comparison osx/include/capnp/arena.h @ 134:41e769c91eca

Add Capnp and KJ builds for OSX

+// Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
+// Licensed under the MIT License:
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+#ifndef CAPNP_ARENA_H_
+#define CAPNP_ARENA_H_
+
+#if defined(__GNUC__) && !defined(CAPNP_HEADER_WARNINGS)
+#pragma GCC system_header
+#endif
+
+#ifndef CAPNP_PRIVATE
+#error "This header is only meant to be included by Cap'n Proto's own source code."
+#endif
+
+#include <kj/common.h>
+#include <kj/mutex.h>
+#include <kj/exception.h>
+#include <kj/vector.h>
+#include "common.h"
+#include "message.h"
+#include "layout.h"
+#include <unordered_map>
+
+#if !CAPNP_LITE
+#include "capability.h"
+#endif  // !CAPNP_LITE
+
+namespace capnp {
+
+#if !CAPNP_LITE
+class ClientHook;
+#endif  // !CAPNP_LITE
+
+namespace _ {  // private
+
+class SegmentReader;
+class SegmentBuilder;
+class Arena;
+class BuilderArena;
+class ReadLimiter;
+
+class Segment;
+typedef kj::Id<uint32_t, Segment> SegmentId;
+
+class ReadLimiter {
+  // Used to keep track of how much data has been processed from a message, and cut off further
+  // processing if and when a particular limit is reached.  This is primarily intended to guard
+  // against maliciously-crafted messages which contain cycles or overlapping structures.  Cycles
+  // and overlapping are not permitted by the Cap'n Proto format because in many cases they could
+  // be used to craft a deceptively small message which could consume excessive server resources to
+  // process, perhaps even sending it into an infinite loop.  Actually detecting overlaps would be
+  // time-consuming, so instead we just keep track of how many words worth of data structures the
+  // receiver has actually dereferenced and error out if this gets too high.
+  //
+  // This counting takes place as you call getters (for non-primitive values) on the message
+  // readers.  If you call the same getter twice, the data it returns may be double-counted.  This
+  // should not be a big deal in most cases -- just set the read limit high enough that it will
+  // only trigger in unreasonable cases.
+  //
+  // This class is "safe" to use from multiple threads for its intended use case.  Threads may
+  // overwrite each others' changes to the counter, but this is OK because it only means that the
+  // limit is enforced a bit less strictly -- it will still kick in eventually.
+
+public:
+  inline explicit ReadLimiter();                     // No limit.
+  inline explicit ReadLimiter(WordCount64 limit);    // Limit to the given number of words.
+
+  inline void reset(WordCount64 limit);
+
+  KJ_ALWAYS_INLINE(bool canRead(WordCount amount, Arena* arena));
+
+  void unread(WordCount64 amount);
+  // Adds back some words to the limit.  Useful when the caller knows they are double-reading
+  // some data.
+
+private:
+  volatile uint64_t limit;
+  // Current limit, decremented each time catRead() is called.  Volatile because multiple threads
+  // could be trying to modify it at once.  (This is not real thread-safety, but good enough for
+  // the purpose of this class.  See class comment.)
+
+  KJ_DISALLOW_COPY(ReadLimiter);
+};
+
+#if !CAPNP_LITE
+class BrokenCapFactory {
+  // Callback for constructing broken caps.  We use this so that we can avoid arena.c++ having a
+  // link-time dependency on capability code that lives in libcapnp-rpc.
+
+public:
+  virtual kj::Own<ClientHook> newBrokenCap(kj::StringPtr description) = 0;
+  virtual kj::Own<ClientHook> newNullCap() = 0;
+};
+#endif  // !CAPNP_LITE
+
+class SegmentReader {
+public:
+  inline SegmentReader(Arena* arena, SegmentId id, kj::ArrayPtr<const word> ptr,
+                       ReadLimiter* readLimiter);
+
+  KJ_ALWAYS_INLINE(bool containsInterval(const void* from, const void* to));
+
+  KJ_ALWAYS_INLINE(bool amplifiedRead(WordCount virtualAmount));
+  // Indicates that the reader should pretend that `virtualAmount` additional data was read even
+  // though no actual pointer was traversed. This is used e.g. when reading a struct list pointer
+  // where the element sizes are zero -- the sender could set the list size arbitrarily high and
+  // cause the receiver to iterate over this list even though the message itself is small, so we
+  // need to defend against DoS attacks based on this.
+
+  inline Arena* getArena();
+  inline SegmentId getSegmentId();
+
+  inline const word* getStartPtr();
+  inline WordCount getOffsetTo(const word* ptr);
+  inline WordCount getSize();
+
+  inline kj::ArrayPtr<const word> getArray();
+
+  inline void unread(WordCount64 amount);
+  // Add back some words to the ReadLimiter.
