Catch internal TooSmallFile exception in BuildFileCompound.

And try with multi parts compound only if file is not found or file
is too small.

We can now fix the tests as we have a clear (new) message thrown.

src/fileimpl.cpp

@@ -164,15 +164,35 @@ class TooSmallFile: public std::exception {};
   //////////////////////////////////////////////////////////////////////
   // FileImpl
   //
-  std::shared_ptr<FileImpl> FileImpl::BuildFileImpl(const std::string& filename) {
+  std::shared_ptr<FileImpl> FileImpl::BuildFileImpl(std::string fname) {
+    bool found = false;
+    std::shared_ptr<FileCompound> fileCompound;
     try {
-      return std::shared_ptr<FileImpl>(
-        new FileImpl(std::make_shared<FileCompound>(filename))
-      );
-    } catch (...) {
-      return std::shared_ptr<FileImpl>(
-        new FileImpl(std::make_shared<FileCompound>(filename, FileCompound::MultiPartToken::Multi))
-      );
+      fileCompound = std::make_shared<FileCompound>(fname);
+      found = true;
+    } catch(...) { }
+    if (found) {
+      try {
+        return std::shared_ptr<FileImpl>(new FileImpl(fileCompound));
+      } catch(TooSmallFile& e) {
+        if (fname.size() > 6 && fname.substr(fname.size()-6) == ".zimaa") {
+          // We have tried to open a split file. Let's continue with "aa" postfix removed.
+          fname.resize(fname.size()-2);
+        } else {
+          // We have found a (not split) file but it is too small.
+          throw ZimFileFormatError("Zim file(s) is too small.");
+        }
+      }
+    }
+
+    // Either we haven't succeed to open fname (.zim) or the file (.zimaa) is too small.
+    // Let's try to open as split files.
+    fileCompound = std::make_shared<FileCompound>(fname, FileCompound::MultiPartToken::Multi);
+    try {
+      return std::shared_ptr<FileImpl>(new FileImpl(fileCompound));
+    } catch (TooSmallFile& e) {
+      // TooSmallFile is internal error.
+      throw ZimFileFormatError("Zim file(s) is too small.");
     }
   }
 

src/fileimpl.h

@@ -97,7 +97,7 @@ namespace zim
       using FindxResult = std::pair<bool, entry_index_t>;
       using FindxTitleResult = std::pair<bool, title_index_t>;
 
-      static std::shared_ptr<FileImpl> BuildFileImpl(const std::string& fname);
+      static std::shared_ptr<FileImpl> BuildFileImpl(std::string fname);
 #ifndef _WIN32
       explicit FileImpl(int fd);
       explicit FileImpl(FdInput fd);

test/archive.cpp

@@ -264,6 +264,31 @@ TEST(ZimArchive, openRealZimArchive)
   }
 }
 
+TEST(ZimArchive, openSplitZimArchive)
+{
+  const char* fname = "wikibooks_be_all_nopic_2017-02_splitted.zim";
+
+  for (auto& testfile: getDataFilePath(fname)) {
+    const TestContext ctx{ {"path", testfile.path+"aa" } };
+    std::unique_ptr<zim::Archive> archive;
+    EXPECT_NO_THROW( archive.reset(new zim::Archive(testfile.path+"aa")) ) << ctx;
+    if ( archive ) {
+      EXPECT_TRUE( archive->check() ) << ctx;
+    }
+  }
+}
+
+TEST(ZimArchive, openDontFallbackOnNonSplitZimArchive)
+{
+  const char* fname = "wikibooks_be_all_nopic_2017-02.zim";
+
+  for (auto& testfile: getDataFilePath(fname)) {
+    const TestContext ctx{ {"path", testfile.path+"aa" } };
+    std::unique_ptr<zim::Archive> archive;
+    EXPECT_THROW( archive.reset(new zim::Archive(testfile.path+"aa")), std::runtime_error) << ctx;
+  }
+}
+
 TEST(ZimArchive, randomEntry)
 {
   const char* const zimfiles[] = {
@@ -404,7 +429,7 @@ TEST(ZimArchive, validate)
 
   TEST_BROKEN_ZIM_NAME(
     "invalid.smaller_than_header.zim",
-    "zim-file is too small to contain a header\n"
+    "Zim file(s) is too small.\n"
   );
 
   TEST_BROKEN_ZIM_NAME(
@@ -434,7 +459,7 @@ TEST(ZimArchive, validate)
 
   TEST_BROKEN_ZIM_NAME(
     "invalid.invalid_checksumpos.zim",
-    "Checksum position is not valid\n"
+    "Zim file(s) is too small.\n"
   );
 
   TEST_BROKEN_ZIM_NAME(