62 lines
2.9 KiB
Go
62 lines
2.9 KiB
Go
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// Package mru defines Mutable resource updates.
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// A Mutable Resource is an entity which allows updates to a resource
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// without resorting to ENS on each update.
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// The update scheme is built on swarm chunks with chunk keys following
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// a predictable, versionable pattern.
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//
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// Updates are defined to be periodic in nature, where the update frequency
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// is expressed in seconds.
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//
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// The root entry of a mutable resource is tied to a unique identifier that
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// is deterministically generated out of the metadata content that describes
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// the resource. This metadata includes a user-defined resource name, a resource
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// start time that indicates when the resource becomes valid,
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// the frequency in seconds with which the resource is expected to be updated, both of
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// which are stored as little-endian uint64 values in the database (for a
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// total of 16 bytes). It also contains the owner's address (ownerAddr)
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// This MRU info is stored in a separate content-addressed chunk
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// (call it the metadata chunk), with the following layout:
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//
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// (00|length|startTime|frequency|name|ownerAddr)
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//
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// (The two first zero-value bytes are used for disambiguation by the chunk validator,
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// and update chunk will always have a value > 0 there.)
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//
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// Each metadata chunk is identified by its rootAddr, calculated as follows:
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// metaHash=H(len(metadata), startTime, frequency,name)
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// rootAddr = H(metaHash, ownerAddr).
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// where H is the SHA3 hash function
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// This scheme effectively locks the root chunk so that only the owner of the private key
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// that ownerAddr was derived from can sign updates.
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//
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// The root entry tells the requester from when the mutable resource was
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// first added (Unix time in seconds) and in which moments to look for the
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// actual updates. Thus, a resource update for identifier "føø.bar"
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// starting at unix time 1528800000 with frequency 300 (every 5 mins) will have updates on 1528800300,
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// 1528800600, 1528800900 and so on.
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//
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// Actual data updates are also made in the form of swarm chunks. The keys
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// of the updates are the hash of a concatenation of properties as follows:
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//
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// updateAddr = H(period, version, rootAddr)
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// where H is the SHA3 hash function
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// The period is (currentTime - startTime) / frequency
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//
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// Using our previous example, this means that a period 3 will happen when the
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// clock hits 1528800900
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//
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// If more than one update is made in the same period, incremental
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// version numbers are used successively.
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//
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// A user looking up a resource would only need to know the rootAddr in order to get the versions
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//
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// the resource update data is:
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// resourcedata = headerlength|period|version|rootAddr|flags|metaHash
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// where flags is a 1-byte flags field. Flag 0 is set to 1 to indicate multihash
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//
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// the full update data that goes in the chunk payload is:
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// resourcedata|sign(resourcedata)
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//
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// headerlength is a 16 bit value containing the byte length of period|version|rootAddr|flags|metaHash
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package mru
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