Add peer-to-peer support into Dendrite via libp2p and fetch (#880)

* Use a fork of pq which supports userCurrent on wasm

* Use sqlite3_js driver when running in JS

* Add cmd/dendritejs to pull in sqlite3_js driver for wasm only

* Update to latest go-sqlite-js version

* Replace prometheus with a stub. sigh

* Hard-code a config and don't use opentracing

* Latest go-sqlite3-js version

* Generate a key for now

* Listen for fetch traffic rather than HTTP

* Latest hacks for js

* libp2p support

* More libp2p

* Fork gjson to allow us to enforce auth checks as before

Previously, all events would come down redacted because the hash
checks would fail. They would fail because sjson.DeleteBytes didn't
remove keys not used for hashing. This didn't work because of a build
tag which included a file which no-oped the index returned.

See https://github.com/tidwall/gjson/issues/157

When it's resolved, let's go back to mainline.

* Use gjson@1.6.0 as it fixes https://github.com/tidwall/gjson/issues/157

* Use latest gomatrixserverlib for sig checks

* Fix a bug which could cause exclude_from_sync to not be set

Caused when sending events over federation.

* Use query variadic to make lookups actually work!

* Latest gomatrixserverlib

* Add notes on getting p2p up and running

Partly so I don't forget myself!

* refactor: Move p2p specific stuff to cmd/dendritejs

This is important or else the normal build of dendrite will fail
because the p2p libraries depend on syscall/js which doesn't work
on normal builds.

Also, clean up main.go to read a bit better.

* Update ho-http-js-libp2p to return errors from RoundTrip

* Add an LRU cache around the key DB

We actually need this for P2P because otherwise we can *segfault*
with things like: "runtime: unexpected return pc for runtime.handleEvent"
where the event is a `syscall/js` event, caused by spamming sql.js
caused by "Checking event signatures for 14 events of room state" which
hammers the key DB repeatedly in quick succession.

Using a cache fixes this, though the underlying cause is probably a bug
in the version of Go I'm on (1.13.7)

* breaking: Add Tracing.Enabled to toggle whether we do opentracing

Defaults to false, which is why this is a breaking change. We need
this flag because WASM builds cannot do opentracing.

* Start adding conditional builds for wasm to handle lib/pq

The general idea here is to have the wasm build have a `NewXXXDatabase`
that doesn't import any postgres package and hence we never import
`lib/pq`, which doesn't work under WASM (undefined `userCurrent`).

* Remove lib/pq for wasm for syncapi

* Add conditional building to remaining storage APIs

* Update build script to set env vars correctly for dendritejs

* sqlite bug fixes

* Docs

* Add a no-op main for dendritejs when not building under wasm

* Use the real prometheus, even for WASM

Instead, the dendrite-sw.js must mock out `process.pid` and
`fs.stat` - which must invoke the callback with an error (e.g `EINVAL`)
in order for it to work:

```
    global.process = {
        pid: 1,
    };
    global.fs.stat = function(path, cb) {
        cb({
            code: "EINVAL",
        });
    }
```

* Linting

go.mod

@@ -1,43 +1,30 @@
 module github.com/matrix-org/dendrite
 
 require (
-	github.com/DataDog/zstd v1.4.4 // indirect
-	github.com/Shopify/toxiproxy v2.1.4+incompatible // indirect
-	github.com/codahale/hdrhistogram v0.0.0-20161010025455-3a0bb77429bd // indirect
-	github.com/eapache/go-resiliency v1.2.0 // indirect
-	github.com/eapache/go-xerial-snappy v0.0.0-20180814174437-776d5712da21 // indirect
-	github.com/eapache/queue v1.1.0 // indirect
-	github.com/frankban/quicktest v1.7.2 // indirect
-	github.com/golang/snappy v0.0.1 // indirect
 	github.com/gorilla/mux v1.7.3
-	github.com/konsorten/go-windows-terminal-sequences v1.0.2 // indirect
+	github.com/hashicorp/golang-lru v0.5.4
 	github.com/lib/pq v1.2.0
 	github.com/matrix-org/dugong v0.0.0-20171220115018-ea0a4690a0d5
+	github.com/matrix-org/go-http-js-libp2p v0.0.0-20200304160008-4ec1129a00c4
+	github.com/matrix-org/go-sqlite3-js v0.0.0-20200304164012-aa524245b658
 	github.com/matrix-org/gomatrix v0.0.0-20190528120928-7df988a63f26
-	github.com/matrix-org/gomatrixserverlib v0.0.0-20200124100636-0c2ec91d1df5
+	github.com/matrix-org/gomatrixserverlib v0.0.0-20200304110715-894c3c86ce3e
 	github.com/matrix-org/naffka v0.0.0-20200127221512-0716baaabaf1
-	github.com/matrix-org/util v0.0.0-20171127121716-2e2df66af2f5
+	github.com/matrix-org/util v0.0.0-20190711121626-527ce5ddefc7
 	github.com/mattn/go-sqlite3 v2.0.2+incompatible
-	github.com/miekg/dns v1.1.12 // indirect
 	github.com/nfnt/resize v0.0.0-20160724205520-891127d8d1b5
-	github.com/opentracing/opentracing-go v1.0.2
-	github.com/pierrec/lz4 v2.4.1+incompatible // indirect
+	github.com/opentracing/opentracing-go v1.1.0
 	github.com/pkg/errors v0.8.1
-	github.com/prometheus/client_golang v1.2.1
-	github.com/rcrowley/go-metrics v0.0.0-20190826022208-cac0b30c2563 // indirect
+	github.com/prometheus/client_golang v1.4.1
 	github.com/sirupsen/logrus v1.4.2
-	github.com/stretchr/testify v1.4.0 // indirect
-	github.com/uber-go/atomic v1.3.0 // indirect
-	github.com/uber/jaeger-client-go v2.15.0+incompatible
-	github.com/uber/jaeger-lib v1.5.0
-	go.uber.org/atomic v1.3.0 // indirect
+	github.com/tidwall/gjson v1.6.0
+	github.com/tidwall/pretty v1.0.1 // indirect
+	github.com/uber/jaeger-client-go v2.22.1+incompatible
+	github.com/uber/jaeger-lib v2.2.0+incompatible
 	golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550
-	golang.org/x/net v0.0.0-20190620200207-3b0461eec859 // indirect
-	golang.org/x/sync v0.0.0-20190227155943-e225da77a7e6 // indirect
 	gopkg.in/Shopify/sarama.v1 v1.20.1
-	gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 // indirect
 	gopkg.in/h2non/bimg.v1 v1.0.18
-	gopkg.in/yaml.v2 v2.2.2
+	gopkg.in/yaml.v2 v2.2.5
 )
 
 go 1.13