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Mobile redirect in nginx with query string

lc flag
cnxsoft

I'm trying to redirect mobile visitors to AMP pages with nginx. I've basically using the script @ https://gist.github.com/dangayle/2919206 with recommended modifications, plus elements from the answer @ add a URL suffix path (for mobile AMP) without causing a redirect loop in nginx_

The main difference here is that I'm not trying to redirect mobile users to a mobile sub-domain, and instead just add a query string ("?amp=1"):

That's the code in the HTTP block for nginx.conf:

    default 0;

    "~* (android|bb\d+|meego).+mobile|avantgo|bada\/|blackberry|blazer|compal|elaine|fennec|hiptop|iemobile|ip(hone|od)|iris|kindle|lge |maemo|midp|mmp|mobile.+firefox|netfront|opera m(ob|in)i|palm( os)?|phone|p(ixi|re)\/|plucker|pocket|psp|series(4|6)0|symbian|treo|up\.(browser|link)|vodafone|wap|windows ce|xda|xiino" 1;

    "~* ^(1207|6310|6590|3gso|4thp|50[1-6]i|770s|802s|a wa|abac|ac(er|oo|s\-)|ai(ko|rn)|al(av|ca|co)|amoi|an(ex|ny|yw)|aptu|ar(ch|go)|as(te|us)|attw|au(di|\-m|r |s )|avan|be(ck|ll|nq)|bi(lb|rd)|bl(ac|az)|br(e|v)w|bumb|bw\-(n|u)|c55\/|capi|ccwa|cdm\-|cell|chtm|cldc|cmd\-|co(mp|nd)|craw|da(it|ll|ng)|dbte|dc\-s|devi|dica|dmob|do(c|p)o|ds(12|\-d)|el(49|ai)|em(l2|ul)|er(ic|k0)|esl8|ez([4-7]0|os|wa|ze)|fetc|fly(\-|_)|g1 u|g560|gene|gf\-5|g\-mo|go(\.w|od)|gr(ad|un)|haie|hcit|hd\-(m|p|t)|hei\-|hi(pt|ta)|hp( i|ip)|hs\-c|ht(c(\-| |_|a|g|p|s|t)|tp)|hu(aw|tc)|i\-(20|go|ma)|i230|iac( |\-|\/)|ibro|idea|ig01|ikom|im1k|inno|ipaq|iris|ja(t|v)a|jbro|jemu|jigs|kddi|keji|kgt( |\/)|klon|kpt |kwc\-|kyo(c|k)|le(no|xi)|lg( g|\/(k|l|u)|50|54|\-[a-w])|libw|lynx|m1\-w|m3ga|m50\/|ma(te|ui|xo)|mc(01|21|ca)|m\-cr|me(rc|ri)|mi(o8|oa|ts)|mmef|mo(01|02|bi|de|do|t(\-| |o|v)|zz)|mt(50|p1|v )|mwbp|mywa|n10[0-2]|n20[2-3]|n30(0|2)|n50(0|2|5)|n7(0(0|1)|10)|ne((c|m)\-|on|tf|wf|wg|wt)|nok(6|i)|nzph|o2im|op(ti|wv)|oran|owg1|p800|pan(a|d|t)|pdxg|pg(13|\-([1-8]|c))|phil|pire|pl(ay|uc)|pn\-2|po(ck|rt|se)|prox|psio|pt\-g|qa\-a|qc(07|12|21|32|60|\-[2-7]|i\-)|qtek|r380|r600|raks|rim9|ro(ve|zo)|s55\/|sa(ge|ma|mm|ms|ny|va)|sc(01|h\-|oo|p\-)|sdk\/|se(c(\-|0|1)|47|mc|nd|ri)|sgh\-|shar|sie(\-|m)|sk\-0|sl(45|id)|sm(al|ar|b3|it|t5)|so(ft|ny)|sp(01|h\-|v\-|v )|sy(01|mb)|t2(18|50)|t6(00|10|18)|ta(gt|lk)|tcl\-|tdg\-|tel(i|m)|tim\-|t\-mo|to(pl|sh)|ts(70|m\-|m3|m5)|tx\-9|up(\.b|g1|si)|utst|v400|v750|veri|vi(rg|te)|vk(40|5[0-3]|\-v)|vm40|voda|vulc|vx(52|53|60|61|70|80|81|83|85|98)|w3c(\-| )|webc|whit|wi(g |nc|nw)|wmlb|wonu|x700|yas\-|your|zeto|zte\-)" 1;
}

