src/lib-index/mail-cache-compress.c

	mail-cache-compress.c revision a817fdcc43aedf423e2134091d5f83f91d64bcc9
06509499ae5b6676db799057108433170a23ed28fuankg/* Copyright (C) 2003-2004 Timo Sirainen */
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg#include "lib.h"
06509499ae5b6676db799057108433170a23ed28fuankg#include "buffer.h"
06509499ae5b6676db799057108433170a23ed28fuankg#include "ostream.h"
06509499ae5b6676db799057108433170a23ed28fuankg#include "file-dotlock.h"
06509499ae5b6676db799057108433170a23ed28fuankg#include "file-cache.h"
06509499ae5b6676db799057108433170a23ed28fuankg#include "file-set-size.h"
06509499ae5b6676db799057108433170a23ed28fuankg#include "mail-cache-private.h"
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg#include <sys/stat.h>
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankgstruct mail_cache_copy_context {
06509499ae5b6676db799057108433170a23ed28fuankg    int new_msg;
06509499ae5b6676db799057108433170a23ed28fuankg    buffer_t *buffer, *field_seen;
06509499ae5b6676db799057108433170a23ed28fuankg    uint8_t field_seen_value;
06509499ae5b6676db799057108433170a23ed28fuankg};
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankgstatic void mail_cache_merge_bitmask(struct mail_cache *cache, buffer_t *buffer,
06509499ae5b6676db799057108433170a23ed28fuankg                     uint32_t field, const void *data,
06509499ae5b6676db799057108433170a23ed28fuankg                     size_t data_size)
06509499ae5b6676db799057108433170a23ed28fuankg{
06509499ae5b6676db799057108433170a23ed28fuankg    void *buf_data;
06509499ae5b6676db799057108433170a23ed28fuankg    uint32_t buf_field;
06509499ae5b6676db799057108433170a23ed28fuankg    unsigned int i, buf_data_size;
06509499ae5b6676db799057108433170a23ed28fuankg    size_t pos, buf_size;
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    buf_data = buffer_get_modifyable_data(buffer, &buf_size);
06509499ae5b6676db799057108433170a23ed28fuankg    for (pos = sizeof(struct mail_cache_record); pos < buf_size; ) {
06509499ae5b6676db799057108433170a23ed28fuankg        buf_field = *((uint32_t *)PTR_OFFSET(buf_data, pos));
06509499ae5b6676db799057108433170a23ed28fuankg        pos += sizeof(uint32_t);
06509499ae5b6676db799057108433170a23ed28fuankg        i_assert(buf_field < cache->fields_count);
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg        buf_data_size = cache->fields[buf_field].field.field_size;
06509499ae5b6676db799057108433170a23ed28fuankg        if (buf_data_size == (unsigned int)-1) {
06509499ae5b6676db799057108433170a23ed28fuankg            buf_data_size =
06509499ae5b6676db799057108433170a23ed28fuankg                *((uint32_t *)PTR_OFFSET(buf_data, pos));
06509499ae5b6676db799057108433170a23ed28fuankg            pos += sizeof(uint32_t);
06509499ae5b6676db799057108433170a23ed28fuankg        }
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg        if (buf_field == field) {
06509499ae5b6676db799057108433170a23ed28fuankg            /* @UNSAFE: found it, do the merging */
06509499ae5b6676db799057108433170a23ed28fuankg            unsigned char *dest = PTR_OFFSET(buf_data, pos);
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg            i_assert(buf_data_size == data_size);
06509499ae5b6676db799057108433170a23ed28fuankg            i_assert(pos + buf_data_size <= buf_size);
06509499ae5b6676db799057108433170a23ed28fuankg            for (i = 0; i < buf_data_size; i++)
06509499ae5b6676db799057108433170a23ed28fuankg                dest[i] |= ((const unsigned char*)data)[i];
06509499ae5b6676db799057108433170a23ed28fuankg            break;
06509499ae5b6676db799057108433170a23ed28fuankg        }
06509499ae5b6676db799057108433170a23ed28fuankg        pos += (buf_data_size + 3) & ~3;
06509499ae5b6676db799057108433170a23ed28fuankg        i_assert(pos <= buf_size);
06509499ae5b6676db799057108433170a23ed28fuankg    }
06509499ae5b6676db799057108433170a23ed28fuankg}
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankgstatic int
06509499ae5b6676db799057108433170a23ed28fuankgmail_cache_compress_callback(struct mail_cache_view *view, uint32_t field,
06509499ae5b6676db799057108433170a23ed28fuankg                 const void *data, size_t data_size, void *context)
06509499ae5b6676db799057108433170a23ed28fuankg{
06509499ae5b6676db799057108433170a23ed28fuankg    struct mail_cache_copy_context *ctx = context;
06509499ae5b6676db799057108433170a23ed28fuankg        struct mail_cache_field *cache_field;
06509499ae5b6676db799057108433170a23ed28fuankg    enum mail_cache_decision_type dec;
