Add split UDF func to ease certain string handling (#2039)

Summary: Add split UDF func to ease certain string handling

This is functionality that I'm planning to use for my upcoming Kubecon
demo/talk. For this use case, I want to access the individual fields of
the XFCC header just like the example in the UDF docstring.

Relevant Issues: N/A

Type of change: /kind feature

Test Plan: New tests pass

Changelog Message: Added `px.split` function to support parsing strings
that contain delimiters

---------

Signed-off-by: Dom Del Nano <[email protected]>

Author: ddelnano

src/carnot/funcs/builtins/json_ops.cc

@@ -31,6 +31,7 @@ void RegisterJSONOpsOrDie(udf::Registry* registry) {
   registry->RegisterOrDie<PluckAsInt64UDF>("pluck_int64");
   registry->RegisterOrDie<PluckAsFloat64UDF>("pluck_float64");
   registry->RegisterOrDie<PluckArrayUDF>("pluck_array");
+  registry->RegisterOrDie<SplitUDF>("split");
 
   // Up to 8 script args are supported for the _script_reference UDF, due to the lack of support for
   // variadic UDF arguments in the UDF registry today. We should clean this up if/when variadic UDF

src/carnot/funcs/builtins/json_ops.h

@@ -228,6 +228,42 @@ class PluckArrayUDF : public udf::ScalarUDF {
   }
 };
 
+class SplitUDF : public udf::ScalarUDF {
+ public:
+  StringValue Exec(FunctionContext*, StringValue in, StringValue delimiter) {
+    rapidjson::StringBuffer sb;
+    rapidjson::Writer<rapidjson::StringBuffer> writer(sb);
+    writer.StartArray();
+
+    for (absl::string_view part : absl::StrSplit(in.data(), delimiter.data())) {
+      writer.String(part.data(), part.size());
+    }
+
+    writer.EndArray();
+    return sb.GetString();
+  }
+
+  static udf::ScalarUDFDocBuilder Doc() {
+    return udf::ScalarUDFDocBuilder(
+               "Splits a string by a delimiter and a returns JSON encoded array of strings.")
+        .Details(
+            "This function splits a string by a delimiter and returns a JSON encoded array of "
+            "strings. The function is useful for splitting strings and then passing the result to "
+            "px.pluck_array in order to access individual values of a delimited string.")
+        .Example(R"doc(
+          | df = px.DataFrame('http_events', start_time='-5m')
+          | # Returns By=http://frontend.px.dev;URI=http://testclient.px.dev
+          | df.xfcc_hdr = px.pluck(df.req_headers, 'X-Forwarded-Client-Cert')
+          | df.xfcc_parts = px.split(df.xfcc_hdr, ';')
+          | df.by = px.pluck_array(df.xfcc_hdr, 0) # Returns "By=http://frontend.px.dev"
+          | df.uri = px.pluck_array(df.xfcc_hdr, 1) # Returns "URI=http://testclient.px.dev"
+      )doc")
+        .Arg("input_str", "The string to split.")
+        .Arg("delimiter", "The string value to split the input string.")
+        .Returns("A JSON encoded array of the split strings.");
+  }
+};
+
 /**
   DocString intentionally omitted, this is a non-public function.
   This function creates a custom deep link by creating a "script reference" from a label,

src/carnot/funcs/builtins/json_ops_test.cc

@@ -111,6 +111,16 @@ TEST(JSONOps, PluckArrayUDF_index_out_of_bound) {
   udf_tester.ForInput(kTestJSONArray, 3).Expect("");
 }
 
+TEST(JSONOps, SplitUDF_with_present_delimiter) {
+  auto udf_tester = udf::UDFTester<SplitUDF>();
+  udf_tester.ForInput("foo,bar,baz", ",").Expect(R"(["foo","bar","baz"])");
+}
+
+TEST(JSONOps, SplitUDF_with_missing_delimiter) {
+  auto udf_tester = udf::UDFTester<SplitUDF>();
+  udf_tester.ForInput("foo,bar,baz", ";").Expect(R"(["foo,bar,baz"])");
+}
+
 TEST(JSONOps, ScriptReferenceUDF_no_args) {
   auto udf_tester = udf::UDFTester<ScriptReferenceUDF<>>();
   auto res = udf_tester.ForInput("text", "px/script").Result();