Add startsWith expression function

data-prepper-expression/src/main/java/org/opensearch/dataprepper/expression/StartsWithExpressionFunction.java

@@ -0,0 +1,53 @@
+package org.opensearch.dataprepper.expression;
+
+import org.opensearch.dataprepper.model.event.Event;
+
+import javax.inject.Named;
+import java.util.List;
+import java.util.function.Function;
+
+@Named
+public class StartsWithExpressionFunction implements ExpressionFunction {
+    private static final int NUMBER_OF_ARGS = 2;
+
+    static final String STARTS_WITH_FUNCTION_NAME = "startsWith";
+    @Override
+    public String getFunctionName() {
+        return STARTS_WITH_FUNCTION_NAME;
+    }
+
+    @Override
+    public Object evaluate(
+            final List<Object> args,
+            final Event event,
+            final Function<Object, Object> convertLiteralType) {
+
+        if (args.size() != NUMBER_OF_ARGS) {
+            throw new RuntimeException("startsWith() takes exactly two arguments");
+        }
+
+        String[] strArgs = new String[NUMBER_OF_ARGS];
+        for (int i = 0; i < NUMBER_OF_ARGS; i++) {
+            Object arg = args.get(i);
+            if (!(arg instanceof String)) {
+                throw new RuntimeException(String.format("startsWith() takes only string type arguments. \"%s\" is not of type string", arg));
+            }
+            String stringOrKey = (String) arg;
+            if (stringOrKey.charAt(0) == '"') {
+                strArgs[i] = stringOrKey.substring(1, stringOrKey.length()-1);
+            } else if (stringOrKey.charAt(0) == '/') {
+                Object obj = event.get(stringOrKey, Object.class);
+                if (obj == null) {
+                    return false;
+                }
+                if (!(obj instanceof String)) {
+                    throw new RuntimeException(String.format("startsWith() only operates on string types. The value at \"%s\" is \"%s\" which is not a string type.", stringOrKey, obj));
+                }
+                strArgs[i] = (String)obj;
+            } else {
+                throw new RuntimeException(String.format("Arguments to startsWith() must be a literal string or a Json Pointer. \"%s\" is not string literal or json pointer", stringOrKey));
+            }
+        }
+        return strArgs[0].startsWith(strArgs[1]);
+    }
+}

data-prepper-expression/src/test/java/org/opensearch/dataprepper/expression/ContainsExpressionFunctionTest.java

@@ -56,8 +56,7 @@ public ContainsExpressionFunction createObjectUnderTest() {
     }
 
     @Test
-    void testContainsBasic() {
-        containsExpressionFunction = createObjectUnderTest();
+    void testContainsBasic() {containsExpressionFunction = createObjectUnderTest();
         assertThat(containsExpressionFunction.evaluate(List.of("\"abcde\"", "\"abcd\""), testEvent, testFunction), equalTo(true));
         assertThat(containsExpressionFunction.evaluate(List.of("/"+testKey, "/"+testKey2), testEvent, testFunction), equalTo(true));
         assertThat(containsExpressionFunction.evaluate(List.of("\""+testValue+"\"", "/"+testKey2), testEvent, testFunction), equalTo(true));

data-prepper-expression/src/test/java/org/opensearch/dataprepper/expression/GenericExpressionEvaluator_ConditionalIT.java

@@ -21,6 +21,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Random;
+import java.util.UUID;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
@@ -234,8 +235,10 @@ private static Stream<Arguments> validExpressionArguments() {
                 arguments("/name =~ \".*dataprepper-[0-9]+\"", event("{\"name\": \"dataprepper-0\"}"), true),
                 arguments("/name =~ \".*dataprepper-[0-9]+\"", event("{\"name\": \"dataprepper-212\"}"), true),
                 arguments("/name =~ \".*dataprepper-[0-9]+\"", event("{\"name\": \"dataprepper-abc\"}"), false),
-                arguments("/name =~ \".*dataprepper-[0-9]+\"", event("{\"other\": \"dataprepper-abc\"}"), false)
-        );
+                arguments("/name =~ \".*dataprepper-[0-9]+\"", event("{\"other\": \"dataprepper-abc\"}"), false),
+                arguments("startsWith(\""+strValue+ UUID.randomUUID() + "\",/status)", event("{\"status\":\""+strValue+"\"}"), true),
+                arguments("startsWith(\""+ UUID.randomUUID() +strValue+ "\",/status)", event("{\"status\":\""+strValue+"\"}"), false)
+                );
     }
 
     private static Stream<Arguments> invalidExpressionArguments() {

data-prepper-expression/src/test/java/org/opensearch/dataprepper/expression/StartsWithExpressionFunctionTest.java

