log/request_size.go

package log

import "net/http"

const (
	// newLineBytes is the number of bytes for a newline:
	// HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
	//
	//	protocol elements except the entity-body (see appendix 19.3 for
	//	tolerant applications).
	newLineBytes = 2

	// requestLineSpaceBytes is the number of bytes in a separator between fields in request line.
	requestLineSpaceBytes = 1

	// headerSeparatorBytes is the number of bytes in a separator between header and its value `X: Y`.
	headerSeparatorBytes = 2

	hostHeaderExtraBytes = len("Host: ")
)

// computeApproximateRequestSize will calculate the approximate request size,
// including the request line, headers and ContentLength (if set).
// Inspired by: https://github.com/prometheus/client_golang/blob/331dfab0cc853dca0242a0d96a80184087a80c1d/prometheus/promhttp/instrument_server.go#L409
// but more accurate as it includes whitespace.
// We do this because it makes verification easier for test data, as we can simply use `len(string)`.
func computeApproximateRequestSize(r *http.Request, bodyByteCount int64) int64 {
	var s int64

	// Request Line
	s += int64(len(r.Method) + requestLineSpaceBytes)
	if r.URL != nil {
		s += int64(len(r.URL.String()) + requestLineSpaceBytes)
	}

	s += int64(len(r.Proto) + newLineBytes)

	// Headers
	if r.Host != "" {
		s += int64(hostHeaderExtraBytes + len(r.Host) + newLineBytes)
	}

	for name, values := range r.Header {
		for _, value := range values {
			s += int64(len(name) + headerSeparatorBytes + len(value) + newLineBytes)
		}
	}

	// Include the trailing newline after the request headers.
	s += newLineBytes

	// Body
	s += bodyByteCount

	return s
}