Rails 7 ActionMailbox报422错误 Service name can't be blank

错误日志 #

本地启动服务后通过Conductor面板提交测试入站邮件，请求失败返回422状态码，日志报错如下：

13:39:20 web.1  | Started POST "/rails/conductor/action_mailbox/inbound_emails" for 
::1 at 2022-07-02 13:39:20 -0400
13:39:20 web.1  |   ActiveRecord::SchemaMigration Pluck (2.1ms)  SELECT "schema_migrations"."version" FROM "schema_migrations" ORDER BY "schema_migrations"."version" ASC
13:39:20 web.1  | Processing by Rails::Conductor::ActionMailbox::InboundEmailsController#create as HTML
13:39:20 web.1  |   Parameters: {"utf8"=>"✓", "authenticity_token"=>"asdfads", "mail"=>{"from"=>"user@gmail.com", "to"=>"support@email.com", "cc"=>"", "bcc"=>"", "x_original_to"=>"", "in_reply_to"=>"", "subject"=>"test", "body"=>"test"}, "commit"=>"Deliver inbound email"}
13:39:20 web.1  | Completed 422 Unprocessable Entity in 53ms (ActiveRecord: 21.3ms | Allocations: 43704)
13:39:20 web.1  | 
13:39:20 web.1  | 
13:39:20 web.1  |   
13:39:20 web.1  | ActiveRecord::RecordInvalid (Validation failed: Service name can't be blank):
13:39:20 web.1  |   
13:39:20 web.1  | activerecord (7.0.0) lib/active_record/validations.rb:80:in `raise_validation_error'
13:39:20 web.1  | activerecord (7.0.0) lib/active_record/validations.rb:53:in `save!'

已完成配置 #

操作前已完成以下Action Mailbox配置：

• 执行安装命令并完成数据库迁移：

$ rails action_mailbox:install
$ rails db:migrate

• 在开发、生产环境配置文件中指定Mailgun作为入站入口：

# config/environments/development.rb & config/environments/production.rb
config.action_mailbox.ingress = :mailgun

• 通过credentials配置Mailgun签名密钥：

action_mailbox:
    mailgun_signing_key: XXX

• 生成自定义邮件处理器：

# app/mailboxes/forwards_mailbox.rb
class ForwardsMailbox < ApplicationMailbox
  def process
    byebug
  end
end

• 配置路由规则将所有入站邮件转发到自定义处理器：

# app/mailboxes/application_mailbox.rb
 class ApplicationMailbox < ActionMailbox::Base
   routing :all => :forwards
 end

问题根因 #

该报错和Mailgun、SendGrid的入口配置完全无关。Rails 7中Action Mailbox存储原始邮件内容、附件时强依赖Active Storage组件，升级到Rails 7后如果没有显式配置Active Storage的存储服务，创建ActiveStorage::Blob记录时会触发Service name can't be blank的校验错误，最终导致入站邮件记录保存失败返回422。

修复步骤 #

1. 确认config/storage.yml中存在各环境对应的存储服务配置，最小配置参考如下：

local:
  service: Disk
  root: <%= Rails.root.join("storage") %>

test:
  service: Disk
  root: <%= Rails.root.join("tmp/storage") %>

# 生产环境按需替换为S3/OSS等对象存储配置
amazon:
  service: S3
  access_key_id: <%= Rails.application.credentials.dig(:aws, :access_key_id) %>
  secret_access_key: <%= Rails.application.credentials.dig(:aws, :secret_access_key) %>
  region: us-east-1
  bucket: your-app-bucket

2. 在各环境配置文件中显式指定Active Storage使用的服务：

• 开发环境config/environments/development.rb添加：

config.active_storage.service = :local

• 测试环境config/environments/test.rb添加：

config.active_storage.service = :test

• 生产环境config/environments/production.rb添加（替换为实际使用的存储服务名）：

config.active_storage.service = :amazon

3. 如果是从低版本Rails升级到7.0，补跑Active Storage的安装迁移（全新安装Rails7可跳过这步）：

$ rails active_storage:install
$ rails db:migrate

4. 重启Rails服务，再次通过Conductor面板发送测试邮件即可正常触发自定义Mailbox的处理逻辑。

内容的提问来源于stack exchange，提问作者nomad