fix(spigot): support Mojang-mapped NMS classes (Paper 1.20.5+ / Spigot 1.20.5+)#23
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robinbraemer merged 1 commit intoconnectfrom May 1, 2026
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Paper has shipped Mojang mappings by default since 1.20.5, so the NMS class names our reflection bootstrap looked up (NetworkManager, ServerConnection, PacketHandshakingInSetProtocol, PacketLoginInStart, LoginListener, LoginListener$LoginHandler) no longer exist on modern Paper builds. The static block in ClassNames threw on load and the plugin failed to inject. Try the Mojang-mapped name first for each class, falling back to the old Spigot name and then the version-prefixed NMS name: NetworkManager -> Connection ServerConnection -> ServerConnectionListener PacketHandshakingInSetProtocol -> ClientIntentionPacket PacketLoginInStart -> ServerboundHelloPacket LoginListener -> ServerLoginPacketListenerImpl LoginListener$LoginHandler -> ServerLoginPacketListenerImpl$LoginHandler Same pattern for the handshake packet field names: try the Mojang names protocolVersion/port/intention, fall back to obfuscated a/c/d (or b/d on the 1.20.5 obfuscated stream-codec layout). Cross-checked against Floodgate master, which uses the same Mojang class names. Backward compatible with older Spigot/Paper.
robinbraemer
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Summary
The Spigot/Paper plugin failed to enable on modern Paper, Spigot, and Mojang-mapped servers with:
Since Paper 1.20.5, NMS classes ship under their Mojang names. Our reflection bootstrap in
ClassNamesonly looked up the old Spigot names, so the static initializer threw on every server that didn't transparently remap the JAR for us.Stock Paper has been hiding the bug at runtime by auto-rewriting the FQN string literals via its
PluginRemapper, but the moment the remapper is bypassed (Spigot, Paper forks, plugins built withapi-version >= 1.20.5orpaperweight-mappings-namespace: mojang, or-Dpaper.disablePluginRemapping=true) the bug is exposed.This change tries the Mojang name first for each NMS class, falls back to the old Spigot name, and finally to the version-prefixed NMS name — so we resolve correctly without depending on Paper's remapper.
Class lookups
NetworkManagerConnectionServerConnectionServerConnectionListenerPacketHandshakingInSetProtocolClientIntentionPacketPacketLoginInStartServerboundHelloPacketLoginListenerServerLoginPacketListenerImplLoginListener$LoginHandlerServerLoginPacketListenerImpl$LoginHandlerSame pattern for the handshake packet field names — try Mojang
protocolVersion/port/intentionfirst, fall back to obfuscateda/c/d(1.20.2–1.20.4) orb/d(1.20.5 stream-codec layout).Cross-checked against Floodgate master — same Mojang names, same fallback strategy.
Builds on the partial Mojmap fix in 4b026ae (which only patched
packetListener/qandstartClientVerification/b).Verification
Tested locally on Paper 1.21.11 (build 69, Java 21):
-Dpaper.disablePluginRemapping=true)ClassNotFoundException: net.minecraft.server.ServerConnectionConfiguration 2 reproduces the original user report; configuration 3 proves the fix stands on its own merits.
Credits
Diagnosis based on a v26.1.2 patch shared by ChannyAnh in our community Discord.