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vcr

A few days ago, I tried to review a cl-vcr - a library which should remember and replay HTTP calls in your tests. But unfortunately it didn’t work.

But Vincent “vindarel” did a good job, finding the similar project called vcr. It is not in Quicklisp, but can be downloaded from GitHub or Ultralisp:

https://github.com/tsikov/vcr

Today we’ll check if vcr will work for remembering our HTTP calls.

First, let’s make Drakma understand that application/json is a text format. Thanks to the @vseloved for this tip!

POFTHEDAY> (push '("application" . "json")
                 drakma:*text-content-types*)
(("application" . "json") ("text"))

POFTHEDAY> (drakma:http-request "https://httpbin.org/delay/5")
"{
  \"args\": {}, 
  \"data\": \"\", 
  \"files\": {}, 
  \"form\": {}, 
  \"headers\": {
    \"Accept\": \"*/*\", 
    \"Host\": \"httpbin.org\", 
    \"User-Agent\": \"Drakma/2.0.7 (SBCL 2.0.8; Darwin; 19.5.0; http://weitz.de/drakma/)\", 
    \"X-Amzn-Trace-Id\": \"Root=1-5f5a7371-a16e828d5dc4cb52867d2d09\"
  }, 
  \"origin\": \"178.176.74.47\", 
  \"url\": \"https://httpbin.org/delay/5\"
}
"
200 (8 bits, #xC8, #o310, #b11001000)
((:DATE . "Thu, 10 Sep 2020 18:41:58 GMT") (:CONTENT-TYPE . "application/json")
 (:CONTENT-LENGTH . "360") (:CONNECTION . "close")
 (:SERVER . "gunicorn/19.9.0") (:ACCESS-CONTROL-ALLOW-ORIGIN . "*")
 (:ACCESS-CONTROL-ALLOW-CREDENTIALS . "true"))
#<PURI:URI https://httpbin.org/delay/5>
#<FLEXI-STREAMS:FLEXI-IO-STREAM {100238A0A3}>
T
"OK"

Now it is time to see if our requests will be cached:

POFTHEDAY> (time
            (vcr:with-vcr "foo"
              (drakma:http-request "https://httpbin.org/delay/10")))
Evaluation took:
  10.849 seconds of real time
  
"{
  \"args\": {}, 
  \"data\": \"\", 
  \"files\": {}, 
  \"form\": {}, 
  \"headers\": {
    \"Accept\": \"*/*\", 
    \"Host\": \"httpbin.org\", 
    \"User-Agent\": \"Drakma/2.0.7 (SBCL 2.0.8; Darwin; 19.5.0; http://weitz.de/drakma/)\", 
    \"X-Amzn-Trace-Id\": \"Root=1-5f5a7b55-4ceacc38a3d473a1e8ce9f01\"
  }, 
  \"origin\": \"178.176.74.47\", 
  \"url\": \"https://httpbin.org/delay/10\"
}
"

;; Second call returns immediately!
POFTHEDAY> (time
            (vcr:with-vcr "foo"
              (drakma:http-request "https://httpbin.org/delay/10")))
Evaluation took:
  0.001 seconds of real time
  
"{
  \"args\": {}, 
  \"data\": \"\", 
  \"files\": {}, 
  \"form\": {}, 
  \"headers\": {
    \"Accept\": \"*/*\", 
    \"Host\": \"httpbin.org\", 
    \"User-Agent\": \"Drakma/2.0.7 (SBCL 2.0.8; Darwin; 19.5.0; http://weitz.de/drakma/)\", 
    \"X-Amzn-Trace-Id\": \"Root=1-5f5a7b55-4ceacc38a3d473a1e8ce9f01\"
  }, 
  \"origin\": \"178.176.74.47\", 
  \"url\": \"https://httpbin.org/delay/10\"
}
"

Seems the library works. But it does not support multiple values and it will break you application if it uses status code or headers, returned as the second and third values.

This is strange because I see in it’s code an attempt to handle multiple values :/

Now, how about making it work with Dexador? To do this, we have to rebind the vcr:*original-fn-symbol* variable:

POFTHEDAY> (let ((vcr:*original-fn-symbol* 'dexador:request))
             (time
              (vcr:with-vcr "foo"
                (dex:get "https://httpbin.org/delay/10"))))
Evaluation took:
  10.721 seconds of real time
  
