[Proposal] Split into multiple middlewares

Just a idea, but I think we should embrace express middleware system.

Maybe something like below:

import { parser, validate, execute, errorHandler, graphiql } from 'express-graphql';
import logger from 'graphql-third-party-query-param-logger';

const app = express();

app.use('/graphql', parser(...));
app.use('/graphql', logger(...));
app.use('/graphql', validate(...));
app.use('/graphql', execute(...));
app.use('/graphql', errorHander(...));
app.use('/graphql', graphiql(...));

app.listen(3000);

And then we can use middlewares at any points to log and measure performance, even have more control on input, output and errors.

Eventually, more reasonable, extendable middlewares will born and enrich the whole graphql ecosystem.

Relative issue: #101 #102 #107

[wincent]

FYI, just closed a couple of other related issues in the interests of centralizing the discussion here. For context, this is the comment I made on #178:

I think there’s clearly a demand for this (as evidenced by this issue, and #113 and #101). In essence, all of these are about the same thing: making express-graphql more extensible and reusable. The actual mechanism we use to do that needs to be decided (whether it be splitting it out into smaller libraries that can be recomposed, or creating a structure that makes it easy for other libraries to insert themselves in some way), but I think there’s value in the core, abstract idea independently of any implementation details.

We should centralize the discussion in a single place though, so I am going to close this issue and request that we concentrate further discussion in issue #113.

Let’s carry on from here.

[lacker]

I think something like this could be useful. What are the important use cases here?

For performance logging it does seem useful to be able to insert some middleware after the query is parsed, but before it is executed. You might also want to do things like rejecting a query that was too complicated at the same point.

It does seem like it is useful to mount graphiql separately but that doesn’t seem like it should work like app.use('/graphql', graphiql(...)); - it seems more like you would want app.use('/graphql/graphiql', graphiql(...)); but then I don’t really see how separating out the middleware buys you anything over just mounting graphiql on a different URL.

What is the benefit of separating validate, execute, and errorHandler?