Add a Base38 fuzzer.

This is split out from #34311
to see which part of that PR is leading to clang-tidy failures.

src/setup_payload/tests/BUILD.gn

@@ -17,6 +17,7 @@ import("//build_overrides/chip.gni")
 import("//build_overrides/pigweed.gni")
 
 import("${chip_root}/build/chip/chip_test_suite.gni")
+import("${chip_root}/build/chip/fuzz_test.gni")
 
 chip_test_suite("tests") {
   output_name = "libSetupPayloadTests"
@@ -38,3 +39,20 @@ chip_test_suite("tests") {
     "${chip_root}/src/setup_payload",
   ]
 }
+
+if (enable_fuzz_test_targets) {
+  chip_fuzz_target("fuzz-setup-payload-base38") {
+    sources = [ "FuzzBase38.cpp" ]
+    public_deps = [
+      "${chip_root}/src/platform/logging:stdio",
+      "${chip_root}/src/setup_payload",
+    ]
+  }
+  chip_fuzz_target("fuzz-setup-payload-base38-decode") {
+    sources = [ "FuzzBase38Decode.cpp" ]
+    public_deps = [
+      "${chip_root}/src/platform/logging:stdio",
+      "${chip_root}/src/setup_payload",
+    ]
+  }
+}

src/setup_payload/tests/FuzzBase38.cpp

@@ -0,0 +1,63 @@
+#include <cstddef>
+#include <cstdint>
+#include <fstream>
+#include <iostream>
+#include <string.h>
+
+#include <setup_payload/Base38Decode.h>
+#include <setup_payload/Base38Encode.h>
+
+using namespace chip;
+
+/**
+ *    @file
+ *      This file describes a base38 roundtrip Fuzzer.
+ *      It starts by encoding the fuzzing value passed
+ *      in Base38. The value encoded will then be decoded.
+ *      The fuzzer verify that the decoded value is the same
+ *      as the one in input.
+ */
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t * data, size_t len)
+{
+    size_t outputSizeNeeded     = base38EncodedLength(len);
+    const size_t kMaxOutputSize = 512;
+
+    if (outputSizeNeeded > kMaxOutputSize)
+    {
+        return 0;
+    }
+
+    ByteSpan span(data, len);
+    char encodedBuf[kMaxOutputSize];
+    MutableCharSpan encodedSpan(encodedBuf);
+    CHIP_ERROR encodingError = base38Encode(span, encodedSpan);
+
+    if (encodingError != CHIP_NO_ERROR)
+    {
+        __builtin_trap();
+    }
+
+    std::string base38EncodedString(encodedSpan.data(), encodedSpan.size());
+
+    std::vector<uint8_t> decodedData;
+    CHIP_ERROR decodingError = base38Decode(base38EncodedString, decodedData);
+
+    if (decodingError == CHIP_NO_ERROR)
+    {
+        if (decodedData.size() != len)
+        {
+            __builtin_trap();
+        }
+
+        if (memcmp(data, decodedData.data(), len) != 0)
+        {
+            __builtin_trap();
+        }
+    }
+    else
+    {
+        __builtin_trap();
+    }
+    return 0;
+}

src/setup_payload/tests/FuzzBase38Decode.cpp

@@ -0,0 +1,24 @@
+#include <cstddef>
+#include <cstdint>
+#include <iostream>
+
+#include <setup_payload/Base38Decode.h>
+
+using namespace chip;
+
+/**
+ *    @file
+ *      This file describes a Fuzzer for decoding base38 encoded strings.
+ */
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t * data, size_t len)
+{
+    std::string base38EncodedString(reinterpret_cast<const char *>(data), len);
+    std::vector<uint8_t> decodedData;
+
+    // Ignoring return value, because in general the data is garbage and won't decode properly.
+    // We're just testing that the decoder does not crash on the fuzzer-generated inputs.
+    chip::base38Decode(base38EncodedString, decodedData);
+
+    return 0;
+}