From ac1a09873d2944d7147efb7c42830d1844fe2c17 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jaime=20Pi=C3=B1a?= <jaime@synadia.com>
Date: Thu, 17 Dec 2020 14:06:09 -0800
Subject: [PATCH] Validate setting JetStream APIPrefix

This adds a check to nats.ApiPrefix that prevents the prefix from
containing wildcards. When @wallyqs and I were exploring the code, we
found that we could end up with invalid API subjects like
foo.>.STREAM.NAMES.

Also, this removes what appears to be outdated prefix TODOs.
---
 js.go        | 23 ++++++++++++++++++---
 nats_test.go | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 78 insertions(+), 3 deletions(-)

diff --git a/js.go b/js.go
index abd71c7ff..e86dd59d6 100644
--- a/js.go
+++ b/js.go
@@ -165,10 +165,27 @@ func (opt jsOptFn) configureJSContext(opts *js) error {
 // APIPrefix changes the default prefix used for the JetStream API.
 func APIPrefix(pre string) JSOpt {
 	return jsOptFn(func(js *js) error {
-		js.pre = pre
-		if !strings.HasSuffix(js.pre, ".") {
-			js.pre = js.pre + "."
+		pre = strings.TrimSuffix(pre, ".")
+
+		if pre == ">" {
+			return ErrJetStreamBadPre
 		}
+
+		toks := strings.Split(pre, ".")
+		for i, tok := range toks {
+			if tok == "" || tok == "*" {
+				return ErrJetStreamBadPre
+			}
+
+			if tok == ">" && i < len(toks)-1 {
+				return ErrBadSubject
+			} else if tok == ">" && i == len(toks)-1 {
+				js.pre = pre
+				return nil
+			}
+		}
+
+		js.pre = fmt.Sprintf("%s.", pre)
 		return nil
 	})
 }
diff --git a/nats_test.go b/nats_test.go
index 665fa6722..b76a4c62d 100644
--- a/nats_test.go
+++ b/nats_test.go
@@ -2599,3 +2599,61 @@ func TestMsg_RespondMsg(t *testing.T) {
 		t.Fatalf("did not get correct response: %q", resp.Data)
 	}
 }
+
+func TestJetStreamAPIPrefix(t *testing.T) {
+	cases := []struct {
+		prefix     string
+		wantPrefix string
+		wantErr    bool
+	}{
+		{
+			prefix:     "foo",
+			wantPrefix: "foo.",
+		},
+		{
+			prefix:     "foo.",
+			wantPrefix: "foo.",
+		},
+		{
+			prefix:     "foo.>",
+			wantPrefix: "foo.>",
+		},
+		{
+			prefix:     "foo.b*r.baz",
+			wantPrefix: "foo.b*r.baz.",
+		},
+		{
+			prefix:  "foo.*",
+			wantErr: true,
+		},
+		{
+			prefix:  "foo.*.bar",
+			wantErr: true,
+		},
+		{
+			prefix:  "foo.>.bar",
+			wantErr: true,
+		},
+		{
+			prefix:  ">",
+			wantErr: true,
+		},
+	}
+	for _, c := range cases {
+		t.Run(c.prefix, func(t *testing.T) {
+			jsOpt := APIPrefix(c.prefix)
+
+			js := new(js)
+			if err := jsOpt.configureJSContext(js); err != nil && !c.wantErr {
+				t.Fatal(err)
+			} else if err == nil && c.wantErr {
+				t.Fatal("unexpected success")
+			}
+
+			if js.pre != c.wantPrefix {
+				t.Error("unexpected api prefix")
+				t.Fatalf("got=%s; want=%s", js.pre, c.wantPrefix)
+			}
+		})
+	}
+}