How do I download and save an image from http address in Common Lisp/dexador?

user_9458627 0
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How would you download an image from a website and save it to the package folder in Common Lisp? I am having difficulty looking for such function in dexador's documentation.

Thanks in advance

common-lisp http
2 Answers

You get a byte vector back, so just save it:

(let ((bytes (dex:get uri)))
  (with-open-file (out filename
                       :direction :output
                       :if-exists :supersede
                       :if-does-not-exist :create
                       :element-type 'unsigned-byte)
    (write-sequence bytes out)))

If you have too much data, you might want to use a buffered stream copy:

(let ((byte-stream (dex:get uri :want-stream t))
      (buffer (make-array buffer-size :element-type 'unsigned-byte)))
  (with-open-file (out filename
                       :direction :output
                       :if-exists :supersede
                       :if-does-not-exist :create
                       :element-type 'unsigned-byte)
    (loop :for p := (read-sequence buffer byte-stream)
          :while (plusp p)
          :do (write-sequence buffer out :end p))))
Harleqin_316150

This is slightly improved first version from Svante's answer:

(alexandria:write-byte-vector-into-file (dex:get "https://httpbin.org/image/png")
                                        #P"/tmp/myfile"
                                       :if-exists :supersede)

And this is slightly simplified version of his second version:

(serapeum:write-stream-into-file (dex:get "https://httpbin.org/image/png"
                                          :want-stream t)
                                 #P"/tmp/myfile"
                                 :if-exists :supersede)

Alexandria and Serapeum both are collections of little helpers to simplify such tasks.

Big_40wt_Svetlyak_702930
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