Fix warnings in C-example

[vixentael]

This is not crucial, but I believe that it's better to fix warnings during compiling of C example.

Just follow C-tutorial step-by-step.

My current configuration:

• MacOS 10.12.6,
• clang Apple LLVM version 9.0.0 (clang-900.0.37)

docs/examples/c/mid_hermes/credential_store_service

main.c:69:39: warning: passing 'const uint8_t [17]' to parameter of type 'const char *' converts between pointers to integer types with different sign
      [-Wpointer-sign]
          credential_store_id, strlen(credential_store_id),
                                      ^~~~~~~~~~~~~~~~~~~
/usr/include/string.h:82:28: note: passing argument to parameter '__s' here
size_t   strlen(const char *__s);

docs/examples/c/mid_hermes/data_store_service

main.c:61:35: warning: passing 'const uint8_t [18]' to parameter of type 'const char *' converts between pointers to integer types with different sign
      [-Wpointer-sign]
            data_store_id, strlen(data_store_id), data_store_private_key, sizeof(data_store_private_key),
                                  ^~~~~~~~~~~~~
/usr/include/string.h:82:28: note: passing argument to parameter '__s' here
size_t   strlen(const char *__s);
                            ^
main.c:63:41: warning: passing 'const uint8_t [17]' to parameter of type 'const char *' converts between pointers to integer types with different sign
      [-Wpointer-sign]
            credential_store_id, strlen(credential_store_id), raw_credential_store_transport, false);
                                        ^~~~~~~~~~~~~~~~~~~
/usr/include/string.h:82:28: note: passing argument to parameter '__s' here
size_t   strlen(const char *__s);
                            ^
main.c:80:35: warning: passing 'const uint8_t [18]' to parameter of type 'const char *' converts between pointers to integer types with different sign
      [-Wpointer-sign]
            data_store_id, strlen(data_store_id),data_store_private_key, sizeof(data_store_private_key),
                                  ^~~~~~~~~~~~~
/usr/include/string.h:82:28: note: passing argument to parameter '__s' here
size_t   strlen(const char *__s);

docs/examples/c/mid_hermes/key_store_service

main.c:60:32: warning: passing 'const uint8_t [17]' to parameter of type 'const char *' converts between pointers to integer types with different sign
      [-Wpointer-sign]
          key_store_id, strlen(key_store_id), key_store_private_key, sizeof(key_store_private_key),
                               ^~~~~~~~~~~~
/usr/include/string.h:82:28: note: passing argument to parameter '__s' here
size_t   strlen(const char *__s);
                            ^
main.c:62:39: warning: passing 'const uint8_t [17]' to parameter of type 'const char *' converts between pointers to integer types with different sign
      [-Wpointer-sign]
          credential_store_id, strlen(credential_store_id), raw_credential_store_transport, false);
                                      ^~~~~~~~~~~~~~~~~~~
/usr/include/string.h:82:28: note: passing argument to parameter '__s' here
size_t   strlen(const char *__s);
                            ^
main.c:78:32: warning: passing 'const uint8_t [17]' to parameter of type 'const char *' converts between pointers to integer types with different sign
      [-Wpointer-sign]
          key_store_id, strlen(key_store_id),key_store_private_key, sizeof(key_store_private_key),
                               ^~~~~~~~~~~~
/usr/include/string.h:82:28: note: passing argument to parameter '__s' here
size_t   strlen(const char *__s);

