Added check to BaseImporter::SearchFileHeaderForToken making sure that a detected token is not in fact just a fraction of a longer token. Microsoft exported binary gltf files were detected as OBJ, because the "gltf " in the string "Microsoft GLTF Exporter 2.4.1.7" was detected as the token "f ". I added a new bool parameter to the method enabling this check. It's default false, and only ObjFileImporter sets it to true, so no other code should be affected.

code/BaseImporter.cpp

@@ -143,7 +143,8 @@ void BaseImporter::GetExtensionList(std::set<std::string>& extensions) {
     const char**        tokens,
     unsigned int        numTokens,
     unsigned int        searchBytes /* = 200 */,
-    bool                tokensSol /* false */)
+    bool                tokensSol /* false */,
+    bool                noAlphaBeforeTokens /* false */)
 {
     ai_assert( nullptr != tokens );
     ai_assert( 0 != numTokens );
@@ -193,6 +194,11 @@ void BaseImporter::GetExtensionList(std::set<std::string>& extensions) {
             if( !r ) {
                 continue;
             }
+            // We need to make sure that we didn't accidentially identify the end of another token as our token,
+            // e.g. in a previous version the "gltf " present in some gltf files was detected as "f "
+            if (noAlphaBeforeTokens && (r != buffer && isalpha(r[-1]))) {
+                continue;
+            }
             // We got a match, either we don't care where it is, or it happens to
             // be in the beginning of the file / line
             if (!tokensSol || r == buffer || r[-1] == '\r' || r[-1] == '\n') {

code/ObjFileImporter.cpp

@@ -100,7 +100,7 @@ bool ObjFileImporter::CanRead( const std::string& pFile, IOSystem*  pIOHandler ,
     } else {
         // Check file Header
         static const char *pTokens[] = { "mtllib", "usemtl", "v ", "vt ", "vn ", "o ", "g ", "s ", "f " };
-        return BaseImporter::SearchFileHeaderForToken(pIOHandler, pFile, pTokens, 9 );
+        return BaseImporter::SearchFileHeaderForToken(pIOHandler, pFile, pTokens, 9, 200, false, true );
     }
 }
 

include/assimp/BaseImporter.h

@@ -244,7 +244,8 @@ public: // static utilities
         const char** tokens,
         unsigned int numTokens,
         unsigned int searchBytes = 200,
-        bool tokensSol = false);
+        bool tokensSol = false,
+        bool noAlphaBeforeTokens = false);
 
     // -------------------------------------------------------------------
     /** @brief Check whether a file has a specific file extension