Exposes method in IndexReaderUtils to fetch raw document (#937)

src/main/java/io/anserini/index/IndexReaderUtils.java

@@ -332,6 +332,25 @@ public static Map<String, Long> getDocumentVector(IndexReader reader, String doc
     return docVector;
   }
 
+  /**
+   * Returns the raw document given its collection docid.
+   * @param reader index reader
+   * @param docid collection docid
+   * @return the raw document given its collection docid, or <code>null</code> if not found.
+   */
+  public static String getRawDocument(IndexReader reader, String docid) {
+    try {
+      Document rawDoc = reader.document(convertDocidToLuceneDocid(reader, docid));
+
+      if (rawDoc == null) {
+        return null;
+      }
+      return rawDoc.get(LuceneDocumentGenerator.FIELD_RAW);
+    } catch (IOException e) {
+      return null;
+    }
+  }
+
   /**
    * Computes the BM25 weight of a term (prior to analysis) in a particular document.
    * @param reader index reader

src/test/java/io/anserini/index/IndexReaderUtilsTest.java

@@ -249,6 +249,16 @@ public void testDocumentVector() throws Exception {
     assertEquals(Long.valueOf(1), documentVector.get("test"));
   }
 
+  @Test
+  public void testRawDoc() throws Exception {
+    Directory dir = FSDirectory.open(tempDir1);
+    IndexReader reader = DirectoryReader.open(dir);
+
+    assertEquals("here is some text here is some more text", IndexReaderUtils.getRawDocument(reader, "doc1"));
+    assertEquals("more texts", IndexReaderUtils.getRawDocument(reader, "doc2"));
+    assertEquals("here is a test", IndexReaderUtils.getRawDocument(reader, "doc3"));
+  }
+
   @Test
   public void testDocidConversion() throws Exception {
     Directory dir = FSDirectory.open(tempDir1);