gen: Encode ML PredictRequest to JSON once only

The ML API expects users to prepare a JSON-encoded string as part of the
payload when building a GoogleCloudMlV1__PredictRequest. However, the
generator produces code which assumes a PredictRequest needs to be
encoded to JSON, even though the data field is in fact already encoded.
Furthermore, the generator produces code that drops the data portion of
the API response.

This commit adds special handling for requests to the ML predict
endpoint, in order to correctly marshal requests and unmarshal
responses. For a discussion of API requests and responses, see
https://cloud.google.com/ml-engine/docs/v1/predict-request

Fixes #241.

Change-Id: I6ce90cae80d319b64173dd285051b65b07ba1255
Reviewed-on: https://code-review.googlesource.com/c/34871
Reviewed-by: Jean de Klerk <deklerk@google.com>

google-api-go-generator/gen.go

@@ -1851,12 +1851,18 @@ func (meth *Method) generateCode() {
 	}
 	pn("var body io.Reader = nil")
 	if ba := args.bodyArg(); ba != nil && httpMethod != "GET" {
-		style := "WithoutDataWrapper"
-		if a.needsDataWrapper() {
-			style = "WithDataWrapper"
+		if meth.m.ID == "ml.projects.predict" {
+			// Skip JSONReader for APIs that require clients to pass in JSON already.
+			pn("body = strings.NewReader(c.%s.HttpBody.Data)", ba.goname)
+		} else {
+			style := "WithoutDataWrapper"
+			if a.needsDataWrapper() {
+				style = "WithDataWrapper"
+			}
+			pn("body, err := googleapi.%s.JSONReader(c.%s)", style, ba.goname)
+			pn("if err != nil { return nil, err }")
 		}
-		pn("body, err := googleapi.%s.JSONReader(c.%s)", style, ba.goname)
-		pn("if err != nil { return nil, err }")
+
 		pn(`reqHeaders.Set("Content-Type", "application/json")`)
 	}
 	pn(`c.urlParams_.Set("alt", alt)`)
@@ -1985,7 +1991,16 @@ func (meth *Method) generateCode() {
 		} else {
 			pn("target := &ret")
 		}
-		pn("if err := gensupport.DecodeResponse(target, res); err != nil { return nil, err }")
+
+		if meth.m.ID == "ml.projects.predict" {
+			pn("var b bytes.Buffer")
+			pn("if _, err := io.Copy(&b, res.Body); err != nil { return nil, err }")
+			pn("if err := res.Body.Close(); err != nil { return nil, err }")
+			pn("if err := json.NewDecoder(bytes.NewReader(b.Bytes())).Decode(target); err != nil { return nil, err }")
+			pn("ret.Data = b.String()")
+		} else {
+			pn("if err := gensupport.DecodeResponse(target, res); err != nil { return nil, err }")
+		}
 		pn("return ret, nil")
 	}
 

google-api-go-generator/gen_test.go

@@ -35,6 +35,7 @@ func TestAPIs(t *testing.T) {
 		"blogger-3",
 		"floats",
 		"getwithoutbody",
+		"json-body",
 		"mapofany",
 		"mapofarrayofobjects",
 		"mapofint64strings",