/* $OpenBSD: filter.c,v 1.10 2024/11/09 18:03:44 op Exp $ */

/* filter - postprocessing of flex output through filters */

/*  This file is part of flex. */

/*  Redistribution and use in source and binary forms, with or without */
/*  modification, are permitted provided that the following conditions */
/*  are met: */

/*  1. Redistributions of source code must retain the above copyright */
/*     notice, this list of conditions and the following disclaimer. */
/*  2. Redistributions in binary form must reproduce the above copyright */
/*     notice, this list of conditions and the following disclaimer in the */
/*     documentation and/or other materials provided with the distribution. */

/*  Neither the name of the University nor the names of its contributors */
/*  may be used to endorse or promote products derived from this software */
/*  without specific prior written permission. */

/*  THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR */
/*  IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED */
/*  WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR */
/*  PURPOSE. */

#include "flexdef.h"
static const char *check_4_gnu_m4 =
"m4_dnl ifdef(`__gnu__', ,"
"`errprint(Flex requires GNU M4. Set the PATH or set the M4 environment variable to its path name.)"
" m4exit(2)')\n";


/** global chain. */
struct filter *output_chain = NULL;

/* Allocate and initialize an external filter.
 * @param chain the current chain or NULL for new chain
 * @param cmd the command to execute.
 * @param ... a NULL terminated list of (const char*) arguments to command,
 *            not including argv[0].
 * @return newest filter in chain
 */
struct filter *
filter_create_ext(struct filter * chain, const char *cmd,
    ...)
{
        struct filter *f;
        int max_args;
        const char *s;
        va_list ap;

        /* allocate and initialize new filter */
        f = calloc(sizeof(struct filter), 1);
        if (!f)
                flexerror(_("calloc failed (f) in filter_create_ext"));
        f->filter_func = NULL;
        f->extra = NULL;
        f->next = NULL;
        f->argc = 0;

        if (chain != NULL) {
                /* append f to end of chain */
                while (chain->next)
                        chain = chain->next;
                chain->next = f;
        }
        /* allocate argv, and populate it with the argument list. */
        max_args = 8;
        f->argv = malloc(sizeof(char *) * (max_args + 1));
        if (!f->argv)
                flexerror(_("malloc failed (f->argv) in filter_create_ext"));
        f->argv[f->argc++] = cmd;

        va_start(ap, cmd);
        while ((s = va_arg(ap, const char *)) != NULL) {
                if (f->argc >= max_args) {
                        max_args += 8;
                        f->argv = realloc(f->argv,
                            sizeof(char *) * (max_args + 1));
                }
                f->argv[f->argc++] = s;
        }
        f->argv[f->argc] = NULL;

        va_end(ap);
        return f;
}

/* Allocate and initialize an internal filter.
 * @param chain the current chain or NULL for new chain
 * @param filter_func The function that will perform the filtering.
 *        filter_func should return 0 if successful, and -1
 *        if an error occurs -- or it can simply exit().
 * @param extra optional user-defined data to pass to the filter.
 * @return newest filter in chain
 */
struct filter *
filter_create_int(struct filter * chain,
    int (*filter_func) (struct filter *),
    void *extra)
{
        struct filter *f;

        /* allocate and initialize new filter */
        f = calloc(sizeof(struct filter), 1);
        if (!f)
                flexerror(_("calloc failed in filter_create_int"));
        f->next = NULL;
        f->argc = 0;
        f->argv = NULL;

        f->filter_func = filter_func;
        f->extra = extra;

        if (chain != NULL) {
                /* append f to end of chain */
                while (chain->next)
                        chain = chain->next;
                chain->next = f;
        }
        return f;
}

/** Fork and exec entire filter chain.
 *  @param chain The head of the chain.
 *  @return true on success.
 */
bool 
filter_apply_chain(struct filter * chain)
{
        int pid, pipes[2];

        /*
         * Tricky recursion, since we want to begin the chain at the END.
         * Why? Because we need all the forked processes to be children of
         * the main flex process.
         */
        if (chain)
                filter_apply_chain(chain->next);
        else
                return true;

