watchdog/checks.go

package watchdog

import (
	"context"
	"fmt"
	"io"
	"net"
	"net/http"
	"net/url"
	"time"
)

// DefaultTimeout is used to limit checks duration
const DefaultTimeout = time.Second * 10

// GetHTTP creates a CheckFunc that operates as follows.
// The check makes a request with GET method to provided addr using http.DefaultClient.
// If request fails within specified timeout the returned status is StatusDown.
// The function then tries to read response body. If it fails,
// the returned status is StatusDown.
//
// If request succeeds but reponse code is not 200, the returned
// status is StatusDown and response body is contained in the
// returned error.
//
// GetHTTP return an error if addr can not be parsed with url.Parse.
// If zero timeout is provided then the DefaultTimeout (10 second) is used.
func GetHTTP(addr string, timeout time.Duration) (CheckFunc, error) {
	u, err := url.Parse(addr)
	if err != nil {
		return nil, fmt.Errorf("coulf not parse URL: %w", err)
	}

	if timeout == 0 {
		timeout = DefaultTimeout
	}

	return func(ctx context.Context) (Status, error) {
		ctx, cancel := context.WithTimeout(ctx, timeout)
		defer cancel()

		req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
		if err != nil {
			return StatusUnknown, fmt.Errorf("failed to create http request: %w", err)
		}

		resp, err := http.DefaultClient.Do(req)
		if err != nil {
			return StatusDown, fmt.Errorf("do request failed: %w", err)
		}

		defer resp.Body.Close()

		body, err := io.ReadAll(resp.Body)
		if err != nil {
			return StatusDown, fmt.Errorf("err reading response body: %w", err)
		}

		if resp.StatusCode != http.StatusOK {
			return StatusDown, fmt.Errorf("got HTTP response code %d, body: %s", resp.StatusCode, string(body))
		}

		return StatusOK, nil
	}, nil
}

// HeadHTTP creates a CheckFunc that operates as follows.
// The check make a request with HEAD method to provided addr using http.DefaultClient.
// If request fails within specified timeout the returned status is StatusDown.
//
// If request succeeds but reponse code is not 200, the returned
// status is StatusDown.
//
// HeadHTTP return an error if addr can not be parsed with url.Parse.
// If zero timeout is provided then the DefaultTimeout (10 second) is used.
func HeadHTTP(addr string, timeout time.Duration) (CheckFunc, error) {
	u, err := url.Parse(addr)
	if err != nil {
		return nil, fmt.Errorf("coulf not parse URL: %w", err)
	}

	if timeout == 0 {
		timeout = DefaultTimeout
	}

	return func(ctx context.Context) (Status, error) {
		ctx, cancel := context.WithTimeout(ctx, timeout)
		defer cancel()

		req, err := http.NewRequestWithContext(ctx, http.MethodHead, u.String(), nil)
		if err != nil {
			return StatusUnknown, fmt.Errorf("failed to create http request: %w", err)
		}

		resp, err := http.DefaultClient.Do(req)
		if err != nil {
			return StatusDown, fmt.Errorf("do request failed: %w", err)
		}

		defer resp.Body.Close()

		if resp.StatusCode != http.StatusOK {
			return StatusDown, fmt.Errorf("got HTTP response code %d", resp.StatusCode)
		}

		return StatusOK, nil
	}, nil
}

// DialTCP creates a CheckFunc that may be used to check tcp connectivity
// to a host.
//
// The check tries to net.DialTimeout to the provided addr. If it fails,
// the returned status is StatusDown.
//
// No validation of addr is made.
//
// If zero timeout is provided then the DefaultTimeout (10 second) is used.
func DialTCP(addr string, timeout time.Duration) (CheckFunc, error) {
	if timeout == 0 {
		timeout = DefaultTimeout
	}

	return func(ctx context.Context) (Status, error) {
		deadline := time.Now().Add(timeout)
		if t, ok := ctx.Deadline(); ok && t.Before(deadline) {
			deadline = t
		}

		conn, err := net.DialTimeout("tcp", addr, time.Until(deadline))
		if err != nil {
			return StatusDown, fmt.Errorf("error dialing: %w", err)
		}

		defer conn.Close()

		return StatusOK, nil
	}, nil
}