feat(inputs.tail): add option to preserve newlines for multiline data (#12281)

plugins/inputs/tail/README.md

@@ -104,6 +104,11 @@ See the [CONFIGURATION.md][CONFIGURATION.md] for more details.
     ## When handling quotes, escaped quotes (e.g. \") are handled correctly.
     #quotation = "ignore"
 
+    ## The preserve_newline option can be true or false (defaults to false).
+    ## If true, the newline character is preserved for multiline elements,
+    ## this is useful to preserve message-structure e.g. for logging outputs.
+    #preserver_newline = false
+
     #After the specified timeout, this plugin sends the multiline event even if no new pattern is found to start a new event. The default is 5s.
     #timeout = 5s
 ```

plugins/inputs/tail/multiline.go

@@ -26,6 +26,7 @@ type MultilineConfig struct {
 	Pattern         string                  `toml:"pattern"`
 	MatchWhichLine  MultilineMatchWhichLine `toml:"match_which_line"`
 	InvertMatch     bool                    `toml:"invert_match"`
+	PreserveNewline bool                    `toml:"preserve_newline"`
 	Quotation       string                  `toml:"quotation"`
 	Timeout         *config.Duration        `toml:"timeout"`
 }
@@ -80,12 +81,11 @@ func (m *Multiline) IsEnabled() bool {
 }
 
 func (m *Multiline) ProcessLine(text string, buffer *bytes.Buffer) string {
-	if m.matchQuotation(text) {
-		// Ignore the returned error as we cannot do anything about it anyway
-		_, _ = buffer.WriteString(text + "\n")
-		return ""
+	if m.matchQuotation(text) || m.matchString(text) {
+		// Restore the newline removed by tail's scanner
+		if buffer.Len() > 0 && m.config.PreserveNewline {
+			_, _ = buffer.WriteString("\n")
 		}
-	if m.matchString(text) {
 		// Ignore the returned error as we cannot do anything about it anyway
 		_, _ = buffer.WriteString(text)
 		return ""
@@ -101,6 +101,9 @@ func (m *Multiline) ProcessLine(text string, buffer *bytes.Buffer) string {
 	} else {
 		// Next
 		if buffer.Len() > 0 {
+			if m.config.PreserveNewline {
+				_, _ = buffer.WriteString("\n")
+			}
 			if _, err := buffer.WriteString(text); err != nil {
 				return ""
 			}

plugins/inputs/tail/multiline_test.go

@@ -239,7 +239,7 @@ func TestMultilineWhat(t *testing.T) {
 	require.Equal(t, MultilineMatchWhichLine(-1), w7)
 }
 
-func TestMultiLineQuoted(t *testing.T) {
+func TestMultilineQuoted(t *testing.T) {
 	tests := []struct {
 		name      string
 		quotation string
@@ -283,6 +283,7 @@ func TestMultiLineQuoted(t *testing.T) {
 			c := &MultilineConfig{
 				MatchWhichLine:  Next,
 				Quotation:       tt.quotation,
+				PreserveNewline: true,
 			}
 			m, err := c.NewMultiline()
 			require.NoError(t, err)
@@ -303,13 +304,16 @@ func TestMultiLineQuoted(t *testing.T) {
 				}
 				result = append(result, text)
 			}
+			if text := m.Flush(&buffer); text != "" {
+				result = append(result, text)
+			}
 
 			require.EqualValues(t, expected, result)
 		})
 	}
 }
 
-func TestMultiLineQuotedError(t *testing.T) {
+func TestMultilineQuotedError(t *testing.T) {
 	tests := []struct {
 		name      string
 		filename  string
@@ -332,7 +336,7 @@ func TestMultiLineQuotedError(t *testing.T) {
 			filename:  "multiline_quoted_missing_close.csv",
 			quotation: "single-quotes",
 			quote:     `'`,
-			expected:  nil,
+			expected:  []string{"1660819827411,2,'some text all quoted,B\n1660819827410,1,some text without quotes,A"},
 		},
 	}
 
@@ -341,6 +345,7 @@ func TestMultiLineQuotedError(t *testing.T) {
 			c := &MultilineConfig{
 				MatchWhichLine:  Next,
 				Quotation:       tt.quotation,
+				PreserveNewline: true,
 			}
 			m, err := c.NewMultiline()
 			require.NoError(t, err)
@@ -361,6 +366,84 @@ func TestMultiLineQuotedError(t *testing.T) {
