[pkg/ottl] Introduce ToLowerCase() converter function

Signed-off-by: odubajDT <ondrej.dubaj@dynatrace.com>

.chloggen/convert-case-lower.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: pkg/ottl
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: "Introduce ToLowerCase() converter function"
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [32942]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

pkg/ottl/e2e/e2e_test.go

@@ -447,6 +447,12 @@ func Test_e2e_converters(t *testing.T) {
 				tCtx.GetLogRecord().Attributes().PutStr("test", "FooBar")
 			},
 		},
+		{
+			statement: `set(attributes["test"], ToLowerCase("PASS"))`,
+			want: func(tCtx ottllog.TransformContext) {
+				tCtx.GetLogRecord().Attributes().PutStr("test", "pass")
+			},
+		},
 		{
 			statement: `set(attributes["test"], ConvertAttributesToElementsXML("<Log id=\"1\"><Message>This is a log message!</Message></Log>"))`,
 			want: func(tCtx ottllog.TransformContext) {

pkg/ottl/ottlfuncs/README.md

@@ -467,6 +467,7 @@ Available Converters:
 - [Substring](#substring)
 - [Time](#time)
 - [ToKeyValueString](#tokeyvaluestring)
+- [ToLowerCase](#tolowercase)
 - [TraceID](#traceid)
 - [TruncateTime](#truncatetime)
 - [Unix](#unix)
@@ -2056,6 +2057,18 @@ Examples:
 - `ToKeyValueString(body)`
 - `ToKeyValueString(body, ":", ",", true)`
 
+### ToLowerCase
+
+`ToLowerCase(target)`
+
+The `ToLowerCase` Converter converts the `target` string into lower case.
+
+`target` is a string.
+
+Examples:
+
+- `ToLowerCase(metric.name)`
+
 ### TraceID
 
 `TraceID(bytes)`

pkg/ottl/ottlfuncs/func_to_lower_case.go

@@ -0,0 +1,46 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package ottlfuncs // import "github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl/ottlfuncs"
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl"
+)
+
+type ToLowerCaseArguments[K any] struct {
+	Target ottl.StringGetter[K]
+}
+
+func NewToLowerCaseFactory[K any]() ottl.Factory[K] {
+	return ottl.NewFactory("ToLowerCase", &ToLowerCaseArguments[K]{}, createToLowerCaseFunction[K])
+}
+
+func createToLowerCaseFunction[K any](_ ottl.FunctionContext, oArgs ottl.Arguments) (ottl.ExprFunc[K], error) {
+	args, ok := oArgs.(*ToLowerCaseArguments[K])
+
+	if !ok {
+		return nil, fmt.Errorf("ToLowerCaseFactory args must be of type *ToLowerCaseArguments[K]")
+	}
+
+	return toLowerCase(args.Target)
+}
+
+//nolint:unparam
+func toLowerCase[K any](target ottl.StringGetter[K]) (ottl.ExprFunc[K], error) {
+	return func(ctx context.Context, tCtx K) (any, error) {
+		val, err := target.Get(ctx, tCtx)
+		if err != nil {
+			return nil, err
+		}
+
+		if val == "" {
+			return val, nil
+		}
+
+		return strings.ToLower(val), nil
+	}, nil
+}

pkg/ottl/ottlfuncs/func_to_lower_case_test.go

@@ -0,0 +1,103 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package ottlfuncs
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl"
+)
+
+func Test_toLowerCase(t *testing.T) {
+	tests := []struct {
+		name     string
+		target   ottl.StringGetter[any]
+		expected any
+	}{
+		{
+			name: "simple",
+			target: &ottl.StandardStringGetter[any]{
+				Getter: func(_ context.Context, _ any) (any, error) {
+					return "SIMPLE", nil
+				},
+			},
+			expected: "simple",
+		},
+		{
+			name: "already lower",
+			target: &ottl.StandardStringGetter[any]{
+				Getter: func(_ context.Context, _ any) (any, error) {
+					return "simple", nil
+				},
+			},
+			expected: "simple",
+		},
+		{
+			name: "complex",
+			target: &ottl.StandardStringGetter[any]{
+				Getter: func(_ context.Context, _ any) (any, error) {
+					return "complex_SET-of.WORDS1234", nil
+				},
+			},
+			expected: "complex_set-of.words1234",
+		},
+		{
+			name: "empty string",
+			target: &ottl.StandardStringGetter[any]{
+				Getter: func(_ context.Context, _ any) (any, error) {
+					return "", nil
+				},
+			},
+			expected: "",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			exprFunc, err := toLowerCase(tt.target)
+			assert.NoError(t, err)
+			result, err := exprFunc(nil, nil)
+			assert.NoError(t, err)
+			assert.Equal(t, tt.expected, result)
+		})
+	}
+}
+
+func Test_toLowerCaseRuntimeError(t *testing.T) {
+	tests := []struct {
+		name          string
+		target        ottl.StringGetter[any]
+		expectedError string
+	}{
+		{
+			name: "non-string",
+			target: &ottl.StandardStringGetter[any]{
+				Getter: func(_ context.Context, _ any) (any, error) {
+					return 10, nil
+				},
+			},
+			expectedError: "expected string but got int",
+		},
+		{
+			name: "nil",
+			target: &ottl.StandardStringGetter[any]{
+				Getter: func(_ context.Context, _ any) (any, error) {
+					return nil, nil
+				},
+			},
+			expectedError: "expected string but got nil",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			exprFunc, err := toLowerCase[any](tt.target)
+			require.NoError(t, err)
+			_, err = exprFunc(context.Background(), nil)
+			assert.ErrorContains(t, err, tt.expectedError)
+		})
+	}
+}

pkg/ottl/ottlfuncs/functions.go

@@ -92,6 +92,7 @@ func converters[K any]() []ottl.Factory[K] {
 		NewFormatTimeFactory[K](),
 		NewTrimFactory[K](),
 		NewToKeyValueStringFactory[K](),
+		NewToLowerCaseFactory[K](),
 		NewTruncateTimeFactory[K](),
 		NewTraceIDFactory[K](),
 		NewUnixFactory[K](),