Fall back to the VARCHAR codec if decoding as a String

If there is no immediately suitable codec can be found and the request is to decode as a String, then fallback to using the VARCHAR codec.

[#454][#429]

Author: jbellassai

src/main/java/io/r2dbc/postgresql/codec/DefaultCodecs.java

@@ -200,6 +200,12 @@ public <T> T decode(@Nullable ByteBuf buffer, int dataType, Format format, Class
         Codec<T> codec = this.codecLookup.findDecodeCodec(dataType, format, type);
         if (codec != null) {
             return codec.decode(buffer, dataType, format, type);
+        } else if (String.class == type) {
+            int varcharType = PostgresqlObjectId.VARCHAR.getObjectId();
+            codec = this.codecLookup.findDecodeCodec(varcharType, format, type);
+            if (codec != null) {
+                return codec.decode(buffer, varcharType, format, type);
+            }
         }
 
         throw new IllegalArgumentException(String.format("Cannot decode value of type %s with OID %d", type.getName(), dataType));

src/test/java/io/r2dbc/postgresql/codec/DefaultCodecsUnitTests.java

@@ -121,6 +121,16 @@ void decodeUnsupportedType() {
             .withMessage("Cannot decode value of type java.lang.Void with OID 23");
     }
 
+    @Test
+    void decodeFallbackToVarcharCodec() {
+        assertThat(this.codecs.decode(ByteBufUtils.encode(TEST, "2018-11-04 15:35:00.847108"), TIMESTAMP.getObjectId(), FORMAT_TEXT, String.class))
+            .isEqualTo("2018-11-04 15:35:00.847108");
+        assertThat(this.codecs.decode(ByteBufUtils.encode(TEST, "2018-11-05 00:35:43.048593+09"), TIMESTAMPTZ.getObjectId(), FORMAT_TEXT, String.class))
+            .isEqualTo("2018-11-05 00:35:43.048593+09");
+        assertThat(this.codecs.decode(ByteBufUtils.encode(TEST, "ENUM_VALUE"), 123456, FORMAT_TEXT, String.class))
+            .isEqualTo("ENUM_VALUE");
+    }
+
     @Test
     void delegatePriority() {
         assertThat(this.codecs.decode(TEST.buffer(2).writeShort((byte) 100), INT2.getObjectId(), FORMAT_BINARY, Object.class)).isInstanceOf(Short.class);