[PATCH v2] xrow: print corrupted rows on decoding error.

[Vladimir Davydov]

On Mon, Apr 01, 2019 at 04:09:06PM +0300, Serge Petrenko wrote:
> Add row hex printing to log on verbose level. This would be useful
> during investigation of errors related to invalid msgpack packet
> arrival.
> 
> Here's some example output:
> ```
> 2019-04-01 16:04:51.629 [31304] iproto V> Corrupted row is: 3D A5 41 55 99 18 A8 08 C2 40 2B BA 50 12 F6 C6 0B 27 66 1C
> 2019-04-01 16:04:51.629 [31304] iproto xrow.c:133 E> ER_INVALID_MSGPACK: Invalid MsgPack - packet header
> ```
> 
> Related to #4040
> ---
> https://github.com/tarantool/tarantool/tree/sp/xrow-decode-verbose-err
> https://github.com/tarantool/tarantool/issues/4040
> 
> Changes in v2:
>   - make xrow_on_decode_err a macro instead of a
>     function to preserve line where error occurs.
>   - add a test case.
>   - always allocate buffer for hex dump with malloc
>   - add logging on all errors related to invalid
>     msgpack and missing request field.
> 
>  src/box/xrow.c            | 116 ++++++++++++++++++++++++++------------
>  test/box/net.box.result   |  34 +++++++++++
>  test/box/net.box.test.lua |  16 ++++++
>  3 files changed, 131 insertions(+), 35 deletions(-)
> 
> diff --git a/src/box/xrow.c b/src/box/xrow.c
> index 73d9e739b..fdd15bef3 100644
> --- a/src/box/xrow.c
> +++ b/src/box/xrow.c
> @@ -88,15 +88,49 @@ mp_decode_vclock(const char **data, struct vclock *vclock)
>  	return 0;
>  }
>  
> +/**
> + * Set diagnostics with an error and log the corrupted row
> + * which caused the error.
> + * Optionally, if log_level is 'verbose' or greater,
> + * dump the corrupted row contents in hex to the log.
> + *
> + * @param what - exception to set.
> + * @param desc_str - error description string.
> + */
> +#define xrow_on_decode_err(_start, _end, _what, _desc_str) do {				\
> +	diag_set(ClientError, _what, _desc_str);					\
> +											\
> +	if (!say_log_level_is_enabled(S_VERBOSE))					\
> +		break;									\
> +											\
> +	size_t _len = 3 * ((const char *)(_end) - (const char *)(_start) + 1);		\

Nit: shouldn't +1 be outside the parentheses?

> +	char *_buf = (char *)malloc(_len);						\

Nit: we don't usually prefix names with underscores, because this may
conflict with libc internal macro definitions.

Other than that this patch looks good to me. Do we need it in 1.10?