io.c

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/*
  This file is part of ethash.

  ethash is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

  ethash is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with ethash.  If not, see <http://www.gnu.org/licenses/>.
*/
#include "io.h"
#include <string.h>
#include <stdio.h>
#include <errno.h>

enum ethash_io_rc ethash_io_prepare(
        char const* dirname,
        ethash_h256_t const seedhash,
        FILE** output_file,
        uint64_t file_size,
        bool force_create
)
{
        char mutable_name[DAG_MUTABLE_NAME_MAX_SIZE];
        enum ethash_io_rc ret = ETHASH_IO_FAIL;
        // reset errno before io calls
        errno = 0;

        // assert directory exists
        if (!ethash_mkdir(dirname)) {
                ETHASH_CRITICAL("Could not create the ethash directory");
                goto end;
        }

        ethash_io_mutable_name(ETHASH_REVISION, &seedhash, mutable_name);
        char* tmpfile = ethash_io_create_filename(dirname, mutable_name, strlen(mutable_name));
        if (!tmpfile) {
                ETHASH_CRITICAL("Could not create the full DAG pathname");
                goto end;
        }

        FILE *f;
        if (!force_create) {
                // try to open the file
                f = ethash_fopen(tmpfile, "rb+");
                if (f) {
                        size_t found_size;
                        if (!ethash_file_size(f, &found_size)) {
                                fclose(f);
                                ETHASH_CRITICAL("Could not query size of DAG file: \"%s\"", tmpfile);
                                goto free_memo;
                        }
                        if (file_size != found_size - ETHASH_DAG_MAGIC_NUM_SIZE) {
                                fclose(f);
                                ret = ETHASH_IO_MEMO_SIZE_MISMATCH;
                                goto free_memo;
                        }
                        // compare the magic number, no need to care about endianess since it's local
                        uint64_t magic_num;
                        if (fread(&magic_num, ETHASH_DAG_MAGIC_NUM_SIZE, 1, f) != 1) {
                                // I/O error
                                fclose(f);
                                ETHASH_CRITICAL("Could not read from DAG file: \"%s\"", tmpfile);
                                ret = ETHASH_IO_MEMO_SIZE_MISMATCH;
                                goto free_memo;
                        }
                        if (magic_num != ETHASH_DAG_MAGIC_NUM) {
                                fclose(f);
                                ret = ETHASH_IO_MEMO_SIZE_MISMATCH;
                                goto free_memo;
                        }
                        ret = ETHASH_IO_MEMO_MATCH;
                        goto set_file;
                }
        }
        
        // file does not exist, will need to be created
        f = ethash_fopen(tmpfile, "wb+");
        if (!f) {
                ETHASH_CRITICAL("Could not create DAG file: \"%s\"", tmpfile);
                goto free_memo;
        }
        // make sure it's of the proper size
        if (fseek(f, (long int)(file_size + ETHASH_DAG_MAGIC_NUM_SIZE - 1), SEEK_SET) != 0) {
                fclose(f);
                ETHASH_CRITICAL("Could not seek to the end of DAG file: \"%s\". Insufficient space?", tmpfile);
                goto free_memo;
        }
        if (fputc('\n', f) == EOF) {
                fclose(f);
                ETHASH_CRITICAL("Could not write in the end of DAG file: \"%s\". Insufficient space?", tmpfile);
                goto free_memo;
        }
        if (fflush(f) != 0) {
                fclose(f);
                ETHASH_CRITICAL("Could not flush at end of DAG file: \"%s\". Insufficient space?", tmpfile);
                goto free_memo;
        }
        ret = ETHASH_IO_MEMO_MISMATCH;
        goto set_file;

        ret = ETHASH_IO_MEMO_MATCH;
set_file:
        *output_file = f;
free_memo:
        free(tmpfile);
end:
        return ret;
}