What causes "微信支付通知请求体超过允许上限 {maxBodyBytes} 字节。" in JeffreySu/WeiXinMPSDK?

Increase maxBodyBytes to a safe size (e.g. 1 MB) when constructing the handler

JeffreySu/WeiXinMPSDK · error · InvalidDataException

微信支付通知请求体超过允许上限字节。

Error message

微信支付通知请求体超过允许上限 {maxBodyBytes} 字节。

What it means

Before buffering, ReadBodyAsync checks request.ContentLength; if the declared body length exceeds the configured maxBodyBytes limit it throws InvalidDataException with the limit in the message. This protects against oversized or malicious notification payloads.

Solutions

Increase maxBodyBytes to a safe size (e.g. 1 MB) when constructing the handler
Set maxBodyBytes to null if no limit is needed
Compare against actual WeChat notification sizes before choosing the cap
Check for duplicated/malformed requests behind a proxy that inflate Content-Length

Example fix

// before
var handler = TenPayNotifyHandler.Create(httpContext, settings, maxBodyBytes: 512);
// after
var handler = TenPayNotifyHandler.Create(httpContext, settings, maxBodyBytes: 1024 * 1024);

Defensive patterns

Strategy: try-catch

Validate before calling

if (httpContext.Request.ContentLength > MaxNotificationBytes)
    return BadRequest("通知体过大。");

Try / catch

try { var body = await ReadBodyAsync(httpContext, maxBodyBytes, ct); }
catch (InvalidDataException ex) when (ex.Message.Contains("超过允许上限"))
{ logger.LogWarning("通知体超限: {0}", ex.Message); return BadRequest(); }

Prevention

Size the limit above the largest legitimate WeChat notification (~a few KB)
Reject oversized requests at the reverse proxy as first line of defense

When it happens

Trigger: A POST/PUT/PATCH notification whose Content-Length header exceeds maxBodyBytes passed to ReadBodyAsync/the notify handler.

Common situations: Very small maxBodyBytes configured (e.g. a few KB) while WeChat sends a normal notification (~1-2 KB JSON plus padding), or proxy/CDN inflating the body.

Understand the failure class

Background: payload too large / request exceeds maximum size: why libraries cap bytes and how to fix oversize payloads — this error's family across 50 libraries.

Related errors

AI-assisted analysis of JeffreySu/WeiXinMPSDK@be573f6f94 (2026-09-12). Data as JSON: /api/errors/bc869bd1a1fa93cd. Report an issue: GitHub.

Appendix: source

Thrown at src/Senparc.Weixin.TenPay/Senparc.Weixin.TenPayV3/HttpHandlers/TenPayNotifyHandler.cs:177

            HttpContext httpContext,
            int? maxBodyBytes,
            CancellationToken cancellationToken)
        {
            _ = httpContext ?? throw new ArgumentNullException(nameof(httpContext));
            if (maxBodyBytes.HasValue && maxBodyBytes.Value <= 0)
            {
                throw new ArgumentOutOfRangeException(nameof(maxBodyBytes), "请求体上限必须大于 0。");
            }

            var request = httpContext.Request;
            if (request.Method != "POST" && request.Method != "PUT" && request.Method != "PATCH")
            {
                return NotificationBody.Empty;
            }

            if (maxBodyBytes.HasValue && request.ContentLength > maxBodyBytes.Value)
            {
                throw new InvalidDataException($"微信支付通知请求体超过允许上限 {maxBodyBytes} 字节。");
            }

            if (maxBodyBytes.HasValue)
            {
                request.EnableBuffering(bufferThreshold: 30 * 1024, bufferLimit: maxBodyBytes.Value);
            }
            else
            {
                request.EnableBuffering(bufferThreshold: 30 * 1024);
            }
            request.Body.Position = 0;

            using (var linkedCancellation = CancellationTokenSource.CreateLinkedTokenSource(
                cancellationToken,
                httpContext.RequestAborted))
            using (var bodyBuffer = new MemoryStream(request.ContentLength.HasValue
                ? (int)Math.Min(request.ContentLength.Value, maxBodyBytes ?? int.MaxValue)
                : 0))

View on GitHub (pinned to be573f6f94)

微信支付通知请求体超过允许上限 字节。