Sync from internal Google development.

Many improvements, too many to mention.  One significant
perf regression warrants investigation:

omitfp.parsetoproto2_googlemessage1.upb_jit: 343 -> 252 (-26.53)
plain.parsetoproto2_googlemessage1.upb_jit: 334 -> 251 (-24.85)

25% regression for this benchmark is bad, but since I don't think
there's any fundamental design issue that caused it I'm going to
go ahead with the commit anyway.  Can investigate and fix later.

Other benchmarks were neutral or showed slight improvement.

3 files changed, 993 insertions, 0 deletions

diff --git a/upb/descriptor/descriptor_const.h b/upb/descriptor/descriptor_const.h
new file mode 100644
index 0000000..52ca803
--- /dev/null
+++ b/upb/descriptor/descriptor_const.h
@@ -0,0 +1,349 @@
+/* This file was generated by upbc (the upb compiler).  Do not edit. */
+
+#ifndef UPB_DESCRIPTOR_CONST_H
+#define UPB_DESCRIPTOR_CONST_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Enums. */
+
+typedef enum google_protobuf_FieldDescriptorProto_Type {
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_TYPE_FIXED64 = 6,
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_TYPE_STRING = 9,
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_TYPE_FLOAT = 2,
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_TYPE_DOUBLE = 1,
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_TYPE_INT32 = 5,
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_TYPE_SFIXED32 = 15,
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_TYPE_FIXED32 = 7,
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_TYPE_MESSAGE = 11,
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_TYPE_INT64 = 3,
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_TYPE_ENUM = 14,
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_TYPE_UINT32 = 13,
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_TYPE_UINT64 = 4,
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_TYPE_SFIXED64 = 16,
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_TYPE_BYTES = 12,
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_TYPE_SINT64 = 18,
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_TYPE_BOOL = 8,
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_TYPE_GROUP = 10,
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_TYPE_SINT32 = 17
+} google_protobuf_FieldDescriptorProto_Type;
+
+typedef enum google_protobuf_FieldDescriptorProto_Label {
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_LABEL_LABEL_REQUIRED = 2,
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_LABEL_LABEL_REPEATED = 3,
+  GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_LABEL_LABEL_OPTIONAL = 1
+} google_protobuf_FieldDescriptorProto_Label;
+
+typedef enum google_protobuf_FieldOptions_CType {
+  GOOGLE_PROTOBUF_FIELDOPTIONS_CTYPE_CORD = 1,
+  GOOGLE_PROTOBUF_FIELDOPTIONS_CTYPE_STRING = 0,
+  GOOGLE_PROTOBUF_FIELDOPTIONS_CTYPE_STRING_PIECE = 2
+} google_protobuf_FieldOptions_CType;
+
+typedef enum google_protobuf_FileOptions_OptimizeMode {
+  GOOGLE_PROTOBUF_FILEOPTIONS_OPTIMIZEMODE_CODE_SIZE = 2,
+  GOOGLE_PROTOBUF_FILEOPTIONS_OPTIMIZEMODE_SPEED = 1,
+  GOOGLE_PROTOBUF_FILEOPTIONS_OPTIMIZEMODE_LITE_RUNTIME = 3
+} google_protobuf_FileOptions_OptimizeMode;
+
+/* Constants for field names and numbers. */
+
+#define GOOGLE_PROTOBUF_SOURCECODEINFO_LOCATION_PATH__FIELDNUM 1
+#define GOOGLE_PROTOBUF_SOURCECODEINFO_LOCATION_PATH__FIELDNAME "path"
+#define GOOGLE_PROTOBUF_SOURCECODEINFO_LOCATION_PATH__FIELDTYPE 5
+
+#define GOOGLE_PROTOBUF_SOURCECODEINFO_LOCATION_SPAN__FIELDNUM 2
+#define GOOGLE_PROTOBUF_SOURCECODEINFO_LOCATION_SPAN__FIELDNAME "span"
+#define GOOGLE_PROTOBUF_SOURCECODEINFO_LOCATION_SPAN__FIELDTYPE 5
+
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_NAME__FIELDNUM 2
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_NAME__FIELDNAME "name"
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_NAME__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_IDENTIFIER_VALUE__FIELDNUM 3
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_IDENTIFIER_VALUE__FIELDNAME "identifier_value"
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_IDENTIFIER_VALUE__FIELDTYPE 9
+
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_POSITIVE_INT_VALUE__FIELDNUM 4
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_POSITIVE_INT_VALUE__FIELDNAME "positive_int_value"
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_POSITIVE_INT_VALUE__FIELDTYPE 4
+
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_NEGATIVE_INT_VALUE__FIELDNUM 5
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_NEGATIVE_INT_VALUE__FIELDNAME "negative_int_value"
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_NEGATIVE_INT_VALUE__FIELDTYPE 3
+
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_AGGREGATE_VALUE__FIELDNUM 8
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_AGGREGATE_VALUE__FIELDNAME "aggregate_value"
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_AGGREGATE_VALUE__FIELDTYPE 9
+
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_DOUBLE_VALUE__FIELDNUM 6
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_DOUBLE_VALUE__FIELDNAME "double_value"
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_DOUBLE_VALUE__FIELDTYPE 1
+
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_STRING_VALUE__FIELDNUM 7
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_STRING_VALUE__FIELDNAME "string_value"
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_STRING_VALUE__FIELDTYPE 12
+
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_NAME__FIELDNUM 1
