Revert supplier accepting list

docs/apidiffs/current_vs_latest/opentelemetry-exporter-otlp.txt

@@ -1,19 +1,19 @@
 Comparing source compatibility of  against 
 ***  MODIFIED CLASS: PUBLIC FINAL io.opentelemetry.exporter.otlp.http.logs.OtlpHttpLogRecordExporterBuilder  (not serializable)
 	===  CLASS FILE FORMAT VERSION: 52.0 <- 52.0
-	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.exporter.otlp.http.logs.OtlpHttpLogRecordExporterBuilder setHeaders(java.util.function.Supplier<java.util.Map<java.lang.String,java.util.List<java.lang.String>>>)
+	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.exporter.otlp.http.logs.OtlpHttpLogRecordExporterBuilder setHeaders(java.util.function.Supplier<java.util.Map<java.lang.String,java.lang.String>>)
 ***  MODIFIED CLASS: PUBLIC FINAL io.opentelemetry.exporter.otlp.http.metrics.OtlpHttpMetricExporterBuilder  (not serializable)
 	===  CLASS FILE FORMAT VERSION: 52.0 <- 52.0
-	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.exporter.otlp.http.metrics.OtlpHttpMetricExporterBuilder setHeaders(java.util.function.Supplier<java.util.Map<java.lang.String,java.util.List<java.lang.String>>>)
+	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.exporter.otlp.http.metrics.OtlpHttpMetricExporterBuilder setHeaders(java.util.function.Supplier<java.util.Map<java.lang.String,java.lang.String>>)
 ***  MODIFIED CLASS: PUBLIC FINAL io.opentelemetry.exporter.otlp.http.trace.OtlpHttpSpanExporterBuilder  (not serializable)
 	===  CLASS FILE FORMAT VERSION: 52.0 <- 52.0
-	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.exporter.otlp.http.trace.OtlpHttpSpanExporterBuilder setHeaders(java.util.function.Supplier<java.util.Map<java.lang.String,java.util.List<java.lang.String>>>)
+	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.exporter.otlp.http.trace.OtlpHttpSpanExporterBuilder setHeaders(java.util.function.Supplier<java.util.Map<java.lang.String,java.lang.String>>)
 ***  MODIFIED CLASS: PUBLIC FINAL io.opentelemetry.exporter.otlp.logs.OtlpGrpcLogRecordExporterBuilder  (not serializable)
 	===  CLASS FILE FORMAT VERSION: 52.0 <- 52.0
-	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.exporter.otlp.logs.OtlpGrpcLogRecordExporterBuilder setHeaders(java.util.function.Supplier<java.util.Map<java.lang.String,java.util.List<java.lang.String>>>)
+	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.exporter.otlp.logs.OtlpGrpcLogRecordExporterBuilder setHeaders(java.util.function.Supplier<java.util.Map<java.lang.String,java.lang.String>>)
 ***  MODIFIED CLASS: PUBLIC FINAL io.opentelemetry.exporter.otlp.metrics.OtlpGrpcMetricExporterBuilder  (not serializable)
 	===  CLASS FILE FORMAT VERSION: 52.0 <- 52.0
-	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.exporter.otlp.metrics.OtlpGrpcMetricExporterBuilder setHeaders(java.util.function.Supplier<java.util.Map<java.lang.String,java.util.List<java.lang.String>>>)
+	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.exporter.otlp.metrics.OtlpGrpcMetricExporterBuilder setHeaders(java.util.function.Supplier<java.util.Map<java.lang.String,java.lang.String>>)
 ***  MODIFIED CLASS: PUBLIC FINAL io.opentelemetry.exporter.otlp.trace.OtlpGrpcSpanExporterBuilder  (not serializable)
 	===  CLASS FILE FORMAT VERSION: 52.0 <- 52.0
-	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.exporter.otlp.trace.OtlpGrpcSpanExporterBuilder setHeaders(java.util.function.Supplier<java.util.Map<java.lang.String,java.util.List<java.lang.String>>>)
+	+++  NEW METHOD: PUBLIC(+) io.opentelemetry.exporter.otlp.trace.OtlpGrpcSpanExporterBuilder setHeaders(java.util.function.Supplier<java.util.Map<java.lang.String,java.lang.String>>)

exporters/common/src/main/java/io/opentelemetry/exporter/internal/grpc/GrpcExporterBuilder.java

