// CountRanges returns the number of ranges that encompass the given key span.
func (ds *DistSender) CountRanges(rs roachpb.RSpan) (int64, *roachpb.Error) {
	var count int64
	for {
		desc, needAnother, _, pErr := ds.getDescriptors(rs, evictionToken{}, false /*useReverseScan*/)
		if pErr != nil {
			return -1, pErr
		}
		count++
		if !needAnother {
			break
		}
		rs.Key = desc.EndKey
	}
	return count, nil
}

// CountRanges returns the number of ranges that encompass the given key span.
func (ds *DistSender) CountRanges(rs roachpb.RSpan) (int64, error) {
	var count int64
	for {
		desc, needAnother, _, err := ds.getDescriptors(
			context.Background(), rs, nil, false /*useReverseScan*/)
		if err != nil {
			return -1, err
		}
		count++
		if !needAnother {
			break
		}
		rs.Key = desc.EndKey
	}
	return count, nil
}

//.........这里部分代码省略.........
			keys:    [][2]string{{loc("a"), loc("b")}},
			expKeys: [][2]string{{locPrefix("b"), loc("b")}},
			from:    "b", to: "e",
		},
		{
			// Range-local range contained in active range.
			keys:    [][2]string{{locPrefix("b"), loc("b")}},
			expKeys: [][2]string{{locPrefix("b"), loc("b")}},
			from:    "b", to: "c",
		},
		{
			// Mixed range-local vs global key range.
			keys: [][2]string{{loc("c"), "d\x00"}},
			from: "b", to: "e",
			err: "local key mixed with global key",
		},
		{
			// Key range touching and intersecting active range.
			keys:    [][2]string{{"a", "b"}, {"a", "c"}, {"p", "q"}, {"p", "r"}, {"a", "z"}},
			expKeys: [][2]string{{}, {"b", "c"}, {"p", "q"}, {"p", "q"}, {"b", "q"}},
			from:    "b", to: "q",
		},
		// Active key range is intersection of descriptor and [from,to).
		{
			keys:    [][2]string{{"c", "q"}},
			expKeys: [][2]string{{"d", "p"}},
			from:    "a", to: "z",
			desc: [2]string{"d", "p"},
		},
		{
			keys:    [][2]string{{"c", "q"}},
			expKeys: [][2]string{{"d", "p"}},
			from:    "d", to: "p",
			desc: [2]string{"a", "z"},
		},
	}

	for i, test := range testCases {
		goldenOriginal := roachpb.BatchRequest{}
		for _, ks := range test.keys {
			if len(ks[1]) > 0 {
				goldenOriginal.Add(&roachpb.ResolveIntentRangeRequest{
					Span:      roachpb.Span{Key: roachpb.Key(ks[0]), EndKey: roachpb.Key(ks[1])},
					IntentTxn: roachpb.TxnMeta{ID: uuid.NewV4()},
				})
			} else {
				goldenOriginal.Add(&roachpb.GetRequest{
					Span: roachpb.Span{Key: roachpb.Key(ks[0])},
				})
			}
		}

		original := roachpb.BatchRequest{Requests: make([]roachpb.RequestUnion, len(goldenOriginal.Requests))}
		for i, request := range goldenOriginal.Requests {
			original.Requests[i].SetValue(request.GetInner().ShallowCopy())
		}

