func previousFetchStatusAndResponse()

in internal/frontend/404.go [219:303]
60 lines of code
21 McCabe index (conditional complexity)

func previousFetchStatusAndResponse(ctx context.Context, db *postgres.DB,
	fullPath, modulePath, requestedVersion string) (_ *fetchResult, err error) {
	defer derrors.Wrap(&err, "previousFetchStatusAndResponse(w, r, %q, %q)", fullPath, requestedVersion)

	// Get all candidate module paths for this path.
	paths, err := modulePathsToFetch(ctx, db, fullPath, modulePath)
	if err != nil {
		var serr *serverError
		if errors.As(err, &serr) && serr.status == http.StatusBadRequest {
			// Return this as an invalid argument so that we don't log it in
			// servePathNotFoundPage above.
			return nil, derrors.InvalidArgument
		}
		return nil, err
	}
	// Check if a row exists in the version_map table for the longest candidate
	// path and version.
	//
	// If we have not fetched the path before, a derrors.NotFound will be
	// returned.
	vm, err := db.GetVersionMap(ctx, paths[0], requestedVersion)
	if err != nil {
		return nil, err
	}
	// If the row has been fetched before, and the result was either a 490,
	// 491, or 5xx, return that result, since it is a final state.
	if vm != nil {
		fr := &fetchResult{
			modulePath: vm.ModulePath,
			goModPath:  vm.GoModPath,
			status:     vm.Status,
			err:        errors.New(vm.Error),
		}
		if vm.Status >= 200 && vm.Status < 300 {
			fr.resolvedVersion = vm.ResolvedVersion
			return fr, nil
		}
		if vm.Status >= 500 ||
			vm.Status == derrors.ToStatus(derrors.AlternativeModule) ||
			vm.Status == derrors.ToStatus(derrors.BadModule) {
			return resultFromFetchRequest([]*fetchResult{fr}, fullPath, requestedVersion)
		}
	}

	// Check if the unit path exists at a higher major version.
	// For example, my.module might not exist, but my.module/v3 might.
	// Similarly, my.module/foo might not exist, but my.module/v3/foo might.
	// In either case, the user will be redirected to the highest major version
	// of the path.
	//
	// Do not bother to look for a specific version if this case. If
	// my.module/foo@v2.1.0 was requested, and my.module/foo/v2 exists, just
	// return the latest version of my.module/foo/v2.
	//
	// Only redirect if the majPath returned is different from the fullPath, and
	// the majPath is not at v1. We don't want to redirect my.module/foo/v3 to
	// my.module/foo, or my.module/foo@v1.5.2 to my.module/foo@v1.0.0.
	majPath, maj, err := db.GetLatestMajorPathForV1Path(ctx, fullPath)
	if err != nil && err != derrors.NotFound {
		return nil, err
	}
	if majPath != fullPath && maj != 1 && majPath != "" {
		return &fetchResult{
			modulePath: majPath,
			goModPath:  majPath,
			status:     http.StatusFound,
		}, nil
	}
	vms, err := db.GetVersionMaps(ctx, paths, requestedVersion)
	if err != nil {
		return nil, err
	}
	var fetchResults []*fetchResult
	for _, vm := range vms {
		fr := fetchResultFromVersionMap(vm)
		fetchResults = append(fetchResults, fr)
		if vm.Status == http.StatusOK || vm.Status == 290 {
			fr.err = errPathDoesNotExistInModule
		}
	}
	if len(fetchResults) == 0 {
		return nil, derrors.NotFound
	}
	return resultFromFetchRequest(fetchResults, fullPath, requestedVersion)
}