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_NAME__FIELDNAME "name"
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_NAME__FIELDTYPE 9
+
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_PACKAGE__FIELDNUM 2
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_PACKAGE__FIELDNAME "package"
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_PACKAGE__FIELDTYPE 9
+
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_DEPENDENCY__FIELDNUM 3
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_DEPENDENCY__FIELDNAME "dependency"
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_DEPENDENCY__FIELDTYPE 9
+
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_MESSAGE_TYPE__FIELDNUM 4
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_MESSAGE_TYPE__FIELDNAME "message_type"
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_MESSAGE_TYPE__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_ENUM_TYPE__FIELDNUM 5
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_ENUM_TYPE__FIELDNAME "enum_type"
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_ENUM_TYPE__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_OPTIONS__FIELDNUM 8
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_OPTIONS__FIELDNAME "options"
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_OPTIONS__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_SOURCE_CODE_INFO__FIELDNUM 9
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_SOURCE_CODE_INFO__FIELDNAME "source_code_info"
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_SOURCE_CODE_INFO__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_SERVICE__FIELDNUM 6
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_SERVICE__FIELDNAME "service"
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_SERVICE__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_EXTENSION__FIELDNUM 7
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_EXTENSION__FIELDNAME "extension"
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_EXTENSION__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_METHODDESCRIPTORPROTO_NAME__FIELDNUM 1
+#define GOOGLE_PROTOBUF_METHODDESCRIPTORPROTO_NAME__FIELDNAME "name"
+#define GOOGLE_PROTOBUF_METHODDESCRIPTORPROTO_NAME__FIELDTYPE 9
+
+#define GOOGLE_PROTOBUF_METHODDESCRIPTORPROTO_INPUT_TYPE__FIELDNUM 2
+#define GOOGLE_PROTOBUF_METHODDESCRIPTORPROTO_INPUT_TYPE__FIELDNAME "input_type"
+#define GOOGLE_PROTOBUF_METHODDESCRIPTORPROTO_INPUT_TYPE__FIELDTYPE 9
+
+#define GOOGLE_PROTOBUF_METHODDESCRIPTORPROTO_OUTPUT_TYPE__FIELDNUM 3
+#define GOOGLE_PROTOBUF_METHODDESCRIPTORPROTO_OUTPUT_TYPE__FIELDNAME "output_type"
+#define GOOGLE_PROTOBUF_METHODDESCRIPTORPROTO_OUTPUT_TYPE__FIELDTYPE 9
+
+#define GOOGLE_PROTOBUF_METHODDESCRIPTORPROTO_OPTIONS__FIELDNUM 4
+#define GOOGLE_PROTOBUF_METHODDESCRIPTORPROTO_OPTIONS__FIELDNAME "options"
+#define GOOGLE_PROTOBUF_METHODDESCRIPTORPROTO_OPTIONS__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_ENUMVALUEOPTIONS_UNINTERPRETED_OPTION__FIELDNUM 999
+#define GOOGLE_PROTOBUF_ENUMVALUEOPTIONS_UNINTERPRETED_OPTION__FIELDNAME "uninterpreted_option"
+#define GOOGLE_PROTOBUF_ENUMVALUEOPTIONS_UNINTERPRETED_OPTION__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORSET_FILE__FIELDNUM 1
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORSET_FILE__FIELDNAME "file"
+#define GOOGLE_PROTOBUF_FILEDESCRIPTORSET_FILE__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_SOURCECODEINFO_LOCATION__FIELDNUM 1
+#define GOOGLE_PROTOBUF_SOURCECODEINFO_LOCATION__FIELDNAME "location"
+#define GOOGLE_PROTOBUF_SOURCECODEINFO_LOCATION__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_EXTENSIONRANGE_START__FIELDNUM 1
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_EXTENSIONRANGE_START__FIELDNAME "start"
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_EXTENSIONRANGE_START__FIELDTYPE 5
+
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_EXTENSIONRANGE_END__FIELDNUM 2
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_EXTENSIONRANGE_END__FIELDNAME "end"
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_EXTENSIONRANGE_END__FIELDTYPE 5
+
+#define GOOGLE_PROTOBUF_ENUMVALUEDESCRIPTORPROTO_NAME__FIELDNUM 1
+#define GOOGLE_PROTOBUF_ENUMVALUEDESCRIPTORPROTO_NAME__FIELDNAME "name"
+#define GOOGLE_PROTOBUF_ENUMVALUEDESCRIPTORPROTO_NAME__FIELDTYPE 9
+
+#define GOOGLE_PROTOBUF_ENUMVALUEDESCRIPTORPROTO_NUMBER__FIELDNUM 2
+#define GOOGLE_PROTOBUF_ENUMVALUEDESCRIPTORPROTO_NUMBER__FIELDNAME "number"
+#define GOOGLE_PROTOBUF_ENUMVALUEDESCRIPTORPROTO_NUMBER__FIELDTYPE 5
+
+#define GOOGLE_PROTOBUF_ENUMVALUEDESCRIPTORPROTO_OPTIONS__FIELDNUM 3
+#define GOOGLE_PROTOBUF_ENUMVALUEDESCRIPTORPROTO_OPTIONS__FIELDNAME "options"
+#define GOOGLE_PROTOBUF_ENUMVALUEDESCRIPTORPROTO_OPTIONS__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_FIELDOPTIONS_CTYPE__FIELDNUM 1
+#define GOOGLE_PROTOBUF_FIELDOPTIONS_CTYPE__FIELDNAME "ctype"
+#define GOOGLE_PROTOBUF_FIELDOPTIONS_CTYPE__FIELDTYPE 14
+
+#define GOOGLE_PROTOBUF_FIELDOPTIONS_PACKED__FIELDNUM 2
+#define GOOGLE_PROTOBUF_FIELDOPTIONS_PACKED__FIELDNAME "packed"
+#define GOOGLE_PROTOBUF_FIELDOPTIONS_PACKED__FIELDTYPE 8
+
+#define GOOGLE_PROTOBUF_FIELDOPTIONS_DEPRECATED__FIELDNUM 3
+#define GOOGLE_PROTOBUF_FIELDOPTIONS_DEPRECATED__FIELDNAME "deprecated"
+#define GOOGLE_PROTOBUF_FIELDOPTIONS_DEPRECATED__FIELDTYPE 8
+
+#define GOOGLE_PROTOBUF_FIELDOPTIONS_EXPERIMENTAL_MAP_KEY__FIELDNUM 9
+#define GOOGLE_PROTOBUF_FIELDOPTIONS_EXPERIMENTAL_MAP_KEY__FIELDNAME "experimental_map_key"
+#define GOOGLE_PROTOBUF_FIELDOPTIONS_EXPERIMENTAL_MAP_KEY__FIELDTYPE 9
+
