Replace QOlmError with OlmErrorCode

QOlmError represents a subset of OlmErrorCode, and the associated
fromString() function uses undocumented strings produced inside Olm;
meanwhile OlmErrorCode is documented in its own header file. Each QOlm*
class now has lastErrorCode() next to lastError() (that, from now,
returns a textual representation straight from Olm, not QOlmError enum).

Also: including olm/error.h in e2ee/e2ee.h required some rearrangement
of the code to make sure non-E2EE configuration still builds.

13 files changed, 232 insertions, 253 deletions

diff --git a/lib/e2ee/e2ee.h b/lib/e2ee/e2ee.h
index 0772b70a..51ceff67 100644
--- a/lib/e2ee/e2ee.h
+++ b/lib/e2ee/e2ee.h
@@ -6,21 +6,20 @@
 #pragma once
 
 #include "converters.h"
-#include "expected.h"
-#include "qolmerrors.h"
 
 #include <QtCore/QMetaType>
 #include <QtCore/QStringBuilder>
 
 #include <array>
-#include <variant>
 
-namespace Quotient {
+#ifdef Quotient_E2EE_ENABLED
+#    include "expected.h"
+
+#    include <olm/error.h>
+#    include <variant>
+#endif
 
-constexpr auto CiphertextKeyL = "ciphertext"_ls;
-constexpr auto SenderKeyKeyL = "sender_key"_ls;
-constexpr auto DeviceIdKeyL = "device_id"_ls;
-constexpr auto SessionIdKeyL = "session_id"_ls;
+namespace Quotient {
 
 constexpr auto AlgorithmKeyL = "algorithm"_ls;
 constexpr auto RotationPeriodMsKeyL = "rotation_period_ms"_ls;
@@ -47,6 +46,7 @@ inline bool isSupportedAlgorithm(const QString& algorithm)
            != SupportedAlgorithms.cend();
 }
 
+#ifdef Quotient_E2EE_ENABLED
 struct Unencrypted {};
 struct Encrypted {
     QByteArray key;
@@ -64,7 +64,8 @@ class QOlmOutboundGroupSession;
 using QOlmOutboundGroupSessionPtr = std::unique_ptr<QOlmOutboundGroupSession>;
 
 template <typename T>
-using QOlmExpected = Expected<T, QOlmError>;
+using QOlmExpected = Expected<T, OlmErrorCode>;
+#endif
 
 struct IdentityKeys
 {
@@ -133,23 +134,6 @@ private:
 
 using OneTimeKeys = QHash<QString, std::variant<QString, SignedOneTimeKey>>;
 
-template <typename T>
-class asKeyValueRange
-{
-public:
-    asKeyValueRange(T& data)
-        : m_data { data }
-    {}
-
-    auto begin() { return m_data.keyValueBegin(); }
-    auto end() { return m_data.keyValueEnd(); }
-
-private:
-    T &m_data;
-};
-template <typename T>
-asKeyValueRange(T&) -> asKeyValueRange<T>;
-
 } // namespace Quotient
 
 Q_DECLARE_METATYPE(Quotient::SignedOneTimeKey)
diff --git a/lib/e2ee/qolmaccount.cpp b/lib/e2ee/qolmaccount.cpp
index ccb191f4..d33db8e3 100644
--- a/lib/e2ee/qolmaccount.cpp
+++ b/lib/e2ee/qolmaccount.cpp
@@ -18,8 +18,13 @@
 using namespace Quotient;
 
 // Convert olm error to enum
-QOlmError lastError(OlmAccount *account) {
-    return fromString(olm_account_last_error(account));
+OlmErrorCode QOlmAccount::lastErrorCode() const {
+    return olm_account_last_error_code(m_account);
+}
+
+const char* QOlmAccount::lastError() const
+{
+    return olm_account_last_error(m_account);
 }
 
 QOlmAccount::QOlmAccount(const QString& userId, const QString& deviceId,
@@ -40,24 +45,24 @@ void QOlmAccount::createNewAccount()
     m_account = olm_account(new uint8_t[olm_account_size()]);
     size_t randomSize = olm_create_account_random_length(m_account);
     QByteArray randomData = getRandom(randomSize);
-    const auto error = olm_create_account(m_account, randomData.data(), randomSize);
-    if (error == olm_error()) {
-        throw lastError(m_account);
+    if (olm_create_account(m_account, randomData.data(), randomSize)
+        == olm_error()) {
+        throw lastError();
     }
     emit needsSave();
 }
 
-void QOlmAccount::unpickle(QByteArray &pickled, const PicklingMode &mode)
+OlmErrorCode QOlmAccount::unpickle(QByteArray &pickled, const PicklingMode &mode)
 {
     m_account = olm_account(new uint8_t[olm_account_size()]);
     const QByteArray key = toKey(mode);
-    const auto error = olm_unpickle_account(m_account, key.data(), key.length(), pickled.data(), pickled.size());
-    if (error == olm_error()) {
-        qCWarning(E2EE) << "Failed to unpickle olm account";
-        //TODO: Do something that is not dying
+    if (olm_unpickle_account(m_account, key.data(), key.length(),
+                             pickled.data(), pickled.size())
+        == olm_error()) {
         // Probably log the user out since we have no way of getting to the keys
-        //throw lastError(m_account);
+        return lastErrorCode();
     }
+    return OLM_SUCCESS;
 }
 
