execution_response: Allow failures to be reported while populating

As populating the containers from remote response only takes place
once, no assumptions should be made that this cannot fail (for
example if wrong or invalid entries were produced). Instead, return
error messages on failure to callers that can log accordingly.

2 files changed, 73 insertions, 29 deletions

diff --git a/src/buildtool/execution_api/remote/bazel/bazel_response.cpp b/src/buildtool/execution_api/remote/bazel/bazel_response.cpp
index c536f5dd..468a2531 100644
--- a/src/buildtool/execution_api/remote/bazel/bazel_response.cpp
+++ b/src/buildtool/execution_api/remote/bazel/bazel_response.cpp
@@ -17,7 +17,7 @@
 #include <cstddef>
 #include <functional>
 
-#include "gsl/gsl"
+#include "fmt/core.h"
 #include "src/buildtool/common/artifact_digest.hpp"
 #include "src/buildtool/common/artifact_digest_factory.hpp"
 #include "src/buildtool/common/bazel_digest_factory.hpp"
@@ -56,20 +56,28 @@ auto BazelResponse::ReadStringBlob(bazel_re::Digest const& id) noexcept
     return std::string{};
 }
 
-auto BazelResponse::Artifacts() noexcept -> ArtifactInfos const& {
-    Populate();
-    return artifacts_;
+auto BazelResponse::Artifacts() noexcept
+    -> expected<gsl::not_null<ArtifactInfos const*>, std::string> {
+    if (auto error_msg = Populate()) {
+        return unexpected{*std::move(error_msg)};
+    }
+    return gsl::not_null<ArtifactInfos const*>(
+        &artifacts_);  // explicit type needed for expected
 }
 
-auto BazelResponse::DirectorySymlinks() noexcept -> DirSymlinks const& {
-    Populate();
-    return dir_symlinks_;
+auto BazelResponse::DirectorySymlinks() noexcept
+    -> expected<gsl::not_null<DirSymlinks const*>, std::string> {
+    if (auto error_msg = Populate()) {
+        return unexpected{*std::move(error_msg)};
+    }
+    return gsl::not_null<DirSymlinks const*>(
+        &dir_symlinks_);  // explicit type needed for expected
 }
 
-void BazelResponse::Populate() noexcept {
+auto BazelResponse::Populate() noexcept -> std::optional<std::string> {
     // Initialized only once lazily
     if (populated_) {
-        return;
+        return std::nullopt;
     }
     populated_ = true;
 
@@ -92,7 +100,9 @@ void BazelResponse::Populate() noexcept {
         auto digest =
             ArtifactDigestFactory::FromBazel(hash_type, file.digest());
         if (not digest) {
-            return;
+            return fmt::format(
+                "BazelResponse: failed to create artifact digest for {}",
+                file.path());
         }
         try {
             artifacts.emplace(
@@ -101,8 +111,12 @@ void BazelResponse::Populate() noexcept {
                                      .type = file.is_executable()
                                                  ? ObjectType::Executable
                                                  : ObjectType::File});
-        } catch (...) {
-            return;
+        } catch (std::exception const& ex) {
+            return fmt::format(
+                "BazelResponse: unexpected failure gathering digest for "
+                "{}:\n{}",
+                file.path(),
+                ex.what());
         }
     }
 
@@ -116,8 +130,12 @@ void BazelResponse::Populate() noexcept {
                         ArtifactDigestFactory::HashDataAs<ObjectType::File>(
                             network_->GetHashFunction(), link.target()),
                     .type = ObjectType::Symlink});
-        } catch (...) {
-            return;
+        } catch (std::exception const& ex) {
+            return fmt::format(
+                "BazelResponse: unexpected failure gathering digest for "
+                "{}:\n{}",
+                link.path(),
+                ex.what());
         }
     }
     for (auto const& link : action_result.output_directory_symlinks()) {
@@ -130,8 +148,12 @@ void BazelResponse::Populate() noexcept {
                             network_->GetHashFunction(), link.target()),
                     .type = ObjectType::Symlink});
             dir_symlinks.emplace(link.path());  // add it to set
-        } catch (...) {
-            return;
+        } catch (std::exception const& ex) {
+            return fmt::format(
+                "BazelResponse: unexpected failure gathering digest for "
+                "{}:\n{}",
+                link.path(),
+                ex.what());
         }
     }
 