		desc := &roachpb.RangeDescriptor{
			StartKey: roachpb.RKey(test.desc[0]), EndKey: roachpb.RKey(test.desc[1]),
		}
		if len(desc.StartKey) == 0 {
			desc.StartKey = roachpb.RKey(test.from)
		}
		if len(desc.EndKey) == 0 {
			desc.EndKey = roachpb.RKey(test.to)
		}
		rs := roachpb.RSpan{Key: roachpb.RKey(test.from), EndKey: roachpb.RKey(test.to)}
		rs, err := rs.Intersect(desc)
		if err != nil {
			t.Errorf("%d: intersection failure: %v", i, err)
			continue
		}
		ba, num, err := truncate(original, rs)
		if err != nil || test.err != "" {
			if test.err == "" || !testutils.IsError(err, test.err) {
				t.Errorf("%d: %v (expected: %s)", i, err, test.err)
			}
			continue
		}
		var reqs int
		for j, arg := range ba.Requests {
			req := arg.GetInner()
			if h := req.Header(); !bytes.Equal(h.Key, roachpb.Key(test.expKeys[j][0])) || !bytes.Equal(h.EndKey, roachpb.Key(test.expKeys[j][1])) {
				t.Errorf("%d.%d: range mismatch: actual [%q,%q), wanted [%q,%q)", i, j,
					h.Key, h.EndKey, test.expKeys[j][0], test.expKeys[j][1])
			} else if _, ok := req.(*roachpb.NoopRequest); ok != (len(h.Key) == 0) {
				t.Errorf("%d.%d: expected NoopRequest, got %T", i, j, req)
			} else if len(h.Key) != 0 {
				reqs++
			}
		}
		if reqs != num {
			t.Errorf("%d: counted %d requests, but truncation indicated %d", i, reqs, num)
		}
		if !reflect.DeepEqual(original, goldenOriginal) {
			t.Errorf("%d: truncation mutated original:\nexpected: %s\nactual: %s",
				i, goldenOriginal, original)
		}
	}
}

// truncate restricts all contained requests to the given key range.
// Even on error, the returned closure must be executed; it undoes any
// truncations performed.
// All requests contained in the batch are "truncated" to the given
// span, inserting NoopRequest appropriately to replace requests which
// are left without a key range to operate on. The number of non-noop
// requests after truncation is returned along with a closure which
// must be executed to undo the truncation, even in case of an error.
// TODO(tschottdorf): Consider returning a new BatchRequest, which has more
// overhead in the common case of a batch which never needs truncation but is
// less magical.
func truncate(br *roachpb.BatchRequest, rs roachpb.RSpan) (func(), int, error) {
	truncateOne := func(args roachpb.Request) (bool, []func(), error) {
		if _, ok := args.(*roachpb.NoopRequest); ok {
			return true, nil, nil
		}
		header := args.Header()
		if !roachpb.IsRange(args) {
			// This is a point request.
			if len(header.EndKey) > 0 {
				return false, nil, util.Errorf("%T is not a range command, but EndKey is set", args)
			}
			if !rs.ContainsKey(keys.Addr(header.Key)) {
				return true, nil, nil
			}
			return false, nil, nil
		}
		// We're dealing with a range-spanning request.
		var undo []func()
		keyAddr, endKeyAddr := keys.Addr(header.Key), keys.Addr(header.EndKey)
		if l, r := !keyAddr.Equal(header.Key), !endKeyAddr.Equal(header.EndKey); l || r {
			if !rs.ContainsKeyRange(keyAddr, endKeyAddr) {
				return false, nil, util.Errorf("local key range must not span ranges")
			}
			if !l || !r {
				return false, nil, util.Errorf("local key mixed with global key in range")
			}
			return false, nil, nil
		}
		// Below, {end,}keyAddr equals header.{End,}Key, so nothing is local.
		if keyAddr.Less(rs.Key) {
			{
				origKey := header.Key
				undo = append(undo, func() { header.Key = origKey })
			}
			header.Key = rs.Key.AsRawKey() // "key" can't be local
			keyAddr = rs.Key
		}
		if !endKeyAddr.Less(rs.EndKey) {
			{
				origEndKey := header.EndKey
				undo = append(undo, func() { header.EndKey = origEndKey })
			}
			header.EndKey = rs.EndKey.AsRawKey() // "endKey" can't be local
			endKeyAddr = rs.EndKey
		}
		// Check whether the truncation has left any keys in the range. If not,
		// we need to cut it out of the request.
		return !keyAddr.Less(endKeyAddr), undo, nil
	}