        /*
         * Now we are the right-most unprocessed link in the chain.
         */

        fflush(stdout);
        fflush(stderr);


        if (pipe(pipes) == -1)
                flexerror(_("pipe failed"));

        if ((pid = fork()) == -1)
                flexerror(_("fork failed"));

        if (pid == 0) {
                /* child */

                /*
                 * We need stdin (the FILE* stdin) to connect to this new
                 * pipe. There is no portable way to set stdin to a new file
                 * descriptor, as stdin is not an lvalue on some systems
                 * (BSD). So we dup the new pipe onto the stdin descriptor
                 * and use a no-op fseek to sync the stream. This is a Hail
                 * Mary situation. It seems to work.
                 */
                close(pipes[1]);
                clearerr(stdin);
                if (dup2(pipes[0], fileno(stdin)) == -1)
                        flexfatal(_("dup2(pipes[0],0)"));
                close(pipes[0]);
                fseek(stdin, 0, SEEK_CUR);

                /* run as a filter, either internally or by exec */
                if (chain->filter_func) {
                        if (chain->filter_func(chain) == -1)
                                flexfatal(_("filter_func failed"));
                        exit(0);
                } else {
                        execvp(chain->argv[0],
                            (char **const) (chain->argv));
                        lerrsf_fatal(_("exec of %s failed"),
                            chain->argv[0]);
                }

                exit(1);
        }
        /* Parent */
        close(pipes[0]);
        if (dup2(pipes[1], fileno(stdout)) == -1)
                flexfatal(_("dup2(pipes[1],1)"));
        close(pipes[1]);
        fseek(stdout, 0, SEEK_CUR);

        return true;
}

/** Truncate the chain to max_len number of filters.
 * @param chain the current chain.
 * @param max_len the maximum length of the chain.
 * @return the resulting length of the chain.
 */
int 
filter_truncate(struct filter * chain, int max_len)
{
        int len = 1;

        if (!chain)
                return 0;

        while (chain->next && len < max_len) {
                chain = chain->next;
                ++len;
        }

        chain->next = NULL;
        return len;
}

/** Splits the chain in order to write to a header file.
 *  Similar in spirit to the 'tee' program.
 *  The header file name is in extra.
 *  @return 0 (zero) on success, and -1 on failure.
 */
int 
filter_tee_header(struct filter * chain)
{
        /*
         * This function reads from stdin and writes to both the C file and
         * the header file at the same time.
         */

        const int readsz = 512;
        char *buf;
        int to_cfd = -1;
        FILE *to_c = NULL, *to_h = NULL;
        bool write_header;

        write_header = (chain->extra != NULL);

        /*
         * Store a copy of the stdout pipe, which is already piped to C file
         * through the running chain. Then create a new pipe to the H file as
         * stdout, and fork the rest of the chain again.
         */

        if ((to_cfd = dup(1)) == -1)
                flexfatal(_("dup(1) failed"));
        to_c = fdopen(to_cfd, "w");

        if (write_header) {
                if (freopen((char *) chain->extra, "w", stdout) == NULL)
                        flexfatal(_("freopen(headerfilename) failed"));

                filter_apply_chain(chain->next);
                to_h = stdout;
        }
        /*
         * Now to_c is a pipe to the C branch, and to_h is a pipe to the H
         * branch.
         */

        if (write_header) {
                fputs(check_4_gnu_m4, to_h);
                fputs("m4_changecom`'m4_dnl\n", to_h);
                fputs("m4_changequote`'m4_dnl\n", to_h);
                fputs("m4_changequote([[,]])[[]]m4_dnl\n", to_h);
                fputs("m4_define([[M4_YY_NOOP]])[[]]m4_dnl\n", to_h);
                fputs("m4_define( [[M4_YY_IN_HEADER]],[[]])m4_dnl\n",
                    to_h);
                fprintf(to_h, "#ifndef %sHEADER_H\n", prefix);
                fprintf(to_h, "#define %sHEADER_H 1\n", prefix);
                fprintf(to_h, "#define %sIN_HEADER 1\n\n", prefix);
                fprintf(to_h,
                    "m4_define( [[M4_YY_OUTFILE_NAME]],[[%s]])m4_dnl\n",
                    headerfilename ? headerfilename : "<stdout>");

        }
        fputs(check_4_gnu_m4, to_c);
        fputs("m4_changecom`'m4_dnl\n", to_c);
        fputs("m4_changequote`'m4_dnl\n", to_c);
        fputs("m4_changequote([[,]])[[]]m4_dnl\n", to_c);
        fputs("m4_define([[M4_YY_NOOP]])[[]]m4_dnl\n", to_c);
        fprintf(to_c, "m4_define( [[M4_YY_OUTFILE_NAME]],[[%s]])m4_dnl\n",
            outfilename ? outfilename : "<stdout>");

        buf = malloc(readsz);
        if (!buf)
                flexerror(_("malloc failed in filter_tee_header"));
        while (fgets(buf, readsz, stdin)) {
                fputs(buf, to_c);
                if (write_header)
                        fputs(buf, to_h);
        }

        if (write_header) {
                fprintf(to_h, "\n");