 QOlmExpected<QByteArray> QOlmAccount::pickle(const PicklingMode &mode)
@@ -65,11 +70,10 @@ QOlmExpected<QByteArray> QOlmAccount::pickle(const PicklingMode &mode)
     const QByteArray key = toKey(mode);
     const size_t pickleLength = olm_pickle_account_length(m_account);
     QByteArray pickleBuffer(pickleLength, '0');
-    const auto error = olm_pickle_account(m_account, key.data(),
-                key.length(), pickleBuffer.data(), pickleLength);
-    if (error == olm_error()) {
-        return lastError(m_account);
-    }
+    if (olm_pickle_account(m_account, key.data(), key.length(),
+                           pickleBuffer.data(), pickleLength)
+        == olm_error())
+        return lastErrorCode();
     return pickleBuffer;
 }
 
@@ -77,9 +81,9 @@ IdentityKeys QOlmAccount::identityKeys() const
 {
     const size_t keyLength = olm_account_identity_keys_length(m_account);
     QByteArray keyBuffer(keyLength, '0');
-    const auto error = olm_account_identity_keys(m_account, keyBuffer.data(), keyLength);
-    if (error == olm_error()) {
-        throw lastError(m_account);
+    if (olm_account_identity_keys(m_account, keyBuffer.data(), keyLength)
+        == olm_error()) {
+        throw lastError();
     }
     const QJsonObject key = QJsonDocument::fromJson(keyBuffer).object();
     return IdentityKeys {
@@ -92,11 +96,10 @@ QByteArray QOlmAccount::sign(const QByteArray &message) const
 {
     QByteArray signatureBuffer(olm_account_signature_length(m_account), '0');
 
-    const auto error = olm_account_sign(m_account, message.data(), message.length(),
-            signatureBuffer.data(), signatureBuffer.length());
-
-    if (error == olm_error()) {
-        throw lastError(m_account);
+    if (olm_account_sign(m_account, message.data(), message.length(),
+                         signatureBuffer.data(), signatureBuffer.length())
+        == olm_error()) {
+        throw lastError();
     }
     return signatureBuffer;
 }
@@ -131,15 +134,15 @@ size_t QOlmAccount::generateOneTimeKeys(size_t numberOfKeys)
         olm_account_generate_one_time_keys_random_length(m_account,
                                                          numberOfKeys);
     QByteArray randomBuffer = getRandom(randomLength);
-    const auto error =
+    const auto result =
         olm_account_generate_one_time_keys(m_account, numberOfKeys,
                                            randomBuffer.data(), randomLength);
 
-    if (error == olm_error()) {
-        throw lastError(m_account);
+    if (result == olm_error()) {
+        throw lastError();
     }
     emit needsSave();
-    return error;
+    return result;
 }
 
 UnsignedOneTimeKeys QOlmAccount::oneTimeKeys() const
@@ -147,11 +150,10 @@ UnsignedOneTimeKeys QOlmAccount::oneTimeKeys() const
     const size_t oneTimeKeyLength = olm_account_one_time_keys_length(m_account);
     QByteArray oneTimeKeysBuffer(static_cast<int>(oneTimeKeyLength), '0');
 
-    const auto error = olm_account_one_time_keys(m_account,
-                                                 oneTimeKeysBuffer.data(),
-                                                 oneTimeKeyLength);
-    if (error == olm_error()) {
-        throw lastError(m_account);
+    if (olm_account_one_time_keys(m_account, oneTimeKeysBuffer.data(),
+                                  oneTimeKeyLength)
+        == olm_error()) {
+        throw lastError();
     }
     const auto json = QJsonDocument::fromJson(oneTimeKeysBuffer).object();
     UnsignedOneTimeKeys oneTimeKeys;
@@ -171,16 +173,16 @@ OneTimeKeys QOlmAccount::signOneTimeKeys(const UnsignedOneTimeKeys &keys) const
     return signedOneTimeKeys;
 }
 
-std::optional<QOlmError> QOlmAccount::removeOneTimeKeys(
-    const QOlmSession& session)
+OlmErrorCode QOlmAccount::removeOneTimeKeys(const QOlmSession& session)
 {
-    const auto error = olm_remove_one_time_keys(m_account, session.raw());
-
-    if (error == olm_error()) {
-        return lastError(m_account);
+    if (olm_remove_one_time_keys(m_account, session.raw()) == olm_error()) {
+        qWarning(E2EE).nospace()
+            << "Failed to remove one-time keys for session "
+            << session.sessionId() << ": " << lastError();
+        return lastErrorCode();
     }
     emit needsSave();
-    return std::nullopt;
+    return OLM_SUCCESS;
 }
 
 OlmAccount* QOlmAccount::data() { return m_account; }
diff --git a/lib/e2ee/qolmaccount.h b/lib/e2ee/qolmaccount.h
index f2a31314..5ad98e47 100644
--- a/lib/e2ee/qolmaccount.h
+++ b/lib/e2ee/qolmaccount.h
@@ -36,7 +36,8 @@ public:
 
     //! Deserialises from encrypted Base64 that was previously obtained by pickling a `QOlmAccount`.
     //! This needs to be called before any other action or use createNewAccount() instead.
-    void unpickle(QByteArray &pickled, const PicklingMode &mode);
+    [[nodiscard]] OlmErrorCode unpickle(QByteArray& pickled,
+                                        const PicklingMode& mode);
 