@@ -0,0 +1,111 @@
+package org.opensearch.dataprepper.expression;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+import org.opensearch.dataprepper.model.event.Event;
+import org.opensearch.dataprepper.model.event.JacksonEvent;
+
+import java.util.List;
+import java.util.Map;
+import java.util.UUID;
+import java.util.function.Function;
+import java.util.stream.Stream;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.equalTo;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.mockito.Mockito.mock;
+import static org.opensearch.dataprepper.expression.StartsWithExpressionFunction.STARTS_WITH_FUNCTION_NAME;
+
+public class StartsWithExpressionFunctionTest {
+
+    private Event testEvent;
+
+    private Event createTestEvent(final Object data) {
+        return JacksonEvent.builder().withEventType("event").withData(data).build();
+    }
+
+    private ExpressionFunction createObjectUnderTest() {
+        return new StartsWithExpressionFunction();
+    }
+
+    @ParameterizedTest
+    @MethodSource("validStartsWithProvider")
+    void startsWith_returns_expected_result_when_evaluated(
+            final String value, final String prefix, final boolean expectedResult) {
+        final String key = "test_key";
+        testEvent = createTestEvent(Map.of(key, value));
+
+        final ExpressionFunction objectUnderTest = createObjectUnderTest();
+        assertThat(objectUnderTest.getFunctionName(), equalTo(STARTS_WITH_FUNCTION_NAME));
+
+        final Object result = objectUnderTest.evaluate(List.of("/" + key, "\"" + prefix + "\""), testEvent, mock(Function.class));
+
+        assertThat(result, equalTo(expectedResult));
+    }
+
+    @Test
+    void startsWith_with_a_key_as_the_prefix_returns_expected_result() {
+
+        final String prefixKey = "prefix";
+        final String prefixValue = "te";
+
+        final String key = "test_key";
+        final String value = "test";
+        testEvent = createTestEvent(Map.of(key, value, prefixKey, prefixValue));
+
+        final ExpressionFunction objectUnderTest = createObjectUnderTest();
+        assertThat(objectUnderTest.getFunctionName(), equalTo(STARTS_WITH_FUNCTION_NAME));
+
+        final Object result = objectUnderTest.evaluate(List.of("/" + key, "/" + prefixKey), testEvent, mock(Function.class));
+
+        assertThat(result, equalTo(true));
+    }
+
+    @Test
+    void startsWith_returns_false_when_key_does_not_exist_in_Event() {
+        final String key = "test_key";
+        testEvent = createTestEvent(Map.of(UUID.randomUUID().toString(), UUID.randomUUID().toString()));
+
+        final ExpressionFunction startsWithExpressionFunction = createObjectUnderTest();
+        final Object result = startsWithExpressionFunction.evaluate(List.of("/" + key, "\"abcd\""), testEvent, mock(Function.class));
+
+        assertThat(result, equalTo(false));
+    }
+
+    @Test
+    void startsWith_without_2_arguments_throws_RuntimeException() {
+        final ExpressionFunction startsWithExpressionFunction = createObjectUnderTest();
+        assertThrows(RuntimeException.class, () -> startsWithExpressionFunction.evaluate(List.of("abcd"), testEvent, mock(Function.class)));
+    }
+
+    @ParameterizedTest
+    @MethodSource("invalidStartsWithProvider")
+    void invalid_startsWith_arguments_throws_RuntimeException(final String firstArg, final Object secondArg, final Object value) {
+        final ExpressionFunction startsWithExpressionFunction = createObjectUnderTest();
+        final String testKey = "test_key";
+
+        assertThrows(RuntimeException.class, () -> startsWithExpressionFunction.evaluate(List.of(firstArg, secondArg), createTestEvent(Map.of(testKey, value)), mock(Function.class)));
+    }
+
+    private static Stream<Arguments> validStartsWithProvider() {
+        return Stream.of(
+                Arguments.of("{test", "{te", true),
+                Arguments.of("{test", "{", true),
+                Arguments.of("test", "{", false),
+                Arguments.of("MyPrefix", "My", true),
+                Arguments.of("MyPrefix", "Prefix", false)
+        );
+    }
+
+    private static Stream<Arguments> invalidStartsWithProvider() {
+        return Stream.of(
+                Arguments.of("\"abc\"", "/test_key", 1234),
+                Arguments.of("abcd", "/test_key", "value"),
+                Arguments.of("\"abcd\"", "/test_key", 1234),
+                Arguments.of("\"/test_key\"", 1234, "value")
+        );
+    }
+}