NextJS 15 cache handler shim for transforming buffers appropriately

bufferTransformCacheHandlerShim.js

/**
 * This cache handler shim ensures compatibility with Redis, by converting
 * buffers to strings on save and back to buffers on read, since the data
 * is stored as JSON.
 *
 * This shim is a temporary workaround until Next 15 support is added to
 * @neshca/cache-handler:
 * https://github.com/caching-tools/next-shared-cache/pull/969
 *
 * @param {import("@neshca/cache-handler").Handler} handler - The original cache handler to wrap.
 * @returns {import("@neshca/cache-handler").Handler} - The transformed cache handler.
 */
function bufferTransformCacheHandlerShim(handler) {
  return {
    name: handler.name,

    async get(key, data) {
      const result = await handler.get(key, data)
      const value = result?.value

      if (value?.kind === 'APP_PAGE') {
        if (value.rscData) {
          // Convert rscData string to Buffer
          // See: https://github.com/vercel/next.js/blob/f5444a16ec2ef7b82d30048890b613aa3865c1f1/packages/next/src/server/response-cache/types.ts#L76
          value.rscData = Buffer.from(value.rscData, 'utf-8')
        }

        if (value.segmentData) {
          // Convert segmentData Record<string, string> to Map<string, Buffer>
          // See: https://github.com/vercel/next.js/blob/f5444a16ec2ef7b82d30048890b613aa3865c1f1/packages/next/src/server/response-cache/types.ts#L80
          value.segmentData = new Map(
            Object.entries(value.segmentData).map(([key, value]) => [
              key,
              Buffer.from(value, 'utf-8'),
            ]),
          )
        }
      }

      if (value?.kind === 'APP_ROUTE' && value?.body) {
        // Convert body string to Buffer
        // See: https://github.com/vercel/next.js/blob/f5444a16ec2ef7b82d30048890b613aa3865c1f1/packages/next/src/server/response-cache/types.ts#L97
        value.body = Buffer.from(value.body, 'utf-8')
      }

      return result
    },

    async set(key, data) {
      const value = data?.value

      if (value?.kind === 'APP_PAGE') {
        if (value.rscData) {
          // Convert rscData Buffer to string
          // See: https://github.com/vercel/next.js/blob/f5444a16ec2ef7b82d30048890b613aa3865c1f1/packages/next/src/server/response-cache/types.ts#L76
          value.rscData = value.rscData.toString()
        }

        if (value.segmentData) {
          // Convert segmentData Map<string, Buffer> to Record<string, string>
          // See: https://github.com/vercel/next.js/blob/f5444a16ec2ef7b82d30048890b613aa3865c1f1/packages/next/src/server/response-cache/types.ts#L80
          value.segmentData = Object.fromEntries(
            Array.from(value.segmentData.entries()).map(([key, value]) => [key, value.toString()]),
          )
        }
      }

      if (value?.kind === 'APP_ROUTE' && value?.body) {
        // Convert body Buffer to string
        // See: https://github.com/vercel/next.js/blob/f5444a16ec2ef7b82d30048890b613aa3865c1f1/packages/next/src/server/response-cache/types.ts#L97
        value.body = value.body.toString()
      }

      await handler.set(key, data)
    },

    async revalidateTag(tag) {
      await handler.revalidateTag(tag)
    },

    async delete(key) {
      await handler.delete?.(key)
    },
  }
}