To correctly handle this case we must add the serialized map entry to the unknown fields. Ideally we could merely preserve the map entry's serialized bytes from the input. However this is tricky to do if we are streaming and the previous buffer where the map entry began is no longer available.
This CL fixes this edge case by using the encoder to re-encode the map entry rather than using the input bytes directly.
While this fix is reasonably simple and reliable, it has two unfortunate properties. One is performance: we now must run the encoder to recreate bytes that we already saw in the input.
The other is dependencies: this fix has the unfortunate property of making the decoder depend on the encoder. In applications that only want the decoder but not the encoder, this will increase binary size. But the practical effects of this are probably minimal (the vast majority of applications that depend on the decoder will also use the encoder).
We can revisit this later and see if there is a better way of preserving the input bytes without re-encoding. For now this fix is simple and correct and fixes the fuzz bug.
PiperOrigin-RevId: 505381927
The initial motivation for this CL was to fix a bug found by fuzzing. But the fuzz bug pointed out a few edge cases that this CL corrects:
1. The core bug is that we were allowing a map entry sub-message to be linked to a group field. This is not allowed in protobuf schemas, but we did not check for this edge case in `upb_MiniTable_SetSubMessage()`, so we were de facto allowing it. This triggered some bad behavior in the parser whereby we pushed a limit without checking its validity first.
2. To defend against this, I added asserts in `upb_MiniTable_SetSubMessage()` to verify the type of the field we are linking, to ensure that a group field is not linked to a map entry sub-message. But this should probably be changed to return an error instead of relying on asserts for this.
3. I changed the fuzz util code that builds the MiniTable so that it will never violate this new invariant. The fuzz util code now can run into situations where a group field has no valid non-map-entry sub-message to select. In those cases it will simply not register any sub-message for that field.
4. Previously group did not support leaving sub-messages unregistered. Previously I added this feature for sub-messages but not for groups. There is no reason why dynamic tree shaking should not work for group fields, so I extended the feature to support groups also.
PiperOrigin-RevId: 504913630
This CL changes the upb compiler to no longer depend on C++ protobuf libraries. upb now uses its own reflection libraries to implement its code generator.
# Key Benefits
1. upb can now use its own reflection libraries throughout the compiler. This makes upb more consistent and principled, and gives us more chances to dogfood our own C++ reflection API. This highlighted several parts of the C++ reflection API that were incomplete.
2. This CL removes code duplication that previously existed in the compiler. The upb reflection library has code to build MiniDescriptors and MiniTables out of descriptors, but prior to this CL the upb compiler could not use it. The upb compiler had a separate copy of this logic, and the compiler's copy of this logic was especially tricky and hard to maintain. This CL removes the separate copy of that logic.
3. This CL (mostly) removes upb's dependency on the C++ protobuf library. We still depend on `protoc` (the binary), but the runtime and compiler no longer link against C++'s libraries. This opens up the possibility of speeding up some builds significantly if we can use a prebuilt `protoc` binary.
# Bootstrap Stages
To bootstrap, we check in a copy of our generated code for `descriptor.proto` and `plugin.proto`. This allows the compiler to depend on the generated code for these two protos without creating a circular dependency. This code is checked in to the `stage0` directory.
The bootstrapping process is divided into a few stages. All `cc_library()`, `upb_proto_library()`, and `cc_binary()` targets that would otherwise be circular participate in this staging process. That currently includes:
* `//third_party/upb:descriptor_upb_proto`
* `//third_party/upb:plugin_upb_proto`
* `//third_party/upb:reflection`
* `//third_party/upb:reflection_internal`
* `//third_party/upbc:common`
* `//third_party/upbc:file_layout`
* `//third_party/upbc:plugin`
* `//third_party/upbc:protoc-gen-upb`
For each of these targets, we produce a rule for each stage (the logic for this is nicely encapsulated in Blaze/Bazel macros like `bootstrap_cc_library()` and `bootstrap_upb_proto_library()`, so the `BUILD` file remains readable). For example:
* `//third_party/upb:descriptor_upb_proto_stage0`
* `//third_party/upb:descriptor_upb_proto_stage1`
* `//third_party/upb:descriptor_upb_proto`
The stages are:
1. `stage0`: This uses the checked-in version of the generated code. The stage0 compiler is correct and outputs the same code as all other compilers, but it is unnecessarily slow because its protos were compiled in bootstrap mode. The stage0 compiler is used to generate protos for stage1.
