parser/keyvalue: handle escaped quotes when parsing (open-telemetry#36176)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description
Currently, the keyvalue parser does handle escaped quotes and instead
will parse this 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 <[email protected]>
Co-authored-by: Daniel Jaglowski <[email protected]>

Author: jadams41

.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 {