path: root/src/lib-storage/index/index-mail-headers.c

/* Copyright (c) 2003-2018 Dovecot authors, see the included COPYING file */

#include "lib.h"
#include "istream.h"
#include "array.h"
#include "buffer.h"
#include "str.h"
#include "message-date.h"
#include "message-part-data.h"
#include "message-parser.h"
#include "message-header-decode.h"
#include "istream-tee.h"
#include "istream-header-filter.h"
#include "imap-envelope.h"
#include "imap-bodystructure.h"
#include "index-storage.h"
#include "index-mail.h"

static const struct message_parser_settings msg_parser_set = {
	.hdr_flags = MESSAGE_HEADER_PARSER_FLAG_SKIP_INITIAL_LWSP |
		MESSAGE_HEADER_PARSER_FLAG_DROP_CR,
	.flags = MESSAGE_PARSER_FLAG_SKIP_BODY_BLOCK,
};

static void index_mail_filter_stream_destroy(struct index_mail *mail);

static int header_line_cmp(const struct index_mail_line *l1,
			   const struct index_mail_line *l2)
{
	int diff;

	diff = (int)l1->field_idx - (int)l2->field_idx;
	return diff != 0 ? diff :
		(int)l1->line_num - (int)l2->line_num;
}

void index_mail_parse_header_deinit(struct index_mail *mail)
{
	mail->data.header_parser_initialized = FALSE;
}

static void index_mail_parse_header_finish(struct index_mail *mail)
{
	struct mail *_mail = &mail->mail.mail;
	const struct index_mail_line *lines;
	const unsigned char *header;
	const uint8_t *match;
	buffer_t *buf;
	unsigned int i, j, count, match_idx, match_count;
	bool noncontiguous;

	/* sort it first so fields are grouped together and ordered by
	   line number */
	array_sort(&mail->header_lines, header_line_cmp);

	lines = array_get(&mail->header_lines, &count);
	match = array_get(&mail->header_match, &match_count);
	header = mail->header_data->data;
	buf = t_buffer_create(256);

	/* go through all the header lines we found */
	for (i = match_idx = 0; i < count; i = j) {
		/* matches and header lines are both sorted, all matches
		   until lines[i] weren't found */
		while (match_idx < lines[i].field_idx &&
		       match_idx < match_count) {
			if (HEADER_MATCH_USABLE(mail, match[match_idx]) &&
			    mail_cache_field_can_add(_mail->transaction->cache_trans,
						     _mail->seq, match_idx)) {
				/* this header doesn't exist. remember that. */
				i_assert((match[match_idx] &
					  HEADER_MATCH_FLAG_FOUND) == 0);
				index_mail_cache_add_idx(mail, match_idx,
							 "", 0);
			}
			match_idx++;
		}

		if (match_idx < match_count) {
			/* save index to first header line */
			i_assert(match_idx == lines[i].field_idx);
			j = i + 1;
			array_idx_set(&mail->header_match_lines, match_idx, &j);
			match_idx++;
		}

		if (!mail_cache_field_can_add(_mail->transaction->cache_trans,
					      _mail->seq, lines[i].field_idx)) {
			/* header is already cached. skip over all the
			   header lines. */
			for (j = i+1; j < count; j++) {
				if (lines[j].field_idx != lines[i].field_idx)
					break;
			}
			continue;
		}

		/* buffer contains: { uint32_t line_num[], 0, header texts }
		   noncontiguous is just a small optimization.. */
		buffer_set_used_size(buf, 0);
		buffer_append(buf, &lines[i].line_num,
			      sizeof(lines[i].line_num));

		noncontiguous = FALSE;
		for (j = i+1; j < count; j++) {
			if (lines[j].field_idx != lines[i].field_idx)
				break;

			if (lines[j].start_pos != lines[j-1].end_pos)
				noncontiguous = TRUE;
			buffer_append(buf, &lines[j].line_num,
				      sizeof(lines[j].line_num));
		}
		buffer_append_zero(buf, sizeof(uint32_t));