+#define GOOGLE_PROTOBUF_FIELDOPTIONS_UNINTERPRETED_OPTION__FIELDNUM 999
+#define GOOGLE_PROTOBUF_FIELDOPTIONS_UNINTERPRETED_OPTION__FIELDNAME "uninterpreted_option"
+#define GOOGLE_PROTOBUF_FIELDOPTIONS_UNINTERPRETED_OPTION__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_FILEOPTIONS_JAVA_PACKAGE__FIELDNUM 1
+#define GOOGLE_PROTOBUF_FILEOPTIONS_JAVA_PACKAGE__FIELDNAME "java_package"
+#define GOOGLE_PROTOBUF_FILEOPTIONS_JAVA_PACKAGE__FIELDTYPE 9
+
+#define GOOGLE_PROTOBUF_FILEOPTIONS_CC_GENERIC_SERVICES__FIELDNUM 16
+#define GOOGLE_PROTOBUF_FILEOPTIONS_CC_GENERIC_SERVICES__FIELDNAME "cc_generic_services"
+#define GOOGLE_PROTOBUF_FILEOPTIONS_CC_GENERIC_SERVICES__FIELDTYPE 8
+
+#define GOOGLE_PROTOBUF_FILEOPTIONS_JAVA_GENERIC_SERVICES__FIELDNUM 17
+#define GOOGLE_PROTOBUF_FILEOPTIONS_JAVA_GENERIC_SERVICES__FIELDNAME "java_generic_services"
+#define GOOGLE_PROTOBUF_FILEOPTIONS_JAVA_GENERIC_SERVICES__FIELDTYPE 8
+
+#define GOOGLE_PROTOBUF_FILEOPTIONS_PY_GENERIC_SERVICES__FIELDNUM 18
+#define GOOGLE_PROTOBUF_FILEOPTIONS_PY_GENERIC_SERVICES__FIELDNAME "py_generic_services"
+#define GOOGLE_PROTOBUF_FILEOPTIONS_PY_GENERIC_SERVICES__FIELDTYPE 8
+
+#define GOOGLE_PROTOBUF_FILEOPTIONS_JAVA_GENERATE_EQUALS_AND_HASH__FIELDNUM 20
+#define GOOGLE_PROTOBUF_FILEOPTIONS_JAVA_GENERATE_EQUALS_AND_HASH__FIELDNAME "java_generate_equals_and_hash"
+#define GOOGLE_PROTOBUF_FILEOPTIONS_JAVA_GENERATE_EQUALS_AND_HASH__FIELDTYPE 8
+
+#define GOOGLE_PROTOBUF_FILEOPTIONS_UNINTERPRETED_OPTION__FIELDNUM 999
+#define GOOGLE_PROTOBUF_FILEOPTIONS_UNINTERPRETED_OPTION__FIELDNAME "uninterpreted_option"
+#define GOOGLE_PROTOBUF_FILEOPTIONS_UNINTERPRETED_OPTION__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_FILEOPTIONS_JAVA_OUTER_CLASSNAME__FIELDNUM 8
+#define GOOGLE_PROTOBUF_FILEOPTIONS_JAVA_OUTER_CLASSNAME__FIELDNAME "java_outer_classname"
+#define GOOGLE_PROTOBUF_FILEOPTIONS_JAVA_OUTER_CLASSNAME__FIELDTYPE 9
+
+#define GOOGLE_PROTOBUF_FILEOPTIONS_OPTIMIZE_FOR__FIELDNUM 9
+#define GOOGLE_PROTOBUF_FILEOPTIONS_OPTIMIZE_FOR__FIELDNAME "optimize_for"
+#define GOOGLE_PROTOBUF_FILEOPTIONS_OPTIMIZE_FOR__FIELDTYPE 14
+
+#define GOOGLE_PROTOBUF_FILEOPTIONS_JAVA_MULTIPLE_FILES__FIELDNUM 10
+#define GOOGLE_PROTOBUF_FILEOPTIONS_JAVA_MULTIPLE_FILES__FIELDNAME "java_multiple_files"
+#define GOOGLE_PROTOBUF_FILEOPTIONS_JAVA_MULTIPLE_FILES__FIELDTYPE 8
+
+#define GOOGLE_PROTOBUF_ENUMDESCRIPTORPROTO_NAME__FIELDNUM 1
+#define GOOGLE_PROTOBUF_ENUMDESCRIPTORPROTO_NAME__FIELDNAME "name"
+#define GOOGLE_PROTOBUF_ENUMDESCRIPTORPROTO_NAME__FIELDTYPE 9
+
+#define GOOGLE_PROTOBUF_ENUMDESCRIPTORPROTO_VALUE__FIELDNUM 2
+#define GOOGLE_PROTOBUF_ENUMDESCRIPTORPROTO_VALUE__FIELDNAME "value"
+#define GOOGLE_PROTOBUF_ENUMDESCRIPTORPROTO_VALUE__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_ENUMDESCRIPTORPROTO_OPTIONS__FIELDNUM 3
+#define GOOGLE_PROTOBUF_ENUMDESCRIPTORPROTO_OPTIONS__FIELDNAME "options"
+#define GOOGLE_PROTOBUF_ENUMDESCRIPTORPROTO_OPTIONS__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_SERVICEDESCRIPTORPROTO_NAME__FIELDNUM 1
+#define GOOGLE_PROTOBUF_SERVICEDESCRIPTORPROTO_NAME__FIELDNAME "name"
+#define GOOGLE_PROTOBUF_SERVICEDESCRIPTORPROTO_NAME__FIELDTYPE 9
+
+#define GOOGLE_PROTOBUF_SERVICEDESCRIPTORPROTO_METHOD__FIELDNUM 2
+#define GOOGLE_PROTOBUF_SERVICEDESCRIPTORPROTO_METHOD__FIELDNAME "method"
+#define GOOGLE_PROTOBUF_SERVICEDESCRIPTORPROTO_METHOD__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_SERVICEDESCRIPTORPROTO_OPTIONS__FIELDNUM 3
+#define GOOGLE_PROTOBUF_SERVICEDESCRIPTORPROTO_OPTIONS__FIELDNAME "options"
+#define GOOGLE_PROTOBUF_SERVICEDESCRIPTORPROTO_OPTIONS__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_NAME__FIELDNUM 1
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_NAME__FIELDNAME "name"
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_NAME__FIELDTYPE 9
+
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_FIELD__FIELDNUM 2
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_FIELD__FIELDNAME "field"
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_FIELD__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_NESTED_TYPE__FIELDNUM 3
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_NESTED_TYPE__FIELDNAME "nested_type"
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_NESTED_TYPE__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_ENUM_TYPE__FIELDNUM 4
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_ENUM_TYPE__FIELDNAME "enum_type"
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_ENUM_TYPE__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_EXTENSION_RANGE__FIELDNUM 5
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_EXTENSION_RANGE__FIELDNAME "extension_range"
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_EXTENSION_RANGE__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_EXTENSION__FIELDNUM 6
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_EXTENSION__FIELDNAME "extension"
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_EXTENSION__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_OPTIONS__FIELDNUM 7
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_OPTIONS__FIELDNAME "options"
+#define GOOGLE_PROTOBUF_DESCRIPTORPROTO_OPTIONS__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_ENUMOPTIONS_UNINTERPRETED_OPTION__FIELDNUM 999
+#define GOOGLE_PROTOBUF_ENUMOPTIONS_UNINTERPRETED_OPTION__FIELDNAME "uninterpreted_option"
+#define GOOGLE_PROTOBUF_ENUMOPTIONS_UNINTERPRETED_OPTION__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_NAME__FIELDNUM 1
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_NAME__FIELDNAME "name"
