8 files changed, 413 insertions, 331 deletions

diff --git a/src/WixToolset.BootstrapperCore.Native/inc/BootstrapperApplication.h b/src/WixToolset.BootstrapperCore.Native/inc/BootstrapperApplication.h
index 2d086f38..cf330c29 100644
--- a/src/WixToolset.BootstrapperCore.Native/inc/BootstrapperApplication.h
+++ b/src/WixToolset.BootstrapperCore.Native/inc/BootstrapperApplication.h
@@ -54,8 +54,13 @@ enum BOOTSTRAPPER_RELATED_OPERATION
 
 enum BOOTSTRAPPER_CACHE_OPERATION
 {
+    // There is no source available.
+    BOOTSTRAPPER_CACHE_OPERATION_NONE,
+    // Copy the payload or container from the chosen local source.
     BOOTSTRAPPER_CACHE_OPERATION_COPY,
+    // Download the payload or container using the download URL.
     BOOTSTRAPPER_CACHE_OPERATION_DOWNLOAD,
+    // Extract the payload from the container.
     BOOTSTRAPPER_CACHE_OPERATION_EXTRACT,
 };
 
@@ -112,7 +117,7 @@ enum BOOTSTRAPPER_APPLICATION_MESSAGE
     BOOTSTRAPPER_APPLICATION_MESSAGE_ONCACHEPACKAGEBEGIN,
     BOOTSTRAPPER_APPLICATION_MESSAGE_ONCACHEACQUIREBEGIN,
     BOOTSTRAPPER_APPLICATION_MESSAGE_ONCACHEACQUIREPROGRESS,
-    BOOTSTRAPPER_APPLICATION_MESSAGE_ONRESOLVESOURCE,
+    BOOTSTRAPPER_APPLICATION_MESSAGE_ONCACHEACQUIRERESOLVING,
     BOOTSTRAPPER_APPLICATION_MESSAGE_ONCACHEACQUIRECOMPLETE,
     BOOTSTRAPPER_APPLICATION_MESSAGE_ONCACHEVERIFYBEGIN,
     BOOTSTRAPPER_APPLICATION_MESSAGE_ONCACHEVERIFYCOMPLETE,
@@ -158,7 +163,7 @@ enum BOOTSTRAPPER_APPLYCOMPLETE_ACTION
 enum BOOTSTRAPPER_CACHEACQUIRECOMPLETE_ACTION
 {
     BOOTSTRAPPER_CACHEACQUIRECOMPLETE_ACTION_NONE,
-    // Instructs the engine to try the acquisition of the package again.
+    // Instructs the engine to try the acquisition of the payload again.
     // Ignored if hrStatus is a success.
     BOOTSTRAPPER_CACHEACQUIRECOMPLETE_ACTION_RETRY,
 };
@@ -202,16 +207,6 @@ enum BOOTSTRAPPER_EXECUTEPACKAGECOMPLETE_ACTION
     BOOTSTRAPPER_EXECUTEPACKAGECOMPLETE_ACTION_SUSPEND,
 };
 
-enum BOOTSTRAPPER_RESOLVESOURCE_ACTION
-{
-    // Instructs the engine that the source can't be found.
-    BOOTSTRAPPER_RESOLVESOURCE_ACTION_NONE,
-    // Instructs the engine to try the local source again.
-    BOOTSTRAPPER_RESOLVESOURCE_ACTION_RETRY,
-    // Instructs the engine to try the download source.
-    BOOTSTRAPPER_RESOLVESOURCE_ACTION_DOWNLOAD,
-};
-
 enum BOOTSTRAPPER_SHUTDOWN_ACTION
 {
     BOOTSTRAPPER_SHUTDOWN_ACTION_NONE,
@@ -315,14 +310,17 @@ struct BA_ONCACHEACQUIREBEGIN_ARGS
     DWORD cbSize;
     LPCWSTR wzPackageOrContainerId;
     LPCWSTR wzPayloadId;
-    BOOTSTRAPPER_CACHE_OPERATION operation;
     LPCWSTR wzSource;
+    LPCWSTR wzDownloadUrl;
+    LPCWSTR wzPayloadContainerId;
+    BOOTSTRAPPER_CACHE_OPERATION recommendation;
 };
 
 struct BA_ONCACHEACQUIREBEGIN_RESULTS
 {
     DWORD cbSize;
     BOOL fCancel;
+    BOOTSTRAPPER_CACHE_OPERATION action;
 };
 
 struct BA_ONCACHEACQUIRECOMPLETE_ARGS
@@ -356,6 +354,28 @@ struct BA_ONCACHEACQUIREPROGRESS_RESULTS
     BOOL fCancel;
 };
 
+struct BA_ONCACHEACQUIRERESOLVING_ARGS
+{
+    DWORD cbSize;
+    LPCWSTR wzPackageOrContainerId;
+    LPCWSTR wzPayloadId;
+    LPCWSTR* rgSearchPaths;
+    DWORD cSearchPaths;
+    BOOL fFoundLocal;
+    DWORD dwRecommendedSearchPath;
+    LPCWSTR wzDownloadUrl;
+    LPCWSTR wzPayloadContainerId;
+    BOOTSTRAPPER_CACHE_OPERATION recommendation;
+};
+
+struct BA_ONCACHEACQUIRERESOLVING_RESULTS
+{
+    DWORD cbSize;
+    DWORD dwChosenSearchPath;
+    BOOTSTRAPPER_CACHE_OPERATION action;
+    BOOL fCancel;
+};
+
 struct BA_ONCACHEBEGIN_ARGS
 {
     DWORD cbSize;
@@ -1013,23 +1033,6 @@ struct BA_ONREGISTERCOMPLETE_RESULTS
     DWORD cbSize;
 };
 