		if (noncontiguous) {
			for (; i < j; i++) {
				buffer_append(buf, header + lines[i].start_pos,
					      lines[i].end_pos -
					      lines[i].start_pos);
			}
			i--;
		} else {
			buffer_append(buf, header + lines[i].start_pos,
				      lines[j-1].end_pos - lines[i].start_pos);
		}

		index_mail_cache_add_idx(mail, lines[i].field_idx,
					 buf->data, buf->used);
	}

	for (; match_idx < match_count; match_idx++) {
		if (HEADER_MATCH_USABLE(mail, match[match_idx]) &&
		    mail_cache_field_can_add(_mail->transaction->cache_trans,
					     _mail->seq, match_idx)) {
			/* this header doesn't exist. remember that. */
			i_assert((match[match_idx] &
				  HEADER_MATCH_FLAG_FOUND) == 0);
			index_mail_cache_add_idx(mail, match_idx, "", 0);
		}
	}

	mail->data.dont_cache_field_idx = UINT_MAX;
	index_mail_parse_header_deinit(mail);
}

static unsigned int
get_header_field_idx(struct mailbox *box, const char *field)
{
	struct mail_cache_field header_field;

	i_zero(&header_field);
	header_field.type = MAIL_CACHE_FIELD_HEADER;
	/* Always register with NO decision. The field should be added soon
	   with mail_cache_add(), which changes the decision to TEMP. Most
	   importantly doing it this way emits mail_cache_decision event. */
	header_field.decision = MAIL_CACHE_DECISION_NO;
	T_BEGIN {
		header_field.name = t_strconcat("hdr.", field, NULL);
		mail_cache_register_fields(box->cache, &header_field, 1);
	} T_END;
	return header_field.idx;
}

bool index_mail_want_parse_headers(struct index_mail *mail)
{
	if (mail->data.wanted_headers != NULL ||
	    mail->data.save_bodystructure_header)
		return TRUE;

	if ((mail->data.cache_fetch_fields & MAIL_FETCH_DATE) != 0 &&
	    !mail->data.sent_date_parsed)
		return TRUE;
	return FALSE;
}

static void index_mail_parse_header_register_all_wanted(struct index_mail *mail)
{
	struct mail *_mail = &mail->mail.mail;
	const struct mail_cache_field *all_cache_fields;
	unsigned int i, count;

	all_cache_fields =
		mail_cache_register_get_list(_mail->box->cache,
					     pool_datastack_create(), &count);
	for (i = 0; i < count; i++) {
		if (strncasecmp(all_cache_fields[i].name, "hdr.", 4) != 0)
			continue;
		if (!mail_cache_field_want_add(_mail->transaction->cache_trans,
					       _mail->seq, i))
			continue;

		array_idx_set(&mail->header_match, all_cache_fields[i].idx,
			      &mail->header_match_value);
	}
}

void index_mail_parse_header_init(struct index_mail *mail,
				  struct mailbox_header_lookup_ctx *headers)
{
	struct index_mail_data *data = &mail->data;
	const uint8_t *match;
	unsigned int i, field_idx, match_count;

	index_mail_filter_stream_destroy(mail);
	i_assert(!mail->data.header_parser_initialized);

	mail->header_seq = mail->mail.mail.seq;
	if (mail->header_data == NULL) {
		mail->header_data = buffer_create_dynamic(default_pool, 4096);
		i_array_init(&mail->header_lines, 32);
		i_array_init(&mail->header_match, 32);
		i_array_init(&mail->header_match_lines, 32);
		mail->header_match_value = HEADER_MATCH_SKIP_COUNT;
	} else {
		buffer_set_used_size(mail->header_data, 0);
		array_clear(&mail->header_lines);
		array_clear(&mail->header_match_lines);

		i_assert((mail->header_match_value &
			  (HEADER_MATCH_SKIP_COUNT-1)) == 0);
		if (mail->header_match_value + HEADER_MATCH_SKIP_COUNT <= UINT8_MAX)
			mail->header_match_value += HEADER_MATCH_SKIP_COUNT;
		else {
			/* wrapped, we'll have to clear the buffer */
			array_clear(&mail->header_match);
			mail->header_match_value = HEADER_MATCH_SKIP_COUNT;
		}
	}

	if (headers != NULL) {
		for (i = 0; i < headers->count; i++) {
			array_idx_set(&mail->header_match, headers->idx[i],
				      &mail->header_match_value);
		}
	}

	if (data->wanted_headers != NULL && data->wanted_headers != headers) {
		headers = data->wanted_headers;
		for (i = 0; i < headers->count; i++) {
			array_idx_set(&mail->header_match, headers->idx[i],
				      &mail->header_match_value);
		}
	}

