From 4690599354559e4a426dc0b013f87971861c2e77 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
 and other debug information

---
 pkg/requestmeta/requestmeta.go   | 39 ++++++++++++++++++++++++++++++++
 pkg/responsemeta/responsemeta.go | 37 ++++++++++++++++++++++++++----
 2 files changed, 71 insertions(+), 5 deletions(-)
 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..b9616ec 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.debug.version"
 )
 
 // ResponseMetadataTrailerKey defines a key in the response metadata trailer.
@@ -52,16 +56,39 @@ func SetResponseTrailerMetadata(ctx context.Context, values map[ResponseMetadata
 	return grpc.SetTrailer(ctx, metadata.Pairs(pairs...))
 }
 
-// GetIntResponseTrailerMetadata retrieves an integer value for the given key in the trailer
+// ListResponseTrailerMetadata retrieves the string value(s) for the given key in the trailer
 // metadata of a SpiceDB API response.
-func GetIntResponseTrailerMetadata(trailer metadata.MD, key ResponseMetadataTrailerKey) (int, error) {
+func ListResponseTrailerMetadata(trailer metadata.MD, key ResponseMetadataTrailerKey) ([]string, error) {
 	values := trailer.Get(string(key))
 	if len(values) == 0 {
-		return 0, fmt.Errorf("key `%s` not found in trailer", key)
+		return []string{}, fmt.Errorf("key `%s` not found in trailer", key)
+	}
+
+	return values, nil
+}
+
+// GetResponseTrailerMetadata retrieves a string value for the given key in the trailer
+// metadata of a SpiceDB API response.
+func GetResponseTrailerMetadata(trailer metadata.MD, key ResponseMetadataTrailerKey) (string, error) {
+	values, err := ListResponseTrailerMetadata(trailer, key)
+	if err != nil {
+		return "", err
 	}
+
 	if len(values) != 1 {
-		return 0, fmt.Errorf("key `%s` found multiple times in trailer", key)
+		return "", fmt.Errorf("key `%s` found multiple times in trailer", key)
+	}
+
+	return values[0], nil
+}
+
+// GetIntResponseTrailerMetadata retrieves an integer value for the given key in the trailer
+// metadata of a SpiceDB API response.
+func GetIntResponseTrailerMetadata(trailer metadata.MD, key ResponseMetadataTrailerKey) (int, error) {
+	found, err := GetResponseTrailerMetadata(trailer, key)
+	if err != nil {
+		return 0, err
 	}
 
-	return strconv.Atoi(values[0])
+	return strconv.Atoi(found)
 }