httputil

type BufferPool interface {
	Get() []byte
	Put([]byte)
}

type ProxyRequest struct {
	// In is the request received by the proxy.
	// The Rewrite function must not modify In.
	In *http.Request

	// Out is the request which will be sent by the proxy.
	// The Rewrite function may modify or replace this request.
	// Hop-by-hop headers are removed from this request
	// before Rewrite is called.
	Out *http.Request
}

type ReverseProxy struct {
	// Rewrite must be a function which modifies
	// the request into a new request to be sent
	// using Transport. Its response is then copied
	// back to the original client unmodified.
	// Rewrite must not access the provided ProxyRequest
	// or its contents after returning.
	//
	// The Forwarded, X-Forwarded, X-Forwarded-Host,
	// and X-Forwarded-Proto headers are removed from the
	// outbound request before Rewrite is called. See also
	// the ProxyRequest.SetXForwarded method.
	//
	// Unparsable query parameters are removed from the
	// outbound request before Rewrite is called.
	// The Rewrite function may copy the inbound URL's
	// RawQuery to the outbound URL to preserve the original
	// parameter string. Note that this can lead to security
	// issues if the proxy's interpretation of query parameters
	// does not match that of the downstream server.
	//
	// At most one of Rewrite or Director may be set.
	Rewrite func(*ProxyRequest)

	// Director is a function which modifies
	// the request into a new request to be sent
	// using Transport. Its response is then copied
	// back to the original client unmodified.
	// Director must not access the provided Request
	// after returning.
	//
	// By default, the X-Forwarded-For header is set to the
	// value of the client IP address. If an X-Forwarded-For
	// header already exists, the client IP is appended to the
	// existing values. As a special case, if the header
	// exists in the Request.Header map but has a nil value
	// (such as when set by the Director func), the X-Forwarded-For
	// header is not modified.
	//
	// To prevent IP spoofing, be sure to delete any pre-existing
	// X-Forwarded-For header coming from the client or
	// an untrusted proxy.
	//
	// Hop-by-hop headers are removed from the request after
	// Director returns, which can remove headers added by
	// Director. Use a Rewrite function instead to ensure
	// modifications to the request are preserved.
	//
	// Unparsable query parameters are removed from the outbound
	// request if Request.Form is set after Director returns.
	//
	// At most one of Rewrite or Director may be set.
	Director func(*http.Request)

	// The transport used to perform proxy requests.
	// If nil, http.DefaultTransport is used.
	Transport http.RoundTripper

	// FlushInterval specifies the flush interval
	// to flush to the client while copying the
	// response body.
	// If zero, no periodic flushing is done.
	// A negative value means to flush immediately
	// after each write to the client.
	// The FlushInterval is ignored when ReverseProxy
	// recognizes a response as a streaming response, or
	// if its ContentLength is -1; for such responses, writes
	// are flushed to the client immediately.
	FlushInterval time.Duration

	// ErrorLog specifies an optional logger for errors
	// that occur when attempting to proxy the request.
	// If nil, logging is done via the log package's standard logger.
	ErrorLog *log.Logger

	// BufferPool optionally specifies a buffer pool to
	// get byte slices for use by io.CopyBuffer when
	// copying HTTP response bodies.
	BufferPool BufferPool

	// ModifyResponse is an optional function that modifies the
	// Response from the backend. It is called if the backend
	// returns a response at all, with any HTTP status code.
	// If the backend is unreachable, the optional ErrorHandler is
	// called without any call to ModifyResponse.
	//
	// If ModifyResponse returns an error, ErrorHandler is called
	// with its error value. If ErrorHandler is nil, its default
	// implementation is used.
	ModifyResponse func(*http.Response) error

	// ErrorHandler is an optional function that handles errors
	// reaching the backend or errors from ModifyResponse.
	//
	// If nil, the default is to log the provided error and return
	// a 502 Status Bad Gateway response.
	ErrorHandler func(http.ResponseWriter, *http.Request, error)
}