[chore][fileconsumer] Extract internal header package (#24264)

This continues from #24036 by moving additional complexity into an
internal package.

Some files contain headers that are different than the rest of the file.
In such cases, we may need to extract file attributes that will be
applied to logs from that file.

pkg/stanza/fileconsumer/config.go

@@ -15,6 +15,8 @@ import (
 
 	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/stanza/fileconsumer/emit"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/stanza/fileconsumer/internal/fingerprint"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/stanza/fileconsumer/internal/header"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/stanza/operator"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/stanza/operator/helper"
 )
 
@@ -72,6 +74,11 @@ type Config struct {
 	Header                  *HeaderConfig         `mapstructure:"header,omitempty"`
 }
 
+type HeaderConfig struct {
+	Pattern           string            `mapstructure:"pattern"`
+	MetadataOperators []operator.Config `mapstructure:"metadata_operators"`
+}
+
 // Build will build a file input operator from the supplied configuration
 func (c Config) Build(logger *zap.SugaredLogger, emit emit.Callback) (*Manager, error) {
 	if err := c.validate(); err != nil {
@@ -120,14 +127,14 @@ func (c Config) buildManager(logger *zap.SugaredLogger, emit emit.Callback, fact
 		return nil, fmt.Errorf("invalid start_at location '%s'", c.StartAt)
 	}
 
-	var hs *headerSettings
+	var hCfg *header.Config
 	if c.Header != nil {
 		enc, err := c.Splitter.EncodingConfig.Build()
 		if err != nil {
 			return nil, fmt.Errorf("failed to create encoding: %w", err)
 		}
 
-		hs, err = c.Header.buildHeaderSettings(enc.Encoding)
+		hCfg, err = header.NewConfig(c.Header.Pattern, c.Header.MetadataOperators, enc.Encoding)
 		if err != nil {
 			return nil, fmt.Errorf("failed to build header config: %w", err)
 		}
@@ -150,7 +157,7 @@ func (c Config) buildManager(logger *zap.SugaredLogger, emit emit.Callback, fact
 			fromBeginning:   startAtBeginning,
 			splitterFactory: factory,
 			encodingConfig:  c.Splitter.EncodingConfig,
-			headerSettings:  hs,
+			headerConfig:    hCfg,
 		},
 		finder:          c.MatchingCriteria,
 		roller:          newRoller(),
@@ -226,13 +233,13 @@ func (c Config) validate() error {
 		return errors.New("`max_batches` must not be negative")
 	}
 
-	_, err := c.Splitter.EncodingConfig.Build()
+	enc, err := c.Splitter.EncodingConfig.Build()
 	if err != nil {
 		return err
 	}
 
 	if c.Header != nil {
-		if err := c.Header.validate(); err != nil {
+		if _, err := header.NewConfig(c.Header.Pattern, c.Header.MetadataOperators, enc.Encoding); err != nil {
 			return fmt.Errorf("invalid config for `header`: %w", err)
 		}
 	}

pkg/stanza/fileconsumer/config_test.go

@@ -790,10 +790,7 @@ func TestBuildWithHeader(t *testing.T) {
 			},
 			require.NoError,
 			func(t *testing.T, f *Manager) {
-				require.NotNil(t, f.readerFactory.headerSettings)
-				require.NotNil(t, f.readerFactory.headerSettings.matchRegex)
-				require.NotNil(t, f.readerFactory.headerSettings.splitFunc)
-				require.NotNil(t, f.readerFactory.headerSettings.config)
+				require.NotNil(t, f.readerFactory.headerConfig.SplitFunc)
 			},
 		},
 	}
@@ -810,7 +807,6 @@ func TestBuildWithHeader(t *testing.T) {
 			if err != nil {
 				return
 			}
-
 			tc.validate(t, input)
 		})
 	}

pkg/stanza/fileconsumer/file_test.go

@@ -1630,7 +1630,6 @@ func TestHeaderPersistanceInHeader(t *testing.T) {
 	})
 
 	require.NoError(t, op2.Stop())
-
 }
 
 func TestStalePartialFingerprintDiscarded(t *testing.T) {