ACK: [PATCH] lib: fwts_json: fix output so that it is machine parsable (LP: #1902249)

[Alex Hung]

On 2020-10-30 11:49 a.m., Colin King wrote:
> From: Colin Ian King <colin.king at canonical.com>
> 
> Currenty the json output is incorrectly places a trailing comma at
> the end of collections.  Fix this by re-working the output to
> not emit commas where they are not required.  Also escape the
> output strings so they can be read by json parsers.
> 
> Fixes: 1a663dd3b37 ("Replace json-c library with minimal replacement")
> Signed-off-by: Colin Ian King <colin.king at canonical.com>
> ---
>  src/lib/src/fwts_json.c | 104 ++++++++++++++++++++++++++++++++++------
>  1 file changed, 89 insertions(+), 15 deletions(-)
> 
> diff --git a/src/lib/src/fwts_json.c b/src/lib/src/fwts_json.c
> index 8f2c396d..130e5ccb 100644
> --- a/src/lib/src/fwts_json.c
> +++ b/src/lib/src/fwts_json.c
> @@ -755,6 +755,44 @@ static char *str_indent(char *str, int indent)
>  	return str_append(str, buf);
>  }
>  
> +static bool char_escape(const int ch)
> +{
> +	switch (ch) {
> +	case '"':
> +	case '\b':
> +	case '\f':
> +	case '\n':
> +	case '\r':
> +	case '\t':
> +		return true;
> +	default:
> +		break;
> +	}
> +	return false;
> +}
> +
> +static char *str_escape(char *oldstr)
> +{
> +	char *oldptr, *newstr, *newptr;
> +	ssize_t n;
> +
> +	for (n = 0, oldptr = oldstr; *oldptr; oldptr++, n++)
> +		if (char_escape(*oldptr))
> +			n++;
> +
> +	newstr = malloc(n + 1);
> +	if (!newstr)
> +		return NULL;
> +
> +	for (oldptr = oldstr, newptr = newstr; *oldptr; oldptr++, newptr++) {
> +		if (char_escape(*oldptr))
> +			*(newptr++) = '\\';
> +		*newptr = *oldptr;
> +	}
> +	*newptr = '\0';
> +	return newstr;
> +}
> +
>  /*
>   *  json_object_to_json_string_indent()
>   *	turn a simplified fwts json object into a C string, returns
> @@ -766,6 +804,7 @@ static char *json_object_to_json_string_indent(json_object *obj, int indent)
>  	int i;
>  	json_object **obj_ptr;
>  	char *str = NULL;
> +	char *tmp;
>  	char buf[64];
>  
>  	if (!obj)
> @@ -775,9 +814,6 @@ static char *json_object_to_json_string_indent(json_object *obj, int indent)
>  		str = str_indent(str, indent);
>  		if (!str)
>  			return NULL;
> -		str = str_append(str, "{\n");
> -		if (!str)
> -			return NULL;
>  	}
>  
>          if (obj->key) {
> @@ -797,15 +833,33 @@ static char *json_object_to_json_string_indent(json_object *obj, int indent)
>  
>  	switch (obj->type) {
>  	case type_array:
> -		str = str_append(str, "[\n");
> +		str = str_append(str, "\n");
> +		if (!str)
> +			return NULL;
> +		str = str_indent(str, indent);
> +		if (!str)
> +			return NULL;
> +		str = str_append(str, "[");
>  		if (!str)
>  			return NULL;
>  
>  		obj_ptr = (json_object **)obj->u.ptr;
>  		if (obj_ptr) {
>  			for (i = 0; i < obj->length; i++) {
> -				char *obj_str = json_object_to_json_string_indent(obj_ptr[i], indent + 1);
> -
> +				char *obj_str;
> +
> +				if (i) {
> +					str = str_append(str, "\n");
> +					if (!str)
> +						return NULL;
> +					str = str_indent(str, indent + 1);
> +					if (!str)
> +						return NULL;
> +					str = str_append(str, ",");
> +					if (!str)
> +						return NULL;
> +				}
> +				obj_str = json_object_to_json_string_indent(obj_ptr[i], indent + 1);
>  				if (!obj_str) {
>  					free(str);
>  					return NULL;
> @@ -821,17 +875,30 @@ static char *json_object_to_json_string_indent(json_object *obj, int indent)
>  		str = str_indent(str, indent);
>  		if (!str)
>  			return NULL;
> -		str = str_append(str, "]\n");
> +		str = str_append(str, "]");
>  		if (!str)
>  			return NULL;
>  		break;
>  
>  	case type_object:
> +		str = str_append(str, "\n");
> +		if (!str)
> +			return NULL;
> +		str = str_indent(str, indent);
> +		if (!str)
> +			return NULL;
> +		str = str_append(str, "{");
> +		if (!str)
> +			return NULL;
>  		obj_ptr = (json_object **)obj->u.ptr;
>  		if (obj_ptr) {
>  			for (i = 0; i < obj->length; i++) {
> -				char *obj_str = json_object_to_json_string_indent(obj_ptr[i], indent + 1);
> +				char *obj_str;
>  
> +				str = str_append(str, (i == 0) ? "\n" : ",\n");
> +				if (!str)
> +					return NULL;
> +				obj_str = json_object_to_json_string_indent(obj_ptr[i], indent + 1);
>  				if (!obj_str) {
>  					free(str);
>  					return NULL;
> @@ -841,6 +908,13 @@ static char *json_object_to_json_string_indent(json_object *obj, int indent)
>  					return NULL;
>  			}
>  		}
> +		str = str_append(str, "\n");
> +		if (!str)
> +			return NULL;
> +		str = str_indent(str, indent);
> +		if (!str)
> +			return NULL;
> +		str = str_append(str, "}");
>  		if (!str)
>  			return NULL;
>  		break;
> @@ -849,22 +923,25 @@ static char *json_object_to_json_string_indent(json_object *obj, int indent)
>  		str = str_append(str, "\"");
>  		if (!str)
>  			return NULL;
> -		str = str_append(str, (char *)obj->u.ptr);
> +		tmp = str_escape((char *)obj->u.ptr);
> +		if (!tmp)
> +			return NULL;
> +		str = str_append(str, tmp);
>  		if (!str)
>  			return NULL;
> -		str = str_append(str, "\",\n");
> +		str = str_append(str, "\"");
>  		if (!str)
>  			return NULL;
>  		break;
>  
>  	case type_null:
> -		str = str_append(str, "(null)\n");
> +		str = str_append(str, "(null)");
>  		if (!str)
>  			return NULL;
>  		break;
>  
>  	case type_int:
> -		snprintf(buf, sizeof(buf), "%d,\n", obj->u.intval);
> +		snprintf(buf, sizeof(buf), "%d", obj->u.intval);
>  		str = str_append(str, buf);
>  		if (!str)
>  			return NULL;
> @@ -877,9 +954,6 @@ static char *json_object_to_json_string_indent(json_object *obj, int indent)
>  		str = str_indent(str, indent);
>  		if (!str)
>  			return NULL;
> -		str = str_append(str, "},\n");
> -		if (!str)
> -			return NULL;
>  	}
>  	return str;
>  }
> 
Acked-by: Alex Hung <alex.hung at canonical.com>