[receiver/filelog] Implement specifying top n files to track when ord…

…ering (open-telemetry#27844)

**Description:**
* Add a new `ordering_criteria.top_n` option, which allows a user to
specify the number of files to track after ordering.
  * Default is 1, which was the existing behavior.

**Link to tracking Issue:** open-telemetry#23788

**Testing:**
Unit tests added.

**Documentation:**
Added new parameter to existing documentation.

.chloggen/feat_top_n_file_sorting.yaml

@@ -0,0 +1,22 @@
+# 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: filelogreceiver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add a new "top_n" option to specify the number of files to track when using ordering criteria
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [23788]
+
+# 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/stanza/fileconsumer/config_test.go

@@ -412,6 +412,16 @@ func TestUnmarshal(t *testing.T) {
 					return newMockOperatorConfig(cfg)
 				}(),
 			},
+			{
+				Name: "ordering_criteria_top_n",
+				Expect: func() *mockOperatorConfig {
+					cfg := NewConfig()
+					cfg.OrderingCriteria = matcher.OrderingCriteria{
+						TopN: 10,
+					}
+					return newMockOperatorConfig(cfg)
+				}(),
+			},
 		},
 	}.Run(t)
 }

pkg/stanza/fileconsumer/matcher/matcher.go

@@ -18,6 +18,10 @@ const (
 	sortTypeAlphabetical = "alphabetical"
 )
 
+const (
+	defaultOrderingCriteriaTopN = 1
+)
+
 type Criteria struct {
 	Include          []string         `mapstructure:"include,omitempty"`
 	Exclude          []string         `mapstructure:"exclude,omitempty"`
@@ -26,6 +30,7 @@ type Criteria struct {
 
 type OrderingCriteria struct {
 	Regex  string `mapstructure:"regex,omitempty"`
+	TopN   int    `mapstructure:"top_n,omitempty"`
 	SortBy []Sort `mapstructure:"sort_by,omitempty"`
 }
 
@@ -62,6 +67,14 @@ func New(c Criteria) (*Matcher, error) {
 		return nil, fmt.Errorf("'regex' must be specified when 'sort_by' is specified")
 	}
 
+	if c.OrderingCriteria.TopN < 0 {
+		return nil, fmt.Errorf("'top_n' must be a positive integer")
+	}
+
+	if c.OrderingCriteria.TopN == 0 {
+		c.OrderingCriteria.TopN = defaultOrderingCriteriaTopN
+	}
+
 	regex, err := regexp.Compile(c.OrderingCriteria.Regex)
 	if err != nil {
 		return nil, fmt.Errorf("compile regex: %w", err)
@@ -97,6 +110,7 @@ func New(c Criteria) (*Matcher, error) {
 		include:    c.Include,
 		exclude:    c.Exclude,
 		regex:      regex,
+		topN:       c.OrderingCriteria.TopN,
 		filterOpts: filterOpts,
 	}, nil
 }
@@ -105,6 +119,7 @@ type Matcher struct {
 	include    []string
 	exclude    []string
 	regex      *regexp.Regexp
+	topN       int
 	filterOpts []filter.Option
 }
 
@@ -127,7 +142,9 @@ func (m Matcher) MatchFiles() ([]string, error) {
 		return result, errors.Join(err, errs)
 	}
 
-	// Return only the first item.
-	// See https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/23788
-	return result[:1], errors.Join(err, errs)
+	if len(result) <= m.topN {
+		return result, errors.Join(err, errs)
+	}
+
+	return result[:m.topN], errors.Join(err, errs)
 }