+
+private:
+  Arena* arena;
+  SegmentId id;
+  kj::ArrayPtr<const word> ptr;
+  ReadLimiter* readLimiter;
+
+  KJ_DISALLOW_COPY(SegmentReader);
+
+  friend class SegmentBuilder;
+};
+
+class SegmentBuilder: public SegmentReader {
+public:
+  inline SegmentBuilder(BuilderArena* arena, SegmentId id, kj::ArrayPtr<word> ptr,
+                        ReadLimiter* readLimiter, size_t wordsUsed = 0);
+  inline SegmentBuilder(BuilderArena* arena, SegmentId id, kj::ArrayPtr<const word> ptr,
+                        ReadLimiter* readLimiter);
+  inline SegmentBuilder(BuilderArena* arena, SegmentId id, decltype(nullptr),
+                        ReadLimiter* readLimiter);
+
+  KJ_ALWAYS_INLINE(word* allocate(WordCount amount));
+
+  KJ_ALWAYS_INLINE(void checkWritable());
+  // Throw an exception if the segment is read-only (meaning it is a reference to external data).
+
+  KJ_ALWAYS_INLINE(word* getPtrUnchecked(WordCount offset));
+  // Get a writable pointer into the segment.  Throws an exception if the segment is read-only (i.e.
+  // a reference to external immutable data).
+
+  inline BuilderArena* getArena();
+
+  inline kj::ArrayPtr<const word> currentlyAllocated();
+
+  inline void reset();
+
+  inline bool isWritable() { return !readOnly; }
+
+  inline void tryTruncate(word* from, word* to);
+  // If `from` points just past the current end of the segment, then move the end back to `to`.
+  // Otherwise, do nothing.
+
+  inline bool tryExtend(word* from, word* to);
+  // If `from` points just past the current end of the segment, and `to` is within the segment
+  // boundaries, then move the end up to `to` and return true. Otherwise, do nothing and return
+  // false.
+
+private:
+  word* pos;
+  // Pointer to a pointer to the current end point of the segment, i.e. the location where the
+  // next object should be allocated.
+
+  bool readOnly;
+
+  void throwNotWritable();
+
+  KJ_DISALLOW_COPY(SegmentBuilder);
+};
+
+class Arena {
+public:
+  virtual ~Arena() noexcept(false);
+
+  virtual SegmentReader* tryGetSegment(SegmentId id) = 0;
+  // Gets the segment with the given ID, or return nullptr if no such segment exists.
+
+  virtual void reportReadLimitReached() = 0;
+  // Called to report that the read limit has been reached.  See ReadLimiter, below.  This invokes
+  // the VALIDATE_INPUT() macro which may throw an exception; if it returns normally, the caller
+  // will need to continue with default values.
+};
+
+class ReaderArena final: public Arena {
+public:
+  ReaderArena(MessageReader* message);
+  ~ReaderArena() noexcept(false);
+  KJ_DISALLOW_COPY(ReaderArena);
+
+  // implements Arena ------------------------------------------------
+  SegmentReader* tryGetSegment(SegmentId id) override;
+  void reportReadLimitReached() override;
+
+private:
+  MessageReader* message;
+  ReadLimiter readLimiter;
+
+  // Optimize for single-segment messages so that small messages are handled quickly.
+  SegmentReader segment0;
+
+  typedef std::unordered_map<uint, kj::Own<SegmentReader>> SegmentMap;
+  kj::MutexGuarded<kj::Maybe<kj::Own<SegmentMap>>> moreSegments;
+  // We need to mutex-guard the segment map because we lazily initialize segments when they are
+  // first requested, but a Reader is allowed to be used concurrently in multiple threads.  Luckily
+  // this only applies to large messages.
+  //
+  // TODO(perf):  Thread-local thing instead?  Some kind of lockless map?  Or do sharing of data
+  //   in a different way, where you have to construct a new MessageReader in each thread (but
+  //   possibly backed by the same data)?
+};
+
+class BuilderArena final: public Arena {
+  // A BuilderArena that does not allow the injection of capabilities.
+
+public:
+  explicit BuilderArena(MessageBuilder* message);
+  BuilderArena(MessageBuilder* message, kj::ArrayPtr<MessageBuilder::SegmentInit> segments);
+  ~BuilderArena() noexcept(false);
+  KJ_DISALLOW_COPY(BuilderArena);
+
+  inline SegmentBuilder* getRootSegment() { return &segment0; }
+
+  kj::ArrayPtr<const kj::ArrayPtr<const word>> getSegmentsForOutput();
+  // Get an array of all the segments, suitable for writing out.  This only returns the allocated
+  // portion of each segment, whereas tryGetSegment() returns something that includes
+  // not-yet-allocated space.
