ESQL: Add url_encode function

x-pack/plugin/esql/qa/testFixtures/src/main/resources/string.csv-spec

@@ -2465,3 +2465,39 @@ warning:Line 2:9: java.lang.IllegalArgumentException: single-value function enco
     @timestamp:date     | message:text
 2023-10-23T13:55:01.544Z|Connected to 10.1.0.1
 ;
+
+url_encode sample for docs
+required_capability: url_encode
+
+// tag::url_encode[]
+ROW u = "https://www.example.com/papers?q=information+retrieval&year=2024&citations=high" | EVAL u = URL_ENCODE(u)
+// end::url_encode[]
+;
+
+// tag::url_encode-result[]
+u:keyword
+https%3A%2F%2Fwww.example.com%2Fpapers%3Fq%3Dinformation%2Bretrieval%26year%3D2024%26citations%3Dhigh
+// end::url_encode-result[]
+;
+
+url_encode mixed functions tests
+required_capability: url_encode
+
+FROM employees 
+| WHERE emp_no == 10001 
+| EVAL a = TRIM(URL_ENCODE(first_name))
+| EVAL b = URL_ENCODE(TO_LOWER(first_name))
+| KEEP a,b;
+
+a:keyword | b:keyword
+Georgi    | georgi 
+;
+
+url_encode mixed input tests
+required_capability: url_encode
+
+ROW u = ["hello elastic!", "a+b-c%d", "", "!#$&'()*+,/:;=?@[]"] | EVAL u = URL_ENCODE(u);
+
+u:keyword
+["hello+elastic%21", "a%2Bb-c%25d", "", "%21%23%24%26%27%28%29*%2B%2C%2F%3A%3B%3D%3F%40%5B%5D"]
+;

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/action/EsqlCapabilities.java

@@ -1399,7 +1399,12 @@ public enum Cap {
         /**
          * Allow qualifiers in attribute names.
          */
-        NAME_QUALIFIERS(Build.current().isSnapshot());
+        NAME_QUALIFIERS(Build.current().isSnapshot()),
+
+        /**
+         * URL encoding function.
+         */
+        URL_ENCODE(Build.current().isSnapshot());
 
         private final boolean enabled;
 

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/ExpressionWritables.java

@@ -34,6 +34,7 @@
 import org.elasticsearch.xpack.esql.expression.function.scalar.convert.ToString;
 import org.elasticsearch.xpack.esql.expression.function.scalar.convert.ToUnsignedLong;
 import org.elasticsearch.xpack.esql.expression.function.scalar.convert.ToVersion;
+import org.elasticsearch.xpack.esql.expression.function.scalar.convert.UrlEncode;
 import org.elasticsearch.xpack.esql.expression.function.scalar.math.Abs;
 import org.elasticsearch.xpack.esql.expression.function.scalar.math.Acos;
 import org.elasticsearch.xpack.esql.expression.function.scalar.math.Asin;
@@ -223,6 +224,7 @@ public static List<NamedWriteableRegistry.Entry> unaryScalars() {
         entries.add(WildcardLike.ENTRY);
         entries.add(WildcardLikeList.ENTRY);
         entries.add(Delay.ENTRY);
+        entries.add(UrlEncode.ENTRY);
         // mv functions
         entries.addAll(MvFunctionWritables.getNamedWriteables());
         return entries;

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/EsqlFunctionRegistry.java

@@ -83,6 +83,7 @@
 import org.elasticsearch.xpack.esql.expression.function.scalar.convert.ToTimeDuration;
 import org.elasticsearch.xpack.esql.expression.function.scalar.convert.ToUnsignedLong;
 import org.elasticsearch.xpack.esql.expression.function.scalar.convert.ToVersion;
+import org.elasticsearch.xpack.esql.expression.function.scalar.convert.UrlEncode;
 import org.elasticsearch.xpack.esql.expression.function.scalar.date.DateDiff;
 import org.elasticsearch.xpack.esql.expression.function.scalar.date.DateExtract;
 import org.elasticsearch.xpack.esql.expression.function.scalar.date.DateFormat;
@@ -513,7 +514,8 @@ private static FunctionDefinition[][] snapshotFunctions() {
                 def(L1Norm.class, L1Norm::new, "v_l1_norm"),
                 def(L2Norm.class, L2Norm::new, "v_l2_norm"),
                 def(Magnitude.class, Magnitude::new, "v_magnitude"),
-                def(Hamming.class, Hamming::new, "v_hamming") } };
+                def(Hamming.class, Hamming::new, "v_hamming"),
+                def(UrlEncode.class, UrlEncode::new, "url_encode") } };
     }
 
     public EsqlFunctionRegistry snapshotRegistry() {