m06：少一些需要处理的错误

void Store::del(const std::string& key, const WriteOptions& wo) {
    const IndexEntry* old = index_.find(key);
    if (!old) throw KeyNotFound(key);
    ...
std::string Store::getRange(const std::string& key, int64_t start, int64_t end) const {
    const IndexEntry* e = index_.find(key);
    if (!e) throw KeyNotFound(key);
    int64_t len = static_cast<int64_t>(e->value.size());
    if (start < 0 || end < start || end >= len) {
        throw std::out_of_range("index out of range");
    }
    ...
// server.cpp
} catch (const KeyNotFound&) {
    return "ERR no such key";
} catch (const std::out_of_range&) {
    return "ERR index out of range";
}

// Makes sure `key` is absent. Returns true if it was present.
bool Store::del(const std::string& key, const WriteOptions& wo) {
    const IndexEntry* old = index_.find(key);
    if (!old) return false;  // already absent: nothing to do, nothing to log
    ...
// Characters start..end of the value, both inclusive. Negative positions
// count from the end (-1 is the last character). Positions outside the
// value are clamped to it, so this never fails: an empty range or a
// missing key gives "".
std::string Store::getRange(...) const {
    const IndexEntry* e = index_.find(key);
    if (!e) return "";
    int64_t len = static_cast<int64_t>(e->value.size());
    if (start < 0) start += len;
    if (end < 0) end += len;
    start = std::max<int64_t>(start, 0);
    end = std::min<int64_t>(end, len - 1);
    if (start > end) return "";
    ...

KeyNotFound 整个类消失了。

std::string Server::handleIncr() {
    ...
    try {
        int64_t v = db_.incr(key, delta, writeOptions_);
        return "(integer) " + std::to_string(v);
    } catch (const std::invalid_argument& e) {
        return std::string("ERR ") + e.what();
    } catch (const std::overflow_error& e) {
        return std::string("ERR ") + e.what();
    } catch (const std::exception& e) {
        return std::string("ERR ") + e.what();   // 连"磁盘写失败"也吞掉
    }
}

// request_error.h
// Thrown when one request cannot be carried out because of what it asks
// for. ... Every other exception means minikv itself is in trouble; those
// are deliberately not caught per request.
class RequestError : public std::runtime_error { ... };

// server.cpp
std::string Server::handle(const std::string& line) {
    ...
    try {
        return (this->*(it->second))();
    } catch (const RequestError& e) {
        return std::string("ERR ") + e.what();
    }
}

std::string Server::handleIncr() {
    ...
    int64_t v = db_.incr(key, delta, writeOptions_);
    return "(integer) " + std::to_string(v);
}