[DO NOT MERGE] Prototype JSON representation for attribute collections

api/all/src/main/java/io/opentelemetry/api/common/ArrayBackedAttributes.java

@@ -43,6 +43,13 @@ public AttributesBuilder toBuilder() {
     return new ArrayBackedAttributesBuilder(new ArrayList<>(data()));
   }
 
+  @Override
+  public String toString() {
+    StringBuilder sb = new StringBuilder();
+    JsonEncoding.appendAttributes(sb, data());
+    return sb.toString();
+  }
+
   @SuppressWarnings("unchecked") // safe cast: values are stored internally keyed by AttributeKey<T>
   @Override
   @Nullable
@@ -111,8 +118,7 @@ private Value<?> getAsValue(String keyName) {
   }
 
   @SuppressWarnings("unchecked")
-  @Nullable
-  private static Value<?> asValue(AttributeType type, Object value) {
+  static Value<?> asValue(AttributeType type, Object value) {
     switch (type) {
       case STRING:
         return Value.of((String) value);
@@ -154,8 +160,8 @@ private static Value<?> asValue(AttributeType type, Object value) {
         // Already a Value
         return (Value<?>) value;
     }
-    // Should not reach here
-    return null;
+    // Every AttributeType must have a non-null Value representation.
+    throw new IllegalStateException("Unknown attribute type: " + type);
   }
 
   static Attributes sortAndFilterToAttributes(Object... data) {

api/all/src/main/java/io/opentelemetry/api/common/JsonEncoding.java

@@ -45,6 +45,20 @@ static void append(StringBuilder sb, Value<?> value) {
     }
   }
 
+  static void appendAttributes(StringBuilder sb, List<Object> data) {
+    sb.append('{');
+    for (int i = 0; i < data.size(); i += 2) {
+      if (i > 0) {
+        sb.append(',');
+      }
+      AttributeKey<?> key = (AttributeKey<?>) data.get(i);
+      appendString(sb, key.getKey());
+      sb.append(':');
+      append(sb, ArrayBackedAttributes.asValue(key.getType(), data.get(i + 1)));
+    }
+    sb.append('}');
+  }
+
   private static void appendString(StringBuilder sb, String value) {
     sb.append('"');
     for (int i = 0; i < value.length(); i++) {

api/all/src/test/java/io/opentelemetry/api/common/AttributesTest.java

@@ -20,6 +20,7 @@
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.assertj.core.api.Assertions.entry;
 
+import java.nio.charset.StandardCharsets;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashMap;
@@ -815,8 +816,38 @@ void attributesToString() {
 
     assertThat(attributes.toString())
         .isEqualTo(
-            "{error=true, http.response_size=100, "
-                + "otel.status_code=\"OK\", process.cpu_consumed=33.44, success=\"true\"}");
+            "{\"error\":true,\"http.response_size\":100,"
+                + "\"otel.status_code\":\"OK\",\"process.cpu_consumed\":33.44,"
+                + "\"success\":\"true\"}");
+  }
+
+  @Test
+  void attributesToStringComplexValues() {
+    Attributes attributes =
+        Attributes.builder()
+            .put(valueKey("bytes"), Value.of("hello world".getBytes(StandardCharsets.UTF_8)))
+            .put("colors", "red", "blue")
+            .put(valueKey("empty"), Value.empty())
+            .put(doubleKey("infinity"), Double.POSITIVE_INFINITY)
+            .put(
+                valueKey("nested"),
+                Value.of(
+                    KeyValue.of("array", Value.of(Value.of("red"), Value.of("blue"))),
+                    KeyValue.of("boolean", Value.of(true))))
+            .build();
+
+    assertThat(attributes.toString())
+        .isEqualTo(
+            "{\"bytes\":\"aGVsbG8gd29ybGQ=\",\"colors\":[\"red\",\"blue\"],"
+                + "\"empty\":null,\"infinity\":\"Infinity\","
+                + "\"nested\":{\"array\":[\"red\",\"blue\"],\"boolean\":true}}");
+  }
+
+  @Test
+  void attributesToStringEscapesKeysAndValues() {
+    Attributes attributes = Attributes.of(stringKey("a\"key\n"), "a \\ value\t");
+
+    assertThat(attributes.toString()).isEqualTo("{\"a\\\"key\\n\":\"a \\\\ value\\t\"}");
   }
 