06509499ae5b6676db799057108433170a23ed28fuankg    uint8_t *field_seen;
06509499ae5b6676db799057108433170a23ed28fuankg    uint32_t size32;
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    cache_field = &view->cache->fields[field].field;
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    field_seen = buffer_get_space_unsafe(ctx->field_seen, field, 1);
06509499ae5b6676db799057108433170a23ed28fuankg    if (*field_seen == ctx->field_seen_value) {
06509499ae5b6676db799057108433170a23ed28fuankg        /* duplicate */
06509499ae5b6676db799057108433170a23ed28fuankg        if (cache_field->type == MAIL_CACHE_FIELD_BITMASK) {
06509499ae5b6676db799057108433170a23ed28fuankg            mail_cache_merge_bitmask(view->cache, ctx->buffer,
06509499ae5b6676db799057108433170a23ed28fuankg                         field, data, data_size);
06509499ae5b6676db799057108433170a23ed28fuankg        }
06509499ae5b6676db799057108433170a23ed28fuankg        return 1;
06509499ae5b6676db799057108433170a23ed28fuankg    }
06509499ae5b6676db799057108433170a23ed28fuankg    *field_seen = ctx->field_seen_value;
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    dec = cache_field->decision & ~MAIL_CACHE_DECISION_FORCED;
06509499ae5b6676db799057108433170a23ed28fuankg    if (ctx->new_msg) {
06509499ae5b6676db799057108433170a23ed28fuankg        if (dec == MAIL_CACHE_DECISION_NO)
06509499ae5b6676db799057108433170a23ed28fuankg            return 1;
06509499ae5b6676db799057108433170a23ed28fuankg    } else {
06509499ae5b6676db799057108433170a23ed28fuankg        if (dec != MAIL_CACHE_DECISION_YES)
06509499ae5b6676db799057108433170a23ed28fuankg            return 1;
06509499ae5b6676db799057108433170a23ed28fuankg    }
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    buffer_append(ctx->buffer, &field, sizeof(field));
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    if (cache_field->field_size == (unsigned int)-1) {
06509499ae5b6676db799057108433170a23ed28fuankg        size32 = (uint32_t)data_size;
06509499ae5b6676db799057108433170a23ed28fuankg        buffer_append(ctx->buffer, &size32, sizeof(size32));
06509499ae5b6676db799057108433170a23ed28fuankg    }
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    buffer_append(ctx->buffer, data, data_size);
06509499ae5b6676db799057108433170a23ed28fuankg    if ((data_size & 3) != 0)
06509499ae5b6676db799057108433170a23ed28fuankg        buffer_append_zero(ctx->buffer, 4 - (data_size & 3));
06509499ae5b6676db799057108433170a23ed28fuankg    return 1;
06509499ae5b6676db799057108433170a23ed28fuankg}
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankgstatic uint32_t
06509499ae5b6676db799057108433170a23ed28fuankgget_next_file_seq(struct mail_cache *cache, struct mail_index_view *view)
06509499ae5b6676db799057108433170a23ed28fuankg{
06509499ae5b6676db799057108433170a23ed28fuankg    const struct mail_index_ext *ext;
06509499ae5b6676db799057108433170a23ed28fuankg    uint32_t file_seq;
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    ext = mail_index_view_get_ext(view, cache->ext_id);
06509499ae5b6676db799057108433170a23ed28fuankg    file_seq = ext != NULL ? ext->reset_id + 1 : (uint32_t)ioloop_time;
06509499ae5b6676db799057108433170a23ed28fuankg    return file_seq != 0 ? file_seq : 1;
06509499ae5b6676db799057108433170a23ed28fuankg}
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankgstatic int
06509499ae5b6676db799057108433170a23ed28fuankgmail_cache_copy(struct mail_cache *cache, struct mail_index_view *view, int fd)
06509499ae5b6676db799057108433170a23ed28fuankg{
06509499ae5b6676db799057108433170a23ed28fuankg        struct mail_cache_copy_context ctx;
06509499ae5b6676db799057108433170a23ed28fuankg    struct mail_cache_view *cache_view;
06509499ae5b6676db799057108433170a23ed28fuankg    struct mail_index_transaction *t;
06509499ae5b6676db799057108433170a23ed28fuankg    const struct mail_index_header *idx_hdr;
06509499ae5b6676db799057108433170a23ed28fuankg    struct mail_cache_header hdr;
06509499ae5b6676db799057108433170a23ed28fuankg    struct mail_cache_record cache_rec;
06509499ae5b6676db799057108433170a23ed28fuankg    struct ostream *output;
06509499ae5b6676db799057108433170a23ed28fuankg    buffer_t *buffer;
06509499ae5b6676db799057108433170a23ed28fuankg    uint32_t i, message_count, seq, first_new_seq, old_offset;
06509499ae5b6676db799057108433170a23ed28fuankg    uoff_t offset;
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    /* get sequence of first message which doesn't need its temp fields
06509499ae5b6676db799057108433170a23ed28fuankg       removed. */