@@ -141,7 +163,9 @@ void BazelResponse::Populate() noexcept {
             auto digest =
                 ArtifactDigestFactory::FromBazel(hash_type, tree.tree_digest());
             if (not digest) {
-                return;
+                return fmt::format(
+                    "BazelResponse: failed to create artifact digest for {}",
+                    tree.path());
             }
             ExpectsAudit(digest->IsTree());
             try {
@@ -149,13 +173,17 @@ void BazelResponse::Populate() noexcept {
                     tree.path(),
                     Artifact::ObjectInfo{.digest = *std::move(digest),
                                          .type = ObjectType::Tree});
-            } catch (...) {
-                return;
+            } catch (std::exception const& ex) {
+                return fmt::format(
+                    "BazelResponse: unexpected failure gathering digest for "
+                    "{}:\n{}",
+                    tree.path(),
+                    ex.what());
             }
         }
         artifacts_ = std::move(artifacts);
         dir_symlinks_ = std::move(dir_symlinks);
-        return;
+        return std::nullopt;
     }
 
     // obtain tree digests for output directories
@@ -176,7 +204,9 @@ void BazelResponse::Populate() noexcept {
                 auto tree = BazelMsgFactory::MessageFromString<bazel_re::Tree>(
                     *tree_blob.data);
                 if (not tree) {
-                    return;
+                    return fmt::format(
+                        "BazelResponse: failed to create Tree for {}",
+                        tree_blob.digest.hash());
                 }
 
                 // The server does not store the Directory messages it just
@@ -185,22 +215,30 @@ void BazelResponse::Populate() noexcept {
                 // have to upload them manually.
                 auto root_digest = UploadTreeMessageDirectories(*tree);
                 if (not root_digest) {
-                    Logger::Log(LogLevel::Error,
-                                "uploading Tree's Directory messages failed");
-                    return;
+                    auto const error = fmt::format(
+                        "BazelResponse: failure in uploading Tree Directory "
+                        "message for {}",
+                        tree_blob.digest.hash());
+                    Logger::Log(LogLevel::Trace, error);
+                    return error;
                 }
                 artifacts.emplace(
                     action_result.output_directories(pos).path(),
                     Artifact::ObjectInfo{.digest = *root_digest,
                                          .type = ObjectType::Tree});
-            } catch (...) {
-                return;
+            } catch (std::exception const& ex) {
+                return fmt::format(
+                    "BazelResponse: unexpected failure gathering digest for "
+                    "{}:\n{}",
+                    tree_blob.digest.hash(),
+                    ex.what());
             }
             ++pos;
         }
     }
     artifacts_ = std::move(artifacts);
     dir_symlinks_ = std::move(dir_symlinks);
+    return std::nullopt;
 }
 
 auto BazelResponse::UploadTreeMessageDirectories(
diff --git a/src/buildtool/execution_api/remote/bazel/bazel_response.hpp b/src/buildtool/execution_api/remote/bazel/bazel_response.hpp
index 6e37d344..ec3e9748 100644
--- a/src/buildtool/execution_api/remote/bazel/bazel_response.hpp
+++ b/src/buildtool/execution_api/remote/bazel/bazel_response.hpp
@@ -20,9 +20,11 @@
 #include <utility>  // std::move
 #include <vector>
 
+#include "gsl/gsl"
 #include "src/buildtool/execution_api/common/execution_api.hpp"
 #include "src/buildtool/execution_api/remote/bazel/bazel_execution_client.hpp"
 #include "src/buildtool/execution_api/remote/bazel/bazel_network.hpp"
+#include "src/utils/cpp/expected.hpp"
 
 class BazelAction;
 
@@ -58,8 +60,10 @@ class BazelResponse final : public IExecutionResponse {
         return action_id_;
     }
 
-    auto Artifacts() noexcept -> ArtifactInfos const& final;
-    auto DirectorySymlinks() noexcept -> DirSymlinks const& final;
+    auto Artifacts() noexcept
+        -> expected<gsl::not_null<ArtifactInfos const*>, std::string> final;
+    auto DirectorySymlinks() noexcept
+        -> expected<gsl::not_null<DirSymlinks const*>, std::string> final;
 
   private:
     std::string action_id_{};
@@ -84,7 +88,9 @@ class BazelResponse final : public IExecutionResponse {
         return id.size_bytes() != 0;
     }
 
-    void Populate() noexcept;
+    /// \brief Populates the stored data, once.
+    /// \returns Error message on failure, nullopt on success.
+    [[nodiscard]] auto Populate() noexcept -> std::optional<std::string>;
 
     [[nodiscard]] auto UploadTreeMessageDirectories(
         bazel_re::Tree const& tree) const -> std::optional<ArtifactDigest>;