Various bug fixes (#778)

zencore fixes:
- filesystem.cpp: ReadFile error reporting logic
- compactbinaryvalue.h: CbValue::As*String error reporting logic

zenhttp fixes:
- httpasio BindAcceptor would `return 0;` in a function returning `std::string` (UB)
- httpsys async workpool initialization race

zenstore fixes:
- cas.cpp: GetFileCasResults Results param passed by value instead of reference (large chunk results were silently lost)
- structuredcachestore.cpp: MissCount unconditionally incremented (counted hits as misses)
- cacherpc.cpp: Wrong boolean in Incomplete response array (all entries marked incomplete)
- cachedisklayer.cpp: sizeof(sizeof(...)) in two validation checks computed sizeof(size_t) instead of struct size
- buildstore.cpp: Wrong hash tracked in GC key list (BlobHash pushed twice instead of MetadataHash)
- buildstore.cpp: Removed duplicate m_LastAccessTimeUpdateCount increment in PutBlob

zenserver fixes:
- httpbuildstore.cpp: Reversed subtraction in HTTP range calculation (unsigned underflow)
- hubservice.cpp: Deadlock in Provision() calling Wake() while holding m_Lock (extracted WakeLocked helper)
- zipfs.cpp: Data race in GetFile() lazy initialization (added RwLock with shared/exclusive paths)

4 files changed, 30 insertions, 14 deletions

diff --git a/src/zenserver/frontend/frontend.cpp b/src/zenserver/frontend/frontend.cpp
index 2b157581f..1cf451e91 100644
--- a/src/zenserver/frontend/frontend.cpp
+++ b/src/zenserver/frontend/frontend.cpp
@@ -38,7 +38,7 @@ HttpFrontendService::HttpFrontendService(std::filesystem::path Directory, HttpSt
 #if ZEN_EMBED_HTML_ZIP
 	// Load an embedded Zip archive
 	IoBuffer HtmlZipDataBuffer(IoBuffer::Wrap, gHtmlZipData, sizeof(gHtmlZipData) - 1);
-	m_ZipFs = ZipFs(std::move(HtmlZipDataBuffer));
+	m_ZipFs = std::make_unique<ZipFs>(std::move(HtmlZipDataBuffer));
 #endif
 
 	if (m_Directory.empty() && !m_ZipFs)
@@ -157,9 +157,12 @@ HttpFrontendService::HandleRequest(zen::HttpServerRequest& Request)
 		}
 	}
 
-	if (IoBuffer FileBuffer = m_ZipFs.GetFile(Uri))
+	if (m_ZipFs)
 	{
-		return Request.WriteResponse(HttpResponseCode::OK, ContentType, FileBuffer);
+		if (IoBuffer FileBuffer = m_ZipFs->GetFile(Uri))
+		{
+			return Request.WriteResponse(HttpResponseCode::OK, ContentType, FileBuffer);
+		}
 	}
 
 	Request.WriteResponse(HttpResponseCode::NotFound, HttpContentType::kText, "Not found"sv);
diff --git a/src/zenserver/frontend/frontend.h b/src/zenserver/frontend/frontend.h
index 84ffaac42..6d8585b72 100644
--- a/src/zenserver/frontend/frontend.h
+++ b/src/zenserver/frontend/frontend.h
@@ -7,6 +7,7 @@
 #include "zipfs.h"
 
 #include <filesystem>
+#include <memory>
 
 namespace zen {
 
@@ -20,9 +21,9 @@ public:
 	virtual void		HandleStatusRequest(HttpServerRequest& Request) override;
 
 private:
-	ZipFs				  m_ZipFs;
-	std::filesystem::path m_Directory;
-	HttpStatusService&	  m_StatusService;
+	std::unique_ptr<ZipFs> m_ZipFs;
+	std::filesystem::path  m_Directory;
+	HttpStatusService&	   m_StatusService;
 };
 
 }  // namespace zen
diff --git a/src/zenserver/frontend/zipfs.cpp b/src/zenserver/frontend/zipfs.cpp
index f9c2bc8ff..42df0520f 100644
--- a/src/zenserver/frontend/zipfs.cpp
+++ b/src/zenserver/frontend/zipfs.cpp
@@ -149,13 +149,25 @@ ZipFs::ZipFs(IoBuffer&& Buffer)
 IoBuffer
 ZipFs::GetFile(const std::string_view& FileName) const
 {
-	FileMap::iterator Iter = m_Files.find(FileName);
-	if (Iter == m_Files.end())
 	{
-		return {};
+		RwLock::SharedLockScope _(m_FilesLock);
+
+		FileMap::const_iterator Iter = m_Files.find(FileName);
+		if (Iter == m_Files.end())
+		{
+			return {};
+		}
+
+		const FileItem& Item = Iter->second;
+		if (Item.GetSize() > 0)
+		{
+			return IoBuffer(IoBuffer::Wrap, Item.GetData(), Item.GetSize());
+		}
 	}
 
-	FileItem& Item = Iter->second;
+	RwLock::ExclusiveLockScope _(m_FilesLock);
+
+	FileItem& Item = m_Files.find(FileName)->second;
 	if (Item.GetSize() > 0)
 	{
 		return IoBuffer(IoBuffer::Wrap, Item.GetData(), Item.GetSize());
diff --git a/src/zenserver/frontend/zipfs.h b/src/zenserver/frontend/zipfs.h
index 1fa7da451..645121693 100644
--- a/src/zenserver/frontend/zipfs.h
+++ b/src/zenserver/frontend/zipfs.h
@@ -3,23 +3,23 @@
 #pragma once
 
 #include <zencore/iobuffer.h>
+#include <zencore/thread.h>
 
 #include <unordered_map>
 
 namespace zen {
 
-//////////////////////////////////////////////////////////////////////////
 class ZipFs
 {
 public:
-	ZipFs() = default;
-	ZipFs(IoBuffer&& Buffer);
+	explicit ZipFs(IoBuffer&& Buffer);
+
 	IoBuffer GetFile(const std::string_view& FileName) const;
-	inline	 operator bool() const { return !m_Files.empty(); }
 
 private:
 	using FileItem = MemoryView;
 	using FileMap  = std::unordered_map<std::string_view, FileItem>;
+	mutable RwLock m_FilesLock;
 	FileMap mutable m_Files;
 	IoBuffer m_Buffer;
 };