {
+				Path nestedRoot = childFs.getPath("/");
+				assertThat(Files.list(nestedRoot)).hasSize(4);
+				Path path = childFs.getPath(components[2]);
+				assertThat(Files.readAllBytes(path)).containsExactly(0x3);
+			}
+		}
+	}
+
 }