multiarch-docker-images/archivist/arch.md

Technical Architecture

1. Overview

Single docker container Go application built on PocketBase as an embedded framework (https://pocketbase.io/). The binary contains:

• PocketBase's HTTP/API server and admin dashboard;
• the custom review dashboard;
• the S3 poller and the PDF processing pipeline, executed through PocketBase's standard job scheduler (app.Cron());
• the declarative rule engine (JSONC config + expr-lang/expr expressions);
• access to the self-hosted S3 storage via the MinIO Go SDK.

Everything runs offline on the server infrastructure: no cloud APIs, no outbound calls other than to the S3 cluster.

2. Stack

Component	Choice
Framework / runtime	PocketBase (Go framework, single binary)
Language	Go
Scheduling	app.Cron() (S3 poller, periodic tasks)
S3	MinIO Go SDK (github.com/minio/minio-go/v7)
PDF text extraction	github.com/ledongthuc/pdf (native text, no OCR)
Rule expressions	github.com/expr-lang/expr
Regex	stdlib regexp (RE2); regexp2 only if a lookaround proves indispensable
Config validation	santhosh-tekuri/jsonschema (schema generated from structs via invopop/jsonschema)
Database	SQLite (embedded in PocketBase)
Full-text search	SQLite FTS5 index synchronized via hooks

3. S3 Layout

A single versioned bucket:

inbox/       # drop zone for new PDFs (via Nextcloud / S3 client)
pending/     # files awaiting human review
files/       # renamed and filed files (configured prefix structure)

Nextcloud mounts the bucket as external storage: it is the user-facing interface for uploading, downloading, and sharing. The application only manipulates S3 keys, never a local filesystem for documents.

4. Data Model (PocketBase Collections)

documents

One row per processed PDF file:

• sha256: the sha256 is a primary key as the system will reject as duplicate any file with the same hash
• original_filename: original file name in inbox/
• file_key: current S3 key of the file
• extracted_text: full text extracted from all pages (base of the FTS5 index)
• first_page_text: first-page text (extraction base)
• size: file size
• processed_at: timestamp of the file initial process
• status: pending | processed | validated
• updated_at: timestamp of the last update to the file metadata

• all the fields declared by the user in the configuration file

The append-only document_events collection is the single source of truth for a document's history; no history is stored on the documents record itself.

document_events

Append-only history: document, event_type (classified, moved, corrected, validated, duplicate), payload as JSON, timestamp.

5. Configuration File (JSONC)

A config.jsonc file kept alongside the binary, reloaded on restart. Three sections:

1. fields: declaration of fields to extract from the files:

   • name: name of the field
   • type: string | number | boolean
   • mandatory: true | false

2. rules: ordered list of rules that will be evaluated one after the other:

   • when: an expr-lang/expr expression evaluated over the document text and the current field values; rules run in order and each when may reference fields set by earlier rules (e.g. firstPageText contains "Relevé de compte", or emittingCompany in ["BRED", "Fortunéo"] && documentType == "Relevé de compte")
   • actions:
     • set: set the value of one field; fields accumulate as rules are applied in order
     • stop: stop rule evaluation; the fields set so far are kept and the usual validations still apply

3. templates: named naming templates (e.g. bank_statement: {sender}/{date}_{type}_{reference}.pdf), with required-field validation — a template with a missing mandatory field renders the result invalid and routes the file to pending/. The template is chosen by the rules themselves: template is a regular field, set with set like any other (e.g. set template = "bank_statement" when emittingCompany in ["BRED", "Fortunéo"] and documentType == "Relevé de compte"). If no rule sets template, the special default template is used. A template value with no matching entry renders the result invalid and routes the file to pending/.

Validation on load: JSON schema, regex compilation, expr expression compilation against a typed context (Document{FirstPageText, ExtractedText, Fields}). Full rejection if invalid, no partial processing.

6. Processing Pipeline

Executed by the PocketBase cron job (configurable interval, e.g. every minute):

1. Poll: list objects in inbox/; an object is a candidate only if no documents record references its key yet, and its size and ETag are stable across two consecutive polls (write-completion wait).
2. Download: fetch the object into memory (streamed), no disk writes. The sha256 is computed during download; if a documents record with the same hash already exists, the object is a duplicate: the inbox/ key is deleted (delete marker, data recoverable), a duplicate event is logged, and processing stops there.
3. Extraction: first-page text (for rule evaluation) + full text (for FTS) via ledongthuc/pdf, including headers and footers
4. Rule evaluation: rules evaluated in order against the extracted text and the fields set so far; full evaluation log written to the application logs (built-in dry-run mode for debugging from the dashboard).
5. Validation: a result is valid if and only if: all rules have been processed with no error, all mandatory fields are identified, and the naming template evaluated with no error. Otherwise: route directly to pending/.
6. Record: create the documents record (sha256, original filename, current inbox key, extracted texts, fields, status) and add a classified event including the original filename. The record exists before any physical move, so an interrupted filing leaves a recoverable state.
7. Filing:
   • valid → copy to the new key (prefix + templated name), verify the target object exists, then delete the inbox/ key only after the copy is confirmed; update file_key, set status processed, add a moved event. If a file with the same name already exists, append a number to the filename to avoid overwriting.
   • invalid → move to pending/ (incremental suffix on name conflict); update file_key; status pending.

The bucket is versioned: any inbox/ object deletion creates a delete marker, the data remains recoverable.

7. Review Dashboard

Custom pages on the PocketBase instance:

• File list: all files with status, filters, combined search over full text (FTS5) + metadata/fields.
• Detail: PDF preview streamed from S3 through a dedicated route, along with extracted fields; debug mode adds detailed log lines explaining every rule evaluation and action performed.
• Correction: forms to edit fields, type, and sender; correcting a processed file re-files it (copy to the new key, delete the old one, history preserved). A corrected pending file follows the same path: once validated, it is copied to its templated key in files/ (incremental suffix on conflict) and removed from pending/.
• Validation: transition to validated; processed files can also be validated. Validation is what takes a corrected pending file out of the review queue.
• Rule management: config display and dry-run on an existing document. The configuration is reloaded only on restart; there is no runtime reload.

Authentication: single account via PocketBase's standard auth.

8. Error Handling

• Transient S3 error: retry with backoff, the object stays in inbox/ and will be polled again.
• Unreadable PDF: pending status, reason recorded.
• Target key conflict (two files renamed identically, whether filing to files/ or moving to pending/): automatic incremental suffix, event logged.
• Invalid config: error message displayed and the application does not start.