[Dovecot] understand the struct message_header_line

[Timo Sirainen]

On Tue, 2010-09-21 at 15:07 -0300, Alex Baule wrote:
> static void filter_callback(struct message_header_line *hdr,
>                 bool *matched, void *context ATTR_UNUSED)
..
> What i try to understand is how the structs work, it's save the entire
> header or every line from header call the callback function ?

The function is called once for each header field and depending on
*matched value after the call it's either filtered out or not.

> hdr->name_offset is the size of elements in the struct ? (like a array of
> message_header_line)

I don't really know what name_offset contains in this case, probably
nothing useful, don't use it. hdr->name, hdr->value and hdr->value_len
are the only things you should need.

> The void *context ATTR_UNUSED i can pass what i want to change ? like a
> pointer to a variable ?

The context pointer contains the same pointer you gave to
i_stream_create_header_filter(). So for example you could do something
like:

char *value = NULL;

i_stream_create_header_filter(..., &value);

static void filter_callback(struct message_header_line *hdr,
                bool *matched, void *context)
{
	char **value = context;
	if (strcmp(hdr, "yourheader") == 0 && *value == NULL)
		*value = i_strndup(hdr->value, hdr->value_len);
}