Introduce Synapse Expression support

.gitignore

@@ -15,4 +15,5 @@
 target/
 
 ## various other file types we don't want to have in the repository:
-.DS_Store
+.DS_Store
+/modules/core/src/main/antlr4/org/apache/synapse/util/synapse_path/gen/

modules/core/pom.xml

@@ -145,6 +145,44 @@
 					</execution>
 				</executions>
 			</plugin>
+			<plugin>
+				<groupId>org.antlr</groupId>
+				<artifactId>antlr4-maven-plugin</artifactId>
+				<executions>
+					<execution>
+						<id>antlr</id>
+						<phase>generate-sources</phase>
+						<goals>
+							<goal>antlr4</goal>
+						</goals>
+						<configuration>
+							<sourceDirectory>${project.basedir}/src/main/antlr4</sourceDirectory>
+							<arguments>
+								<argument>-visitor</argument>
+							</arguments>
+						</configuration>
+					</execution>
+				</executions>
+			</plugin>
+			<!-- Build Helper Maven Plugin -->
+			<plugin>
+				<groupId>org.codehaus.mojo</groupId>
+				<artifactId>build-helper-maven-plugin</artifactId>
+				<executions>
+					<execution>
+						<id>add-source</id>
+						<phase>generate-sources</phase>
+						<goals>
+							<goal>add-source</goal>
+						</goals>
+						<configuration>
+							<sources>
+								<source>${project.build.directory}/generated-sources/antlr4</source>
+							</sources>
+						</configuration>
+					</execution>
+				</executions>
+			</plugin>
 
 			<!-- Attach a JAR with the test classes so that we can reuse them in other 
 				modules (see http://maven.apache.org/guides/mini/guide-attached-tests.html). -->
@@ -506,5 +544,9 @@
 			<groupId>org.apache.logging.log4j</groupId>
 			<artifactId>log4j-slf4j-impl</artifactId>
 		</dependency>
+		<dependency>
+			<groupId>org.antlr</groupId>
+			<artifactId>antlr4-runtime</artifactId>
+		</dependency>
 	</dependencies>
 </project>

modules/core/src/main/antlr4/org/apache/synapse/util/synapse_expression/ExpressionLexer.g4

@@ -0,0 +1,80 @@
+lexer grammar ExpressionLexer;
+
+JSONPATH_PARAMS:  'in' | 'nin' | 'subsetof' | 'anyof' | 'noneof' | 'size' | 'empty' | '=~';
+
+JSONPATH_FUNCTIONS: 'length()' | 'size()' | 'min()' | 'max()' | 'avg()' | 'sum()' | 'stddev()' | 'keys()' | 'first()' | 'last()';
+
+// Tokens for identifiers, operators, and keywords
+VAR: 'var';
+PAYLOAD: 'payload' | '$';
+HEADERS: 'headers';
+CONFIG: 'config';
+ATTRIBUTES: 'attributes' | 'attr';
+AND: 'and' | '&&';
+OR: 'or' | '||';
+NOT: '!';
+
+DOUBLE_DOT : '..';
+ASTERISK : '*';
+
+// Operators
+PLUS: '+';
+MINUS: '-';
+DIV: '/';
+MODULO: '%';
+EQ: '==';
+NEQ: '!=';
+GT: '>';
+LT: '<';
+GTE: '>=';
+LTE: '<=';
+
+// Delimiters
+LPAREN: '(';
+RPAREN: ')';
+LBRACKET: '[';
+RBRACKET: ']';
+DOT: '.';
+COMMA: ',';
+COLON: ':';
+QUOTE: '"' | '\'';
+
+// Literals
+BOOLEAN_LITERAL: 'true' | 'false';
+NUMBER: '-'? [0-9]+ ('.' [0-9]+)?;
+
+
+STRING_LITERAL : ('"' (ESC | ~["\\])* '"' | '\'' (ESC | ~['\\])* '\'');
+
+
+fragment ESC
+    :   '\\' [btnfr"'\\/]  // Basic escape sequences
+    |   UNICODE_ESC
+    |   OCTAL_ESC
+    ;
+
+fragment UNICODE_ESC
+    :   '\\' 'u' HEX_DIGIT HEX_DIGIT HEX_DIGIT HEX_DIGIT
+    ;
+
+fragment OCTAL_ESC
+    :   '\\' [0-3]? [0-7] [0-7]
+    ;
+
+fragment HEX_DIGIT
+    :   [0-9a-fA-F]
+    ;
+
+NULL_LITERAL
+    : 'null'           // Define null as a recognized keyword
+    ;
+
+// Identifiers
+ID: [a-zA-Z_][a-zA-Z_0-9]*;
+
+// Special symbols for JSONPath filter expressions
+QUESTION: '?';
+AT: '@';
+
+// Whitespace
+WS: [ \t\n\r]+ -> skip;

modules/core/src/main/antlr4/org/apache/synapse/util/synapse_expression/ExpressionParser.g4