	/* register also all the other headers that exist in cache file */
	T_BEGIN {
		index_mail_parse_header_register_all_wanted(mail);
	} T_END;

	/* if we want sent date, it doesn't mean that we also want to cache
	   Date: header. if we have Date field's index set at this point we
	   know that we want it. otherwise add it and remember that we don't
	   want it cached. */
	field_idx = get_header_field_idx(mail->mail.mail.box, "Date");
	match = array_get(&mail->header_match, &match_count);
	if (field_idx < match_count &&
	    match[field_idx] == mail->header_match_value) {
		/* cache Date: header */
	} else if ((data->cache_fetch_fields & MAIL_FETCH_DATE) != 0 ||
		   data->save_sent_date) {
		/* parse Date: header, but don't cache it. */
		data->dont_cache_field_idx = field_idx;
		array_idx_set(&mail->header_match, field_idx,
			      &mail->header_match_value);
	}
	mail->data.header_parser_initialized = TRUE;
	mail->data.parse_line_num = 0;
	i_zero(&mail->data.parse_line);
}

static void index_mail_parse_finish_imap_envelope(struct index_mail *mail)
{
	struct mail *_mail = &mail->mail.mail;
	const unsigned int cache_field_envelope =
		mail->ibox->cache_fields[MAIL_CACHE_IMAP_ENVELOPE].idx;
	string_t *str;

	str = str_new(mail->mail.data_pool, 256);
	imap_envelope_write(mail->data.envelope_data, str);
	mail->data.envelope = str_c(str);
	mail->data.save_envelope = FALSE;

	if (mail_cache_field_can_add(_mail->transaction->cache_trans,
				     _mail->seq, cache_field_envelope)) {
		index_mail_cache_add_idx(mail, cache_field_envelope,
					 str_data(str), str_len(str));
	}
}

void index_mail_parse_header(struct message_part *part,
			     struct message_header_line *hdr,
			     struct index_mail *mail)
{
	struct mail *_mail = &mail->mail.mail;
	struct index_mail_data *data = &mail->data;
	unsigned int field_idx, count;
	uint8_t *match;

	i_assert(data->header_parser_initialized);

        data->parse_line_num++;

	if (data->save_bodystructure_header &&
	    !data->parsed_bodystructure_header) {
		i_assert(part != NULL);
		message_part_data_parse_from_header(mail->mail.data_pool, part, hdr);
	}

	if (data->save_envelope) {
		message_part_envelope_parse_from_header(mail->mail.data_pool,
					   &data->envelope_data, hdr);

		if (hdr == NULL)
                        index_mail_parse_finish_imap_envelope(mail);
	}

	if (hdr == NULL) {
		/* end of headers */
		if (mail->data.save_sent_date)
			mail->data.sent_date_parsed = TRUE;
		T_BEGIN {
			index_mail_parse_header_finish(mail);
		} T_END;
		if (data->save_bodystructure_header) {
			i_assert(data->parser_ctx != NULL);
			data->parsed_bodystructure_header = TRUE;
		}
		return;
	}

	if (!hdr->continued) {
		T_BEGIN {
			const char *cache_field_name =
				t_strconcat("hdr.", hdr->name, NULL);
			data->parse_line.field_idx =
				mail_cache_register_lookup(_mail->box->cache,
							   cache_field_name);
		} T_END;
	}
	field_idx = data->parse_line.field_idx;
	match = array_get_modifiable(&mail->header_match, &count);
	if (field_idx >= count ||
	    !HEADER_MATCH_USABLE(mail, match[field_idx])) {
		/* we don't want this header. */
		return;
	}

	if (!hdr->continued) {
		/* beginning of a line. add the header name. */
		data->parse_line.start_pos = str_len(mail->header_data);
		data->parse_line.line_num = data->parse_line_num;
		str_append(mail->header_data, hdr->name);
		str_append_data(mail->header_data, hdr->middle, hdr->middle_len);

