<html> <head> <meta content="text/html; charset=UTF-8" http-equiv="Content-Type"> </head> <body text="#000000" bgcolor="#FFFFFF"> <div style="" data-md-original="On%2021%2F05%2F14%2010%3A07%2C%20Klaus%20Darilion%20wrote%3A%3Cbr%3E%26gt%3B%20Thanks.%20Meanwhile%20I%20managed%20to%20iterate%20over%20the%20JSON%20list%20and%20print%20the%3Cbr%3E%26gt%3B%20nsid%3A%3Cbr%3E%26gt%3B%3Cbr%3E%26gt%3B%20...%3Cbr%3E%26gt%3B%3Cbr%3E%26gt%3B%20But%20the%20problem%20is%20if%20there%20was%20an%20error%20during%20the%20measurement%20(eg%3Cbr%3E%26gt%3B%20timeout)%2C%20then%20my%20script%20terminates%3A%3Cbr%3E%26gt%3B%3Cbr%3E%26gt%3B%20...%3Cbr%3E%26gt%3B%3Cbr%3E%26gt%3B%20What%20is%20the%20suggested%20way%20to%20find%20out%20if%20a%20result%20is%20valid%20and%20exists%3F%3Cbr%3E%3Cbr%3E%3Cbr%3EFirst%20of%20all%2C%20i%20should%20say%20thanks%20for%20working%20with%20us%20on%20this.%C2%A0%20The%20trouble%20with%20a%20parsing%20library%20is%20that%20it's%20supposed%20to%20be%20able%20to%20handle%20all%20of%20the%20edge%20cases%2C%20but%20finding%20them%20independently%20is%20quite%20difficult.%C2%A0%20When%20you%20post%20examples%20to%20the%20 list%20of%20result%20blobs%20that%20act%20in%20unexpected%20ways%2C%20this%20really%20helps%20in%20polishing%20the%20parser%20and%20making%20it%20more%20intuitive.%3Cbr%3E%3Cbr%3EGiven%20that%2C%20and%20other%20comments%20from%20John%20regarding%20error%20handling%20for%20DNS%20results%2C%20I've%20added%20a%20little%20more%20code%20to%20better%20handle%20errors%2C%20so%20if%20you%20update%20Sagan%20to%200.1.12%20(or%20just%20%60git%20pull%60)%2C%20and%20re-run%20your%20code%20you'll%20find%20that%20%60result.is_error%60%20is%20now%20set%20to%20%60True%60%20in%20your%20case.%C2%A0%20Additionally%2C%20if%20you%20pass%20%60on_error%3DResult.ERROR_FAIL%60%20to%20the%20parsing%20argument%2C%20it'll%20explode%20with%20a%20%60ResultParseError%60%20which%20you%20can%20handle%20any%20way%20you%20please.%3Cbr%3E%3Cbr%3ESo%20given%20your%20example%2C%20you%20could%20do%20something%20like%3A%3Cbr%3E%3Cbr%3E%60%60%60python%3Cbr%3E%C2%A0%C2%A0%C2%A0%20result%20%3D%20DnsResult(d)%3Cbr%3E%C2%A0%C2%A0 %C2%A0%20if%20not%20result.is_error%3A%3Cbr%3E%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%20%23%20Do%20stuff%3Cbr%3E%60%60%60%3Cbr%3E%3Cbr%3EHowever%2C%20there's%20likely%20cases%20where%20you%20might%20see%20results%20that%20*aren't*%20errors%2C%20but%20still%20don't%20have%20any%20responses%2C%20or%20where%20%60edns0.options%60%20is%20an%20empty%20list.%C2%A0%20Unfortunately%2C%20you%20have%20to%20write%20your%20code%20to%20account%20for%20these%2C%20since%20they're%20perfectly%20valid%20parsings%3A%3Cbr%3E%3Cbr%3E%60%60%60python%3Cbr%3E%C2%A0%C2%A0%C2%A0%20result%20%3D%20DnsResult(d)%3Cbr%3E%C2%A0%C2%A0%C2%A0%20if%20not%20result.is_error%3A%3Cbr%3E%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%20for%20response%20in%20responses%3A%3Cbr%3E%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%20if%20response.edns0%3A%3Cbr%3E%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%20for%20option%20in%20response.edns0.options%3A%3Cbr%3E%C2%A0%C2 %A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%C2%A0%20print(option.nsid)%3Cbr%3E%60%60%60%3Cbr%3E%3Cbr%3ENote%20that%20I'm%20not%20really%20checking%20that%20much%20here%2C%20just%20looping%20over%20(potentially%20empty)%20lists.%C2%A0%20This%20keeps%20your%20code%20free%20of%20checks%2C%20and%20will%20make%20sure%20that%20it%20accounts%20for%20cases%20where%20the%20number%20of%20responses%20is%20%26gt%3B%201%20or%20the%20number%20of%20edns0%20options%20is%20%26gt%3B%201.%3Cbr%3E%3Cbr%3EBut%20please%2C%20if%20you%20find%20another%20result%20blob%20that%20isn't%20performing%20the%20way%20you'd%20expect%2C%20please%20feel%20free%20to%20post%20it%20here%20or%20send%20it%20to%20atlas-bugs%40ripe.net%20so%20we%20can%20look%20into%20it%20and%20make%20sure%20that%20Sagan%20has%20complete%20coverage.