Lowercase for chitin.key

#include <stdio.h>
#include <stdlib.h>
#include <inttypes.h>
#include <errno.h>
#include <string.h>
#include <sys/stat.h>
#include <ctype.h>

struct key_header {
    uint8_t sig[4];        /* 0x00: "KEY " */
    uint8_t ver[4];        /* 0x04: "V1  " */
    uint32_t bifcnt;       /* 0x08: Count of BIF entries */
    uint32_t rescnt;       /* 0x0c: Count of resource entries */
    uint32_t bifoff;       /* 0x10: Offest to BIF entries */
    uint32_t resoff;       /* 0x14: Offest to resource entries */
} __attribute__((packed));

struct bif_header {
    uint32_t biflen;       /* 0x00: Length of BIF file */
    uint32_t fileoff;      /* 0x04: Offset to ASCIIZ BIF filename */
    uint16_t filelen;      /* 0x08: Length of ASCIIZ BIF filename */
    uint16_t location;     /* 0x0a: Location of the file */
} __attribute__((packed));

struct res_header {
    uint8_t resname[8];    /* 0x00: Resource name */
    uint16_t restype;      /* 0x08: Resource type */
    uint32_t locator;      /* 0x0a: Resource locator */
} __attribute__((packed));

struct chitin {
    struct key_header header;
    struct bif_header *bif;
    struct res_header *res;
    char *name;
    size_t size;
};


struct chitin *init_chitin(void)
{

    struct chitin *chitin;

    chitin = calloc(1, sizeof *chitin);
    if (chitin == NULL) {
        errno = -ENOMEM;
        return NULL;
    }

    chitin->bif = NULL;
    chitin->res = NULL;
    chitin->name = NULL;

    return chitin;
}

void free_chitin(struct chitin *chitin)
{
    free(chitin->name);
    free(chitin->bif);
    free(chitin->res);
    free(chitin);
}

int read_key(const char *filename, struct chitin *chitin)
{
    FILE *f;
    struct stat st;
    int r;
    int i, j;
    int len;
    int off;
    char buf[512];

    errno = 0;

    if ((filename == NULL) || (chitin == NULL)) {
        errno = -EFAULT;
        goto out;
    }
    f = fopen(filename, "r+b");
    if (f == NULL) {
        errno = -ENOENT;
        goto out;
    }
    r = fstat(fileno(f), &st);
    if (r < 0) {
        errno = -ENOENT;
        goto fc;
    }

    r = fread(&chitin->header, sizeof chitin->header, 1, f);
    if (r < 1) {
        errno = -ENODATA;
        goto fc;
    }

    r = memcmp(chitin->header.sig, "KEY ", 4);
    if (r != 0) {
        errno = -EINVAL;
        goto fc;
    }
    r = memcmp(chitin->header.ver, "V1  ", 4);
    if (r != 0) {
        errno = -EINVAL;
        goto fc;
    }

    chitin->bif = calloc(chitin->header.bifcnt, sizeof *chitin->bif);
    if (chitin->bif == NULL) {
        errno = -ENOMEM;
        goto fc;
    }
    fseek(f, chitin->header.bifoff, SEEK_SET);
    r = fread(chitin->bif, sizeof *chitin->bif, chitin->header.bifcnt, f);
    if (r < chitin->header.bifcnt) {
        errno = -ENODATA;
        goto fc;
    }

    for (i = 0; i < chitin->header.bifcnt; i++) {
        off = chitin->bif[i].fileoff;
        len = chitin->bif[i].filelen;
        fseek(f, off, SEEK_SET);
        fread(buf, 1, len, f);
        for (j = 0; j < len - 1; j++) {
            if isupper(buf[j]) {
                buf[j] = tolower(buf[j]);
            }
        }
        fseek(f, off, SEEK_SET);
        fwrite(buf, 1, len, f);
    }

    fseek(f, chitin->header.resoff, SEEK_SET);
    chitin->res = calloc(chitin->header.rescnt, sizeof *chitin->res);
    if (chitin->res == NULL) {
        errno = -ENOMEM;
        goto fc;
    }
    r = fread(chitin->res, sizeof *chitin->res, chitin->header.rescnt, f);
    if (r < chitin->header.rescnt) {
        errno = -ENODATA;
        goto fc;
    }

    for (i = 0; i < chitin->header.rescnt; i++) {
        for (j = 0; j < 8; j++) {
            if (isupper(chitin->res[i].resname[j])) {
                chitin->res[i].resname[j] = tolower(chitin->res[i].resname[j]);
            }
        }
    }
    fseek(f, chitin->header.resoff, SEEK_SET);
    r = fwrite(chitin->res, sizeof *chitin->res, chitin->header.rescnt, f);

    chitin->name = strdup(filename);

fc:
    fclose(f);
out:
    return errno;
}

int main(int argc, char *argv[])
{
    int i, j;
    int r;
    struct chitin *chitin;

    if (argc != 2)
        return -1;

    chitin = init_chitin();

    read_key(argv[1], chitin);

    if (chitin) {
        printf("Processing chitin %s - %s\n", argv[1], chitin->name);
        printf("Found %d BIF entries\n", chitin->header.bifcnt);
        printf("Found %d resource entries\n", chitin->header.rescnt);
    }

    free_chitin(chitin);

    return 0;
}