		/* remember that we saw this header so we don't add it to
		   cache as nonexistent. */
		match[field_idx] |= HEADER_MATCH_FLAG_FOUND;
	}
	str_append_data(mail->header_data, hdr->value, hdr->value_len);
	if (!hdr->no_newline)
		str_append(mail->header_data, "\n");
	if (!hdr->continues) {
		data->parse_line.end_pos = str_len(mail->header_data);
		array_push_back(&mail->header_lines, &data->parse_line);
	}
}

static void
index_mail_parse_part_header_cb(struct message_part *part,
				struct message_header_line *hdr,
				struct index_mail *mail)
{
	index_mail_parse_header(part, hdr, mail);
}

static void
index_mail_parse_header_cb(struct message_header_line *hdr,
			   struct index_mail *mail)
{
	index_mail_parse_header(mail->data.parts, hdr, mail);
}

struct istream *
index_mail_cache_parse_init(struct mail *_mail, struct istream *input)
{
	struct index_mail *mail = INDEX_MAIL(_mail);
	struct istream *input2;

	i_assert(mail->data.tee_stream == NULL);
	i_assert(mail->data.parser_ctx == NULL);

	/* we're doing everything for now, figure out later if we want to
	   save them. */
	mail->data.save_sent_date = TRUE;
	mail->data.save_bodystructure_header = TRUE;
	mail->data.save_bodystructure_body = TRUE;
	/* Don't unnecessarily waste time generating a snippet, since it's
	   not as cheap as the others to generate. */
	if (index_mail_want_cache(mail, MAIL_CACHE_BODY_SNIPPET))
		mail->data.save_body_snippet = TRUE;

	mail->data.tee_stream = tee_i_stream_create(input);
	input = tee_i_stream_create_child(mail->data.tee_stream);
	input2 = tee_i_stream_create_child(mail->data.tee_stream);

	index_mail_parse_header_init(mail, NULL);
	mail->data.parser_input = input;
	mail->data.parser_ctx =
		message_parser_init(mail->mail.data_pool, input,
				    &msg_parser_set);
	i_stream_unref(&input);
	return input2;
}

static void index_mail_init_parser(struct index_mail *mail)
{
	struct index_mail_data *data = &mail->data;
	struct message_part *parts;
	const char *error;

	if (data->parser_ctx != NULL) {
		data->parser_input = NULL;
		if (message_parser_deinit_from_parts(&data->parser_ctx, &parts, &error) < 0) {
			index_mail_set_message_parts_corrupted(&mail->mail.mail, error);
			index_mail_parts_reset(mail);
		}
		if (data->parts == NULL || data->parts != parts) {
			/* The previous parsing didn't finish, so we're
			   re-parsing the header. The new parts don't have data
			   filled anymore. */
			data->parsed_bodystructure_header = FALSE;
		}
	}

	/* make sure parsing starts from the beginning of the stream */
	i_stream_seek(mail->data.stream, 0);
	if (data->parts == NULL) {
		data->parser_input = data->stream;
		data->parser_ctx = message_parser_init(mail->mail.data_pool,
						       data->stream,
						       &msg_parser_set);
	} else {
		data->parser_ctx =
			message_parser_init_from_parts(data->parts,
						       data->stream,
						       &msg_parser_set);
	}
}

int index_mail_parse_headers_internal(struct index_mail *mail,
				      struct mailbox_header_lookup_ctx *headers)
{
	struct index_mail_data *data = &mail->data;

	i_assert(data->stream != NULL);

	index_mail_parse_header_init(mail, headers);

