protobuf/upb/pb/decoder.h

/*
** upb::pb::Decoder
**
** A high performance, streaming, resumable decoder for the binary protobuf
** format.
**
** This interface works the same regardless of what decoder backend is being
** used.  A client of this class does not need to know whether decoding is using
** a JITted decoder (DynASM, LLVM, etc) or an interpreted decoder.  By default,
** it will always use the fastest available decoder.  However, you can call
** set_allow_jit(false) to disable any JIT decoder that might be available.
** This is primarily useful for testing purposes.
*/

#ifndef UPB_DECODER_H_
#define UPB_DECODER_H_

#include "upb/sink.h"

#ifdef __cplusplus
namespace upb {
namespace pb {
class CodeCache;
class DecoderPtr;
class DecoderMethodPtr;
class DecoderMethodOptions;
}  /* namespace pb */
}  /* namespace upb */
#endif

/* The maximum number of bytes we are required to buffer internally between
 * calls to the decoder.  The value is 14: a 5 byte unknown tag plus ten-byte
 * varint, less one because we are buffering an incomplete value.
 *
 * Should only be used by unit tests. */
#define UPB_DECODER_MAX_RESIDUAL_BYTES 14

/* upb_pbdecodermethod ********************************************************/

struct upb_pbdecodermethod;
typedef struct upb_pbdecodermethod upb_pbdecodermethod;

#ifdef __cplusplus
extern "C" {
#endif

const upb_handlers *upb_pbdecodermethod_desthandlers(
    const upb_pbdecodermethod *m);
const upb_byteshandler *upb_pbdecodermethod_inputhandler(
    const upb_pbdecodermethod *m);
bool upb_pbdecodermethod_isnative(const upb_pbdecodermethod *m);

#ifdef __cplusplus
}  /* extern "C" */

/* Represents the code to parse a protobuf according to a destination
 * Handlers. */
class upb::pb::DecoderMethodPtr {
 public:
  DecoderMethodPtr() : ptr_(nullptr) {}
  DecoderMethodPtr(const upb_pbdecodermethod* ptr) : ptr_(ptr) {}

  const upb_pbdecodermethod* ptr() { return ptr_; }

  /* The destination handlers that are statically bound to this method.
   * This method is only capable of outputting to a sink that uses these
   * handlers. */
  const Handlers *dest_handlers() const {
    return upb_pbdecodermethod_desthandlers(ptr_);
  }

  /* The input handlers for this decoder method. */
  const BytesHandler* input_handler() const {
    return upb_pbdecodermethod_inputhandler(ptr_);
  }

  /* Whether this method is native. */
  bool is_native() const {
    return upb_pbdecodermethod_isnative(ptr_);
  }

 private:
  const upb_pbdecodermethod* ptr_;
};

#endif

/* upb_pbdecoder **************************************************************/

/* Preallocation hint: decoder won't allocate more bytes than this when first
 * constructed.  This hint may be an overestimate for some build configurations.
 * But if the decoder library is upgraded without recompiling the application,
 * it may be an underestimate. */
#define UPB_PB_DECODER_SIZE 4416

struct upb_pbdecoder;
typedef struct upb_pbdecoder upb_pbdecoder;

#ifdef __cplusplus
extern "C" {
#endif

upb_pbdecoder *upb_pbdecoder_create(upb_arena *arena,
                                    const upb_pbdecodermethod *method,
                                    upb_sink output, upb_status *status);
const upb_pbdecodermethod *upb_pbdecoder_method(const upb_pbdecoder *d);
upb_bytessink upb_pbdecoder_input(upb_pbdecoder *d);
uint64_t upb_pbdecoder_bytesparsed(const upb_pbdecoder *d);
size_t upb_pbdecoder_maxnesting(const upb_pbdecoder *d);
bool upb_pbdecoder_setmaxnesting(upb_pbdecoder *d, size_t max);
void upb_pbdecoder_reset(upb_pbdecoder *d);

#ifdef __cplusplus
}  /* extern "C" */

/* A Decoder receives binary protobuf data on its input sink and pushes the
 * decoded data to its output sink. */
class upb::pb::DecoderPtr {
 public:
  DecoderPtr() : ptr_(nullptr) {}
  DecoderPtr(upb_pbdecoder* ptr) : ptr_(ptr) {}

  upb_pbdecoder* ptr() { return ptr_; }

  /* Constructs a decoder instance for the given method, which must outlive this
   * decoder.  Any errors during parsing will be set on the given status, which
   * must also outlive this decoder.
   *
   * The sink must match the given method. */
  static DecoderPtr Create(Arena *arena, DecoderMethodPtr method,
                           upb::Sink output, Status *status) {
    return DecoderPtr(upb_pbdecoder_create(arena->ptr(), method.ptr(),
                                           output.sink(), status->ptr()));
  }

