SwiftUI中发起HTTP请求时遭遇「Unsupported URL」错误

我在SwiftUI中开发了一款应用，尝试通过URLSession向外部服务器发起HTTP请求以获取JSON数据，但始终遭遇「Unsupported URL」错误。我已反复检查URL格式，确认其无误。

我的代码示例如下：

struct GroupsResponse: Decodable {
        let results: [Groups]
    }

    struct Groups: Decodable {
        let Id: Int
        let Descriere: String
    }
    
    private func fetchGroupsFromAPI() async throws -> [Groups] {
        let url = URL(string: "http://orar.usarb.md/api/access/getGroups")!
        var request = URLRequest(url: url)
        request.httpMethod = "POST"
        
        let (data, _) = try await URLSession.shared.data(for: request)
        
        let decoded = try JSONDecoder().decode(GroupsResponse.self, from: data)
        print(decoded)
        return decoded.results
    }

 private func button(_ title: String, color: Color) -> some View {
        Button(action: {
            Task {
                do {
                    let movies = try await fetchGroupsFromAPI()

                    print(movies)
                } catch {
                    print(error)
                }
            }
        }) {
            Text(title)
                .frame(height: 40)
                .frame(maxWidth: .infinity)
                .background(color.opacity(0.5))
                .foregroundColor(.black)
        }
    }
}

触发请求时得到的错误信息为：

Error Domain=NSURLErrorDomain Code=-1002 "unsupported URL" UserInfo={NSLocalizedDescription=unsupported URL, NSErrorFailingURLStringKey=/api/access/getGroups, NSErrorFailingURLKey=/api/access/getGroups, _NSURLErrorRelatedURLSessionTaskErrorKey=(
"LocalDataTask <39D779DF-E734-4D65-8722-23F3843FB2D9>.<3>"
), _NSURLErrorFailingURLSessionTaskErrorKey=LocalDataTask <39D779DF-E734-4D65-8722-23F3843FB2D9>.<3>, NSUnderlyingError=0x600000c68390 {Error Domain=kCFErrorDomainCFNetwork Code=-1002 "(null)"}}

根据接口文档要求，该请求需使用POST而非GET方法。我已修改Info.plist文件、重建项目并调整代码结构，但问题仍未解决。请问我遗漏了什么？该如何修复此错误？

1. 排查服务器重定向问题 #

从错误日志看，最终请求的URL缺失了域名，变成了/api/access/getGroups，大概率是服务器返回了相对路径的重定向地址，URLSession无法自动解析相对URL导致报错。可以先用curl命令测试接口行为：

curl -X POST http://orar.usarb.md/api/access/getGroups -v

如果确认是重定向问题，需要手动处理：创建URLSession时关闭自动重定向，然后在响应中手动拼接完整URL：

let config = URLSessionConfiguration.default
config.httpShouldHandleRedirects = false
let session = URLSession(configuration: config)

// 发起请求后，检查响应状态码是否为3xx，手动拼接重定向URL
let (data, response) = try await session.data(for: request)
if let httpResponse = response as? HTTPURLResponse, (300...399).contains(httpResponse.statusCode), let redirectUrlString = httpResponse.allHeaderFields["Location"] as? String {
    guard let redirectUrl = URL(string: redirectUrlString, relativeTo: url) else {
        throw NSError(domain: "RedirectError", code: -1, userInfo: [NSLocalizedDescriptionKey: "无效的重定向地址"])
    }
    // 使用redirectUrl重新发起请求
    let redirectRequest = URLRequest(url: redirectUrl)
    let (finalData, _) = try await session.data(for: redirectRequest)
    // 解析finalData
}

2. 避免URL强制解包 #

不要用!强制解包URL(string:)，添加校验逻辑提前发现无效URL：

guard let url = URL(string: "http://orar.usarb.md/api/access/getGroups") else {
    throw NSError(domain: "InvalidURL", code: -1, userInfo: [NSLocalizedDescriptionKey: "无效的请求地址"])
}

3. 确认ATS配置正确 #

再次检查Info.plist中的App Transport Security配置，确保允许该域名的HTTP请求：

<key>NSAppTransportSecurity</key>
<dict>
    <key>NSExceptionDomains</key>
    <dict>
        <key>usarb.md</key>
        <dict>
            <key>NSIncludesSubdomains</key>
            <true/>
            <key>NSTemporaryExceptionAllowsInsecureHTTPLoads</key>
            <true/>
        </dict>
    </dict>
</dict>

4. 补充POST请求必要参数 #

部分POST接口要求必须携带请求体（即使是空的），尝试添加请求体和Content-Type头：

request.setValue("application/json", forHTTPHeaderField: "Content-Type")
request.httpBody = "{}".data(using: .utf8)

5. 排除URLSession配置干扰 #

如果项目中自定义了URLSession配置，先改用默认的URLSession.shared测试，排除自定义配置（如代理、缓存策略）带来的问题。

内容的提问来源于stack exchange，提问作者Pogor Cristian