	if (data->parts == NULL || data->save_bodystructure_header ||
	    (data->access_part & PARSE_BODY) != 0) {
		/* initialize bodystructure parsing in case we read the whole
		   message. */
		index_mail_init_parser(mail);
		message_parser_parse_header(data->parser_ctx, &data->hdr_size,
					    index_mail_parse_part_header_cb,
					    mail);
	} else {
		/* just read the header */
		i_assert(!data->save_bodystructure_body ||
			 data->parser_ctx != NULL);
		message_parse_header(data->stream, &data->hdr_size,
				     msg_parser_set.hdr_flags,
				     index_mail_parse_header_cb, mail);
	}
	if (index_mail_stream_check_failure(mail) < 0) {
		index_mail_parse_header_deinit(mail);
		return -1;
	}
	i_assert(!mail->data.header_parser_initialized);
	data->hdr_size_set = TRUE;
	data->access_part &= ENUM_NEGATE(PARSE_HDR);
	return 0;
}

int index_mail_parse_headers(struct index_mail *mail,
			     struct mailbox_header_lookup_ctx *headers,
			     const char *reason)
{
	struct index_mail_data *data = &mail->data;
	struct istream *input;
	uoff_t old_offset;

	old_offset = data->stream == NULL ? 0 : data->stream->v_offset;

	if (mail_get_hdr_stream_because(&mail->mail.mail, NULL, reason, &input) < 0)
		return -1;

	int ret = index_mail_parse_headers_internal(mail, headers);
	i_stream_seek(data->stream, old_offset);
	return ret;
}

static void
imap_envelope_parse_callback(struct message_header_line *hdr,
			     struct index_mail *mail)
{
	message_part_envelope_parse_from_header(mail->mail.data_pool,
				   &mail->data.envelope_data, hdr);

	if (hdr == NULL)
		index_mail_parse_finish_imap_envelope(mail);
}

int index_mail_headers_get_envelope(struct index_mail *mail)
{
	const unsigned int cache_field_envelope =
		mail->ibox->cache_fields[MAIL_CACHE_IMAP_ENVELOPE].idx;
	struct mailbox_header_lookup_ctx *header_ctx;
	struct istream *stream;
	uoff_t old_offset;
	string_t *str;

	str = str_new(mail->mail.data_pool, 256);
	if (index_mail_cache_lookup_field(mail, str,
					  cache_field_envelope) > 0) {
		mail->data.envelope = str_c(str);
		return 0;
	}
	str_free(&str);

	old_offset = mail->data.stream == NULL ? 0 :
		mail->data.stream->v_offset;

	/* Make sure header_cache_callback() isn't also parsing the ENVELOPE.
	   Otherwise two callbacks are doing it and mixing up results. */
	mail->data.save_envelope = FALSE;

	header_ctx = mailbox_header_lookup_init(mail->mail.mail.box,
						message_part_envelope_headers);
	if (mail_get_header_stream(&mail->mail.mail, header_ctx, &stream) < 0) {
		mailbox_header_lookup_unref(&header_ctx);
		return -1;
	}
	mailbox_header_lookup_unref(&header_ctx);

	if (mail->data.envelope == NULL) {
		/* we got the headers from cache - parse them to get the
		   envelope */
		message_parse_header(stream, NULL, msg_parser_set.hdr_flags,
				     imap_envelope_parse_callback, mail);
		if (stream->stream_errno != 0) {
			index_mail_stream_log_failure_for(mail, stream);
			return -1;
		}
		i_assert(mail->data.envelope != NULL);
	}

	if (mail->data.stream != NULL)
		i_stream_seek(mail->data.stream, old_offset);
	return 0;
}

static size_t get_header_size(buffer_t *buffer, size_t pos)
{
	const unsigned char *data = buffer->data;
	size_t i, size = buffer->used;

	i_assert(pos <= size);

	for (i = pos; i < size; i++) {
		if (data[i] == '\n') {
			if (i+1 == size ||
			    (data[i+1] != ' ' && data[i+1] != '\t'))
				return i - pos;
		}
	}
	return size - pos;
}

static int index_mail_header_is_parsed(struct index_mail *mail,
				       unsigned int field_idx)
{
	const uint8_t *match;
	unsigned int count;

	match = array_get(&mail->header_match, &count);
	if (field_idx < count && HEADER_MATCH_USABLE(mail, match[field_idx]))
		return (match[field_idx] & HEADER_MATCH_FLAG_FOUND) != 0 ? 1 : 0;
	return -1;
}

