Prevent stdio trimming from creating invalid unicode data (#701)

Author: rmuir

src/main/java/hudson/tasks/junit/CaseResult.java

@@ -375,6 +375,23 @@ static void parseProperty(Map<String, String> r, final XMLStreamReader reader, S
         }
     }
 
+    /**
+     * Cleans up a truncated string, that might contain unpaired surrogates
+     * @param str input string
+     * @return input string, possibly truncated to avoid unpaired surrogates
+     */
+    static CharSequence cleanupTruncated(CharSequence str) {
+        // remove unpaired trailing surrogates at the start
+        if (str.length() > 0 && Character.isLowSurrogate(str.charAt(0))) {
+            str = str.subSequence(1, str.length());
+        }
+        // remove unpaired leading surrogates at the end
+        if (str.length() > 0 && Character.isHighSurrogate(str.charAt(str.length() - 1))) {
+            str = str.subSequence(0, str.length() - 1);
+        }
+        return str;
+    }
+
     static String possiblyTrimStdio(
             Collection<CaseResult> results, StdioRetention stdioRetention, String stdio) { // HUDSON-6516
         if (stdio == null) {
@@ -391,8 +408,8 @@ static String possiblyTrimStdio(
         if (middle <= 0) {
             return stdio;
         }
-        return stdio.subSequence(0, halfMaxSize) + "\n...[truncated " + middle + " chars]...\n"
-                + stdio.subSequence(len - halfMaxSize, len);
+        return cleanupTruncated(stdio.subSequence(0, halfMaxSize)) + "\n...[truncated " + middle + " chars]...\n"
+                + cleanupTruncated(stdio.subSequence(len - halfMaxSize, len));
     }
 
     static String fixNULs(String stdio) { // JENKINS-71139
@@ -432,7 +449,7 @@ static String possiblyTrimStdio(Collection<CaseResult> results, StdioRetention s
             return FileUtils.readFileToString(stdio);
         }
 
-        return head + "\n...[truncated " + middle + " bytes]...\n" + tail;
+        return cleanupTruncated(head) + "\n...[truncated " + middle + " bytes]...\n" + cleanupTruncated(tail);
     }
 
     private static final int HALF_MAX_SIZE = 500;

src/test/java/hudson/tasks/junit/CaseResultTest.java

@@ -442,6 +442,23 @@ public boolean perform(AbstractBuild<?, ?> build, Launcher launcher, BuildListen
         assertEquals(0, cr.getProperties().size());
     }
 
+    /**
+     * Test truncation works along unicode codepoint boundaries.
+     */
+    @Test
+    void testCleanupTruncated() throws Exception {
+        // empty
+        assertEquals("", CaseResult.cleanupTruncated("").toString());
+        // ordinary
+        assertEquals("abc", CaseResult.cleanupTruncated("abc").toString());
+        // starts with a trail surrogate.
+        assertEquals("abc", CaseResult.cleanupTruncated("\uDC00abc").toString());
+        // ends with a lead surrogate.
+        assertEquals("abc", CaseResult.cleanupTruncated("abc\uD800").toString());
+        // starts with trail surrogate and ends with lead surrogate
+        assertEquals("abc", CaseResult.cleanupTruncated("\uDC00abc\uD800").toString());
+    }
+
     private String composeXPath(String[] fields) {
         StringBuilder tmp = new StringBuilder(100);
         for (String f : fields) {