chore: extract channel building logic rough sketch DONT MERGE

gax-java/gax-grpc/src/main/java/com/google/api/gax/grpc/GrpcCapabilities.java

@@ -0,0 +1,89 @@
+package com.google.api.gax.grpc;
+
+import com.google.api.core.InternalApi;
+import com.google.api.gax.rpc.internal.EnvironmentProvider;
+import com.google.auth.Credentials;
+import com.google.auth.oauth2.ComputeEngineCredentials;
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.io.Files;
+import java.io.File;
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+
+@InternalApi
+class GrpcCapabilities {
+  private final EnvironmentProvider envProvider;
+  private String systemProductName;
+
+  static final String DIRECT_PATH_ENV_DISABLE_DIRECT_PATH = "GOOGLE_CLOUD_DISABLE_DIRECT_PATH";
+  static final String DIRECT_PATH_ENV_ENABLE_XDS = "GOOGLE_CLOUD_ENABLE_DIRECT_PATH_XDS";
+  static final String GCE_PRODUCTION_NAME_PRIOR_2016 = "Google";
+  static final String GCE_PRODUCTION_NAME_AFTER_2016 = "Google Compute Engine";
+
+  GrpcCapabilities(EnvironmentProvider envProvider) {
+    this.envProvider = envProvider;
+  }
+
+  @VisibleForTesting
+  void setSystemProductName(String systemProductName) {
+    this.systemProductName = systemProductName;
+  }
+
+  public boolean isOnComputeEngine() {
+    String osName = System.getProperty("os.name");
+    if ("Linux".equals(osName)) {
+      String productName = getSystemProductName();
+      return productName.contains(GCE_PRODUCTION_NAME_PRIOR_2016)
+          || productName.contains(GCE_PRODUCTION_NAME_AFTER_2016);
+    }
+    return false;
+  }
+
+  private String getSystemProductName() {
+    if (systemProductName != null) {
+      return systemProductName;
+    }
+    try {
+      return Files.asCharSource(new File("/sys/class/dmi/id/product_name"), StandardCharsets.UTF_8)
+          .readFirstLine();
+    } catch (IOException e) {
+      return "";
+    }
+  }
+
+  public boolean canUseDirectPath(GrpcChannelConfig config) {
+    return isDirectPathEnabled(config)
+        && isCredentialDirectPathCompatible(config)
+        && isOnComputeEngine()
+        && canUseDirectPathWithUniverseDomain(config.endpoint());
+  }
+
+  private boolean isDirectPathEnabled(GrpcChannelConfig config) {
+    String disableDirectPathEnv = envProvider.getenv(DIRECT_PATH_ENV_DISABLE_DIRECT_PATH);
+    if (Boolean.parseBoolean(disableDirectPathEnv)) {
+      return false;
+    }
+    return Boolean.TRUE.equals(config.attemptDirectPath());
+  }
+
+  public boolean isDirectPathXdsEnabled(GrpcChannelConfig config) {
+    String directPathXdsEnv = envProvider.getenv(DIRECT_PATH_ENV_ENABLE_XDS);
+    return Boolean.parseBoolean(directPathXdsEnv)
+        || Boolean.TRUE.equals(config.attemptDirectPathXds());
+  }
+
+  private boolean isCredentialDirectPathCompatible(GrpcChannelConfig config) {
+    Credentials credentials = config.credentials();
+    if (credentials == null) {
+      return false;
+    }
+    if (Boolean.TRUE.equals(config.allowNonDefaultServiceAccount())) {
+      return true;
+    }
+    return credentials instanceof ComputeEngineCredentials;
+  }
+
+  private boolean canUseDirectPathWithUniverseDomain(String endpoint) {
+    return endpoint.contains(Credentials.GOOGLE_DEFAULT_UNIVERSE);
+  }
+}

gax-java/gax-grpc/src/main/java/com/google/api/gax/grpc/GrpcChannelConfig.java

@@ -0,0 +1,67 @@
+package com.google.api.gax.grpc;
+
+import com.google.api.core.InternalApi;
+import com.google.auth.Credentials;
+import com.google.auto.value.AutoValue;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
+import java.util.List;
+import javax.annotation.Nullable;
+
+@InternalApi
+@AutoValue
+abstract class GrpcChannelConfig {
+
+  abstract String endpoint();
+
+  @Nullable
+  abstract String mtlsEndpoint();
+
+  @Nullable
+  abstract Credentials credentials();
+
+  abstract boolean useS2A();
+
+  @Nullable
+  abstract Boolean attemptDirectPath();
+
+  @Nullable
+  abstract Boolean attemptDirectPathXds();
+
+  @Nullable
+  abstract Boolean allowNonDefaultServiceAccount();
+
+  @Nullable
+  abstract ImmutableMap<String, ?> directPathServiceConfig();
+
+  abstract ImmutableList<InstantiatingGrpcChannelProvider.HardBoundTokenTypes>
+      allowedHardBoundTokenTypes();
+
+  static Builder builder() {
+    return new AutoValue_GrpcChannelConfig.Builder();
+  }
+
+  @AutoValue.Builder
+  abstract static class Builder {
+    abstract Builder setEndpoint(String endpoint);
+
+    abstract Builder setMtlsEndpoint(String mtlsEndpoint);
+
+    abstract Builder setCredentials(Credentials credentials);
+
+    abstract Builder setUseS2A(boolean useS2A);
+
+    abstract Builder setAttemptDirectPath(Boolean attemptDirectPath);
+
+    abstract Builder setAttemptDirectPathXds(Boolean attemptDirectPathXds);
+
+    abstract Builder setAllowNonDefaultServiceAccount(Boolean allowNonDefaultServiceAccount);
+
+    abstract Builder setDirectPathServiceConfig(ImmutableMap<String, ?> directPathServiceConfig);
+
+    abstract Builder setAllowedHardBoundTokenTypes(
+        List<InstantiatingGrpcChannelProvider.HardBoundTokenTypes> types);
+
+    abstract GrpcChannelConfig build();
+  }
+}