static bool skip_header(const unsigned char **data, size_t len)
{
	const unsigned char *p = *data;
	size_t i;

	for (i = 0; i < len; i++) {
		if (p[i] == ':')
			break;
	}
	if (i == len)
		return FALSE;

	for (i++; i < len; i++) {
		if (!IS_LWSP(p[i]))
			break;
	}

	*data = p + i;
	return TRUE;
}

static const char *const *
index_mail_get_parsed_header(struct index_mail *mail, unsigned int field_idx)
{
	ARRAY(const char *) header_values;
        const struct index_mail_line *lines;
	const unsigned char *header, *value_start, *value_end;
	const unsigned int *line_idx;
	const char *value;
	unsigned int i, lines_count, first_line_idx;

	line_idx = array_idx(&mail->header_match_lines, field_idx);
	i_assert(*line_idx != 0);
	first_line_idx = *line_idx - 1;

	p_array_init(&header_values, mail->mail.data_pool, 4);
	header = mail->header_data->data;

	lines = array_get(&mail->header_lines, &lines_count);
	for (i = first_line_idx; i < lines_count; i++) {
		if (lines[i].field_idx != lines[first_line_idx].field_idx)
			break;

		/* skip header: and drop ending LF */
		value_start = header + lines[i].start_pos;
		value_end = header + lines[i].end_pos;
		if (skip_header(&value_start, value_end - value_start)) {
			if (value_start != value_end && value_end[-1] == '\n')
				value_end--;
			value = message_header_strdup(mail->mail.data_pool,
						      value_start,
						      value_end - value_start);
			array_push_back(&header_values, &value);
		}
	}

	array_append_zero(&header_values);
	return array_front(&header_values);
}

static int
index_mail_get_raw_headers(struct index_mail *mail, const char *field,
			   const char *const **value_r)
{
	struct mail *_mail = &mail->mail.mail;
	const char *headers[2], *value;
	struct mailbox_header_lookup_ctx *headers_ctx;
	const unsigned char *data;
	unsigned int field_idx;
	string_t *dest;
	size_t i, len, len2;
	int ret;
	ARRAY(const char *) header_values;

	i_assert(field != NULL);

	field_idx = get_header_field_idx(_mail->box, field);

	dest = t_str_new(128);
	if (mail_cache_lookup_headers(_mail->transaction->cache_view, dest,
				      _mail->seq, &field_idx, 1) <= 0) {
		/* not in cache / error - first see if it's already parsed */
		p_free(mail->mail.data_pool, dest);
		if (mail->data.header_parser_initialized) {
			/* don't try to parse headers recursively. we're here
			   because message size was wrong and istream-mail
			   wants to log some cached headers. */
			i_assert(mail->mail.mail.lookup_abort >= MAIL_LOOKUP_ABORT_NOT_IN_CACHE);
			mail_set_aborted(&mail->mail.mail);
			return -1;
		}
		if (mail->header_seq != mail->mail.mail.seq ||
		    index_mail_header_is_parsed(mail, field_idx) < 0) {
			/* parse */
			const char *reason = index_mail_cache_reason(_mail,
				t_strdup_printf("header %s", field));
			headers[0] = field; headers[1] = NULL;
			headers_ctx = mailbox_header_lookup_init(_mail->box,
								 headers);
			ret = index_mail_parse_headers(mail, headers_ctx, reason);
			mailbox_header_lookup_unref(&headers_ctx);
			if (ret < 0)
				return -1;
		}

		if ((ret = index_mail_header_is_parsed(mail, field_idx)) <= 0) {
			/* not found */
			i_assert(ret != -1);
			*value_r = p_new(mail->mail.data_pool, const char *, 1);
			return 0;
		}
		*value_r = index_mail_get_parsed_header(mail, field_idx);
		return 0;
	}
	_mail->transaction->stats.cache_hit_count++;
	data = buffer_get_data(dest, &len);

	if (len == 0) {
		/* cached as nonexistent. */
		*value_r = p_new(mail->mail.data_pool, const char *, 1);
		return 0;
	}

	p_array_init(&header_values, mail->mail.data_pool, 4);