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_NAME__FIELDTYPE 9
+
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_EXTENDEE__FIELDNUM 2
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_EXTENDEE__FIELDNAME "extendee"
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_EXTENDEE__FIELDTYPE 9
+
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_NUMBER__FIELDNUM 3
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_NUMBER__FIELDNAME "number"
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_NUMBER__FIELDTYPE 5
+
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_LABEL__FIELDNUM 4
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_LABEL__FIELDNAME "label"
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_LABEL__FIELDTYPE 14
+
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE__FIELDNUM 5
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE__FIELDNAME "type"
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE__FIELDTYPE 14
+
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_OPTIONS__FIELDNUM 8
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_OPTIONS__FIELDNAME "options"
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_OPTIONS__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_NAME__FIELDNUM 6
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_NAME__FIELDNAME "type_name"
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_TYPE_NAME__FIELDTYPE 9
+
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_DEFAULT_VALUE__FIELDNUM 7
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_DEFAULT_VALUE__FIELDNAME "default_value"
+#define GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_DEFAULT_VALUE__FIELDTYPE 9
+
+#define GOOGLE_PROTOBUF_SERVICEOPTIONS_UNINTERPRETED_OPTION__FIELDNUM 999
+#define GOOGLE_PROTOBUF_SERVICEOPTIONS_UNINTERPRETED_OPTION__FIELDNAME "uninterpreted_option"
+#define GOOGLE_PROTOBUF_SERVICEOPTIONS_UNINTERPRETED_OPTION__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_MESSAGEOPTIONS_MESSAGE_SET_WIRE_FORMAT__FIELDNUM 1
+#define GOOGLE_PROTOBUF_MESSAGEOPTIONS_MESSAGE_SET_WIRE_FORMAT__FIELDNAME "message_set_wire_format"
+#define GOOGLE_PROTOBUF_MESSAGEOPTIONS_MESSAGE_SET_WIRE_FORMAT__FIELDTYPE 8
+
+#define GOOGLE_PROTOBUF_MESSAGEOPTIONS_NO_STANDARD_DESCRIPTOR_ACCESSOR__FIELDNUM 2
+#define GOOGLE_PROTOBUF_MESSAGEOPTIONS_NO_STANDARD_DESCRIPTOR_ACCESSOR__FIELDNAME "no_standard_descriptor_accessor"
+#define GOOGLE_PROTOBUF_MESSAGEOPTIONS_NO_STANDARD_DESCRIPTOR_ACCESSOR__FIELDTYPE 8
+
+#define GOOGLE_PROTOBUF_MESSAGEOPTIONS_UNINTERPRETED_OPTION__FIELDNUM 999
+#define GOOGLE_PROTOBUF_MESSAGEOPTIONS_UNINTERPRETED_OPTION__FIELDNAME "uninterpreted_option"
+#define GOOGLE_PROTOBUF_MESSAGEOPTIONS_UNINTERPRETED_OPTION__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_METHODOPTIONS_UNINTERPRETED_OPTION__FIELDNUM 999
+#define GOOGLE_PROTOBUF_METHODOPTIONS_UNINTERPRETED_OPTION__FIELDNAME "uninterpreted_option"
+#define GOOGLE_PROTOBUF_METHODOPTIONS_UNINTERPRETED_OPTION__FIELDTYPE 11
+
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_NAMEPART_NAME_PART__FIELDNUM 1
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_NAMEPART_NAME_PART__FIELDNAME "name_part"
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_NAMEPART_NAME_PART__FIELDTYPE 9
+
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_NAMEPART_IS_EXTENSION__FIELDNUM 2
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_NAMEPART_IS_EXTENSION__FIELDNAME "is_extension"
+#define GOOGLE_PROTOBUF_UNINTERPRETEDOPTION_NAMEPART_IS_EXTENSION__FIELDTYPE 8
+
+#ifdef __cplusplus
+}  /* extern "C" */
+#endif
+
+#endif  /* UPB_DESCRIPTOR_CONST_H */
diff --git a/upb/descriptor/reader.c b/upb/descriptor/reader.c
new file mode 100644
index 0000000..8177560
--- /dev/null
+++ b/upb/descriptor/reader.c
@@ -0,0 +1,561 @@
+/*
+ * upb - a minimalist implementation of protocol buffers.
+ *
+ * Copyright (c) 2008-2009 Google Inc.  See LICENSE for details.
+ * Author: Josh Haberman <jhaberman@gmail.com>
+ */
+
+#include <stdlib.h>
+#include <errno.h>
+#include "upb/def.h"
+#include "upb/descriptor/descriptor_const.h"
+#include "upb/descriptor/reader.h"
+
+// Returns a newly allocated string that joins input strings together, for example:
+//   join("Foo.Bar", "Baz") -> "Foo.Bar.Baz"
+//   join("", "Baz") -> "Baz"
+// Caller owns a ref on the returned string. */
+static char *upb_join(const char *base, const char *name) {
+  if (!base || strlen(base) == 0) {
+    return strdup(name);
+  } else {
+    char *ret = malloc(strlen(base) + strlen(name) + 2);
+    ret[0] = '\0';
+    strcat(ret, base);
+    strcat(ret, ".");
+    strcat(ret, name);
+    return ret;
+  }
+}
+
+void upb_deflist_init(upb_deflist *l) {
+  l->size = 8;
+  l->defs = malloc(l->size * sizeof(void*));
+  l->len = 0;
+  l->owned = true;
+}
+
+void upb_deflist_uninit(upb_deflist *l) {
+  if (l->owned)
+    for(size_t i = 0; i < l->len; i++)
+      upb_def_unref(l->defs[i], &l->defs);
+  free(l->defs);
+}
+
+void upb_deflist_push(upb_deflist *l, upb_def *d) {
+  if(l->len == l->size) {
+    l->size *= 2;
+    l->defs = realloc(l->defs, l->size * sizeof(void*));
+  }
+  l->defs[l->len++] = d;
+}
+
+void upb_deflist_donaterefs(upb_deflist *l, void *owner) {
+  assert(l->owned);
+  for (size_t i = 0; i < l->len; i++)
+    upb_def_donateref(l->defs[i], &l->defs, owner);
+  l->owned = false;
+}
+
+
+/* upb_descreader  ************************************************************/
+
+static upb_def *upb_deflist_last(upb_deflist *l) {
+  return l->defs[l->len-1];
+}
+
+// Qualify the defname for all defs starting with offset "start" with "str".