     //! Serialises an OlmAccount to encrypted Base64.
     QOlmExpected<QByteArray> pickle(const PicklingMode &mode);
@@ -69,8 +70,7 @@ public:
     DeviceKeys deviceKeys() const;
 
     //! Remove the one time key used to create the supplied session.
-    [[nodiscard]] std::optional<QOlmError> removeOneTimeKeys(
-        const QOlmSession& session);
+    [[nodiscard]] OlmErrorCode removeOneTimeKeys(const QOlmSession& session);
 
     //! Creates an inbound session for sending/receiving messages from a received 'prekey' message.
     //!
@@ -92,6 +92,9 @@ public:
 
     void markKeysAsPublished();
 
+    OlmErrorCode lastErrorCode() const;
+    const char *lastError() const;
+
     // HACK do not use directly
     QOlmAccount(OlmAccount *account);
     OlmAccount *data();
diff --git a/lib/e2ee/qolmerrors.cpp b/lib/e2ee/qolmerrors.cpp
deleted file mode 100644
index 5a60b7e6..00000000
--- a/lib/e2ee/qolmerrors.cpp
+++ /dev/null
@@ -1,25 +0,0 @@
-// SPDX-FileCopyrightText: 2021 Carl Schwan <carlschwan@kde.org>
-//
-// SPDX-License-Identifier: LGPL-2.1-or-later
-
-
-#include "qolmerrors.h"
-#include "util.h"
-#include <QtCore/QLatin1String>
-
-Quotient::QOlmError Quotient::fromString(const char* error_raw) {
-    const QLatin1String error { error_raw };
-    if (error_raw == "BAD_ACCOUNT_KEY"_ls) {
-        return QOlmError::BadAccountKey;
-    } else if (error_raw == "BAD_MESSAGE_KEY_ID"_ls) {
-        return QOlmError::BadMessageKeyId;
-    } else if (error_raw == "INVALID_BASE64"_ls) {
-        return QOlmError::InvalidBase64;
-    } else if (error_raw == "NOT_ENOUGH_RANDOM"_ls) {
-        return QOlmError::NotEnoughRandom;
-    } else if (error_raw == "OUTPUT_BUFFER_TOO_SMALL"_ls) {
-        return QOlmError::OutputBufferTooSmall;
-    } else {
-        return QOlmError::Unknown;
-    }
-}
diff --git a/lib/e2ee/qolmerrors.h b/lib/e2ee/qolmerrors.h
deleted file mode 100644
index 20e61c12..00000000
--- a/lib/e2ee/qolmerrors.h
+++ /dev/null
@@ -1,28 +0,0 @@
-// SPDX-FileCopyrightText: 2021 Carl Schwan <carlschwan@kde.org>
-//
-// SPDX-License-Identifier: LGPL-2.1-or-later
-
-#pragma once
-
-#include "quotient_export.h"
-
-namespace Quotient {
-//! All errors that could be caused by an operation regarding Olm
-//! Errors are named exactly like the ones in libolm.
-enum QOlmError
-{
-    BadAccountKey,
-    BadMessageFormat,
-    BadMessageKeyId,
-    BadMessageMac,
-    BadMessageVersion,
-    InvalidBase64,
-    NotEnoughRandom,
-    OutputBufferTooSmall,
-    UnknownMessageIndex,
-    Unknown,
-};
-
-QUOTIENT_API QOlmError fromString(const char* error_raw);
-
-} //namespace Quotient
diff --git a/lib/e2ee/qolminboundsession.cpp b/lib/e2ee/qolminboundsession.cpp
index 17f06205..870070c2 100644
--- a/lib/e2ee/qolminboundsession.cpp
+++ b/lib/e2ee/qolminboundsession.cpp
@@ -3,20 +3,27 @@
 // SPDX-License-Identifier: LGPL-2.1-or-later
 
 #include "e2ee/qolminboundsession.h"
-#include <iostream>
+#include "logging.h"
+
 #include <cstring>
+#include <iostream>
+#include <olm/olm.h>
 
 using namespace Quotient;
 
-QOlmError lastError(OlmInboundGroupSession *session) {
-    return fromString(olm_inbound_group_session_last_error(session));
+OlmErrorCode QOlmInboundGroupSession::lastErrorCode() const {
+    return olm_inbound_group_session_last_error_code(m_groupSession);
 }
 
-QOlmInboundGroupSession::QOlmInboundGroupSession(OlmInboundGroupSession *session)
-    : m_groupSession(session)
+const char* QOlmInboundGroupSession::lastError() const
 {
+    return olm_inbound_group_session_last_error(m_groupSession);
 }
 
