Unified Kotlin Multiplatform document generation and printing. Build thermal receipts (80mm / 58mm ESC/POS) and page-bound business documents (A4 invoices, purchase orders, reports) from a single common-code API, then send them to the OS print spooler, a thermal printer, or save them to a file. Runs on Android, iOS, Desktop (JVM), and Web (Wasm/JS).

• One API, every layout. The same fluent builder produces continuous thermal receipts and page-bound A4 documents; DocumentType decides the page geometry.
• Common-code layout. Documents are built as HTML5 + CSS3 strings in commonMain using flexbox rows, so a single definition renders identically across platforms.
• Fully offline. Logos and images are embedded as Base64 data URIs — no native asset paths, no network, no file plumbing.
• Colors and logos. Business documents support a brand accent color and colored header rows; receipts stay monochrome for thermal hardware.
• Bring your own HTML. Already have document markup? Print it directly, or drop it into a builder with addRawHtml.
• Native output per platform. WebView + PrintManager (Android), UIPrintInteractionController (iOS), OpenHtmlToPdf + javax.print (Desktop), and an iframe + Blob pipeline (Web), plus a raw ESC/POS command path on Desktop.

// settings.gradle.kts -> dependencyResolutionManagement { repositories { mavenCentral() } }

// build.gradle.kts (commonMain)
implementation("io.github.ellykits:spooler:1.0.0-alpha01")

The document below is the invoice shown in the screenshot above:

val invoice =
  UnifiedDocument(DocumentType.A4_DOCUMENT, title = "Tax Invoice", accentColor = "#0F766E")
    .addLogo(logoBytes, ImageType.PNG)
    .addHeader("Northwind Hardware Ltd")
    .addText("12 Kiln Road, Riverside Industrial Park, Portford 40100 • VAT PIN: P000123456Z")
    .addDivider()
    .addTableRow("Invoice", "INV-2026-0042")
    .addTableRow("Bill To", "Meridian Contractors Ltd")
    .addDivider()
    .addHeaderRow("Description", "Qty", "Unit", "Total")
    .addTableRow("PPR Pipe 1in", "40", "300.00", "12,000.00")
    .addTableRow("Cement 50kg", "25", "780.00", "19,500.00")
    .addDivider()
    .addTableRow("TOTAL DUE", "", "", "116,580.00")
    .addText("Payment due within 30 days.")

val result = engine.print(invoice, PrintTarget.SaveToFile("invoice.pdf"))
if (result.isSuccess) println("Done: $result")

print(document, target) is the primary entry point — it builds the HTML and forwards the document's DocumentType for you. engine is a PrintEngine; see Constructing the engine.

A thermal receipt is the same builder with a continuous DocumentType:

val receipt =
  UnifiedDocument(DocumentType.RECEIPT_80MM, title = "Receipt")
    .addLogo(logoBytes, ImageType.PNG)
    .addHeader("NORTHWIND HARDWARE")
    .addTableRow("PPR Pipe 1in", "4", "1,200.00")
    .addDivider()
    .addTableRow("TOTAL", "", "2,308.40")

engine.print(receipt, PrintTarget.SendToPrinter(EscPosDriver(paperWidthMm = 80)))

The :demo module builds three business documents and two receipts for a fictitious hardware business. Rendered output:

Invoice	Purchase order	Stock report	Sale receipt	Compact receipt

Embed a centered logo or a full-width inline image — both are Base64-encoded into the document, so nothing is loaded from disk or network at print time:

document.addLogo(logoBytes, ImageType.PNG)   // centered brand mark
document.addImage(photoBytes, ImageType.JPEG) // full-width inline image

Give page-bound documents a brand accent color and colored table headers (receipts stay monochrome for thermal printers, so leave accentColor unset for them):

UnifiedDocument(DocumentType.A4_DOCUMENT, accentColor = "#0F766E")
  .addHeaderRow("Description", "Qty", "Total") // rendered in the accent color
  .addTableRow("PPR Pipe 1in", "40", "12,000.00")

Already have document markup? Print a complete HTML document directly:

engine.execute(myExistingHtml, PrintTarget.SaveToFile("report.pdf"), DocumentType.A4_DOCUMENT)

…or fold an existing HTML fragment into a spooler document (inserted verbatim):

UnifiedDocument(DocumentType.A4_DOCUMENT)
  .addHeader("Summary")
  .addRawHtml("<table class=\"legacy\">…your markup…</table>")

PrintEngine is an expect class; its constructor differs only because Android needs a Context to drive WebView/PrintManager:

• Android: PrintEngine(context)
• iOS / Desktop / Web: PrintEngine()

A common pattern is a small expect fun factory in your app (the :demo module's EngineFactory shows this) so shared code has one entry point.

• Android SaveToFile presents the system print dialog (which offers "Save as PDF"); WebView has no silent file-write API, so it returns PrintResult.Success rather than Saved(path). Desktop and iOS write the file directly and return Saved(path).
• Web SaveToFile downloads an .html file (the browser has no PDF renderer); the requested path's extension is coerced to .html.
• iOS SendToPrinter uses UIPrintInteractionController. On iPhone it presents animated; on iPad it presents from the key window's root view. Apps built on the modern multi-scene lifecycle may need to supply their own presentation anchor.
• ESC/POS text is emitted as ASCII; non-ASCII characters are replaced with ?, and lines are wrapped to charactersPerLine. Thermal printing on Desktop uses this raw path; the other platforms render the HTML.

The :demo module is a Compose Multiplatform app that generates the five sample documents above and prints or saves them with spooler.

• Desktop: ./gradlew :demo:run
• Web: ./gradlew :demo:wasmJsBrowserDevelopmentRun
• Android / iOS: open the project in an IDE and run the demo app target.

:spooler uses the vanniktech maven-publish plugin to publish to Maven Central via the Central Portal. Releasing requires a GPG signing key and Central Portal credentials configured locally or in CI:

./gradlew publishAndReleaseToMavenCentral

Apache 2.0. See LICENSE.