docs/examples/c/mid_hermes/client

hermes_client.c:44:12: warning: duplicate 'const' declaration specifier [-Wduplicate-decl-specifier]
const char const* HELP = "usage: client <command> <user id> <base64 encoded user private key>  <name of file for proceed> <meta> <for user>.\n"
           ^
hermes_client.c:100:25: warning: format string is not a string literal (potentially insecure) [-Wformat-security]
        fprintf(stdout, HELP);
                        ^~~~
hermes_client.c:100:25: note: treat the string as an argument to avoid this
        fprintf(stdout, HELP);
                        ^
                        "%s", 
hermes_client.c:124:41: warning: passing 'const uint8_t [17]' to parameter of type 'const char *' converts between pointers to integer types with different
      sign [-Wpointer-sign]
            credential_store_id, strlen(credential_store_id), container.raw_credential_store_transport, false);
                                        ^~~~~~~~~~~~~~~~~~~
/usr/include/string.h:82:28: note: passing argument to parameter '__s' here
size_t   strlen(const char *__s);
                            ^
hermes_client.c:123:13: warning: passing 'char *' to parameter of type 'const uint8_t *' (aka 'const unsigned char *') converts between pointers to integer
      types with different sign [-Wpointer-sign]
            argv[2], strlen(argv[2]), sk, sk_length, credential_store_pk, sizeof(credential_store_pk),
            ^~~~~~~
../../../../../include/hermes/secure_transport/transport.h:32:24: note: passing argument to parameter 'user_id' here
        const uint8_t *user_id, size_t user_id_length,
                       ^
hermes_client.c:139:34: warning: passing 'const uint8_t [17]' to parameter of type 'const char *' converts between pointers to integer types with different
      sign [-Wpointer-sign]
            key_store_id, strlen(key_store_id), container.raw_key_store_transport, false);
                                 ^~~~~~~~~~~~
/usr/include/string.h:82:28: note: passing argument to parameter '__s' here
size_t   strlen(const char *__s);
                            ^
hermes_client.c:138:13: warning: passing 'char *' to parameter of type 'const uint8_t *' (aka 'const unsigned char *') converts between pointers to integer
      types with different sign [-Wpointer-sign]
            argv[2], strlen(argv[2]), sk, sk_length, key_store_pk, sizeof(key_store_pk),
            ^~~~~~~
../../../../../include/hermes/secure_transport/transport.h:32:24: note: passing argument to parameter 'user_id' here
        const uint8_t *user_id, size_t user_id_length,
                       ^
hermes_client.c:154:35: warning: passing 'const uint8_t [18]' to parameter of type 'const char *' converts between pointers to integer types with different
      sign [-Wpointer-sign]
            data_store_id, strlen(data_store_id), container.raw_data_store_transport, false);
                                  ^~~~~~~~~~~~~
/usr/include/string.h:82:28: note: passing argument to parameter '__s' here
size_t   strlen(const char *__s);
                            ^
hermes_client.c:153:13: warning: passing 'char *' to parameter of type 'const uint8_t *' (aka 'const unsigned char *') converts between pointers to integer
      types with different sign [-Wpointer-sign]
            argv[2], strlen(argv[2]), sk, sk_length, data_store_pk, sizeof(data_store_pk),
            ^~~~~~~
../../../../../include/hermes/secure_transport/transport.h:32:24: note: passing argument to parameter 'user_id' here
        const uint8_t *user_id, size_t user_id_length,
                       ^
hermes_client.c:161:13: warning: passing 'char *' to parameter of type 'const uint8_t *' (aka 'const unsigned char *') converts between pointers to integer
      types with different sign [-Wpointer-sign]
            argv[2], strlen(argv[2]), sk, sk_length, container.key_store_transport, container.data_store_transport,
            ^~~~~~~
../../../../../include/hermes/mid_hermes/mid_hermes.h:35:24: note: passing argument to parameter 'user_id' here
        const uint8_t *user_id, const size_t user_id_length,
                       ^
hermes_client.c:175:93: warning: passing 'char *' to parameter of type 'const uint8_t *' (aka 'const unsigned char *') converts between pointers to integer
      types with different sign [-Wpointer-sign]
            || (0 != mid_hermes_create_block(mh, &idBuffer, &idLength, block, block_length, argv[5], strlen(argv[5])))) {
                                                                                            ^~~~~~~
../../../../../include/hermes/mid_hermes/mid_hermes.h:47:24: note: passing argument to parameter 'meta' here
        const uint8_t *meta, const size_t meta_length);
                       ^
hermes_client.c:191:44: warning: passing 'char *' to parameter of type 'const uint8_t *' (aka 'const unsigned char *') converts between pointers to integer
      types with different sign [-Wpointer-sign]
            0 != mid_hermes_read_block(mh, argv[4], strlen(argv[4]), &data, &data_length, &meta, &meta_length)) {
                                           ^~~~~~~
../../../../../include/hermes/mid_hermes/mid_hermes.h:51:24: note: passing argument to parameter 'block_id' here
        const uint8_t *block_id, const size_t block_id_length,
                       ^
hermes_client.c:205:49: warning: passing 'char *' to parameter of type 'const uint8_t *' (aka 'const unsigned char *') converts between pointers to integer
      types with different sign [-Wpointer-sign]
            || 0 != mid_hermes_delete_block(mh, argv[4], strlen(argv[4]))) {
                                                ^~~~~~~
../../../../../include/hermes/mid_hermes/mid_hermes.h:62:50: note: passing argument to parameter 'block_id' here
        mid_hermes_t *mid_hermes, const uint8_t *block_id, const size_t block_id_length);
                                                 ^
hermes_client.c:215:50: warning: passing 'char *' to parameter of type 'const uint8_t *' (aka 'const unsigned char *') converts between pointers to integer
      types with different sign [-Wpointer-sign]
            || (0 != mid_hermes_update_block(mh, argv[4], strlen(argv[4]), block, block_length, argv[5], strlen(argv[5])))) {