	/* cached. skip "header name: " parts in dest. */
	for (i = 0; i < len; i++) {
		if (data[i] == ':') {
			i++;
			while (i < len && IS_LWSP(data[i])) i++;

			/* @UNSAFE */
			len2 = get_header_size(dest, i);
			value = message_header_strdup(mail->mail.data_pool,
						     data + i, len2);
			i += len2 + 1;

			array_push_back(&header_values, &value);
		}
	}

	array_append_zero(&header_values);
	*value_r = array_front(&header_values);
	return 0;
}

static int unfold_header(pool_t pool, const char **_str)
{
	const char *str = *_str;
	char *new_str;
	unsigned int i, j;

	for (i = 0; str[i] != '\0'; i++) {
		if (str[i] == '\n')
			break;
	}
	if (str[i] == '\0')
		return 0;

	/* @UNSAFE */
	new_str = p_malloc(pool, i + strlen(str+i) + 1);
	memcpy(new_str, str, i);
	for (j = i; str[i] != '\0'; i++) {
		if (str[i] == '\n') {
			new_str[j++] = ' ';
			i++;
			if (str[i] == '\0')
				break;

			if (str[i] != ' ' && str[i] != '\t') {
				/* corrupted */
				return -1;
			}
		} else {
			new_str[j++] = str[i];
		}
	}
	new_str[j] = '\0';
	*_str = new_str;
	return 0;
}

static void str_replace_nuls(string_t *str)
{
	char *data = str_c_modifiable(str);
	size_t i, len = str_len(str);

	for (i = 0; i < len; i++) {
		if (data[i] == '\0')
			data[i] = ' ';
	}
}

static int
index_mail_headers_decode(struct index_mail *mail, const char *const **_list,
			  unsigned int max_count)
{
	const char *const *list = *_list;
	const char **decoded_list, *input;
	unsigned int i, count;
	string_t *str;

	count = str_array_length(list);
	if (count > max_count)
		count = max_count;
	decoded_list = p_new(mail->mail.data_pool, const char *, count + 1);

	str = t_str_new(512);
	for (i = 0; i < count; i++) {
		str_truncate(str, 0);
		input = list[i];
		/* unfold all lines into a single line */
		if (unfold_header(mail->mail.data_pool, &input) < 0)
			return -1;

		/* decode MIME encoded-words. decoding may also add new LFs. */
		message_header_decode_utf8((const unsigned char *)input,
					   strlen(input), str, NULL);
		if (strcmp(str_c(str), input) != 0) {
			if (strlen(str_c(str)) != str_len(str)) {
				/* replace NULs with spaces */
				str_replace_nuls(str);
			}
			input = p_strdup(mail->mail.data_pool, str_c(str));
		}
		decoded_list[i] = input;
	}
	*_list = decoded_list;
	return 0;
}

int index_mail_get_headers(struct mail *_mail, const char *field,
			   bool decode_to_utf8, const char *const **value_r)
{
	struct index_mail *mail = INDEX_MAIL(_mail);
	bool retry = TRUE;
	int ret;

	for (;; retry = FALSE) {
		if (index_mail_get_raw_headers(mail, field, value_r) < 0)
			return -1;
		if (**value_r == NULL)
			return 0;
		if (!decode_to_utf8)
			return 1;

		T_BEGIN {
			ret = index_mail_headers_decode(mail, value_r, UINT_MAX);
		} T_END;

		if (ret < 0 && retry) {
			mail_set_mail_cache_corrupted(_mail, "Broken header %s",
						      field);
		} else {
			break;
		}
	}
	if (ret < 0) {
		i_panic("BUG: Broken header %s for mail UID %u "
			"wasn't fixed by re-parsing the header",
			field, _mail->uid);
	}
	return 1;
}

int index_mail_get_first_header(struct mail *_mail, const char *field,
				bool decode_to_utf8, const char **value_r)
{
	struct index_mail *mail = INDEX_MAIL(_mail);
	const char *const *list;
	bool retry = TRUE;
	int ret;

	for (;; retry = FALSE) {
		if (index_mail_get_raw_headers(mail, field, &list) < 0)
			return -1;
		if (!decode_to_utf8 || list[0] == NULL) {
			ret = 0;
			break;
		}