06509499ae5b6676db799057108433170a23ed28fuankg    idx_hdr = mail_index_get_header(view);
06509499ae5b6676db799057108433170a23ed28fuankg    if (idx_hdr->day_first_uid[7] == 0) {
06509499ae5b6676db799057108433170a23ed28fuankg        first_new_seq = 1;
06509499ae5b6676db799057108433170a23ed28fuankg        message_count = mail_index_view_get_messages_count(view);
06509499ae5b6676db799057108433170a23ed28fuankg    } else {
06509499ae5b6676db799057108433170a23ed28fuankg        if (mail_index_lookup_uid_range(view, idx_hdr->day_first_uid[7],
06509499ae5b6676db799057108433170a23ed28fuankg                        (uint32_t)-1, &first_new_seq,
06509499ae5b6676db799057108433170a23ed28fuankg                        &message_count) < 0)
06509499ae5b6676db799057108433170a23ed28fuankg            return -1;
06509499ae5b6676db799057108433170a23ed28fuankg        if (first_new_seq == 0)
06509499ae5b6676db799057108433170a23ed28fuankg            first_new_seq = message_count+1;
06509499ae5b6676db799057108433170a23ed28fuankg    }
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    cache_view = mail_cache_view_open(cache, view);
06509499ae5b6676db799057108433170a23ed28fuankg    t = mail_index_transaction_begin(view, FALSE, TRUE);
06509499ae5b6676db799057108433170a23ed28fuankg    output = o_stream_create_file(fd, default_pool, 0, FALSE);
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    memset(&hdr, 0, sizeof(hdr));
06509499ae5b6676db799057108433170a23ed28fuankg    hdr.version = MAIL_CACHE_VERSION;
06509499ae5b6676db799057108433170a23ed28fuankg    hdr.indexid = idx_hdr->indexid;
06509499ae5b6676db799057108433170a23ed28fuankg    hdr.file_seq = get_next_file_seq(cache, view);
06509499ae5b6676db799057108433170a23ed28fuankg    o_stream_send(output, &hdr, sizeof(hdr));
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    memset(&ctx, 0, sizeof(ctx));
06509499ae5b6676db799057108433170a23ed28fuankg    ctx.buffer = buffer_create_dynamic(default_pool, 4096);
06509499ae5b6676db799057108433170a23ed28fuankg    ctx.field_seen = buffer_create_dynamic(default_pool, 64);
06509499ae5b6676db799057108433170a23ed28fuankg    ctx.field_seen_value = 0;
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    mail_index_ext_reset(t, cache->ext_id, hdr.file_seq);
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    for (seq = 1; seq <= message_count; seq++) {
06509499ae5b6676db799057108433170a23ed28fuankg        ctx.new_msg = seq >= first_new_seq;
06509499ae5b6676db799057108433170a23ed28fuankg        buffer_set_used_size(ctx.buffer, 0);
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg        if (++ctx.field_seen_value == 0) {
06509499ae5b6676db799057108433170a23ed28fuankg            memset(buffer_get_modifyable_data(ctx.field_seen, NULL),
06509499ae5b6676db799057108433170a23ed28fuankg                   0, buffer_get_size(ctx.field_seen));
06509499ae5b6676db799057108433170a23ed28fuankg            ctx.field_seen_value++;
06509499ae5b6676db799057108433170a23ed28fuankg        }
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg        memset(&cache_rec, 0, sizeof(cache_rec));
06509499ae5b6676db799057108433170a23ed28fuankg        buffer_append(ctx.buffer, &cache_rec, sizeof(cache_rec));
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg        (void)mail_cache_foreach(cache_view, seq,
06509499ae5b6676db799057108433170a23ed28fuankg                     mail_cache_compress_callback, &ctx);
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg        cache_rec.size = buffer_get_used_size(ctx.buffer);
06509499ae5b6676db799057108433170a23ed28fuankg        if (cache_rec.size == sizeof(cache_rec))
06509499ae5b6676db799057108433170a23ed28fuankg            continue;
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg        mail_index_update_ext(t, seq, cache->ext_id, &output->offset,
06509499ae5b6676db799057108433170a23ed28fuankg                      &old_offset);
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg        buffer_write(ctx.buffer, 0, &cache_rec, sizeof(cache_rec));
06509499ae5b6676db799057108433170a23ed28fuankg        o_stream_send(output, ctx.buffer->data, cache_rec.size);
06509499ae5b6676db799057108433170a23ed28fuankg    }
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    if (cache->fields_count != 0) {
06509499ae5b6676db799057108433170a23ed28fuankg        hdr.field_header_offset =
06509499ae5b6676db799057108433170a23ed28fuankg            mail_index_uint32_to_offset(output->offset);
