From fd904b0d34e9d78ab93f630846c8c512157027ae Mon Sep 17 00:00:00 2001
From: Joseph Schorr <josephschorr@users.noreply.github.com>
Date: Tue, 26 Apr 2022 15:46:18 -0400
Subject: [PATCH] Add headers for requesting and receiving the server version

---
 pkg/requestmeta/requestmeta.go   | 39 ++++++++++++++++++++++++++++++++
 pkg/responsemeta/responsemeta.go |  4 ++++
 2 files changed, 43 insertions(+)
 create mode 100644 pkg/requestmeta/requestmeta.go

diff --git a/pkg/requestmeta/requestmeta.go b/pkg/requestmeta/requestmeta.go
new file mode 100644
index 0000000..a859b9f
--- /dev/null
+++ b/pkg/requestmeta/requestmeta.go
@@ -0,0 +1,39 @@
+package requestmeta
+
+import (
+	"context"
+
+	"google.golang.org/grpc/metadata"
+)
+
+// RequestMetadataHeaderKey defines a key in the request metadata header.
+type RequestMetadataHeaderKey string
+
+// BoolRequestMetadataHeaderKey defines a key for a boolean vlaue in the request metadata header.
+type BoolRequestMetadataHeaderKey RequestMetadataHeaderKey
+
+const (
+	// RequestServerVersion, if specified in a request header, asks SpiceDB to return its
+	// server version in the response header (if supported).
+	// Value: `1`
+	RequestServerVersion BoolRequestMetadataHeaderKey = "io.spicedb.requestversion"
+)
+
+// AddRequestHeaders returns a new context with the given values as request headers.
+func AddRequestHeaders(ctx context.Context, keys ...BoolRequestMetadataHeaderKey) context.Context {
+	values := make(map[RequestMetadataHeaderKey]string, len(keys))
+	for _, key := range keys {
+		values[RequestMetadataHeaderKey(key)] = "1"
+	}
+	return SetRequestHeaders(ctx, values)
+}
+
+// SetRequestHeaders returns a new context with the given values as request headers.
+func SetRequestHeaders(ctx context.Context, values map[RequestMetadataHeaderKey]string) context.Context {
+	pairs := make([]string, 0, len(values)*2)
+	for key, value := range values {
+		pairs = append(pairs, string(key))
+		pairs = append(pairs, value)
+	}
+	return metadata.NewOutgoingContext(ctx, metadata.Pairs(pairs...))
+}
diff --git a/pkg/responsemeta/responsemeta.go b/pkg/responsemeta/responsemeta.go
index 8e81204..0483aa4 100644
--- a/pkg/responsemeta/responsemeta.go
+++ b/pkg/responsemeta/responsemeta.go
@@ -15,6 +15,10 @@ type ResponseMetadataHeaderKey string
 const (
 	// RequestID is the key in the response header metadata for the request's tracking ID, if any.
 	RequestID ResponseMetadataHeaderKey = "io.spicedb.respmeta.requestid"
+
+	// ServerVersion is the key in the response header metadata holding the version of the server
+	// handling the API request, if requested via a request header.
+	ServerVersion ResponseMetadataHeaderKey = "io.spicedb.version"
 )
 
 // ResponseMetadataTrailerKey defines a key in the response metadata trailer.