+QOlmInboundGroupSession::QOlmInboundGroupSession(OlmInboundGroupSession *session)
+    : m_groupSession(session)
+{}
+
 QOlmInboundGroupSession::~QOlmInboundGroupSession()
 {
     olm_clear_inbound_group_session(m_groupSession);
@@ -26,11 +33,12 @@ QOlmInboundGroupSession::~QOlmInboundGroupSession()
 std::unique_ptr<QOlmInboundGroupSession> QOlmInboundGroupSession::create(const QByteArray &key)
 {
     const auto olmInboundGroupSession = olm_inbound_group_session(new uint8_t[olm_inbound_group_session_size()]);
-    const auto error = olm_init_inbound_group_session(olmInboundGroupSession,
-            reinterpret_cast<const uint8_t *>(key.constData()), key.size());
-
-    if (error == olm_error()) {
-        throw lastError(olmInboundGroupSession);
+    if (olm_init_inbound_group_session(
+            olmInboundGroupSession,
+            reinterpret_cast<const uint8_t*>(key.constData()), key.size())
+        == olm_error()) {
+        // FIXME: create QOlmInboundGroupSession earlier and use lastError()
+        throw olm_inbound_group_session_last_error_code(olmInboundGroupSession);
     }
 
     return std::make_unique<QOlmInboundGroupSession>(olmInboundGroupSession);
@@ -41,10 +49,12 @@ std::unique_ptr<QOlmInboundGroupSession> QOlmInboundGroupSession::import(const Q
     const auto olmInboundGroupSession = olm_inbound_group_session(new uint8_t[olm_inbound_group_session_size()]);
     QByteArray keyBuf = key;
 
-    const auto error = olm_import_inbound_group_session(olmInboundGroupSession,
-            reinterpret_cast<const uint8_t *>(keyBuf.data()), keyBuf.size());
-    if (error == olm_error()) {
-        throw lastError(olmInboundGroupSession);
+    if (olm_import_inbound_group_session(
+            olmInboundGroupSession,
+            reinterpret_cast<const uint8_t*>(keyBuf.data()), keyBuf.size())
+        == olm_error()) {
+        // FIXME: create QOlmInboundGroupSession earlier and use lastError()
+        throw olm_inbound_group_session_last_error_code(olmInboundGroupSession);
     }
 
     return std::make_unique<QOlmInboundGroupSession>(olmInboundGroupSession);
@@ -62,10 +72,11 @@ QByteArray QOlmInboundGroupSession::pickle(const PicklingMode &mode) const
 {
     QByteArray pickledBuf(olm_pickle_inbound_group_session_length(m_groupSession), '0');
     const QByteArray key = toKey(mode);
-    const auto error = olm_pickle_inbound_group_session(m_groupSession, key.data(), key.length(), pickledBuf.data(),
-            pickledBuf.length());
-    if (error == olm_error()) {
-        throw lastError(m_groupSession);
+    if (olm_pickle_inbound_group_session(m_groupSession, key.data(),
+                                         key.length(), pickledBuf.data(),
+                                         pickledBuf.length())
+        == olm_error()) {
+        throw lastError();
     }
     return pickledBuf;
 }
@@ -76,10 +87,12 @@ QOlmExpected<QOlmInboundGroupSessionPtr> QOlmInboundGroupSession::unpickle(
     QByteArray pickledBuf = pickled;
     const auto groupSession = olm_inbound_group_session(new uint8_t[olm_inbound_group_session_size()]);
     QByteArray key = toKey(mode);
-    const auto error = olm_unpickle_inbound_group_session(groupSession, key.data(), key.length(),
-            pickledBuf.data(), pickledBuf.size());
-    if (error == olm_error()) {
-        return lastError(groupSession);
+    if (olm_unpickle_inbound_group_session(groupSession, key.data(),
+                                           key.length(), pickledBuf.data(),
+                                           pickledBuf.size())
+        == olm_error()) {
+        // FIXME: create QOlmInboundGroupSession earlier and use lastError()
+        return olm_inbound_group_session_last_error_code(groupSession);
     }
     key.clear();
 
@@ -105,12 +118,9 @@ QOlmExpected<std::pair<QByteArray, uint32_t>> QOlmInboundGroupSession::decrypt(
 
     const auto plaintextLen = olm_group_decrypt(m_groupSession, reinterpret_cast<uint8_t *>(messageBuf.data()),
             messageBuf.length(), reinterpret_cast<uint8_t *>(plaintextBuf.data()), plaintextBuf.length(), &messageIndex);
-
-    // Error code or plaintext length is returned
-    const auto decryptError = plaintextLen;
-
-    if (decryptError == olm_error()) {
-        return lastError(m_groupSession);
+    if (plaintextLen == olm_error()) {
+        qWarning(E2EE) << "Failed to decrypt the message:" << lastError();
+        return lastErrorCode();
     }
 
     QByteArray output(plaintextLen, '0');
@@ -123,10 +133,11 @@ QOlmExpected<QByteArray> QOlmInboundGroupSession::exportSession(uint32_t message
 {
     const auto keyLength = olm_export_inbound_group_session_length(m_groupSession);
     QByteArray keyBuf(keyLength, '0');
-    const auto error = olm_export_inbound_group_session(m_groupSession, reinterpret_cast<uint8_t *>(keyBuf.data()), keyLength, messageIndex);
-
-    if (error == olm_error()) {
-        return lastError(m_groupSession);
+    if (olm_export_inbound_group_session(
+            m_groupSession, reinterpret_cast<uint8_t*>(keyBuf.data()),
+            keyLength, messageIndex)
+        == olm_error()) {
+        return lastErrorCode();
     }
     return keyBuf;
 }
@@ -139,10 +150,11 @@ uint32_t QOlmInboundGroupSession::firstKnownIndex() const
 QByteArray QOlmInboundGroupSession::sessionId() const
 {
     QByteArray sessionIdBuf(olm_inbound_group_session_id_length(m_groupSession), '0');
-    const auto error = olm_inbound_group_session_id(m_groupSession, reinterpret_cast<uint8_t *>(sessionIdBuf.data()),
-            sessionIdBuf.length());
-    if (error == olm_error()) {
-        throw lastError(m_groupSession);
+    if (olm_inbound_group_session_id(
+            m_groupSession, reinterpret_cast<uint8_t*>(sessionIdBuf.data()),
+            sessionIdBuf.length())
+        == olm_error()) {
+        throw lastError();
     }
     return sessionIdBuf;
 }
diff --git a/lib/e2ee/qolminboundsession.h b/lib/e2ee/qolminboundsession.h
index 1a9b4415..e8da6355 100644
--- a/lib/e2ee/qolminboundsession.h
+++ b/lib/e2ee/qolminboundsession.h
@@ -6,7 +6,7 @@
 
