fmesh-export

Export an F-Mesh mesh as data or as a diagram. One Go module, one package per format:

Format	Package	Render with
JSON	json	any JSON tool; unmarshal into json.Mesh / json.Cycle
YAML	yaml	any YAML tool; unmarshal into yaml.Mesh / yaml.Cycle
Graphviz DOT	dot	dot -Tpng, edotor.net
Mermaid	mermaid	GitHub markdown, mermaid.live
D2	d2	d2, play.d2lang.com
PlantUML	plantuml	plantuml -tpng, plantuml.com server

Every exporter implements export.Exporter, the interface in this module's root package, so one format can replace another.

Install

go get github.com/hovsep/fmesh-export/<format>  # e.g. /mermaid

Usage

Every format has the same shape:

import "github.com/hovsep/fmesh-export/mermaid"

e := mermaid.New() // options go here, e.g. mermaid.WithDirection("TB")

// ... build and seed fm ...

static, err := e.Export(fm) // the structure
if err != nil {
    return err
}

ri, err := fm.Run(ctx)
if err != nil {
    return err
}
for _, c := range ri.Cycles.All() {
    frame, err := e.ExportCycle(fm, c) // the structure, colored by the results of cycle c
    if err != nil {
        return err
    }
    // ... write frame ...
}

• New(opts...) creates an exporter. It cannot fail.
• Export(fm) returns the structure: components, ports, pipes, descriptions.
• ExportCycle(fm, c) returns the structure in the state of one cycle. Components are colored by their activation result. A component with no result in c had no input.
• An invalid option (for example an unknown direction) is returned as an error by Export and ExportCycle.
• Options set one thing on top of the defaults. Anything you do not set keeps its default. See each package's README.
• An exporter holds only its options. Reuse one value for many meshes.
• An exporter never changes the mesh. Equal meshes give byte-identical output.

Streaming: one frame per cycle while the mesh runs

fmesh.WithCyclesHistoryLimit keeps only the last cycles in ri.Cycles. To get every cycle, or to see frames while the mesh runs, export from an AfterCycle hook:

e := mermaid.New()
fm.SetupHooks(func(h *fmesh.Hooks) {
    h.AfterCycle(func(ctx context.Context, cc *fmesh.CycleContext) error {
        frame, err := e.ExportCycle(cc.FMesh, cc.Cycle)
        if err != nil {
            return err
        }
        // ... write or send frame ...
        return nil
    })
})

Any format through one interface

Code that does not care about the format can take an export.Exporter:

import "github.com/hovsep/fmesh-export" // package export

func save(e export.Exporter, fm *fmesh.FMesh) ([]byte, error) {
    return e.Export(fm)
}

save(dot.New(), fm)
save(json.New(), fm)

Live examples

After a merge, CI renders the showcase mesh in internal/cmd/showcase (fan-out, fan-in, an error and a wait) in each diagram format the merge touched, and shows the pictures on the run's summary page. One workflow per format: DOT, Mermaid, D2, PlantUML.

Format	Structure	Run replay
DOT
Mermaid
D2
PlantUML

Run it locally: go run ./internal/cmd/showcase -format d2 out.

Writing a new exporter

Copy the d2 package: it is a complete exporter with the full set of tests. A new data format is smaller: build the documents with internal/doc and only encode them (add the format's struct tags to the types there). A new format xyz needs:

1. A package xyz/ with xyz.go, xyz_test.go and a README.md.

2. The shared shape, the same as every other format:

   • type Exporter struct{...} that holds only the options.
   • type Option func(*Exporter), and single options that change one thing on top of the defaults. No config struct that replaces everything.
   • func New(opts ...Option) *Exporter. It cannot fail.
   • Export(fm *fmesh.FMesh) ([]byte, error) for the structure.
   • ExportCycle(fm *fmesh.FMesh, c *cycle.Cycle) ([]byte, error) for one cycle.
   • var _ export.Exporter = (*Exporter)(nil), so the compiler checks the interface.

3. Rendering through fm.Walk(visitor). Implement VisitMesh, VisitComponent, VisitPort and VisitPipe. Rules:

   • Never change the mesh.
   • Keep no state in the Exporter between calls. Put per-export state in the visitor.
   • Check the options in Export and ExportCycle, and return an error for a bad one.
   • The output must be byte-identical for equal meshes.
   • Use generated IDs (c1, p2, ...) and put names only in quoted, escaped labels.
   • In a cycle graph, a component with no result had no input (ActivationCodeNoInput).

4. Tests:

   • one exact expected output for Export;
   • cycle colors and an error text for ExportCycle;
   • determinism;
   • awkward names (quotes, dots, colons, newlines);
   • each option, and option checks in both Export and ExportCycle;
   • one Exporter reused for two meshes;
   • ExportCycle from an AfterCycle hook gives one frame per cycle.

   The d2 tests cover all of these.

5. The showcase: add the format to formats in internal/cmd/showcase.

6. CI (diagram formats only; data formats have nothing to render): copy .github/workflows/d2.yml to xyz.yml, and add an xyz) case to the "Install renderer" and "Render images" steps of render.yml. Pin the renderer version and check its SHA-256 there.

7. Docs: add a row to the format table and the live-example table above.

Run make check before you open a pull request. The PR's checks upload the rendered images as an artifact, so you can look at your format before it is merged.

Contributing

See CONTRIBUTING.md.

License

See LICENSE.