   @Test

exporters/logging/src/test/java/io/opentelemetry/exporter/logging/LoggingSpanExporterTest.java

@@ -115,9 +115,9 @@ void export() {
         .isEqualTo(
             "'testSpan1' : 12345678876543211234567887654321 8765432112345678 "
                 + "INTERNAL [tracer: tracer1:] "
-                + "{animal=\"cat\", bytes=ValueBytes{AQID}, empty=ValueEmpty{}, "
-                + "heterogeneousArray=ValueArray{[\"string\",123]}, lives=9, "
-                + "map=KeyValueList{{\"nested\":\"value\"}}}");
+                + "{\"animal\":\"cat\",\"bytes\":\"AQID\",\"empty\":null,"
+                + "\"heterogeneousArray\":[\"string\",123],\"lives\":9,"
+                + "\"map\":{\"nested\":\"value\"}}");
     assertThat(logs.getEvents().get(1).getMessage())
         .isEqualTo(
             "'testSpan2' : 12340000000043211234000000004321 8765000000005678 "

exporters/logging/src/test/java/io/opentelemetry/exporter/logging/SystemOutLogRecordExporterTest.java

@@ -48,9 +48,10 @@ void format() {
     assertThat(output.toString())
         .isEqualTo(
             "1970-08-07T10:00:00Z ERROR3 'message' : 00000000000000010000000000000002 0000000000000003 "
-                + "[scopeInfo: logTest:1.0] {amount=1, bytes=ValueBytes{AQID}, cheese=\"cheddar\", "
-                + "empty=ValueEmpty{}, heterogeneousArray=ValueArray{[\"string\",123]}, "
-                + "map=KeyValueList{{\"nested\":\"value\"}}}");
+                + "[scopeInfo: logTest:1.0] {\"amount\":1,\"bytes\":\"AQID\","
+                + "\"cheese\":\"cheddar\",\"empty\":null,"
+                + "\"heterogeneousArray\":[\"string\",123],"
+                + "\"map\":{\"nested\":\"value\"}}");
   }
 
   @Test

sdk-extensions/declarative-config/src/test/java/io/opentelemetry/sdk/autoconfigure/declarativeconfig/DeclarativeConfigurationCreateTest.java

@@ -186,12 +186,12 @@ void create_ModelCustomizer() {
     assertThat(sdk.toString())
         .contains(
             "resource=Resource{schemaUrl=null, attributes={"
-                + "color=\"blue\", "
-                + "foo=\"bar\", "
-                + "service.name=\"unknown_service:java\", "
-                + "telemetry.sdk.language=\"java\", "
-                + "telemetry.sdk.name=\"opentelemetry\", "
-                + "telemetry.sdk.version=\"");
+                + "\"color\":\"blue\","
+                + "\"foo\":\"bar\","
+                + "\"service.name\":\"unknown_service:java\","
+                + "\"telemetry.sdk.language\":\"java\","
+                + "\"telemetry.sdk.name\":\"opentelemetry\","
+                + "\"telemetry.sdk.version\":\"");
   }
 
   @Test

sdk-extensions/incubator/src/test/java/io/opentelemetry/sdk/extension/incubator/trace/samplers/ComposableAnnotatingSamplerTest.java

@@ -29,7 +29,7 @@ void testDescription() {
     assertThat(
             ComposableSampler.annotating(ComposableSampler.alwaysOn(), ATTRIBUTES).getDescription())
         .isEqualTo(
-            "ComposableAnnotatingSampler{ComposableAlwaysOnSampler,{http.route=\"/bear\", size=100}}");
+            "ComposableAnnotatingSampler{ComposableAlwaysOnSampler,{\"http.route\":\"/bear\",\"size\":100}}");
   }
 
