Support for ASCII in Jackson codec & converter

This commit introduces support for writing JSON with an US-ASCII
character encoding in the Jackson encoder and message converter,
treating it like UTF-8.

See gh-25322

spring-web/src/main/java/org/springframework/http/codec/json/AbstractJackson2Encoder.java

@@ -76,10 +76,11 @@ public abstract class AbstractJackson2Encoder extends Jackson2CodecSupport imple
 		STREAM_SEPARATORS.put(MediaType.APPLICATION_STREAM_JSON, NEWLINE_SEPARATOR);
 		STREAM_SEPARATORS.put(MediaType.parseMediaType("application/stream+x-jackson-smile"), new byte[0]);
 
-		ENCODINGS = new HashMap<>(JsonEncoding.values().length);
+		ENCODINGS = new HashMap<>(JsonEncoding.values().length + 1);
 		for (JsonEncoding encoding : JsonEncoding.values()) {
 			ENCODINGS.put(encoding.getJavaName(), encoding);
 		}
+		ENCODINGS.put("US-ASCII", JsonEncoding.UTF8);
 	}
 
 

spring-web/src/main/java/org/springframework/http/converter/json/AbstractJackson2HttpMessageConverter.java

@@ -24,11 +24,9 @@ import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
 import java.util.Arrays;
 import java.util.Collections;
-import java.util.EnumSet;
+import java.util.HashMap;
 import java.util.Map;
 import java.util.concurrent.atomic.AtomicReference;
-import java.util.function.Function;
-import java.util.stream.Collectors;
 
 import com.fasterxml.jackson.core.JsonEncoding;
 import com.fasterxml.jackson.core.JsonGenerator;
@@ -76,7 +74,16 @@ import org.springframework.util.TypeUtils;
  */
 public abstract class AbstractJackson2HttpMessageConverter extends AbstractGenericHttpMessageConverter<Object> {
 
-	private static final Map<String, JsonEncoding> ENCODINGS = jsonEncodings();
+	private static final Map<String, JsonEncoding> ENCODINGS;
+
+	static {
+		ENCODINGS = new HashMap<>(JsonEncoding.values().length + 1);
+		for (JsonEncoding encoding : JsonEncoding.values()) {
+			ENCODINGS.put(encoding.getJavaName(), encoding);
+		}
+		ENCODINGS.put("US-ASCII", JsonEncoding.UTF8);
+	}
+
 
 	/**
 	 * The default charset used by the converter.
@@ -399,9 +406,4 @@ public abstract class AbstractJackson2HttpMessageConverter extends AbstractGener
 		return super.getContentLength(object, contentType);
 	}
 
-	private static Map<String, JsonEncoding> jsonEncodings() {
-		return EnumSet.allOf(JsonEncoding.class).stream()
-				.collect(Collectors.toMap(JsonEncoding::getJavaName, Function.identity()));
-	}
-
 }

spring-web/src/test/java/org/springframework/http/codec/json/Jackson2JsonDecoderTests.java

@@ -87,6 +87,8 @@ public class Jackson2JsonDecoderTests extends AbstractDecoderTests<Jackson2JsonD
 		assertThat(decoder.canDecode(forClass(Pojo.class), APPLICATION_XML)).isFalse();
 		assertThat(this.decoder.canDecode(ResolvableType.forClass(Pojo.class),
 				new MediaType("application", "json", StandardCharsets.UTF_8))).isTrue();
+		assertThat(this.decoder.canDecode(ResolvableType.forClass(Pojo.class),
+				new MediaType("application", "json", StandardCharsets.US_ASCII))).isTrue();
 		assertThat(this.decoder.canDecode(ResolvableType.forClass(Pojo.class),
 				new MediaType("application", "json", StandardCharsets.ISO_8859_1))).isTrue();
 	}
@@ -227,8 +229,7 @@ public class Jackson2JsonDecoderTests extends AbstractDecoderTests<Jackson2JsonD
 	public void decodeNonUtf8Encoding() {
 		Mono<DataBuffer> input = stringBuffer("{\"foo\":\"bar\"}", StandardCharsets.UTF_16);
 
-		testDecode(input, ResolvableType.forType(new ParameterizedTypeReference<Map<String, String>>() {
+		testDecode(input, ResolvableType.forType(new ParameterizedTypeReference<Map<String, String>>() {}),
-				}),
 				step -> step.assertNext(o -> assertThat((Map<String, String>) o).containsEntry("foo", "bar"))
 						.verifyComplete(),
 				MediaType.parseMediaType("application/json; charset=utf-16"),
@@ -242,8 +243,7 @@ public class Jackson2JsonDecoderTests extends AbstractDecoderTests<Jackson2JsonD
 				stringBuffer("{\"føø\":\"bår\"}", StandardCharsets.ISO_8859_1)
 		);
 
-		testDecode(input, ResolvableType.forType(new ParameterizedTypeReference<Map<String, String>>() {
+		testDecode(input, ResolvableType.forType(new ParameterizedTypeReference<Map<String, String>>() {}),
-				}),
 				step -> step.assertNext(o -> assertThat((Map<String, String>) o).containsEntry("føø", "bår"))
 						.verifyComplete(),
 				MediaType.parseMediaType("application/json; charset=iso-8859-1"),
@@ -255,14 +255,28 @@ public class Jackson2JsonDecoderTests extends AbstractDecoderTests<Jackson2JsonD
 	public void decodeMonoNonUtf8Encoding() {
 		Mono<DataBuffer> input = stringBuffer("{\"foo\":\"bar\"}", StandardCharsets.UTF_16);
 
