@reedchan/koa-http-proxy/app/steps/decorateUserRes.js

http proxy middleware for koa

"use strict";

var as = require("../../lib/as.js");
var zlib = require("zlib");

function isResGzipped(res) {
  return res.headers["content-encoding"] === "gzip";
}

function zipOrUnzip(method) {
  return function (rspData, res) {
    return isResGzipped(res) ? zlib[method](rspData) : rspData;
  };
}

var maybeUnzipResponse = zipOrUnzip("gunzipSync");
var maybeZipResponse = zipOrUnzip("gzipSync");

function verifyBuffer(rspd, reject) {
  if (!Buffer.isBuffer(rspd)) {
    return reject(
      new Error("userResDecorator should return string or buffer as data"),
    );
  }
}

function updateHeaders(ctx, rspdBefore, rspdAfter, reject) {
  if (!ctx.headerSent) {
    ctx.set("content-length", rspdAfter.length);
  } else if (rspdAfter.length !== rspdBefore.length) {
    var error =
      '"Content-Length" is already sent,' +
      "the length of response data can not be changed";
    return reject(new Error(error));
  }
}

function decorateProxyResBody(container) {
  if (container.user.ctx.status === 504) {
    return Promise.resolve(container);
  }
  var resolverFn = container.options.userResDecorator;
  if (!resolverFn) {
    return Promise.resolve(container);
  }

  var proxyResData = maybeUnzipResponse(
    container.proxy.resData,
    container.proxy.res,
  );
  var proxyRes = container.proxy.res;
  var ctx = container.user.ctx;

  return Promise.resolve(resolverFn(proxyRes, proxyResData, ctx)).then(
    function (modifiedResData) {
      return new Promise(function (resolve, reject) {
        var rspd = as.buffer(modifiedResData, container.options);
        verifyBuffer(rspd, reject);
        updateHeaders(ctx, proxyResData, rspd, reject);
        container.proxy.resData = maybeZipResponse(rspd, container.proxy.res);
        resolve(container);
      });
    },
  );
}

module.exports = decorateProxyResBody;