Struct Writer 

pub struct Writer { /* private fields */ }

Builder for a new btree file.

Writer::create_new(path) initialises the in-memory state with an empty root leaf; finish() flushes that plus the meta page to disk. Dropping a Writer without calling finish() leaves the newly-created file empty on disk - nothing is written until finish.

Implementations

impl Writer

pub fn create_new(path: impl AsRef<Path>) -> Result<Self>

Create a new file at path and stage an empty btree.

Mirrors std::fs::File::create_new: the file is opened with create_new, so an existing file at path causes an I/O error. Nothing is written to disk until Writer::finish is called.

Errors

Returns Error::Io if the file cannot be created.

pub fn del(&mut self, key: &[u8]) -> Result<bool>

Delete the entry for key from the tree.

Returns true if an entry was removed, false if key wasn’t present. Mirrors __bt_delete / __bt_dleaf from libnbcompat: the leaf is compacted in place and the tree’s nrecs field is left alone (the btree access method ignores it). Page underflow doesn’t trigger merges - the BSD btree just leaves underfull pages alone.

Errors

Returns an Error if any in-memory page fails its own decoder invariants while descending to find key. That would only happen if the writer’s own state were corrupted, which indicates a bug in this crate, not bad input.

Panics

Panics if the writer’s internal page map is inconsistent (i.e. a page reached via descent isn’t present in the map). Reaching this branch indicates a bug in this crate.

pub fn put(&mut self, key: &[u8], val: &[u8]) -> Result<bool>

Insert key / val into the tree.

Mirrors dbopen(3)’s R_NOOVERWRITE semantics: returns Ok(true) on a successful insert, or Ok(false) if key is already present (in which case the existing value is left untouched). Matches std::collections::HashSet::insert.

Errors

Returns an Error if any in-memory page fails its own decoder invariants while descending to find the insertion point. That would only happen if the writer’s own state were corrupted, which indicates a bug in this crate, not bad input.

Panics

Panics if the writer’s internal page map is inconsistent (i.e. a page reached via descent isn’t present in the map). Reaching this branch indicates a bug in this crate.

pub fn finish(self) -> Result<()>

Flush all buffered pages to disk, consuming the writer.

Pages are written in pgno order through a single buffered writer (no per-page seeks): the in-memory arena is one contiguous psize-aligned buffer indexed by pgno, so finish writes the meta page into slot 0 and then flushes the whole buffer as a single write_all.

No fsync is issued: this matches libnbcompat’s dbopen, where the close path just unmaps and flushes userspace buffers. Callers that need on-disk durability should fsync the containing directory themselves.

Errors

Returns Error::Io if any of the writes fail.

Panics

Panics if the arena is not a positive whole multiple of psize bytes. This is a writer-internal invariant established at construction; a failure here indicates a bug in this crate, and asserting rather than silently truncating is the only safe choice at the persistence boundary.