HADOOP-11664. Loading predefined EC schemas from configuration. Contributed by Kai Zheng.

hadoop-common-project/hadoop-common/src/main/conf/ecschema-def.xml

@@ -0,0 +1,40 @@
+<?xml version="1.0"?>
+
+<!--
+ 
+ Licensed to the Apache Software Foundation (ASF) under one
+ or more contributor license agreements.  See the NOTICE file
+ distributed with this work for additional information
+ regarding copyright ownership.  The ASF licenses this file
+ to you under the Apache License, Version 2.0 (the
+ "License"); you may not use this file except in compliance
+ with the License.  You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+
+-->
+
+<!--
+Please define your EC schemas here. Note, once these schemas are loaded
+and referenced by EC storage policies, any change to them will be ignored.
+You can modify and remove those not used yet, or add new ones.
+-->
+
+<schemas>
+  <schema name="RS-6-3">
+    <k>6</k>
+    <m>3</m>
+    <codec>RS</codec>
+  </schema>
+  <schema name="RS-10-4">
+    <k>10</k>
+    <m>4</m>
+    <codec>RS</codec>
+  </schema>
+</schemas>

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/CommonConfigurationKeys.java

@@ -143,6 +143,11 @@ public class CommonConfigurationKeys extends CommonConfigurationKeysPublic {
   /** Supported erasure codec classes */
   public static final String IO_ERASURECODE_CODECS_KEY = "io.erasurecode.codecs";
 
+  public static final String IO_ERASURECODE_SCHEMA_FILE_KEY =
+      "io.erasurecode.schema.file";
+  public static final String IO_ERASURECODE_SCHEMA_FILE_DEFAULT =
+      "ecschema-def.xml";
+
   /** Use XOR raw coder when possible for the RS codec */
   public static final String IO_ERASURECODE_CODEC_RS_USEXOR_KEY =
       "io.erasurecode.codec.rs.usexor";

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/SchemaLoader.java

@@ -0,0 +1,147 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.io.erasurecode;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.CommonConfigurationKeys;
+import org.w3c.dom.*;
+import org.xml.sax.SAXException;
+
+import javax.xml.parsers.DocumentBuilder;
+import javax.xml.parsers.DocumentBuilderFactory;
+import javax.xml.parsers.ParserConfigurationException;
+import java.io.File;
+import java.io.IOException;
+import java.net.URL;
+import java.util.*;
+
+/**
+ * A EC schema loading utility that loads predefined EC schemas from XML file
+ */
+public class SchemaLoader {
+  private static final Log LOG = LogFactory.getLog(SchemaLoader.class.getName());
+
+  /**
+   * Load predefined ec schemas from configuration file. This file is
+   * expected to be in the XML format.
+   */
+  public List<ECSchema> loadSchema(Configuration conf) {
+    File confFile = getSchemaFile(conf);
+    if (confFile == null) {
+      LOG.warn("Not found any predefined EC schema file");
+      return Collections.emptyList();
+    }
+
+    try {
+      return loadSchema(confFile);
+    } catch (ParserConfigurationException e) {
+      throw new RuntimeException("Failed to load schema file: " + confFile);
+    } catch (IOException e) {
+      throw new RuntimeException("Failed to load schema file: " + confFile);
+    } catch (SAXException e) {
+      throw new RuntimeException("Failed to load schema file: " + confFile);
+    }
+  }
+
+  private List<ECSchema> loadSchema(File schemaFile)
+      throws ParserConfigurationException, IOException, SAXException {
+
+    LOG.info("Loading predefined EC schema file " + schemaFile);
+
+    // Read and parse the schema file.
+    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
+    dbf.setIgnoringComments(true);
+    DocumentBuilder builder = dbf.newDocumentBuilder();
+    Document doc = builder.parse(schemaFile);
+    Element root = doc.getDocumentElement();
+
+    if (!"schemas".equals(root.getTagName())) {
+      throw new RuntimeException("Bad EC schema config file: " +
+          "top-level element not <schemas>");
+    }
+
+    NodeList elements = root.getChildNodes();
+    List<ECSchema> schemas = new ArrayList<ECSchema>();
+    for (int i = 0; i < elements.getLength(); i++) {
+      Node node = elements.item(i);
+      if (node instanceof Element) {
+        Element element = (Element) node;
+        if ("schema".equals(element.getTagName())) {
+          ECSchema schema = loadSchema(element);
+            schemas.add(schema);
+        } else {
+          LOG.warn("Bad element in EC schema configuration file: " +
+              element.getTagName());
+        }
+      }
+    }
+
+    return schemas;
+  }
+
+  /**
+   * Path to the XML file containing predefined ec schemas. If the path is
+   * relative, it is searched for in the classpath.
+   */
+  private File getSchemaFile(Configuration conf) {
+    String schemaFilePath = conf.get(
+        CommonConfigurationKeys.IO_ERASURECODE_SCHEMA_FILE_KEY,
+        CommonConfigurationKeys.IO_ERASURECODE_SCHEMA_FILE_DEFAULT);
+    File schemaFile = new File(schemaFilePath);
+    if (! schemaFile.isAbsolute()) {
+      URL url = Thread.currentThread().getContextClassLoader()
+          .getResource(schemaFilePath);
+      if (url == null) {
+        LOG.warn(schemaFilePath + " not found on the classpath.");
+        schemaFile = null;
+      } else if (! url.getProtocol().equalsIgnoreCase("file")) {
+        throw new RuntimeException(
+            "EC predefined schema file " + url +
+                " found on the classpath is not on the local filesystem.");
+      } else {
+        schemaFile = new File(url.getPath());
+      }
+    }
+
+    return schemaFile;
+  }
+
+  /**
+   * Loads a schema from a schema element in the configuration file
+   */
+  private ECSchema loadSchema(Element element) {
+    String schemaName = element.getAttribute("name");
+    Map<String, String> ecOptions = new HashMap<String, String>();
+    NodeList fields = element.getChildNodes();
+
+    for (int i = 0; i < fields.getLength(); i++) {
+      Node fieldNode = fields.item(i);
+      if (fieldNode instanceof Element) {
+        Element field = (Element) fieldNode;
+        String tagName = field.getTagName();
+        String value = ((Text) field.getFirstChild()).getData().trim();
+        ecOptions.put(tagName, value);
+      }
+    }
+
+    ECSchema schema = new ECSchema(schemaName, ecOptions);
+    return schema;
+  }
+}

