ArtifactBlob: Allow different content sources

3 files changed, 35 insertions, 6 deletions

diff --git a/src/buildtool/common/TARGETS b/src/buildtool/common/TARGETS
index 33e88829..40539325 100644
--- a/src/buildtool/common/TARGETS
+++ b/src/buildtool/common/TARGETS
@@ -95,6 +95,7 @@
     [ "artifact_digest_factory"
     , ["@", "fmt", "", "fmt"]
     , ["src/utils/cpp", "hash_combine"]
+    , ["src/utils/cpp", "in_place_visitor"]
     ]
   , "stage": ["src", "buildtool", "common"]
   }
diff --git a/src/buildtool/common/artifact_blob.cpp b/src/buildtool/common/artifact_blob.cpp
index c25e1db1..78a9d54e 100644
--- a/src/buildtool/common/artifact_blob.cpp
+++ b/src/buildtool/common/artifact_blob.cpp
@@ -19,6 +19,7 @@
 #include "fmt/core.h"
 #include "src/buildtool/common/artifact_digest_factory.hpp"
 #include "src/utils/cpp/hash_combine.hpp"
+#include "src/utils/cpp/in_place_visitor.hpp"
 
 auto ArtifactBlob::FromMemory(HashFunction hash_function,
                               ObjectType type,
@@ -45,16 +46,39 @@ auto ArtifactBlob::FromMemory(HashFunction hash_function,
 
 auto ArtifactBlob::ReadContent() const noexcept
     -> std::shared_ptr<std::string const> {
-    return content_;
+    using Result = std::shared_ptr<std::string const>;
+    static constexpr InPlaceVisitor kVisitor{
+        [](InMemory const& value) -> Result { return value; },
+    };
+    try {
+        return std::visit(kVisitor, content_);
+    } catch (...) {
+        return nullptr;
+    }
 }
 
 auto ArtifactBlob::ReadIncrementally(std::size_t chunk_size) const& noexcept
     -> expected<IncrementalReader, std::string> {
-    if (content_ == nullptr) {
+    using Result = expected<IncrementalReader, std::string>;
+    const InPlaceVisitor visitor{
+        [chunk_size](InMemory const& value) -> Result {
+            if (value == nullptr) {
+                return unexpected<std::string>{
+                    "ArtifactBlob::ReadIncrementally: missing memory source"};
+            }
+            return IncrementalReader::FromMemory(chunk_size, value.get());
+        },
+    };
+    try {
+        return std::visit(visitor, content_);
+    } catch (std::exception const& e) {
+        return unexpected{fmt::format(
+            "ArtifactBlob::ReadIncrementally: Got an exception:\n{}",
+            e.what())};
+    } catch (...) {
         return unexpected<std::string>{
-            "ArtifactBlob::ReadIncrementally: missing memory source"};
+            "ArtifactBlob::ReadIncrementally: Got an unknown exception"};
     }
-    return IncrementalReader::FromMemory(chunk_size, content_.get());
 }
 
 namespace std {
diff --git a/src/buildtool/common/artifact_blob.hpp b/src/buildtool/common/artifact_blob.hpp
index 800b78c1..c5a03cf9 100644
--- a/src/buildtool/common/artifact_blob.hpp
+++ b/src/buildtool/common/artifact_blob.hpp
@@ -20,6 +20,7 @@
 #include <memory>
 #include <string>
 #include <utility>
+#include <variant>
 
 #include "src/buildtool/common/artifact_digest.hpp"
 #include "src/buildtool/crypto/hash_function.hpp"
@@ -79,12 +80,15 @@ class ArtifactBlob final {
     }
 
   private:
+    using InMemory = std::shared_ptr<std::string const>;
+    using ContentSource = std::variant<InMemory>;
+
     ArtifactDigest digest_;
-    std::shared_ptr<std::string const> content_;
+    ContentSource content_;
     bool is_executable_;
 
     explicit ArtifactBlob(ArtifactDigest digest,
-                          std::shared_ptr<std::string const> content,
+                          ContentSource content,
                           bool is_executable) noexcept
         : digest_{std::move(digest)},
           content_{std::move(content)},