Nettle's sha256 usage example

sha256-test.c

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

#include "rsa.h"

static uint8_t * hash_sha_256 (const struct nettle_hash *hash, const char *s,
    const size_t len) {
  void *ctx = malloc (hash->context_size);
  uint8_t *digest = malloc (hash->digest_size);
  hash->init (ctx);
  hash->update (ctx, len, (const uint8_t *) s);
  hash->digest (ctx, hash->digest_size, digest);
  free (ctx);

  return digest;
}

int main (int argc, char **argv) {
  char* input = "abc";
  struct stat st;
  st.st_size = strlen(input);

  if (argc > 1) {
    // get file as an argument
    char *filename = argv[1];
    FILE *file = fopen(filename, "r");
    if (file == NULL) {
      fprintf(stderr, "Error opening %s. %s\n", argv[1],
      strerror(errno));
      return errno;
    }

    // Get file size
    if (stat(argv[1], &st) != 0) {
      fprintf(stderr, "Cannot determine size of %s: %s\n", argv[1],
      strerror(errno));
      fclose(file);
      return errno;
    }

    input = (char *) calloc(st.st_size, sizeof(unsigned char));
    if (input == NULL) {
      fprintf(stderr, "%s\n.", strerror(errno));
      return errno;
    }

    if (fread(input, sizeof(char), st.st_size, file) != (size_t)st.st_size) {
      fprintf(stderr, "Read error on file %s. %s\n", argv[1],
          strerror(errno));
      fclose(file);
      return errno;
    }
    fclose(file);
  }

  uint8_t* hash = hash_sha_256 (&nettle_sha256, input, st.st_size);
  for (size_t i=0; i < nettle_sha256.digest_size; i++)
    printf("%02x", hash[i]);

  printf("\n");

  return EXIT_SUCCESS;
}