 #include "e2ee/e2ee.h"
 
-#include <olm/olm.h>
+struct OlmInboundGroupSession;
 
 namespace Quotient {
 
@@ -46,6 +46,9 @@ public:
     QString senderId() const;
     void setSenderId(const QString& senderId);
 
+    OlmErrorCode lastErrorCode() const;
+    const char* lastError() const;
+
     QOlmInboundGroupSession(OlmInboundGroupSession* session);
 private:
     OlmInboundGroupSession* m_groupSession;
diff --git a/lib/e2ee/qolmoutboundsession.cpp b/lib/e2ee/qolmoutboundsession.cpp
index a2eff2c8..79c16e01 100644
--- a/lib/e2ee/qolmoutboundsession.cpp
+++ b/lib/e2ee/qolmoutboundsession.cpp
@@ -3,12 +3,20 @@
 // SPDX-License-Identifier: LGPL-2.1-or-later
 
 #include "e2ee/qolmoutboundsession.h"
+
 #include "e2ee/qolmutils.h"
 
+#include <olm/olm.h>
+
 using namespace Quotient;
 
-QOlmError lastError(OlmOutboundGroupSession *session) {
-    return fromString(olm_outbound_group_session_last_error(session));
+OlmErrorCode QOlmOutboundGroupSession::lastErrorCode() const {
+    return olm_outbound_group_session_last_error_code(m_groupSession);
+}
+
+const char* QOlmOutboundGroupSession::lastError() const
+{
+    return olm_outbound_group_session_last_error(m_groupSession);
 }
 
 QOlmOutboundGroupSession::QOlmOutboundGroupSession(OlmOutboundGroupSession *session)
@@ -27,11 +35,12 @@ QOlmOutboundGroupSessionPtr QOlmOutboundGroupSession::create()
     const auto randomLength = olm_init_outbound_group_session_random_length(olmOutboundGroupSession);
     QByteArray randomBuf = getRandom(randomLength);
 
-    const auto error = olm_init_outbound_group_session(olmOutboundGroupSession,
-            reinterpret_cast<uint8_t *>(randomBuf.data()), randomBuf.length());
-
-    if (error == olm_error()) {
-        throw lastError(olmOutboundGroupSession);
+    if (olm_init_outbound_group_session(
+            olmOutboundGroupSession,
+            reinterpret_cast<uint8_t*>(randomBuf.data()), randomBuf.length())
+        == olm_error()) {
+        // FIXME: create the session object earlier and use lastError()
+        throw olm_outbound_group_session_last_error_code(olmOutboundGroupSession);
     }
 
     const auto keyMaxLength = olm_outbound_group_session_key_length(olmOutboundGroupSession);
@@ -48,12 +57,11 @@ QOlmExpected<QByteArray> QOlmOutboundGroupSession::pickle(const PicklingMode &mo
 {
     QByteArray pickledBuf(olm_pickle_outbound_group_session_length(m_groupSession), '0');
     QByteArray key = toKey(mode);
-    const auto error = olm_pickle_outbound_group_session(m_groupSession, key.data(), key.length(),
-            pickledBuf.data(), pickledBuf.length());
-
-    if (error == olm_error()) {
-        return lastError(m_groupSession);
-    }
+    if (olm_pickle_outbound_group_session(m_groupSession, key.data(),
+                                          key.length(), pickledBuf.data(),
+                                          pickledBuf.length())
+        == olm_error())
+        return lastErrorCode();
 
     key.clear();
 
