From: Mark Walters <markwalters1009@gmail.com>
To: Austin Clements <amdragon@MIT.EDU>, notmuch@notmuchmail.org
Subject: Re: [PATCH v3 2/5] util: Function to parse boolean term queries
In-Reply-To: <1356719189-2837-3-git-send-email-amdragon@mit.edu>
References: <1356719189-2837-1-git-send-email-amdragon@mit.edu>
	<1356719189-2837-3-git-send-email-amdragon@mit.edu>
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Date: Sat, 29 Dec 2012 16:50:51 +0000
Message-ID: <87y5ggssyc.fsf@qmul.ac.uk>
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On Fri, 28 Dec 2012, Austin Clements <amdragon@MIT.EDU> wrote:
> This parses the subset of Xapian's boolean term quoting rules that are
> used by make_boolean_term.  This is provided as a generic string
> utility, but will be used shortly in notmuch restore to parse and
> optimize for ID queries.
> ---
>  util/string-util.c |   55 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  util/string-util.h |   11 +++++++++++
>  2 files changed, 66 insertions(+)
>
> diff --git a/util/string-util.c b/util/string-util.c
> index e4bea21..83b4953 100644
> --- a/util/string-util.c
> +++ b/util/string-util.c
> @@ -96,3 +96,58 @@ make_boolean_term (void *ctx, const char *prefix, const char *term,
>  
>      return 0;
>  }
> +
> +int
> +parse_boolean_term (void *ctx, const char *str,
> +		    char **prefix_out, char **term_out)
> +{
> +    *prefix_out = *term_out = NULL;
> +
> +    /* Parse prefix */
> +    const char *pos = strchr (str, ':');
> +    if (! pos)
> +	goto FAIL;
> +    *prefix_out = talloc_strndup (ctx, str, pos - str);
> +    ++pos;
> +
> +    /* Implement de-quoting compatible with make_boolean_term. */
> +    if (*pos == '"') {
> +	char *out = talloc_array (ctx, char, strlen (pos));
> +	int closed = 0;
> +	*term_out = out;
> +	/* Skip the opening quote, find the closing quote, and
> +	 * un-double doubled internal quotes. */
> +	for (++pos; *pos; ) {
> +	    if (*pos == '"') {
> +		++pos;
> +		if (*pos != '"') {
> +		    /* Found the closing quote. */
> +		    closed = 1;
> +		    break;
> +		}
> +	    }
> +	    *out++ = *pos++;
> +	}
> +	/* Did the term terminate without a closing quote or is there
> +	 * trailing text after the closing quote? */
> +	if (!closed || *pos)
> +	    goto FAIL;
> +	*out = '\0';
> +    } else {
> +	const char *start = pos;
> +	/* Check for text after the boolean term. */
> +	while (*pos > ' ' && *pos != ')')
> +	    ++pos;
> +	if (*pos)
> +	    goto FAIL;
> +	/* No trailing text; dup the string so the caller can free
> +	 * it. */
> +	*term_out = talloc_strdup (ctx, start);
> +    }
> +    return 0;

This looks like it will fail if a line contains trailing white space
(and that seemed to be the case from my experiment). Is that wanted?

If yes we may want to make the error message clearer as I got an error
of the form
Warning: cannot parse query: id:message-id@example.com   
and the fact that line contained trailing spaces was not clear.

> +
> + FAIL:
> +    talloc_free (*prefix_out);
> +    talloc_free (*term_out);
> +    return 1;
> +}
> diff --git a/util/string-util.h b/util/string-util.h
> index b8844a3..43d49d0 100644
> --- a/util/string-util.h
> +++ b/util/string-util.h
> @@ -33,4 +33,15 @@ char *strtok_len (char *s, const char *delim, size_t *len);
>  int make_boolean_term (void *talloc_ctx, const char *prefix, const char *term,
>  		       char **buf, size_t *len);
>  
> +/* Parse a boolean term query produced by make_boolean_term, returning
> + * the prefix in *prefix_out and the term in *term_out.  *prefix_out
> + * and *term_out will be talloc'd with context ctx.
> + *
> + * Return: 0 on success, non-zero on parse error (including trailing
> + * data in str).
> + */

I think it would be worth detailing what requirements a boolean term
here should meet to be parsed.  In particular, since make_boolean_term
is more restrictive than Xapian we should say whether this is like
make_boolean_term, like Xapian or somewhere in between.


Best wishes

Mark


> +int
> +parse_boolean_term (void *ctx, const char *str,
> +		    char **prefix_out, char **term_out);
> +
>  #endif
> -- 
> 1.7.10.4