Print Queue — System Flow¶

Visual overview of the file-based print queue: how PDFs are written by the backend and consumed by the external print client on the store server.

End-to-end flow¶

sequenceDiagram
    participant Backend as zwerfkei (backend)
    participant LockFile as henk.lock
    participant FS as print_queue/{type}/
    participant API as GET /api/printqueue
    participant Client as Print client (store server)
    participant Printer as Physical printer

    Note over Backend,FS: Writing a PDF
    Backend->>LockFile: Create henk.lock
    Backend->>FS: Write {filename}.pdf
    Backend->>LockFile: Delete henk.lock

    Note over Client,Printer: Print client polling loop
    Client->>API: GET /api/printqueue
    alt Lock file exists
        API-->>Client: 202 Please wait
    else Queue empty
        API-->>Client: 204 No content
    else PDF available
        API->>LockFile: Check lock
        API->>FS: Read first .pdf in queue
        API->>FS: Rename → sent_{timestamp}.pdf
        API-->>Client: 200 { path, timestamp, contents: base64 }
        Client->>Printer: Print PDF
        Client->>API: DELETE /api/printqueue/{timestamp}
        API->>FS: Delete sent_{timestamp}.pdf
    end

PDF types and folders¶

graph LR
    Backend["zwerfkei\nbackend"]

    Backend -->|"printOutput('a4')"| A4["print_queue/a4/"]
    Backend -->|"printOutput('a5')"| A5["print_queue/a5/"]
    Backend -->|"printOutput('a3')"| A3["print_queue/a3/"]
    Backend -->|"printOutput('factuur')"| FAC["print_queue/a4_bypasstray_duplex/"]
    Backend -->|"printOutput('bypass')"| BYP["print_queue/a4_bypasstray/"]
    Backend -->|"printOutput('shipping_label')"| SL["print_queue/shipping_label_{device}/"]
    Backend -->|"printOutput('plak')"| PL["print_queue/plak/"]
    Backend -->|"printOutput('hang')"| HA["print_queue/hang/"]
    Backend -->|"printOutput('bon')"| BON["print_queue/bon/"]

    A4 --> Client["Print client\n(store server)"]
    A5 --> Client
    A3 --> Client
    FAC --> Client
    BYP --> Client
    SL --> Client
    PL --> Client
    HA --> Client
    BON --> Client

Related pages¶

Print Queue — Full Documentation Noodkassa Flow