* Returns a view of a slice of this byte source that is at most {@code length} bytes long
   * starting at the given {@code offset}. If {@code offset} is greater than the size of this
   * source, the returned source will be empty. If {@code offset + length} is greater than the size
   * of this source, the returned source will contain the slice starting at {@code offset} and
   * ending at the end of this source.
   *

        // merge implicitly assumes that merge is only called on the same GAV and does not perform any validation here!
        Metadata source = new Metadata();
        source.setArtifactId("source-artifact");
        source.setGroupId("source-group");
        source.setVersion("2.0");
        assertFalse(target.merge(source));
        assertEquals("myArtifact", target.getArtifactId());
        assertEquals("myGroup", target.getGroupId());

        if (!source.isEmpty()) {
          return false;
        }
      }
      return true;
    }

    @Override
    public Optional<Long> lengthIfKnown() {
      long result = 0L;
      for (CharSource source : sources) {
        Optional<Long> lengthIfKnown = source.lengthIfKnown();
        if (!lengthIfKnown.isPresent()) {
          return Optional.absent();
        }

        if (!source.isEmpty()) {
          return false;
        }
      }
      return true;
    }

    @Override
    public Optional<Long> lengthIfKnown() {
      long result = 0L;
      for (CharSource source : sources) {
        Optional<Long> lengthIfKnown = source.lengthIfKnown();
        if (!lengthIfKnown.isPresent()) {
          return Optional.absent();
        }

	// S3 extensions
	AmzCopySourceIfModifiedSince   = "x-amz-copy-source-if-modified-since"
	AmzCopySourceIfUnmodifiedSince = "x-amz-copy-source-if-unmodified-since"

	AmzCopySourceIfNoneMatch = "x-amz-copy-source-if-none-match"
	AmzCopySourceIfMatch     = "x-amz-copy-source-if-match"

	AmzCopySource                 = "X-Amz-Copy-Source"
	AmzCopySourceVersionID        = "X-Amz-Copy-Source-Version-Id"

            result.setCreatedTime(DfTypeUtil.toLong(source.get("createdTime")));
            result.setDepth(DfTypeUtil.toInteger(source.get("depth")));
            result.setDescription(DfTypeUtil.toString(source.get("description")));
            result.setExcludedDocPaths(DfTypeUtil.toString(source.get("excludedDocPaths")));
            result.setExcludedPaths(DfTypeUtil.toString(source.get("excludedPaths")));

    assertEquals(STRING.length(), source.copyTo(sink));
    assertTrue(source.wasStreamOpened() && source.wasStreamClosed());
    assertTrue(sink.wasStreamOpened() && sink.wasStreamClosed());

    assertEquals(STRING, sink.getString());
  }

  public void testRead_toString() throws IOException {
    assertEquals(STRING, source.read());
    assertTrue(source.wasStreamOpened() && source.wasStreamClosed());
  }

            result.setLanguages(DfTypeUtil.toString(source.get("languages")));
            result.setQueryId(DfTypeUtil.toString(source.get("queryId")));
            result.setQueryOffset(DfTypeUtil.toInteger(source.get("queryOffset")));
            result.setQueryPageSize(DfTypeUtil.toInteger(source.get("queryPageSize")));
            result.setQueryTime(DfTypeUtil.toLong(source.get("queryTime")));

    // +---------------------------------------------------------------+
    val length = source.readMedium()
    if (length > INITIAL_MAX_FRAME_SIZE) {
      throw IOException("FRAME_SIZE_ERROR: $length")
    }
    val type = source.readByte() and 0xff
    val flags = source.readByte() and 0xff
    val streamId = source.readInt() and 0x7fffffff // Ignore reserved bit.

        return builder(requireNonNull(request, "request cannot be null"))
                .source(requireNonNull(source, "source cannot be null"))
                .build();
    }

    @Nonnull
    static ModelBuilderRequest build(@Nonnull Session session, @Nonnull ModelSource source) {
        return builder()