[clang] [OffloadBundler] Expose function to parse compressed bundle headers (PR #130284)

[Yaxun Liu via cfe-commits]

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@@ -1121,13 +1122,116 @@ CompressedOffloadBundle::compress(llvm::compression::Params P,
       llvm::StringRef(FinalBuffer.data(), FinalBuffer.size()));
 }
 
+// Use packed structs to avoid padding, such that the structs map the serialized
+// format.
+LLVM_PACKED_START
+union RawCompressedBundleHeader {
+  struct CommonFields {
+    uint32_t Magic;
+    uint16_t Version;
+    uint16_t Method;
+  };
+
+  struct V1Header {
+    CommonFields Common;
+    uint32_t UncompressedFileSize;
+    uint64_t Hash;
+  };
+
+  struct V2Header {
+    CommonFields Common;
+    uint32_t FileSize;
+    uint32_t UncompressedFileSize;
+    uint64_t Hash;
+  };
+
+  struct V3Header {
+    CommonFields Common;
+    uint64_t FileSize;
+    uint64_t UncompressedFileSize;
+    uint64_t Hash;
+  };
+
+  CommonFields Common;
+  V1Header V1;
+  V2Header V2;
+  V3Header V3;
+};
+LLVM_PACKED_END
+
+// Helper method to get header size based on version
+static size_t getHeaderSize(uint16_t Version) {
+  switch (Version) {
+  case 1:
+    return sizeof(RawCompressedBundleHeader::V1Header);
+  case 2:
+    return sizeof(RawCompressedBundleHeader::V2Header);
+  case 3:
+    return sizeof(RawCompressedBundleHeader::V3Header);
+  default:
+    llvm_unreachable("Unsupported version");
+  }
+}
+
+Expected<CompressedOffloadBundle::CompressedBundleHeader>
+CompressedOffloadBundle::CompressedBundleHeader::tryParse(StringRef Blob) {
+  assert(Blob.size() > sizeof(RawCompressedBundleHeader::CommonFields));
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yxsamliu wrote:

should this be >= ?

https://github.com/llvm/llvm-project/pull/130284