fix(rust): name the storage basis only when it bounds inflate

A padded PE section above 128 KiB derives an allowance larger than the fixed
8 MiB cap, so the cap is what inflate enforces. Name the padded storage size
only when its allowance is below the cap.

Co-Authored-By: gensokyo-dev <342580529+gensokyo-dev@users.noreply.github.com>

src/rust/RustAuditableReader.test.ts

@@ -283,6 +283,30 @@ it("names the padded-storage basis when a padded section overflows inflate alloc
   );
 });
 
+it("names the fixed cap when it bounds a large padded section's inflate allocation", () => {
+  // Storage above 128 KiB derives more than the fixed 8 MiB cap, so the cap,
+  // not the padded storage size, is the enforced bound.
+  const compressed = deflateSync(Buffer.alloc(9 * 1024 * 1024, 0x20));
+  const fileAlignment = 512;
+  const stored = Buffer.alloc(132 * 1024);
+  compressed.copy(stored);
+  let failure: unknown;
+  try {
+    readAuditableSection(".dep-v0", 0, stored, {
+      peFileAlignment: fileAlignment,
+    });
+  } catch (cause: unknown) {
+    failure = cause;
+  }
+  expect(failure).toMatchObject({
+    constraint: {
+      resource: "memory",
+      reported_limits: { maximum_bytes: 8 * 1024 * 1024 },
+    },
+  });
+  expect((failure as Error).message).not.toContain("storage size");
+});
+
 it.each([0, 8])("reads documented cargo-auditable revision %i", (format) => {
   const parsed = section({
     format,

src/rust/RustAuditableReader.ts

@@ -148,10 +148,14 @@ const inflateSection = (
       }),
     );
   } catch (cause) {
+    // Only a padded section whose storage-derived allowance is below the fixed
+    // cap is bounded by its storage size; otherwise the fixed cap applies.
     throw inflateFailure(
       cause,
       allocationMaximum,
-      peFileAlignment !== undefined && peFileAlignment > 0,
+      peFileAlignment !== undefined &&
+        peFileAlignment > 0 &&
+        allocationMaximum < RUST_UNCOMPRESSED_BYTES,
     );
   }
   const compressedBytes = result.consumedBytes;
@@ -196,7 +200,7 @@ const inflateSection = (
 const inflateFailure = (
   cause: unknown,
   maximum: number,
-  paddedStorage: boolean,
+  storageBounded: boolean,
 ): Error => {
   const code =
     cause instanceof Error && "code" in cause ? String(cause.code) : "";
@@ -206,7 +210,7 @@ const inflateFailure = (
       // The stream length is unknown until inflate finishes, so a padded PE
       // section is bounded by its storage size; say so instead of implying the
       // smaller limit derived from the consumed stream.
-      paddedStorage
+      storageBounded
         ? `Inflated dependency JSON exceeds the ${String(maximum)}-byte allowance derived from the padded section's storage size; the zlib stream length is unknown until it inflates, so the smaller stream-based limit could not be applied first`
         : "Inflated dependency JSON exceeds the size limit",
     );