3 files changed, 72 insertions, 4 deletions
diff --git a/app/models/ci/build_trace_chunks/database.rb b/app/models/ci/build_trace_chunks/database.rb
index 73cb8abf381..3b8e23510d9 100644
--- a/app/models/ci/build_trace_chunks/database.rb
+++ b/app/models/ci/build_trace_chunks/database.rb
@@ -19,8 +19,22 @@ module Ci
         model.raw_data
       end
 
-      def set_data(model, data)
-        model.raw_data = data
+      def set_data(model, new_data)
+        model.raw_data = new_data
+      end
+
+      def append_data(model, new_data, offset)
+        if offset > 0
+          truncated_data = data(model).to_s.byteslice(0, offset)
+          new_data = truncated_data + new_data
+        end
+
+        model.raw_data = new_data
+        model.raw_data.to_s.bytesize
+      end
+
+      def size(model)
+        data(model).to_s.bytesize
       end
 
       def delete_data(model)
diff --git a/app/models/ci/build_trace_chunks/fog.rb b/app/models/ci/build_trace_chunks/fog.rb
index a849bd08427..b1e9fd1faeb 100644
--- a/app/models/ci/build_trace_chunks/fog.rb
+++ b/app/models/ci/build_trace_chunks/fog.rb
@@ -9,10 +9,26 @@ module Ci
 
       def data(model)
         connection.get_object(bucket_name, key(model))[:body]
+      rescue Excon::Error::NotFound
+        # If the object does not exist in the object storage, this method returns nil.
       end
 
-      def set_data(model, data)
-        connection.put_object(bucket_name, key(model), data)
+      def set_data(model, new_data)
+        connection.put_object(bucket_name, key(model), new_data)
+      end
+
+      def append_data(model, new_data, offset)
+        if offset > 0
+          truncated_data = data(model).to_s.byteslice(0, offset)
+          new_data = truncated_data + new_data
+        end
+
+        set_data(model, new_data)
+        new_data.bytesize
+      end
+
+      def size(model)
+        data(model).to_s.bytesize
       end
 
       def delete_data(model)
diff --git a/app/models/ci/build_trace_chunks/redis.rb b/app/models/ci/build_trace_chunks/redis.rb
index c3864f78b01..0ae563f6ce8 100644
--- a/app/models/ci/build_trace_chunks/redis.rb
+++ b/app/models/ci/build_trace_chunks/redis.rb
@@ -4,6 +4,32 @@ module Ci
   module BuildTraceChunks
     class Redis
       CHUNK_REDIS_TTL = 1.week
+      LUA_APPEND_CHUNK = <<~EOS.freeze
+        local key, new_data, offset = KEYS[1], ARGV[1], ARGV[2]
+        local length = new_data:len()
+        local expire = #{CHUNK_REDIS_TTL.seconds}
+        local current_size = redis.call("strlen", key)
+        offset = tonumber(offset)
+
+        if offset == 0 then
+          -- overwrite everything
+          redis.call("set", key, new_data, "ex", expire)
+          return redis.call("strlen", key)
+        elseif offset > current_size then
+          -- offset range violation
+          return -1
+        elseif offset + length >= current_size then
+          -- efficiently append or overwrite and append
+          redis.call("expire", key, expire)
+          return redis.call("setrange", key, offset, new_data)
+        else
+          -- append and truncate
+          local current_data = redis.call("get", key)
+          new_data = current_data:sub(1, offset) .. new_data
+          redis.call("set", key, new_data, "ex", expire)
+          return redis.call("strlen", key)
+        end
+      EOS
 
       def available?
         true
@@ -21,6 +47,18 @@ module Ci
         end
       end
 
+      def append_data(model, new_data, offset)
+        Gitlab::Redis::SharedState.with do |redis|
+          redis.eval(LUA_APPEND_CHUNK, keys: [key(model)], argv: [new_data, offset])
+        end
+      end
+
+      def size(model)
+        Gitlab::Redis::SharedState.with do |redis|
+          redis.strlen(key(model))
+        end
+      end
+
       def delete_data(model)
         delete_keys([[model.build_id, model.chunk_index]])
       end