storage from keys and shallow discovery (without listing)

pom.xml

@@ -5,13 +5,13 @@
 	<parent>
 		<groupId>org.scijava</groupId>
 		<artifactId>pom-scijava</artifactId>
-		<version>38.0.1</version>
+		<version>40.0.0</version>
 		<relativePath />
 	</parent>
 
 	<groupId>org.janelia.saalfeldlab</groupId>
 	<artifactId>n5-universe</artifactId>
-	<version>1.6.1-SNAPSHOT</version>
+	<version>1.7.0-SNAPSHOT</version>
 
 	<name>N5-Universe</name>
 	<description>Utilities spanning all of the N5 repositories</description>
@@ -111,16 +111,16 @@
 		<!-- NB: Deploy releases to the SciJava Maven repository. -->
 		<releaseProfiles>sign,deploy-to-scijava</releaseProfiles>
 
-		<n5.version>3.3.0</n5.version>
-		<n5-aws-s3.version>4.2.1</n5-aws-s3.version>
-		<n5-google-cloud.version>4.1.1</n5-google-cloud.version>
-		<n5-zarr.version>1.3.5</n5-zarr.version>
+		<n5-aws-s3.version>4.2.2</n5-aws-s3.version>
+		<n5-google-cloud.version>4.1.2</n5-google-cloud.version>
+		<n5-zarr.version>1.4.0</n5-zarr.version>
 
 		<jackson-jq.version>1.0.0-preview.20191208</jackson-jq.version>
 		<alphanumeric-comparator.version>1.4.1</alphanumeric-comparator.version>
 
 		<s3mock_2.12.version>0.2.5</s3mock_2.12.version>
 		<jaxb-api.version>2.2.2</jaxb-api.version>
+		<json-simple.version>1.1.1</json-simple.version>
 	</properties>
 
 	<dependencies>
@@ -203,7 +203,7 @@
 		<dependency>
 			<groupId>com.googlecode.json-simple</groupId>
 			<artifactId>json-simple</artifactId>
-			<version>1.1.1</version>
+			<version>${json-simple.version}</version>
 			<scope>test</scope>
 		</dependency>
 		<dependency>