   @Test

sdk/logs/src/test/java/io/opentelemetry/sdk/logs/SdkLoggerProviderTest.java

@@ -347,7 +347,7 @@ void toString_Valid() {
         .isEqualTo(
             "SdkLoggerProvider{"
                 + "clock=SystemClock{}, "
-                + "resource=Resource{schemaUrl=null, attributes={key=\"value\"}}, "
+                + "resource=Resource{schemaUrl=null, attributes={\"key\":\"value\"}}, "
                 + "logLimits=LogLimits{maxNumberOfAttributes=128, maxAttributeValueLength=2147483647}, "
                 + "logRecordProcessor=MockLogRecordProcessor, "
                 + "loggerConfigurator=ScopeConfiguratorImpl{conditions=[]}"

sdk/metrics/src/test/java/io/opentelemetry/sdk/metrics/internal/data/MutableExponentialHistogramPointDataTest.java

@@ -66,7 +66,7 @@ public void testSanity() {
     assertThat(pointData.toString())
         .isEqualTo(
             "MutableExponentialHistogramPointData{startEpochNanos=10, epochNanos=20, "
-                + "attributes={foo=\"bar\"}, scale=1, sum=2.0, count=43, zeroCount=10, hasMin=true, "
+                + "attributes={\"foo\":\"bar\"}, scale=1, sum=2.0, count=43, zeroCount=10, hasMin=true, "
                 + "min=100.0, hasMax=true, max=1000.0, "
                 + "positiveBuckets=MutableExponentialHistogramBuckets{scale=1, offset=2, "
                 + "bucketCounts=[1, 2, 3], totalCount=3}, "

sdk/metrics/src/test/java/io/opentelemetry/sdk/metrics/internal/data/MutableHistogramPointDataTest.java

@@ -58,7 +58,7 @@ void testSanity() {
         .isEqualTo(
             "MutableHistogramPointData{startEpochNanos=10, "
                 + "epochNanos=20, "
-                + "attributes={foo=\"bar\"}, "
+                + "attributes={\"foo\":\"bar\"}, "
                 + "sum=2.0, "
                 + "count=550, "
                 + "hasMin=true, "

sdk/metrics/src/test/java/io/opentelemetry/sdk/metrics/internal/view/AttributesProcessorTest.java

@@ -64,7 +64,7 @@ void append_toString() {
         AttributesProcessor.append(Attributes.builder().put("key", "value").build());
 
     assertThat(processor.toString())
-        .isEqualTo("AppendingAttributesProcessor{additionalAttributes={key=\"value\"}}");
+        .isEqualTo("AppendingAttributesProcessor{additionalAttributes={\"key\":\"value\"}}");
   }
 
   @Test
@@ -141,7 +141,7 @@ void joinedAttributes_toString() {
         .isEqualTo(
             "JoinedAttributesProcessor{processors=["
                 + "BaggageAppendingAttributesProcessor{nameFilter=IncludeExcludePredicate{globMatchingEnabled=false, included=[keep]}}, "
-                + "AppendingAttributesProcessor{additionalAttributes={key=\"value\"}}"
+                + "AppendingAttributesProcessor{additionalAttributes={\"key\":\"value\"}}"
                 + "]}");
   }
 }

sdk/trace/src/test/java/io/opentelemetry/sdk/trace/SdkSpanBuilderTest.java

@@ -1110,9 +1110,9 @@ void spanDataToString() {
                 + "traceFlags=00, "
                 + "traceState=ArrayBasedTraceState\\{entries=\\[]}, remote=false, valid=false}, "
                 + "resource=Resource\\{schemaUrl=null, "
-                + "attributes=\\{service.name=\"unknown_service:java\", "
-                + "telemetry.sdk.language=\"java\", telemetry.sdk.name=\"opentelemetry\", "
-                + "telemetry.sdk.version=\"\\d+.\\d+.\\d+(-rc.\\d+)?(-SNAPSHOT)?\"}}, "
+                + "attributes=\\{\"service.name\":\"unknown_service:java\","
+                + "\"telemetry.sdk.language\":\"java\",\"telemetry.sdk.name\":\"opentelemetry\","
+                + "\"telemetry.sdk.version\":\"\\d+.\\d+.\\d+(-rc.\\d+)?(-SNAPSHOT)?\"}}, "
                 + "instrumentationScopeInfo=InstrumentationScopeInfo\\{"
                 + "name=SpanBuilderSdkTest, version=null, schemaUrl=null, attributes=\\{}}, "
                 + "name=span_name, "