  /* Returns the DecoderMethod this decoder is parsing from. */
  const DecoderMethodPtr method() const {
    return DecoderMethodPtr(upb_pbdecoder_method(ptr_));
  }

  /* The sink on which this decoder receives input. */
  BytesSink input() { return BytesSink(upb_pbdecoder_input(ptr())); }

  /* Returns number of bytes successfully parsed.
   *
   * This can be useful for determining the stream position where an error
   * occurred.
   *
   * This value may not be up-to-date when called from inside a parsing
   * callback. */
  uint64_t BytesParsed() { return upb_pbdecoder_bytesparsed(ptr()); }

  /* Gets/sets the parsing nexting limit.  If the total number of nested
   * submessages and repeated fields hits this limit, parsing will fail.  This
   * is a resource limit that controls the amount of memory used by the parsing
   * stack.
   *
   * Setting the limit will fail if the parser is currently suspended at a depth
   * greater than this, or if memory allocation of the stack fails. */
  size_t max_nesting() { return upb_pbdecoder_maxnesting(ptr()); }
  bool set_max_nesting(size_t max) { return upb_pbdecoder_maxnesting(ptr()); }

  void Reset() { upb_pbdecoder_reset(ptr()); }

  static const size_t kSize = UPB_PB_DECODER_SIZE;

 private:
  upb_pbdecoder *ptr_;
};

#endif  /* __cplusplus */

/* upb_pbcodecache ************************************************************/

/* Lazily builds and caches decoder methods that will push data to the given
 * handlers.  The destination handlercache must outlive this object. */

struct upb_pbcodecache;
typedef struct upb_pbcodecache upb_pbcodecache;

#ifdef __cplusplus
extern "C" {
#endif

upb_pbcodecache *upb_pbcodecache_new(upb_handlercache *dest);
void upb_pbcodecache_free(upb_pbcodecache *c);
bool upb_pbcodecache_allowjit(const upb_pbcodecache *c);
void upb_pbcodecache_setallowjit(upb_pbcodecache *c, bool allow);
void upb_pbcodecache_setlazy(upb_pbcodecache *c, bool lazy);
const upb_pbdecodermethod *upb_pbcodecache_get(upb_pbcodecache *c,
                                               const upb_msgdef *md);

#ifdef __cplusplus
}  /* extern "C" */

/* A class for caching protobuf processing code, whether bytecode for the
 * interpreted decoder or machine code for the JIT.
 *
 * This class is not thread-safe. */
class upb::pb::CodeCache {
 public:
  CodeCache(upb::HandlerCache *dest)
      : ptr_(upb_pbcodecache_new(dest->ptr()), upb_pbcodecache_free) {}
  CodeCache(CodeCache&&) = default;
  CodeCache& operator=(CodeCache&&) = default;

  upb_pbcodecache* ptr() { return ptr_.get(); }
  const upb_pbcodecache* ptr() const { return ptr_.get(); }

  /* Whether the cache is allowed to generate machine code.  Defaults to true.
   * There is no real reason to turn it off except for testing or if you are
   * having a specific problem with the JIT.
   *
   * Note that allow_jit = true does not *guarantee* that the code will be JIT
   * compiled.  If this platform is not supported or the JIT was not compiled
   * in, the code may still be interpreted. */
  bool allow_jit() const { return upb_pbcodecache_allowjit(ptr()); }

  /* This may only be called when the object is first constructed, and prior to
   * any code generation. */
  void set_allow_jit(bool allow) { upb_pbcodecache_setallowjit(ptr(), allow); }

  /* Should the decoder push submessages to lazy handlers for fields that have
   * them?  The caller should set this iff the lazy handlers expect data that is
   * in protobuf binary format and the caller wishes to lazy parse it. */
  void set_lazy(bool lazy) { upb_pbcodecache_setlazy(ptr(), lazy); }

  /* Returns a DecoderMethod that can push data to the given handlers.
   * If a suitable method already exists, it will be returned from the cache. */
  const DecoderMethodPtr Get(MessageDefPtr md) {
    return DecoderMethodPtr(upb_pbcodecache_get(ptr(), md.ptr()));
  }

 private:
  std::unique_ptr<upb_pbcodecache, decltype(&upb_pbcodecache_free)> ptr_;
};

#endif  /* __cplusplus */

#endif  /* UPB_DECODER_H_ */