github · pelikhan · Jun 16, 2026 · Jun 16, 2026 · Jun 16, 2026 · Jun 16, 2026
diff --git a/actions/setup/js/error_helpers.cjs b/actions/setup/js/error_helpers.cjs
@@ -1,20 +1,46 @@
 // @ts-check
 
+/**
+ * Detect whether a string looks like an HTML page rather than a plain error message.
+ * Used to sanitize GitHub's "Unicorn" / gateway error HTML responses so they don't
+ * pollute CI logs with hundreds of lines of markup.
+ *
+ * @param {string} str - The string to inspect
+ * @returns {boolean} True when the string appears to be an HTML document
+ */
+function isHtmlContent(str) {
+  return /^\s*<!DOCTYPE\s/i.test(str) || /^\s*<html[\s>]/i.test(str);
+}
+
 /**
  * Safely extract an error message from an unknown error value.
  * Handles Error instances, objects with message properties, and other values.
  *
+ * When the extracted message looks like an HTML page (e.g. GitHub's "Unicorn"
+ * 504 error page), it is replaced with a concise human-readable description so
+ * that CI logs stay readable.  The HTTP status code is included when available.
+ *
  * @param {unknown} error - The error value to extract a message from
  * @returns {string} The error message as a string
  */
 function getErrorMessage(error) {
+  // prettier-ignore
+  const errorAsAny = /** @type {any} */ (error);
+  let message;
   if (error instanceof Error) {
-    return error.message;
+    message = error.message;
+  } else if (error && typeof error === "object" && "message" in error && typeof error.message === "string") {
+    message = error.message;
+  } else {
+    message = String(error);
   }
-  if (error && typeof error === "object" && "message" in error && typeof error.message === "string") {
-    return error.message;
+
+  if (isHtmlContent(message)) {
+    const status = errorAsAny != null && typeof errorAsAny.status === "number" ? errorAsAny.status : null;
+    return status != null ? `GitHub returned an unexpected HTML response (HTTP ${status})` : "GitHub returned an unexpected HTML response";
   }
-  return String(error);
+
+  return message;
 }
 
 /**
@@ -54,4 +80,4 @@ function isRateLimitError(error) {
   return /\bapi rate limit\b|\brate limit exceeded\b/i.test(errorMessage);
 }
 
-module.exports = { getErrorMessage, isLockedError, isRateLimitError };
+module.exports = { getErrorMessage, isHtmlContent, isLockedError, isRateLimitError };
diff --git a/actions/setup/js/error_helpers.test.cjs b/actions/setup/js/error_helpers.test.cjs
@@ -1,5 +1,5 @@
 import { describe, it, expect } from "vitest";
-import { getErrorMessage, isLockedError, isRateLimitError } from "./error_helpers.cjs";
+import { getErrorMessage, isHtmlContent, isLockedError, isRateLimitError } from "./error_helpers.cjs";
 
 describe("error_helpers", () => {
   describe("getErrorMessage", () => {
@@ -38,6 +38,71 @@ describe("error_helpers", () => {
       const error = { code: "ERROR_CODE", status: 500 };
       expect(getErrorMessage(error)).toBe("[object Object]");
     });
+
+    it("should sanitize HTML DOCTYPE error response with status", () => {
+      const html = "<!DOCTYPE html>\n<html><head><title>Unicorn!</title></head><body>...</body></html>";
+      const error = new Error(html);
+      /** @type {any} */ error.status = 504;
+      expect(getErrorMessage(error)).toBe("GitHub returned an unexpected HTML response (HTTP 504)");
+    });
+
+    it("should sanitize HTML DOCTYPE error response without status", () => {
+      const html = "<!DOCTYPE html>\n<html><head><title>Unicorn!</title></head><body>...</body></html>";
+      const error = new Error(html);
+      expect(getErrorMessage(error)).toBe("GitHub returned an unexpected HTML response");
+    });
+
+    it("should sanitize bare <html> error response with status", () => {
+      const html = "<html><head><title>Service Unavailable</title></head><body>...</body></html>";
+      const error = { message: html, status: 503 };
+      expect(getErrorMessage(error)).toBe("GitHub returned an unexpected HTML response (HTTP 503)");
+    });
+
+    it("should sanitize html with leading whitespace", () => {
+      const html = "  \n<!DOCTYPE html><html>...</html>";
+      const error = new Error(html);
+      expect(getErrorMessage(error)).toBe("GitHub returned an unexpected HTML response");
+    });
+
+    it("should sanitize raw HTML string throw", () => {
+      const html = "<!DOCTYPE html><html><body>Unicorn</body></html>";
+      expect(getErrorMessage(html)).toBe("GitHub returned an unexpected HTML response");
+    });
+
+    it("should not sanitize plain-text error messages that happen to mention html", () => {
+      const error = new Error("Validation failed: invalid html content provided");
+      expect(getErrorMessage(error)).toBe("Validation failed: invalid html content provided");
+    });
+  });
+
+  describe("isHtmlContent", () => {
+    it("should return true for DOCTYPE HTML string", () => {
+      expect(isHtmlContent("<!DOCTYPE html><html></html>")).toBe(true);
+    });
+
+    it("should return true for bare html tag", () => {
+      expect(isHtmlContent("<html><head></head><body></body></html>")).toBe(true);
+    });
+
+    it("should return true with leading whitespace", () => {
+      expect(isHtmlContent("\n  <!DOCTYPE html>...")).toBe(true);
+    });
+
+    it("should return true for case-insensitive DOCTYPE", () => {
+      expect(isHtmlContent("<!doctype HTML><html></html>")).toBe(true);
+    });
+
+    it("should return false for plain text", () => {
+      expect(isHtmlContent("Resource not accessible by integration")).toBe(false);
+    });
+
+    it("should return false for JSON-like content", () => {
+      expect(isHtmlContent('{"message":"Not Found","documentation_url":"..."}')).toBe(false);
+    });
+
+    it("should return false for empty string", () => {
+      expect(isHtmlContent("")).toBe(false);
+    });
   });
 
   describe("isLockedError", () => {

diff --git a/actions/setup/js/error_recovery.cjs b/actions/setup/js/error_recovery.cjs
@@ -65,7 +65,7 @@ function isTransientError(error) {
   // GitHub REST APIs may crash and return an HTML error page (e.g. the "Unicorn!"
   // 500 page) instead of JSON. Detect this by checking for an HTML doctype at the
   // start of the error message and treat it as a transient server error.
-  if (errorMsgLower.startsWith("<!doctype html")) {
+  if (errorMsgLower.startsWith("<!doctype html") || errorMsgLower.includes("unexpected html response")) {
     return true;
   }