TCustomRESTRequest.AddFile转换文件名报错及文件上传失败求助

问题背景 #

API提供方给出的C#上传文件示例代码：

var client = new RestClient("hisurl");
client.Timeout = -1;
var request = new RestRequest(Method.POST);
request.AddHeader("Content-Type", "multipart/form-data");
request.AddHeader("v", "4.2");
request.AddHeader("j_token", "histoken");
request.AddFile("file", "/C:/Users/olivm/Documents/QA API Swagger/smartpacte2.pdf","application/.pdf");
IRestResponse response = client.Execute(request);
Console.WriteLine(response.Content);

我用Delphi的TCustomRESTRequest编写了对应代码：

procedure AttachDocument(contract_id : Integer; pathFile : String);
var 
  RESTClient : TRESTClient;
  RESTRequest : TCustomRESTRequest;
  Response : TCustomRESTResponse;
begin
  RESTClient := TRESTClient.Create('');
  RESTRequest := TCustomRESTRequest.Create(nil);
  try
    RESTClient.BaseURL := 'myurl';
    RESTRequest.Client := RESTClient;
    RESTRequest.Accept := 'application/json';
    RESTRequest.Params.AddHeader('j_token','mytoken',[poDoNotEncode]);
    RESTRequest.Method := rmPOST;
    RESTRequest.AddFile('file',pathFile);
    RESTRequest.Execute; 
    Response := RESTRequest.Response;
    ShowMessage(Response.Content);
  finally
    RESTRequest.Free;
    RESTClient.Free;
  end;
end;

遇到的错误 #

运行时触发异常：

RUNTIME ERROR : Impossible converting variant of type (UnicodeString) to type (Int64)

误以为AddFile第一个参数是文件路径、第二个是Int64类型，尝试了两种写法：

RESTRequest.AddFile(pathFile,0);

RESTRequest.AddFile(pathFile,ctAPPLICATION_PDF);

但API始终返回错误：

{"errors":"no files found"}

解决方案 #

问题出在对Delphi TCustomRESTRequest.AddFile方法参数的误解上，正确的重载方法应该是：

procedure AddFile(const AName: string; const AFileName: string; const AContentType: string = ''; const AContentTransferEncoding: string = ''); overload;

也就是第一个参数是API期望的表单字段名（对应C#示例里的"file"），第二个是文件路径，第三个可选参数是文件MIME类型。

你之前的错误是因为调用了另一个重载（比如基于流或字节的版本），导致参数类型不匹配。修正后的代码如下：

procedure AttachDocument(contract_id : Integer; pathFile : String);
var 
  RESTClient : TRESTClient;
  RESTRequest : TCustomRESTRequest;
  Response : TCustomRESTResponse;
begin
  RESTClient := TRESTClient.Create('');
  RESTRequest := TCustomRESTRequest.Create(nil);
  try
    RESTClient.BaseURL := 'myurl';
    RESTRequest.Client := RESTClient;
    RESTRequest.Accept := 'application/json';
    // 补充API要求的v头部
    RESTRequest.Params.AddHeader('v', '4.2', [poDoNotEncode]);
    RESTRequest.Params.AddHeader('j_token','mytoken',[poDoNotEncode]);
    RESTRequest.Method := rmPOST;
    // 正确调用AddFile：表单字段名、文件路径、MIME类型
    RESTRequest.AddFile('file', pathFile, 'application/pdf');
    RESTRequest.Execute; 
    Response := RESTRequest.Response;
    ShowMessage(Response.Content);
  finally
    RESTRequest.Free;
    RESTClient.Free;
  end;
end;

另外需要注意几个点：

• 补充C#示例里的v:4.2头部，之前的Delphi代码漏掉了这个必要参数
• MIME类型要写正确的application/pdf，不是application/.pdf
• Delphi的REST组件会自动处理multipart/form-data内容类型，不需要手动添加这个头部，避免冲突

内容的提问来源于stack exchange，提问作者Damky