 				}
 				result = append(result, text)
 			}
+			if text := m.Flush(&buffer); text != "" {
+				result = append(result, text)
+			}
+
+			require.EqualValues(t, tt.expected, result)
+		})
+	}
+}
+
+func TestMultilineNewline(t *testing.T) {
+	tests := []struct {
+		name     string
+		filename string
+		cfg      *MultilineConfig
+		expected []string
+	}{
+		{
+			name: "do not preserve newline",
+			cfg: &MultilineConfig{
+				Pattern:     `\[[0-9]{2}/[A-Za-z]{3}/[0-9]{4}:[0-9]{2}:[0-9]{2}:[0-9]{2} \+[0-9]{4}\]`,
+				InvertMatch: true,
+			},
+			filename: "test_multiline.log",
+			expected: []string{
+				`[04/Jun/2016:12:41:45 +0100] DEBUG HelloExample: This is debug`,
+				`[04/Jun/2016:12:41:48 +0100] INFO HelloExample: This is info`,
+				"[04/Jun/2016:12:41:46 +0100] ERROR HelloExample: Sorry, something wrong! " +
+					"java.lang.ArithmeticException: / by zero" +
+					"\tat com.foo.HelloExample2.divide(HelloExample2.java:24)" +
+					"\tat com.foo.HelloExample2.main(HelloExample2.java:14)",
+				`[04/Jun/2016:12:41:48 +0100] WARN HelloExample: This is warn`,
+			},
+		},
+		{
+			name: "preserve newline",
+			cfg: &MultilineConfig{
+				Pattern:         `\[[0-9]{2}/[A-Za-z]{3}/[0-9]{4}:[0-9]{2}:[0-9]{2}:[0-9]{2} \+[0-9]{4}\]`,
+				InvertMatch:     true,
+				PreserveNewline: true,
+			},
+			filename: "test_multiline.log",
+			expected: []string{
+				`[04/Jun/2016:12:41:45 +0100] DEBUG HelloExample: This is debug`,
+				`[04/Jun/2016:12:41:48 +0100] INFO HelloExample: This is info`,
+				`[04/Jun/2016:12:41:46 +0100] ERROR HelloExample: Sorry, something wrong!` + ` ` + `
+java.lang.ArithmeticException: / by zero
+	at com.foo.HelloExample2.divide(HelloExample2.java:24)
+	at com.foo.HelloExample2.main(HelloExample2.java:14)`,
+				`[04/Jun/2016:12:41:48 +0100] WARN HelloExample: This is warn`,
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			m, err := tt.cfg.NewMultiline()
+			require.NoError(t, err)
+
+			f, err := os.Open(filepath.Join("testdata", tt.filename))
+			require.NoError(t, err)
+
+			scanner := bufio.NewScanner(f)
+
+			var buffer bytes.Buffer
+			var result []string
+			for scanner.Scan() {
+				line := scanner.Text()
+
+				text := m.ProcessLine(line, &buffer)
+				if text == "" {
+					continue
+				}
+				result = append(result, text)
+			}
+			if text := m.Flush(&buffer); text != "" {
+				result = append(result, text)
+			}
+
 			require.EqualValues(t, tt.expected, result)
 		})
 	}
@@ -371,6 +454,7 @@ func TestMultiLineQuotedAndPattern(t *testing.T) {
 		Pattern:         "=>$",
 		MatchWhichLine:  Next,
 		Quotation:       "double-quotes",
+		PreserveNewline: true,
 	}
 	m, err := c.NewMultiline()
 	require.NoError(t, err, "Configuration was OK.")
@@ -397,7 +481,7 @@ func TestMultiLineQuotedAndPattern(t *testing.T) {
 	require.NotZero(t, buffer.Len())
 
 	text = m.ProcessLine("4", &buffer)
-	require.Equal(t, "1=>2=>\"a quoted\nmultiline string\"=>3=>4", text)
+	require.Equal(t, "1=>\n2=>\n\"a quoted\nmultiline string\"=>\n3=>\n4", text)
 	require.Zero(t, buffer.Len())
 
 	text = m.ProcessLine("5", &buffer)

plugins/inputs/tail/sample.conf

@@ -71,5 +71,10 @@
     ## When handling quotes, escaped quotes (e.g. \") are handled correctly.
     #quotation = "ignore"
 
+    ## The preserve_newline option can be true or false (defaults to false).
+    ## If true, the newline character is preserved for multiline elements,
+    ## this is useful to preserve message-structure e.g. for logging outputs.
+    #preserver_newline = false
+
     #After the specified timeout, this plugin sends the multiline event even if no new pattern is found to start a new event. The default is 5s.
     #timeout = 5s