		T_BEGIN {
			ret = index_mail_headers_decode(mail, &list, 1);
		} T_END;

		if (ret < 0 && retry) {
			mail_set_mail_cache_corrupted(_mail, "Broken header %s",
						      field);
			/* retry by parsing the full header */
		} else {
			break;
		}
	}
	if (ret < 0) {
		i_panic("BUG: Broken header %s for mail UID %u "
			"wasn't fixed by re-parsing the header",
			field, _mail->uid);
	}
	*value_r = list[0];
	return list[0] != NULL ? 1 : 0;
}

static void
header_cache_callback(struct header_filter_istream *input ATTR_UNUSED,
		      struct message_header_line *hdr,
		      bool *matched ATTR_UNUSED, struct index_mail *mail)
{
	index_mail_parse_header(NULL, hdr, mail);
}

static void index_mail_filter_stream_destroy(struct index_mail *mail)
{
	if (mail->data.filter_stream == NULL)
		return;

	const unsigned char *data;
	size_t size;

	/* read through the previous filter_stream. this makes sure that the
	   fields are added to cache, and most importantly it resets
	   header_parser_initialized=FALSE so we don't assert on it. */
	while (i_stream_read_more(mail->data.filter_stream, &data, &size) > 0)
		i_stream_skip(mail->data.filter_stream, size);
	if (mail->data.header_parser_initialized) {
		/* istream failed while reading the header */
		i_assert(mail->data.filter_stream->stream_errno != 0);
		index_mail_parse_header_deinit(mail);
	}
	i_stream_destroy(&mail->data.filter_stream);
}

int index_mail_get_header_stream(struct mail *_mail,
				 struct mailbox_header_lookup_ctx *headers,
				 struct istream **stream_r)
{
	struct index_mail *mail = INDEX_MAIL(_mail);
	struct istream *input;
	string_t *dest;

	index_mail_filter_stream_destroy(mail);

	if (mail->data.save_bodystructure_header) {
		/* we have to parse the header. */
		const char *reason =
			index_mail_cache_reason(_mail, "bodystructure");
		mail->data.access_reason_code = "mail:header_fields";
		if (index_mail_parse_headers(mail, headers, reason) < 0)
			return -1;
	}

	dest = str_new(mail->mail.data_pool, 256);
	if (mail_cache_lookup_headers(_mail->transaction->cache_view, dest,
				      _mail->seq, headers->idx,
				      headers->count) > 0) {
		str_append(dest, "\n");
		_mail->transaction->stats.cache_hit_count++;
		mail->data.filter_stream =
			i_stream_create_from_data(str_data(dest),
						  str_len(dest));
		*stream_r = mail->data.filter_stream;
		return 0;
	}
	/* not in cache / error */
	p_free(mail->mail.data_pool, dest);

	unsigned int first_not_found = UINT_MAX, not_found_count = 0;
	for (unsigned int i = 0; i < headers->count; i++) {
		if (mail_cache_field_exists(_mail->transaction->cache_view,
					    _mail->seq, headers->idx[i]) <= 0) {
			if (not_found_count++ == 0)
				first_not_found = i;
		}
	}

	const char *reason;
	if (not_found_count == 0)
		reason = "BUG: all headers seem to exist in cache";
	else {
		i_assert(first_not_found != UINT_MAX);
		reason = index_mail_cache_reason(_mail, t_strdup_printf(
			"%u/%u headers not cached (first=%s)",
			not_found_count, headers->count, headers->name[first_not_found]));
	}
	mail->data.access_reason_code = "mail:header_fields";
	if (mail_get_hdr_stream_because(_mail, NULL, reason, &input) < 0)
		return -1;

	index_mail_parse_header_init(mail, headers);
	mail->data.filter_stream =
		i_stream_create_header_filter(mail->data.stream,
					      HEADER_FILTER_INCLUDE |
					      HEADER_FILTER_ADD_MISSING_EOH |
					      HEADER_FILTER_HIDE_BODY,
					      headers->name, headers->count,
					      header_cache_callback, mail);
	*stream_r = mail->data.filter_stream;
	return 0;
}