Added:

- Initial implementation of a user defined function.
- TCK tests for user defined functions.
- Instructions on using user defined functions in README file.

Signed-off-by: Dimitar Georgievski <dgeorgievski@gmail.com>

sql/v2/README.md

@@ -18,6 +18,54 @@ expression, err := cesqlparser.Parse("subject = 'Hello world'")
 res, err := expression.Evaluate(event)
 ```
 
+Add a user defined function
+```go
+import (
+    cesql "github.com/cloudevents/sdk-go/sql/v2"
+    cefn "github.com/cloudevents/sdk-go/sql/v2/function"
+    cesqlparser "github.com/cloudevents/sdk-go/sql/v2/parser"
+    ceruntime "github.com/cloudevents/sdk-go/sql/v2/runtime"
+    cloudevents "github.com/cloudevents/sdk-go/v2"
+)
+
+// Create a test event
+event := cloudevents.NewEvent()
+event.SetID("aaaa-bbbb-dddd")
+event.SetSource("https://my-source")
+event.SetType("dev.tekton.event")
+
+// Create and add a new user defined function
+var HasPrefixFunction cesql.Function = cefn.NewFunction(
+    "HASPREFIX",
+    []cesql.Type{cesql.StringType, cesql.StringType},
+    nil,
+    func(event cloudevents.Event, i []interface{}) (interface{}, error) {
+        str := i[0].(string)
+        prefix := i[1].(string)
+
+        return strings.HasPrefix(str, prefix), nil
+    },
+)
+
+err := ceruntime.AddFunction(HasPrefixFunction)
+
+// parse the expression 
+expression, err := cesqlparser.Parse("HASPREFIX(type, 'dev.tekton.event')")
+	if err != nil {
+		fmt.Println("parser err: ", err)
+		os.Exit(1)
+	}
+
+// Evalute the expression with the test event
+res, err := expression.Evaluate(event)
+
+if res.(bool) {
+    fmt.Println("Event type has the prefix")
+} else {
+    fmt.Println("Event type doesn't have the prefix")
+}
+```
+
 ## Development guide
 
 To regenerate the parser, make sure you have [ANTLR4 installed](https://github.com/antlr/antlr4/blob/master/doc/getting-started.md) and then run:

sql/v2/function/function.go

@@ -10,11 +10,13 @@ import (
 	cloudevents "github.com/cloudevents/sdk-go/v2"
 )
 
+type FuncType func(cloudevents.Event, []interface{}) (interface{}, error)
+
 type function struct {
 	name         string
 	fixedArgs    []cesql.Type
 	variadicArgs *cesql.Type
-	fn           func(cloudevents.Event, []interface{}) (interface{}, error)
+	fn           FuncType
 }
 
 func (f function) Name() string {
@@ -39,3 +41,15 @@ func (f function) ArgType(index int) *cesql.Type {
 func (f function) Run(event cloudevents.Event, arguments []interface{}) (interface{}, error) {
 	return f.fn(event, arguments)
 }
+
+func NewFunction(name string,
+	fixedargs []cesql.Type,
+	variadicArgs *cesql.Type,
+	fn FuncType) cesql.Function {
+	return function{
+		name:         name,
+		fixedArgs:    fixedargs,
+		variadicArgs: variadicArgs,
+		fn:           fn,
+	}
+}

sql/v2/runtime/functions_resolver.go

@@ -58,6 +58,11 @@ func (table functionTable) AddFunction(function cesql.Function) error {
 	}
 }
 
+// Adds user defined function
+func AddFunction(fn cesql.Function) error {
+	return globalFunctionTable.AddFunction(fn)
+}
+
 func (table functionTable) ResolveFunction(name string, args int) cesql.Function {
 	item := table[strings.ToUpper(name)]
 	if item == nil {

sql/v2/runtime/functions_resolver_test.go

@@ -0,0 +1,70 @@
+/*
+ Copyright 2021 The CloudEvents Authors
+ SPDX-License-Identifier: Apache-2.0
+*/
+
+package runtime
+
+import (
+	"os"
+	"strings"
+	"testing"
+
+	cesql "github.com/cloudevents/sdk-go/sql/v2"
+	"github.com/cloudevents/sdk-go/sql/v2/function"
+	cloudevents "github.com/cloudevents/sdk-go/v2"
+)
+
+var HasPrefixCustomFunction cesql.Function
+
+func TestMain(m *testing.M) {