and the remaining code in location /:

set $mobile_rewrite do_not_perform;

if ($mobile_agent = 1){
    set $mobile_rewrite perform;
}

if ($mobile_agent = 1){
    set $mobile_rewrite perform;
}

#check if query arg = yes (example.com?mobile=yes), set variable
if ($arg_mobile = 'yes') { 
    add_header Set-Cookie mobile=yes;
    set $mobile_rewrite perform;
}

#check if cookie mobile=yes, set variable
if ($cookie_mobile = 'yes') { 
    set $mobile_rewrite perform;
}

#check if cookie mobile=no, break
if ($cookie_mobile = 'no') { 
    set $mobile_rewrite do_not_perform;
}

#check if query arg = no (example.com?mobile=no), break
if ($arg_mobile = 'no') { 
    add_header Set-Cookie mobile=no;
}

#if $mobile_rewrite = perform, do the redirect
if ($mobile_rewrite = perform) {
    rewrite ^.*(?<!/?amp=1)$ $scheme://www.cnx-software.es$request_uri?amp=1 break;
}

I still get troubles with redirects stuck in a loop. For example: https://www.cnx-software.es/2021/08/31/arm-china-ahora-es-totalmente-independiente-de-arm/?amp=1?amp=1&amp=1?amp=1&amp=1?amp=1&amp=1?amp=1&amp=1?amp=1&amp=1...

The problem is probably the rewrite line, but I have been able to pinpoint the exact issue.

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1 + 0
Score:1
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us flag
Tero Kilkanen

You are trying to do a negative match in regex to prevent rewrites when amp query argument is 1 in the request URL.

It is better to do this check with one more if block:

if ($arg_amp = 1) {
    set $mobile_rewrite do_not_perform;
}

Then your rewrite can be:

if ($mobile_rewrite = perform) {
    rewrite ^ $scheme://www.cnx-software.es$request_uri?amp=1 break;
}
0 + 2
lc flag
cnxsoft
Thank you. It works, it's much simpler than what I attempted to do. I have read we should avoid using "if" in location blocks. But anyway, somehow for some reason, the redirection caused a 404 error on mobile only, and after moving the code up right below the server_name line, it's OK now. Another note. nginx says return should be used instead of rewrite when possible in https://www.nginx.com/blog/creating-nginx-rewrite-rules/ So would it be better to use something like ```return 301 $scheme://www.cnx-software.es$request_uri?amp=1;``` Or it does not really matter?
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us flag
Tero Kilkanen
I was thinking about using `return`, but since you used `break` with the `rewrite`, it only performs an internal rewrie. Also, I think a permanent redirect isn't good in this case.
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lc flag
cnxsoft
I've just noticed this creates a problem with links shared on Facebook, or other sources that add one or more query strings. So I created a map `map $is_args $separator { default "?"; "?" "&"; }` and changed the rewrite as follows: `rewrite ^ $scheme://www.cnx-software.es$request_uri${separator}amp=1 break;` It almost work, but for some reasons after a first redirect that does: https://www.cnx-software.es/2021/09/23/un-primer-vistazo-a-la-placa-de-desarrollo-microchip-polarfire-soc-fpga-icicle/?fbclid=xxx&amp=1, it goes in a loop with $arg_amp=1 not detected.
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lc flag
cnxsoft
Interesting... If I click on the link with ?fbclid=xxx&amp=1, then it works, but not when going to a link with just ?fbclid=xxx. It looks like my redirection creates a link with "?fbclid=xxx&amp=1?fbclid=xxx" instead... So the amp arg value is "1?fblcid=xxx" instead... How is that possible?
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us flag
Tero Kilkanen
This might happen because of the default behavior of nginx to append query strings on rewrites. I will refine my answer to address this.
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