1 files changed, 100 insertions, 0 deletions
diff --git a/src/common/platform/web/WebFileStream.cpp b/src/common/platform/web/WebFileStream.cpp
index dd44acdf..036be9a6 100644
--- a/src/common/platform/web/WebFileStream.cpp
+++ b/src/common/platform/web/WebFileStream.cpp
@@ -1,11 +1,111 @@
 #include "cru/common/platform/web/WebFileStream.h"
 #include "cru/common/io/OpenFileFlag.h"
+#include "cru/common/platform/web/WebException.h"
 
 #include <cstdio>
+#include <stdexcept>
 
 namespace cru::platform::web {
 WebFileStream::WebFileStream(String path, io::OpenFileFlag flags)
     : path_(std::move(path)), flags_(flags) {
+  // 1. Check all invalid flag combinations.
+
+  using io::OpenFileFlags;
+
+  if (!(flags & OpenFileFlags::Read) && !(flags & OpenFileFlags::Write)) {
+    throw std::invalid_argument(
+        "At least one of Read and Write flag must be specified when opening a "
+        "file.");
+  }
+
+  if (!(flags & OpenFileFlags::Write) &&
+      (flags & OpenFileFlags::Truncate || flags & OpenFileFlags::Append)) {
+    throw std::invalid_argument(
+        "Truncate and Append flag can only be used when opening a file with "
+        "Write flag.");
+  }
+
+  if (flags & OpenFileFlags::Truncate && flags & OpenFileFlags::Append) {
+    throw std::invalid_argument(
+        "Truncate and Append flag can not be used together.");
+  }
+
+  if (!(flags & OpenFileFlags::Create) && flags & OpenFileFlags::Exclusive) {
+    // Although linux doc says that this is an undefined behavior, but let's
+    // make it an error so you won't get some unexpected flags without noticing.
+    throw std::invalid_argument("Exclusive flag must be set with Create flag.");
+  }
+
+  // 2. Handle with OpenFileFlags::Create and OpenFileFlags::Exclusive.
+  const auto utf8_path = path.ToUtf8();
+
+  if (!(flags & OpenFileFlags::Create)) {
+    auto file = std::fopen(utf8_path.c_str(), "r");
+    if (file == NULL) {
+      // Note: Is there any other possible reason why fopen fails?
+      throw WebException(u"File does not exist.");
+    } else {
+      if (!(flags & OpenFileFlags::Write)) {
+        // We are not going to write the file, so we can just use this handle.
+        file_ = file;
+        return;
+      } else {
+        // We are going to write the file, so we have to close this handle and
+        // create a new one.
+        std::fclose(file);
+      }
+    }
+  } else {
+    if (flags & OpenFileFlags::Exclusive) {
+      auto file = std::fopen(utf8_path.c_str(), "r");
+      if (file != NULL) {
+        std::fclose(file);
+        throw WebException(u"File already exists.");
+      }
+    }
+  }
+
+  // 3. Now everything is ok, we can open the file with correct flags.
+  // There is only one edge case for C fopen: if you open a file read-only and
+  // specify Create flag, fopen won't create the file for you.
+
+  if (flags & OpenFileFlags::Write) {
+    if (flags & OpenFileFlags::Read) {
+      if (flags & OpenFileFlags::Append) {
+        file_ = std::fopen(utf8_path.c_str(), "a+");
+      } else {
+        file_ = std::fopen(utf8_path.c_str(), "w+");
+      }
+    } else {
+      if (flags & OpenFileFlags::Append) {
+        file_ = std::fopen(utf8_path.c_str(), "a");
+      } else {
+        file_ = std::fopen(utf8_path.c_str(), "w");
+      }
+    }
+  } else {
+    // Open file read-only.
+    auto file = std::fopen(utf8_path.c_str(), "r");
+    if (file == NULL) {
+      file = std::fopen(utf8_path.c_str(), "w");
+      if (file == NULL) {
+        throw WebException(u"Failed to create file.");
+      }
+      std::fclose(file);
+      // Open it again.
+      file = std::fopen(utf8_path.c_str(), "r");
+    }
+    file_ = file;
+  }
+
+  if (file_ == NULL) {
+    throw WebException(u"Failed to open file.");
+  }
 }
 
+WebFileStream::~WebFileStream() {
+  if (file_ != NULL) {
+    std::fclose(file_);
+  }
+}
 }  // namespace cru::platform::web