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Re: [patch][bugfix]Http mp4: replace strtod() with improved ngx_atofp() because precision problem.

胡聪 (hucc)
October 26, 2016 05:12AM
Hello!


On Wed, Oct 26, 2016 3:34 AM, Maxim Dounin wrote:

>Using strtod() should be avoided as it has other problems, see
>https://trac.nginx.org/nginx/ticket/475. That is, an additional
>variant of ngx_atofp() is a way to go.
>
>
>Last time we've looked into this, we've stumbled upon selecting a
>proper name for the additional function. Looking into this again
>I tend to think that proper solution would be to use a special
>function withing the ngx_http_mp4_module itself. Patch below.


VOD (video on demand) module which support requesting time range
also need the special function, so i would like to see that nginx-devel
add a function in Core, that would be helpful. Possible patch below.



# HG changeset patch

# User hucongcong <hucong.c@foxmail.com>

# Date 1477468236 -28800

# Wed Oct 26 15:50:36 2016 +0800

# Node ID 6376b8da3689011dfc8805381970f9ea2251c0a6

# Parent 56d6bfe6b609c565a9f500bde573fd9b488ff960

Core: add ngx_atosp().




This allows to correctly parse "start" and "end" arguments without

null-termination (ticket #475), and also fixes rounding errors observed

with strtod() when using i387 instructions.




diff -r 56d6bfe6b609 -r 6376b8da3689 src/core/ngx_string.c

--- a/src/core/ngx_string.c Fri Oct 21 16:28:39 2016 +0300

+++ b/src/core/ngx_string.c Wed Oct 26 15:50:36 2016 +0800

@@ -926,7 +926,9 @@

}





-/* parse a fixed point number, e.g., ngx_atofp("10.5", 4, 2) returns 1050 */

+/* parse a fixed point number, e.g., ngx_atofp("10.5", 4, 2) returns 1050.

+ * can be replaced by ngx_atosp(line, n, point, 1).

+ */



ngx_int_t

ngx_atofp(u_char *line, size_t n, size_t point)

@@ -982,6 +984,76 @@

}





+/* parse a fixed point number and do bounds check when strict is true, e.g.,

+ * ngx_atosp("12.2193", 3, 0, 0) returns 12,

+ * ngx_atosp("12.2193", 3, 0, 1) returns NGX_ERROR,

+ * ngx_atosp("12.2193", 6, 3, 1) returns 12219,

+ * ngx_atosp("12.2193", 7, 3, 1) returns NGX_ERROR,

+ * ngx_atosp("12.2193", 7, 3, 0) returns 12219.

+ */

+

+ngx_int_t

+ngx_atosp(u_char *line, size_t n, size_t point, unsigned strict)

+{

+ ngx_int_t value, cutoff, cutlim;

+ ngx_uint_t dot;

+

+ if (n == 0) {

+ return NGX_ERROR;

+ }

+

+ cutoff = NGX_MAX_INT_T_VALUE / 10;

+ cutlim = NGX_MAX_INT_T_VALUE % 10;

+

+ dot = 0;

+

+ for (value = 0; n--; line++) {

+

+ if (*line == '.') {

+ if (dot) {

+ return NGX_ERROR;

+ }

+

+ if (strict && point == 0) {

+ return NGX_ERROR;

+ }

+

+ dot = 1;

+ continue;

+ }

+

+ if (*line < '0' || *line > '9') {

+ return NGX_ERROR;

+ }

+

+ if (dot && point == 0) {

+ if (strict) {

+ return NGX_ERROR;

+ }

+

+ continue;

+ }

+

+ if (value >= cutoff && (value > cutoff || *line - '0' > cutlim)) {

+ return NGX_ERROR;

+ }

+

+ value = value * 10 + (*line - '0');

+ point -= dot;

+ }

+

+ while (point--) {

+ if (value > cutoff) {

+ return NGX_ERROR;

+ }

+

+ value = value * 10;

+ }

+

+ return value;

+}

+

+

ssize_t

ngx_atosz(u_char *line, size_t n)

{

diff -r 56d6bfe6b609 -r 6376b8da3689 src/http/modules/ngx_http_mp4_module.c

--- a/src/http/modules/ngx_http_mp4_module.c Fri Oct 21 16:28:39 2016 +0300

+++ b/src/http/modules/ngx_http_mp4_module.c Wed Oct 26 15:50:36 2016 +0800

@@ -537,26 +537,15 @@



/*

* A Flash player may send start value with a lot of digits

- * after dot so strtod() is used instead of atofp(). NaNs and

- * infinities become negative numbers after (int) conversion.

+ * after dot so ngx_atosp() is used instead of ngx_atofp().

*/



- ngx_set_errno(0);

- start = (int) (strtod((char *) value.data, NULL) * 1000);

-

- if (ngx_errno != 0) {

- start = -1;

- }

+ start = ngx_atosp(value.data, value.len, 3, 0);

}



if (ngx_http_arg(r, (u_char *) "end", 3, &value) == NGX_OK) {



- ngx_set_errno(0);

- end = (int) (strtod((char *) value.data, NULL) * 1000);

-

- if (ngx_errno != 0) {

- end = -1;

- }

+ end = ngx_atosp(value.data, value.len, 3, 0);



if (end > 0) {

if (start < 0) {_______________________________________________
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Subject Author Views Posted

[patch][bugfix]Http mp4: replace strtod() with improved ngx_atofp() because precision problem.

月耳 414 October 13, 2016 04:48AM

Re: [patch][bugfix]Http mp4: replace strtod() with improved ngx_atofp() because precision problem.

Maxim Dounin 149 October 18, 2016 02:28PM

Re: [patch][bugfix]Http mp4: replace strtod() with improved ngx_atofp() because precision problem.

胡聪 (hucc) 173 October 19, 2016 02:46AM

Re: [patch][bugfix]Http mp4: replace strtod() with improved ngx_atofp() because precision problem.

Maxim Dounin 238 October 25, 2016 03:36PM

Re: [patch][bugfix]Http mp4: replace strtod() with improved ngx_atofp() because precision problem.

胡聪 (hucc) 141 October 26, 2016 05:12AM

Re: [patch][bugfix]Http mp4: replace strtod() with improved ngx_atofp() because precision problem.

Maxim Dounin 145 October 26, 2016 08:32AM

Re: [patch][bugfix]Http mp4: replace strtod() with improved ngx_atofp() because precision problem.

胡聪 (hucc) 156 October 26, 2016 05:48AM

Re: [patch][bugfix]Http mp4: replace strtod() with improved ngx_atofp() because precision problem.

胡聪 (hucc) 143 October 26, 2016 12:42PM

Re: [patch][bugfix]Http mp4: replace strtod() with improved ngx_atofp() because precision problem.

Maxim Dounin 168 October 26, 2016 01:58PM



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