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg        /* we wrote everything using our internal field ids. so we want
06509499ae5b6676db799057108433170a23ed28fuankg           mail_cache_header_fields_get() to use them and ignore any
06509499ae5b6676db799057108433170a23ed28fuankg           existing id mappings in the old cache file. */
06509499ae5b6676db799057108433170a23ed28fuankg        cache->file_fields_count = 0;
06509499ae5b6676db799057108433170a23ed28fuankg        for (i = 0; i < cache->fields_count; i++)
06509499ae5b6676db799057108433170a23ed28fuankg                        cache->field_file_map[i] = (uint32_t)-1;
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg        t_push();
06509499ae5b6676db799057108433170a23ed28fuankg        buffer = buffer_create_dynamic(pool_datastack_create(), 256);
06509499ae5b6676db799057108433170a23ed28fuankg        mail_cache_header_fields_get(cache, buffer);
06509499ae5b6676db799057108433170a23ed28fuankg        o_stream_send(output, buffer_get_data(buffer, NULL),
06509499ae5b6676db799057108433170a23ed28fuankg                  buffer_get_used_size(buffer));
06509499ae5b6676db799057108433170a23ed28fuankg        t_pop();
06509499ae5b6676db799057108433170a23ed28fuankg    }
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    hdr.used_file_size = output->offset;
06509499ae5b6676db799057108433170a23ed28fuankg    buffer_free(ctx.buffer);
06509499ae5b6676db799057108433170a23ed28fuankg    buffer_free(ctx.field_seen);
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    o_stream_seek(output, 0);
06509499ae5b6676db799057108433170a23ed28fuankg    o_stream_send(output, &hdr, sizeof(hdr));
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    mail_cache_view_close(cache_view);
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    if (o_stream_flush(output) < 0) {
06509499ae5b6676db799057108433170a23ed28fuankg        errno = output->stream_errno;
06509499ae5b6676db799057108433170a23ed28fuankg        mail_cache_set_syscall_error(cache, "o_stream_flush()");
06509499ae5b6676db799057108433170a23ed28fuankg        (void)mail_index_transaction_rollback(t);
06509499ae5b6676db799057108433170a23ed28fuankg        o_stream_unref(output);
06509499ae5b6676db799057108433170a23ed28fuankg        return -1;
06509499ae5b6676db799057108433170a23ed28fuankg    }
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    if (hdr.used_file_size < MAIL_CACHE_INITIAL_SIZE) {
06509499ae5b6676db799057108433170a23ed28fuankg        /* grow the file some more. doesn't matter if it fails */
06509499ae5b6676db799057108433170a23ed28fuankg        (void)file_set_size(fd, MAIL_CACHE_INITIAL_SIZE);
06509499ae5b6676db799057108433170a23ed28fuankg    }
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    o_stream_unref(output);
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    if (fdatasync(fd) < 0) {
06509499ae5b6676db799057108433170a23ed28fuankg        mail_cache_set_syscall_error(cache, "fdatasync()");
06509499ae5b6676db799057108433170a23ed28fuankg        (void)mail_index_transaction_rollback(t);
06509499ae5b6676db799057108433170a23ed28fuankg        return -1;
06509499ae5b6676db799057108433170a23ed28fuankg    }
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    return mail_index_transaction_commit(t, &seq, &offset);
06509499ae5b6676db799057108433170a23ed28fuankg}
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankgstatic int mail_cache_compress_locked(struct mail_cache *cache,
06509499ae5b6676db799057108433170a23ed28fuankg                      struct mail_index_view *view)
06509499ae5b6676db799057108433170a23ed28fuankg{
06509499ae5b6676db799057108433170a23ed28fuankg    struct dotlock *dotlock;
06509499ae5b6676db799057108433170a23ed28fuankg        mode_t old_mask;
06509499ae5b6676db799057108433170a23ed28fuankg    int fd;
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    /* get the latest info on fields */
06509499ae5b6676db799057108433170a23ed28fuankg    if (mail_cache_header_fields_read(cache) < 0)
06509499ae5b6676db799057108433170a23ed28fuankg        return -1;
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg#ifdef DEBUG
06509499ae5b6676db799057108433170a23ed28fuankg    i_warning("Compressing cache file %s", cache->filepath);
06509499ae5b6676db799057108433170a23ed28fuankg#endif
06509499ae5b6676db799057108433170a23ed28fuankg
06509499ae5b6676db799057108433170a23ed28fuankg    old_mask = umask(cache->index->mode ^ 0666);
06509499ae5b6676db799057108433170a23ed28fuankg    fd = file_dotlock_open(&cache->dotlock_settings, cache->filepath,
                   0, &dotlock);
    umask(old_mask);

