feat: Fuzz Infrastructure Setup (TASK-500) (#98)

Comprehensive fuzz testing infrastructure for parser robustness:

- Created 4 new fuzz test files for HTTP/1.1, HTTP/2, HPACK, and Scenario parsers
- Added 60+ corpus seed files across 5 target directories (http1_response, http2_frame, hpack, scenario, event)
- Implemented fuzz-targets build step in build.zig
- Added scripts/run-fuzz.sh for running fuzz tests
- Added scripts/minimize-corpus.sh for corpus management (placeholder)
- Fixed parser assertions that caused crashes during fuzzing:
  - HPACK decodeString: removed assertion, use error return for empty input
  - HTTP/2 parseHeader: moved assertion after input validation
- Exported HTTP2_MAX_FRAME_SIZE constant from z6.zig

Test results:
- HPACK decoder: 6/6 tests pass, 1M iterations
- HTTP/2 frame: 5/5 tests pass, 1M iterations

Note: HTTP/1.1, Scenario, and Event fuzz tests have pre-existing Zig 0.14
API compatibility issues (ArrayList.deinit signature) in the main codebase
that need separate fixes.

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: copyleftdev

build.zig

@@ -428,12 +428,63 @@ pub fn build(b: *std.Build) void {
     test_step.dependOn(&run_checker_tests.step);
     test_step.dependOn(&run_loop_tests.step);
 
-    // Fuzz targets (placeholder for TASK-300+)
-    _ = b.step("fuzz-targets", "Build all fuzz targets");
-    // TODO: Add fuzz targets when parsers are implemented:
-    // - fuzz_http1_response
-    // - fuzz_http2_frame
-    // - fuzz_event_serialization
+    // Fuzz targets (TASK-500)
+    const fuzz_step = b.step("fuzz-targets", "Build and run all fuzz targets");
+
+    // HTTP/1.1 Parser fuzz tests
+    const http1_fuzz = b.addTest(.{
+        .name = "http1_parser_fuzz",
+        .root_source_file = b.path("tests/fuzz/http1_parser_fuzz.zig"),
+        .target = target,
+        .optimize = optimize,
+    });
+    http1_fuzz.root_module.addImport("z6", z6_module);
+    const run_http1_fuzz = b.addRunArtifact(http1_fuzz);
+    fuzz_step.dependOn(&run_http1_fuzz.step);
+
+    // HTTP/2 Frame Parser fuzz tests
+    const http2_fuzz = b.addTest(.{
+        .name = "http2_frame_fuzz",
+        .root_source_file = b.path("tests/fuzz/http2_frame_fuzz.zig"),
+        .target = target,
+        .optimize = optimize,
+    });
+    http2_fuzz.root_module.addImport("z6", z6_module);
+    const run_http2_fuzz = b.addRunArtifact(http2_fuzz);
+    fuzz_step.dependOn(&run_http2_fuzz.step);
+
+    // HPACK Decoder fuzz tests
+    const hpack_fuzz = b.addTest(.{
+        .name = "hpack_decoder_fuzz",
+        .root_source_file = b.path("tests/fuzz/hpack_decoder_fuzz.zig"),
+        .target = target,
+        .optimize = optimize,
+    });
+    hpack_fuzz.root_module.addImport("z6", z6_module);
+    const run_hpack_fuzz = b.addRunArtifact(hpack_fuzz);
+    fuzz_step.dependOn(&run_hpack_fuzz.step);
+
+    // Scenario Parser fuzz tests
+    const scenario_fuzz = b.addTest(.{
+        .name = "scenario_parser_fuzz",
+        .root_source_file = b.path("tests/fuzz/scenario_parser_fuzz.zig"),
+        .target = target,
+        .optimize = optimize,
+    });
+    scenario_fuzz.root_module.addImport("z6", z6_module);
+    const run_scenario_fuzz = b.addRunArtifact(scenario_fuzz);
+    fuzz_step.dependOn(&run_scenario_fuzz.step);
+
+    // Event Serialization fuzz tests (existing)
+    const event_fuzz = b.addTest(.{
+        .name = "event_serialization_fuzz",
+        .root_source_file = b.path("tests/fuzz/event_serialization_fuzz.zig"),
+        .target = target,
+        .optimize = optimize,
+    });
+    event_fuzz.root_module.addImport("z6", z6_module);
+    const run_event_fuzz = b.addRunArtifact(event_fuzz);
+    fuzz_step.dependOn(&run_event_fuzz.step);
 
     // Documentation generation (placeholder for TASK-400+)
     _ = b.step("docs", "Generate documentation");

corpus/event/empty.bin

@@ -0,0 +1,2 @@
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corpus/event/random.bin

@@ -0,0 +1 @@
+�

corpus/event/too_long.bin

@@ -0,0 +1 @@
+���

corpus/event/truncated.bin

@@ -0,0 +1 @@
+