@@ -65,10 +73,13 @@ QOlmExpected<QOlmOutboundGroupSessionPtr> QOlmOutboundGroupSession::unpickle(con
     QByteArray pickledBuf = pickled;
     auto *olmOutboundGroupSession = olm_outbound_group_session(new uint8_t[olm_outbound_group_session_size()]);
     QByteArray key = toKey(mode);
-    const auto error = olm_unpickle_outbound_group_session(olmOutboundGroupSession, key.data(), key.length(),
-            pickledBuf.data(), pickledBuf.length());
-    if (error == olm_error()) {
-        return lastError(olmOutboundGroupSession);
+    if (olm_unpickle_outbound_group_session(olmOutboundGroupSession, key.data(),
+                                            key.length(), pickledBuf.data(),
+                                            pickledBuf.length())
+        == olm_error()) {
+        // FIXME: create the session object earlier and use lastError()
+        return olm_outbound_group_session_last_error_code(
+            olmOutboundGroupSession);
     }
     const auto idMaxLength = olm_outbound_group_session_id_length(olmOutboundGroupSession);
     QByteArray idBuffer(idMaxLength, '0');
@@ -84,12 +95,13 @@ QOlmExpected<QByteArray> QOlmOutboundGroupSession::encrypt(const QString &plaint
     QByteArray plaintextBuf = plaintext.toUtf8();
     const auto messageMaxLength = olm_group_encrypt_message_length(m_groupSession, plaintextBuf.length());
     QByteArray messageBuf(messageMaxLength, '0');
-    const auto error = olm_group_encrypt(m_groupSession, reinterpret_cast<uint8_t *>(plaintextBuf.data()),
-            plaintextBuf.length(), reinterpret_cast<uint8_t *>(messageBuf.data()), messageBuf.length());
-
-    if (error == olm_error()) {
-        return lastError(m_groupSession);
-    }
+    if (olm_group_encrypt(m_groupSession,
+                          reinterpret_cast<uint8_t*>(plaintextBuf.data()),
+                          plaintextBuf.length(),
+                          reinterpret_cast<uint8_t*>(messageBuf.data()),
+                          messageBuf.length())
+        == olm_error())
+        return lastErrorCode();
 
     return messageBuf;
 }
@@ -103,11 +115,12 @@ QByteArray QOlmOutboundGroupSession::sessionId() const
 {
     const auto idMaxLength = olm_outbound_group_session_id_length(m_groupSession);
     QByteArray idBuffer(idMaxLength, '0');
-    const auto error = olm_outbound_group_session_id(m_groupSession, reinterpret_cast<uint8_t *>(idBuffer.data()),
-            idBuffer.length());
-    if (error == olm_error()) {
-        throw lastError(m_groupSession);
-    }
+    if (olm_outbound_group_session_id(
+            m_groupSession, reinterpret_cast<uint8_t*>(idBuffer.data()),
+            idBuffer.length())
+        == olm_error())
+        throw lastError();
+
     return idBuffer;
 }
 
@@ -115,12 +128,12 @@ QOlmExpected<QByteArray> QOlmOutboundGroupSession::sessionKey() const
 {
     const auto keyMaxLength = olm_outbound_group_session_key_length(m_groupSession);
     QByteArray keyBuffer(keyMaxLength, '0');
-    const auto error = olm_outbound_group_session_key(
-        m_groupSession, reinterpret_cast<uint8_t*>(keyBuffer.data()),
-        keyMaxLength);
-    if (error == olm_error()) {
-        return lastError(m_groupSession);
-    }
+    if (olm_outbound_group_session_key(
+            m_groupSession, reinterpret_cast<uint8_t*>(keyBuffer.data()),
+            keyMaxLength)
+        == olm_error())
+        return lastErrorCode();
+
     return keyBuffer;
 }
 
diff --git a/lib/e2ee/qolmoutboundsession.h b/lib/e2ee/qolmoutboundsession.h
index 9a82d22a..cd26fc67 100644
--- a/lib/e2ee/qolmoutboundsession.h
+++ b/lib/e2ee/qolmoutboundsession.h
@@ -6,8 +6,7 @@
 
 #include "e2ee/e2ee.h"
 
-#include <memory>
-#include <olm/olm.h>
+struct OlmOutboundGroupSession;
 
 namespace Quotient {
 
@@ -51,6 +50,10 @@ public:
 
     QDateTime creationTime() const;
     void setCreationTime(const QDateTime& creationTime);
+
+    OlmErrorCode lastErrorCode() const;
+    const char* lastError() const;
+
 private:
     OlmOutboundGroupSession *m_groupSession;
     int m_messageCount = 0;
diff --git a/lib/e2ee/qolmsession.cpp b/lib/e2ee/qolmsession.cpp
index 2a98d5d8..771d310d 100644
--- a/lib/e2ee/qolmsession.cpp
+++ b/lib/e2ee/qolmsession.cpp
@@ -12,8 +12,13 @@
 
 using namespace Quotient;
 
-QOlmError lastError(OlmSession* session) {
-    return fromString(olm_session_last_error(session));
+OlmErrorCode QOlmSession::lastErrorCode() const {
+    return olm_session_last_error_code(m_session);
+}
+
+const char* QOlmSession::lastError() const
+{
+    return olm_session_last_error(m_session);
 }
 
 Quotient::QOlmSession::~QOlmSession()
@@ -32,7 +37,8 @@ QOlmExpected<QOlmSessionPtr> QOlmSession::createInbound(
     const QString& theirIdentityKey)
 {
     if (preKeyMessage.type() != QOlmMessage::PreKey) {
-        qCCritical(E2EE) << "The message is not a pre-key in when creating inbound session" << BadMessageFormat;
+        qCCritical(E2EE) << "The message is not a pre-key; will try to create "
+                            "the inbound session anyway";
     }
 
     const auto olmSession = create();
@@ -47,7 +53,8 @@ QOlmExpected<QOlmSessionPtr> QOlmSession::createInbound(
     }
 
     if (error == olm_error()) {
-        const auto lastErr = lastError(olmSession);
+        // FIXME: the QOlmSession object should be created earlier
+        const auto lastErr = olm_session_last_error_code(olmSession);
         qCWarning(E2EE) << "Error when creating inbound session" << lastErr;
         return lastErr;
     }
@@ -78,15 +85,17 @@ QOlmExpected<QOlmSessionPtr> QOlmSession::createOutboundSession(
 
