[pkg/ottl] Support for append

.chloggen/ottl_append.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: Introducing `append` function for appending items into an existing array
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [32141]
+
+# (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: [user]

pkg/ottl/e2e/e2e_test.go

@@ -229,6 +229,45 @@ func Test_e2e_editors(t *testing.T) {
 				tCtx.GetLogRecord().Attributes().PutStr("total.string", "1")
 			},
 		},
+		{
+			statement: `append(attributes["foo"]["slice"], "sample_value")`,
+			want: func(tCtx ottllog.TransformContext) {
+				v, _ := tCtx.GetLogRecord().Attributes().Get("foo")
+				sv, _ := v.Map().Get("slice")
+				s := sv.Slice()
+				s.AppendEmpty().SetStr("sample_value")
+
+			},
+		},
+		{
+			statement: `append(attributes["foo"]["flags"], "sample_value")`,
+			want: func(tCtx ottllog.TransformContext) {
+				v, _ := tCtx.GetLogRecord().Attributes().Get("foo")
+				s := v.Map().PutEmptySlice("flags")
+				s.AppendEmpty().SetStr("pass")
+				s.AppendEmpty().SetStr("sample_value")
+
+			},
+		},
+		{
+			statement: `append(attributes["foo"]["slice"], values=[5,6])`,
+			want: func(tCtx ottllog.TransformContext) {
+				v, _ := tCtx.GetLogRecord().Attributes().Get("foo")
+				sv, _ := v.Map().Get("slice")
+				s := sv.Slice()
+				s.AppendEmpty().SetInt(5)
+				s.AppendEmpty().SetInt(6)
+			},
+		},
+		{
+			statement: `append(attributes["foo"]["new_slice"], values=[5,6])`,
+			want: func(tCtx ottllog.TransformContext) {
+				v, _ := tCtx.GetLogRecord().Attributes().Get("foo")
+				s := v.Map().PutEmptySlice("new_slice")
+				s.AppendEmpty().SetInt(5)
+				s.AppendEmpty().SetInt(6)
+			},
+		},
 	}
 
 	for _, tt := range tests {

pkg/ottl/ottlfuncs/README.md

@@ -45,6 +45,7 @@ Editors:
 
 Available Editors:
 
+- [append](#append)
 - [delete_key](#delete_key)
 - [delete_matching_keys](#delete_matching_keys)
 - [flatten](#flatten)
@@ -58,6 +59,19 @@ Available Editors:
 - [set](#set)
 - [truncate_all](#truncate_all)
 
+### append
+
+`append(target, Optional[value], Optional[values])`
+
+The `append` function appens single or multiple string values to target. 
+`append` converts scalar values into an array if the field exists but is not an array and creates an array containing the provided values if the field doesn’t exist.
+
+Resulting field is always of type `pcommon.Slice` keeping types of existing values appending values as set not performing any conversions.
+
+  - `append(attributes["tags"], "prod")`
+  - `append(attributes["tags"], values = ["staging", "staging:east"])`
+  - `append(attributes["tags_copy"], attributes["tags"])`
+
 ### delete_key
 
 `delete_key(target, key)`

pkg/ottl/ottlfuncs/func_append.go

@@ -0,0 +1,134 @@
+// 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"
+
+	"go.opentelemetry.io/collector/pdata/pcommon"
+
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl"
+)
+
+type AppendArguments[K any] struct {
+	Target ottl.GetSetter[K]
+	Value  ottl.Optional[ottl.Getter[K]]
+	Values ottl.Optional[[]ottl.Getter[K]]
+}
+
+func NewAppendFactory[K any]() ottl.Factory[K] {
+	return ottl.NewFactory("append", &AppendArguments[K]{}, createAppendFunction[K])
+}
+func createAppendFunction[K any](_ ottl.FunctionContext, oArgs ottl.Arguments) (ottl.ExprFunc[K], error) {
+	args, ok := oArgs.(*AppendArguments[K])
+	if !ok {
+		return nil, fmt.Errorf("AppendFactory args must be of type *Appendrguments[K]")
+	}
+
+	return appendTo(args.Target, args.Value, args.Values)
+}
+
+func appendTo[K any](target ottl.GetSetter[K], value ottl.Optional[ottl.Getter[K]], values ottl.Optional[[]ottl.Getter[K]]) (ottl.ExprFunc[K], error) {
+	if value.IsEmpty() && values.IsEmpty() {
+		return nil, fmt.Errorf("at least one of the optional arguments must be provided be provided")
+	}
+
+	return func(ctx context.Context, tCtx K) (any, error) {
+		t, err := target.Get(ctx, tCtx)
+		if err != nil {
+			return nil, err
+		}
+
+		// init res with target values
+		var res []any
+
+		if t != nil {
+			switch targetType := t.(type) {
+			case pcommon.Slice:
+				res = append(res, targetType.AsRaw()...)
+			case pcommon.Value:
+				switch targetType.Type() {
+				case pcommon.ValueTypeEmpty:
+					res = append(res, targetType.Str())
+				case pcommon.ValueTypeStr:
+					res = append(res, targetType.Str())
+				case pcommon.ValueTypeInt:
+					res = append(res, targetType.Int())
+				case pcommon.ValueTypeDouble:
+					res = append(res, targetType.Double())
+				case pcommon.ValueTypeBool:
+					res = append(res, targetType.Bool())
+				case pcommon.ValueTypeSlice:
+					res = append(res, targetType.Slice().AsRaw()...)
+				default:
+					return nil, fmt.Errorf("unsupported type of target field")
+				}
+
+			case []string:
+				res = appendMultiple(res, targetType)
+			case []any:
+				res = append(res, targetType...)
+			case []int64:
+				res = appendMultiple(res, targetType)
+			case []bool:
+				res = appendMultiple(res, targetType)
+			case []float64:
+				res = appendMultiple(res, targetType)
+
+			case string:
+				res = append(res, targetType)
+			case int64:
+				res = append(res, targetType)
+			case bool:
+				res = append(res, targetType)
+			case float64:
+				res = append(res, targetType)
+			case any:
+				res = append(res, targetType)
+			default:
+				return nil, fmt.Errorf("unsupported type of target field")
+			}
+		}
+
+		appendGetterFn := func(g ottl.Getter[K]) error {
+			v, err := g.Get(ctx, tCtx)
+			if err != nil {
+				return err
+			}
+			res = append(res, v)
+			return nil
+		}
+
+		if !value.IsEmpty() {
+			getter := value.Get()
+			if err := appendGetterFn(getter); err != nil {
+				return nil, err
+			}
+		}
+		if !values.IsEmpty() {
+			getters := values.Get()
+			for _, g := range getters {
+				if err := appendGetterFn(g); err != nil {
+					return nil, err
+				}
+			}
+		}
+
+		// retype []any to Slice, having []any sometimes misbehaves and nils pcommon.Value
+		resSlice := pcommon.NewSlice()
+		if err := resSlice.FromRaw(res); err != nil {
+			return nil, err
+		}
+
+		return nil, target.Set(ctx, tCtx, resSlice)
+	}, nil
+}
+
+func appendMultiple[K any](target []any, values []K) []any {
+	for _, v := range values {
+		target = append(target, v)
+	}
+	return target
+}