feat(multitenancy): Add support for namespace aware query and mutation

[ahsanbarkati]

This PR adds support for query and mutation of data in a namespace aware environment.
It also adds graphQL resolvers for creation and deletion of namespaces.

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This change is 

[manishrjain]

Reviewable status: 0 of 11 files reviewed, 1 unresolved discussion (waiting on @ahsanbarkati, @danielmai, @martinmr, @pawanrawal, and @vvbalaji-dgraph)

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x/keys.go, line 57 at r1 (raw file):

	// refer:
	// https://theasciicode.com.ar/ascii-control-characters/unit-separator-ascii-code-31.html
	NamespaceSeparator = byte(30)

no need now. Use namespace as uint64.

[manishrjain]

Will defer to @jarifibrahim for deeper look and approval. Do address my comments.

Reviewed 18 of 18 files at r2.
Reviewable status: all files reviewed, 12 unresolved discussions (waiting on @ahsanbarkati, @danielmai, @martinmr, @pawanrawal, and @vvbalaji-dgraph)

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dgraph/cmd/alpha/http.go, line 151 at r2 (raw file):

// namespaceHandler will helps to create namespace
func namespaceHandler(w http.ResponseWriter, r *http.Request) {

This should be done via GraphQL interface.

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dgraph/cmd/alpha/http.go, line 157 at r2 (raw file):

		return
	}
	// TODO(Ahsan): Need to add check for ns being convertible to uint64.

Add a TODO to handle delete namespace. Also a TODO for auth checking. The user should belong to the guardians group.

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dgraph/cmd/alpha/run.go, line 434 at r2 (raw file):

	http.HandleFunc("/state", stateHandler)
	http.HandleFunc("/jemalloc", x.JemallocHandler)
	http.HandleFunc("/namespace", namespaceHandler)

this should be in GraphQL admin endpoint.

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edgraph/server.go, line 261 at r2 (raw file):

// parseSchemaFromAlterOperation parses the string schema given in input operation to a Go
// struct, and performs some checks to make sure that the schema is valid.
func parseSchemaFromAlterOperation(namespace uint64, op *api.Operation) (*schema.ParsedSchema, error) {

100 chars.

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query/mutation.go, line 207 at r2 (raw file):

		// Get edge from nquad using newUids.
		var edge *pb.DirectedEdge
		if wnq.Predicate != x.Star {

You might want to check what happens when you do a deletion of star, for a same name predicate across two different namespaces.

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query/query.go, line 208 at r2 (raw file):

	AllowedPreds []string
	// Namespace of the given subgraph
	Namespace uint64

SubGraph shouldn't need it. Context should be sufficient.

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query/query.go, line 2862 at r2 (raw file):

	if req.GqlQuery.Schema != nil {
		preds := []string{}
		for _, pred := range req.GqlQuery.Schema.Predicates {

Just create a func, which can take a list of strings, and just add the namespace to them and return.

preds := x.AppendNamespace(...)

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x/keys.go, line 62 at r2 (raw file):

	buf := make([]byte, 8)
	binary.BigEndian.PutUint64(buf, ns)
	namespace := fmt.Sprintf("%s", buf)

this is expensive for critical paths.

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x/keys.go, line 63 at r2 (raw file):

	binary.BigEndian.PutUint64(buf, ns)
	namespace := fmt.Sprintf("%s", buf)
	return namespace + attr

return string(buf) + attr

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x/x.go, line 256 at r2 (raw file):

	md, ok := metadata.FromIncomingContext(ctx)
	if !ok {
		return DefaultNamespace

shouldn't this be a check failure?

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x/x.go, line 260 at r2 (raw file):

	ns := md.Get("namespace")
	if len(ns) == 0 {
		return DefaultNamespace

and this should be a check failure?

Ensure that when we get a request, Dgraph sets the namespace in the context, overwriting anything that the user might have passed. If no ACL, then set to DefaultNamespace.

[jarifibrahim]

Reviewed 9 of 18 files at r2, 3 of 9 files at r3, 15 of 15 files at r4.
Reviewable status: all files reviewed, 14 unresolved discussions (waiting on @ahsanbarkati, @danielmai, @martinmr, @pawanrawal, and @vvbalaji-dgraph)