2. `stage1`: The stage1 compiler is correct and fast, and therefore we use it in almost all cases (eg. `upb_proto_library()`). However its own protos were not generated using `upb_proto_library()`, so its `cc_library()` targets cannot be safely mixed with `upb_proto_library()`, as this would lead to duplicate symbols.
3. final (no stage): The final compiler is identical to the `stage1` compiler. The only difference is that its protos were built with `upb_proto_library()`. This doesn't matter very much for the compiler binary, but for the `cc_library()` targets like `//third_party/upb:reflection`, only the final targets can be safely linked in by other applications.
# "Bootstrap Mode" Protos
The checked-in generated code is generated in a special "bootstrap" mode that is a bit different than normal generated code. Bootstrap mode avoids depending on the internal representation of MiniTables or the messages, at the cost of slower runtime performance.
Bootstrap mode only interacts with MiniTables and messages using public APIs such as `upb_MiniTable_Build()`, `upb_Message_GetInt32()`, etc. This is very important as it allows us to change the internal representation without needing to regenerate our bootstrap protos. This will make it far easier to write CLs that change the internal representation, because it avoids the awkward dance of trying to regenerate the bootstrap protos when the compiler itself is broken due to bootstrap protos being out of date.
The bootstrap generated code does have two downsides:
1. The accessors are less efficient, because they look up MiniTable fields by number instead of hard-coding the MiniTableField into the generated code.
2. It requires runtime initialization of the MiniTables, which costs CPU cycles at startup, and also allocates memory which is never freed. Per google3 rules this is not really a leak, since this memory is still reachable via static variables, but it is undesirable in many contexts. We could fix this part by introducing the equivalent of `google::protobuf::ShutdownProtobufLibrary()`).
These downsides are fine for the bootstrapping process, but they are reason enough not to enable bootstrap mode in general for all protos.
# Bootstrapping Always Uses OSS Protos
To enable smooth syncing between Google3 and OSS, we always use an OSS version of the checked in generated code for `stage0`, even in google3.
This requires that the google3 code can be switched to reference the OSS proto names using a preprocessor define. We introduce the `UPB_DESC(xyz)` macro for this, which will expand into either `proto2_xyz` or `google_protobuf_xyz`. Any libraries used in `stage0` must use `UPB_DESC(xyz)` rather than refer to the symbol names directly.
PiperOrigin-RevId: 501458451
Remove circular dependencies that were bouncing back and forth between
msg_internal.h and mini_table/, including:
- splitting out each mini table subtype into its own header
- moving the non-reflection message code into message/
- moving the accessors from mini_table/ to message/
PiperOrigin-RevId: 489121042
We had _upb_Message_New(), which created a message from a mini table and was
being used outside of upb even though it is an internal-only function.
We also had upb_Message_New(), which created a message from a message def.
Now there is a single public function, upb_Message_New(), which creates a
message from a mini table and covers all use cases. (The internal version has the same definition and is used for inlining.)
PiperOrigin-RevId: 480169804
Continuing the trend of giving individual build targets their own subdirs
where appropriate, and leaving behind temporary stub headers for compatibility.
JSON is a particularly good choice for this because of how little interaction
it has with the rest of upb.
PiperOrigin-RevId: 476792865
If the extension MiniDescriptor did not contain any fields, we would read an uninitialized value. We need to add a check that the extension descriptor contains exactly one field.
PiperOrigin-RevId: 475075831
Eric Salo
Joshua Haberman
Protobuf Team Bot
Protobuf Team
Joshua Haberman
theodorerose