protobuf/upb/extension_registry.h

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#ifndef UPB_EXTENSION_REGISTRY_H_
#define UPB_EXTENSION_REGISTRY_H_

#include "upb/msg.h"

// Must be last.
#include "upb/port/def.inc"

#ifdef __cplusplus
extern "C" {
#endif

/* Extension registry: a dynamic data structure that stores a map of:
 *   (upb_MiniTable, number) -> extension info
 *
 * upb_decode() uses upb_ExtensionRegistry to look up extensions while parsing
 * binary format.
 *
 * upb_ExtensionRegistry is part of the mini-table (msglayout) family of
 * objects. Like all mini-table objects, it is suitable for reflection-less
 * builds that do not want to expose names into the binary.
 *
 * Unlike most mini-table types, upb_ExtensionRegistry requires dynamic memory
 * allocation and dynamic initialization:
 * * If reflection is being used, then upb_DefPool will construct an appropriate
 *   upb_ExtensionRegistry automatically.
 * * For a mini-table only build, the user must manually construct the
 *   upb_ExtensionRegistry and populate it with all of the extensions the user
 * cares about.
 * * A third alternative is to manually unpack relevant extensions after the
 *   main parse is complete, similar to how Any works. This is perhaps the
 *   nicest solution from the perspective of reducing dependencies, avoiding
 *   dynamic memory allocation, and avoiding the need to parse uninteresting
 *   extensions.  The downsides are:
 *     (1) parse errors are not caught during the main parse
 *     (2) the CPU hit of parsing comes during access, which could cause an
 *         undesirable stutter in application performance.
 *
 * Users cannot directly get or put into this map. Users can only add the
 * extensions from a generated module and pass the extension registry to the
 * binary decoder.
 *
 * A upb_DefPool provides a upb_ExtensionRegistry, so any users who use
 * reflection do not need to populate a upb_ExtensionRegistry directly.
 */

typedef struct upb_ExtensionRegistry upb_ExtensionRegistry;
typedef struct upb_MiniTableExtension upb_MiniTableExtension;

// Creates a upb_ExtensionRegistry in the given arena.
// The arena must outlive any use of the extreg.
upb_ExtensionRegistry* upb_ExtensionRegistry_New(upb_Arena* arena);

// Adds the given extension info for the array |e| of size |count| into the
// registry. If there are any errors, the entire array is backed out.
// The extensions must outlive the registry.
// Possible errors include OOM or an extension number that already exists.
// TODO: There is currently no way to determine the exact reason for failure.
bool upb_ExtensionRegistry_AddArray(upb_ExtensionRegistry* r,
                                    const upb_MiniTableExtension** e,
                                    size_t count);

// Looks up the extension (if any) defined for message type |t| and field
// number |num|. Returns the extension if found, otherwise NULL.
const upb_MiniTableExtension* upb_ExtensionRegistry_Lookup(
    const upb_ExtensionRegistry* r, const upb_MiniTable* t, uint32_t num);

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

#include "upb/port/undef.inc"

#endif /* UPB_EXTENSION_REGISTRY_H_ */