feat(graphiql): Set 'X-GraphQL-Event-Stream' header when --watch enab…

…led (#728)

* Dev script assumes less

* Don't support event stream unless watchPg

* Set header pointing to event stream

scripts/dev

@@ -15,7 +15,7 @@ $npm_bin/nodemon \
   --ignore __mocks__ \
   --ignore src/postgraphile/graphiql \
   --ext js,ts \
-  --exec "$npm_bin/ts-node --ignore node_modules --disableWarnings src/postgraphile/cli.ts --schema a,b,c --show-error-stack json --watch $@" &
+  --exec "$npm_bin/ts-node --ignore node_modules --disableWarnings src/postgraphile/cli.ts --show-error-stack json --extended-errors hint,detail,errcode $@" &
 
 # Ensure forked process is killed even if we die unexpectedly
 trap 'trap - SIGINT SIGTERM EXIT; JOBS="$(jobs -p)"; [[ "$JOBS" != "" ]] && kill $JOBS 2>/dev/null || true' SIGINT SIGTERM EXIT

src/postgraphile/http/createPostGraphileHttpRequestHandler.js

@@ -285,7 +285,7 @@ export default function createPostGraphileHttpRequestHandler(options) {
 
       // Setup an event stream so we can broadcast events to graphiql, etc.
       if (parseUrl(req).pathname === '/_postgraphile/stream') {
-        if (req.headers.accept !== 'text/event-stream') {
+        if (!options.watchPg || req.headers.accept !== 'text/event-stream') {
           res.statusCode = 405
           res.end()
           return
@@ -339,6 +339,11 @@ export default function createPostGraphileHttpRequestHandler(options) {
 
     // If we didn’t call `next` above, all requests will return 200 by default!
     res.statusCode = 200
+    if (options.watchPg) {
+      // Inform GraphiQL and other clients that they can subscribe to events
+      // (such as the schema being updated) at the following URL
+      res.setHeader('X-GraphQL-Event-Stream', '/_postgraphile/stream')
+    }
 
     // Don’t execute our GraphQL stuffs for `OPTIONS` requests.
     if (req.method === 'OPTIONS') {