Idea: extract libssh2_knownhost_frommemory from libssh2_knownhost_readfile

[paxan]

Currently the only way to read a set of known host keys is to read it from a file using libssh2_knownhost_readfile.
But what if the set of known host keys is already in memory (e.g. our database of known host keys in our application returns it as string that looks like typical contents of ~/.ssh/known_hosts)?

We could remix libssh2_knownhost_readstream from libssh2_knownhost_readfile like this:

LIBSSH2_API int
libssh2_knownhost_readstream(LIBSSH2_KNOWNHOSTS *hosts,
                             FILE *file, int type)
{
    int num = 0;
    char buf[4092];

    if(type != LIBSSH2_KNOWNHOST_FILE_OPENSSH)
        return _libssh2_error(hosts->session,
                              LIBSSH2_ERROR_METHOD_NOT_SUPPORTED,
                              "Unsupported type of known-host information store");

    while(fgets(buf, sizeof(buf), file)) {
        if(libssh2_knownhost_readline(hosts, buf, strlen(buf), type)) {
            num = _libssh2_error(hosts->session, LIBSSH2_ERROR_KNOWN_HOSTS,
                                    "Failed to parse known hosts file");
            break;
        }
        num++;
    }

    return num;
}

If libssh2_knownhost_readstream existed, then libssh2_knownhost_readfile can be implemented in terms of it.
And any application that has known hosts in memory, could use fmemopen and then call libssh2_knownhost_readstream.

Thoughts?

[vszakats]

Passing FILE * through an API boundary is generally frowned upon in certain envs (Windows). Using a string would avoid these issues. We have APIs doing that, ending with _frommemory.

[paxan]

@vszakats so maybe something like this instead?

LIBSSH2_API int
libssh2_knownhost_frommemory(LIBSSH2_KNOWNHOSTS *hosts,
                             const char *knownhostsdata,
                             size_t knownhostsdata_len,
                             int type)
{
    FILE *file;
    int num = 0;
    char buf[4092];

    if(type != LIBSSH2_KNOWNHOST_FILE_OPENSSH)
        return _libssh2_error(hosts->session,
                              LIBSSH2_ERROR_METHOD_NOT_SUPPORTED,
                              "Unsupported type of known-host information "
                              "store");

    file = fmemopen(knownhostsdata, knownhostsdata_len, FOPEN_READTEXT);
    if(file) {
        while(fgets(buf, sizeof(buf), file)) {
            if(libssh2_knownhost_readline(hosts, buf, strlen(buf), type)) {
                num = _libssh2_error(hosts->session, LIBSSH2_ERROR_KNOWN_HOSTS,
                                     "Failed to parse known hosts data");
                break;
            }
            num++;
        }
        fclose(file);
    }
    else
        return _libssh2_error(hosts->session, LIBSSH2_ERROR_FILE,
                              "Failed to open known hosts data");

    return num;
}

[vszakats]

fmemopen() isn't available on all platforms libssh2 supports, so this would need something that parses lines without fgets().