nginx module regex unable to match

Question

Hi guys im trying to build a module for nginx and need to match a substring here is what im using to try and match

int match_chan(ngx_http_request_t *r, ngx_pool_t *temp_pool, ngx_str_t *body, ngx_str_t *channel) {
    u_char errstr[NGX_MAX_CONF_ERRSTR];
    ngx_regex_compile_t *rc;
    int captures[2];
    if ((rc = ngx_pcalloc(temp_pool, sizeof(ngx_regex_compile_t))) == NULL) {
        ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "unable to allocate memory to compile agent patterns");
        return 0;
    }
    //ngx_memzero(rc, sizeof(ngx_regex_compile_t));
    ngx_str_t pat = ngx_string("test(:|%3[Aa])([a-zA-Z0-9]+)");
    rc->pattern = pat;
    rc->pool = temp_pool;
    rc->err.len = NGX_MAX_CONF_ERRSTR;
    rc->err.data = errstr;
    if (ngx_regex_compile(rc) != NGX_OK) {
        ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "unable to compile regex pattern %V", rc->pattern);
        return 0;
    }
    ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "%V, %V", &pat, body);
    if (ngx_regex_exec(rc->regex, body, captures, 2) >= 0) {
        ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "It Matched");
        //ngx_memcpy(channel->data, body->data + captures[0], body->len);
        return 1;
    }
    ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "It did not match");
    return 0;
}

ngx_str_t *channel = NULL;
if(match_chan(r, temp_pool, aux, channel)) {
  //ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, " match: %c", match);
}

and the message that is passed looks like this

2014/07/04 13:28:49 [error] 10695#0: *38 test:([a-z0-9]+), MSG%0Atest%3Ahello%0A%0A%0Awins%00
2014/07/04 13:28:49 [error] 10695#0: *38 It did not match

taken from nginx log

ive tested the regex in a pure C app and that worked fine i thought nginx was similar but i guess it has its differences

ive looked all over google and ive tried looking at nginx modules with still no luck please help me :)

Thanks Dave

I know somone is going to reply to me saying its because the string is encoded but how do i accout for that regex101.com/r/yV1xW1/1 — BigDave
– BigDave, Commented Jul 4, 2014 at 13:51
well i got it to match with ngx_str_t pat = ngx_string("test%3A([a-zA-Z0-9]+)"); but it seems to end the thread on every message recieved so im still going wrong somewhere — BigDave
– BigDave, Commented Jul 4, 2014 at 15:09

Maxim Dounin · Accepted Answer · 2014-07-05 16:16:29Z

1

The problem is that the string you are trying to match is URL-encoded, and due to this it doesn't match the pattern provided. There are two options:

Construct a regular expression so it will match encoded string as well ("test(:|%3[Aa])([a-zA-Z0-9]+)" will match both unescaped and escaped forms);
Unescape the string you are matching. In nginx, this is done with the ngx_unescape_uri() function.

answered Jul 5, 2014 at 16:16

Maxim Dounin

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1 Comment

BigDave Over a year ago

OK thanks so much for taking the time to reply so ive rebuilt nginx with the changes it matches ok but the thread is still exiting i have no idea why could you help with that ill edit the post above with what i have now

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