C#集成Amazon Products API遇内部错误，求可行实现方案

算力阿峰

2026-7-19

C#调用Amazon Products API返回InternalFailure的解决方法

有开发者成功用C#实现Amazon Products API吗？我将scratchpad网站上的PHP示例代码转换为C#后，调用时收到如下响应：

{"Output":{"__type":"com.amazon.coral.service#InternalFailure","message":null},"Version":"1.0"}

截至2023年，Amazon似乎未为该API提供官方SDK，以下是我的C#代码：

public class Program
{
    static async Task Main(string[] args)
    {
        string serviceName = "ProductAdvertisingAPI";
        string region = "us-east-1";
        string accessKey = "**************";
        string secretKey = "**************";
        string payload = "{"
            + "\"Keywords\": \"notebook\","
            + "\"PartnerTag\": \"x0d-20\","
            + "\"PartnerType\": \"Associates\","
            + "\"Marketplace\": \"www.amazon.com\""
            + "}";
        string host = "webservices.amazon.com";
        string uriPath = "/paapi5/searchitems";
        AwsV4 awsv4 = new AwsV4(accessKey, secretKey);
        awsv4.SetRegionName(region);
        awsv4.SetServiceName(serviceName);
        awsv4.SetPath(uriPath);
        awsv4.SetPayload(payload);
        awsv4.SetRequestMethod("POST");
        awsv4.AddHeader("content-encoding", "amz-1.0");
        awsv4.AddHeader("content-type", "application/json; charset=utf-8");
        awsv4.AddHeader("host", host);
        awsv4.AddHeader("x-amz-target", "com.amazon.paapi5.v1.ProductAdvertisingAPIv1.SearchItems");
        Dictionary<string, string> headers = awsv4.GetHeaders();

        using (HttpClient client = new HttpClient())
        {
            HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Post, $"https://{host}{uriPath}");
            foreach (var header in headers)
            {
                request.Headers.TryAddWithoutValidation(header.Key, header.Value);
            }
            request.Content = new StringContent(payload, Encoding.UTF8, "application/json");

            HttpResponseMessage response = await client.SendAsync(request);

            string responseContent = await response.Content.ReadAsStringAsync();
            Console.WriteLine(responseContent);
        }
        Console.ReadLine();
    }

    public class AwsV4
    {
        private string accessKey = null;
        private string secretKey = null;
        private string path = null;
        private string regionName = null;
        private string serviceName = null;
        private string httpMethodName = null;
        private Dictionary<string, string> queryParameters = new Dictionary<string, string>();
        private Dictionary<string, string> awsHeaders = new Dictionary<string, string>();
        private string payload = "";

        private string HMACAlgorithm = "AWS4-HMAC-SHA256";
        private string aws4Request = "aws4_request";
        private string strSignedHeader = null;
        private string xAmzDate = null;
        private string currentDate = null;

        public AwsV4(string accessKey, string secretKey)
        {
            this.accessKey = accessKey;
            this.secretKey = secretKey;
            this.xAmzDate = GetTimeStamp();
            this.currentDate = GetDate();
        }

        public void SetPath(string path)
        {
            this.path = path;
        }

        public void SetServiceName(string serviceName)
        {
            this.serviceName = serviceName;
        }

        public void SetRegionName(string regionName)
        {
            this.regionName = regionName;
        }

        public void SetPayload(string payload)
        {
            this.payload = payload;
        }

        public void SetRequestMethod(string method)
        {
            this.httpMethodName = method;
        }

        public void AddHeader(string headerName, string headerValue)
        {
            this.awsHeaders[headerName] = headerValue;
        }

        private string PrepareCanonicalRequest()
        {
            StringBuilder canonicalURL = new StringBuilder();
            canonicalURL.Append(httpMethodName).Append("\n");
            canonicalURL.Append(path).Append("\n").Append("\n");
            string signedHeaders = "";
            foreach (var header in awsHeaders)
            {
                signedHeaders += header.Key + ";";
                canonicalURL.Append(header.Key).Append(":").Append(header.Value).Append("\n");
            }
            canonicalURL.Append("\n");
            strSignedHeader = signedHeaders.TrimEnd(';');
            canonicalURL.Append(strSignedHeader).Append("\n");
            canonicalURL.Append(GenerateHex(payload));
            return canonicalURL.ToString();
        }

        private string PrepareStringToSign(string canonicalURL)
        {
            StringBuilder stringToSign = new StringBuilder();
            stringToSign.Append(HMACAlgorithm).Append("\n");
            stringToSign.Append(xAmzDate).Append("\n");
            stringToSign.Append(currentDate).Append("/").Append(regionName).Append("/").Append(serviceName).Append("/").Append(aws4Request).Append("\n");
            stringToSign.Append(GenerateHex(canonicalURL));
            return stringToSign.ToString();
        }

        private string CalculateSignature(string stringToSign)
        {
            byte[] signatureKey = GetSignatureKey(secretKey, currentDate, regionName, serviceName);
            byte[] signature = HashHMAC(Encoding.UTF8.GetBytes(stringToSign), signatureKey);
            string strHexSignature = BitConverter.ToString(signature).Replace("-", "").ToLower();
            return strHexSignature;
        }

