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+/*
+ * upb - a minimalist implementation of protocol buffers.
+ *
+ * Copyright (c) 2009 Joshua Haberman.  See LICENSE for details.
+ *
+ * Provides definitions of .proto constructs:
+ * - upb_msgdef: describes a "message" construct.
+ * - upb_fielddef: describes a message field.
+ * - upb_enumdef: describes an enum.
+ * (TODO: definitions of extensions and services).
+ *
+ * Defs are obtained from a upb_symtab object.  A upb_symtab is empty when
+ * constructed, and definitions can be added by supplying serialized
+ * descriptors.
+ *
+ * Defs are immutable and reference-counted.  Symbol tables reference any defs
+ * that are the "current" definitions.  If an extension is loaded that adds a
+ * field to an existing message, a new msgdef is constructed that includes the
+ * new field and the old msgdef is unref'd.  The old msgdef will still be ref'd
+ * by messages (if any) that were constructed with that msgdef.
+ *
+ * This file contains routines for creating and manipulating the definitions
+ * themselves.  To create and manipulate actual messages, see upb_msg.h.
+ */
+
+#ifndef UPB_DEF_H_
+#define UPB_DEF_H_
+
+#include "upb_atomic.h"
+#include "upb_stream.h"
+#include "upb_table.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* upb_def: base class for defs  **********************************************/
+
+// All the different kind of defs we support.  These correspond 1:1 with
+// declarations in a .proto file.
+typedef enum {
+  UPB_DEF_MSG = 0,
+  UPB_DEF_ENUM,
+  UPB_DEF_SVC,
+  UPB_DEF_EXT,
+  // Internal-only, placeholder for a def that hasn't be resolved yet.
+  UPB_DEF_UNRESOLVED,
+
+  // For specifying that defs of any type are requsted from getdefs.
+  UPB_DEF_ANY = -1
+} upb_def_type;
+
+// This typedef is more space-efficient than declaring an enum var directly.
+typedef int8_t upb_def_type_t;
+
+typedef struct {
+  upb_string *fqname;  // Fully qualified.
+  upb_atomic_refcount_t refcount;
+  upb_def_type_t type;
+
+  // The is_cyclic flag could go in upb_msgdef instead of here, because only
+  // messages can be involved in cycles.  However, putting them here is free
+  // from a space perspective because structure alignment will otherwise leave
+  // three bytes empty after type.  It is also makes ref and unref more
+  // efficient, because we don't have to downcast to msgdef before checking the
+  // is_cyclic flag.
+  bool is_cyclic;
+  uint16_t search_depth;  // Used during initialization dfs.
+} upb_def;
+
+// These must not be called directly!
+void _upb_def_cyclic_ref(upb_def *def);
+void _upb_def_reftozero(upb_def *def);
+
+// Call to ref/deref a def.
+INLINE void upb_def_ref(upb_def *def) {
+  if(upb_atomic_ref(&def->refcount) && def->is_cyclic) _upb_def_cyclic_ref(def);
+}
+INLINE void upb_def_unref(upb_def *def) {
+  if(upb_atomic_unref(&def->refcount)) _upb_def_reftozero(def);
+}
+
+/* upb_fielddef ***************************************************************/
+
+// A upb_fielddef describes a single field in a message.  It isn't a full def
+// in the sense that it derives from upb_def.  It cannot stand on its own; it
+// is either a field of a upb_msgdef or contained inside a upb_extensiondef.
+// It is also reference-counted.
+typedef struct _upb_fielddef {
+  upb_atomic_refcount_t refcount;
+  upb_string *name;
+  upb_field_number_t number;
+  upb_field_type_t type;
+  upb_label_t label;
+  upb_value default_value;
+
+  // For the case of an enum or a submessage, points to the def for that type.
+  upb_def *def;
+
+  // True if we own a ref on "def" (above).  This is true unless this edge is
+  // part of a cycle.
+  bool owned;
+
+  // These are set only when this fielddef is part of a msgdef.
+  uint32_t byte_offset;           // Where in a upb_msg to find the data.
+  upb_field_count_t field_index;  // Indicates set bit.
+} upb_fielddef;
+
+// A variety of tests about the type of a field.
