Function rewriteConfigReadOldFile

app/redis-6.2.6/src/config.c:1134–1210

Read the old file, split it into lines to populate a newly created * config rewrite state, and return it to the caller. * * If it is impossible to read the old file, NULL is returned. * If the old file does not exist at all, an empty state is returned. */

 * If it is impossible to read the old file, NULL is returned.
 * If the old file does not exist at all, an empty state is returned. */
struct rewriteConfigState *rewriteConfigReadOldFile(char *path) {
    FILE *fp = fopen(path,"r");
    if (fp == NULL && errno != ENOENT) return NULL;

    char buf[CONFIG_MAX_LINE+1];
    int linenum = -1;
    struct rewriteConfigState *state = zmalloc(sizeof(*state));
    state->option_to_line = dictCreate(&optionToLineDictType,NULL);
    state->rewritten = dictCreate(&optionSetDictType,NULL);
    state->numlines = 0;
    state->lines = NULL;
    state->has_tail = 0;
    state->force_all = 0;
    if (fp == NULL) return state;

    /* Read the old file line by line, populate the state. */
    while(fgets(buf,CONFIG_MAX_LINE+1,fp) != NULL) {
        int argc;
        sds *argv;
        sds line = sdstrim(sdsnew(buf),"\r\n\t ");

        linenum++; /* Zero based, so we init at -1 */

        /* Handle comments and empty lines. */
        if (line[0] == '#' || line[0] == '\0') {
            if (!state->has_tail && !strcmp(line,REDIS_CONFIG_REWRITE_SIGNATURE))
                state->has_tail = 1;
            rewriteConfigAppendLine(state,line);
            continue;
        }

        /* Not a comment, split into arguments. */
        argv = sdssplitargs(line,&argc);
        if (argv == NULL) {
            /* Apparently the line is unparsable for some reason, for
             * instance it may have unbalanced quotes. Load it as a
             * comment. */
            sds aux = sdsnew("# ??? ");
            aux = sdscatsds(aux,line);
            sdsfree(line);
            rewriteConfigAppendLine(state,aux);
            continue;
        }

        sdstolower(argv[0]); /* We only want lowercase config directives. */

        /* Now we populate the state according to the content of this line.
         * Append the line and populate the option -> line numbers map. */
        rewriteConfigAppendLine(state,line);

        /* Translate options using the word "slave" to the corresponding name
         * "replica", before adding such option to the config name -> lines
         * mapping. */
        char *p = strstr(argv[0],"slave");
        if (p) {
            sds alt = sdsempty();
            alt = sdscatlen(alt,argv[0],p-argv[0]);
            alt = sdscatlen(alt,"replica",7);