Merge pull request #158 from daveray/hystrix-clj-expose-command-instance

Expose current HystrixCommand to fns

hystrix-contrib/hystrix-clj/src/main/clojure/com/netflix/hystrix/core.clj

@@ -277,6 +277,21 @@
 
 ;################################################################################
 
+(def ^:dynamic *command*
+ "A dynamic var which is bound to the HystrixCommand instance during execution of
+ :run-fn and :fallback-fn.
+
+ It's occasionally useful, especially for fallbacks, to base the result on the state of
+ the comand. The fallback might vary based on whether it was triggered by an application
+ error versus a timeout.
+
+ Note: As always with dynamic vars be careful about scoping. This binding only holds for
+ the duration of the :run-fn or :fallback-fn.
+ "
+ nil)
+
+;################################################################################
+
 (defmacro with-request-context
  "Executes body within a new Hystrix Context.
 
@@ -616,10 +631,14 @@
  (when (not (instance? HystrixCommand$Setter setter))
  (throw (IllegalStateException. (str ":init-fn didn't return HystrixCommand$Setter instance"))))
  (proxy [HystrixCommand] [^HystrixCommand$Setter setter]
- (run [] (apply run-fn args))
- (getFallback [] (if fallback-fn
- (apply fallback-fn args)
- (throw (UnsupportedOperationException. "No :fallback-fn provided"))))
+ (run []
+ (binding [*command* this]
+ (apply run-fn args)))
+ (getFallback []
+ (if fallback-fn
+ (binding [*command* this]
+ (apply fallback-fn args))
+ (throw (UnsupportedOperationException. "No :fallback-fn provided"))))
  (getCacheKey [] (if cache-key-fn
  (apply cache-key-fn args))))))
 

hystrix-contrib/hystrix-clj/src/test/clojure/com/netflix/hystrix/core_test.clj

@@ -172,6 +172,31 @@
  (is (= "hello-world" (.get qc) @qc))
  (is (.isDone qc))))))
 
+(deftest test-this-command-binding
+ (let [base-def {:type :command
+ :group-key :test-this-command-binding-group
+ :command-key :test-this-command-binding
+ }]
+ (testing "this is bound while :run-fn is executing"
+ (let [captured (atom nil)
+ command-def (normalize (assoc base-def
+ :run-fn (fn []
+ (reset! captured *command*))))
+ command (instantiate command-def)]
+ (.execute command)
+ (is (identical? command @captured))))
+
+
+ (testing "this is bound while :fallback-fn is executing"
+ (let [captured (atom nil)
+ command-def (normalize (assoc base-def
+ :run-fn (fn [] (throw (Exception. "FALLBACK!")))
+ :fallback-fn (fn [] (reset! captured *command*))
+ ))
+ command (instantiate command-def)]
+ (.execute command)
+ (is (identical? command @captured))))))
+
 (deftest test-collapser
  ; These atoms are only for testing. In real life, collapser functions should *never*
  ; have side effects.