@@ -52,8 +52,8 @@ public class GrpcExporterBuilder<T extends Marshaler> {
   private long timeoutNanos;
   private URI endpoint;
   private boolean compressionEnabled = false;
-  private final Map<String, List<String>> constantHeaders = new HashMap<>();
-  private Supplier<Map<String, List<String>>> headerSupplier = Collections::emptyMap;
+  private final Map<String, String> constantHeaders = new HashMap<>();
+  private Supplier<Map<String, String>> headerSupplier = Collections::emptyMap;
   private TlsConfigHelper tlsConfigHelper = new TlsConfigHelper();
   @Nullable private RetryPolicy retryPolicy;
   private Supplier<MeterProvider> meterProviderSupplier = GlobalOpenTelemetry::getMeterProvider;
@@ -118,12 +118,11 @@ public GrpcExporterBuilder<T> setSslContext(
   }
 
   public GrpcExporterBuilder<T> addConstantHeader(String key, String value) {
-    constantHeaders.computeIfAbsent(key, unused -> new ArrayList<>()).add(value);
+    constantHeaders.put(key, value);
     return this;
   }
 
-  public GrpcExporterBuilder<T> setHeadersSupplier(
-      Supplier<Map<String, List<String>>> headerSupplier) {
+  public GrpcExporterBuilder<T> setHeadersSupplier(Supplier<Map<String, String>> headerSupplier) {
     this.headerSupplier = headerSupplier;
     return this;
   }
@@ -167,15 +166,16 @@ public GrpcExporter<T> build() {
     Supplier<Map<String, List<String>>> headerSupplier =
         () -> {
           Map<String, List<String>> result = new HashMap<>();
-          Map<String, List<String>> supplierResult = this.headerSupplier.get();
+          Map<String, String> supplierResult = this.headerSupplier.get();
           if (supplierResult != null) {
-            result.putAll(supplierResult);
+            supplierResult.forEach(
+                (key, value) -> result.put(key, Collections.singletonList(value)));
           }
           constantHeaders.forEach(
               (key, value) ->
                   result.merge(
                       key,
-                      value,
+                      Collections.singletonList(value),
                       (v1, v2) -> {
                         List<String> merged = new ArrayList<>(v1);
                         merged.addAll(v2);
@@ -215,7 +215,7 @@ public String toString(boolean includePrefixAndSuffix) {
     joiner.add("compressionEnabled=" + compressionEnabled);
     StringJoiner headersJoiner = new StringJoiner(", ", "Headers{", "}");
     constantHeaders.forEach((key, value) -> headersJoiner.add(key + "=OBFUSCATED"));
-    Map<String, List<String>> headers = headerSupplier.get();
+    Map<String, String> headers = headerSupplier.get();
     if (headers != null) {
       headers.forEach((key, value) -> headersJoiner.add(key + "=OBFUSCATED"));
     }

exporters/common/src/main/java/io/opentelemetry/exporter/internal/http/HttpExporterBuilder.java