+static void upb_deflist_qualify(upb_deflist *l, char *str, int32_t start) {
+  for(uint32_t i = start; i < l->len; i++) {
+    upb_def *def = l->defs[i];
+    char *name = upb_join(str, upb_def_fullname(def));
+    upb_def_setfullname(def, name);
+    free(name);
+  }
+}
+
+// Forward declares for top-level file descriptors.
+static upb_mhandlers *upb_msgdef_register_DescriptorProto(upb_handlers *h);
+static upb_mhandlers * upb_enumdef_register_EnumDescriptorProto(upb_handlers *h);
+
+void upb_descreader_init(upb_descreader *r) {
+  upb_deflist_init(&r->defs);
+  upb_status_init(&r->status);
+  r->stack_len = 0;
+  r->name = NULL;
+  r->default_string = NULL;
+}
+
+void upb_descreader_uninit(upb_descreader *r) {
+  free(r->name);
+  upb_status_uninit(&r->status);
+  upb_deflist_uninit(&r->defs);
+  free(r->default_string);
+  while (r->stack_len > 0) {
+    upb_descreader_frame *f = &r->stack[--r->stack_len];
+    free(f->name);
+  }
+}
+
+upb_def **upb_descreader_getdefs(upb_descreader *r, void *owner, int *n) {
+  *n = r->defs.len;
+  upb_deflist_donaterefs(&r->defs, owner);
+  return r->defs.defs;
+}
+
+static upb_msgdef *upb_descreader_top(upb_descreader *r) {
+  if (r->stack_len <= 1) return NULL;
+  int index = r->stack[r->stack_len-1].start - 1;
+  assert(index >= 0);
+  return upb_downcast_msgdef(r->defs.defs[index]);
+}
+
+static upb_def *upb_descreader_last(upb_descreader *r) {
+  return upb_deflist_last(&r->defs);
+}
+
+// Start/end handlers for FileDescriptorProto and DescriptorProto (the two
+// entities that have names and can contain sub-definitions.
+void upb_descreader_startcontainer(upb_descreader *r) {
+  upb_descreader_frame *f = &r->stack[r->stack_len++];
+  f->start = r->defs.len;
+  f->name = NULL;
+}
+
+void upb_descreader_endcontainer(upb_descreader *r) {
+  upb_descreader_frame *f = &r->stack[--r->stack_len];
+  upb_deflist_qualify(&r->defs, f->name, f->start);
+  free(f->name);
+  f->name = NULL;
+}
+
+void upb_descreader_setscopename(upb_descreader *r, char *str) {
+  upb_descreader_frame *f = &r->stack[r->stack_len-1];
+  free(f->name);
+  f->name = str;
+}
+
+// Handlers for google.protobuf.FileDescriptorProto.
+static upb_flow_t upb_descreader_FileDescriptorProto_startmsg(void *_r) {
+  upb_descreader *r = _r;
+  upb_descreader_startcontainer(r);
+  return UPB_CONTINUE;
+}
+
+static void upb_descreader_FileDescriptorProto_endmsg(void *_r,
+                                                      upb_status *status) {
+  (void)status;
+  upb_descreader *r = _r;
+  upb_descreader_endcontainer(r);
+}
+
+static upb_flow_t upb_descreader_FileDescriptorProto_package(void *_r,
+                                                             upb_value fval,
+                                                             upb_value val) {
+  (void)fval;
+  upb_descreader *r = _r;
+  upb_descreader_setscopename(
+      r, upb_byteregion_strdup(upb_value_getbyteregion(val)));
+  return UPB_CONTINUE;
+}
+
+static upb_mhandlers *upb_descreader_register_FileDescriptorProto(
+    upb_handlers *h) {
+  upb_mhandlers *m = upb_handlers_newmhandlers(h);
+  upb_mhandlers_setstartmsg(m, &upb_descreader_FileDescriptorProto_startmsg);
+  upb_mhandlers_setendmsg(m, &upb_descreader_FileDescriptorProto_endmsg);
+
+#define FNUM(field) GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_ ## field ## __FIELDNUM
+#define FTYPE(field) GOOGLE_PROTOBUF_FILEDESCRIPTORPROTO_ ## field ## __FIELDTYPE
+  upb_fhandlers *f =
+      upb_mhandlers_newfhandlers(m, FNUM(PACKAGE), FTYPE(PACKAGE), false);
+  upb_fhandlers_setvalue(f, &upb_descreader_FileDescriptorProto_package);
+
+  upb_mhandlers_newfhandlers_subm(m, FNUM(MESSAGE_TYPE), FTYPE(MESSAGE_TYPE), true,
+                                  upb_msgdef_register_DescriptorProto(h));
+  upb_mhandlers_newfhandlers_subm(m, FNUM(ENUM_TYPE), FTYPE(ENUM_TYPE), true,
+                                  upb_enumdef_register_EnumDescriptorProto(h));
+  // TODO: services, extensions
+  return m;
+}
+#undef FNUM
+#undef FTYPE
+
+static upb_mhandlers *upb_descreader_register_FileDescriptorSet(upb_handlers *h) {
+  upb_mhandlers *m = upb_handlers_newmhandlers(h);
+
+#define FNUM(field) GOOGLE_PROTOBUF_FILEDESCRIPTORSET_ ## field ## __FIELDNUM
+#define FTYPE(field) GOOGLE_PROTOBUF_FILEDESCRIPTORSET_ ## field ## __FIELDTYPE
+  upb_mhandlers_newfhandlers_subm(m, FNUM(FILE), FTYPE(FILE), true,
+                                   upb_descreader_register_FileDescriptorProto(h));
+  return m;
+}
+#undef FNUM
+#undef FTYPE
+
+upb_mhandlers *upb_descreader_reghandlers(upb_handlers *h) {
+  h->should_jit = false;
+  return upb_descreader_register_FileDescriptorSet(h);
+}
+
+// google.protobuf.EnumValueDescriptorProto.