     QByteArray theirIdentityKeyBuf = theirIdentityKey.toUtf8();
     QByteArray theirOneTimeKeyBuf = theirOneTimeKey.toUtf8();
-    const auto error = olm_create_outbound_session(olmOutboundSession,
-                                                   account->data(),
-                                                   reinterpret_cast<uint8_t *>(theirIdentityKeyBuf.data()), theirIdentityKeyBuf.length(),
-                                                   reinterpret_cast<uint8_t *>(theirOneTimeKeyBuf.data()), theirOneTimeKeyBuf.length(),
-                                                   reinterpret_cast<uint8_t *>(randomBuf.data()), randomBuf.length());
-
-    if (error == olm_error()) {
-        const auto lastErr = lastError(olmOutboundSession);
-        if (lastErr == QOlmError::NotEnoughRandom) {
+    if (olm_create_outbound_session(
+            olmOutboundSession, account->data(),
+            reinterpret_cast<uint8_t*>(theirIdentityKeyBuf.data()),
+            theirIdentityKeyBuf.length(),
+            reinterpret_cast<uint8_t*>(theirOneTimeKeyBuf.data()),
+            theirOneTimeKeyBuf.length(),
+            reinterpret_cast<uint8_t*>(randomBuf.data()), randomBuf.length())
+        == olm_error()) {
+        // FIXME: the QOlmSession object should be created earlier
+        const auto lastErr = olm_session_last_error_code(olmOutboundSession);
+        if (lastErr == OLM_NOT_ENOUGH_RANDOM) {
             throw lastErr;
         }
         return lastErr;
@@ -100,16 +109,12 @@ QOlmExpected<QByteArray> QOlmSession::pickle(const PicklingMode &mode) const
 {
     QByteArray pickledBuf(olm_pickle_session_length(m_session), '0');
     QByteArray key = toKey(mode);
-    const auto error = olm_pickle_session(m_session, key.data(), key.length(),
-                                          pickledBuf.data(),
-                                          pickledBuf.length());
-
-    if (error == olm_error()) {
-        return lastError(m_session);
-    }
+    if (olm_pickle_session(m_session, key.data(), key.length(),
+                           pickledBuf.data(), pickledBuf.length())
+        == olm_error())
+        return lastErrorCode();
 
     key.clear();
-
     return pickledBuf;
 }
 
@@ -119,10 +124,11 @@ QOlmExpected<QOlmSessionPtr> QOlmSession::unpickle(const QByteArray& pickled,
     QByteArray pickledBuf = pickled;
     auto *olmSession = create();
     QByteArray key = toKey(mode);
-    const auto error = olm_unpickle_session(olmSession, key.data(), key.length(),
-            pickledBuf.data(), pickledBuf.length());
-    if (error == olm_error()) {
-        return lastError(olmSession);
+    if (olm_unpickle_session(olmSession, key.data(), key.length(),
+                             pickledBuf.data(), pickledBuf.length())
+        == olm_error()) {
+        // FIXME: the QOlmSession object should be created earlier
+        return olm_session_last_error_code(olmSession);
     }
 
     key.clear();
@@ -137,13 +143,14 @@ QOlmMessage QOlmSession::encrypt(const QString &plaintext)
     const auto messageType = encryptMessageType();
     const auto randomLen = olm_encrypt_random_length(m_session);
     QByteArray randomBuf = getRandom(randomLen);
-    const auto error = olm_encrypt(m_session,
-                                   reinterpret_cast<uint8_t *>(plaintextBuf.data()), plaintextBuf.length(),
-                                   reinterpret_cast<uint8_t *>(randomBuf.data()), randomBuf.length(),
-                                   reinterpret_cast<uint8_t *>(messageBuf.data()), messageBuf.length());
-
-    if (error == olm_error()) {
-        throw lastError(m_session);
+    if (olm_encrypt(m_session, reinterpret_cast<uint8_t*>(plaintextBuf.data()),
+                    plaintextBuf.length(),
+                    reinterpret_cast<uint8_t*>(randomBuf.data()),
+                    randomBuf.length(),
+                    reinterpret_cast<uint8_t*>(messageBuf.data()),
+                    messageBuf.length())
+        == olm_error()) {
+        throw lastError();
     }
 
     return QOlmMessage(messageBuf, messageType);
@@ -163,9 +170,8 @@ QOlmExpected<QByteArray> QOlmSession::decrypt(const QOlmMessage &message) const
 
     const auto plaintextMaxLen = olm_decrypt_max_plaintext_length(m_session, messageTypeValue,
             reinterpret_cast<uint8_t *>(messageBuf.data()), messageBuf.length());
-
     if (plaintextMaxLen == olm_error()) {
-        return lastError(m_session);
+        return lastError();
     }
 