@@ -50,8 +50,8 @@ public final class HttpExporterBuilder<T extends Marshaler> {
   private long timeoutNanos = TimeUnit.SECONDS.toNanos(DEFAULT_TIMEOUT_SECS);
   private boolean compressionEnabled = false;
   private boolean exportAsJson = false;
-  private final Map<String, List<String>> constantHeaders = new HashMap<>();
-  private Supplier<Map<String, List<String>>> headerSupplier = Collections::emptyMap;
+  private final Map<String, String> constantHeaders = new HashMap<>();
+  private Supplier<Map<String, String>> headerSupplier = Collections::emptyMap;
 
   private TlsConfigHelper tlsConfigHelper = new TlsConfigHelper();
   @Nullable private RetryPolicy retryPolicy;
@@ -86,12 +86,11 @@ public HttpExporterBuilder<T> setCompression(String compressionMethod) {
   }
 
   public HttpExporterBuilder<T> addConstantHeaders(String key, String value) {
-    constantHeaders.computeIfAbsent(key, unused -> new ArrayList<>()).add(value);
+    constantHeaders.put(key, value);
     return this;
   }
 
-  public HttpExporterBuilder<T> setHeadersSupplier(
-      Supplier<Map<String, List<String>>> headerSupplier) {
+  public HttpExporterBuilder<T> setHeadersSupplier(Supplier<Map<String, String>> headerSupplier) {
     this.headerSupplier = headerSupplier;
     return this;
   }
@@ -155,15 +154,16 @@ public HttpExporter<T> build() {
     Supplier<Map<String, List<String>>> headerSupplier =
         () -> {
           Map<String, List<String>> result = new HashMap<>();
-          Map<String, List<String>> supplierResult = this.headerSupplier.get();
+          Map<String, String> supplierResult = this.headerSupplier.get();
           if (supplierResult != null) {
-            result.putAll(supplierResult);
+            supplierResult.forEach(
+                (key, value) -> result.put(key, Collections.singletonList(value)));
           }
           constantHeaders.forEach(
               (key, value) ->
                   result.merge(
                       key,
-                      value,
+                      Collections.singletonList(value),
                       (v1, v2) -> {
                         List<String> merged = new ArrayList<>(v1);
                         merged.addAll(v2);
@@ -202,7 +202,7 @@ public String toString(boolean includePrefixAndSuffix) {
     joiner.add("exportAsJson=" + exportAsJson);
     StringJoiner headersJoiner = new StringJoiner(", ", "Headers{", "}");
     constantHeaders.forEach((key, value) -> headersJoiner.add(key + "=OBFUSCATED"));
-    Map<String, List<String>> headers = headerSupplier.get();
+    Map<String, String> headers = headerSupplier.get();
     if (headers != null) {
       headers.forEach((key, value) -> headersJoiner.add(key + "=OBFUSCATED"));
     }

exporters/otlp/all/src/main/java/io/opentelemetry/exporter/otlp/http/logs/OtlpHttpLogRecordExporterBuilder.java

@@ -15,7 +15,6 @@
 import io.opentelemetry.exporter.otlp.internal.OtlpUserAgent;
 import io.opentelemetry.sdk.common.export.RetryPolicy;
 import java.time.Duration;
-import java.util.List;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Supplier;
@@ -98,8 +97,7 @@ public OtlpHttpLogRecordExporterBuilder addHeader(String key, String value) {
    * Set the supplier of headers to add to requests. If a key from the map collides with a constant
    * from {@link #addHeader(String, String)}, the values from both are included.
    */
-  public OtlpHttpLogRecordExporterBuilder setHeaders(
-      Supplier<Map<String, List<String>>> headerSupplier) {
+  public OtlpHttpLogRecordExporterBuilder setHeaders(Supplier<Map<String, String>> headerSupplier) {
     delegate.setHeadersSupplier(headerSupplier);
     return this;
   }

exporters/otlp/all/src/main/java/io/opentelemetry/exporter/otlp/http/metrics/OtlpHttpMetricExporterBuilder.java

