I should have said the code for reading from stdin was 
stolen from Peter's patch for notmuch-insert
id:1343223767-9812-4-git-send-email-novalazy@gmail.com
(errors are of course mine)

My apologies for not mentioning this in the commit message.

Mark



On Sat, 24 Nov 2012, markwalters1009 <markwalters1009@gmail.com> wrote:
> From: Mark Walters <markwalters1009@gmail.com>
>
> After this series there will be times when a caller will want to pass
> a very large query string to notmuch (eg a list of 10,000 message-ids)
> and this can exceed the size of ARG_MAX. Hence allow notmuch to take
> the query from stdin (if the query is -).
> ---
>  query-string.c |   41 +++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 41 insertions(+), 0 deletions(-)
>
> diff --git a/query-string.c b/query-string.c
> index 6536512..b1fbdeb 100644
> --- a/query-string.c
> +++ b/query-string.c
> @@ -20,6 +20,44 @@
>  
>  #include "notmuch-client.h"
>  
> +/* Read a single query string from STDIN, using
> + * 'ctx' as the talloc owner for all allocations.
> + *
> + * This function returns NULL in case of insufficient memory or read
> + * errors.
> + */
> +static char *
> +query_string_from_stdin (void *ctx)
> +{
> +    char *query_string;
> +    char buf[4096];
> +    ssize_t remain;
> +
> +    query_string = talloc_strdup (ctx, "");
> +    if (query_string == NULL)
> +	return NULL;
> +
> +    for (;;) {
> +	remain = read (STDIN_FILENO, buf, sizeof(buf) - 1);
> +	if (remain == 0)
> +	    break;
> +	if (remain < 0) {
> +	    if (errno == EINTR)
> +		continue;
> +	    fprintf (stderr, "Error: reading from standard input: %s\n",
> +		     strerror (errno));
> +	    return NULL;
> +	}
> +
> +	buf[remain] = '\0';
> +	query_string = talloc_strdup_append (query_string, buf);
> +	if (query_string == NULL)
> +	    return NULL;
> +    }
> +
> +    return query_string;
> +}
> +
>  /* Construct a single query string from the passed arguments, using
>   * 'ctx' as the talloc owner for all allocations.
>   *
> @@ -35,6 +73,9 @@ query_string_from_args (void *ctx, int argc, char *argv[])
>      char *query_string;
>      int i;
>  
> +    if ((argc == 1) && (strcmp ("-", argv[0]) == 0))
> +	return query_string_from_stdin (ctx);
> +
>      query_string = talloc_strdup (ctx, "");
>      if (query_string == NULL)
>  	return NULL;
> -- 
> 1.7.9.1