	var fns []func()
	gUndo := func() {
		for _, f := range fns {
			f()
		}
	}

	var numNoop int
	for pos, arg := range br.Requests {
		omit, undo, err := truncateOne(arg.GetInner())
		if omit {
			numNoop++
			nReq := &roachpb.RequestUnion{}
			if !nReq.SetValue(&roachpb.NoopRequest{}) {
				panic("RequestUnion excludes NoopRequest")
			}
			oReq := br.Requests[pos]
			br.Requests[pos] = *nReq
			posCpy := pos // for closure
			undo = append(undo, func() {
				br.Requests[posCpy] = oReq
			})
		}
		fns = append(fns, undo...)
		if err != nil {
			return gUndo, 0, err
		}
	}
	return gUndo, len(br.Requests) - numNoop, nil
}

// truncate restricts all contained requests to the given key range
// and returns a new BatchRequest.
// All requests contained in that batch are "truncated" to the given
// span, inserting NoopRequest appropriately to replace requests which
// are left without a key range to operate on. The number of non-noop
// requests after truncation is returned.
func truncate(ba roachpb.BatchRequest, rs roachpb.RSpan) (roachpb.BatchRequest, int, error) {
	truncateOne := func(args roachpb.Request) (bool, roachpb.Span, error) {
		if _, ok := args.(*roachpb.NoopRequest); ok {
			return true, emptySpan, nil
		}
		header := args.Header()
		if !roachpb.IsRange(args) {
			// This is a point request.
			if len(header.EndKey) > 0 {
				return false, emptySpan, errors.Errorf("%T is not a range command, but EndKey is set", args)
			}
			keyAddr, err := keys.Addr(header.Key)
			if err != nil {
				return false, emptySpan, err
			}
			if !rs.ContainsKey(keyAddr) {
				return false, emptySpan, nil
			}
			return true, header, nil
		}
		// We're dealing with a range-spanning request.
		local := false
		keyAddr, err := keys.Addr(header.Key)
		if err != nil {
			return false, emptySpan, err
		}
		endKeyAddr, err := keys.Addr(header.EndKey)
		if err != nil {
			return false, emptySpan, err
		}
		if l, r := !keyAddr.Equal(header.Key), !endKeyAddr.Equal(header.EndKey); l || r {
			if !l || !r {
				return false, emptySpan, errors.Errorf("local key mixed with global key in range")
			}
			local = true
		}
		if keyAddr.Less(rs.Key) {
			// rs.Key can't be local because it contains range split points, which
			// are never local.
			if !local {
				header.Key = rs.Key.AsRawKey()
			} else {
				// The local start key should be truncated to the boundary of local keys which
				// address to rs.Key.
				header.Key = keys.MakeRangeKeyPrefix(rs.Key)
			}
		}
		if !endKeyAddr.Less(rs.EndKey) {
			// rs.EndKey can't be local because it contains range split points, which
			// are never local.
			if !local {
				header.EndKey = rs.EndKey.AsRawKey()
			} else {
				// The local end key should be truncated to the boundary of local keys which
				// address to rs.EndKey.
				header.EndKey = keys.MakeRangeKeyPrefix(rs.EndKey)
			}
		}
		// Check whether the truncation has left any keys in the range. If not,
		// we need to cut it out of the request.
		if header.Key.Compare(header.EndKey) >= 0 {
			return false, emptySpan, nil
		}
		return true, header, nil
	}