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/erasurecode/TestSchemaLoader.java

@@ -0,0 +1,80 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.io.erasurecode;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.CommonConfigurationKeys;
+import org.junit.Test;
+
+import java.io.File;
+import java.io.FileWriter;
+import java.io.PrintWriter;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+
+public class TestSchemaLoader {
+
+  final static String TEST_DIR = new File(System.getProperty(
+      "test.build.data", "/tmp")).getAbsolutePath();
+
+  final static String SCHEMA_FILE = new File(TEST_DIR, "test-ecschema")
+      .getAbsolutePath();
+
+  @Test
+  public void testLoadSchema() throws Exception {
+    PrintWriter out = new PrintWriter(new FileWriter(SCHEMA_FILE));
+    out.println("<?xml version=\"1.0\"?>");
+    out.println("<schemas>");
+    out.println("  <schema name=\"RSk6m3\">");
+    out.println("    <k>6</k>");
+    out.println("    <m>3</m>");
+    out.println("    <codec>RS</codec>");
+    out.println("  </schema>");
+    out.println("  <schema name=\"RSk10m4\">");
+    out.println("    <k>10</k>");
+    out.println("    <m>4</m>");
+    out.println("    <codec>RS</codec>");
+    out.println("  </schema>");
+    out.println("</schemas>");
+    out.close();
+
+    Configuration conf = new Configuration();
+    conf.set(CommonConfigurationKeys.IO_ERASURECODE_SCHEMA_FILE_KEY,
+        SCHEMA_FILE);
+
+    SchemaLoader schemaLoader = new SchemaLoader();
+    List<ECSchema> schemas = schemaLoader.loadSchema(conf);
+
+    assertEquals(2, schemas.size());
+
+    ECSchema schema1 = schemas.get(0);
+    assertEquals("RSk6m3", schema1.getSchemaName());
+    assertEquals(3, schema1.getOptions().size());
+    assertEquals(6, schema1.getNumDataUnits());
+    assertEquals(3, schema1.getNumParityUnits());
+    assertEquals("RS", schema1.getCodecName());
+
+    ECSchema schema2 = schemas.get(1);
+    assertEquals("RSk10m4", schema2.getSchemaName());
+    assertEquals(3, schema2.getOptions().size());
+    assertEquals(10, schema2.getNumDataUnits());
+    assertEquals(4, schema2.getNumParityUnits());
+    assertEquals("RS", schema2.getCodecName());
+  }
+}