                /*
                 * write a fake line number. It will get fixed by the linedir
                 * filter.
                 */
                fprintf(to_h, "#line 4000 \"M4_YY_OUTFILE_NAME\"\n");

                fprintf(to_h, "#undef %sIN_HEADER\n", prefix);
                fprintf(to_h, "#endif /* %sHEADER_H */\n", prefix);
                fputs("m4_undefine( [[M4_YY_IN_HEADER]])m4_dnl\n", to_h);

                fflush(to_h);
                if (ferror(to_h))
                        lerrsf(_("error writing output file %s"),
                            (char *) chain->extra);

                else if (fclose(to_h))
                        lerrsf(_("error closing output file %s"),
                            (char *) chain->extra);
        }
        fflush(to_c);
        if (ferror(to_c))
                lerrsf(_("error writing output file %s"),
                    outfilename ? outfilename : "<stdout>");

        else if (fclose(to_c))
                lerrsf(_("error closing output file %s"),
                    outfilename ? outfilename : "<stdout>");

        while (wait(0) > 0);

        exit(0);
        return 0;
}

/** Adjust the line numbers in the #line directives of the generated scanner.
 * After the m4 expansion, the line numbers are incorrect since the m4 macros
 * can add or remove lines.  This only adjusts line numbers for generated code,
 * not user code. This also happens to be a good place to squeeze multiple
 * blank lines into a single blank line.
 */
int 
filter_fix_linedirs(struct filter * chain)
{
        char *buf;
        const int readsz = 512;
        int lineno = 1;
        bool in_gen = true;     /* in generated code */
        bool last_was_blank = false;

        if (!chain)
                return 0;

        buf = malloc(readsz);
        if (!buf)
                flexerror(_("malloc failed in filter_fix_linedirs"));

        while (fgets(buf, readsz, stdin)) {

                regmatch_t m[10];

                /* Check for #line directive. */
                if (buf[0] == '#'
                    && regexec(&regex_linedir, buf, 3, m, 0) == 0) {

                        char *fname;

                        /* extract the line number and filename */
                        regmatch_strtol(&m[1], buf, NULL, 0);
                        fname = regmatch_dup(&m[2], buf);

                        if (strcmp(fname,
                                outfilename ? outfilename : "<stdout>") == 0 ||
                            strcmp(fname, headerfilename ? headerfilename :
                                "<stdout>") == 0) {

                                char *s1, *s2;
                                char filename[MAXLINE];

                                s1 = fname;
                                s2 = filename;

                                while ((s2 - filename) < (MAXLINE - 1) && *s1) {
                                        /* Escape the backslash */
                                        if (*s1 == '\\')
                                                *s2++ = '\\';
                                        /* Escape the double quote */
                                        if (*s1 == '\"')
                                                *s2++ = '\\';
                                        /* Copy the character as usual */
                                        *s2++ = *s1++;
                                }

                                *s2 = '\0';

                                /* Adjust the line directives. */
                                in_gen = true;
                                snprintf(buf, readsz, "#line %d \"%s\"\n",
                                    lineno + 1, filename);
                        } else {
                                /*
                                 * it's a #line directive for code we didn't
                                 * write
                                 */
                                in_gen = false;
                        }

                        free(fname);
                        last_was_blank = false;
                }
                /* squeeze blank lines from generated code */
                else if (in_gen &&
                    regexec(&regex_blank_line, buf, 0, NULL, 0) == 0) {
                        if (last_was_blank)
                                continue;
                        else
                                last_was_blank = true;
                } else {
                        /* it's a line of normal, non-empty code. */
                        last_was_blank = false;
                }

                fputs(buf, stdout);
                lineno++;
        }
        fflush(stdout);
        if (ferror(stdout))
                lerrsf(_("error writing output file %s"),
                    outfilename ? outfilename : "<stdout>");

        else if (fclose(stdout))
                lerrsf(_("error closing output file %s"),
                    outfilename ? outfilename : "<stdout>");

        return 0;
}