const failable patch()

in components/sqldb/sqldb.cpp [69:123]

• 37 lines of code
• 10 McCabe index (conditional complexity)

const failable<value> patch(const list<value>& params, const pgsql::PGSql& pg) {
    // Read patch
    value p = assoc<value>("patch", assoc<value>("content", car<value>(cadr(params))));
    if (isNull(p))
        return mkfailure<value>("Couldn't read patch script");
    const string script = cadr<value>(p);
    debug(script, "pgsql::patch::script");

    const lambda<const failable<value>(const value&, const pgsql::PGSql&, const string&, const int)> tryPatch = [&tryPatch](const value& key, const pgsql::PGSql& pg, const string& script, const int count) -> const failable<value> {

        // Begin database transaction
        const failable<bool> brc = pgsql::begin(pg);
        if (!hasContent(brc))
            return mkfailure<value>(brc);

        // Get existing value from database
        const failable<value> ival = pgsql::get(key, pg);
        if (!hasContent(ival) && rcode(ival) != 404) {
            pgsql::rollback(pg);
            return mkfailure<value>(ival);
        }

        // Apply patch
        istringstream is(script);
        scheme::Env env = scheme::setupEnvironment();
        const value pval = scheme::evalScript(cons<value>("patch", scheme::quotedParameters(mklist<value>(key, hasContent(ival)? content(ival) : (value)list<value>()))), is, env);
        if (isNull(pval)) {
            ostringstream os;
            os << "Couldn't patch postgresql entry: " << key;
            return mkfailure<value>(str(os), 404, false);
        }

        // Push patched value to database
        const failable<bool> val = pgsql::patch(key, pval, pg);
        if (!hasContent(val)) {
            pgsql::rollback(pg);

            // Retry on a transaction serialization error
            if (rcode(val) == 409 && count > 0)
                return tryPatch(key, pg, script, count - 1);
            return mkfailure<value>(val);
        }

        // Commit database transaction
        const failable<bool> crc = pgsql::commit(pg);
        if (!hasContent(crc))
            return mkfailure<value>(crc);

        return value(content(val));
    };

    // Try patching the entry and automatically retry a few times on transaction
    // serialization errors
    return tryPatch(car(params), pg, script, 5);
}