    if (fd == -1) {
        mail_cache_set_syscall_error(cache, "file_dotlock_open()");
        return -1;
    }

    if (cache->index->gid != (gid_t)-1 &&
        fchown(fd, (uid_t)-1, cache->index->gid) < 0) {
        mail_cache_set_syscall_error(cache, "fchown()");
        file_dotlock_delete(&dotlock);
        return -1;
    }

    // FIXME: check that cache file wasn't just recreated

    if (mail_cache_copy(cache, view, fd) < 0) {
        (void)file_dotlock_delete(&dotlock);
        return -1;
    }

    if (file_dotlock_replace(&dotlock,
                 DOTLOCK_REPLACE_FLAG_DONT_CLOSE_FD) < 0) {
        mail_cache_set_syscall_error(cache,
                         "file_dotlock_replace()");
        (void)close(fd);
        return -1;
    }

    mail_cache_file_close(cache);
    cache->fd = fd;

    if (cache->file_cache != NULL)
        file_cache_set_fd(cache->file_cache, cache->fd);

    if (mail_cache_map(cache, 0, 0) < 0)
        return -1;
    if (mail_cache_header_fields_read(cache) < 0)
        return -1;

    cache->need_compress = FALSE;
    return 0;
}

int mail_cache_compress(struct mail_cache *cache, struct mail_index_view *view)
{
    int ret;

    if (MAIL_INDEX_IS_IN_MEMORY(cache->index))
        return 0;

    if (cache->index->lock_method == MAIL_INDEX_LOCK_DOTLOCK) {
        /* we're using dotlocking, cache file creation itself creates
           the dotlock file we need. */
        return mail_cache_compress_locked(cache, view);
    }

    switch (mail_cache_lock(cache)) {
    case -1:
        return -1;
    case 0:
        /* couldn't lock, either it's broken or doesn't exist.
           just start creating it. */
        return mail_cache_compress_locked(cache, view);
    default:
        /* locking succeeded. */
        ret = mail_cache_compress_locked(cache, view);
        if (mail_cache_unlock(cache) < 0)
            ret = -1;
        return ret;
    }
}

int mail_cache_need_compress(struct mail_cache *cache)
{
    return cache->need_compress;
}