ESQL: Add url_decode function (#133494)

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

@@ -2587,3 +2587,73 @@ ROW u = ["hello elastic!", "a+b-c%d", "", "!#$&'()*+,/:;=?@[]"] | EVAL u = URL_E
 u:keyword
 ["hello+elastic%21", "a%2Bb-c%25d", "", "%21%23%24%26%27%28%29*%2B%2C%2F%3A%3B%3D%3F%40%5B%5D"]
 ;
+
+url_decode sample for docs
+required_capability: url_decode
+
+// tag::url_decode[]
+ROW u = "https%3A%2F%2Fwww.example.com%2Fpapers%3Fq%3Dinformation%2Bretrieval%26year%3D2024%26citations%3Dhigh" | EVAL u = URL_DECODE(u)
+// end::url_decode[]
+;
+
+// tag::url_decode-result[]
+u:keyword
+https://www.example.com/papers?q=information+retrieval&year=2024&citations=high
+// end::url_decode-result[]
+;
+
+url_decode mixed functions tests
+required_capability: url_decode
+
+FROM employees 
+| WHERE emp_no == 10001 
+| EVAL a = TRIM(URL_DECODE(first_name))
+| EVAL b = URL_DECODE(TO_LOWER(first_name))
+| KEEP a,b;
+
+a:keyword | b:keyword
+Georgi    | georgi 
+;
+
+url_decode mixed input tests
+required_capability: url_decode
+
+ROW u = "%21%23%24%26%27%28%29*%2B%2C%2F%3A%3B%3D%3F%40%5B%5D" | EVAL u = URL_DECODE(u);
+
+u:keyword
+"!#$&'()*+,/:;=?@[]"
+;
+
+combined url encode decode tests with table reads
+required_capability: url_encode
+required_capability: url_decode
+
+FROM employees 
+| SORT emp_no
+| LIMIT 10
+| EVAL name = URL_DECODE(URL_ENCODE(CONCAT(gender, " - ", first_name, "+", last_name, "; ", CONCAT("@", first_name, last_name))))
+| KEEP emp_no, name;
+
+emp_no:integer | name:keyword
+10001          | M - Georgi+Facello; @GeorgiFacello
+10002          | F - Bezalel+Simmel; @BezalelSimmel
+10003          | M - Parto+Bamford; @PartoBamford
+10004          | M - Chirstian+Koblick; @ChirstianKoblick
+10005          | M - Kyoichi+Maliniak; @KyoichiMaliniak
+10006          | F - Anneke+Preusig; @AnnekePreusig
+10007          | F - Tzvetan+Zielinski; @TzvetanZielinski
+10008          | M - Saniya+Kalloufi; @SaniyaKalloufi
+10009          | F - Sumant+Peac; @SumantPeac
+10010          | null
+;
+
+combined url encode decode tests with random strings
+required_capability: url_encode
+required_capability: url_decode
+
+ROW u = ["https://www.example.com/papers?q=information+retrieval&year=2024&citations=high", "", "!#$&'()+/:;=?@[]", "💨🔥🪨💧"] 
+| eval u = URL_DECODE(URL_ENCODE(u));
+
+u:keyword
+["https://www.example.com/papers?q=information+retrieval&year=2024&citations=high", "", "!#$&'()+/:;=?@[]", "💨🔥🪨💧"]
+;

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

@@ -1411,7 +1411,12 @@ public enum Cap {
         /**
          * URL encoding function.
          */
-        URL_ENCODE(Build.current().isSnapshot());
+        URL_ENCODE(Build.current().isSnapshot()),
+
+        /**
+         * URL decoding function.
+         */
+        URL_DECODE(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.UrlDecode;
 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;
@@ -225,6 +226,7 @@ public static List<NamedWriteableRegistry.Entry> unaryScalars() {
         entries.add(WildcardLikeList.ENTRY);
         entries.add(Delay.ENTRY);
         entries.add(UrlEncode.ENTRY);
+        entries.add(UrlDecode.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.UrlDecode;
 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;
@@ -517,7 +518,8 @@ private static FunctionDefinition[][] snapshotFunctions() {
                 def(L2Norm.class, L2Norm::new, "v_l2_norm"),
                 def(Magnitude.class, Magnitude::new, "v_magnitude"),
                 def(Hamming.class, Hamming::new, "v_hamming"),
-                def(UrlEncode.class, UrlEncode::new, "url_encode") } };
+                def(UrlEncode.class, UrlEncode::new, "url_encode"),
+                def(UrlDecode.class, UrlDecode::new, "url_decode") } };
     }
 
     public EsqlFunctionRegistry snapshotRegistry() {