feat(ottl): Add a new ottl trim function that trims leading and trailing whitespace from a string (open-telemetry#36400)

#### Description

A field test exists in an event, which contains the string " this is a
test ".

I would like to be able to transform this using an ottl function trim,
that I would define as trim(attribute["test"]), which would trim this
down to "this is a test".

- Trim(" this is a test ") results in `this is a test`

Link to the issue -
open-telemetry#34100

---------

Co-authored-by: Tyler Helmuth <[email protected]>
Co-authored-by: Evan Bradley <[email protected]>

Author: 3 people

.chloggen/ottl-trim-function.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: ottl
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add a new ottl trim function that trims leading and trailing characters from a string (default- whitespace).
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [34100]
+
+# (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/ottlfuncs/README.md

@@ -1792,9 +1792,21 @@ The `Split` Converter separates a string by the delimiter, and returns an array
 
 If the `target` is not a string or does not exist, the `Split` Converter will return an error.
 
+### Trim
+
+```Trim(target, Optional[replacement])```
+
+The `Trim` Converter removes the leading and trailing character (default: a space character).
+
+If the `target` is not a string or does not exist, the `Trim` Converter will return an error.
+
+`target` is a string.
+`replacement` is an optional string representing the character to replace with (default: a space character).
+
 Examples:
 
-- `Split("A|B|C", "|")`
+- `Trim(" this is a test ", " ")`
+- `Trim("!!this is a test!!", "!!")`
 
 ### String
 

pkg/ottl/ottlfuncs/func_trim.go

@@ -0,0 +1,45 @@
+// 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 TrimArguments[K any] struct {
+	Target      ottl.StringGetter[K]
+	Replacement ottl.Optional[string]
+}
+
+func NewTrimFactory[K any]() ottl.Factory[K] {
+	return ottl.NewFactory("Trim", &TrimArguments[K]{}, createTrimFunction[K])
+}
+
+func createTrimFunction[K any](_ ottl.FunctionContext, oArgs ottl.Arguments) (ottl.ExprFunc[K], error) {
+	args, ok := oArgs.(*TrimArguments[K])
+
+	if !ok {
+		return nil, fmt.Errorf("TrimFactory args must be of type *TrimArguments[K]")
+	}
+
+	return trim(args.Target, args.Replacement), nil
+}
+
+func trim[K any](target ottl.StringGetter[K], replacement ottl.Optional[string]) ottl.ExprFunc[K] {
+	replacementString := " "
+	if !replacement.IsEmpty() {
+		replacementString = replacement.Get()
+	}
+	return func(ctx context.Context, tCtx K) (any, error) {
+		val, err := target.Get(ctx, tCtx)
+		if err != nil {
+			return nil, err
+		}
+		return strings.Trim(val, replacementString), nil
+	}
+}

pkg/ottl/ottlfuncs/func_trim_test.go

@@ -0,0 +1,80 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package ottlfuncs
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl"
+)
+
+func Test_trim(t *testing.T) {
+	tests := []struct {
+		name        string
+		target      ottl.StringGetter[any]
+		replacement ottl.Optional[string]
+		expected    any
+		shouldError bool
+	}{
+		{
+			name: "trim string",
+			target: &ottl.StandardStringGetter[any]{
+				Getter: func(_ context.Context, _ any) (any, error) {
+					return " this is a test ", nil
+				},
+			},
+			replacement: ottl.NewTestingOptional[string](" "),
+			expected:    "this is a test",
+			shouldError: false,
+		},
+		{
+			name: "trim empty string",
+			target: &ottl.StandardStringGetter[any]{
+				Getter: func(_ context.Context, _ any) (any, error) {
+					return "", nil
+				},
+			},
+			replacement: ottl.NewTestingOptional[string](" "),
+			expected:    "",
+			shouldError: false,
+		},
+		{
+			name: "No replacement string",
+			target: &ottl.StandardStringGetter[any]{
+				Getter: func(_ context.Context, _ any) (any, error) {
+					return " this is a test ", nil
+				},
+			},
+			replacement: ottl.Optional[string]{},
+			expected:    "this is a test",
+			shouldError: false,
+		},
+		{
+			name: "Set replacement string to \"\"",
+			target: &ottl.StandardStringGetter[any]{
+				Getter: func(_ context.Context, _ any) (any, error) {
+					return " this is a test ", nil
+				},
+			},
+			replacement: ottl.NewTestingOptional[string](""),
+			expected:    " this is a test ",
+			shouldError: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			exprFunc := trim(tt.target, tt.replacement)
+			result, err := exprFunc(nil, nil)
+			if tt.shouldError {
+				assert.Error(t, err)
+				return
+			}
+			assert.NoError(t, err)
+			assert.Equal(t, tt.expected, result)
+		})
+	}
+}

pkg/ottl/ottlfuncs/functions.go

@@ -87,6 +87,7 @@ func converters[K any]() []ottl.Factory[K] {
 		NewStringFactory[K](),
 		NewSubstringFactory[K](),
 		NewTimeFactory[K](),
+		NewTrimFactory[K](),
 		NewToKeyValueStringFactory[K](),
 		NewTruncateTimeFactory[K](),
 		NewTraceIDFactory[K](),