"{
  \"args\": {}, 
  \"data\": \"\", 
  \"files\": {}, 
  \"form\": {}, 
  \"headers\": {
    \"Accept\": \"*/*\", 
    \"Host\": \"httpbin.org\", 
    \"User-Agent\": \"Drakma/2.0.7 (SBCL 2.0.8; Darwin; 19.5.0; http://weitz.de/drakma/)\", 
    \"X-Amzn-Trace-Id\": \"Root=1-5f5a7d84-7de184b7a8524404e7ecc234\"
  }, 
  \"origin\": \"178.176.74.47\", 
  \"url\": \"https://httpbin.org/delay/10\"
}
"
POFTHEDAY> (let ((vcr:*original-fn-symbol* 'dexador:request))
             (time
              (vcr:with-vcr "foo"
                (dex:get "https://httpbin.org/delay/10"))))
Evaluation took:
  0.001 seconds of real time
  
"{
  \"args\": {}, 
  \"data\": \"\", 
  \"files\": {}, 
  \"form\": {}, 
  \"headers\": {
    \"Accept\": \"*/*\", 
    \"Host\": \"httpbin.org\", 
    \"User-Agent\": \"Drakma/2.0.7 (SBCL 2.0.8; Darwin; 19.5.0; http://weitz.de/drakma/)\", 
    \"X-Amzn-Trace-Id\": \"Root=1-5f5a7d84-7de184b7a8524404e7ecc234\"
  }, 
  \"origin\": \"178.176.74.47\", 
  \"url\": \"https://httpbin.org/delay/10\"
}
"

Ups! Why did we send “Drakma” in the User-Agent header??? Let’s recheck without the vcr wrapper:

POFTHEDAY> (dex:get "https://httpbin.org/delay/10")
"{
  \"args\": {}, 
  \"data\": \"\", 
  \"files\": {}, 
  \"form\": {}, 
  \"headers\": {
    \"Accept\": \"*/*\", 
    \"Host\": \"httpbin.org\", 
    \"User-Agent\": \"Drakma/2.0.7 (SBCL 2.0.8; Darwin; 19.5.0; http://weitz.de/drakma/)\", 
    \"X-Amzn-Trace-Id\": \"Root=1-5f5a7e04-fed39a80da9ac640b6835a00\"
  }, 
  \"origin\": \"178.176.74.47\", 
  \"url\": \"https://httpbin.org/delay/10\"
}
"
200 (8 bits, #xC8, #o310, #b11001000)
((:DATE . "Thu, 10 Sep 2020 19:27:10 GMT") (:CONTENT-TYPE . "application/json")
 (:CONTENT-LENGTH . "361") (:CONNECTION . "close")
 (:SERVER . "gunicorn/19.9.0") (:ACCESS-CONTROL-ALLOW-ORIGIN . "*")
 (:ACCESS-CONTROL-ALLOW-CREDENTIALS . "true"))
#<PURI:URI https://httpbin.org/delay/10>
#<FLEXI-STREAMS:FLEXI-IO-STREAM {1006A2DB43}>
T
"OK"

Hmm, but if we’ll restart our lisp process and check it on the fresh, the result will be different (and correct):

POFTHEDAY> (dex:get "https://httpbin.org/delay/10")
"{
  \"args\": {}, 
  \"data\": \"\", 
  \"files\": {}, 
  \"form\": {}, 
  \"headers\": {
    \"Accept\": \"*/*\", 
    \"Content-Length\": \"0\", 
    \"Host\": \"httpbin.org\", 
    \"User-Agent\": \"Dexador/0.9.14 (SBCL 2.0.8); Darwin; 19.5.0\", 
    \"X-Amzn-Trace-Id\": \"Root=1-5f5a7ef4-ede1ef0036cd44c08b326080\"
  }, 
  \"origin\": \"178.176.74.47\", 
  \"url\": \"https://httpbin.org/delay/10\"
}
"
200 (8 bits, #xC8, #o310, #b11001000)
#<HASH-TABLE :TEST EQUAL :COUNT 7 {1004BD1153}>
#<QURI.URI.HTTP:URI-HTTPS https://httpbin.org/delay/10>
#<CL+SSL::SSL-STREAM for #<FD-STREAM for "socket 192.168.43.216:63549, peer: 3.221.81.55:443" {1003F79823}>>

Oh, seems, vcr is always calling dexador:http-request, because that is what it does on the top level:

(defparameter *original-fn-symbol* 'drakma:http-request)

;; The symbol original-fn is internal for the package so
;; no name conflict is possible.
(setf (symbol-function 'original-fn)
      (symbol-function *original-fn-symbol*))

Also, I found the same problem as with the original cl-vcr - this library does not use unwind-protect and in case if some error will be signalled, it will break the original drakma:http-request function :(

To finalize, I think it can be used by those who are using Drakma if somebody will fix how the multiple values are handled and original function restoration.