                                                 ^~~~~~~
../../../../../include/hermes/mid_hermes/mid_hermes.h:57:24: note: passing argument to parameter 'block_id' here
        const uint8_t *block_id, const size_t block_id_length,
                       ^
hermes_client.c:215:97: warning: passing 'char *' to parameter of type 'const uint8_t *' (aka 'const unsigned char *') converts between pointers to integer
      types with different sign [-Wpointer-sign]
            || (0 != mid_hermes_update_block(mh, argv[4], strlen(argv[4]), block, block_length, argv[5], strlen(argv[5])))) {
                                                                                                ^~~~~~~
../../../../../include/hermes/mid_hermes/mid_hermes.h:59:24: note: passing argument to parameter 'meta' here
        const uint8_t *meta, const size_t meta_length);
                       ^
hermes_client.c:224:54: warning: passing 'char *' to parameter of type 'const uint8_t *' (aka 'const unsigned char *') converts between pointers to integer
      types with different sign [-Wpointer-sign]
            || 0 != mid_hermes_grant_read_access(mh, argv[4], strlen(argv[4]), argv[5], strlen(argv[5]))) {
                                                     ^~~~~~~
../../../../../include/hermes/mid_hermes/mid_hermes.h:69:24: note: passing argument to parameter 'block_id' here
        const uint8_t *block_id, const size_t bloc_id_length,
                       ^
hermes_client.c:224:80: warning: passing 'char *' to parameter of type 'const uint8_t *' (aka 'const unsigned char *') converts between pointers to integer
      types with different sign [-Wpointer-sign]
            || 0 != mid_hermes_grant_read_access(mh, argv[4], strlen(argv[4]), argv[5], strlen(argv[5]))) {
                                                                               ^~~~~~~
../../../../../include/hermes/mid_hermes/mid_hermes.h:70:24: note: passing argument to parameter 'user_id' here
        const uint8_t *user_id, const size_t user_id_length);
                       ^
hermes_client.c:231:56: warning: passing 'char *' to parameter of type 'const uint8_t *' (aka 'const unsigned char *') converts between pointers to integer
      types with different sign [-Wpointer-sign]
            || 0 != mid_hermes_grant_update_access(mh, argv[4], strlen(argv[4]), argv[5], strlen(argv[5]))) {
                                                       ^~~~~~~
../../../../../include/hermes/mid_hermes/mid_hermes.h:74:24: note: passing argument to parameter 'block_id' here
        const uint8_t *block_id, const size_t bloc_id_length,
                       ^
hermes_client.c:231:82: warning: passing 'char *' to parameter of type 'const uint8_t *' (aka 'const unsigned char *') converts between pointers to integer
      types with different sign [-Wpointer-sign]
            || 0 != mid_hermes_grant_update_access(mh, argv[4], strlen(argv[4]), argv[5], strlen(argv[5]))) {
                                                                                 ^~~~~~~
../../../../../include/hermes/mid_hermes/mid_hermes.h:75:24: note: passing argument to parameter 'user_id' here
        const uint8_t *user_id, const size_t user_id_length);
                       ^
hermes_client.c:238:53: warning: passing 'char *' to parameter of type 'const uint8_t *' (aka 'const unsigned char *') converts between pointers to integer
      types with different sign [-Wpointer-sign]
            || 0 != mid_hermes_deny_read_access(mh, argv[4], strlen(argv[4]), argv[5], strlen(argv[5]))) {
                                                    ^~~~~~~
../../../../../include/hermes/mid_hermes/mid_hermes.h:79:24: note: passing argument to parameter 'block_id' here
        const uint8_t *block_id, const size_t bloc_id_length,
                       ^
hermes_client.c:238:79: warning: passing 'char *' to parameter of type 'const uint8_t *' (aka 'const unsigned char *') converts between pointers to integer
      types with different sign [-Wpointer-sign]
            || 0 != mid_hermes_deny_read_access(mh, argv[4], strlen(argv[4]), argv[5], strlen(argv[5]))) {
                                                                              ^~~~~~~
../../../../../include/hermes/mid_hermes/mid_hermes.h:80:24: note: passing argument to parameter 'user_id' here
        const uint8_t *user_id, const size_t user_id_length);
                       ^
hermes_client.c:245:55: warning: passing 'char *' to parameter of type 'const uint8_t *' (aka 'const unsigned char *') converts between pointers to integer
      types with different sign [-Wpointer-sign]
            || 0 != mid_hermes_deny_update_access(mh, argv[4], strlen(argv[4]), argv[5], strlen(argv[5]))) {
                                                      ^~~~~~~
../../../../../include/hermes/mid_hermes/mid_hermes.h:84:24: note: passing argument to parameter 'block_id' here
        const uint8_t *block_id, const size_t bloc_id_length,
                       ^
hermes_client.c:245:81: warning: passing 'char *' to parameter of type 'const uint8_t *' (aka 'const unsigned char *') converts between pointers to integer
      types with different sign [-Wpointer-sign]
            || 0 != mid_hermes_deny_update_access(mh, argv[4], strlen(argv[4]), argv[5], strlen(argv[5]))) {
                                                                                ^~~~~~~
../../../../../include/hermes/mid_hermes/mid_hermes.h:85:24: note: passing argument to parameter 'user_id' here
        const uint8_t *user_id, const size_t user_id_length);
                       ^
hermes_client.c:253:49: warning: passing 'char *' to parameter of type 'const uint8_t *' (aka 'const unsigned char *') converts between pointers to integer
      types with different sign [-Wpointer-sign]
            || 0 != mid_hermes_rotate_block(mh, argv[4], strlen(argv[4]))) {
                                                ^~~~~~~
../../../../../include/hermes/mid_hermes/mid_hermes.h:65:50: note: passing argument to parameter 'block_id' here
        mid_hermes_t *mid_hermes, const uint8_t *block_id, const size_t block_id_length);

[Lagovas]

fixed by #100