+	HasPrefixCustomFunction = function.NewFunction(
+		"HASPREFIX",
+		[]cesql.Type{cesql.StringType, cesql.StringType},
+		nil,
+		func(event cloudevents.Event, i []interface{}) (interface{}, error) {
+			str := i[0].(string)
+			prefix := i[1].(string)
+
+			return strings.HasPrefix(str, prefix), nil
+		},
+	)
+	os.Exit(m.Run())
+}
+
+func Test_functionTable_AddFunction(t *testing.T) {
+
+	type args struct {
+		function cesql.Function
+	}
+	tests := []struct {
+		name    string
+		table   functionTable
+		args    args
+		wantErr bool
+	}{
+		{
+			name:  "Add custom fixedArgs func",
+			table: globalFunctionTable,
+			args: args{
+				function: HasPrefixCustomFunction,
+			},
+			wantErr: false,
+		},
+		{
+			name:  "Fail add custom fixedArgs func if it exists",
+			table: globalFunctionTable,
+			args: args{
+				function: HasPrefixCustomFunction,
+			},
+			wantErr: true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if err := tt.table.AddFunction(tt.args.function); (err != nil) != tt.wantErr {
+				t.Errorf("functionTable.AddFunction() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}

sql/v2/test/tck/user_defined_functions.yaml

@@ -0,0 +1,27 @@
+name: User defined functions
+tests:
+  - name: HASPREFIX (1)
+    expression: "HASPREFIX('abcdef', 'ab')"
+    result: true
+  - name: HASPREFIX (2)
+    expression: "HASPREFIX('abcdef', 'abcdef')"
+    result: true  
+  - name: HASPREFIX (3)
+    expression: "HASPREFIX('abcdef', '')"
+    result: true  
+  - name: HASPREFIX (4)
+    expression: "HASPREFIX('abcdef', 'gh')"
+    result: false  
+  - name: HASPREFIX (5)
+    expression: "HASPREFIX('abcdef', 'abcdefg')"
+    result: false
+
+  - name: KONKAT (1)
+    expression: "KONKAT('a', 'b', 'c')"
+    result: abc
+  - name: KONKAT (2)
+    expression: "KONKAT()"
+    result: ""
+  - name: KONKAT (3)
+    expression: "KONKAT('a')"
+    result: "a"

sql/v2/test/tck_test.go

@@ -10,12 +10,16 @@ import (
 	"os"
 	"path"
 	"runtime"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/require"
 	"sigs.k8s.io/yaml"
 
+	cesql "github.com/cloudevents/sdk-go/sql/v2"
+	"github.com/cloudevents/sdk-go/sql/v2/function"
 	"github.com/cloudevents/sdk-go/sql/v2/parser"
+	ceruntime "github.com/cloudevents/sdk-go/sql/v2/runtime"
 	cloudevents "github.com/cloudevents/sdk-go/v2"
 	"github.com/cloudevents/sdk-go/v2/binding/spec"
 	"github.com/cloudevents/sdk-go/v2/event"
@@ -41,6 +45,33 @@ var TCKFileNames = []string{
 	"string_builtin_functions",
 	"sub_expression",
 	"subscriptions_api_recreations",
+	"user_defined_functions",
+}
+
+var TCKUserDefinedFunctions = []cesql.Function{
+	function.NewFunction(
+		"HASPREFIX",
+		[]cesql.Type{cesql.StringType, cesql.StringType},
+		nil,
+		func(event cloudevents.Event, i []interface{}) (interface{}, error) {
+			str := i[0].(string)
+			prefix := i[1].(string)
+
+			return strings.HasPrefix(str, prefix), nil
+		},
+	),
+	function.NewFunction(
+		"KONKAT",
+		[]cesql.Type{},
+		cesql.TypePtr(cesql.StringType),
+		func(event cloudevents.Event, i []interface{}) (interface{}, error) {
+			var sb strings.Builder
+			for _, v := range i {
+				sb.WriteString(v.(string))
+			}
+			return sb.String(), nil
+		},
+	),
 }
 
 type ErrorType string
@@ -70,6 +101,13 @@ type TckTestCase struct {
 	EventOverrides map[string]interface{} `json:"eventOverrides"`
 }
 
+func TestMain(m *testing.M) {
+	for _, f := range TCKUserDefinedFunctions {
+		ceruntime.AddFunction(f)
+	}
+	os.Exit(m.Run())
+}
+
 func (tc TckTestCase) InputEvent(t *testing.T) cloudevents.Event {
 	var inputEvent cloudevents.Event
 	if tc.Event != nil {