+static upb_flow_t upb_enumdef_EnumValueDescriptorProto_startmsg(void *_r) {
+  upb_descreader *r = _r;
+  r->saw_number = false;
+  r->saw_name = false;
+  return UPB_CONTINUE;
+}
+
+static upb_flow_t upb_enumdef_EnumValueDescriptorProto_name(void *_r,
+                                                            upb_value fval,
+                                                            upb_value val) {
+  (void)fval;
+  upb_descreader *r = _r;
+  free(r->name);
+  r->name = upb_byteregion_strdup(upb_value_getbyteregion(val));
+  r->saw_name = true;
+  return UPB_CONTINUE;
+}
+
+static upb_flow_t upb_enumdef_EnumValueDescriptorProto_number(void *_r,
+                                                              upb_value fval,
+                                                              upb_value val) {
+  (void)fval;
+  upb_descreader *r = _r;
+  r->number = upb_value_getint32(val);
+  r->saw_number = true;
+  return UPB_CONTINUE;
+}
+
+static void upb_enumdef_EnumValueDescriptorProto_endmsg(void *_r,
+                                                        upb_status *status) {
+  upb_descreader *r = _r;
+  if(!r->saw_number || !r->saw_name) {
+    upb_status_seterrliteral(status, "Enum value missing name or number.");
+    return;
+  }
+  upb_enumdef *e = upb_downcast_enumdef(upb_descreader_last(r));
+  if (upb_enumdef_numvals(e) == 0) {
+    // The default value of an enum (in the absence of an explicit default) is
+    // its first listed value.
+    upb_enumdef_setdefault(e, r->number);
+  }
+  upb_enumdef_addval(e, r->name, r->number);
+  free(r->name);
+  r->name = NULL;
+}
+
+static upb_mhandlers *upb_enumdef_register_EnumValueDescriptorProto(
+    upb_handlers *h) {
+  upb_mhandlers *m = upb_handlers_newmhandlers(h);
+  upb_mhandlers_setstartmsg(m, &upb_enumdef_EnumValueDescriptorProto_startmsg);
+  upb_mhandlers_setendmsg(m, &upb_enumdef_EnumValueDescriptorProto_endmsg);
+
+#define FNUM(f) GOOGLE_PROTOBUF_ENUMVALUEDESCRIPTORPROTO_ ## f ## __FIELDNUM
+#define FTYPE(f) GOOGLE_PROTOBUF_ENUMVALUEDESCRIPTORPROTO_ ## f ## __FIELDTYPE
+  upb_fhandlers *f;
+  f = upb_mhandlers_newfhandlers(m, FNUM(NAME), FTYPE(NAME), false);
+  upb_fhandlers_setvalue(f, &upb_enumdef_EnumValueDescriptorProto_name);
+
+  f = upb_mhandlers_newfhandlers(m, FNUM(NUMBER), FTYPE(NUMBER), false);
+  upb_fhandlers_setvalue(f, &upb_enumdef_EnumValueDescriptorProto_number);
+  return m;
+}
+#undef FNUM
+#undef FTYPE
+
+// google.protobuf.EnumDescriptorProto.
+static upb_flow_t upb_enumdef_EnumDescriptorProto_startmsg(void *_r) {
+  upb_descreader *r = _r;
+  upb_deflist_push(&r->defs, UPB_UPCAST(upb_enumdef_new(&r->defs)));
+  return UPB_CONTINUE;
+}
+
+static void upb_enumdef_EnumDescriptorProto_endmsg(void *_r, upb_status *status) {
+  upb_descreader *r = _r;
+  upb_enumdef *e = upb_downcast_enumdef(upb_descreader_last(r));
+  if (upb_def_fullname(upb_descreader_last((upb_descreader*)_r)) == NULL) {
+    upb_status_seterrliteral(status, "Enum had no name.");
+    return;
+  }
+  if (upb_enumdef_numvals(e) == 0) {
+    upb_status_seterrliteral(status, "Enum had no values.");
+    return;
+  }
+}
+
+static upb_flow_t upb_enumdef_EnumDescriptorProto_name(void *_r,
+                                                       upb_value fval,
+                                                       upb_value val) {
+  (void)fval;
+  upb_descreader *r = _r;
+  char *fullname = upb_byteregion_strdup(upb_value_getbyteregion(val));
+  upb_def_setfullname(upb_descreader_last(r), fullname);
+  free(fullname);
+  return UPB_CONTINUE;
+}
+
+static upb_mhandlers *upb_enumdef_register_EnumDescriptorProto(upb_handlers *h) {
+  upb_mhandlers *m = upb_handlers_newmhandlers(h);
+  upb_mhandlers_setstartmsg(m, &upb_enumdef_EnumDescriptorProto_startmsg);
+  upb_mhandlers_setendmsg(m, &upb_enumdef_EnumDescriptorProto_endmsg);
+
+#define FNUM(f) GOOGLE_PROTOBUF_ENUMDESCRIPTORPROTO_ ## f ## __FIELDNUM
+#define FTYPE(f) GOOGLE_PROTOBUF_ENUMDESCRIPTORPROTO_ ## f ## __FIELDTYPE
+  upb_fhandlers *f =
+      upb_mhandlers_newfhandlers(m, FNUM(NAME), FTYPE(NAME), false);
+  upb_fhandlers_setvalue(f, &upb_enumdef_EnumDescriptorProto_name);
+
+  upb_mhandlers_newfhandlers_subm(m, FNUM(VALUE), FTYPE(VALUE), true,
+                               upb_enumdef_register_EnumValueDescriptorProto(h));
+  return m;
+}
+#undef FNUM
+#undef FTYPE
+
+static upb_flow_t upb_fielddef_startmsg(void *_r) {
+  upb_descreader *r = _r;
+  r->f = upb_fielddef_new(&r->defs);
+  free(r->default_string);
+  r->default_string = NULL;
+  return UPB_CONTINUE;
+}
+
+// Converts the default value in string "str" into "d".  Passes a ref on str.
+// Returns true on success.
