/* pb_decode.c -- decode a protobuf using minimal resources * * 2011 Petteri Aimonen <jpa@kapsi.fi> */ #ifdef __GNUC__ /* Verify that we remember to check all return values for proper error propagation */ #define checkreturn __attribute__((warn_unused_result)) #else #define checkreturn #endif #include "pb.h" #include "pb_decode.h" #include <string.h> typedef bool (*pb_decoder_t)(pb_istream_t *stream, const pb_field_t *field, void *dest) checkreturn; /* --- Function pointers to field decoders --- * Order in the array must match pb_action_t LTYPE numbering. */ static const pb_decoder_t PB_DECODERS[PB_LTYPES_COUNT] = { &pb_dec_varint, &pb_dec_svarint, &pb_dec_fixed32, &pb_dec_fixed64, &pb_dec_bytes, &pb_dec_string, &pb_dec_submessage }; /************** * pb_istream * **************/ bool checkreturn pb_read(pb_istream_t *stream, uint8_t *buf, size_t count) { if (stream->bytes_left < count) return false; if (!stream->callback(stream, buf, count)) return false; stream->bytes_left -= count; return true; } static bool checkreturn buf_read(pb_istream_t *stream, uint8_t *buf, size_t count) { uint8_t *source = (uint8_t*)stream->state; if (buf != NULL) memcpy(buf, source, count); stream->state = source + count; return true; } pb_istream_t pb_istream_from_buffer(uint8_t *buf, size_t bufsize) { pb_istream_t stream; stream.callback = &buf_read; stream.state = buf; stream.bytes_left = bufsize; return stream; } /******************** * Helper functions * ********************/ static bool checkreturn pb_decode_varint32(pb_istream_t *stream, uint32_t *dest) { uint64_t temp; bool status = pb_decode_varint(stream, &temp); *dest = (uint32_t)temp; return status; } bool checkreturn pb_decode_varint(pb_istream_t *stream, uint64_t *dest) { uint8_t byte; uint8_t bitpos = 0; *dest = 0; while (bitpos < 64 && pb_read(stream, &byte, 1)) { *dest |= (uint64_t)(byte & 0x7F) << bitpos; bitpos += 7; if (!(byte & 0x80)) return true; } return false; } bool checkreturn pb_skip_varint(pb_istream_t *stream) { uint8_t byte; do { if (!pb_read(stream, &byte, 1)) return false; } while (byte & 0x80); return true; } bool checkreturn pb_skip_string(pb_istream_t *stream) { uint32_t length; if (!pb_decode_varint32(stream, &length)) return false; return pb_read(stream, NULL, length); } /* Currently the wire type related stuff is kept hidden from * callbacks. They shouldn't need it. It's better for performance * to just assume the correct type and fail safely on corrupt message. */ static bool checkreturn skip(pb_istream_t *stream, pb_wire_type_t wire_type) { switch (wire_type) { case PB_WT_VARINT: return pb_skip_varint(stream); case PB_WT_64BIT: return pb_read(stream, NULL, 8); case PB_WT_STRING: return pb_skip_string(stream); case PB_WT_32BIT: return pb_read(stream, NULL, 4); default: return false; } } /* Read a raw value to buffer, for the purpose of passing it to callback as * a substream. Size is maximum size on call, and actual size on return. */ static bool checkreturn read_raw_value(pb_istream_t *stream, pb_wire_type_t wire_type, uint8_t *buf, size_t *size) { size_t max_size = *size; switch (wire_type) { case PB_WT_VARINT: *size = 0; do { (*size)++; if (*size > max_size) return false; if (!pb_read(stream, buf, 1)) return false; } while (*buf++ & 0x80); return true; case PB_WT_64BIT: *size = 8; return pb_read(stream, buf, 8); case PB_WT_32BIT: *size = 4; return pb_read(stream, buf, 4); default: return false; } } /* Decode string length from stream and return a substream with limited length. * Before disposing the substream, remember to copy the substream->state back * to stream->state. */ static bool checkreturn make_string_substream(pb_istream_t *stream, pb_istream_t *substream) { uint32_t size; if (!pb_decode_varint32(stream, &size)) return false; *substream = *stream; if (substream->bytes_left < size) return false; substream->bytes_left = size; stream->bytes_left -= size; return true; } /* Iterator for pb_field_t list */ typedef struct { const pb_field_t *start; const pb_field_t *current; int field_index; void *dest_struct; void *pData; void *pSize; } pb_field_iterator_t; static void pb_field_init(pb_field_iterator_t *iter, const