@@ -0,0 +1,147 @@
+parser grammar ExpressionParser;
+
+options {
+    tokenVocab = ExpressionLexer;
+}
+
+expression
+    : comparisonExpression
+    | conditionalExpression
+    | EOF
+    ;
+
+conditionalExpression
+    : comparisonExpression (QUESTION expression COLON expression)?
+    ;
+
+comparisonExpression
+    : logicalExpression ( (GT | LT | GTE | LTE | EQ | NEQ) logicalExpression )*
+    | logicalExpression (EQ | NEQ) NULL_LITERAL
+    ;
+
+logicalExpression
+    : arithmeticExpression (AND logicalExpression | OR logicalExpression)?
+    ;
+
+arithmeticExpression
+    : term ( (PLUS | MINUS) term )*
+    ;
+
+term
+    : factor ( (ASTERISK | DIV | MODULO) factor )*
+    ;
+
+factor
+    : literal
+    | functionCall
+    | variableAccess
+    | payloadAccess
+    | headerAccess
+    | configAccess
+    | attributeAccess
+    | LPAREN expression RPAREN
+    ;
+
+configAccess
+    : CONFIG propertyName
+    ;
+
+headerAccess
+    : HEADERS propertyName
+    ;
+
+attributeAccess
+    : ATTRIBUTES (DOT ID  propertyName)
+    ;
+
+propertyName
+    : DOT ID
+    | (DOT)? LBRACKET STRING_LITERAL RBRACKET
+    ;
+
+literal
+    : arrayLiteral
+    | BOOLEAN_LITERAL
+    | NUMBER
+    | STRING_LITERAL
+    | NULL_LITERAL
+    ;
+
+jsonPathExpression
+    :( DOT JSONPATH_FUNCTIONS
+     |DOUBLE_DOT ASTERISK
+     | DOUBLE_DOT ID
+     | DOT ID
+     | (DOT)? LBRACKET arrayIndex RBRACKET
+     | DOT ASTERISK
+     | DOUBLE_DOT ID (LBRACKET arrayIndex RBRACKET)?)+
+     ;
+
+
+variableAccess
+    : VAR ( DOT ID
+          | DOT STRING_LITERAL
+          | (DOT)? LBRACKET STRING_LITERAL RBRACKET  // Bracket notation: var["variableName"]
+          )
+      ( jsonPathExpression )?
+    ;
+
+arrayLiteral
+    : LBRACKET (expression (COMMA expression)*)? RBRACKET // Array with zero or more literals, separated by commas
+    ;
+
+payloadAccess
+    : PAYLOAD ( jsonPathExpression)?
+    ;
+
+arrayIndex
+    : NUMBER
+    | STRING_LITERAL
+    | expression
+    | multipleArrayIndices
+    | sliceArrayIndex
+    | expression ( (PLUS | MINUS | ASTERISK | DIV ) expression)*
+    | ASTERISK
+    | QUESTION? filterExpression
+    ;
+
+multipleArrayIndices
+    : expression (COMMA expression)+
+    ;
+
+sliceArrayIndex
+    : signedExpressions? COLON signedExpressions? (COLON signedExpressions?)?
+    ;
+
+signedExpressions
+    : MINUS? expression
+    ;
+
+filterExpression
+    : (filterComponent)+
+    ;
+
+filterComponent
+    : variableAccess
+    | payloadAccess
+    | headerAccess
+    | configAccess
+    | attributeAccess
+    | functionCall
+    | stringOrOperator
+    ;
+
+stringOrOperator
+    : QUESTION | AT | JSONPATH_PARAMS | STRING_LITERAL |NUMBER | BOOLEAN_LITERAL | ID | GT | LT | GTE | LTE | EQ | NEQ
+    | PLUS | MINUS | DIV | LPAREN | RPAREN | DOT | COMMA | COLON | WS | AND | OR | NOT | ASTERISK
+    ;
+
+
+functionCall
+    : ID LPAREN (expression (COMMA expression)*)? RPAREN functionCallSuffix?
+    ;
+
+functionCallSuffix
+    : DOT ID LPAREN (expression (COMMA expression)*)? RPAREN   // Method chaining
+    | jsonPathExpression
+    ;

