[tarantool-patches] Re: [PATCH] sql: fix bug with BLOB TRIM() when X'00' in char set

["n.pettik" <korablev@tarantool.org>]

> commit 39b2481341cd2e71d67a04bec9aeed0e1189740c
> Author: Roman Khabibov <roman.habibov@tarantool.org>
> Date:   Sat Dec 15 13:21:59 2018 +0300
> 
>     sql: fix bug with BLOB TRIM() when X'00' in char set
> 
>     The reason for the bug was that X'00' is a terminal symbol. If the char set
>     contained X'00', all characters are ignored after it (including itself).
> 
>     Closes #3543
> 
> diff --git a/src/box/sql/func.c b/src/box/sql/func.c
> index 9667aead5..f397e23c1 100644
> --- a/src/box/sql/func.c
> +++ b/src/box/sql/func.c
> @@ -1223,9 +1223,19 @@ trimFunc(sqlite3_context * context, int argc, sqlite3_value ** argv)
>      } else if ((zCharSet = sqlite3_value_text(argv[1])) == 0) {
>          return;
>      } else {
> -        const unsigned char *z;
> -        for (z = zCharSet, nChar = 0; *z; nChar++) {
> +        const unsigned char *z = zCharSet;
> +        int sizeOfCharSet = \

We don’t use backslashes to carry code (it is used for macroses and
sometimes for comments).

> +        sqlite3_value_bytes(argv[1]); /* Size of char set in bytes. */

We put comments on the top of code to be commented:

 /* Size of char set in bytes. */
 int sizeOfCharSet = sqlite3_value_bytes(argv[1]);

I guess this comment is completely useless:
name of var and function say exactly the same as comment does.

> +        int nProcessedBytes = 0;
> +        nChar = 0;
> +        const unsigned char *zStepBack;
> +        /* Count the number of UTF-8 characters passing through the
> +        * entire char set, but not up to the '\0' or X'00' character. */

Use tnt-style comments.

> +        while(sizeOfCharSet - nProcessedBytes > 0) {
> +            zStepBack = z;
>              SQLITE_SKIP_UTF8(z);
> +            nProcessedBytes += z - zStepBack;
> +            nChar++;
>          }
>          if (nChar > 0) {
>              azChar =
> @@ -1235,10 +1245,18 @@ trimFunc(sqlite3_context * context, int argc, sqlite3_value ** argv)
>                  return;
>              }
>              aLen = (unsigned char *)&azChar[nChar];
> -            for (z = zCharSet, nChar = 0; *z; nChar++) {
> +            z = zCharSet;
> +            nChar = 0;
> +            nProcessedBytes = 0;

This comment is again useless.

> +            /* Similar to the previous cycle. But

I see trailing space. Use git diff to spot such places.

> +            * now write into "azCharSet". */

Use tnt-style comments.

> +            while(sizeOfCharSet - nProcessedBytes > 0) {
>                  azChar[nChar] = (unsigned char *)z;
> +                zStepBack = z;

You don’t need here ‘zStepBack’, you already saved current str
position to azChar.

>                  SQLITE_SKIP_UTF8(z);
> +                nProcessedBytes += z - zStepBack;
>                  aLen[nChar] = (u8) (z - azChar[nChar]);
> +                nChar++;
>              }
>          }
>      }

All points considered, I suggest diff like this:

diff --git a/src/box/sql/func.c b/src/box/sql/func.c
index f397e23c1..9b5773321 100644
--- a/src/box/sql/func.c
+++ b/src/box/sql/func.c
@@ -1203,7 +1203,8 @@ trimFunc(sqlite3_context * context, int argc, sqlite3_value ** argv)
        int i;                  /* Loop counter */
        unsigned char *aLen = 0;        /* Length of each character in zCharSet */
        unsigned char **azChar = 0;     /* Individual characters in zCharSet */
-       int nChar;              /* Number of characters in zCharSet */
+       /* Number of UTF-8 characters in zCharSet. */
+       int nChar;
 
        if (sqlite3_value_type(argv[0]) == SQLITE_NULL) {
                return;
@@ -1224,17 +1225,20 @@ trimFunc(sqlite3_context * context, int argc, sqlite3_value ** argv)
                return;
        } else {
                const unsigned char *z = zCharSet;
-               int sizeOfCharSet = \
-               sqlite3_value_bytes(argv[1]); /* Size of char set in bytes. */
-               int nProcessedBytes = 0;
+               int trim_set_sz = sqlite3_value_bytes(argv[1]);
+               int handled_bytes_cnt = trim_set_sz;
                nChar = 0;
-               const unsigned char *zStepBack;
-               /* Count the number of UTF-8 characters passing through the
-               * entire char set, but not up to the '\0' or X'00' character. */
-               while(sizeOfCharSet - nProcessedBytes > 0) {
-                       zStepBack = z;
+               /*
+                * Count the number of UTF-8 characters passing
+                * through the entire char set, but not up
+                * to the '\0' or X'00' character. This allows
+                * to handle trimming set containing such
+                * characters.
+                */
+               while(handled_bytes_cnt > 0) {
+                       const unsigned char *prev_byte = z;
                        SQLITE_SKIP_UTF8(z);
-                       nProcessedBytes += z - zStepBack;
+                       handled_bytes_cnt -= (z - prev_byte);
                        nChar++;
                }
                if (nChar > 0) {
@@ -1247,15 +1251,12 @@ trimFunc(sqlite3_context * context, int argc, sqlite3_value ** argv)
                        aLen = (unsigned char *)&azChar[nChar];
                        z = zCharSet;
                        nChar = 0;
-                       nProcessedBytes = 0;
-                       /* Similar to the previous cycle. But 
-                       * now write into "azCharSet". */
-                       while(sizeOfCharSet - nProcessedBytes > 0) {
+                       handled_bytes_cnt = trim_set_sz;
+                       while(handled_bytes_cnt > 0) {
                                azChar[nChar] = (unsigned char *)z;
-                               zStepBack = z;
                                SQLITE_SKIP_UTF8(z);
-                               nProcessedBytes += z - zStepBack;
                                aLen[nChar] = (u8) (z - azChar[nChar]);
+                               handled_bytes_cnt -= aLen[nChar];
                                nChar++;

Check it out. If you are ok with it, you can apply it (partially or fully).