Panic when using sessions

[hsanjuan]

This:

func TestSession(t *testing.T) {
	ctx := context.Background()
	p1, p2, closer := setupPeers(t)
	defer closer(t)

	m := map[string]string{
		"akey": "avalue",
	}

	codec := uint64(multihash.SHA2_256)
	node, err := cbor.WrapObject(m, codec, multihash.DefaultLengths[codec])
	if err != nil {
		t.Fatal(err)
	}

	t.Log("created node: ", node.Cid())
	err = p1.Add(ctx, node)
	if err != nil {
		t.Fatal(err)
	}

	sesGetter := p2.Session(ctx)
	_, err = sesGetter.Get(ctx, node.Cid())
	if err != nil {
		t.Fatal(err)
	}
}

results in:

--- FAIL: TestSession (0.63s)
    ipfs_test.go:151: created node:  bafyreigzkampgfuhmld36ljrywwcxogf5zyjbkasehbggbmgpy5tmrygpe
panic: runtime error: invalid memory address or nil pointer dereference [recovered]
        panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x4ee586]

goroutine 597 [running]:
testing.tRunner.func1(0xc0003a5e00)
        /usr/lib64/go/1.12/src/testing/testing.go:830 +0x392
panic(0xbbefc0, 0x150a8c0)
        /usr/lib64/go/1.12/src/runtime/panic.go:522 +0x1b5
context.propagateCancel(0x0, 0x0, 0xed0760, 0xc000372b80)
        /usr/lib64/go/1.12/src/context/context.go:242 +0x26
context.WithCancel(0x0, 0x0, 0x7, 0x2a, 0x0)
        /usr/lib64/go/1.12/src/context/context.go:231 +0x9c
github.com/ipfs/go-bitswap/sessionmanager.(*SessionManager).NewSession(0xc00065a180, 0x0, 0x0, 0x0, 0xc0005e3ce8)
        /home/hector/go/pkg/mod/github.com/ipfs/go-bitswap@v0.0.9/sessionmanager/sessionmanager.go:69 +0x6b
github.com/ipfs/go-bitswap.(*Bitswap).NewSession(0xc0000c5970, 0x0, 0x0, 0x40452f, 0xc0005e3d50)
        /home/hector/go/pkg/mod/github.com/ipfs/go-bitswap@v0.0.9/bitswap.go:401 +0x46
github.com/ipfs/go-blockservice.(*Session).getSession(0xc00036eaa0, 0x0, 0x0)
        /home/hector/go/pkg/mod/github.com/ipfs/go-blockservice@v0.0.6/blockservice.go:337 +0xbe
github.com/ipfs/go-blockservice.getBlock(0xedb4c0, 0xc0000ac010, 0xc000456450, 0x24, 0xee2360, 0xc0003131a0, 0xc0005e3e50, 0xc0000100f0, 0xc0005e3e78, 0x8de929, ...)
        /home/hector/go/pkg/mod/github.com/ipfs/go-blockservice@v0.0.6/blockservice.go:224 +0x209
github.com/ipfs/go-blockservice.(*Session).GetBlock(0xc00036eaa0, 0xedb4c0, 0xc0000ac010, 0xc000456450, 0x24, 0xc0004b4aa0, 0x7f924dc83f50, 0xc0004b4aa0, 0xc0003a5e01)
        /home/hector/go/pkg/mod/github.com/ipfs/go-blockservice@v0.0.6/blockservice.go:345 +0x92
github.com/ipfs/go-merkledag.(*sesGetter).Get(0xc0000100f0, 0xedb4c0, 0xc0000ac010, 0xc000456450, 0x24, 0x0, 0x0, 0xc0000b27c0, 0x29)
        /home/hector/go/pkg/mod/github.com/ipfs/go-merkledag@v0.0.3/merkledag.go:136 +0x66
github.com/hsanjuan/ipfs-lite.TestSession(0xc0003a5e00)
        /home/hector/go/src/github.com/hsanjuan/ipfs-lite/ipfs_test.go:158 +0x361
testing.tRunner(0xc0003a5e00, 0xe00b40)

[hsanjuan]

This seems to come from: ipfs/go-blockservice@4b230aa

The s.sessCtx field is never set and a nil object travels down the stack

[Stebalien]

ipfs/go-blockservice#28