src/main/java/org/janelia/saalfeldlab/n5/universe/KeyValueAccessBackend.java

@@ -0,0 +1,116 @@
+package org.janelia.saalfeldlab.n5.universe;
+
+import com.amazonaws.services.s3.AmazonS3;
+import org.janelia.saalfeldlab.googlecloud.GoogleCloudStorageURI;
+import org.janelia.saalfeldlab.googlecloud.GoogleCloudUtils;
+import org.janelia.saalfeldlab.n5.FileSystemKeyValueAccess;
+import org.janelia.saalfeldlab.n5.KeyValueAccess;
+import org.janelia.saalfeldlab.n5.N5Reader;
+import org.janelia.saalfeldlab.n5.N5Writer;
+import org.janelia.saalfeldlab.n5.googlecloud.GoogleCloudStorageKeyValueAccess;
+import org.janelia.saalfeldlab.n5.s3.AmazonS3KeyValueAccess;
+import org.janelia.saalfeldlab.n5.s3.AmazonS3Utils;
+
+import javax.annotation.Nullable;
+import java.net.URI;
+import java.nio.file.FileSystems;
+import java.util.function.BiFunction;
+import java.util.function.Predicate;
+import java.util.regex.Pattern;
+
+/**
+ * Enum to discover and provide {@link KeyValueAccess} for {@link N5Reader}s and {@link N5Writer}s.
+ * IMPORTANT: If ever new {@link KeyValueAccess} backends are adding, they MUST be re-ordered
+ * such that the earliest predicates are the most restrictive, and the later predicates
+ * are the least restrictive. This ensures that when iterating through the values of
+ * {@link KeyValueAccessBackend} you can test them in order, and stop at the first
+ * {@link KeyValueAccess} that is generated.
+ */
+public enum KeyValueAccessBackend implements Predicate<URI>, BiFunction<URI, N5Factory, KeyValueAccess> {
+	GOOGLE_CLOUD(uri -> {
+		final String scheme = uri.getScheme();
+		final boolean hasScheme = scheme != null;
+		return hasScheme && GoogleCloudUtils.GS_SCHEME.asPredicate().test(scheme)
+				|| hasScheme && N5Factory.HTTPS_SCHEME.asPredicate().test(scheme)
+				&& uri.getHost() != null && GoogleCloudUtils.GS_HOST.asPredicate().test(uri.getHost());
+	}, KeyValueAccessBackend::newGoogleCloudKeyValueAccess),
+	AWS(uri -> {
+		final String scheme = uri.getScheme();
+		final boolean hasScheme = scheme != null;
+		return hasScheme && AmazonS3Utils.S3_SCHEME.asPredicate().test(scheme)
+				|| uri.getHost() != null && hasScheme && N5Factory.HTTPS_SCHEME.asPredicate().test(scheme);
+	}, KeyValueAccessBackend::newAmazonS3KeyValueAccess),
+	FILE(uri -> {
+		final String scheme = uri.getScheme();
+		final boolean hasScheme = scheme != null;
+		return !hasScheme || N5Factory.FILE_SCHEME.asPredicate().test(scheme);
+	}, KeyValueAccessBackend::newFileSystemKeyValueAccess);
+
+	private final Predicate<URI> backendTest;
+	private final BiFunction<URI, N5Factory, KeyValueAccess> backendGenerator;
+
+	KeyValueAccessBackend(Predicate<URI> test, BiFunction<URI, N5Factory, KeyValueAccess> generator) {
+
+		backendTest = test;
+		backendGenerator = generator;
+	}
+
+	@Override public KeyValueAccess apply(final URI uri, final N5Factory factory) {
+
+		if (test(uri))
+			return backendGenerator.apply(uri, factory);
+		return null;
+	}
+
+	@Override public boolean test(URI uri) {
+
+		return backendTest.test(uri);
+	}
+
+	/**
+	 * Test the provided {@link URI} to and return the appropriate {@link KeyValueAccess}.
+	 * If no appropriate {@link KeyValueAccess} is found, may be null
+	 *
+	 * @param uri to create a {@link KeyValueAccess} from.
+	 * @return the {@link KeyValueAccess} and container path, or null if none are valid
+	 */
+	@Nullable
+	public static KeyValueAccess getKeyValueAccess(final URI uri) {
+
+		return getKeyValueAccess(uri, N5Factory.FACTORY);
+	}
+
+	@Nullable
+	static KeyValueAccess getKeyValueAccess(final URI uri, final N5Factory factory) {
+
+		/*NOTE: The order of these tests is very important, as the predicates for each
+		 * backend take into account reasonable defaults when possible.
+		 * Here we test from most to least restrictive.
+		 * See the Javadoc for more details.  */
+		for (final KeyValueAccessBackend backend : KeyValueAccessBackend.values()) {
+			final KeyValueAccess kva = backend.apply(uri, factory);
+			if (kva != null)
+				return kva;
+		}
+		return null;
+	}
+
+	private static GoogleCloudStorageKeyValueAccess newGoogleCloudKeyValueAccess(final URI uri, final N5Factory factory) {
+
+		final GoogleCloudStorageURI googleCloudUri = new GoogleCloudStorageURI(uri);
+		return new GoogleCloudStorageKeyValueAccess(factory.createGoogleCloudStorage(), googleCloudUri, true);
+	}
+
+	private static AmazonS3KeyValueAccess newAmazonS3KeyValueAccess(final URI uri, final N5Factory factory) {
+
+		final String uriString = uri.toString();
+		final AmazonS3 s3 = factory.createS3(uriString);
+
+		return new AmazonS3KeyValueAccess(s3, uri, true);
+	}
+
+	private static FileSystemKeyValueAccess newFileSystemKeyValueAccess(final URI uri, final N5Factory factory) {
+
+		return new FileSystemKeyValueAccess(FileSystems.getDefault());
+	}
+}