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Re: Trouble parsing a response

From: Roel Janssen
Subject: Re: Trouble parsing a response
Date: Fri, 14 Dec 2018 16:59:12 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1

On 13-12-18 23:29, address@hidden wrote:
On 2018-12-13 23:03, Roel Janssen wrote:
On 13-12-18 17:06, address@hidden wrote:
On 2018-12-13 16:01, address@hidden wrote:

I tried with the file attached but got this because the driver does not
support URIs but only host, port, type, token:

Ah, I saw now that you already implemented URI on master :)

When I try calling this
;; Example query to wikidata listing cats
   "SELECT ?item
                                         ?item wdt:P31 wd:Q146.
                                         LIMIT 10
   #:uri "";
   ;; #:port 80
   ;;  #:token "..."
                                           #:store-backend 'blazegraph

I get this fine result:
#<<response> version: (1 . 1) code: 200 reason-phrase: "OK" headers:
((date . #<date nanosecond: 0 second: 12 minute: 32 hour: 15 day: 13
month: 12 year: 2018 zone-offset: 0>) (content-type
application/sparql-results+json (charset . "utf-8")) (transfer-encoding
(chunked)) (connection close) (server . "nginx/1.13.6") (x-served-by .
"wdqs1005") (access-control-allow-origin . "*") (cache-control public
(max-age . 300)) (vary accept accept-encoding) (x-varnish . "644531744,
572094009, 417977651") (via "1.1 varnish (Varnish/5.1)" "1.1 varnish
(Varnish/5.1)" "1.1 varnish (Varnish/5.1)") (accept-ranges bytes) (age .
0) (x-cache . "cp1079 pass, cp3030 pass, cp3030 pass") (x-cache-status .
"pass") (server-timing . "cache;desc=\"pass\"")
(strict-transport-security . "max-age=106384710; includeSubDomains;
preload") (set-cookie .
"WMF-Last-Access=13-Dec-2018;Path=/;HttpOnly;secure;Expires=Mon, 14 Jan
2019 12:00:00 GMT") (set-cookie .
14 Jan 2019 12:00:00 GMT") (x-analytics . "https=1;nocookies=1")
(x-client-ip . "")) port: #<input-output: file 8c37e70>>

My problem now is that I don't know how to separate the header from the

Ah, reading here
I found (response-port).

Here's what I did in SPARQLing-genomics:

So basically:

   (ice-9 receive)
   (ice-9 rdelim)
   (web response))

(receive (header port)
   ;; Note: "text/csv" is the only format that is consistent for
multiple SPARQL back-ends (Virtuoso, BlazeGraph, ...)
   (sparql-query ... #:type "text/csv")
   (if (= (response-code header) 200) ; This means the query went OK.
     (call-some-function port)
     #f)) ; Deal with errors at the #f.

(define (call-some-function port)
   (let ((line (read-line port)))
     (if (eof-object? line)
         (format #t "Line: ~a~%" line)
         ;; Tail-recurse until we have processed each line.
         (call-some-function port)))))

This would be a really nice addition to the guile manual. Can I submit
it as a patch crediting you?


The SPARQLing-genomics code deals with more error codes, and processes
the lines in a more useful way.

Unfortunately this only took me one step further as I run into this
instead when trying to parse the port with (json->scm):

             7 (apply-smob/1 #<catch-closure 9769550>)
In ice-9/boot-9.scm:
      705:2  6 (call-with-prompt _ _ #<procedure default-prompt-handle…>)
In ice-9/eval.scm:
      619:8  5 (_ #(#(#<directory (guile-user) 9759910>)))
In ice-9/boot-9.scm:
     2312:4  4 (save-module-excursion _)
    3831:12  3 (_)
In sdb-test.scm:
       24:1  2 (_)
In json/parser.scm:
     311:18  1 (json-read-number _)
     148:28  0 (read-number _)

json/parser.scm:148:28: In procedure read-number:
Throw to key `json-invalid' with args `(#<json-parser port:
#<input-output: string 98dea80>>)'.

Maybe this is a bug in (json)?

It looks like the JSON response is not (only) JSON, or simply invalid.
Maybe the "text/xml" or "text/csv" content-type will work better for
you.  I noticed that each back-end provides their own structure for
XML and JSON, so I used the somewhat quirky CSV format as a
work-for-all response type.

Ok, good to know. Is this documented in your guile-sparql docs?

No. I think what SPARQL endpoints actually return is beyond the scope of guile-sparql, and may change in the future anyway.

I hope this helps.

Thanks a lot for taking the time to write this. :)
I already met receive in the npm importer but I did not really learn to
use it yet. So whenever I see multiple objects returned I can part them
with receive! Nice.

Exactly.  I'm glad my snippet helped.

Kind regards,
Roel Janssen

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