modules/core/src/main/java/org/apache/synapse/SynapseConstants.java

@@ -625,4 +625,57 @@ public enum ENDPOINT_TIMEOUT_TYPE { ENDPOINT_TIMEOUT, GLOBAL_TIMEOUT, HTTP_CONNE
     public static final String JAEGER_SPAN_ID = "jaeger_span_id";
 
     public static final String ANALYTICS_METADATA = "ANALYTICS_METADATA";
+
+    // Constants related to Synapse Expressions
+    public static final String AND = "and";
+    public static final String OR = "or";
+    public static final String NOT = "not";
+    public static final String  TO_LOWER  = "toLower";
+    public static final String  TO_UPPER  = "toUpper";
+    public static final String  LENGTH    = "length";
+    public static final String  SUBSTRING = "subString";
+    public static final String  STARTS_WITH = "startsWith";
+    public static final String  ENDS_WITH = "endsWith";
+    public static final String  CONTAINS = "contains";
+    public static final String  TRIM = "trim";
+    public static final String  REPLACE = "replace";
+    public static final String  SPLIT = "split";
+    public static final String  NOW = "now";
+    public static final String  ABS = "abs";
+    public static final String  CEIL = "ceil";
+    public static final String  FLOOR = "floor";
+    public static final String  SQRT = "sqrt";
+    public static final String  LOG = "log";
+    public static final String  POW = "pow";
+    public static final String  B64ENCODE = "base64encode";
+    public static final String  B64DECODE = "base64decode";
+    public static final String  URL_ENCODE = "urlEncode";
+    public static final String  URL_DECODE = "urlDecode";
+    public static final String  IS_NUMBER = "isNumber";
+    public static final String  IS_STRING = "isString";
+    public static final String  IS_ARRAY = "isArray";
+    public static final String  IS_OBJECT = "isObject";
+    public static final String  OBJECT = "object";
+    public static final String  ARRAY = "array";
+    public static final String  REGISTRY = "registry";
+    public static final String  EXISTS = "exists";
+    public static final String  XPATH = "xpath";
+    public static final String  SECRET = "secret";
+
+    public static final String  ROUND = "round";
+    public static final String  INTEGER = "integer";
+    public static final String  FLOAT = "float";
+    public static final String  STRING = "string";
+    public static final String  BOOLEAN = "boolean";
+
+    public static final String  PAYLOAD = "payload";
+    public static final String  PAYLOAD_$ = "$";
+    public static final String  SYNAPSE_EXPRESSION_IDENTIFIER_START = "${";
+    public static final String  SYNAPSE_EXPRESSION_IDENTIFIER_END = "}";
+    public static final String  AXIS2 = "axis2";
+    public static final String  QUERY_PARAM = "queryParams";
+    public static final String  URI_PARAM = "uriParams";
+
+    public static final String  UNKNOWN = "unknown";
+    public static final String  VAULT_LOOKUP = "wso2:vault-lookup('";
 }

modules/core/src/main/java/org/apache/synapse/config/xml/PropertyMediatorFactory.java

@@ -22,11 +22,13 @@
 import org.apache.axiom.om.OMAttribute;
 import org.apache.axiom.om.OMElement;
 import org.apache.synapse.Mediator;
+import org.apache.synapse.SynapseConstants;
 import org.apache.synapse.SynapseException;
 import org.apache.synapse.mediators.Value;
 import org.apache.synapse.mediators.builtin.PropertyMediator;
 import org.apache.synapse.util.MediatorPropertyUtils;
 import org.apache.synapse.util.xpath.SynapseJsonPath;
+import org.apache.synapse.util.xpath.SynapseExpression;
 import org.apache.synapse.util.xpath.SynapseXPath;
 import org.jaxen.JaxenException;
 
@@ -83,6 +85,9 @@ public Mediator createSpecificMediator(OMElement elem, Properties properties) {
                 String nameExpression = nameAttributeValue.substring(1, nameAttributeValue.length() - 1);
                 if(nameExpression.startsWith("json-eval(")) {
                     new SynapseJsonPath(nameExpression.substring(10, nameExpression.length() - 1));
+                } else if (nameExpression.startsWith(SynapseConstants.SYNAPSE_EXPRESSION_IDENTIFIER_START) &&
+                        nameExpression.endsWith(SynapseConstants.SYNAPSE_EXPRESSION_IDENTIFIER_END)) {
+                    new SynapseExpression(nameExpression.substring(2, nameExpression.length() - 1));
                 } else {
                     new SynapseXPath(nameExpression);
                 }