+INLINE bool upb_issubmsg(upb_fielddef *f) {
+  return upb_issubmsgtype(f->type);
+}
+INLINE bool upb_isstring(upb_fielddef *f) {
+  return upb_isstringtype(f->type);
+}
+INLINE bool upb_isarray(upb_fielddef *f) {
+  return f->label == UPB_LABEL(REPEATED);
+}
+// Does the type of this field imply that it should contain an associated def?
+INLINE bool upb_hasdef(upb_fielddef *f) {
+  return upb_issubmsg(f) || f->type == UPB_TYPE(ENUM);
+}
+
+INLINE bool upb_field_ismm(upb_fielddef *f) {
+  return upb_isarray(f) || upb_isstring(f) || upb_issubmsg(f);
+}
+
+INLINE bool upb_elem_ismm(upb_fielddef *f) {
+  return upb_isstring(f) || upb_issubmsg(f);
+}
+
+/* upb_msgdef *****************************************************************/
+
+// Structure that describes a single .proto message type.
+typedef struct _upb_msgdef {
+  upb_def base;
+  upb_atomic_refcount_t cycle_refcount;
+  size_t size;
+  upb_field_count_t num_fields;
+  uint32_t set_flags_bytes;
+  uint32_t num_required_fields;  // Required fields have the lowest set bytemasks.
+  upb_fielddef *fields;   // We have exclusive ownership of these.
+
+  // Tables for looking up fields by number and name.
+  upb_inttable itof;  // int to field
+  upb_strtable ntof;  // name to field
+} upb_msgdef;
+
+// Hash table entries for looking up fields by name or number.
+typedef struct {
+  upb_inttable_entry e;
+  upb_fielddef *f;
+} upb_itof_ent;
+typedef struct {
+  upb_strtable_entry e;
+  upb_fielddef *f;
+} upb_ntof_ent;
+
+// Looks up a field by name or number.  While these are written to be as fast
+// as possible, it will still be faster to cache the results of this lookup if
+// possible.  These return NULL if no such field is found.
+INLINE upb_fielddef *upb_msg_itof(upb_msgdef *m, uint32_t num) {
+  upb_itof_ent *e =
+      (upb_itof_ent*)upb_inttable_fastlookup(&m->itof, num, sizeof(*e));
+  return e ? e->f : NULL;
+}
+
+INLINE upb_fielddef *upb_msg_ntof(upb_msgdef *m, upb_string *name) {
+  upb_ntof_ent *e = (upb_ntof_ent*)upb_strtable_lookup(&m->ntof, name);
+  return e ? e->f : NULL;
+}
+
+/* upb_enumdef ****************************************************************/
+
+typedef struct _upb_enumdef {
+  upb_def base;
+  upb_strtable ntoi;
+  upb_inttable iton;
+} upb_enumdef;
+
+typedef int32_t upb_enumval_t;
+
+// Lookups from name to integer and vice-versa.
+bool upb_enumdef_ntoi(upb_enumdef *e, upb_string *name, upb_enumval_t *num);
+upb_string *upb_enumdef_iton(upb_enumdef *e, upb_enumval_t num);
+
+// Iteration over name/value pairs.  The order is undefined.
+//   upb_enum_iter i;
+//   for(upb_enum_begin(&i, e); !upb_enum_done(&i); upb_enum_next(&i)) {
+//     // ...
+//   }
+typedef struct {
+  upb_enumdef *e;
+  void *state;   // Internal iteration state.
+  upb_string *name;
+  upb_enumval_t val;
+} upb_enum_iter;
+void upb_enum_begin(upb_enum_iter *iter, upb_enumdef *e);
+void upb_enum_next(upb_enum_iter *iter);
+bool upb_enum_done(upb_enum_iter *iter);
+
+/* upb_symtab *****************************************************************/
+
+// A SymbolTable is where upb_defs live.  It is empty when first constructed.
+// Clients add definitions to the symtab by supplying unserialized or
+// serialized descriptors (as defined in descriptor.proto).
+typedef struct {
+  upb_atomic_refcount_t refcount;
+  upb_rwlock_t lock;       // Protects all members except the refcount.
+  upb_msgdef *fds_msgdef;  // In psymtab, ptr here for convenience.
+
+  // Our symbol tables; we own refs to the defs therein.
+  upb_strtable symtab;     // The main symbol table.
+  upb_strtable psymtab;    // Private symbols, for internal use.
+} upb_symtab;
+
+// Initializes a upb_symtab.  Contexts are not freed explicitly, but unref'd
+// when the caller is done with them.
