gofiber/fiber · error

Internal Server Error

Error message

Internal Server Error

What it means

Returns HTTP 500 'Internal Server Error' from middleware/adaptor/adaptor.go:521 when copyBody fails while streaming the net/http request body into the fasthttp request buffer. copyBody uses a pooled buffer with io.CopyBuffer (adaptor.go:132-141); any read error from r.Body (client disconnect, network reset, decompression fault) surfaces here. The error is mapped to a 500 because the body is already partially consumed and the request cannot be reliably processed.

Source

Thrown at middleware/adaptor/adaptor.go:521

			var n int64
			// http.NoBody never yields any bytes, so skip the copy machinery
			// entirely for the (very common) bodyless request.
			if r.Body != http.NoBody {
				limit := maxBodySize
				if limit < math.MaxInt64 {
					limit++
				}
				// The LimitedReader lives in the pooled ctx and the copy
				// buffer comes from the shared pool: io.Copy would otherwise
				// allocate a fresh 32 KiB buffer on every single request.
				pctx.lr.R = r.Body
				pctx.lr.N = limit

				var err error
				n, err = copyBody(req.BodyWriter(), &pctx.lr)
				pctx.lr.R = nil // don't keep the request body alive in the pool
				if err != nil {
					http.Error(w, utils.StatusMessage(fiber.StatusInternalServerError), fiber.StatusInternalServerError)
					return
				}

				if n > maxBodySize {
					http.Error(w, utils.StatusMessage(fiber.StatusRequestEntityTooLarge), fiber.StatusRequestEntityTooLarge)
					return
				}
			}

			req.Header.SetContentLength(int(n))
		}
		req.Header.SetMethod(r.Method)
		req.SetRequestURI(r.RequestURI)
		req.SetHost(r.Host)
		req.Header.SetHost(r.Host)
		// Propagate the real protocol version so protocol-dependent behavior
		// (e.g. skipping interim 1xx responses for non-HTTP/1.1 requests,
		// RFC 9110 Section 15.2) sees the truth instead of fasthttp's

View on GitHub (pinned to 9a4c7e57fe)

Solutions

1. Verify the client is not disconnecting; check upstream proxy read/connect timeouts and raise them for slow uploads.
2. Ensure any custom wrapping of http.Request.Body preserves io.ReadCloser semantics.
3. Log the underlying error (instrument copyBody's caller) to distinguish client disconnects from real server faults.

Example fix

// before
// proxy read timeout too tight for uploads
srv := &http.Server{ReadTimeout: 2 * time.Second}

// after
srv := &http.Server{
    ReadTimeout:  60 * time.Second,
    WriteTimeout: 60 * time.Second,
}

// The adaptor returns a 500 internally; recover at the handler boundary
// for downstream errors, but body-stream faults must be prevented upstream.
func recoverer(c fiber.Ctx) error {
    defer func() {
        if r := recover(); r != nil {
            log.Printf("adaptor body error: %v", r)
        }
    }()
    return c.Next()
}

When it happens

Trigger: Client closes the connection mid-upload; a TLS reset or proxy timeout; a request body whose stream returns an io error; chained middleware that wraps r.Body incorrectly.

Common situations: Flaky mobile clients dropping connections; reverse proxy timeouts on slow uploads; misbehaving request body wrappers; very slow producers hitting network idle timeouts.

Related errors

• Request Entity Too Large
• remote address cannot be empty
• value not found
• cache: insufficient space and no entries to evict
• csrf: token not found

AI-assisted analysis of gofiber/fiber@9a4c7e57fe (2026-08-04). Data as JSON: /data/errors/d7cc43004215ea5d.json. Report an issue: GitHub.