[pkg/ottl] Fix escape sequences in strings (#30839)

**Description:** <Describe what has changed.>
<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
Fix ottl parsing to properly handle escape sequences.
@TylerHelmuth

**Link to tracking Issue:**
#23238

**Testing:** <Describe what testing was performed and which tests were
added.>
Added a new unit test with the example from the linked issue

**Documentation:** <Describe the documentation added.>
None (pure bugfix)

.chloggen/ottl-string.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: pkg/ottl
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Fix parsing of string escapes in OTTL
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [23238]
+
+# (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: []

pkg/ottl/e2e/e2e_test.go

@@ -518,6 +518,44 @@ func Test_e2e_converters(t *testing.T) {
 				tCtx.GetLogRecord().Attributes().PutStr("test", "pass")
 			},
 		},
+		{
+			statement: `set(attributes["test"], "\\")`,
+			want: func(tCtx ottllog.TransformContext) {
+				tCtx.GetLogRecord().Attributes().PutStr("test", "\\")
+			},
+		},
+		{
+			statement: `set(attributes["test"], "\\\\")`,
+			want: func(tCtx ottllog.TransformContext) {
+				tCtx.GetLogRecord().Attributes().PutStr("test", "\\\\")
+			},
+		},
+		{
+			statement: `set(attributes["test"], "\\\\\\")`,
+			want: func(tCtx ottllog.TransformContext) {
+				tCtx.GetLogRecord().Attributes().PutStr("test", "\\\\\\")
+			},
+		},
+		{
+			statement: `set(attributes["test"], "\\\\\\\\")`,
+			want: func(tCtx ottllog.TransformContext) {
+				tCtx.GetLogRecord().Attributes().PutStr("test", "\\\\\\\\")
+			},
+		},
+		{
+			statement: `set(attributes["test"], "\"")`,
+			want: func(tCtx ottllog.TransformContext) {
+				tCtx.GetLogRecord().Attributes().PutStr("test", `"`)
+			},
+		},
+		{
+			statement: `keep_keys(attributes["foo"], ["\\", "bar"])`,
+			want: func(tCtx ottllog.TransformContext) {
+				// keep_keys should see two arguments
+				m := tCtx.GetLogRecord().Attributes().PutEmptyMap("foo")
+				m.PutStr("bar", "pass")
+			},
+		},
 	}
 
 	for _, tt := range tests {

pkg/ottl/grammar.go

@@ -433,7 +433,7 @@ func buildLexer() *lexer.StatefulDefinition {
 		{Name: `Bytes`, Pattern: `0x[a-fA-F0-9]+`},
 		{Name: `Float`, Pattern: `[-+]?\d*\.\d+([eE][-+]?\d+)?`},
 		{Name: `Int`, Pattern: `[-+]?\d+`},
-		{Name: `String`, Pattern: `"(\\"|[^"])*"`},
+		{Name: `String`, Pattern: `"(\\.|[^\\"])*"`},
 		{Name: `OpNot`, Pattern: `\b(not)\b`},
 		{Name: `OpOr`, Pattern: `\b(or)\b`},
 		{Name: `OpAnd`, Pattern: `\b(and)\b`},

pkg/ottl/lexer_test.go

@@ -92,6 +92,15 @@ func Test_lexer(t *testing.T) {
 			{"Bytes", "0x0102030405060708"},
 			{"RParen", ")"},
 		}},
+		{"string escape with trailing backslash", `a("\\", "b")`, false, []result{
+			{"Lowercase", "a"},
+			{"LParen", "("},
+			{"String", `"\\"`},
+			{"Punct", ","},
+			{"String", `"b"`},
+			{"RParen", ")"},
+		}},
+		{"string escape with mismatched backslash", `"\"`, true, nil},
 		{"Mixing case numbers and underscores", `aBCd_123E_4`, false, []result{
 			{"Lowercase", "a"},
 			{"Uppercase", "BC"},

pkg/ottl/ottlfuncs/README.md

@@ -254,9 +254,6 @@ The `replace_all_matches` function replaces any matching string value with the r
 
 Each string value in `target` that matches `pattern` will get replaced with `replacement`. Non-string values are ignored.
 
-There is currently a bug with OTTL that does not allow the pattern to end with `\\"`.
-[See Issue 23238 for details](https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/23238).
-
 Examples:
 
 - `replace_all_matches(attributes, "/user/*/list/*", "/user/{userId}/list/{listId}")`
@@ -278,10 +275,6 @@ The `replacement` string can refer to matched groups using [regexp.Expand syntax
 
 The `function` is an optional argument that can take in any Converter that accepts a (`replacement`) string and returns a string. An example is a hash function that replaces any matching regex pattern with the hash value of `replacement`.
 
-There is currently a bug with OTTL that does not allow the pattern to end with `\\"`.
-If your pattern needs to end with backslashes, add something inconsequential to the end of the pattern such as `{1}`, `$`, or `.*`.
-[See Issue 23238 for details](https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/23238).
-
 Examples:
 
 - `replace_all_patterns(attributes, "value", "/account/\\d{4}", "/account/{accountId}")`
@@ -305,9 +298,6 @@ If `target` matches `pattern` it will get replaced with `replacement`.
 
 The `function` is an optional argument that can take in any Converter that accepts a (`replacement`) string and returns a string. An example is a hash function that replaces any matching glob pattern with the hash value of `replacement`.
 
-There is currently a bug with OTTL that does not allow the pattern to end with `\\"`.
-[See Issue 23238 for details](https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/23238).
-
 Examples:
 
 - `replace_match(attributes["http.target"], "/user/*/list/*", "/user/{userId}/list/{listId}")`
@@ -327,10 +317,6 @@ The `replacement` string can refer to matched groups using [regexp.Expand syntax
 
 The `function` is an optional argument that can take in any Converter that accepts a (`replacement`) string and returns a string. An example is a hash function that replaces a matching regex pattern with the hash value of `replacement`.
 
-There is currently a bug with OTTL that does not allow the pattern to end with `\\"`.
-If your pattern needs to end with backslashes, add something inconsequential to the end of the pattern such as `{1}`, `$`, or `.*`.
-[See Issue 23238 for details](https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/23238).
-
 Examples:
 
 - `replace_pattern(resource.attributes["process.command_line"], "password\\=[^\\s]*(\\s?)", "password=***")`
@@ -674,9 +660,6 @@ If target is not a string, it will be converted to one:
 
 If target is nil, false is always returned.
 
-There is currently a bug with OTTL that does not allow the target string to end with `\\"`.
-[See Issue 23238 for details](https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/23238).
-
 Examples:
 
 - `IsMatch(attributes["http.path"], "foo")`
@@ -918,9 +901,6 @@ The `Split` Converter separates a string by the delimiter, and returns an array
 
 If the `target` is not a string or does not exist, the `Split` Converter will return an error.
 
-There is currently a bug with OTTL that does not allow the target string to end with `\\"`.
-[See Issue 23238 for details](https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/23238).
-
 Examples:
 
 - `Split("A|B|C", "|")`