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40 lines
1.9 KiB
Markdown
40 lines
1.9 KiB
Markdown
# internal/index
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A key-split (radix) index over strings, and a forward/reverse pair of them that answers prefix and
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suffix lookups. Ported from a prototype directory-scan package and kept close to the original so the
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two can be diffed.
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## Types
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- `KeySplitIndex[T]` / `Node[T]`: a radix tree. Each node holds at most one value and splits its
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children on the longest common prefix of their keys, so `pom.xml` and `pom.properties` share a
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`pom.` node. Reads take a read lock per node; writes upgrade to a write lock only where the tree
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changes. `KeySplitIndex` also marshals to and from a flat JSON object of key → value.
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- `PrefixSuffix[T]`: two `KeySplitIndex` values, one keyed by the string and one by its reverse, so
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`ByPrefix("pom")` and `BySuffix(".jar")` are both a single descent followed by a collect.
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## Operations
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| call | answers |
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|---|---|
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| `Get(key)` | the value at exactly `key` |
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| `Set(key, v)` / `Update(key, fn)` | store, or read-modify-write, the value at `key` |
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| `ByPrefix(p)` | every value whose key starts with `p` |
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| `BySuffix(s)` (PrefixSuffix only) | every value whose key ends with `s` |
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Values are whatever the caller stores; `internal/archive` stores `[]*node` per base name because a
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name repeats across directories.
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## Where it is used
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`internal/archive.Index` keeps one `PrefixSuffix[[]*node]` of files by base name. A cataloger glob
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whose last segment is a literal, `*suffix` or `prefix*` (nearly all of them: `**/*.jar`,
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`**/pom.properties`) is answered from it instead of by walking every path.
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## Notes
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- Lookups are byte-wise; `reverse` works on runes so a multi-byte name reverses correctly.
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- `lock.go` returns unlock functions rather than exposing `Unlock`, which is how a node tells a read
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lock from a write lock when deciding whether to upgrade.
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- `_find`, `_collect` and `_makeNodeP` are the prototype's internals and are left with its naming.
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