+upb_symtab *upb_symtab_new(void);
+void _upb_symtab_free(upb_symtab *s);  // Must not be called directly!
+
+INLINE void upb_symtab_ref(upb_symtab *s) { upb_atomic_ref(&s->refcount); }
+INLINE void upb_symtab_unref(upb_symtab *s) {
+  if(upb_atomic_unref(&s->refcount)) _upb_symtab_free(s);
+}
+
+// Resolves the given symbol using the rules described in descriptor.proto,
+// namely:
+//
+//    If the name starts with a '.', it is fully-qualified.  Otherwise, C++-like
+//    scoping rules are used to find the type (i.e. first the nested types
+//    within this message are searched, then within the parent, on up to the
+//    root namespace).
+//
+// If a def is found, the caller owns one ref on the returned def.  Otherwise
+// returns NULL.
+upb_def *upb_symtab_resolve(upb_symtab *s, upb_string *base, upb_string *sym);
+
+// Find an entry in the symbol table with this exact name.  If a def is found,
+// the caller owns one ref on the returned def.  Otherwise returns NULL.
+upb_def *upb_symtab_lookup(upb_symtab *s, upb_string *sym);
+
+// Gets an array of pointers to all currently active defs in this symtab.  The
+// caller owns the returned array (which is of length *count) as well as a ref
+// to each symbol inside.  If type is UPB_DEF_ANY then defs of all types are
+// returned, otherwise only defs of the required type are returned.
+upb_def **upb_symtab_getdefs(upb_symtab *s, int *count, upb_def_type_t type);
+
+// "fds" is a upb_src that will yield data from the
+// google.protobuf.FileDescriptorSet message type.  upb_symtab_addfds() adds
+// all the definitions from the given FileDescriptorSet and adds them to the
+// symtab.  status indicates whether the operation was successful or not, and
+// the error message (if any).
+//
+// TODO: should this allow redefinition?  Either is possible, but which is
+// more useful?  Maybe it should be an option.
+void upb_symtab_addfds(upb_symtab *s, upb_src *desc, upb_status *status);
+
+// Returns a symtab that defines google.protobuf.DescriptorProto and all other
+// types that are defined in descriptor.proto.  This allows you to load other
+// proto types.  The caller owns a ref on the returned symtab.
+upb_symtab *upb_get_descriptor_symtab();
+
+
+/* upb_def casts **************************************************************/
+
+// Dynamic casts, for determining if a def is of a particular type at runtime.
+#define UPB_DYNAMIC_CAST_DEF(lower, upper) \
+  struct _upb_ ## lower;  /* Forward-declare. */ \
+  INLINE struct _upb_ ## lower *upb_dyncast_ ## lower(upb_def *def) { \
+    if(def->type != UPB_DEF_ ## upper) return NULL; \
+    return (struct _upb_ ## lower*)def; \
+  }
+UPB_DYNAMIC_CAST_DEF(msgdef, MSG);
+UPB_DYNAMIC_CAST_DEF(enumdef, ENUM);
+UPB_DYNAMIC_CAST_DEF(svcdef, SVC);
+UPB_DYNAMIC_CAST_DEF(extdef, EXT);
+UPB_DYNAMIC_CAST_DEF(unresolveddef, UNRESOLVED);
+#undef UPB_DYNAMIC_CAST_DEF
+
+// Downcasts, for when some wants to assert that a def is of a particular type.
+// These are only checked if we are building debug.
+#define UPB_DOWNCAST_DEF(lower, upper) \
+  struct _upb_ ## lower;  /* Forward-declare. */ \
+  INLINE struct _upb_ ## lower *upb_downcast_ ## lower(upb_def *def) { \
+    assert(def->type == UPB_DEF_ ## upper); \
+    return (struct _upb_ ## lower*)def; \
+  }
+UPB_DOWNCAST_DEF(msgdef, MSG);
+UPB_DOWNCAST_DEF(enumdef, ENUM);
+UPB_DOWNCAST_DEF(svcdef, SVC);
+UPB_DOWNCAST_DEF(extdef, EXT);
+UPB_DOWNCAST_DEF(unresolveddef, UNRESOLVED);
+#undef UPB_DOWNCAST_DEF
+
+#define UPB_UPCAST(ptr) (&(ptr)->base)
+
+#ifdef __cplusplus
+}  /* extern "C" */
+#endif
+
+#endif  /* UPB_DEF_H_ */