+static bool upb_fielddef_parsedefault(char *str, upb_value *d, int type) {
+  bool success = true;
+  if (str) {
+    switch(type) {
+      case UPB_TYPE(INT32):
+      case UPB_TYPE(SINT32):
+      case UPB_TYPE(SFIXED32): upb_value_setint32(d, 0); break;
+      case UPB_TYPE(INT64):
+      case UPB_TYPE(SINT64):
+      case UPB_TYPE(SFIXED64): upb_value_setint64(d, 0); break;
+      case UPB_TYPE(UINT32):
+      case UPB_TYPE(FIXED32): upb_value_setuint32(d, 0);
+      case UPB_TYPE(UINT64):
+      case UPB_TYPE(FIXED64): upb_value_setuint64(d, 0); break;
+      case UPB_TYPE(DOUBLE): upb_value_setdouble(d, 0); break;
+      case UPB_TYPE(FLOAT): upb_value_setfloat(d, 0); break;
+      case UPB_TYPE(BOOL): upb_value_setbool(d, false); break;
+      default: abort();
+    }
+  } else {
+    char *end;
+    switch (type) {
+      case UPB_TYPE(INT32):
+      case UPB_TYPE(SINT32):
+      case UPB_TYPE(SFIXED32): {
+        long val = strtol(str, &end, 0);
+        if (val > INT32_MAX || val < INT32_MIN || errno == ERANGE || *end)
+          success = false;
+        else
+          upb_value_setint32(d, val);
+        break;
+      }
+      case UPB_TYPE(INT64):
+      case UPB_TYPE(SINT64):
+      case UPB_TYPE(SFIXED64):
+        upb_value_setint64(d, strtoll(str, &end, 0));
+        if (errno == ERANGE || *end) success = false;
+        break;
+      case UPB_TYPE(UINT32):
+      case UPB_TYPE(FIXED32): {
+        unsigned long val = strtoul(str, &end, 0);
+        if (val > UINT32_MAX || errno == ERANGE || *end)
+          success = false;
+        else
+          upb_value_setuint32(d, val);
+        break;
+      }
+      case UPB_TYPE(UINT64):
+      case UPB_TYPE(FIXED64):
+        upb_value_setuint64(d, strtoull(str, &end, 0));
+        if (errno == ERANGE || *end) success = false;
+        break;
+      case UPB_TYPE(DOUBLE):
+        upb_value_setdouble(d, strtod(str, &end));
+        if (errno == ERANGE || *end) success = false;
+        break;
+      case UPB_TYPE(FLOAT):
+        upb_value_setfloat(d, strtof(str, &end));
+        if (errno == ERANGE || *end) success = false;
+        break;
+      case UPB_TYPE(BOOL): {
+        if (strcmp(str, "false") == 0)
+          upb_value_setbool(d, false);
+        else if (strcmp(str, "true") == 0)
+          upb_value_setbool(d, true);
+        else
+          success = false;
+      }
+      default: abort();
+    }
+  }
+  return success;
+}
+
+static void upb_fielddef_endmsg(void *_r, upb_status *status) {
+  upb_descreader *r = _r;
+  upb_fielddef *f = r->f;
+  // TODO: verify that all required fields were present.
+  assert(f->number != -1 && upb_fielddef_name(f) != NULL);
+  assert((upb_fielddef_subtypename(f) != NULL) == upb_hassubdef(f));
+
+  // Field was successfully read, add it as a field of the msgdef.
+  upb_msgdef *m = upb_descreader_top(r);
+  upb_msgdef_addfield(m, f, &r->defs);
+  r->f = NULL;
+
+  if (r->default_string) {
+    if (upb_issubmsg(f)) {
+      upb_status_seterrliteral(status, "Submessages cannot have defaults.");
+      return;
+    }
+    if (upb_isstring(f) || f->type == UPB_TYPE(ENUM)) {
+      upb_fielddef_setdefaultcstr(f, r->default_string);
+    } else {
+      upb_value val;
+      upb_value_setptr(&val, NULL);  // Silence inaccurate compiler warnings.
+      if (!upb_fielddef_parsedefault(r->default_string, &val, f->type)) {
+        // We don't worry too much about giving a great error message since the
+        // compiler should have ensured this was correct.
+        upb_status_seterrliteral(status, "Error converting default value.");
+        return;
+      }
+      upb_fielddef_setdefault(f, val);
+    }
+  }
+}
+
+static upb_flow_t upb_fielddef_ontype(void *_r, upb_value fval, upb_value val) {
+  (void)fval;
+  upb_descreader *r = _r;
+  upb_fielddef_settype(r->f, upb_value_getint32(val));
+  return UPB_CONTINUE;
+}
+
+static upb_flow_t upb_fielddef_onlabel(void *_r, upb_value fval, upb_value val) {
+  (void)fval;
+  upb_descreader *r = _r;
+  upb_fielddef_setlabel(r->f, upb_value_getint32(val));
+  return UPB_CONTINUE;
+}
+
+static upb_flow_t upb_fielddef_onnumber(void *_r, upb_value fval, upb_value val) {
+  (void)fval;
+  upb_descreader *r = _r;
+  upb_fielddef_setnumber(r->f, upb_value_getint32(val));
+  return UPB_CONTINUE;
+}
+
+static upb_flow_t upb_fielddef_onname(void *_r, upb_value fval, upb_value val) {
+  (void)fval;
+  upb_descreader *r = _r;
+  char *name = upb_byteregion_strdup(upb_value_getbyteregion(val));
+  upb_fielddef_setname(r->f, name);
+  free(name);
+  return UPB_CONTINUE;
+}
+
+static upb_flow_t upb_fielddef_ontypename(void *_r, upb_value fval,
+                                          upb_value val) {
+  (void)fval;
+  upb_descreader *r = _r;
+  char *name = upb_byteregion_strdup(upb_value_getbyteregion(val));
+  upb_fielddef_setsubtypename(r->f, name);
+  free(name);
+  return UPB_CONTINUE;
+}
+
+static upb_flow_t upb_fielddef_ondefaultval(void *_r, upb_value fval,
+                                            upb_value val) {
+  (void)fval;
+  upb_descreader *r = _r;
+  // Have to convert from string to the correct type, but we might not know the
+  // type yet.
