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fix: serialize socket writes to prevent protocol corruption under concurrent goroutines #2

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fix: serialize socket writes to prevent protocol corruption under concurrent goroutines #2

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9 changes: 8 additions & 1 deletion contract/plugin.go
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Original file line number Diff line number Diff line change
Expand Up @@ -24,7 +24,8 @@ type Plugin struct {
conn net.Conn // the underlying unix sock file connection
pending map[uint64]chan isFSMToPlugin_Payload // the outstanding requests from the contract
requestContract map[uint64]*Contract // maps request IDs to their contract context for concurrent operations
l sync.Mutex // thread safety
l sync.Mutex // thread safety for pending/requestContract maps
writeMu sync.Mutex // thread safety for concurrent writes to the socket connection
config Config // general app config
}

Expand Down Expand Up @@ -266,6 +267,12 @@ func (p *Plugin) sendLengthPrefixed(bz []byte) *PluginError {
// create the length prefix (4 bytes, big endian)
lengthPrefix := make([]byte, 4)
binary.BigEndian.PutUint32(lengthPrefix, uint32(len(bz)))
// serialize writes: ListenForInbound() spawns a goroutine per inbound message, and each
// can independently write to the shared connection (either as a direct FSM response or
// via a nested StateRead/StateWrite call). Without this lock, concurrent writers can
// interleave mid-message and corrupt the length-prefixed framing on the wire.
p.writeMu.Lock()
defer p.writeMu.Unlock()
// write the message (length prefixed)
if _, er := p.conn.Write(append(lengthPrefix, bz...)); er != nil {
return ErrFailedPluginWrite(er)
Expand Down