Add mscgen support (yuzutech#12)

Install msc-generator [1] into the server docker image and provide a
corresponding under "/mscgen".

[1] https://gitlab.com/msc-generator/msc-generator

server/ops/docker/jdk17-noble/Dockerfile

@@ -235,6 +235,8 @@ RUN wget "https://github.com/yuzutech/blockdiag/releases/download/v${BLOCKDIAG_V
 RUN wget "https://github.com/yuzutech/WireViz/releases/download/v${WIREVIZ_VERSION}/wireviz-linux-${TARGETARCH}.bin" -O /usr/bin/wireviz && \
     chmod +x /usr/bin/wireviz
 
+RUN apt-get install --no-install-recommends --yes msc-generator-nox
+
 COPY --from=erd /root/.cabal/bin/erd /usr/bin/erd
 COPY --from=kroki-builder-bytefield /app/app.bin /usr/bin/bytefield
 COPY --from=kroki-builder-dbml /app/app.bin /usr/bin/dbml

server/src/main/java/io/kroki/server/Server.java

@@ -122,6 +122,7 @@ static void start(Vertx vertx, VertxOptions vertxOptions, JsonObject config, Han
     registry.register(new TikZ(vertx, config, commander), "tikz");
     registry.register(new Dbml(vertx, config, commander), "dbml");
     registry.register(new Wireviz(vertx, config, commander), "wireviz");
+    registry.register(new MscGenerator(vertx, config, commander), "mscgen");
 
     router.post("/")
       .handler(bodyHandler)

server/src/main/java/io/kroki/server/service/MscGenerator.java

@@ -0,0 +1,85 @@
+package io.kroki.server.service;
+
+import io.kroki.server.action.Commander;
+import io.kroki.server.decode.DiagramSource;
+import io.kroki.server.decode.SourceDecoder;
+import io.kroki.server.error.DecodeException;
+import io.kroki.server.format.FileFormat;
+import io.vertx.core.AsyncResult;
+import io.vertx.core.Handler;
+import io.vertx.core.Vertx;
+import io.vertx.core.buffer.Buffer;
+import io.vertx.core.json.JsonObject;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+public class MscGenerator implements DiagramService {
+
+  private static final List<FileFormat> SUPPORTED_FORMATS = Arrays.asList(FileFormat.PNG, FileFormat.SVG, FileFormat.PDF);
+
+  private final Vertx vertx;
+  private final String binPath;
+  private final SourceDecoder sourceDecoder;
+  private final Commander commander;
+
+  public MscGenerator(Vertx vertx, JsonObject config, Commander commander) {
+    this.vertx = vertx;
+    this.binPath = config.getString("KROKI_MSCGEN_BIN_PATH", "msc-gen");
+    this.sourceDecoder = new SourceDecoder() {
+      @Override
+      public String decode(String encoded) throws DecodeException {
+        return DiagramSource.decode(encoded);
+      }
+    };
+    this.commander = commander;
+  }
+
+  @Override
+  public List<FileFormat> getSupportedFormats() {
+    return SUPPORTED_FORMATS;
+  }
+
+  @Override
+  public SourceDecoder getSourceDecoder() {
+    return sourceDecoder;
+  }
+
+  @Override
+  public String getVersion() {
+    try {
+      Process process = new ProcessBuilder(binPath, "--version").start();
+      String line = new BufferedReader(new InputStreamReader(process.getInputStream())).readLine();
+      return line.split("\\s+")[1].substring(1);
+    } catch (IOException e) {
+      return "unknown";
+    }
+  }
+
+  @Override
+  public void convert(String sourceDecoded, String serviceName, FileFormat fileFormat, JsonObject options, Handler<AsyncResult<Buffer>> handler) {
+    vertx.executeBlocking(future -> {
+      try {
+        byte[] result = mscgen(sourceDecoded.getBytes(), fileFormat.getName(), options);
+        future.complete(result);
+      } catch (IOException | InterruptedException | IllegalStateException e) {
+        future.fail(e);
+      }
+    }, res -> handler.handle(res.map(o -> Buffer.buffer((byte[]) o))));
+  }
+
+  private byte[] mscgen(byte[] source, String format, JsonObject options) throws IOException, InterruptedException, IllegalStateException {
+    return commander.execute(
+      source,
+      binPath,
+      "-S", options.getString("lang", "signalling"), // Supported languages: signalling | msc, graph, block
+      "-T", format,
+      "-s=" + options.getFloat("scale", 1.f),
+      "-"
+    );
+  }
+}