ScriptREPL: generalize input and output streams

ctrueden · ctrueden · commit 0f3bf4449bbc · 2023-07-26T21:26:38.000-05:00
The use of InputStream and OutputStream was natural, but those are heavy
abstract classes, not lightweight interfaces. It is more flexible to
allow specifying a Supplier from which to draw the REPL input, and/or a
Consumer to receive the REPL output. This will be useful e.g. from
Python via JPype, which allows to implement Java interfaces in Python
backed by proxies. But you cannot proxy an abstract class like
InputStream or OutputStream. Nonetheless, the ability to simply use
InputStream/OutputStream like System.in+System.out is also nice,
so we keep those method signatures as well.
diff --git a/pom.xml b/pom.xml
@@ -10,7 +10,7 @@
 	</parent>
 
 	<artifactId>scijava-common</artifactId>
-	<version>2.94.3-SNAPSHOT</version>
+	<version>2.95.0-SNAPSHOT</version>
 
 	<name>SciJava Common</name>
 	<description>SciJava Common is a shared library for SciJava software. It provides a plugin framework, with an extensible mechanism for service discovery, backed by its own annotation processor, so that plugins can be loaded dynamically. It is used by downstream projects in the SciJava ecosystem, such as ImageJ and SCIFIO.</description>
diff --git a/src/main/java/org/scijava/script/ScriptREPL.java b/src/main/java/org/scijava/script/ScriptREPL.java
@@ -30,6 +30,7 @@
 package org.scijava.script;
 
 import java.io.BufferedReader;
+import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
@@ -38,6 +39,8 @@
 import java.lang.reflect.Constructor;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.function.Consumer;
+import java.util.function.Supplier;
 
 import javax.script.Bindings;
 import javax.script.ScriptException;
@@ -67,9 +70,9 @@ public class ScriptREPL {
 	@Parameter(required = false)
 	private PluginService pluginService;
 
-	private final PrintStream out;
+	private final Consumer<String> out;
 
-	private String languagePreference = null;
+	private String languagePreference;
 
 	/** List of interpreter-friendly script languages. */
 	private List<ScriptLanguage> languages;
@@ -84,19 +87,26 @@ public ScriptREPL(final Context context) {
 		this(context, System.out);
 	}
 
+	public ScriptREPL(final Context context, final String language) {
+		this(context, language, System.out);
+	}
+
 	public ScriptREPL(final Context context, final OutputStream out) {
-		context.inject(this);
-		this.out = out instanceof PrintStream ?
-			(PrintStream) out : new PrintStream(out);
+		this(context, null, out);
 	}
 
-	public ScriptREPL(final Context context, final String language) {
-		this(context, language, System.out);
+	public ScriptREPL(final Context context, final String language,
+		final OutputStream out)
+	{
+		this(context, language, outputStreamConsumer(out));
 	}
 
-	public ScriptREPL(final Context context, final String language, final OutputStream out) {
-		this(context, out);
+	public ScriptREPL(final Context context, final String language,
+		final Consumer<String> out)
+	{
+		context.inject(this);
 		languagePreference = language;
+		this.out = out;
 	}
 
