[dart-dio] Adds support for multipart form data post body (#4797)

* [dart-dio] Adds support for multipart form data post body

* [dart-dio] Fixes issues around formData

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartDioClientCodegen.java

@@ -232,6 +232,8 @@ public class DartDioClientCodegen extends DartClientCodegen {
         supportingFiles.add(new SupportingFile("pubspec.mustache", "", "pubspec.yaml"));
         supportingFiles.add(new SupportingFile("analysis_options.mustache", "", "analysis_options.yaml"));
         supportingFiles.add(new SupportingFile("apilib.mustache", libFolder, "api.dart"));
+        supportingFiles.add(new SupportingFile("api_util.mustache", libFolder, "api_util.dart"));
+
         supportingFiles.add(new SupportingFile("serializers.mustache", libFolder, "serializers.dart"));
 
         supportingFiles.add(new SupportingFile("gitignore.mustache", "", ".gitignore"));
@@ -346,6 +348,10 @@ public class DartDioClientCodegen extends DartClientCodegen {
             op.vendorExtensions.put("isForm", isForm);
             op.vendorExtensions.put("isMultipart", isMultipart);
 
+            if (op.getHasFormParams()) {
+                fullImports.add("package:" + pubName + "/api_util.dart");
+            }
+
             Set<String> imports = new HashSet<>();
             for (String item : op.imports) {
                 if (!modelToIgnore.contains(item.toLowerCase(Locale.ROOT))) {
@@ -356,6 +362,7 @@ public class DartDioClientCodegen extends DartClientCodegen {
             }
             modelImports.addAll(imports);
             op.imports = imports;
+
         }
 
         objs.put("modelImports", modelImports);

modules/openapi-generator/src/main/resources/dart-dio/api.mustache

@@ -25,10 +25,9 @@ class {{classname}} {
 
             String path = "{{{path}}}"{{#pathParams}}.replaceAll("{" + "{{baseName}}" + "}", {{{paramName}}}.toString()){{/pathParams}};
 
-            // query params
+        Map<String, dynamic> queryParams = {};
-            Map<String, dynamic> queryParams = {};
+        Map<String, String> headerParams = Map.from(headers ?? {});
-            Map<String, String> headerParams = Map.from(headers ?? {});
+        dynamic bodyData;
-            Map<String, String> formParams = {};
 
         {{#headerParams}}
                 headerParams["{{baseName}}"] = {{paramName}};
@@ -36,12 +35,29 @@ class {{classname}} {
         {{#queryParams}}
                 queryParams["{{baseName}}"] = {{paramName}};
         {{/queryParams}}
-            queryParams.removeWhere((key, value) => value == null);
+        queryParams.removeWhere((key, value) => value == null);
-            headerParams.removeWhere((key, value) => value == null);
+        headerParams.removeWhere((key, value) => value == null);
-            formParams.removeWhere((key, value) => value == null);
 
-            List<String> contentTypes = [{{#consumes}}
+        List<String> contentTypes = [{{#consumes}}"{{{mediaType}}}"{{#hasMore}},{{/hasMore}}{{/consumes}}];
-                "{{{mediaType}}}"{{#hasMore}},{{/hasMore}}{{/consumes}}];
+
+        {{#hasFormParams}}
+        Map<String, dynamic> formData = {};
+        {{#formParams}}
+        {{#isMultipart}}
+            {{^isFile}}
+                if ({{paramName}} != null) {
+                    formData['{{baseName}}'] = parameterToString({{paramName}});
+                }
+            {{/isFile}}
+            {{#isFile}}
+                if ({{paramName}} != null) {
+                    formData['{{baseName}}'] = MultipartFile.fromBytes({{paramName}}, filename: "{{baseName}}");
+                }
+            {{/isFile}}
+        {{/isMultipart}}
+        {{/formParams}}
+        bodyData = FormData.fromMap(formData);
+        {{/hasFormParams}}
 
         {{#bodyParam}}
             {{#isListContainer}}
@@ -52,14 +68,13 @@ class {{classname}} {
             var serializedBody = _serializers.serialize({{paramName}});
             {{/isListContainer}}
             var json{{paramName}} = json.encode(serializedBody);
+            bodyData = json{{paramName}};
         {{/bodyParam}}
 
             return _dio.request(
             path,
             queryParameters: queryParams,
-        {{#bodyParam}}
+            data: bodyData,
-                data: json{{paramName}},
-        {{/bodyParam}}
             options: Options(
             method: '{{httpMethod}}'.toUpperCase(),
             headers: headerParams,

modules/openapi-generator/src/main/resources/dart-dio/api_util.mustache

@@ -0,0 +1,18 @@
+/// Format the given parameter object into string.
+String parameterToString(dynamic value) {
+  if (value == null) {
+    return '';
+  } else if (value is DateTime) {
+    return value.toUtc().toIso8601String();
+  {{#models}}
+    {{#model}}
+      {{#isEnum}}
+  } else if (value is {{classname}}) {
+    return {{classname}}TypeTransformer().encode(value).toString();
+      {{/isEnum}}
+    {{/model}}
+  {{/models}}
+  } else {
+    return value.toString();
+  }
+}