+  free(r->default_string);
+  r->default_string = upb_byteregion_strdup(upb_value_getbyteregion(val));
+  return UPB_CONTINUE;
+}
+
+static upb_mhandlers *upb_fielddef_register_FieldDescriptorProto(
+    upb_handlers *h) {
+  upb_mhandlers *m = upb_handlers_newmhandlers(h);
+  upb_mhandlers_setstartmsg(m, &upb_fielddef_startmsg);
+  upb_mhandlers_setendmsg(m, &upb_fielddef_endmsg);
+
+#define FIELD(name, handler) \
+  upb_fhandlers_setvalue( \
+      upb_mhandlers_newfhandlers(m, \
+          GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_ ## name ## __FIELDNUM, \
+          GOOGLE_PROTOBUF_FIELDDESCRIPTORPROTO_ ## name ## __FIELDTYPE, \
+          false), \
+      handler);
+  FIELD(TYPE, &upb_fielddef_ontype);
+  FIELD(LABEL, &upb_fielddef_onlabel);
+  FIELD(NUMBER, &upb_fielddef_onnumber);
+  FIELD(NAME, &upb_fielddef_onname);
+  FIELD(TYPE_NAME, &upb_fielddef_ontypename);
+  FIELD(DEFAULT_VALUE, &upb_fielddef_ondefaultval);
+  return m;
+}
+#undef FNUM
+#undef FTYPE
+
+
+// google.protobuf.DescriptorProto.
+static upb_flow_t upb_msgdef_startmsg(void *_r) {
+  upb_descreader *r = _r;
+  upb_deflist_push(&r->defs, UPB_UPCAST(upb_msgdef_new(&r->defs)));
+  upb_descreader_startcontainer(r);
+  return UPB_CONTINUE;
+}
+
+static void upb_msgdef_endmsg(void *_r, upb_status *status) {
+  upb_descreader *r = _r;
+  upb_msgdef *m = upb_descreader_top(r);
+  if(!upb_def_fullname(UPB_UPCAST(m))) {
+    upb_status_seterrliteral(status, "Encountered message with no name.");
+    return;
+  }
+  upb_descreader_endcontainer(r);
+}
+
+static upb_flow_t upb_msgdef_onname(void *_r, upb_value fval, upb_value val) {
+  (void)fval;
+  upb_descreader *r = _r;
+  upb_msgdef *m = upb_descreader_top(r);
+  char *name = upb_byteregion_strdup(upb_value_getbyteregion(val));
+  upb_def_setfullname(UPB_UPCAST(m), name);
+  upb_descreader_setscopename(r, name);  // Passes ownership of name.
+  return UPB_CONTINUE;
+}
+
+static upb_mhandlers *upb_msgdef_register_DescriptorProto(upb_handlers *h) {
+  upb_mhandlers *m = upb_handlers_newmhandlers(h);
+  upb_mhandlers_setstartmsg(m, &upb_msgdef_startmsg);
+  upb_mhandlers_setendmsg(m, &upb_msgdef_endmsg);
+
+#define FNUM(f) GOOGLE_PROTOBUF_DESCRIPTORPROTO_ ## f ## __FIELDNUM
+#define FTYPE(f) GOOGLE_PROTOBUF_DESCRIPTORPROTO_ ## f ## __FIELDTYPE
+  upb_fhandlers *f =
+      upb_mhandlers_newfhandlers(m, FNUM(NAME), FTYPE(NAME), false);
+  upb_fhandlers_setvalue(f, &upb_msgdef_onname);
+
+  upb_mhandlers_newfhandlers_subm(m, FNUM(FIELD), FTYPE(FIELD), true,
+                                  upb_fielddef_register_FieldDescriptorProto(h));
+  upb_mhandlers_newfhandlers_subm(m, FNUM(ENUM_TYPE), FTYPE(ENUM_TYPE), true,
+                                  upb_enumdef_register_EnumDescriptorProto(h));
+
+  // DescriptorProto is self-recursive, so we must link the definition.
+  upb_mhandlers_newfhandlers_subm(
+      m, FNUM(NESTED_TYPE), FTYPE(NESTED_TYPE), true, m);
+
+  // TODO: extensions.
+  return m;
+}
+#undef FNUM
+#undef FTYPE
diff --git a/upb/descriptor/reader.h b/upb/descriptor/reader.h
new file mode 100644
index 0000000..0e1bfa0
--- /dev/null
+++ b/upb/descriptor/reader.h
@@ -0,0 +1,83 @@
+/*
+ * upb - a minimalist implementation of protocol buffers.
+ *
+ * Copyright (c) 2011 Google Inc.  See LICENSE for details.
+ * Author: Josh Haberman <jhaberman@gmail.com>
+ *
+ * upb_descreader provides a set of sink handlers that will build defs from a
+ * data source that uses the descriptor.proto schema (like a protobuf binary
+ * descriptor).
+ */
+
+#ifndef UPB_DESCRIPTOR_H
+#define UPB_DESCRIPTOR_H
+
+#include "upb/handlers.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* upb_deflist ****************************************************************/
+
+// upb_deflist is an internal-only dynamic array for storing a growing list of
+// upb_defs.
+typedef struct {
+  upb_def **defs;
+  size_t len;
+  size_t size;
+  bool owned;
+} upb_deflist;
+
+void upb_deflist_init(upb_deflist *l);
+void upb_deflist_uninit(upb_deflist *l);
+void upb_deflist_push(upb_deflist *l, upb_def *d);
+
+/* upb_descreader  ************************************************************/
+
+// We keep a stack of all the messages scopes we are currently in, as well as
+// the top-level file scope.  This is necessary to correctly qualify the
+// definitions that are contained inside.  "name" tracks the name of the
+// message or package (a bare name -- not qualified by any enclosing scopes).
+typedef struct {
+  char *name;
+  // Index of the first def that is under this scope.  For msgdefs, the
+  // msgdef itself is at start-1.
+  int start;
+} upb_descreader_frame;
+
+typedef struct {
+  upb_deflist defs;
+  upb_descreader_frame stack[UPB_MAX_TYPE_DEPTH];
+  int stack_len;
+  upb_status status;
+
+  uint32_t number;
+  char *name;
+  bool saw_number;
+  bool saw_name;
+
+  char *default_string;
+
+  upb_fielddef *f;
+} upb_descreader;
+
+void upb_descreader_init(upb_descreader *r);
+void upb_descreader_uninit(upb_descreader *r);
+
+// Registers handlers that will build the defs.  Pass the descreader as the
+// closure.
+upb_mhandlers *upb_descreader_reghandlers(upb_handlers *h);
+
+// Gets the array of defs that have been parsed and removes them from the
+// descreader.  Ownership of the defs is passed to the caller using the given
+// owner), but the ownership of the returned array is retained and is
+// invalidated by any other call into the descreader.  The defs will not have
+// been resolved, and are ready to be added to a symtab.
+upb_def **upb_descreader_getdefs(upb_descreader *r, void *owner, int *n);
+
+#ifdef __cplusplus
+}  /* extern "C" */
+#endif
+
+#endif