header values are be expected to be W3C baggage encoded (#6164)

Co-authored-by: jack-berg <34418638+jack-berg@users.noreply.github.com>
Co-authored-by: Jack Berg <jberg@newrelic.com>

exporters/otlp/all/src/main/java/io/opentelemetry/exporter/otlp/internal/OtlpConfigUtil.java

@@ -21,6 +21,8 @@
 import java.io.RandomAccessFile;
 import java.net.MalformedURLException;
 import java.net.URL;
+import java.net.URLDecoder;
+import java.nio.charset.StandardCharsets;
 import java.time.Duration;
 import java.util.Locale;
 import java.util.Map;
@@ -89,7 +91,17 @@ public static void configureOtlpExporterBuilder(
     if (headers.isEmpty()) {
       headers = config.getMap("otel.exporter.otlp.headers");
     }
-    headers.forEach(addHeader);
+    for (Map.Entry<String, String> entry : headers.entrySet()) {
+      String key = entry.getKey();
+      String value = entry.getValue();
+      try {
+        // headers are encoded as URL - see
+        // https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/protocol/exporter.md#specifying-headers-via-environment-variables
+        addHeader.accept(key, URLDecoder.decode(value, StandardCharsets.UTF_8.displayName()));
+      } catch (Exception e) {
+        throw new ConfigurationException("Cannot decode header value: " + value, e);
+      }
+    }
 
     String compression = config.getString("otel.exporter.otlp." + dataType + ".compression");
     if (compression == null) {

exporters/otlp/all/src/test/java/io/opentelemetry/exporter/otlp/internal/OtlpSpanExporterProviderTest.java

@@ -29,6 +29,7 @@
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
+import org.assertj.core.api.Assertions;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
@@ -219,7 +220,8 @@ void createExporter_HttpWithGeneralConfiguration() throws CertificateEncodingExc
     config.put("otel.exporter.otlp.certificate", certificatePath);
     config.put("otel.exporter.otlp.client.key", clientKeyPath);
     config.put("otel.exporter.otlp.client.certificate", clientCertificatePath);
-    config.put("otel.exporter.otlp.headers", "header-key=header-value");
+    config.put(
+        "otel.exporter.otlp.headers", "header-key1=header%20value1,header-key2=header value2");
     config.put("otel.exporter.otlp.compression", "gzip");
     config.put("otel.exporter.otlp.timeout", "15s");
     config.put("otel.experimental.exporter.otlp.retry.enabled", "true");
@@ -229,7 +231,8 @@ void createExporter_HttpWithGeneralConfiguration() throws CertificateEncodingExc
       assertThat(exporter).isInstanceOf(OtlpHttpSpanExporter.class);
       verify(httpBuilder, times(1)).build();
       verify(httpBuilder).setEndpoint("https://localhost:443/v1/traces");
-      verify(httpBuilder).addHeader("header-key", "header-value");
+      verify(httpBuilder).addHeader("header-key1", "header value1");
+      verify(httpBuilder).addHeader("header-key2", "header value2");
       verify(httpBuilder).setCompression("gzip");
       verify(httpBuilder).setTimeout(Duration.ofSeconds(15));
       verify(httpBuilder).setTrustedCertificates(serverTls.certificate().getEncoded());
@@ -274,4 +277,16 @@ void createExporter_HttpWithSignalConfiguration() throws CertificateEncodingExce
     }
     Mockito.verifyNoInteractions(grpcBuilder);
   }
+
+  @Test
+  void createExporter_decodingError() {
+    Assertions.assertThatThrownBy(
+            () -> {
+              provider.createExporter(
+                  DefaultConfigProperties.createFromMap(
+                      Collections.singletonMap("otel.exporter.otlp.headers", "header-key=%-1")));
+            })
+        .isInstanceOf(ConfigurationException.class)
+        .hasMessage("Cannot decode header value: %-1");
+  }
 }