Decoder for Rust-style Punycode encodings of bounded length.

PiperOrigin-RevId: 647093624
Change-Id: Ic76bfa4aa8fb616cb23095ce7bfa30c3812dcb21

CMake/AbseilDll.cmake

@@ -125,6 +125,8 @@ set(ABSL_INTERNAL_DLL_FILES
   "debugging/internal/address_is_readable.cc"
   "debugging/internal/address_is_readable.h"
   "debugging/internal/bounded_utf8_length_sequence.h"
+  "debugging/internal/decode_rust_punycode.cc"
+  "debugging/internal/decode_rust_punycode.h"
   "debugging/internal/demangle.cc"
   "debugging/internal/demangle.h"
   "debugging/internal/demangle_rust.cc"

absl/debugging/BUILD.bazel

@@ -220,12 +220,14 @@ cc_library(
 cc_library(
     name = "demangle_internal",
     srcs = [
+        "internal/decode_rust_punycode.cc",
         "internal/demangle.cc",
         "internal/demangle_rust.cc",
         "internal/utf8_for_code_point.cc",
     ],
     hdrs = [
         "internal/bounded_utf8_length_sequence.h",
+        "internal/decode_rust_punycode.h",
         "internal/demangle.h",
         "internal/demangle_rust.h",
         "internal/utf8_for_code_point.h",
@@ -240,6 +242,7 @@ cc_library(
         "//absl/base",
         "//absl/base:config",
         "//absl/base:core_headers",
+        "//absl/base:nullability",
         "//absl/numeric:bits",
     ],
 )
@@ -258,6 +261,19 @@ cc_test(
 )
 
 cc_test(
+    name = "decode_rust_punycode_test",
+    srcs = ["internal/decode_rust_punycode_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        ":demangle_internal",
+        "//absl/base:config",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
     name = "demangle_rust_test",
     srcs = ["internal/demangle_rust_test.cc"],
     copts = ABSL_TEST_COPTS,

absl/debugging/CMakeLists.txt

@@ -196,10 +196,12 @@ absl_cc_library(
     demangle_internal
   HDRS
     "internal/bounded_utf8_length_sequence.h"
+    "internal/decode_rust_punycode.h"
     "internal/demangle.h"
     "internal/demangle_rust.h"
     "internal/utf8_for_code_point.h"
   SRCS
+    "internal/decode_rust_punycode.cc"
     "internal/demangle.cc"
     "internal/demangle_rust.cc"
     "internal/utf8_for_code_point.cc"
@@ -209,6 +211,7 @@ absl_cc_library(
     absl::base
     absl::bits
     absl::core_headers
+    absl::nullability
   PUBLIC
 )
 
@@ -227,6 +230,19 @@ absl_cc_test(
 
 absl_cc_test(
   NAME
+    decode_rust_punycode_test
+  SRCS
+    "internal/decode_rust_punycode_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::demangle_internal
+    absl::config
+    GTest::gmock_main
+)
+
+absl_cc_test(
+  NAME
     demangle_rust_test
   SRCS
     "internal/demangle_rust_test.cc"

absl/debugging/internal/decode_rust_punycode.h

+// Copyright 2024 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_DEBUGGING_INTERNAL_DECODE_RUST_PUNYCODE_H_
+#define ABSL_DEBUGGING_INTERNAL_DECODE_RUST_PUNYCODE_H_
+
+#include "absl/base/config.h"
+#include "absl/base/nullability.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+
+struct DecodeRustPunycodeOptions {
+  const char* punycode_begin;
+  const char* punycode_end;
+  char* out_begin;
+  char* out_end;
+};
+
+// Given Rust Punycode in `punycode_begin .. punycode_end`, writes the
+// corresponding UTF-8 plaintext into `out_begin .. out_end`, followed by a NUL
+// character, and returns a pointer to that final NUL on success.  On failure
+// returns a null pointer, and the contents of `out_begin .. out_end` are
+// unspecified.
+//
+// Failure occurs in precisely these cases:
+//   - Any input byte does not match [0-9a-zA-Z_].
+//   - The first input byte is an underscore, but no other underscore appears in
+//     the input.
+//   - The delta sequence does not represent a valid sequence of code-point
+//     insertions.
+//   - The plaintext would contain more than 256 code points.
+//
+// DecodeRustPunycode is async-signal-safe with bounded runtime and a small
+// stack footprint, making it suitable for use in demangling Rust symbol names
+// from a signal handler.
+absl::Nullable<char*> DecodeRustPunycode(DecodeRustPunycodeOptions options);
+
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_DEBUGGING_INTERNAL_DECODE_RUST_PUNYCODE_H_