summercms/surf/cors.go

package surf

import (
	"net/http"
	"regexp"
	"strconv"
	"strings"

	"git.golem15.com/golem15/summercms/compass"
)

// CORSConfig matches Laravel config/cors.php keys.
type CORSConfig struct {
	Paths                  []string `koanf:"paths"`
	AllowedMethods         []string `koanf:"allowed_methods"`
	AllowedOrigins         []string `koanf:"allowed_origins"`
	AllowedOriginsPatterns []string `koanf:"allowed_origins_patterns"`
	AllowedHeaders         []string `koanf:"allowed_headers"`
	ExposedHeaders         []string `koanf:"exposed_headers"`
	MaxAge                 int      `koanf:"max_age"`
	SupportsCredentials    bool     `koanf:"supports_credentials"`
}

// LoadCORSConfig reads http.cors. Missing section yields a zero config (no
// path matches, so no CORS headers).
func LoadCORSConfig(cfg *compass.Config) (CORSConfig, error) {
	var out CORSConfig
	if cfg == nil || !cfg.Has("http.cors") {
		return out, nil
	}
	if err := cfg.LoadSection("http.cors", &out); err != nil {
		return out, err
	}
	return out, nil
}

func pathScopedCORS(cfg CORSConfig, next http.Handler) http.Handler {
	globs := make([]*regexp.Regexp, 0, len(cfg.Paths))
	for _, p := range cfg.Paths {
		if re := compileLaravelGlob(p); re != nil {
			globs = append(globs, re)
		}
	}
	originPats := make([]*regexp.Regexp, 0, len(cfg.AllowedOriginsPatterns))
	for _, p := range cfg.AllowedOriginsPatterns {
		re, err := regexp.Compile(p)
		if err != nil {
			continue
		}
		originPats = append(originPats, re)
	}
	allowAnyOrigin := containsStar(cfg.AllowedOrigins)
	allowAnyMethod := containsStar(cfg.AllowedMethods)
	allowAnyHeader := containsStar(cfg.AllowedHeaders)
	origins := make(map[string]struct{}, len(cfg.AllowedOrigins))
	for _, o := range cfg.AllowedOrigins {
		if o != "" && o != "*" {
			origins[o] = struct{}{}
		}
	}
	methods := strings.Join(cfg.AllowedMethods, ", ")
	headers := strings.Join(cfg.AllowedHeaders, ", ")
	exposed := strings.Join(cfg.ExposedHeaders, ", ")
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if !pathMatchesCORS(globs, r.URL.Path) {
			next.ServeHTTP(w, r)
			return
		}
		origin := r.Header.Get("Origin")
		allowed, value := corsAllowOrigin(allowAnyOrigin, origins, originPats, origin)
		if allowed {
			w.Header().Set("Access-Control-Allow-Origin", value)
			if value != "*" {
				w.Header().Set("Vary", "Origin")
			}
			if allowAnyMethod {
				w.Header().Set("Access-Control-Allow-Methods", "*")
			} else if methods != "" {
				w.Header().Set("Access-Control-Allow-Methods", methods)
			}
			if allowAnyHeader {
				w.Header().Set("Access-Control-Allow-Headers", "*")
			} else if headers != "" {
				w.Header().Set("Access-Control-Allow-Headers", headers)
			}
			if exposed != "" {
				w.Header().Set("Access-Control-Expose-Headers", exposed)
			}
			if cfg.MaxAge > 0 {
				w.Header().Set("Access-Control-Max-Age", strconv.Itoa(cfg.MaxAge))
			}
			if cfg.SupportsCredentials {
				w.Header().Set("Access-Control-Allow-Credentials", "true")
			}
		}
		if r.Method == http.MethodOptions {
			w.WriteHeader(http.StatusNoContent)
			return
		}
		next.ServeHTTP(w, r)
	})
}

func corsAllowOrigin(allowAny bool, origins map[string]struct{}, pats []*regexp.Regexp, origin string) (bool, string) {
	if allowAny {
		return true, "*"
	}
	if origin == "" {
		return false, ""
	}
	if _, ok := origins[origin]; ok {
		return true, origin
	}
	for _, re := range pats {
		if re.MatchString(origin) {
			return true, origin
		}
	}
	return false, ""
}

func pathMatchesCORS(globs []*regexp.Regexp, urlPath string) bool {
	trimmed := strings.TrimPrefix(urlPath, "/")
	for _, re := range globs {
		if re.MatchString(trimmed) {
			return true
		}
	}
	return false
}

func compileLaravelGlob(pattern string) *regexp.Regexp {
	pattern = strings.TrimPrefix(pattern, "/")
	var b strings.Builder
	b.WriteString("(?s)^")
	for i := 0; i < len(pattern); i++ {
		switch pattern[i] {
		case '*':
			b.WriteString(".*")
		case '?':
			b.WriteByte('.')
		default:
			b.WriteString(regexp.QuoteMeta(pattern[i : i+1]))
		}
	}
	b.WriteByte('$')
	re, err := regexp.Compile(b.String())
	if err != nil {
		return nil
	}
	return re
}

func containsStar(vals []string) bool {
	for _, v := range vals {
		if v == "*" {
			return true
		}
	}
	return false
}