@@ -18,7 +18,6 @@
 import io.opentelemetry.sdk.metrics.export.DefaultAggregationSelector;
 import io.opentelemetry.sdk.metrics.export.MetricExporter;
 import java.time.Duration;
-import java.util.List;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Supplier;
@@ -110,8 +109,7 @@ public OtlpHttpMetricExporterBuilder addHeader(String key, String value) {
    * Set the supplier of headers to add to requests. If a key from the map collides with a constant
    * from {@link #addHeader(String, String)}, the values from both are included.
    */
-  public OtlpHttpMetricExporterBuilder setHeaders(
-      Supplier<Map<String, List<String>>> headerSupplier) {
+  public OtlpHttpMetricExporterBuilder setHeaders(Supplier<Map<String, String>> headerSupplier) {
     delegate.setHeadersSupplier(headerSupplier);
     return this;
   }

exporters/otlp/all/src/main/java/io/opentelemetry/exporter/otlp/http/trace/OtlpHttpSpanExporterBuilder.java

@@ -15,7 +15,6 @@
 import io.opentelemetry.exporter.otlp.internal.OtlpUserAgent;
 import io.opentelemetry.sdk.common.export.RetryPolicy;
 import java.time.Duration;
-import java.util.List;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Supplier;
@@ -98,8 +97,7 @@ public OtlpHttpSpanExporterBuilder addHeader(String key, String value) {
    * Set the supplier of headers to add to requests. If a key from the map collides with a constant
    * from {@link #addHeader(String, String)}, the values from both are included.
    */
-  public OtlpHttpSpanExporterBuilder setHeaders(
-      Supplier<Map<String, List<String>>> headerSupplier) {
+  public OtlpHttpSpanExporterBuilder setHeaders(Supplier<Map<String, String>> headerSupplier) {
     delegate.setHeadersSupplier(headerSupplier);
     return this;
   }

exporters/otlp/all/src/main/java/io/opentelemetry/exporter/otlp/logs/OtlpGrpcLogRecordExporterBuilder.java

@@ -17,7 +17,6 @@
 import io.opentelemetry.sdk.common.export.RetryPolicy;
 import java.net.URI;
 import java.time.Duration;
-import java.util.List;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Supplier;
@@ -172,8 +171,7 @@ public OtlpGrpcLogRecordExporterBuilder addHeader(String key, String value) {
    * from {@link #addHeader(String, String)}, the values from both are included. Applicable only if
    * {@link OtlpGrpcLogRecordExporterBuilder#setChannel(ManagedChannel)} is not used to set channel.
    */
-  public OtlpGrpcLogRecordExporterBuilder setHeaders(
-      Supplier<Map<String, List<String>>> headerSupplier) {
+  public OtlpGrpcLogRecordExporterBuilder setHeaders(Supplier<Map<String, String>> headerSupplier) {
     delegate.setHeadersSupplier(headerSupplier);
     return this;
   }

exporters/otlp/all/src/main/java/io/opentelemetry/exporter/otlp/metrics/OtlpGrpcMetricExporterBuilder.java

@@ -20,7 +20,6 @@
 import io.opentelemetry.sdk.metrics.export.MetricExporter;
 import java.net.URI;
 import java.time.Duration;
-import java.util.List;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Supplier;
@@ -185,8 +184,7 @@ public OtlpGrpcMetricExporterBuilder addHeader(String key, String value) {
    * from {@link #addHeader(String, String)}, the values from both are included. Applicable only if
    * {@link OtlpGrpcMetricExporterBuilder#setChannel(ManagedChannel)} is not used to set channel.
    */
-  public OtlpGrpcMetricExporterBuilder setHeaders(
-      Supplier<Map<String, List<String>>> headerSupplier) {
+  public OtlpGrpcMetricExporterBuilder setHeaders(Supplier<Map<String, String>> headerSupplier) {
     delegate.setHeadersSupplier(headerSupplier);
     return this;
   }

exporters/otlp/all/src/main/java/io/opentelemetry/exporter/otlp/trace/OtlpGrpcSpanExporterBuilder.java

