iOS 호스트: 브리지와 커스텀 스킴

  const browserFetch = window.fetch.bind(window);
  window.fetch = async (input, init = {}) => {
    const u = new URL(typeof input === 'string' ? input : input.url, location.href);
    if (u.protocol !== location.protocol || u.host !== location.host || !u.pathname.startsWith('/api/')) return browserFetch(input, init);
    const values = {path:u.pathname+u.search, method:init.method || 'GET'};
    if (init.body instanceof FormData) {
      values.fields = [];
      for (const [name, value] of init.body.entries()) {
        if (typeof value === 'string') values.fields.push({name, value});
        else {
          if (value.size > 100*1024*1024) throw new Error('Choose an image up to 100 MB.');
          values.fields.push({name, data:await base64(value)});
        }
      }
    } else if (init.body != null) values.body = String(init.body);
    // `onUploadProgress` (not a fetch option; the page's upload passes it) hears
    // an original's bytes as native sends them (cwkSiblingKit todo #545).
    const reply = await call('fetch', values, init.onUploadProgress);
    return new Response(reply.body, {status:reply.status, headers:{'Content-Type':'application/json'}});
  };

    static func url(_ path: String) throws -> URL {
        guard path.hasPrefix("/api/"), !path.contains("\\"), !path.contains("#"),
              let parts = URLComponents(string: path), parts.host == nil, parts.scheme == nil,
              !parts.percentEncodedPath.lowercased().contains("%2f"),
              !parts.percentEncodedPath.lowercased().contains("%5c"),
              !parts.path.split(separator: "/").contains(".."),
              let result = URL(string: path, relativeTo: origin)?.absoluteURL,
              result.host == origin.host, result.port == origin.port else { throw BridgeError.invalidPath }
        return result
    }

    private func relay(_ range: ByteRange, of url: URL, to schemeTask: WKURLSchemeTask) async throws {
        await blocks.validateScope()
        let path = url.path + (url.query.map { "?" + $0 } ?? "")
        let size = blocks.size
        if blocks.file(path) == nil {
            // The first block read tells the clip's length.
            if case .from(let first, _) = range { _ = try await blocks.block(path, first / size) } else { _ = try await blocks.block(path, 0) }
        }
        guard let file = blocks.file(path), let span = range.span(in: file.total),
              let head = MediaRange.partial(url: url, span: span, total: file.total, type: file.type) else { throw BridgeError.badReply }
        try Task.checkCancellation()
        schemeTask.didReceive(head)
        for index in (span.lowerBound / size)...(span.upperBound / size) {
            let block = try await blocks.block(path, index)
            blocks.prefetch(path, index + 1)
            try Task.checkCancellation()
            let start = index * size
            let lower = max(span.lowerBound, start) - start, upper = min(span.upperBound, start + block.data.count - 1) - start
            guard lower <= upper else { throw BridgeError.badReply }
            schemeTask.didReceive(block.data.subdata(in: lower..<(upper + 1)))
        }
        try Task.checkCancellation()
        schemeTask.didFinish()
    }