func fetchAndVerify()

in getdeps/fetch.go [86:153]
54 lines of code
16 McCabe index (conditional complexity)

func fetchAndVerify(label, projectDir, urlStr string, hashMode HashMode, hash *string, urlOverrides *URLOverrides) ([]byte, os.FileInfo, error) {
	if urlOverrides != nil {
		urlStr = urlOverrides.Override(urlStr)
	}

	u, err := url.Parse(urlStr)
	if err != nil {
		return nil, nil, fmt.Errorf("%s: invalid URL %q: %w", label, urlStr, err)
	}

	if strings.ToLower(u.Scheme) == "file" {
		filePath := path.Join(projectDir, u.Host, u.Path)
		fileInfo, err := os.Stat(filePath)
		if err != nil {
			return nil, nil, err
		}
		data, err := ioutil.ReadFile(filePath)
		return data, fileInfo, err
	}

	switch hashMode {
	case hashModeStrict:
		if hash == nil || *hash == "" {
			return nil, nil, fmt.Errorf("%s: %s: hash mode is strict and no hash supplied", label, urlStr)
		}
	case hashModeUpdate:
		if hash != nil {
			*hash = ""
		}
	case hashModePermissive:
		// Proceed
	}

	var data []byte
	if hash != nil {
		var actualHash string
		// blindly retry to downloading the file when hash check fails. This is
		// to work around an odd behaviour of the GNU mirrors where the files
		// are updated but their content is wrong for a few seconds (e.g. the
		// tar.gz file with tar'ed but not gzip'ed content, like it's being
		// compressed in prod).
		for attempts := 0; attempts < 3; attempts++ {
			data, err = fetch(label, urlStr)
			if err != nil {
				return nil, nil, err
			}
			actualHash, err = verifyHash(data, *hash)
			if err != nil {
				log.Printf("Hash validation for %s failed, will try downloading the file again. Error is: %v", label, err)
				continue
			}
			if *hash == "" {
				*hash = actualHash
				log.Printf("%s: Hash %s", label, actualHash)
			} else {
				log.Printf("%s: Hash %s (verified)", label, actualHash)
			}
			return data, nil, nil
		}

		// at this point err is `nil` if the last attempt was successful,
		// and not `nil` otherwise.
		return data, nil, err
	}

	data, err = fetch(label, urlStr)
	return data, nil, err
}