@@ -17,7 +17,6 @@
 import io.opentelemetry.sdk.common.export.RetryPolicy;
 import java.net.URI;
 import java.time.Duration;
-import java.util.List;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Supplier;
@@ -169,8 +168,7 @@ public OtlpGrpcSpanExporterBuilder addHeader(String key, String value) {
    * from {@link #addHeader(String, String)}, the values from both are included. Applicable only if
    * {@link OtlpGrpcSpanExporterBuilder#setChannel(ManagedChannel)} is not used to set channel.
    */
-  public OtlpGrpcSpanExporterBuilder setHeaders(
-      Supplier<Map<String, List<String>>> headerSupplier) {
+  public OtlpGrpcSpanExporterBuilder setHeaders(Supplier<Map<String, String>> headerSupplier) {
     delegate.setHeadersSupplier(headerSupplier);
     return this;
   }

exporters/otlp/testing-internal/src/main/java/io/opentelemetry/exporter/otlp/testing/internal/AbstractGrpcTelemetryExporterTest.java

@@ -296,10 +296,7 @@ void withHeaders() {
         exporterBuilder()
             .setEndpoint(server.httpUri().toString())
             .addHeader("key1", "value1")
-            .setHeaders(
-                () ->
-                    Collections.singletonMap(
-                        "key2", Collections.singletonList("value" + count.incrementAndGet())))
+            .setHeaders(() -> Collections.singletonMap("key2", "value" + count.incrementAndGet()))
             .build();
     try {
       // Export twice to ensure header supplier gets invoked twice

exporters/otlp/testing-internal/src/main/java/io/opentelemetry/exporter/otlp/testing/internal/AbstractHttpTelemetryExporterTest.java

@@ -331,10 +331,7 @@ void withHeaders() {
         exporterBuilder()
             .setEndpoint(server.httpUri() + path)
             .addHeader("key1", "value1")
-            .setHeaders(
-                () ->
-                    Collections.singletonMap(
-                        "key2", Collections.singletonList("value" + count.incrementAndGet())))
+            .setHeaders(() -> Collections.singletonMap("key2", "value" + count.incrementAndGet()))
             .build();
     try {
       // Export twice to ensure header supplier gets invoked twice

exporters/otlp/testing-internal/src/main/java/io/opentelemetry/exporter/otlp/testing/internal/GrpcLogRecordExporterBuilderWrapper.java

@@ -11,7 +11,6 @@
 import io.opentelemetry.sdk.common.export.RetryPolicy;
 import io.opentelemetry.sdk.logs.data.LogRecordData;
 import java.time.Duration;
-import java.util.List;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Supplier;
@@ -57,7 +56,7 @@ public TelemetryExporterBuilder<LogRecordData> addHeader(String key, String valu
 
   @Override
   public TelemetryExporterBuilder<LogRecordData> setHeaders(
-      Supplier<Map<String, List<String>>> headerSupplier) {
+      Supplier<Map<String, String>> headerSupplier) {
     builder.setHeaders(headerSupplier);
     return this;
   }

exporters/otlp/testing-internal/src/main/java/io/opentelemetry/exporter/otlp/testing/internal/GrpcMetricExporterBuilderWrapper.java

@@ -11,7 +11,6 @@
 import io.opentelemetry.sdk.common.export.RetryPolicy;
 import io.opentelemetry.sdk.metrics.data.MetricData;
 import java.time.Duration;
-import java.util.List;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Supplier;
@@ -57,7 +56,7 @@ public TelemetryExporterBuilder<MetricData> addHeader(String key, String value)
 
   @Override
   public TelemetryExporterBuilder<MetricData> setHeaders(
-      Supplier<Map<String, List<String>>> headerSupplier) {
+      Supplier<Map<String, String>> headerSupplier) {
     builder.setHeaders(headerSupplier);
     return this;
   }

exporters/otlp/testing-internal/src/main/java/io/opentelemetry/exporter/otlp/testing/internal/GrpcSpanExporterBuilderWrapper.java

