fix: sanitize lone Unicode surrogates in YAML serialization#39316
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alexmakeev wants to merge 1 commit intomicrosoft:mainfrom
Open
fix: sanitize lone Unicode surrogates in YAML serialization#39316alexmakeev wants to merge 1 commit intomicrosoft:mainfrom
alexmakeev wants to merge 1 commit intomicrosoft:mainfrom
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Lone surrogates (U+D800–U+DFFF) in DOM textContent are valid in JavaScript strings but produce invalid JSON when serialized. The yamlEscapeValueIfNeeded() function escapes control characters but does not handle lone surrogates, causing 'no low surrogate in string' errors in MCP clients. Apply the same toWellFormed() pattern already used in driver.ts for non-JavaScript language bindings, with a regex fallback for older environments. Fixes microsoft/playwright-mcp#1410
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Problem
yamlEscapeValueIfNeeded()inpackages/injected/src/yaml.tsescapes control characters (\x00-\x1f,\x7f-\x9f) but does not handle lone Unicode surrogates (\uD800-\uDFFF).When a page assigns text containing lone surrogates to DOM nodes (e.g. via
element.textContent = 'text\uD800more'), the aria snapshot captures these verbatim. The resulting YAML string produces invalid JSON per RFC 8259 §8.2, causing"no low surrogate in string"errors in MCP clients.Fix
Apply the same
String.prototype.toWellFormed()pattern already used inpackages/playwright-core/src/cli/driver.tsfor non-JavaScript language bindings, with a regex fallback for environments withouttoWellFormed().Lone surrogates are replaced with U+FFFD (Unicode replacement character). Valid surrogate pairs (emoji, etc.) are preserved.
Changes
packages/injected/src/yaml.ts— sanitize lone surrogates inyamlEscapeValueIfNeeded()before escaping control characterstests/mcp/snapshot-unicode.spec.ts— test coverage for lone high/low surrogates, valid emoji preservation, and mixed contentTest plan
\uD800) → replaced with\uFFFD\uDC00) → replaced with\uFFFD\uD83D\uDE00= 😀) → preservedRef: microsoft/playwright-mcp#1410