pw_protobuf extended size report#
pw_protobuf: Expressive interface for encoding and decoding protocol buffers
pw_protobuf can impact binary size very differently depending on how it’s
used. A series of examples are provided below to illustrate how much certain
use cases affect binary size.
Overview#
This module includes a proto encoder, two different proto decoders (one that
operates on a pw::stream::StreamReader and another that operates on an in-
memory buffer), codegen for direct wire-format encoders/decoders, and a
table-based codegen system for constructing proto messages as in-memory structs.
Here’s a brief overview of the different encoder/decoder costs:
Label |
Segment |
Delta |
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Full wire-format proto encode/decode library |
FLASH
|
+3,888 |
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Including table-based Message encoder and decoder |
FLASH
|
+6,426 |
Note
There’s some overhead involved in ensuring all of the encoder/decoder functionality is pulled in. Check the per-symbol breakdown for more details.
Encoder/decoder codegen overhead#
The different proto serialization/deserialization codegen methods have different overhead. Some have a higher up-front cost, but lower complexity (and therefore smaller compiler generated code) at the sites of usage. Others trade lower up-front code size cost for more complexity at the proto construction and read sites.
This example uses the following proto message to construct a variety of use cases to illustrate how code and memory requirements can change depending on the complexity of the proto message being encoded/decoded.
syntax = "proto3";
package pw.protobuf_size_report;
message ItemInfo {
enum Access {
NONE = 0;
READ = 1;
WRITE = 2;
READ_AND_WRITE = 3;
}
uint64 offset = 1;
uint32 size = 2;
Access access_level = 3;
}
message ResponseInfo {
oneof key {
string key_string = 1;
fixed32 key_token = 2;
}
optional int64 timestamp = 3;
optional bool has_value = 4;
ItemInfo item_info = 5;
}
message Response {
repeated ResponseInfo responses = 1;
}
message LookupRequest {
message AuthInfo {
optional uint32 id = 1;
optional uint32 token = 2;
}
oneof key {
string key_string = 1;
fixed32 key_token = 2;
}
optional uint32 items_per_response = 3;
AuthInfo auth_info = 4;
bool add_timestamp = 5;
}
This proto is configured with the following options file:
pw.protobuf_size_report.Reponse.responses max_count:4
Trivial proto#
This is a size report for encoding/decoding the pw.protobuf.test.ItemInfo
message. This is a pretty trivial message with just a few integers.
Label |
Segment |
Delta |
||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Direct wire-format proto encoder |
FLASH
|
+160 |
||||||||||||||||||
RAM
|
+108 |
|||||||||||||||||||
Generated wrapped wire-format encoder |
FLASH
|
+140 |
||||||||||||||||||
RAM
|
+156 |
|||||||||||||||||||
Generated message encoder |
FLASH
|
+116 |
||||||||||||||||||
RAM
|
+172 |
Optional and oneof#
This is a size report for encoding/decoding the
pw.protobuf.test.ResponseInfo message. This is slightly more complex message
that has a few explicitly optional fields, a oneof, and a submessage.
Label |
Segment |
Delta |
||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Direct wire-format proto encoder |
FLASH
|
+508 |
||||||||||||||||||
RAM
|
+108 |
|||||||||||||||||||
Generated wrapped wire-format encoder |
FLASH
|
+462 |
||||||||||||||||||
RAM
|
+196 |
|||||||||||||||||||
Generated message encoder |
FLASH
|
+386 |
||||||||||||||||||
RAM
|
+252 |