fetchr-koa-middleware.js

/**
 * Fetchr middleware for koa
 * 
 * Translate Fetchr.middleware() from express.js to koa
 * This is pretty rough and might be buggy but it does the job nicely for me at the moment.
 * 
 * Tested with fetchr v0.5.14
 */
export default function () {
  return function * (next) {
    let ctx = this
    // construct expressjs-like request
    const modifiedReq = {
      path: ctx.request.url,
      method: ctx.request.method,
      body: ctx.request.body
    }
    yield new Promise((resolve, reject) => {
      // mock an expressjs response that modifies the actual koa response
      const modifiedRes = {
        status(code) {
          ctx.response.status = code
          return this
        },
        json(data) {
          ctx.response.body = data
          /**
           * cheap trick: fetchr does not support promises yet and does not return anything
           * when fetching is successful. however, req.json is always called last when fetches are successful
           * so let's just inject the promise resolve here. no need to touch the fetchr library at all.
           */
          resolve()
          return this
        },
        set(headers) {
          ctx.response.headers = headers
          return this
        }
      }
      Fetchr.middleware()(modifiedReq, modifiedRes, err => {
        if (err) {
          throw err
        }
        else resolve()
      })
    })
  }
}