[parseutils] Handle escaped quotes when parsing in SplitString

Currently, the SplitString parser does not handle escaped quotes and instead
will parse these as independent '\', '"' characters. This results in
unexpected breakages between fields for strings like:
> <key>="...\" ..."
Here, the backslash will be appended to the result pair, while the
(now un-)escaped quotation will result in the pair being terminated early.

Add handling of escaped quotation marks (for both ", ') in the
keyvalue parser along with a testcase to exercise this functionality.

Signed-off-by: Ethan Adams <eadams@netflix.com>

.chloggen/eadams_escaped-quotes-in-keyvalue-parser.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: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: parseutils
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Handle escaped quotes when parsing pairs using SplitString.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [36176]
+
+# (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: []

internal/coreinternal/parseutils/parser.go

@@ -18,6 +18,7 @@ func SplitString(input, delimiter string) ([]string, error) {
 	current := ""
 	delimiterLength := len(delimiter)
 	quoteChar := "" // "" means we are not in quotes
+	escaped := false
 
 	for i := 0; i < len(input); i++ {
 		if quoteChar == "" && i+delimiterLength <= len(input) && input[i:i+delimiterLength] == delimiter { // delimiter
@@ -31,13 +32,19 @@ func SplitString(input, delimiter string) ([]string, error) {
 			continue
 		}
 
-		if quoteChar == "" && (input[i] == '"' || input[i] == '\'') { // start of quote
-			quoteChar = string(input[i])
-			continue
-		}
-		if string(input[i]) == quoteChar { // end of quote
-			quoteChar = ""
-			continue
+		if !escaped { // consider quote termination so long as previous character wasn't backslash
+			if quoteChar == "" && (input[i] == '"' || input[i] == '\'') { // start of quote
+				quoteChar = string(input[i])
+				continue
+			}
+			if string(input[i]) == quoteChar { // end of quote
+				quoteChar = ""
+				continue
+			}
+			// Only if we weren't escaped could the next character result in escaped state
+			escaped = input[i] == '\\' // potentially escaping next character
+		} else {
+			escaped = false
 		}
 
 		current += string(input[i])

internal/coreinternal/parseutils/parser_test.go

@@ -85,6 +85,17 @@ func Test_SplitString(t *testing.T) {
 				`c=this is a "co ol"`,
 			},
 		},
+		{
+			name:      "embedded escaped quotes",
+			input:     `ab c="this \"is \"" d='a \'co ol\' value' e="\""`,
+			delimiter: " ",
+			expected: []string{
+				"ab",
+				`c=this \"is \"`,
+				`d=a \'co ol\' value`,
+				`e=\"`,
+			},
+		},
 		{
 			name:      "quoted values include whitespace",
 			input:     `name="    ottl " func="  key_ value"`,
@@ -259,6 +270,17 @@ func Test_ParseKeyValuePairs(t *testing.T) {
 				"c": "d",
 			},
 		},
+		{
+			name:      "escaped quotes",
+			pairs:     []string{"key=foobar", `key2="foo bar"`, `key3="foo \"bar\""`, `key4='\'foo\' \'bar\''`},
+			delimiter: "=",
+			expected: map[string]any{
+				"key": "foobar",
+				"key2": `"foo bar"`,
+				"key3": `"foo \"bar\""`,
+				"key4": `'\'foo\' \'bar\''`,
+			},
+		},
 	}
 
 	for _, tc := range testCases {

pkg/stanza/operator/parser/keyvalue/parser_test.go

@@ -688,6 +688,24 @@ key=value`,
 			true,
 			false,
 		},
+		{
+			"containerd output",
+			func(_ *Config) {},
+			&entry.Entry{
+				Body: `time="2024-11-01T12:38:17.992190505Z" level=warning msg="cleanup warnings time='2024-11-01T12:38:17Z' level=debug msg=\"starting signal loop\" namespace=moby-10000.10000 pid=1608080 runtime=io.containerd.runc.v2" namespace=moby-10000.10000`,
+			},
+			&entry.Entry{
+				Attributes: map[string]any{
+					"time":      "2024-11-01T12:38:17.992190505Z",
+					"level":     "warning",
+					"msg":       `cleanup warnings time='2024-11-01T12:38:17Z' level=debug msg=\"starting signal loop\" namespace=moby-10000.10000 pid=1608080 runtime=io.containerd.runc.v2`,
+					"namespace": "moby-10000.10000",
+				},
+				Body: `time="2024-11-01T12:38:17.992190505Z" level=warning msg="cleanup warnings time='2024-11-01T12:38:17Z' level=debug msg=\"starting signal loop\" namespace=moby-10000.10000 pid=1608080 runtime=io.containerd.runc.v2" namespace=moby-10000.10000`,
+			},
+			false,
+			false,
+		},
 	}
 
 	for _, tc := range cases {