Add support for CBOR stringref extension (CBORGenerator.Feature.STRINGREF)

cbor/src/main/java/com/fasterxml/jackson/dataformat/cbor/CBORConstants.java

@@ -57,6 +57,18 @@ public final class CBORConstants
      */
     public final static int TAG_ID_SELF_DESCRIBE = 55799;
 
+    /**
+     * Tag denoting a namespace for string references in the following value.
+     * @since 2.15
+     */
+    public final static int TAG_ID_STRINGREF_NAMESPACE = 256;
+
+    /**
+     * Tag denoting the next integer value should be an index for a previous string.
+     * @since 2.15
+     */
+    public final static int TAG_ID_STRINGREF = 25;
+
     /*
     /**********************************************************
     /* Actual type and marker bytes
@@ -141,4 +153,13 @@ public static boolean hasMajorType(int expType, byte encoded) {
         int actual = (encoded & MASK_MAJOR_TYPE) >> 5;
         return (actual == expType);
     }
+
+    public static boolean shouldReferenceString(int index, int stringBytes) {
+        // See table in specification: http://cbor.schmorp.de/stringref
+        // Only support 32-bit indices.
+        return (index >= 0 && index <= 23 && stringBytes >= 3) ||
+                (index >= 24 && index <= 255 && stringBytes >= 4) ||
+                (index >= 256 && index <= 65535 && stringBytes >= 5) ||
+                (index >= 65536 && stringBytes >= 7);
+    }
 }

cbor/src/main/java/com/fasterxml/jackson/dataformat/cbor/CBORFactory.java

@@ -453,6 +453,9 @@ private final CBORGenerator _createCBORGenerator(IOContext ctxt,
         if (CBORGenerator.Feature.WRITE_TYPE_HEADER.enabledIn(formatFeat)) {
             gen.writeTag(CBORConstants.TAG_ID_SELF_DESCRIBE);
         }
+        if (CBORGenerator.Feature.STRINGREF.enabledIn(formatFeat)) {
+            gen.writeTag(CBORConstants.TAG_ID_STRINGREF_NAMESPACE);
+        }
         return gen;
     }