@@ -11,7 +11,6 @@
 import io.opentelemetry.sdk.common.export.RetryPolicy;
 import io.opentelemetry.sdk.trace.data.SpanData;
 import java.time.Duration;
-import java.util.List;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Supplier;
@@ -58,7 +57,7 @@ public TelemetryExporterBuilder<SpanData> addHeader(String key, String value) {
 
   @Override
   public TelemetryExporterBuilder<SpanData> setHeaders(
-      Supplier<Map<String, List<String>>> headerSupplier) {
+      Supplier<Map<String, String>> headerSupplier) {
     builder.setHeaders(headerSupplier);
     return this;
   }

exporters/otlp/testing-internal/src/main/java/io/opentelemetry/exporter/otlp/testing/internal/HttpLogRecordExporterBuilderWrapper.java

@@ -10,7 +10,6 @@
 import io.opentelemetry.sdk.common.export.RetryPolicy;
 import io.opentelemetry.sdk.logs.data.LogRecordData;
 import java.time.Duration;
-import java.util.List;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Supplier;
@@ -58,7 +57,7 @@ public TelemetryExporterBuilder<LogRecordData> addHeader(String key, String valu
 
   @Override
   public TelemetryExporterBuilder<LogRecordData> setHeaders(
-      Supplier<Map<String, List<String>>> headerSupplier) {
+      Supplier<Map<String, String>> headerSupplier) {
     builder.setHeaders(headerSupplier);
     return this;
   }

exporters/otlp/testing-internal/src/main/java/io/opentelemetry/exporter/otlp/testing/internal/HttpMetricExporterBuilderWrapper.java

@@ -10,7 +10,6 @@
 import io.opentelemetry.sdk.common.export.RetryPolicy;
 import io.opentelemetry.sdk.metrics.data.MetricData;
 import java.time.Duration;
-import java.util.List;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Supplier;
@@ -57,7 +56,7 @@ public TelemetryExporterBuilder<MetricData> addHeader(String key, String value)
 
   @Override
   public TelemetryExporterBuilder<MetricData> setHeaders(
-      Supplier<Map<String, List<String>>> headerSupplier) {
+      Supplier<Map<String, String>> headerSupplier) {
     builder.setHeaders(headerSupplier);
     return this;
   }

exporters/otlp/testing-internal/src/main/java/io/opentelemetry/exporter/otlp/testing/internal/HttpSpanExporterBuilderWrapper.java

@@ -10,7 +10,6 @@
 import io.opentelemetry.sdk.common.export.RetryPolicy;
 import io.opentelemetry.sdk.trace.data.SpanData;
 import java.time.Duration;
-import java.util.List;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Supplier;
@@ -57,7 +56,7 @@ public TelemetryExporterBuilder<SpanData> addHeader(String key, String value) {
 
   @Override
   public TelemetryExporterBuilder<SpanData> setHeaders(
-      Supplier<Map<String, List<String>>> headerSupplier) {
+      Supplier<Map<String, String>> headerSupplier) {
     builder.setHeaders(headerSupplier);
     return this;
   }

exporters/otlp/testing-internal/src/main/java/io/opentelemetry/exporter/otlp/testing/internal/ManagedChannelTelemetryExporterBuilder.java

@@ -21,7 +21,6 @@
 import java.net.URI;
 import java.time.Duration;
 import java.util.Collection;
-import java.util.List;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Supplier;
@@ -92,8 +91,7 @@ public TelemetryExporterBuilder<T> addHeader(String key, String value) {
   }
 
   @Override
-  public TelemetryExporterBuilder<T> setHeaders(
-      Supplier<Map<String, List<String>>> headerSupplier) {
+  public TelemetryExporterBuilder<T> setHeaders(Supplier<Map<String, String>> headerSupplier) {
     delegate.setHeaders(headerSupplier);
     return this;
   }