+
+  inline CapTableBuilder* getLocalCapTable() {
+    // Return a CapTableBuilder that merely implements local loopback. That is, you can set
+    // capabilities, then read the same capabilities back, but there is no intent ever to transmit
+    // these capabilities. A MessageBuilder that isn't imbued with some other CapTable uses this
+    // by default.
+    //
+    // TODO(cleanup): It's sort of a hack that this exists. In theory, perhaps, unimbued
+    //   MessageBuilders should throw exceptions on any attempt to access capability fields, like
+    //   unimbued MessageReaders do. However, lots of code exists which uses MallocMessageBuilder
+    //   as a temporary holder for data to be copied in and out (without being serialized), and it
+    //   is expected that such data can include capabilities, which is admittedly reasonable.
+    //   Therefore, all MessageBuilders must have a cap table by default. Arguably we should
+    //   deprecate this usage and instead define a new helper type for this exact purpose.
+
+    return &localCapTable;
+  }
+
+  SegmentBuilder* getSegment(SegmentId id);
+  // Get the segment with the given id.  Crashes or throws an exception if no such segment exists.
+
+  struct AllocateResult {
+    SegmentBuilder* segment;
+    word* words;
+  };
+
+  AllocateResult allocate(WordCount amount);
+  // Find a segment with at least the given amount of space available and allocate the space.
+  // Note that allocating directly from a particular segment is much faster, but allocating from
+  // the arena is guaranteed to succeed.  Therefore callers should try to allocate from a specific
+  // segment first if there is one, then fall back to the arena.
+
+  SegmentBuilder* addExternalSegment(kj::ArrayPtr<const word> content);
+  // Add a new segment to the arena which points to some existing memory region.  The segment is
+  // assumed to be completley full; the arena will never allocate from it.  In fact, the segment
+  // is considered read-only.  Any attempt to get a Builder pointing into this segment will throw
+  // an exception.  Readers are allowed, however.
+  //
+  // This can be used to inject some external data into a message without a copy, e.g. embedding a
+  // large mmap'd file into a message as `Data` without forcing that data to actually be read in
+  // from disk (until the message itself is written out).  `Orphanage` provides the public API for
+  // this feature.
+
+  // implements Arena ------------------------------------------------
+  SegmentReader* tryGetSegment(SegmentId id) override;
+  void reportReadLimitReached() override;
+
+private:
+  MessageBuilder* message;
+  ReadLimiter dummyLimiter;
+
+  class LocalCapTable: public CapTableBuilder {
+#if !CAPNP_LITE
+  public:
+    kj::Maybe<kj::Own<ClientHook>> extractCap(uint index) override;
+    uint injectCap(kj::Own<ClientHook>&& cap) override;
+    void dropCap(uint index) override;
+
+  private:
+    kj::Vector<kj::Maybe<kj::Own<ClientHook>>> capTable;
+#endif // ! CAPNP_LITE
+  };
+
+  LocalCapTable localCapTable;
+
+  SegmentBuilder segment0;
+  kj::ArrayPtr<const word> segment0ForOutput;
+
+  struct MultiSegmentState {
+    kj::Vector<kj::Own<SegmentBuilder>> builders;
+    kj::Vector<kj::ArrayPtr<const word>> forOutput;
+  };
+  kj::Maybe<kj::Own<MultiSegmentState>> moreSegments;
+
+  SegmentBuilder* segmentWithSpace = nullptr;
+  // When allocating, look for space in this segment first before resorting to allocating a new
+  // segment.  This is not necessarily the last segment because addExternalSegment() may add a
+  // segment that is already-full, in which case we don't update this pointer.
+
+  template <typename T>  // Can be `word` or `const word`.
+  SegmentBuilder* addSegmentInternal(kj::ArrayPtr<T> content);
+};
+
+// =======================================================================================
+
+inline ReadLimiter::ReadLimiter()
+    : limit(kj::maxValue) {}
+
+inline ReadLimiter::ReadLimiter(WordCount64 limit): limit(limit / WORDS) {}
+
+inline void ReadLimiter::reset(WordCount64 limit) { this->limit = limit / WORDS; }
+
+inline bool ReadLimiter::canRead(WordCount amount, Arena* arena) {
+  // Be careful not to store an underflowed value into `limit`, even if multiple threads are
+  // decrementing it.