	var numNoop int
	origRequests := ba.Requests
	ba.Requests = make([]roachpb.RequestUnion, len(ba.Requests))
	for pos, arg := range origRequests {
		hasRequest, newHeader, err := truncateOne(arg.GetInner())
		if !hasRequest {
			// We omit this one, i.e. replace it with a Noop.
			numNoop++
			union := roachpb.RequestUnion{}
			union.MustSetInner(&noopRequest)
			ba.Requests[pos] = union
		} else {
			// Keep the old one. If we must adjust the header, must copy.
			if inner := origRequests[pos].GetInner(); newHeader.Equal(inner.Header()) {
				ba.Requests[pos] = origRequests[pos]
			} else {
				shallowCopy := inner.ShallowCopy()
				shallowCopy.SetHeader(newHeader)
				union := &ba.Requests[pos] // avoid operating on copy
				union.MustSetInner(shallowCopy)
			}
		}
		if err != nil {
			return roachpb.BatchRequest{}, 0, err
		}
	}
	return ba, len(ba.Requests) - numNoop, nil
}

//.........这里部分代码省略.........
		},
		{
			// Range-local range contained in active range.
			keys:    [][2]string{{loc("b"), loc("e") + "\x00"}},
			expKeys: [][2]string{{loc("b"), loc("e") + "\x00"}},
			from:    "b", to: "e\x00",
		},

		{
			// Range-local range not contained in active range.
			keys: [][2]string{{loc("a"), loc("b")}},
			from: "b", to: "e",
			err: "local key range must not span ranges",
		},
		{
			// Mixed range-local vs global key range.
			keys: [][2]string{{loc("c"), "d\x00"}},
			from: "b", to: "e",
			err: "local key mixed with global key",
		},
		{
			// Key range touching and intersecting active range.
			keys:    [][2]string{{"a", "b"}, {"a", "c"}, {"p", "q"}, {"p", "r"}, {"a", "z"}},
			expKeys: [][2]string{{}, {"b", "c"}, {"p", "q"}, {"p", "q"}, {"b", "q"}},
			from:    "b", to: "q",
		},
		// Active key range is intersection of descriptor and [from,to).
		{
			keys:    [][2]string{{"c", "q"}},
			expKeys: [][2]string{{"d", "p"}},
			from:    "a", to: "z",
			desc: [2]string{"d", "p"},
		},
		{
			keys:    [][2]string{{"c", "q"}},
			expKeys: [][2]string{{"d", "p"}},
			from:    "d", to: "p",
			desc: [2]string{"a", "z"},
		},
	}

	for i, test := range testCases {
		ba := &roachpb.BatchRequest{}
		for _, ks := range test.keys {
			if len(ks[1]) > 0 {
				ba.Add(&roachpb.ScanRequest{
					Span: roachpb.Span{Key: roachpb.Key(ks[0]), EndKey: roachpb.Key(ks[1])},
				})
			} else {
				ba.Add(&roachpb.GetRequest{
					Span: roachpb.Span{Key: roachpb.Key(ks[0])},
				})
			}
		}
		original := proto.Clone(ba).(*roachpb.BatchRequest)

		desc := &roachpb.RangeDescriptor{
			StartKey: roachpb.RKey(test.desc[0]), EndKey: roachpb.RKey(test.desc[1]),
		}
		if len(desc.StartKey) == 0 {
			desc.StartKey = roachpb.RKey(test.from)
		}
		if len(desc.EndKey) == 0 {
			desc.EndKey = roachpb.RKey(test.to)
		}
		rs := roachpb.RSpan{Key: roachpb.RKey(test.from), EndKey: roachpb.RKey(test.to)}
		rs, err := rs.Intersect(desc)
		if err != nil {
			t.Errorf("%d: intersection failure: %v", i, err)
			continue
		}
		undo, num, err := truncate(ba, rs)
		if err != nil || test.err != "" {
			if test.err == "" || !testutils.IsError(err, test.err) {
				t.Errorf("%d: %v (expected: %s)", i, err, test.err)
			}
			continue
		}
		var reqs int
		for j, arg := range ba.Requests {
			req := arg.GetInner()
			if h := req.Header(); !bytes.Equal(h.Key, roachpb.Key(test.expKeys[j][0])) || !bytes.Equal(h.EndKey, roachpb.Key(test.expKeys[j][1])) {
				t.Errorf("%d.%d: range mismatch: actual [%q,%q), wanted [%q,%q)", i, j,
					h.Key, h.EndKey, test.expKeys[j][0], test.expKeys[j][1])
			} else if _, ok := req.(*roachpb.NoopRequest); ok != (len(h.Key) == 0) {
				t.Errorf("%d.%d: expected NoopRequest, got %T", i, j, req)
			} else if len(h.Key) != 0 {
				reqs++
			}
		}
		if reqs != num {
			t.Errorf("%d: counted %d requests, but truncation indicated %d", i, reqs, num)
		}
		undo()
		if !reflect.DeepEqual(ba, original) {
			t.Errorf("%d: undoing truncation failed:\nexpected: %s\nactual: %s",
				i, original, ba)
		}
	}
}

