Strange behaviour with koa-router and koa.session middlewares

It looks like that if you use koa.session and koa-router middlewares you have to watch out for the order in which you install them.

Take a look at this example:

var app = require('koa')(),
    session = require('koa.session'),
    router = require('koa-router');
app.keys = ['secret'];

app.use(session())
app.use(router(app));

app.get('/test/print', function*(){
    var v = this.session.value || 'Not FOUND';
    this.body = 'You value is ' + v;
})

app.post('/test/:v', function*(){
    this.session.value = this.params.v;
    this.body = 'OK'
})

app.listen(8080);
console.log('Listening...')

If you execute this everything goes fine and you get back your value if you GET on the correct url.

If you switch the ``use` as follows:

app.use(router(app));
app.use(session())

and issue the exact command than before you get instead a

TypeError: Cannot read property 'value' of undefined
    at Object.<anonymous> (index.js:14:22)

Where line 14:22 is around this.session.value meaning that session is undefined.

I’ve created a makefile to reproduce the error and am posting this issue on the middleware’s repos as well.

Makefile:

POST_FILE=post
GET_FILE=get
COOKIE_JAR=biscotti

all: 
    @make example
    @make show
    #@make end
    @killall node

clean:
    rm -f ${POST_FILE}.txt ${POST_FILE}-debug.txt  ${GET_FILE}.txt ${GET_FILE}-debug.txt ${COOKIE_JAR}

node:
    DEBUG=koa node --harmony index.js&
    @sleep 2

post:
    @curl -s --cookie-jar ${COOKIE_JAR} --trace-ascii ${POST_FILE}-debug.txt -X POST http://127.0.0.1:8080/test/42 -o ${POST_FILE}.txt

get:
    @sleep 2
    @curl -s -b ${COOKIE_JAR} --trace-ascii ${GET_FILE}-debug.txt -X GET http://127.0.0.1:8080/test/print -o ${GET_FILE}.txt
    @cat ${GET_FILE}.txt
    @echo "\n"
redis:
    redis-server&
    @sleep 1

end:
    @killall node
    @echo 'shutdown nosave' | redis-cli --pipe&


example:
    @make clean
#@make redis
    @make node
    @make post
    @make get

show:
    @echo "POST:\n"
    @cat ${POST_FILE}.txt
    @echo "\n\n"
    @echo "GET:\n"
    @cat ${GET_FILE}.txt
    @echo "\n"



.PHONY = example post get node redis end show all

[slaskis]

Isn’t this what would be expected? I believe you can think of the middlewares as a stack like this:

session(
  router(
    get('/test/print'),
    post('/test/:v')
  )
)

while reordering would make it something like this:

router(
  get('/test/print'),
  post('/test/:v')
  session()
)

so if it’s the other way around the router is run (and thus the routes?) before the session middleware which makes this.session undefined.

But please correct me if I misunderstood the issue.

[ghost]

And thank you for reporting it 👍