Pull replication endpoint (gen_statem) - phase 1#213
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couchbeam_replicator is a gen_statem that pulls documents and their full
revision history from a source CouchDB into a pluggable local target behaviour.
Pull only, resumable via a target-stored checkpoint. Attachment bodies are
deferred to phase 2 (target entries are {Doc, #{}} for now).
- couchbeam_replicator: engine + target behaviour (revs_diff, write_docs,
read/write_checkpoint); oneshot and continuous modes; status/pause/resume
- couchbeam_replicator_ets: ets/dets reference target preserving _revisions
- guides/replication.md, ex_doc Replication group
- e2e group pull_replication_ops (docs + history + deletion + resume), wired
into run-e2e.sh and the CI CouchDB matrix
- CHANGELOG
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Phase 1 of 2. Adds a client-side CouchDB pull replicator. Phase 2 will add attachment bodies; the target behaviour contract is already final so phase 2 is additive.
What it does
couchbeam_replicatoris agen_statemthat reads the changes feed and document revisions from a source CouchDB and writes them into a pluggable local target (a behaviour the app implements). It preserves each document's full revision history (_revisions), handles deletions, and is resumable. Pull only (CouchDB -> app).The source side reuses existing couchbeam APIs:
couchbeam_changes:follow_once/2(withstyle=all_docs,since,limit),couchbeam:open_doc/3({rev,R},{revs,true}to fetch a revision with its history), anddb_info/1. The target does therevs_diff/write_docs, so no push path is involved.API
start_link(Source, TargetMod, TargetArgs, Opts);status/1,pause/1,resume/1,stop/1.mode(oneshot|continuous),batch_size,interval,repl_id,notify,changes_options.init/1,revs_diff/2,write_docs/2,read_checkpoint/2,write_checkpoint/3, optionalterminate/2.write_docstakes[{Doc, Atts}](Atts#{}in phase 1, populated in phase 2).Resume
Stable
repl_id+ target-persisted sourcelast_seq+revs_diff-gated idempotent writes. No CouchDB_localdoc needed. With the dets backend, resume survives a restart.Reference target + docs
couchbeam_replicator_ets(ets or dets backend) stores every revision, leaf revs, and the checkpoint.guides/replication.mddocuments usage, resume, and writing a target.Tests
New e2e group
pull_replication_ops(wired intorun-e2e.shand the CI CouchDB matrix): replicates docs with multi-rev history and a deletion into an ets target and asserts the import; a second run with the samerepl_idresumes from the checkpoint and imports only the new changes.Verified:
rebar3 eunit(32),xref,dialyzerclean;make e2egreen (all 16 groups) against CouchDB 3.5.x.