// truncate restricts all contained requests to the given key range
// and returns a new BatchRequest.
// All requests contained in that batch are "truncated" to the given
// span, inserting NoopRequest appropriately to replace requests which
// are left without a key range to operate on. The number of non-noop
// requests after truncation is returned.
func truncate(ba roachpb.BatchRequest, rs roachpb.RSpan) (roachpb.BatchRequest, int, error) {
	truncateOne := func(args roachpb.Request) (bool, roachpb.Span, error) {
		if _, ok := args.(*roachpb.NoopRequest); ok {
			return true, emptySpan, nil
		}
		header := *args.Header()
		if !roachpb.IsRange(args) {
			// This is a point request.
			if len(header.EndKey) > 0 {
				return false, emptySpan, util.Errorf("%T is not a range command, but EndKey is set", args)
			}
			if !rs.ContainsKey(keys.Addr(header.Key)) {
				return false, emptySpan, nil
			}
			return true, header, nil
		}
		// We're dealing with a range-spanning request.
		keyAddr, endKeyAddr := keys.Addr(header.Key), keys.Addr(header.EndKey)
		if l, r := !keyAddr.Equal(header.Key), !endKeyAddr.Equal(header.EndKey); l || r {
			if !rs.ContainsKeyRange(keyAddr, endKeyAddr) {
				return false, emptySpan, util.Errorf("local key range must not span ranges")
			}
			if !l || !r {
				return false, emptySpan, util.Errorf("local key mixed with global key in range")
			}
			// Range-local local key range.
			return true, header, nil
		}
		// Below, {end,}keyAddr equals header.{End,}Key, so nothing is local.
		if keyAddr.Less(rs.Key) {
			header.Key = rs.Key.AsRawKey() // "key" can't be local
			keyAddr = rs.Key
		}
		if !endKeyAddr.Less(rs.EndKey) {
			header.EndKey = rs.EndKey.AsRawKey() // "endKey" can't be local
			endKeyAddr = rs.EndKey
		}
		// Check whether the truncation has left any keys in the range. If not,
		// we need to cut it out of the request.
		if !keyAddr.Less(endKeyAddr) {
			return false, emptySpan, nil
		}
		return true, header, nil
	}

	var numNoop int
	origRequests := ba.Requests
	ba.Requests = make([]roachpb.RequestUnion, len(ba.Requests))
	for pos, arg := range origRequests {
		hasRequest, newHeader, err := truncateOne(arg.GetInner())
		if !hasRequest {
			// We omit this one, i.e. replace it with a Noop.
			numNoop++
			nReq := roachpb.RequestUnion{}
			if !nReq.SetValue(&roachpb.NoopRequest{}) {
				panic("RequestUnion excludes NoopRequest")
			}
			ba.Requests[pos] = nReq
		} else {
			// Keep the old one. If we must adjust the header, must copy.
			// TODO(tschottdorf): this could wind up cloning big chunks of data.
			// Can optimize by creating a new Request manually, but with the old
			// data.
			if newHeader.Equal(*origRequests[pos].GetInner().Header()) {
				ba.Requests[pos] = origRequests[pos]
			} else {
				ba.Requests[pos] = *proto.Clone(&origRequests[pos]).(*roachpb.RequestUnion)
				*ba.Requests[pos].GetInner().Header() = newHeader
			}
		}
		if err != nil {
			return roachpb.BatchRequest{}, 0, err
		}
	}
	return ba, len(ba.Requests) - numNoop, nil
}

