FELIX-6835 - CommentRemovingReader incorrectly handles escaped quotes and drops characters at buffer boundaries

cm.json/src/main/java/org/apache/felix/cm/json/io/impl/JsonSupport.java

@@ -245,6 +245,7 @@ private static class CommentRemovingReader extends FilterReader {
         private boolean insideLineComment = false;
         private boolean insideString = false;
         private boolean isSkippedSlash = false;
+        private int trailingBackslashCount = 0;
         private char oldChar = 0; // priming with 0 as it is not part of comment or string escaping chars
 
         public CommentRemovingReader(Reader reader) {
@@ -258,7 +259,9 @@ public int read() throws IOException {
 
         @Override
         public int read(char[] cbuf, int off, int len) throws IOException {
-            int charsRead = super.read(cbuf, off, len);
+            // When a slash is pending from a prior read, reserve one slot so that the
+            // recovered '/' plus the new chars never exceeds len and no char is truncated.
+            int charsRead = super.read(cbuf, off, isSkippedSlash ? Math.max(1, len - 1) : len);
                 if (charsRead > 0) {
                     StringBuilder filteredContent = new StringBuilder();
                     StringBuilder currentLine = new StringBuilder();
@@ -270,11 +273,12 @@ public int read(char[] cbuf, int off, int len) throws IOException {
                         // Detect String start/end if not inside a comment
                         if (!insideComment && !insideLineComment) {
                             if (c == '"') {
-                                // only flip if not escaped quotes
-                                if (oldChar != '\\') {
+                                // Quotes are escaped only when preceded by an odd number of backslashes.
+                                if (trailingBackslashCount % 2 == 0) {
                                     insideString = !insideString;
                                 }
                                 currentLine.append(c);
+                                trailingBackslashCount = 0;
                                 oldChar = c;
                                 continue;
                             }
@@ -350,6 +354,12 @@ public int read(char[] cbuf, int off, int len) throws IOException {
                     if (!insideComment && !insideLineComment) {
                         currentLine.append(c);
                     }
+
+                    if (insideString && c == '\\') {
+                        trailingBackslashCount++;
+                    } else {
+                        trailingBackslashCount = 0;
+                    }
                     oldChar = c;
                 }
 
@@ -373,6 +383,7 @@ public void close() throws IOException {
                 insideLineComment = false;
                 insideString = false;
                 isSkippedSlash = false;
+                trailingBackslashCount = 0;
                 in.close();
                 super.close();
             }

cm.json/src/test/java/org/apache/felix/cm/json/io/impl/JsonSupportTest.java

@@ -307,6 +307,44 @@ public void testEscapedQuotes() throws IOException {
                 + "}\n", parse(input));
     }
 
+    @Test
+    public void testMultiLineStartTokenAfterSingleBackslashString() throws IOException {
+        final String input = "{\n"
+                             + "  \"illegal.characters\" : [\n"
+                             + "    \"\\\\\"\n"
+                             + "  ],\n"
+                             + "  \"filter.safe.user.agents\" : [\n"
+                             + "    \"Apache-HttpClient/*\"\n"
+                             + "  ]\n"
+                             + "}\n";
+
+        assertEquals(input, parse(input));
+    }
+
+    @Test
+    public void testQuoteAfterEvenNumberOfBackslashesEndsString() throws IOException {
+        final String input = "{\n"
+                             + "  \"a\" : \"\\\\\\\\\",\n"
+                             + "  \"b\" : \"value/*\"\n"
+                             + "}\n";
+
+        assertEquals(input, parse(input));
+    }
+
+    @Test
+    public void testSkippedSlashAtBufferBoundaryDoesNotDropLastChar() throws Exception {
+        String input = "abc/xyz";
+        Reader reader = JsonSupport.createCommentRemovingReader(new StringReader(input));
+
+        char[] buffer = new char[4];
+        int numRead = reader.read(buffer, 0, 4);
+        assertEquals("abc", new String(buffer, 0, numRead));
+
+        buffer = new char[4];
+        numRead = reader.read(buffer, 0, 4);
+        assertEquals("/xyz", new String(buffer, 0, numRead));
+    }
+
     @Test
     public void testSlashAtEndOfRead() throws Exception {
         String input = "This is a test string // Next string \n"