pkg/stanza/fileconsumer/matcher/matcher_test.go

@@ -98,6 +98,23 @@ func TestNew(t *testing.T) {
 			},
 			expectedErr: "compile regex: error parsing regexp: missing closing ]: `[a-z`",
 		},
+		{
+			name: "TopN is negative",
+			criteria: Criteria{
+				Include: []string{"*.log"},
+				OrderingCriteria: OrderingCriteria{
+					Regex: "[a-z]",
+					TopN:  -1,
+					SortBy: []Sort{
+						{
+							SortType: "numeric",
+							RegexKey: "key",
+						},
+					},
+				},
+			},
+			expectedErr: "'top_n' must be a positive integer",
+		},
 		{
 			name: "SortTypeEmpty",
 			criteria: Criteria{
@@ -249,6 +266,46 @@ func TestMatcher(t *testing.T) {
 			},
 			expected: []string{"err.2023020612.log"},
 		},
+		{
+			name:    "TopN > number of files",
+			files:   []string{"err.2023020611.log", "err.2023020612.log"},
+			include: []string{"err.*.log"},
+			exclude: []string{},
+			filterCriteria: OrderingCriteria{
+				Regex: `err\.(?P<value>\d{4}\d{2}\d{2}\d{2}).*log`,
+				TopN:  3,
+				SortBy: []Sort{
+					{
+						SortType:  sortTypeTimestamp,
+						RegexKey:  "value",
+						Ascending: false,
+						Location:  "UTC",
+						Layout:    `%Y%m%d%H`,
+					},
+				},
+			},
+			expected: []string{"err.2023020612.log", "err.2023020611.log"},
+		},
+		{
+			name:    "TopN == number of files",
+			files:   []string{"err.2023020611.log", "err.2023020612.log"},
+			include: []string{"err.*.log"},
+			exclude: []string{},
+			filterCriteria: OrderingCriteria{
+				Regex: `err\.(?P<value>\d{4}\d{2}\d{2}\d{2}).*log`,
+				TopN:  2,
+				SortBy: []Sort{
+					{
+						SortType:  sortTypeTimestamp,
+						RegexKey:  "value",
+						Ascending: false,
+						Location:  "UTC",
+						Layout:    `%Y%m%d%H`,
+					},
+				},
+			},
+			expected: []string{"err.2023020612.log", "err.2023020611.log"},
+		},
 		{
 			name:    "Timestamp Sorting Ascending",
 			files:   []string{"err.2023020612.log", "err.2023020611.log", "err.2023020609.log", "err.2023020610.log"},
@@ -319,6 +376,24 @@ func TestMatcher(t *testing.T) {
 			},
 			expected: []string{"err.d.log"},
 		},
+		{
+			name:    "Alphabetical Sorting - Top 2",
+			files:   []string{"err.a.log", "err.d.log", "err.b.log", "err.c.log"},
+			include: []string{"err.*.log"},
+			exclude: []string{},
+			filterCriteria: OrderingCriteria{
+				Regex: `err\.(?P<value>[a-zA-Z]+).*log`,
+				TopN:  2,
+				SortBy: []Sort{
+					{
+						SortType:  sortTypeAlphabetical,
+						RegexKey:  "value",
+						Ascending: false,
+					},
+				},
+			},
+			expected: []string{"err.d.log", "err.c.log"},
+		},
 		{
 			name:    "Alphabetical Sorting Ascending",
 			files:   []string{"err.b.log", "err.a.log", "err.c.log", "err.d.log"},
@@ -336,6 +411,45 @@ func TestMatcher(t *testing.T) {
 			},
 			expected: []string{"err.a.log"},
 		},
+		{
+			name: "Multiple Sorting - timestamp priority sort - Top 4",
+			files: []string{
+				"err.b.1.2023020601.log",
+				"err.b.2.2023020601.log",
+				"err.a.1.2023020601.log",
+				"err.a.2.2023020601.log",
+				"err.b.1.2023020602.log",
+				"err.a.2.2023020602.log",
+				"err.b.2.2023020602.log",
+				"err.a.1.2023020602.log",
+			},
+			include: []string{"err.*.log"},
+			exclude: []string{},
+			filterCriteria: OrderingCriteria{
+				Regex: `err\.(?P<alpha>[a-zA-Z])\.(?P<number>\d+)\.(?P<time>\d{10})\.log`,
+				TopN:  4,
+				SortBy: []Sort{
+					{
+						SortType:  sortTypeAlphabetical,
+						RegexKey:  "alpha",
+						Ascending: false,
+					},
+					{
+						SortType:  sortTypeNumeric,
+						RegexKey:  "number",
+						Ascending: false,
+					},
+					{
+						SortType:  sortTypeTimestamp,
+						RegexKey:  "time",
+						Ascending: false,
+						Location:  "UTC",
+						Layout:    `%Y%m%d%H`,
+					},
+				},
+			},
+			expected: []string{"err.b.2.2023020602.log", "err.a.2.2023020602.log", "err.b.1.2023020602.log", "err.a.1.2023020602.log"},
+		},
 		{
 			name: "Multiple Sorting - timestamp priority sort",
 			files: []string{

pkg/stanza/fileconsumer/testdata/config.yaml

@@ -180,3 +180,7 @@ header_config:
     pattern: "^#"
     metadata_operators:
       - type: "regex_parser"
+ordering_criteria_top_n:
+  type: mock
+  ordering_criteria:
+    top_n: 10

receiver/filelogreceiver/README.md

@@ -51,6 +51,7 @@ Tails and parses logs from files.
 | `retry_on_failure.max_interval`     | `30s`                                | Upper bound on retry backoff [interval](#time-parameters). Once this value is reached the delay between consecutive retries will remain constant at the specified value.                                                                                        |
 | `retry_on_failure.max_elapsed_time` | `5m`                                 | Maximum amount of [time](#time-parameters) (including retries) spent trying to send a logs batch to a downstream consumer. Once this value is reached, the data is discarded. Retrying never stops if set to `0`.     
 | `ordering_criteria.regex`     |                                      | Regular expression used for sorting, should contain a named capture groups that are to be used in `regex_key`.                                                                                                                               |
+| `ordering_criteria.top_n`     | 1 | The number of files to track when using file ordering. The top N files are tracked after applying the ordering criteria. |
 | `ordering_criteria.sort_by.sort_type` |                                      | Type of sorting to be performed (e.g., `numeric`, `alphabetical`, `timestamp`)                                                                                                                                                                                  |
 | `ordering_criteria.sort_by.location`  |                                      | Relevant if `sort_type` is set to `timestamp`. Defines the location of the timestamp of the file.                                                                                                                                                               |
 | `ordering_criteria.sort_by.format`    |                                      | Relevant if `sort_type` is set to `timestamp`. Defines the strptime format of the timestamp being sorted.                                                                                                                                                       |