+  uint64_t current = limit;
+  if (KJ_UNLIKELY(amount / WORDS > current)) {
+    arena->reportReadLimitReached();
+    return false;
+  } else {
+    limit = current - amount / WORDS;
+    return true;
+  }
+}
+
+// -------------------------------------------------------------------
+
+inline SegmentReader::SegmentReader(Arena* arena, SegmentId id, kj::ArrayPtr<const word> ptr,
+                                    ReadLimiter* readLimiter)
+    : arena(arena), id(id), ptr(ptr), readLimiter(readLimiter) {}
+
+inline bool SegmentReader::containsInterval(const void* from, const void* to) {
+  return from >= this->ptr.begin() && to <= this->ptr.end() && from <= to &&
+      readLimiter->canRead(
+          intervalLength(reinterpret_cast<const byte*>(from),
+                         reinterpret_cast<const byte*>(to)) / BYTES_PER_WORD,
+          arena);
+}
+
+inline bool SegmentReader::amplifiedRead(WordCount virtualAmount) {
+  return readLimiter->canRead(virtualAmount, arena);
+}
+
+inline Arena* SegmentReader::getArena() { return arena; }
+inline SegmentId SegmentReader::getSegmentId() { return id; }
+inline const word* SegmentReader::getStartPtr() { return ptr.begin(); }
+inline WordCount SegmentReader::getOffsetTo(const word* ptr) {
+  return intervalLength(this->ptr.begin(), ptr);
+}
+inline WordCount SegmentReader::getSize() { return ptr.size() * WORDS; }
+inline kj::ArrayPtr<const word> SegmentReader::getArray() { return ptr; }
+inline void SegmentReader::unread(WordCount64 amount) { readLimiter->unread(amount); }
+
+// -------------------------------------------------------------------
+
+inline SegmentBuilder::SegmentBuilder(
+    BuilderArena* arena, SegmentId id, kj::ArrayPtr<word> ptr, ReadLimiter* readLimiter,
+    size_t wordsUsed)
+    : SegmentReader(arena, id, ptr, readLimiter), pos(ptr.begin() + wordsUsed), readOnly(false) {}
+inline SegmentBuilder::SegmentBuilder(
+    BuilderArena* arena, SegmentId id, kj::ArrayPtr<const word> ptr, ReadLimiter* readLimiter)
+    : SegmentReader(arena, id, ptr, readLimiter),
+      // const_cast is safe here because the member won't ever be dereferenced because it appears
+      // to point to the end of the segment anyway.
+      pos(const_cast<word*>(ptr.end())),
+      readOnly(true) {}
+inline SegmentBuilder::SegmentBuilder(BuilderArena* arena, SegmentId id, decltype(nullptr),
+                                      ReadLimiter* readLimiter)
+    : SegmentReader(arena, id, nullptr, readLimiter), pos(nullptr), readOnly(false) {}
+
+inline word* SegmentBuilder::allocate(WordCount amount) {
+  if (intervalLength(pos, ptr.end()) < amount) {
+    // Not enough space in the segment for this allocation.
+    return nullptr;
+  } else {
+    // Success.
+    word* result = pos;
+    pos = pos + amount;
+    return result;
+  }
+}
+
+inline void SegmentBuilder::checkWritable() {
+  if (KJ_UNLIKELY(readOnly)) throwNotWritable();
+}
+
+inline word* SegmentBuilder::getPtrUnchecked(WordCount offset) {
+  return const_cast<word*>(ptr.begin() + offset);
+}
+
+inline BuilderArena* SegmentBuilder::getArena() {
+  // Down-cast safe because SegmentBuilder's constructor always initializes its SegmentReader base
+  // class with an Arena pointer that actually points to a BuilderArena.
+  return static_cast<BuilderArena*>(arena);
+}
+
+inline kj::ArrayPtr<const word> SegmentBuilder::currentlyAllocated() {
+  return kj::arrayPtr(ptr.begin(), pos - ptr.begin());
+}
+
+inline void SegmentBuilder::reset() {
+  word* start = getPtrUnchecked(0 * WORDS);
+  memset(start, 0, (pos - start) * sizeof(word));
+  pos = start;
+}
+
+inline void SegmentBuilder::tryTruncate(word* from, word* to) {
+  if (pos == from) pos = to;
+}
+
+inline bool SegmentBuilder::tryExtend(word* from, word* to) {
+  // Careful about overflow.
+  if (pos == from && to <= ptr.end() && to >= from) {
+    pos = to;
+    return true;
+  } else {
+    return false;
+  }
+}
+
+}  // namespace _ (private)
+}  // namespace capnp
+
+#endif  // CAPNP_ARENA_H_