 	/**
@@ -132,11 +142,39 @@ public void loop() throws IOException {
 	 * @param in Input stream from which commands are read.
 	 */
 	public void loop(final InputStream in) throws IOException {
-		initialize();
 		final BufferedReader bin = new BufferedReader(new InputStreamReader(in));
+		try {
+			loop(() -> {
+				try {
+					return bin.readLine();
+				}
+				catch (final IOException exc) {
+					throw new RuntimeException(exc);
+				}
+			});
+		}
+		catch (final RuntimeException exc) {
+			// NB: This convolution lets us throw IOException from inside a
+			// Supplier.get implementation, by wrapping in a RuntimeException.
+			// We then unwrap it again and throw it here, where we said we would.
+			final Throwable cause = exc.getCause();
+			if (cause instanceof IOException) throw (IOException) cause;
+			else throw exc;
+		}
+	}
+
+	/**
+	 * Starts a Read-Eval-Print-Loop from the given source, returning when
+	 * the loop terminates.
+	 *
+	 * @param in Source from which commands are read.
+	 */
+	public void loop(final Supplier<?> in) {
+		initialize();
 		while (true) {
 			prompt();
-			final String line = bin.readLine();
+			final Object input = in.get();
+			final String line = input == null ? null : input.toString();
 			if (line == null) break;
 			if (!evaluate(line)) return;
 		}
@@ -157,54 +195,40 @@ public void initialize() {
 	 */
 	public void initialize(final boolean verbose) {
 		if (verbose) {
-			out.println("Welcome to the SciJava REPL!");
-			out.println();
+			println("Welcome to the SciJava REPL!");
+			println();
 			help();
 		}
 		final List<ScriptLanguage> langs = getInterpretedLanguages();
 		if (verbose) {
 			if (langs.isEmpty()) {
-				out.println("--------------------------------------------------------------");
-				out.println("Uh oh! There are no SciJava script languages available!");
-				out.println("Are any on your classpath? E.g.: org.scijava:scripting-groovy?");
-				out.println("--------------------------------------------------------------");
-				out.println();
+				println("--------------------------------------------------------------");
+				println("Uh oh! There are no SciJava script languages available!");
+				println("Are any on your classpath? E.g.: org.scijava:scripting-groovy?");
+				println("--------------------------------------------------------------");
+				println();
 				return;
 			}
-			out.println("Have fun!");
-			out.println();
-
-			if(languagePreference != null) {
-			    selectPreferredLanguage(langs);
-			} else {
-				lang(langs.get(0).getLanguageName());
-			}
+			println("Have fun!");
+			println();
 		}
-		else if (!langs.isEmpty()) {
-			if(languagePreference != null) {
-				selectPreferredLanguage(langs);
-			} else {
-				lang(langs.get(0));
-			}
+		if (!langs.isEmpty()) {
+			if (languagePreference != null) selectPreferredLanguage(langs);
+			else lang(langs.get(0));
 		}
-
 		populateBindings(interpreter.getBindings());
 	}
 
 	private void selectPreferredLanguage(List<ScriptLanguage> langs) {
-		final ScriptLanguage preference = langs
-				.stream().filter(lang -> languagePreference.equals(lang.getLanguageName()))
-				.findAny().orElse(null);
-		if(preference != null) {
-			lang(preference);
-		} else {
-			lang(langs.get(0).getLanguageName());
-		}
+		final ScriptLanguage preference = langs.stream()
+				.filter(lang -> languagePreference.equals(lang.getLanguageName()))
+				.findFirst().orElse(langs.get(0));
+		lang(preference);
 	}
 
 	/** Outputs the prompt. */
 	public void prompt() {
-		out.print(interpreter == null || interpreter.isReady() ? "> " : "\\ ");
+		print(interpreter == null || interpreter.isReady() ? "> " : "\\ ");
 	}
 
 	/**
@@ -230,22 +254,22 @@ public boolean evaluate(final String line) {
 				// pass the input to the current interpreter for evaluation
 				final Object result = interpreter.interpret(line);
 				if (result != ScriptInterpreter.MORE_INPUT_PENDING) {
-					out.println(s(result));
+					println(s(result));
 				}
 			}
 		}
 		catch (final ScriptException exc) {
 			// NB: Something went wrong interpreting the line of code.
 			// Let's just display the error message, unless we are in debug mode.
-			if (debug) exc.printStackTrace(out);
+			if (debug) printStackTrace(exc);
 			else {
 				final String msg = exc.getMessage();
-				out.println(msg == null ? exc.getClass().getName() : msg);
+				println(msg == null ? exc.getClass().getName() : msg);
 			}
 		}
 		catch (final Throwable exc) {
 			// NB: Something unusual went wrong. Dump the whole exception always.
-			exc.printStackTrace(out);
+			printStackTrace(exc);
 		}
 		return true;
 	}
@@ -254,17 +278,17 @@ public boolean evaluate(final String line) {
 