-		testDecodeToMono(input, ResolvableType.forType(new ParameterizedTypeReference<Map<String, String>>() {
+		testDecodeToMono(input, ResolvableType.forType(new ParameterizedTypeReference<Map<String, String>>() {}),
-				}),
 				step -> step.assertNext(o -> assertThat((Map<String, String>) o).containsEntry("foo", "bar"))
 						.verifyComplete(),
 				MediaType.parseMediaType("application/json; charset=utf-16"),
 				null);
 	}
 
+	@Test
+	@SuppressWarnings("unchecked")
+	public void decodeAscii() {
+		Flux<DataBuffer> input = Flux.concat(
+				stringBuffer("{\"foo\":\"bar\"}", StandardCharsets.US_ASCII)
+		);
+
+		testDecode(input, ResolvableType.forType(new ParameterizedTypeReference<Map<String, String>>() {}),
+				step -> step.assertNext(o -> assertThat((Map<String, String>) o).containsEntry("foo", "bar"))
+						.verifyComplete(),
+				MediaType.parseMediaType("application/json; charset=us-ascii"),
+				null);
+	}
+
+
 	private Mono<DataBuffer> stringBuffer(String value) {
 		return stringBuffer(value, StandardCharsets.UTF_8);
 	}

spring-web/src/test/java/org/springframework/http/codec/json/Jackson2JsonEncoderTests.java

@@ -71,6 +71,8 @@ public class Jackson2JsonEncoderTests extends AbstractEncoderTests<Jackson2JsonE
 
 		assertThat(this.encoder.canEncode(ResolvableType.forClass(Pojo.class),
 				new MediaType("application", "json", StandardCharsets.UTF_8))).isTrue();
+		assertThat(this.encoder.canEncode(ResolvableType.forClass(Pojo.class),
+				new MediaType("application", "json", StandardCharsets.US_ASCII))).isTrue();
 		assertThat(this.encoder.canEncode(ResolvableType.forClass(Pojo.class),
 				new MediaType("application", "json", StandardCharsets.ISO_8859_1))).isFalse();
 
@@ -225,6 +227,17 @@ public class Jackson2JsonEncoderTests extends AbstractEncoderTests<Jackson2JsonE
 				.verify(Duration.ofSeconds(5));
 	}
 
+	@Test
+	public void encodeAscii() {
+		Mono<Object> input = Mono.just(new Pojo("foo", "bar"));
+
+		testEncode(input, ResolvableType.forClass(Pojo.class), step -> step
+				.consumeNextWith(expectString("{\"foo\":\"foo\",\"bar\":\"bar\"}"))
+				.verifyComplete(),
+				new MimeType("application", "json", StandardCharsets.US_ASCII), null);
+
+	}
+
 
 	@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, property = "type")
 	private static class ParentClass {

spring-web/src/test/java/org/springframework/http/converter/json/MappingJackson2HttpMessageConverterTests.java

@@ -67,6 +67,7 @@ public class MappingJackson2HttpMessageConverterTests {
 		assertThat(converter.canRead(MyBean.class, new MediaType("application", "json"))).isTrue();
 		assertThat(converter.canRead(Map.class, new MediaType("application", "json"))).isTrue();
 		assertThat(converter.canRead(MyBean.class, new MediaType("application", "json", StandardCharsets.UTF_8))).isTrue();
+		assertThat(converter.canRead(MyBean.class, new MediaType("application", "json", StandardCharsets.US_ASCII))).isTrue();
 		assertThat(converter.canRead(MyBean.class, new MediaType("application", "json", StandardCharsets.ISO_8859_1))).isTrue();
 	}
 
@@ -75,6 +76,7 @@ public class MappingJackson2HttpMessageConverterTests {
 		assertThat(converter.canWrite(MyBean.class, new MediaType("application", "json"))).isTrue();
 		assertThat(converter.canWrite(Map.class, new MediaType("application", "json"))).isTrue();
 		assertThat(converter.canWrite(MyBean.class, new MediaType("application", "json", StandardCharsets.UTF_8))).isTrue();
+		assertThat(converter.canWrite(MyBean.class, new MediaType("application", "json", StandardCharsets.US_ASCII))).isTrue();
 		assertThat(converter.canWrite(MyBean.class, new MediaType("application", "json", StandardCharsets.ISO_8859_1))).isFalse();
 	}
 
@@ -460,6 +462,33 @@ public class MappingJackson2HttpMessageConverterTests {
 		assertThat(result).containsExactly(entry("føø", "bår"));
 	}
 
+	@Test
+	@SuppressWarnings("unchecked")
+	public void readAscii() throws Exception {
+		String body = "{\"foo\":\"bar\"}";
+		Charset charset = StandardCharsets.US_ASCII;
+		MockHttpInputMessage inputMessage = new MockHttpInputMessage(body.getBytes(charset));
+		inputMessage.getHeaders().setContentType(new MediaType("application", "json", charset));
+		HashMap<String, Object> result = (HashMap<String, Object>) this.converter.read(HashMap.class, inputMessage);
+
+		assertThat(result).containsExactly(entry("foo", "bar"));
+	}
+
+	@Test
+	@SuppressWarnings("unchecked")
+	public void writeAscii() throws Exception {
+		MockHttpOutputMessage outputMessage = new MockHttpOutputMessage();
+		Map<String,Object> body = new HashMap<>();
+		body.put("foo", "bar");
+		Charset charset = StandardCharsets.US_ASCII;
+		MediaType contentType = new MediaType("application", "json", charset);
+		converter.write(body, contentType, outputMessage);
+
+		String result = outputMessage.getBodyAsString(charset);
+		assertThat(result).isEqualTo("{\"foo\":\"bar\"}");
+		assertThat(outputMessage.getHeaders().getContentType()).as("Invalid content-type").isEqualTo(contentType);
+	}
+
 
 	interface MyInterface {