Clojure.spec URL and email specs with generators

url-gen.clj

(require '[cemerick.url :as url]
         '[clojure.spec.alpha :as s]
         '[clojure.spec.gen.alpha :as gen]
         '[clojure.string :as string])

(def non-empty-string-alphanumeric
  "Generator for non-empty alphanumeric strings"
  (gen/such-that #(not= "" %)
    (gen/string-alphanumeric)))

(def non-empty-url-encoded-string
  "Generator for url-encoded strings"
  (gen/fmap
    url/url-encode
    (gen/such-that #(not= "" %)
      (gen/string))))

(def email-gen
  "Generator for email addresses"
  (gen/fmap
    (fn [[name host tld]]
      (str name "@" host "." tld))
    (gen/tuple
      non-empty-string-alphanumeric
      non-empty-string-alphanumeric
      non-empty-string-alphanumeric)))

(def url-path-gen
  "Generator that creates a string made up of one or more forward slash-separated non-empty strings"
  (gen/fmap #(->> %
                  (map url/url-encode)
                  (interleave (repeat "/"))
                  (apply str))
    (gen/such-that #(not= [] %)
      (gen/vector
        (gen/such-that #(not= "" %)
          (gen/string-alphanumeric))))))

(def url-gen
  "Generator for generating URLs; note that it may generate http URLs on port 443 and https URLs on port 80,
  and that usernames and passwords only use alphanumerics"
  (gen/fmap (partial apply (comp str url/->URL))
    (gen/tuple
      ;; protocol
      (gen/elements #{"http" "https"})
      ;; username
      (gen/string-alphanumeric)
      ;; password
      (gen/string-alphanumeric)
      ;; host
      (gen/string-alphanumeric)
      ;; port
      (gen/choose 1 65535)
      ;; path
      url-path-gen
      ;; query
      (gen/map
        non-empty-url-encoded-string
        non-empty-url-encoded-string
        {:max-elements 10})
      ;; anchor
      (gen/fmap url/url-encode (gen/string)))))

(s/def ::email 
  (s/with-gen 
    #(re-matches #".+@.+\..+" %) 
    (fn [] email-gen)))

(s/def ::url 
  (s/with-gen 
    #(try (url/url %) (catch Throwable t false)) 
    (fn [] url-gen)))

Hope it helps! I love spec