[chore][pkg/stanza]: add new fileset package (open-telemetry#30550)

**Description:** Following up from
open-telemetry#30219.
Adding a new package for fileset.

**Link to tracking Issue:**
[29273](open-telemetry#29273 (comment))

**Testing:** <Describe what testing was performed and which tests were
added.>

**Documentation:** <Describe the documentation added.>

pkg/stanza/fileconsumer/internal/fileset/fileset.go

@@ -0,0 +1,81 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package fileset // import "github.com/open-telemetry/opentelemetry-collector-contrib/pkg/stanza/fileconsumer/internal/fileset"
+
+import (
+	"errors"
+
+	"golang.org/x/exp/slices"
+
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/stanza/fileconsumer/internal/fingerprint"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/stanza/fileconsumer/internal/reader"
+)
+
+var errFilesetEmpty = errors.New("pop() on empty Fileset")
+
+var (
+	_ Matchable = (*reader.Reader)(nil)
+	_ Matchable = (*reader.Metadata)(nil)
+)
+
+type Matchable interface {
+	GetFingerprint() *fingerprint.Fingerprint
+}
+
+type Fileset[T Matchable] struct {
+	readers []T
+}
+
+func New[T Matchable](capacity int) *Fileset[T] {
+	return &Fileset[T]{readers: make([]T, 0, capacity)}
+}
+
+func (set *Fileset[T]) Len() int {
+	return len(set.readers)
+}
+
+func (set *Fileset[T]) Get() []T {
+	return set.readers
+}
+
+func (set *Fileset[T]) Pop() (T, error) {
+	// return first element from the array and remove it
+	var val T
+	if len(set.readers) == 0 {
+		return val, errFilesetEmpty
+	}
+	r := set.readers[0]
+	set.readers = slices.Delete(set.readers, 0, 1)
+	return r, nil
+}
+
+func (set *Fileset[T]) Add(readers ...T) {
+	// add open readers
+	set.readers = append(set.readers, readers...)
+}
+
+func (set *Fileset[T]) Clear() {
+	// clear the underlying readers
+	set.readers = make([]T, 0, cap(set.readers))
+}
+
+func (set *Fileset[T]) Reset(readers ...T) []T {
+	// empty the underlying set and return the old array
+	arr := make([]T, len(set.readers))
+	copy(arr, set.readers)
+	set.Clear()
+	set.readers = append(set.readers, readers...)
+	return arr
+}
+
+func (set *Fileset[T]) Match(fp *fingerprint.Fingerprint) T {
+	var val T
+	for idx, r := range set.readers {
+		if fp.StartsWith(r.GetFingerprint()) {
+			set.readers = append(set.readers[:idx], set.readers[idx+1:]...)
+			return r
+		}
+	}
+	return val
+}

pkg/stanza/fileconsumer/internal/fileset/fileset_test.go

@@ -0,0 +1,123 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package fileset // import "github.com/open-telemetry/opentelemetry-collector-contrib/pkg/stanza/fileconsumer/internal/fileset"
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/stanza/fileconsumer/internal/fingerprint"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/stanza/fileconsumer/internal/reader"
+)
+
+type test[T Matchable] struct {
+	name    string
+	fileset *Fileset[T]
+	ops     []func(t *testing.T, fileset *Fileset[T])
+}
+
+func (t *test[T]) init() {
+	t.fileset = New[T](10)
+}
+
+func push[T Matchable](ele ...T) func(t *testing.T, fileset *Fileset[T]) {
+	return func(t *testing.T, fileset *Fileset[T]) {
+		pr := fileset.Len()
+		fileset.Add(ele...)
+		require.Equal(t, pr+len(ele), fileset.Len())
+	}
+}
+
+func pop[T Matchable](expectedErr error, expectedElemet T) func(t *testing.T, fileset *Fileset[T]) {
+	return func(t *testing.T, fileset *Fileset[T]) {
+		el, err := fileset.Pop()
+		if expectedErr == nil {
+			require.NoError(t, err)
+			require.Equal(t, el, expectedElemet)
+		} else {
+			require.ErrorIs(t, err, expectedErr)
+		}
+	}
+}
+
+func reset[T Matchable](ele ...T) func(t *testing.T, fileset *Fileset[T]) {
+	return func(t *testing.T, fileset *Fileset[T]) {
+		fileset.Reset(ele...)
+		require.Equal(t, fileset.Len(), len(ele))
+	}
+}
+
+func match[T Matchable](ele T, expect bool) func(t *testing.T, fileset *Fileset[T]) {
+	return func(t *testing.T, fileset *Fileset[T]) {
+		pr := fileset.Len()
+		r := fileset.Match(ele.GetFingerprint())
+		if expect {
+			require.NotNil(t, r)
+			require.Equal(t, pr-1, fileset.Len())
+		} else {
+			require.Nil(t, r)
+			require.Equal(t, pr, fileset.Len())
+		}
+
+	}
+}
+
+func newFingerprint(bytes []byte) *fingerprint.Fingerprint {
+	return &fingerprint.Fingerprint{
+		FirstBytes: bytes,
+	}
+}
+func newMetadata(bytes []byte) *reader.Metadata {
+	return &reader.Metadata{
+		Fingerprint: newFingerprint(bytes),
+	}
+}
+
+func newReader(bytes []byte) *reader.Reader {
+	return &reader.Reader{
+		Metadata: newMetadata(bytes),
+	}
+}
+
+func TestFilesetReader(t *testing.T) {
+	testCases := []test[*reader.Reader]{
+		{
+			name: "test_match_push_reset",
+			ops: []func(t *testing.T, fileset *Fileset[*reader.Reader]){
+				push(newReader([]byte("ABCDEF")), newReader([]byte("QWERT"))),
+
+				// match() removes the matched item and returns it
+				match(newReader([]byte("ABCDEFGHI")), true),
+				match(newReader([]byte("ABCEFGHI")), false),
+
+				reset(newReader([]byte("XYZ"))),
+				match(newReader([]byte("ABCDEF")), false),
+				match(newReader([]byte("QWERT")), false),
+				match(newReader([]byte("XYZabc")), true),
+			},
+		},
+		{
+			name: "test_pop",
+			ops: []func(t *testing.T, fileset *Fileset[*reader.Reader]){
+				push(newReader([]byte("ABCDEF")), newReader([]byte("QWERT"))),
+				pop(nil, newReader([]byte("ABCDEF"))),
+				pop(nil, newReader([]byte("QWERT"))),
+				pop(errFilesetEmpty, newReader([]byte(""))),
+
+				reset(newReader([]byte("XYZ"))),
+				pop(nil, newReader([]byte("XYZ"))),
+				pop(errFilesetEmpty, newReader([]byte(""))),
+			},
+		},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			tc.init()
+			for _, op := range tc.ops {
+				op(t, tc.fileset)
+			}
+		})
+	}
+}

pkg/stanza/fileconsumer/internal/reader/reader.go

@@ -179,3 +179,7 @@ func (r *Reader) Validate() bool {
 	}
 	return false
 }
+
+func (m Metadata) GetFingerprint() *fingerprint.Fingerprint {
+	return m.Fingerprint
+}

pkg/stanza/go.mod

@@ -25,6 +25,7 @@ require (
 	go.uber.org/goleak v1.3.0
 	go.uber.org/multierr v1.11.0
 	go.uber.org/zap v1.26.0
+	golang.org/x/exp v0.0.0-20230711023510-fffb14384f22
 	golang.org/x/sys v0.16.0
 	golang.org/x/text v0.14.0
 	gonum.org/v1/gonum v0.14.0