Support "application/json" in Blubberoid

JSON seems a better option for a web service in general—other toolchains
in the Docker/Kubernetes space typically prefer YAML for human-edited
configs but convert to JSON on the wire. The "application/json" media
type is well established—unlike "application/yaml" which has no official
assignment by IANA—and is better supported by the OpenAPI (formerly
Swagger) specification.

Added content-type media type validation in the Blubberoid HTTP server
handler, and added a check for `json.Valid(body)` upon receiving a
"application/json" media type. Since any given valid JSON is also valid
YAML, Blubberoid simply does a shallow validation of the JSON body
before punting to `config.ReadConfig` for YAML unmarshalling and
thorough config validation.

Bug: T205920
Change-Id: I970acbde497ed446eb8eed568b1328f8c6f5aa55

1 files changed, 19 insertions, 0 deletions

diff --git a/cmd/blubberoid/main.go b/cmd/blubberoid/main.go
index 73b10a6..d436390 100644
--- a/cmd/blubberoid/main.go
+++ b/cmd/blubberoid/main.go
@@ -3,9 +3,11 @@
 package main
 
 import (
+	"encoding/json"
 	"fmt"
 	"io/ioutil"
 	"log"
+	"mime"
 	"net/http"
 	"os"
 	"path"
@@ -71,6 +73,23 @@ func blubberoid(res http.ResponseWriter, req *http.Request) {
 		return
 	}
 
+	switch mt, _, _ := mime.ParseMediaType(req.Header.Get("content-type")); mt {
+	case "application/json":
+		// Enforce strict JSON syntax if specified, even though the config parser
+		// would technically handle anything that's at least valid YAML
+		if !json.Valid(body) {
+			res.WriteHeader(http.StatusBadRequest)
+			res.Write(responseBody("'%s' media type given but request contains invalid JSON", mt))
+			return
+		}
+	case "application/yaml", "application/x-yaml":
+		// Let the config parser validate YAML syntax
+	default:
+		res.WriteHeader(http.StatusUnsupportedMediaType)
+		res.Write(responseBody("'%s' media type is not supported", mt))
+		return
+	}
+
 	cfg, err := config.ReadYAMLConfig(body)
 
 	if err != nil {