Ramón MárquezandGitHub
ef925b70b4
The `copySlice` function inside `tcp_packet.go` wouldn't copy elements from the `from` slices to the `to` slice, even when the `to` slice has "space" to spare due to its `cap` being larger than the `totalLen`:
```go
func copySlice(to []byte, skip int, from ...[]byte) ([]byte, int) {
var totalLen int
for _, s := range from {
totalLen += len(s)
}
totalLen += skip
if cap(to) < totalLen {
diff := totalLen - cap(to)
to = append(to, make([]byte, diff)...)
}
for _, s := range from {
skip += copy(to[skip:], s)
}
return to, skip
}
```
This is caused because Go's `copy` function used in `copySlice` will copy a number of elements ["which will be the minimum of len(src) and len(dst)."](https://pkg.go.dev/builtin#copy). For the built-in copy function to copy elements into a slice, the destination slots must be initialized for this slice, not just allocated in the underlying array. In other words, `len` must be used instead of `cap` to allow `copy` to work properly.
This PR closes #1095, which is an example of the effects of this issue: when mirroring packets using VXLAN, the raw payloads obtained using the vxlan engine can be large due to encapsulation. This has the effect of giving the `tmp` slice a large `cap` when `PacketData()` is called inside `tcp_message.go`. Then, the `to` slice is never resized in `copySlice` and only the first packet is read, without the rest (e.g. no response body, only headers are read).
https://goreplay.org/
GoReplay is an open-source network monitoring tool which can record your live traffic and use it for shadowing, load testing, monitoring and detailed analysis.
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As your application grows, the effort required to test it also grows exponentially. GoReplay offers you the simple idea of reusing your existing traffic for testing, which makes it incredibly powerful. Our state of art technique allows you to analyze and record your application traffic without affecting it. This eliminates the risks that come with putting a third party component in the critical path.
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