Index out of range in generated code

[keks]

I ran into a panic in generated code, specifically version 0.2.0 of go-graphsync. The code uses gogo version 1.3.1, but I checked the diff to 1.3.2 and it doesn't look like the issue has been fixed.

When calling message.FromNet with a reader that returns the following bytes/string, the generated code panics with the attached stack trace. The affected code does not use gogo anymore, but other users of gogo may experience similar issues.

Input: $\x1a \x8000\x1a\x16002\xf4\xff\xff\xff\xff\xff\xff\xff\xff00000000000000000

Stack Trace:

panic: runtime error: index out of range [-9223372036854775802]
goroutine 6 [running]:
runtime/debug.Stack(0xc00008f5e0, 0x8824e0, 0xc000028bc0)
        /usr/local/go/src/runtime/debug/stack.go:24 +0x9f
github.com/leastauthority/fleece/fuzzing.(*Crasher).Recover(0xc0000a4b80, 0xc00018fd80)
        /home/user/Projects/fleece/fuzzing/crasher.go:23 +0x57
panic(0x8824e0, 0xc000028bc0)    
        /usr/local/go/src/runtime/panic.go:969 +0x175       
github.com/ipfs/go-graphsync/message/pb.(*Message_Response).Unmarshal(0xc000093470, 0xc0001da1b2, 0x20, 0x22, 0x1, 0xc000093470)       
        /home/user/go/pkg/mod/github.com/ipfs/[email protected]/message/pb/message.pb.go:1343 +0x1025
github.com/ipfs/go-graphsync/message/pb.(*Message).Unmarshal(0xc0000b0460, 0xc0001da1b0, 0x24, 0x24, 0x7ff5c
4e00f01, 0x7ff5c45d5c58)   
        /home/user/go/pkg/mod/github.com/ipfs/[email protected]/message/pb/message.pb.go:843 +0x773
github.com/ipfs/go-graphsync/message/pb.(*Message).XXX_Unmarshal(0xc0000b0460, 0xc0001da1b0, 0x24, 0x24, 0xc
0000b0460, 0x1)            
        /home/user/go/pkg/mod/github.com/ipfs/[email protected]/message/pb/message.pb.go:42 +0x49
github.com/gogo/protobuf/proto.Unmarshal(0xc0001da1b0, 0x24, 0x24, 0xa58360, 0xc0000b0460, 0x24, 0x24)      
        /home/user/go/pkg/mod/github.com/gogo/[email protected]/proto/decode.go:337 +0x1aa
github.com/gogo/protobuf/io.(*varintReader).ReadMsg(0xc0000a4bc0, 0xa58360, 0xc0000b0460, 0x7fb18d, 0x0)    
        /home/user/go/pkg/mod/github.com/gogo/[email protected]/io/varint.go:125 +0x147
github.com/ipfs/go-graphsync/message.FromPBReader(0x7ff5c45d5c38, 0xc0000a4bc0, 0xc0000a4bc0, 0x7ff5c45d5c38
, 0xc0000a4bc0, 0xc0000bbc20)                         
        /home/user/go/pkg/mod/github.com/ipfs/[email protected]/message/message.go:270 +0x74
github.com/ipfs/go-graphsync/message.FromNet(0xa514a0, 0xc0000bbc20, 0xc00008fbf8, 0x5099ff, 0xc000001b00, 0
x7ff5c45d5bf8)             
        /home/user/go/pkg/mod/github.com/ipfs/[email protected]/message/message.go:264 +0x85
github.com/ipfs/go-graphsync/message.FuzzFromNetToNet(0xc0000e4240, 0x25, 0x225, 0x0)
        /home/user/go/pkg/mod/github.com/ipfs/[email protected]/message/message_fuzz.go:16 +0x75
github.com/leastauthority/fleece/fuzzing.(*Crasher).Test(0xc0000a4b80, 0xc00008fd80)
        /home/user/Projects/fleece/fuzzing/crasher.go:31 +0x7b
github.com/leastauthority/fleece/fuzzing.CrasherIterator.TestFailingLimit(0xc0000933c0, 0x1, 0x0, 0xc0000100
80, 0x1, 0x1, 0xc0001a7200, 0x8d, 0x8d, 0x9f1b78, ...)
        /home/user/Projects/fleece/fuzzing/iterator.go:109 +0xf0
github.com/ipfs/go-graphsync/message.TestFuzzFromNetToNet(0xc000001b00)
        /home/user/go/pkg/mod/github.com/ipfs/[email protected]/message/message_fuzz_test.go:38 +0x151
testing.tRunner(0xc000001b00, 0x9f1ba0)
        /usr/local/go/src/testing/testing.go:1108 +0xef
created by testing.(*T).Run 
        /usr/local/go/src/testing/testing.go:1159 +0x386