pb_field_t *fields, void *dest_struct) { iter->start = iter->current = fields; iter->field_index = 0; iter->pData = (char*)dest_struct + iter->current->data_offset; iter->pSize = (char*)iter->pData + iter->current->size_offset; iter->dest_struct = dest_struct; } static bool pb_field_next(pb_field_iterator_t *iter) { bool notwrapped = true; size_t prev_size = iter->current->data_size; if (PB_HTYPE(iter->current->type) == PB_HTYPE_ARRAY) prev_size *= iter->current->array_size; iter->current++; iter->field_index++; if (iter->current->tag == 0) { iter->current = iter->start; iter->field_index = 0; iter->pData = iter->dest_struct; prev_size = 0; notwrapped = false; } iter->pData = (char*)iter->pData + prev_size + iter->current->data_offset; iter->pSize = (char*)iter->pData + iter->current->size_offset; return notwrapped; } static bool checkreturn pb_field_find(pb_field_iterator_t *iter, int tag) { int start = iter->field_index; do { if (iter->current->tag == tag) return true; pb_field_next(iter); } while (iter->field_index != start); return false; } /************************* * Decode a single field * *************************/ static bool checkreturn decode_field(pb_istream_t *stream, pb_wire_type_t wire_type, pb_field_iterator_t *iter) { pb_decoder_t func = PB_DECODERS[PB_LTYPE(iter->current->type)]; switch (PB_HTYPE(iter->current->type)) { case PB_HTYPE_REQUIRED: return func(stream, iter->current, iter->pData); case PB_HTYPE_OPTIONAL: *(bool*)iter->pSize = true; return func(stream, iter->current, iter->pData); case PB_HTYPE_ARRAY: if (wire_type == PB_WT_STRING && PB_LTYPE(iter->current->type) <= PB_LTYPE_LAST_PACKABLE) { /* Packed array */ size_t *size = (size_t*)iter->pSize; pb_istream_t substream; if (!make_string_substream(stream, &substream)) return false; while (substream.bytes_left && *size < iter->current->array_size) { void *pItem = (uint8_t*)iter->pData + iter->current->data_size * (*size); if (!func(&substream, iter->current, pItem)) return false; (*size)++; } return (substream.bytes_left == 0); } else { /* Repeated field */ size_t *size = (size_t*)iter->pSize; void *pItem = (uint8_t*)iter->pData + iter->current->data_size * (*size); if (*size >= iter->current->array_size) return false; (*size)++; return func(stream, iter->current, pItem); } case PB_HTYPE_CALLBACK: { pb_callback_t *pCallback = (pb_callback_t*)iter->pData; if (pCallback->funcs.decode == NULL) return skip(stream, wire_type); if (wire_type == PB_WT_STRING) { pb_istream_t substream; if (!make_string_substream(stream, &substream)) return false; while (substream.bytes_left) { if (!pCallback->funcs.decode(&substream, iter->current, pCallback->arg)) return false; } stream->state = substream.state; return true; } else { /* Copy the single scalar value to stack. * This is required so that we can limit the stream length, * which in turn allows to use same callback for packed and * not-packed fields. */ pb_istream_t substream; uint8_t buffer[10]; size_t size = sizeof(buffer); if (!read_raw_value(stream, wire_type, buffer, &size)) return false; substream = pb_istream_from_buffer(buffer, size); return pCallback->funcs.decode(&substream, iter->current, pCallback->arg); } } default: return false; } } /* Initialize message fields to default values, recursively */ static void pb_message_set_to_defaults(const pb_field_t fields[], void *dest_struct) { pb_field_iterator_t iter; pb_field_init(&iter, fields, dest_struct); /* Initialize size/has fields and apply default values */ do { if (iter.current->tag == 0) continue; /* Initialize the size field for optional/repeated fields to 0. */ if (PB_HTYPE(iter.current->type) == PB_HTYPE_OPTIONAL) { *(bool*)iter.pSize = false; } else if (PB_HTYPE(iter.current->type) == PB_HTYPE_ARRAY) { *(size_t*)iter.pSize = 0; continue; /* Array is empty, no need to initialize contents */ } /* Initialize field contents to default value */ if (PB_HTYPE(iter.current->type) == PB_HTYPE_CALLBACK) { continue; /* Don't overwrite callback */ } else if (PB_LTYPE(iter.current->type) == PB_LTYPE_SUBMESSAGE) { pb_message_set_to_defaults(iter.current->ptr, iter.pData); } else if (iter.current->ptr != NULL) { memcpy(iter.pData, iter.current->ptr, iter.current->data_size); } else { memset(iter.pData, 0, iter.current->data_size); } } while (pb_field_next(&iter)); } /********************* * Decode all fields * *********************/ bool checkreturn pb_decode(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct) { uint32_t fields_seen = 0; /* Used to check for required fields */ pb_field_iterator_t iter; int i; pb_message_set_to_defaults(fields, dest_struct); pb_field_init(&iter, fields, dest_struct); while (stream->bytes_left) { uint32_t temp; int tag; pb_wire_type_t wire_type; if (!pb_decode_varint32(stream, &temp)) { if (stream->bytes_left == 0) break; /* It was EOF */ else return false; /* It was error */ } if (temp == 0) break; /* Special feature: allow 0-terminated messages. */ tag = temp >> 3; wire_type = (pb_wire_type_t)(temp & 7); if (!pb_field_find(&iter, tag)) { /* No match found, skip data */ if (!skip(stream, wire_type)) return false; continue; } fields_seen |= 1 << (iter.field_index & 31); if (!decode_field(stream, wire_type, &iter)) return false; } /* Check that all required fields (mod 31) were present. */ for (i = 0; fields[i].tag != 0; i++) { if (PB_HTYPE(fields[i].type) == PB_HTYPE_REQUIRED && !(fields_seen & (1 << (i & 31)))) { return false; } } return true; } /* Field decoders */ /* Copy destsize bytes from src so that values are casted properly. * On little endian machine, copy first n bytes of src * On big endian machine, copy last n bytes of src * srcsize must always be larger than destsize */ static void endian_copy(void *dest, void *src, size_t destsize, size_t srcsize) { #ifdef __BIG_ENDIAN__ memcpy(dest, (char*)src + (srcsize - destsize), destsize); #else UNUSED(srcsize); memcpy(dest, src, destsize); #endif } bool checkreturn pb_dec_varint(pb_istream_t *stream, const pb_field_t *field, void *dest) { uint64_t temp; bool status = pb_decode_varint(stream, &temp); endian_copy(dest, &temp, field->data_size, sizeof(temp)); return status; } bool checkreturn pb_dec_svarint(pb_istream_t *stream, const pb_field_t *field, void *dest) { uint64_t temp; bool status = pb_decode_varint(stream, &temp); temp = (temp >> 1) ^ -(int64_t)(temp & 1); endian_copy(dest, &temp, field->data_size, sizeof(temp)); return status; } bool checkreturn pb_dec_fixed32(pb_istream_t *stream, const pb_field_t *field, void *dest) { #ifdef __BIG_ENDIAN__ uint8_t bytes[4] = {0}; bool status = pb_read(stream, bytes, 4); if (status) { uint8_t bebytes[4] = {bytes[3], bytes[2], bytes[1], bytes[0]}; memcpy(dest, bebytes, 4); } return status; #else UNUSED(field); return pb_read(stream, (uint8_t*)dest, 4); #endif } bool checkreturn pb_dec_fixed64(pb_istream_t *stream, const pb_field_t *field, void *dest) { #ifdef __BIG_ENDIAN__ uint8_t bytes[8] = {0}; bool status = pb_read(stream, bytes, 8); if (status) { uint8_t bebytes[8] = {bytes[7], bytes[6], bytes[5], bytes[4], bytes[3], bytes[2], bytes[1], bytes[0]}; memcpy(dest, bebytes, 8); } return status; #else UNUSED(field); return pb_read(stream, (uint8_t*)dest, 8); #endif } bool checkreturn pb_dec_bytes(pb_istream_t *stream, const pb_field_t *field, void *dest) { pb_bytes_array_t *x = (pb_bytes_array_t*)dest; uint32_t temp; if (!pb_decode_varint32(stream, &temp)) return false; x->size = temp; /* Check length, noting the space taken by the size_t header. */ if (x->size > field->data_size - offsetof(pb_bytes_array_t, bytes)) return false; return pb_read(stream, x->bytes, x->size); } bool checkreturn pb_dec_string(pb_istream_t *stream, const pb_field_t *field, void *dest) { uint32_t size; bool status; if (!pb_decode_varint32(stream, &size)) return false; /* Check length, noting the null terminator */ if (size + 1 > field->data_size) return false; status = pb_read(stream, (uint8_t*)dest, size); *((uint8_t*)dest + size) = 0; return status; } bool checkreturn pb_dec_submessage(pb_istream_t *stream, const pb_field_t *field, void *dest) { bool status; pb_istream_t substream; if (!make_string_substream(stream, &substream)) return false; if (field->ptr == NULL) return false; status = pb_decode(&substream, (pb_field_t*)field->ptr, dest); stream->state = substream.state; return status; }