Re: Trouble parsing a response

[swedebugia]

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:
>> snip
>>
>>>
>>> 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 :)
>> https://github.com/roelj/guile-sparql/blob/master/sparql/driver.scm
>>
>> When I try calling this
>> ;; Example query to wikidata listing cats
>>                                         (sparql-query
>>   "SELECT ?item
>>                                         WHERE
>>                                         {
>>                                         ?item wdt:P31 wd:Q146.
>>                                         }
>>                                         LIMIT 10
>>                                         "
>>   #:uri "https://query.wikidata.org/sparql";
>>   ;; #:port 80
>>                                           #:type 
>> "application/sparql-results+json"
>>   ;;  #: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 .
>> "WMF-Last-Access-Global=13-Dec-2018;Path=/;Domain=.wikidata.org;HttpOnly;secure;Expires=Mon,
>> 14 Jan 2019 12:00:00 GMT") (x-analytics . "https=1;nocookies=1")
>> (x-client-ip . "83.185.90.53")) port: #<input-output: file 8c37e70>>
>>
>> My problem now is that I don't know how to separate the header from the
>> port-file.
>>
>> Ah, reading here
>> https://www.gnu.org/software/guile/manual/html_node/Responses.html#Responses
>> I found (response-port).
>>
> 
> Here's what I did in SPARQLing-genomics:
> https://github.com/UMCUGenetics/sparqling-genomics/blob/master/web/www/pages/query-response.scm#L86
> 
> So basically:
> 
> (use-modules
>   (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)
>       #t
>       (begin
>         (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):
>>
>> Backtrace:
>>             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?

> 
> 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.

Guile is super nice. And fast it seems when you get it right.
-- 
Cheers 
Swedebugia