// truncate restricts all contained requests to the given key range
// and returns a new BatchRequest.
// All requests contained in that batch are "truncated" to the given
// span, inserting NoopRequest appropriately to replace requests which
// are left without a key range to operate on. The number of non-noop
// requests after truncation is returned.
func truncate(ba roachpb.BatchRequest, rs roachpb.RSpan) (roachpb.BatchRequest, int, error) {
	truncateOne := func(args roachpb.Request) (bool, roachpb.Span, error) {
		if _, ok := args.(*roachpb.NoopRequest); ok {
			return true, emptySpan, nil
		}
		header := args.Header()
		if !roachpb.IsRange(args) {
			// This is a point request.
			if len(header.EndKey) > 0 {
				return false, emptySpan, util.Errorf("%T is not a range command, but EndKey is set", args)
			}
			if !rs.ContainsKey(keys.Addr(header.Key)) {
				return false, emptySpan, nil
			}
			return true, header, nil
		}
		// We're dealing with a range-spanning request.
		keyAddr, endKeyAddr := keys.Addr(header.Key), keys.Addr(header.EndKey)
		if l, r := !keyAddr.Equal(header.Key), !endKeyAddr.Equal(header.EndKey); l || r {
			if !rs.ContainsKeyRange(keyAddr, endKeyAddr) {
				return false, emptySpan, util.Errorf("local key range must not span ranges")
			}
			if !l || !r {
				return false, emptySpan, util.Errorf("local key mixed with global key in range")
			}
			// Range-local local key range.
			return true, header, nil
		}
		// Below, {end,}keyAddr equals header.{End,}Key, so nothing is local.
		if keyAddr.Less(rs.Key) {
			header.Key = rs.Key.AsRawKey() // "key" can't be local
			keyAddr = rs.Key
		}
		if !endKeyAddr.Less(rs.EndKey) {
			header.EndKey = rs.EndKey.AsRawKey() // "endKey" can't be local
			endKeyAddr = rs.EndKey
		}
		// Check whether the truncation has left any keys in the range. If not,
		// we need to cut it out of the request.
		if !keyAddr.Less(endKeyAddr) {
			return false, emptySpan, nil
		}
		return true, header, nil
	}

	var numNoop int
	origRequests := ba.Requests
	ba.Requests = make([]roachpb.RequestUnion, len(ba.Requests))
	for pos, arg := range origRequests {
		hasRequest, newHeader, err := truncateOne(arg.GetInner())
		if !hasRequest {
			// We omit this one, i.e. replace it with a Noop.
			numNoop++
			union := roachpb.RequestUnion{}
			if !union.SetInner(&noopRequest) {
				panic(fmt.Sprintf("%T excludes %T", union, noopRequest))
			}
			ba.Requests[pos] = union
		} else {
			// Keep the old one. If we must adjust the header, must copy.
			if inner := origRequests[pos].GetInner(); newHeader.Equal(inner.Header()) {
				ba.Requests[pos] = origRequests[pos]
			} else {
				shallowCopy := inner.ShallowCopy()
				shallowCopy.SetHeader(newHeader)
				if union := &ba.Requests[pos]; !union.SetInner(shallowCopy) {
					panic(fmt.Sprintf("%T excludes %T", union, shallowCopy))
				}
			}
		}
		if err != nil {
			return roachpb.BatchRequest{}, 0, err
		}
	}
	return ba, len(ba.Requests) - numNoop, nil
}