使用RestSharp调用Freshdesk outbound_email接口带附件报错求助

调用Freshdesk的outbound_email接口发送带附件邮件时，不带附件的请求可正常执行并收到邮件，但添加附件后返回Bad Request，所有字段被标记为无效。该功能在Postman中可正常运行，更换为HttpClient后仍出现相同错误。

原代码 #

var client = new RestClient(outboundEmail);
var request = new RestRequest("", Method.Post);

request.AddHeader("Authorization", "Basic " + Convert.ToBase64String(Encoding.Default.GetBytes(apiKey + ":X")));

request.AddHeader("Accept", "application/json");
request.AddHeader("Content-Type", "multipart/form-data");

request.AddFile("attachments[]", "filePath");

request.AddParameter("email", myEmail);
request.AddParameter("subject", subject);
request.AddParameter("description", description);
request.AddParameter("status", status);
request.AddParameter("priority", priority);
request.AddParameter("email_config_id", emailConfigID);

var response = client.Execute(request);

返回错误信息 #

"description":"Validation failed","errors":
[{"field":"email\n","message":"Unexpected/invalid field in request","code":"invalid_field"},
{"field":"subject\n","message":"Unexpected/invalid field in request","code":"invalid_field"},{"field":"description\n","message":"Unexpected/invalid field in request","code":"invalid_field"},{"field":"status\n","message":"Unexpected/invalid field in request","code":"invalid_field"},{"field":"priority\n","message":"Unexpected/invalid field in request","code":"invalid_field"},{"field":"email_config_id\n","message":"Unexpected/invalid field in request","code":"invalid_field"}]}

问题原因 #

1. 手动设置Content-Type: multipart/form-data会覆盖RestSharp自动生成的包含boundary的Content-Type头，导致请求格式异常。
2. 使用AddParameter添加普通字段时，字段名被错误编码（末尾多出换行符\n），Freshdesk API无法识别这些带换行的字段名，因此返回无效字段错误。

修复方案 #

RestSharp修复代码 #

var client = new RestClient(outboundEmail);
var request = new RestRequest("", Method.Post);

// 保留授权和Accept头
request.AddHeader("Authorization", "Basic " + Convert.ToBase64String(Encoding.Default.GetBytes(apiKey + ":X")));
request.AddHeader("Accept", "application/json");

// 移除手动设置的Content-Type，RestSharp会自动处理multipart请求的Content-Type及boundary
// request.AddHeader("Content-Type", "multipart/form-data");

// 添加附件
request.AddFile("attachments[]", "filePath");

// 使用AddStringParameter替代AddParameter，确保字段名和值正确编码
request.AddStringParameter("email", myEmail);
request.AddStringParameter("subject", subject);
request.AddStringParameter("description", description);
request.AddStringParameter("status", status);
request.AddStringParameter("priority", priority);
request.AddStringParameter("email_config_id", emailConfigID);

var response = client.Execute(request);

HttpClient修复代码 #

using (var client = new HttpClient())
{
    // 设置授权头
    client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", 
        Convert.ToBase64String(Encoding.Default.GetBytes(apiKey + ":X")));
    client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

    using (var content = new MultipartFormDataContent())
    {
        // 添加普通文本字段
        content.Add(new StringContent(myEmail), "email");
        content.Add(new StringContent(subject), "subject");
        content.Add(new StringContent(description), "description");
        content.Add(new StringContent(status), "status");
        content.Add(new StringContent(priority), "priority");
        content.Add(new StringContent(emailConfigID), "email_config_id");

        // 添加附件，设置正确的内容类型和文件名
        var fileBytes = File.ReadAllBytes("filePath");
        var fileContent = new ByteArrayContent(fileBytes);
        fileContent.Headers.ContentType = MediaTypeHeaderValue.Parse("application/octet-stream");
        content.Add(fileContent, "attachments[]", Path.GetFileName("filePath"));

        var response = await client.PostAsync(outboundEmail, content);
        var responseString = await response.Content.ReadAsStringAsync();
    }
}

内容的提问来源于stack exchange，提问作者James Wilson