[pkg/ottl] Add new ottl/Unix function (open-telemetry#31556)

Solves open-telemetry#27868.

---------

Signed-off-by: Israel Blancas <iblancasa@gmail.com>
Co-authored-by: Tyler Helmuth <12352919+TylerHelmuth@users.noreply.github.com>

.chloggen/27868-add-unix-function-ottl.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 new Unix function to convert from epoch timestamp to time.Time"
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [27868]
+
+# (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

@@ -413,6 +413,7 @@ Available Converters:
 - [Time](#time)
 - [TraceID](#traceid)
 - [TruncateTime](#truncatetime)
+- [Unix](#unix)
 - [UnixMicro](#unixmicro)
 - [UnixMilli](#unixmilli)
 - [UnixNano](#unixnano)
@@ -1121,6 +1122,21 @@ Examples:
 
 - `TruncateTime(start_time, Duration("1s"))`
 
+### Unix
+
+`Unix(seconds, Optional[nanoseconds])`
+
+The `Unix` Converter returns an epoch timestamp as a Unix time. Similar to [Golang's Unix function](https://pkg.go.dev/time#Unix).
+
+`seconds` is `int64`. If `seconds` is another type an error is returned.
+`nanoseconds` is `int64`. It is optional and its default value is 0. If `nanoseconds` is another type an error is returned.
+
+The returned type is `time.Time`.
+
+Examples:
+
+- `Unix(1672527600)`
+
 ### UnixMicro
 
 `UnixMicro(value)`

pkg/ottl/ottlfuncs/func_unix.go

@@ -0,0 +1,50 @@
+// 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"
+	"time"
+
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl"
+)
+
+type UnixArguments[K any] struct {
+	Seconds     ottl.IntGetter[K]
+	Nanoseconds ottl.Optional[ottl.IntGetter[K]]
+}
+
+func NewUnixFactory[K any]() ottl.Factory[K] {
+	return ottl.NewFactory("Unix", &UnixArguments[K]{}, createUnixFunction[K])
+}
+func createUnixFunction[K any](_ ottl.FunctionContext, oArgs ottl.Arguments) (ottl.ExprFunc[K], error) {
+	args, ok := oArgs.(*UnixArguments[K])
+
+	if !ok {
+		return nil, fmt.Errorf("UnixFactory args must be of type *UnixArguments[K]")
+	}
+
+	return Unix(args.Seconds, args.Nanoseconds)
+}
+
+func Unix[K any](seconds ottl.IntGetter[K], nanoseconds ottl.Optional[ottl.IntGetter[K]]) (ottl.ExprFunc[K], error) {
+	return func(ctx context.Context, tCtx K) (any, error) {
+		sec, err := seconds.Get(ctx, tCtx)
+		if err != nil {
+			return nil, err
+		}
+
+		var nsec int64
+
+		if !nanoseconds.IsEmpty() {
+			nsec, err = nanoseconds.Get().Get(ctx, tCtx)
+			if err != nil {
+				return nil, err
+			}
+		}
+
+		return time.Unix(sec, nsec), nil
+	}, nil
+}

pkg/ottl/ottlfuncs/func_unix_test.go

@@ -0,0 +1,44 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package ottlfuncs
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl"
+)
+
+func Test_Unix(t *testing.T) {
+	tests := []struct {
+		name        string
+		seconds     ottl.IntGetter[any]
+		nanoseconds ottl.Optional[ottl.IntGetter[any]]
+		expected    int64
+	}{
+		{
+			name: "January 1, 2023",
+			seconds: &ottl.StandardIntGetter[any]{
+				Getter: func(ctx context.Context, tCtx any) (any, error) {
+					return int64(1672527600), nil
+				},
+			},
+			nanoseconds: ottl.Optional[ottl.IntGetter[any]]{},
+			expected:    int64(1672527600),
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			exprFunc, err := Unix(tt.seconds, tt.nanoseconds)
+			assert.NoError(t, err)
+			result, err := exprFunc(nil, nil)
+			assert.NoError(t, err)
+			want := time.Unix(tt.expected, 0)
+			assert.Equal(t, want, result)
+		})
+	}
+}

pkg/ottl/ottlfuncs/functions.go

@@ -71,6 +71,7 @@ func converters[K any]() []ottl.Factory[K] {
 		NewTimeFactory[K](),
 		NewTruncateTimeFactory[K](),
 		NewTraceIDFactory[K](),
+		NewUnixFactory[K](),
 		NewUnixMicroFactory[K](),
 		NewUnixMilliFactory[K](),
 		NewUnixNanoFactory[K](),