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NewManifestFromReader reads at most one byte past MaxManifestSize, a new constant of 258 MiB: the 256 MiB decompressed limit grown by zstd's worst case of 1/256, plus 1 MiB for the signature, the signing key and the other outer fields. It refuses a larger manifest. fetch, and check given a URL, stop downloading a manifest one byte past the same size and report it as too large; tests lower that size to keep their memory small. fetch stops reading a file one byte past its listed size, so a longer body ends in the size mismatch at once instead of filling the disk. docs/FORMAT.md states the limit and gives the decompressed limit as 256 MiB, the size the code uses. Model: opus-5-5
52 lines
1.9 KiB
Go
52 lines
1.9 KiB
Go
package mfer
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const (
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// Version is the current mfer release version.
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Version = "0.1.0"
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// ReleaseDate is the date on which Version was released.
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ReleaseDate = "2025-12-17"
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// MaxDecompressedSize is the maximum allowed size of decompressed manifest
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// data (256 MiB). This prevents decompression bombs from consuming excessive
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// memory.
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MaxDecompressedSize int64 = 256 * 1024 * 1024
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// MaxManifestSize is the largest manifest file mfer reads (258 MiB).
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// zstd's worst case grows data it cannot compress by 1/256, so an inner
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// message of MaxDecompressedSize compresses to at most 257 MiB; the
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// last MiB is room for the signature, the signing key and the other
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// outer fields.
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MaxManifestSize = MaxDecompressedSize + MaxDecompressedSize/256 + 1<<20
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// zstdWindowSize is the zstd window zstd.SpeedBestCompression gives mfer's writer.
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zstdWindowSize = 8 << 20
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// uuidLength is the length in bytes of a binary UUID.
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uuidLength = 16
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// Numbers in mf.proto of MFFile.files and of the MFFilePath fields
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// that decoding sets aside a fixed amount of memory for.
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filesFieldNumber = 101
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hashesFieldNumber = 3
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mimeTypeFieldNumber = 301
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mtimeFieldNumber = 302
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ctimeFieldNumber = 303
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// Bytes decoding sets aside for each file entry, hash, timestamp and
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// MIME type, however short its encoding. checkDecodedSize refuses an
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// inner message for which these add up to more than maxDecodedGrowth
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// times its size. The mode is held in the file entry itself.
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decodedFileEntrySize = 176
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decodedHashSize = 112
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decodedTimestampSize = 64
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decodedMIMETypeSize = 16
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// Each file entry mfer writes holds a path of at least one byte, a
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// multihash at least as long as SHA-256's 34 bytes (AddFileWithHash
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// refuses shorter ones) and a modification time: at least 47 bytes,
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// counted at 352. So its manifests add up to at most about 7.49 times
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// their size, and this limit is about 7% above that.
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maxDecodedGrowth = 8
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)
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