Enable sub-attesters content type selection

Now users may pick the desired output content type of each sub-attester
by specifying field "content-type" in "attester-selection" as shown in
the following example:

"attester-selection": {
    mocktsm:{
        "content-type": "application/vnd.veraison.configfs-tsm+json",
        "privilege_level": 3
    }
}

Signed-off-by: Ian Chin Wang <[email protected]>

Author: cowbon

api/server.go

@@ -147,14 +147,53 @@ func (s *Server) RatsdChares(w http.ResponseWriter, r *http.Request, param Ratsd
 			return
 		}
 
+		outputCt := formatOut.Formats[0].ContentType
 		params, hasOption := options[pn]
 		if !hasOption {
 			params = json.RawMessage{}
+		} else {
+			attesterOptions := make(map[string]string)
+			if err := json.Unmarshal(params, &attesterOptions); err != nil {
+				errMsg := fmt.Sprintf(
+					"failed to parse options for %s: %v", pn, err)
+				p := &problems.DefaultProblem{
+					Type:   string(TagGithubCom2024VeraisonratsdErrorInvalidrequest),
+					Title:  string(InvalidRequest),
+					Detail: errMsg,
+					Status: http.StatusBadRequest,
+				}
+				s.reportProblem(w, p)
+				return
+			}
+
+			validCt := false
+			if desiredCt, ok := attesterOptions["content-type"]; ok {
+				for _, f := range formatOut.Formats {
+					if f.ContentType == desiredCt {
+						outputCt = desiredCt
+						validCt = true
+						break
+					}
+				}
+
+				if !validCt {
+					errMsg := fmt.Sprintf(
+						"%s does not support content type %s", pn, desiredCt)
+					p := &problems.DefaultProblem{
+						Type:   string(TagGithubCom2024VeraisonratsdErrorInvalidrequest),
+						Title:  string(InvalidRequest),
+						Detail: errMsg,
+						Status: http.StatusBadRequest,
+					}
+					s.reportProblem(w, p)
+					return
+				}
+			}
 		}
 
-		s.logger.Info(pn, " output content type: ", formatOut.Formats[0].ContentType)
+		s.logger.Info(pn, " output content type: ", outputCt)
 		in := &compositor.EvidenceIn{
-			ContentType: formatOut.Formats[0].ContentType,
+			ContentType: outputCt,
 			Nonce:       nonce,
 			Options:     params,
 		}

api/server_test.go

@@ -103,6 +103,15 @@ func TestRatsdChares_invalid_body(t *testing.T) {
 		"attester-selection": "attester-slection"}`, validNonce),
 			"failed to parse attester selection: json: cannot unmarshal string into" +
 				` Go value of type map[string]json.RawMessage`},
+		{"invalid attester options",
+			fmt.Sprintf(`{"nonce": "%s",
+			"attester-selection": {"mock-tsm":"invalid"}}`, validNonce),
+			"failed to parse options for mock-tsm: json: cannot unmarshal string into" +
+				` Go value of type map[string]string`},
+		{"request content type unavailable",
+			fmt.Sprintf(`{"nonce": "%s",
+			"attester-selection": {"mock-tsm":{"content-type":"invalid"}}}`, validNonce),
+			"mock-tsm does not support content type invalid"},
 	}
 
 	for _, tt := range tests {