%3Cbr%3E" class="markdown-here-wrapper" data-md-url="Thunderbird" id="markdown-here-wrapper-662896"> On 21/05/14 10:07, Klaus Darilion wrote: <blockquote style="margin: 1.2em 0px;border-left: 4px solid rgb(221, 221, 221); padding: 0px 1em; color: rgb(119, 119, 119); quotes: none;"> Thanks. Meanwhile I managed to iterate over the JSON list and print the nsid: … But the problem is if there was an error during the measurement (eg timeout), then my script terminates: … What is the suggested way to find out if a result is valid and exists? </blockquote> First of all, i should say thanks for working with us on this. The trouble with a parsing library is that it’s supposed to be able to handle all of the edge cases, but finding them independently is quite difficult. When you post examples to the list of result blobs that act in unexpected ways, this really helps in polishing the parser and making it more intuitive. Given that, and other comments from John regarding error handling for DNS results, I’ve added a little more code to better handle errors, so if you update Sagan to 0.1.12 (or just <code style="font-family: Consolas,Inconsolata,Courier,monospace;margin: 0px 0.15em; padding: 0px 0.3em; white-space: pre-wrap; border: 1px solid rgb(234, 234, 234); background-color: rgb(248, 248, 248); border-radius: 3px 3px 3px 3px; display: inline;">git pull</code>), and re-run your code you’ll find that <code style="font-family: Consolas,Inconsolata,Courier,monospace;margin: 0px 0.15em; padding: 0px 0.3em; white-space: pre-wrap; border: 1px solid rgb(234, 234, 234); background-color: rgb(248, 248, 248); border-radius: 3px 3px 3px 3px; display: inline;">result.is_error</code> is now set to <code style="font-family: Consolas,Inconsolata,Courier,monospace;margin: 0px 0.15em; padding: 0px 0.3em; white-space: pre-wrap; border: 1px solid rgb(234, 234, 234); background-color: rgb(248, 248, 248); border-radius: 3px 3px 3px 3px; display: inline;">True</code> in your case. Additionally, if you pass <code style="font-family: Consolas,Inconsolata,Courier,monospace;margin: 0px 0.15em; padding: 0px 0.3em; white-space: pre-wrap; border: 1px solid rgb(234, 234, 234); background-color: rgb(248, 248, 248); border-radius: 3px 3px 3px 3px; display: inline;">on_error=Result.ERROR_FAIL</code> to the parsing argument, it’ll explode with a <code style="font-family: Consolas,Inconsolata,Courier,monospace;margin: 0px 0.15em; padding: 0px 0.3em; white-space: pre-wrap; border: 1px solid rgb(234, 234, 234); background-color: rgb(248, 248, 248); border-radius: 3px 3px 3px 3px; display: inline;">ResultParseError</code> which you can handle any way you please. So given your example, you could do something like: <pre style="font-family: Consolas,Inconsolata,Courier,monospace;font-size: 1em; line-height: 1.2em;margin: 1.2em 0px;"><code style="font-family: Consolas,Inconsolata,Courier,monospace;margin: 0px 0.15em; padding: 0px 0.3em; white-space: pre-wrap; border: 1px solid rgb(234, 234, 234); background-color: rgb(248, 248, 248); border-radius: 3px 3px 3px 3px; display: inline;white-space: pre; overflow: auto; border-radius: 3px 3px 3px 3px; border: 1px solid rgb(204, 204, 204); padding: 0.5em 0.7em; display: block ! important;display: block; padding: 0.5em; color: rgb(51, 51, 51);" class="language-python"> result = DnsResult(d) if not result.is_error: # Do stuff </code></pre> However, there’s likely cases where you might see results that aren’t errors, but still don’t have any responses, or where <code style="font-family: Consolas,Inconsolata,Courier,monospace;margin: 0px 0.15em; padding: 0px 0.3em; white-space: pre-wrap; border: 1px solid rgb(234, 234, 234); background-color: rgb(248, 248, 248); border-radius: 3px 3px 3px 3px; display: inline;">edns0.options</code> is an empty list. Unfortunately, you have to write your code to account for these, since they’re perfectly valid parsings: <pre style="font-family: Consolas,Inconsolata,Courier,monospace;font-size: 1em; line-height: 1.2em;margin: 1.2em 0px;"><code style="font-family: Consolas,Inconsolata,Courier,monospace;margin: 0px 0.15em; padding: 0px 0.3em; white-space: pre-wrap; border: 1px solid rgb(234, 234, 234); background-color: rgb(248, 248, 248); border-radius: 3px 3px 3px 3px; display: inline;white-space: pre; overflow: auto; border-radius: 3px 3px 3px 3px; border: 1px solid rgb(204, 204, 204); padding: 0.5em 0.7em; display: block ! important;display: block; padding: 0.5em; color: rgb(51, 51, 51);" class="language-python"> result = DnsResult(d) if not result.is_error: for response in responses: if response.edns0: for option in response.edns0.options: print(option.nsid) </code></pre> Note that I’m not really checking that much here, just looping over (potentially empty) lists. This keeps your code free of checks, and will make sure that it accounts for cases where the number of responses is > 1 or the number of edns0 options is > 1. But please, if you find another result blob that isn’t performing the way you’d expect, please feel free to post it here or send it to <a class="moz-txt-link-abbreviated" href="mailto:atlas-bugs@ripe.net">atlas-bugs@ripe.net</a> so we can look into it and make sure that Sagan has complete coverage. </div> </body> </html>