        public Dictionary<string, string> GetHeaders()
        {
            awsHeaders["x-amz-date"] = xAmzDate;
            SortedDictionary<string, string> sortedHeaders = new SortedDictionary<string, string>(awsHeaders);
            StringBuilder canonicalURL = new StringBuilder(PrepareCanonicalRequest());
            string stringToSign = PrepareStringToSign(canonicalURL.ToString());
            string signature = CalculateSignature(stringToSign);

            awsHeaders["Authorization"] = BuildAuthorizationString(signature);

            return awsHeaders;
        }

        private string BuildAuthorizationString(string strSignature)
        {
            return HMACAlgorithm + " " + "Credential=" + accessKey + "/" + GetDate() + "/" + regionName + "/" + serviceName + "/" + aws4Request + "," + "SignedHeaders=" + strSignedHeader + "," + "Signature=" + strSignature;
        }

        private string GenerateHex(string data)
        {
            using (SHA256 sha256Hash = SHA256.Create())
            {
                byte[] bytes = sha256Hash.ComputeHash(Encoding.UTF8.GetBytes(data));
                StringBuilder builder = new StringBuilder();
                for (int i = 0; i < bytes.Length; i++)
                {
                    builder.Append(bytes[i].ToString("x2"));
                }
                return builder.ToString();
            }
        }

        private byte[] GetSignatureKey(string key, string date, string regionName, string serviceName)
        {
            byte[] kSecret = Encoding.UTF8.GetBytes("AWS4" + key);
            byte[] kDate = HashHMAC(Encoding.UTF8.GetBytes(date), kSecret);
            byte[] kRegion = HashHMAC(Encoding.UTF8.GetBytes(regionName), kDate);
            byte[] kService = HashHMAC(Encoding.UTF8.GetBytes(serviceName), kRegion);
            byte[] kSigning = HashHMAC(Encoding.UTF8.GetBytes(aws4Request), kService);

            return kSigning;
        }

        private byte[] HashHMAC(byte[] data, byte[] key)
        {
            using (HMACSHA256 hmac = new HMACSHA256(key))
            {
                return hmac.ComputeHash(data);
            }
        }

        private string GetTimeStamp()
        {
            return DateTime.UtcNow.ToString("yyyyMMdd\\THHmmss\\Z");
        }

        private string GetDate()
        {
            return DateTime.UtcNow.ToString("yyyyMMdd");
        }
    }
}

问题分析与修复方案

1. Header重复与格式错误

你在AwsV4类中手动添加了content-type、host等header，之后又通过StringContent再次设置content-type，同时host会由HttpClient自动处理，重复设置会导致签名验证失败。

修复：移除AwsV4中添加的content-encoding、content-type、host header，只保留x-amz-target。

2. Canonical Request的Header排序问题

AWS V4签名要求Canonical Request中的header必须按小写字母顺序排序，且header名称需转为小写。你的代码直接遍历未排序的原字典，且未转小写，会导致签名计算错误。

修复：在PrepareCanonicalRequest中使用SortedDictionary排序header，并将header名称转为小写：

private string PrepareCanonicalRequest()
{
    StringBuilder canonicalURL = new StringBuilder();
    canonicalURL.Append(httpMethodName).Append("\n");
    canonicalURL.Append(path).Append("\n").Append("\n");
    
    // 按小写排序header
    var sortedHeaders = new SortedDictionary<string, string>(awsHeaders, StringComparer.OrdinalIgnoreCase);
    string signedHeaders = "";
    foreach (var header in sortedHeaders)
    {
        string lowerKey = header.Key.ToLowerInvariant();
        signedHeaders += lowerKey + ";";
        canonicalURL.Append(lowerKey).Append(":").Append(header.Value.Trim()).Append("\n");
    }
    canonicalURL.Append("\n");
    strSignedHeader = signedHeaders.TrimEnd(';');
    canonicalURL.Append(strSignedHeader).Append("\n");
    canonicalURL.Append(GenerateHex(payload));
    return canonicalURL.ToString();
}

3. 时间戳一致性问题

BuildAuthorizationString中重新调用GetDate()，可能和构造函数中生成的currentDate时间不一致（跨秒场景），导致签名验证失败。

修复：直接使用构造函数中已保存的currentDate变量：

private string BuildAuthorizationString(string strSignature)
{
    return $"{HMACAlgorithm} Credential={accessKey}/{currentDate}/{regionName}/{serviceName}/{aws4Request},SignedHeaders={strSignedHeader},Signature={strSignature}";
}

4. Payload手动拼接风险

手动拼接JSON容易出现格式错误，建议用序列化生成：

// 定义请求实体类
public class SearchItemRequest
{
    public string Keywords { get; set; }
    public string PartnerTag { get; set; }
    public string PartnerType { get; set; }
    public string Marketplace { get; set; }
}

// 在Main方法中生成Payload
var requestBody = new SearchItemRequest
{
    Keywords = "notebook",
    PartnerTag = "x0d-20",
    PartnerType = "Associates",
    Marketplace = "www.amazon.com"
};
string payload = System.Text.Json.JsonSerializer.Serialize(requestBody);

额外注意事项

确保Access Key、Secret Key拥有Product Advertising API的权限，且PartnerTag（关联ID）有效。
确认Region与Marketplace匹配（比如us-east-1对应www.amazon.com）。
控制请求频率，避免触发Amazon限流机制。

内容的提问来源于stack exchange，提问作者QuietWorld