Bart BroereandClaude Opus 5.5
47b8f5f746
A single container image with: - neo4j-browser built from source and served on :7474 - PostgreSQL with Apache AGE (based on apache/age) - a Python bridge speaking Bolt 4.4/5.0-5.4 over TCP and WebSocket on :7687 that runs Cypher through AGE's cypher() function, emulates the Neo4j procedures neo4j-browser relies on, and maps databases to AGE graphs Includes workarounds for AGE limitations (parameters are inlined as literals, `id(x) IN [...]` and the browser's expand-node query are rewritten) and an end-to-end smoke test using the Neo4j Python driver. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
100 lines
4.8 KiB
Markdown
100 lines
4.8 KiB
Markdown
# peo4c
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[neo4j-browser](https://github.com/neo4j/neo4j-browser) running on PostgreSQL, using
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[Apache AGE](https://github.com/apache/age) as the graph engine.
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Everything ships in one container image:
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```
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neo4j-browser (static files) peo4c bridge (Python) PostgreSQL + AGE
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┌──────────────────────┐ Bolt ┌──────────────────────────┐ SQL ┌────────────────┐
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│ in your web browser │───────▶│ Bolt server (TCP + WS) │──────▶│ cypher('g',$$ │
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│ served on :7474 │ :7687 │ Cypher → AGE translation │ :5432 │ ... $$) │
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└──────────────────────┘ │ emulated Neo4j procedures │ └────────────────┘
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└──────────────────────────┘
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```
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## Quick start
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```sh
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podman build -t peo4c .
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podman run -d --name peo4c -e POSTGRES_PASSWORD=secret \
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-p 7474:7474 -p 7687:7687 -p 5432:5432 \
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-v peo4c-data:/var/lib/postgresql peo4c
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```
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Open <http://localhost:7474/> and log in with your **PostgreSQL** credentials:
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user `postgres`, password the value of `POSTGRES_PASSWORD`. Bolt clients (the Neo4j
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drivers, cypher-shell) can connect to `neo4j://localhost:7687` the same way, and
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`psql` works on port 5432.
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`docker` works as a drop-in replacement for `podman` in the commands above.
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## How it works
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- **Databases are AGE graphs.** Every AGE graph shows up as a Neo4j database, and
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`:use <name>` switches between them. A graph named `neo4j` is created on first start
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(`PEO4C_DEFAULT_GRAPH`). `CREATE DATABASE x` and `DROP DATABASE x` on the `system`
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database call `create_graph` / `drop_graph`; AGE requires names of at least 3 characters.
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- **Queries** are sent to AGE as `SELECT * FROM cypher('<graph>', $$ <query> $$) AS (...)`.
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The bridge works out the result columns from the final `RETURN` clause and inlines
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query parameters as Cypher literals.
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- **Neo4j procedures** that neo4j-browser relies on (`dbms.components`, `SHOW DATABASES`,
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`db.labels`, `db.schema.visualization`, `SHOW PROCEDURES`, ...) are emulated from the
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AGE catalog.
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- **Workarounds for AGE**: neo4j-browser's "expand node" query uses a pattern
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comprehension, and its relationship lookup uses `id(n) IN [...]`, which AGE rejects
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for lists of more than one element. The bridge rewrites both into equivalent Cypher
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that AGE accepts.
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- **Authentication** is passed straight through: every Bolt connection opens its own
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PostgreSQL connection with the credentials you log in with.
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## Configuration
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| Variable | Default | Purpose |
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| --- | --- | --- |
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| `POSTGRES_PASSWORD` | (required) | Password of the PostgreSQL superuser, see the [postgres image docs](https://hub.docker.com/_/postgres). `POSTGRES_USER` and `POSTGRES_DB` work too. |
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| `PEO4C_DEFAULT_GRAPH` | `neo4j` | Graph created at initialisation and used when a client does not pick a database. |
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| `PEO4C_PG_DATABASE` | `$POSTGRES_DB` | PostgreSQL database holding the graphs. |
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| `PEO4C_ADVERTISED_BOLT_PORT` | `7687` | Bolt port advertised to the browser; set it when you publish 7687 on another host port. |
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| `PEO4C_ADVERTISED_HOST` | `localhost` | Host reported in `SHOW DATABASES` and to clients that do not send a routing address. |
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| `PEO4C_LOG_LEVEL` | `INFO` | `DEBUG` logs every generated SQL statement. |
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Build arguments: `AGE_IMAGE` (base image, default `apache/age:release_PG18_1.8.0`) and
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`NEO4J_BROWSER_REF` (neo4j-browser commit to build).
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## Limitations
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This is a first version. Things that do not work (yet):
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- `RETURN *`, `EXPLAIN` and `PROFILE`.
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- Write statistics: write queries report "(no changes, no records)" even when they
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changed the graph.
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- Anything AGE does not support, for example multiple labels per node, pattern
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comprehensions, temporal and spatial types, indexes and constraints through Cypher.
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- User and role management, `SHOW TRANSACTIONS`, `:sysinfo`.
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- TLS (`bolt+s://`, HTTPS).
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- Each query's full result is fetched from PostgreSQL before it is streamed to the
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client, so very large results use memory in the bridge.
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## Development
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The bridge is a dependency-light Python package in [`bridge/peo4c`](bridge/peo4c)
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(only `psycopg` 3). To run it outside the container against any AGE-enabled
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PostgreSQL:
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```sh
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pip install 'psycopg[binary]'
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cd bridge
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PEO4C_PG_HOST=localhost PEO4C_PG_DATABASE=postgres PEO4C_BROWSER_DIR=/path/to/neo4j-browser/dist \
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python -m peo4c
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```
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[`tests/smoke_test.py`](tests/smoke_test.py) runs end-to-end checks through the official
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Neo4j Python driver against a running instance:
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```sh
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pip install neo4j
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python tests/smoke_test.py neo4j://localhost:7687 postgres secret
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```
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