 	/** Prints a usage guide. */
 	public void help() {
-		out.println("Available built-in commands:");
-		out.println();
-		out.println("  :help           | this handy list of commands");
-		out.println("  :vars           | dump a list of variables");
-		out.println("  :lang <name>    | switch the active language");
-		out.println("  :langs          | list available languages");
-		out.println("  :debug          | toggle full stack traces");
-		out.println("  :quit           | exit the REPL");
-		out.println();
-		out.println("Or type a statement to evaluate it with the active language.");
-		out.println();
+		println("Available built-in commands:");
+		println();
+		println("  :help           | this handy list of commands");
+		println("  :vars           | dump a list of variables");
+		println("  :lang <name>    | switch the active language");
+		println("  :langs          | list available languages");
+		println("  :debug          | toggle full stack traces");
+		println("  :quit           | exit the REPL");
+		println();
+		println("Or type a statement to evaluate it with the active language.");
+		println();
 	}
 
 	/** Lists variables in the script context. */
@@ -294,11 +318,11 @@ public void lang(final String langName) {
 		// create the new interpreter
 		final ScriptLanguage language = scriptService.getLanguageByName(langName);
 		if (language == null) {
-			out.println("No such language: " + langName);
+			println("No such language: " + langName);
 			return;
 		}
 		lang(language);
-		out.println("language -> " + interpreter.getLanguage().getLanguageName());
+		println("language -> " + interpreter.getLanguage().getLanguageName());
 	}
 
 	/**
@@ -316,7 +340,7 @@ public void lang(final ScriptLanguage language) {
 			copyBindings(interpreter, newInterpreter);
 		}
 		catch (final Throwable t) {
-			t.printStackTrace(out);
+			printStackTrace(t);
 		}
 		interpreter = newInterpreter;
 	}
@@ -335,7 +359,7 @@ public void langs() {
 
 	public void debug() {
 		debug = !debug;
-		out.println("debug mode -> " + debug);
+		println("debug mode -> " + debug);
 	}
 
 	// -- Main method --
@@ -417,7 +441,7 @@ private List<Gateway> gateways() {
 				gateways.add(gateway);
 			}
 			catch (final Throwable t) {
-				t.printStackTrace(out);
+				printStackTrace(t);
 			}
 		}
 		return gateways;
@@ -442,6 +466,17 @@ private String type(final Object value) {
 		return "[" + decoded.getClass().getName() + "]";
 	}
 
+	private static final String NL = System.getProperty("line.separator");
+	private void print(String s) { out.accept(s); }
+	private void println() { print(NL); }
+	private void println(final String s) { print(s + NL); }
+
+	private void printStackTrace(final Throwable t) {
+		final ByteArrayOutputStream baos = new ByteArrayOutputStream();
+		t.printStackTrace(new PrintStream(baos));
+		println(baos.toString());
+	}
+
 	private void printColumns(final List<?>... columns) {
 		final int pad = 2;
 
@@ -456,18 +491,26 @@ private void printColumns(final List<?>... columns) {
 		}
 
 		// output the columns
+		final StringBuilder sb = new StringBuilder();
 		for (int i = 0; i < columns[0].size(); i++) {
+			sb.setLength(0);
 			for (int c = 0; c < columns.length; c++) {
 				final String s = s(columns[c].get(i));
-				out.print(s);
+				sb.append(s);
 				for (int p = s.length(); p < widths[c] + pad; p++) {
-					out.print(' ');
+					sb.append(' ');
 				}
 			}
-			out.println();
+			println(sb.toString());
 		}
 	}
 
+	private static Consumer<String> outputStreamConsumer(final OutputStream out) {
+		final PrintStream ps = out instanceof PrintStream ?
+			(PrintStream) out : new PrintStream(out);
+		return s -> { ps.print(s); ps.flush(); };
+	}
+
 	private static String lowerCamelCase(final String s) {
 		final StringBuilder sb = new StringBuilder(s);
 		for (int i=0; i<sb.length(); i++) {
@@ -481,5 +524,4 @@ private static String lowerCamelCase(final String s) {
 	private static String s(final Object o) {
 		return o == null ? NULL : o.toString();
 	}
-
 }