     QByteArray plaintextBuf(plaintextMaxLen, '0');
@@ -175,10 +181,9 @@ QOlmExpected<QByteArray> QOlmSession::decrypt(const QOlmMessage &message) const
     const auto plaintextResultLen = olm_decrypt(m_session, messageTypeValue,
             reinterpret_cast<uint8_t *>(messageBuf2.data()), messageBuf2.length(),
             reinterpret_cast<uint8_t *>(plaintextBuf.data()), plaintextMaxLen);
-
     if (plaintextResultLen == olm_error()) {
-        const auto lastErr = lastError(m_session);
-        if (lastErr == QOlmError::OutputBufferTooSmall) {
+        const auto lastErr = lastErrorCode();
+        if (lastErr == OLM_OUTPUT_BUFFER_TOO_SMALL) {
             throw lastErr;
         }
         return lastErr;
@@ -193,7 +198,7 @@ QOlmMessage::Type QOlmSession::encryptMessageType()
 {
     const auto messageTypeResult = olm_encrypt_message_type(m_session);
     if (messageTypeResult == olm_error()) {
-        throw lastError(m_session);
+        throw lastError();
     }
     if (messageTypeResult == OLM_MESSAGE_TYPE_PRE_KEY) {
         return QOlmMessage::PreKey;
@@ -205,10 +210,10 @@ QByteArray QOlmSession::sessionId() const
 {
     const auto idMaxLength = olm_session_id_length(m_session);
     QByteArray idBuffer(idMaxLength, '0');
-    const auto error = olm_session_id(m_session, reinterpret_cast<uint8_t *>(idBuffer.data()),
-            idBuffer.length());
-    if (error == olm_error()) {
-        throw lastError(m_session);
+    if (olm_session_id(m_session, reinterpret_cast<uint8_t*>(idBuffer.data()),
+                       idBuffer.length())
+        == olm_error()) {
+        throw lastError();
     }
     return idBuffer;
 }
@@ -225,11 +230,10 @@ bool QOlmSession::matchesInboundSession(const QOlmMessage& preKeyMessage) const
     const auto maybeMatches =
         olm_matches_inbound_session(m_session, oneTimeKeyBuf.data(),
                                     oneTimeKeyBuf.length());
-
-    if (maybeMatches == olm_error()) {
-        return lastError(m_session);
-    }
-    return maybeMatches == 1;
+    if (maybeMatches == olm_error())
+        qWarning(E2EE) << "Error matching an inbound session:"
+                       << olm_session_last_error(m_session);
+    return maybeMatches == 1; // Any errors are treated as non-match
 }
 
 bool QOlmSession::matchesInboundSessionFrom(
diff --git a/lib/e2ee/qolmsession.h b/lib/e2ee/qolmsession.h
index 021092c7..cc988a03 100644
--- a/lib/e2ee/qolmsession.h
+++ b/lib/e2ee/qolmsession.h
@@ -6,7 +6,6 @@
 
 #include "e2ee/e2ee.h"
 #include "e2ee/qolmmessage.h"
-#include "e2ee/qolmerrors.h"
 #include "e2ee/qolmaccount.h"
 
 struct OlmSession;
@@ -71,6 +70,9 @@ public:
         return *lhs < *rhs;
     }
 
+    OlmErrorCode lastErrorCode() const;
+    const char* lastError() const;
+
     OlmSession* raw() const { return m_session; }
 
     QOlmSession(OlmSession* session);
diff --git a/lib/e2ee/qolmutility.cpp b/lib/e2ee/qolmutility.cpp
index 84559085..15c875c0 100644
--- a/lib/e2ee/qolmutility.cpp
+++ b/lib/e2ee/qolmutility.cpp
@@ -8,9 +8,13 @@
 
 using namespace Quotient;
 
-// Convert olm error to enum
-QOlmError lastError(OlmUtility *utility) {
-    return fromString(olm_utility_last_error(utility));
+OlmErrorCode QOlmUtility::lastErrorCode() const {
+    return olm_utility_last_error_code(m_utility);
+}
+
+const char* QOlmUtility::lastError() const
+{
+    return olm_utility_last_error(m_utility);
 }
 
 QOlmUtility::QOlmUtility()
@@ -48,15 +52,15 @@ QOlmExpected<bool> QOlmUtility::ed25519Verify(const QByteArray& key,
     std::copy(signature.begin(), signature.end(), signatureBuf.begin());
 
     const auto ret = olm_ed25519_verify(m_utility, key.data(), key.size(),
-            message.data(), message.size(), (void *)signatureBuf.data(), signatureBuf.size());
-
+                                        message.data(), message.size(),
+                                        (void*)signatureBuf.data(),
+                                        signatureBuf.size());
     if (ret == olm_error()) {
-        auto error = lastError(m_utility);
-        if (error == QOlmError::BadMessageMac) {
+        auto error = lastErrorCode();
+        if (error == OLM_BAD_MESSAGE_MAC)
             return false;
-        }
         return error;
     }
 
-    return !ret; // ret == 0 means success
+    return ret == 0;
 }
diff --git a/lib/e2ee/qolmutility.h b/lib/e2ee/qolmutility.h
index 5f6bcdc5..89277385 100644
--- a/lib/e2ee/qolmutility.h
+++ b/lib/e2ee/qolmutility.h
@@ -32,8 +32,10 @@ public:
     QOlmExpected<bool> ed25519Verify(const QByteArray &key,
             const QByteArray &message, const QByteArray &signature);
 
+    OlmErrorCode lastErrorCode() const;
+    const char* lastError() const;
+
 private:
     OlmUtility *m_utility;
-
 };
 }