-struct BA_ONRESOLVESOURCE_ARGS
-{
-    DWORD cbSize;
-    LPCWSTR wzPackageOrContainerId;
-    LPCWSTR wzPayloadId;
-    LPCWSTR wzLocalSource;
-    LPCWSTR wzDownloadSource;
-    BOOTSTRAPPER_RESOLVESOURCE_ACTION recommendation;
-};
-
-struct BA_ONRESOLVESOURCE_RESULTS
-{
-    DWORD cbSize;
-    BOOTSTRAPPER_RESOLVESOURCE_ACTION action;
-    BOOL fCancel;
-};
-
 struct BA_ONROLLBACKMSITRANSACTIONBEGIN_ARGS
 {
     DWORD cbSize;
diff --git a/src/engine/apply.cpp b/src/engine/apply.cpp
index dffbc6d6..dc9f905b 100644
--- a/src/engine/apply.cpp
+++ b/src/engine/apply.cpp
@@ -23,6 +23,9 @@ typedef struct _BURN_CACHE_CONTEXT
     DWORD64 qwTotalCacheSize;
     DWORD64 qwSuccessfulCacheProgress;
     LPCWSTR wzLayoutDirectory;
+    LPWSTR* rgSearchPaths;
+    DWORD cSearchPaths;
+    DWORD cSearchPathsMax;
 } BURN_CACHE_CONTEXT;
 
 typedef struct _BURN_CACHE_ACQUIRE_PROGRESS_CONTEXT
@@ -113,15 +116,6 @@ static HRESULT LayoutOrCacheContainerOrPayload(
     __in DWORD cTryAgainAttempts,
     __out BOOL* pfRetry
     );
-static HRESULT PromptForSource(
-    __in BURN_USER_EXPERIENCE* pUX,
-    __in_z LPCWSTR wzPackageOrContainerId,
-    __in_z_opt LPCWSTR wzPayloadId,
-    __in_z LPCWSTR wzLocalSource,
-    __in_z_opt LPCWSTR wzDownloadSource,
-    __out BOOL* pfRetry,
-    __out BOOL* pfDownload
-    );
 static HRESULT CopyPayload(
     __in BURN_CACHE_ACQUIRE_PROGRESS_CONTEXT* pProgress,
     __in HANDLE hSourceFile,
@@ -485,6 +479,9 @@ extern "C" HRESULT ApplyCache(
     cacheContext.qwTotalCacheSize = pPlan->qwCacheSizeTotal;
     cacheContext.wzLayoutDirectory = pPlan->sczLayoutDirectory;
 
+    hr = MemAllocArray(reinterpret_cast<LPVOID*>(&cacheContext.rgSearchPaths), sizeof(LPWSTR), BURN_CACHE_MAX_SEARCH_PATHS);
+    ExitOnNull(cacheContext.rgSearchPaths, hr, E_OUTOFMEMORY, "Failed to allocate cache search paths array.");
+
     for (DWORD i = 0; i < pPlan->cCacheActions; ++i)
     {
         BURN_CACHE_ACTION* pCacheAction = pPlan->rgCacheActions + i;
@@ -561,6 +558,12 @@ LExit:
 
     CacheCleanup(FALSE, pPlan->wzBundleId);
 
+    for (DWORD i = 0; i < cacheContext.cSearchPathsMax; ++i)
+    {
+        ReleaseNullStr(cacheContext.rgSearchPaths[i]);
+    }
+    ReleaseMem(cacheContext.rgSearchPaths);
+
     UserExperienceOnCacheComplete(pUX, hr);
     return hr;
 }
@@ -949,17 +952,8 @@ static HRESULT ApplyProcessPayload(
     {
         fRetry = FALSE;
 
-        if (pPayload->pContainer)
-        {
-            // TODO: only extract container if payload isn't already extracted
-            hr = ApplyExtractContainer(pContext, pPayload->pContainer);
-            ExitOnFailure(hr, "Failed to extract container for payload: %ls", pPayload->sczKey);
-        }
-        else
-        {
-            hr = AcquireContainerOrPayload(pContext, NULL, pPackage, pPayload);
-            LogExitOnFailure(hr, MSG_FAILED_ACQUIRE_PAYLOAD, "Failed to acquire payload: %ls to working path: %ls", pPayload->sczKey, pPayload->sczUnverifiedPath);
-        }
+        hr = AcquireContainerOrPayload(pContext, NULL, pPackage, pPayload);
+        LogExitOnFailure(hr, MSG_FAILED_ACQUIRE_PAYLOAD, "Failed to acquire payload: %ls to working path: %ls", pPayload->sczKey, pPayload->sczUnverifiedPath);
 
         pContext->qwSuccessfulCacheProgress += pPayload->qwFileSize;
 
@@ -1054,8 +1048,10 @@ static HRESULT LayoutBundle(
 {
     HRESULT hr = S_OK;
     LPWSTR sczBundlePath = NULL;
+    LPWSTR sczBundleDownloadUrl = NULL;
     LPWSTR sczDestinationPath = NULL;
     int nEquivalentPaths = 0;
+    BOOTSTRAPPER_CACHE_OPERATION cacheOperation = BOOTSTRAPPER_CACHE_OPERATION_NONE;
     BURN_CACHE_ACQUIRE_PROGRESS_CONTEXT progress = { };
     BOOL fRetry = FALSE;
     BOOL fRetryAcquire = FALSE;
@@ -1096,7 +1092,7 @@ static HRESULT LayoutBundle(
             fRetryAcquire = FALSE;
             progress.fCancel = FALSE;
 
-            hr = UserExperienceOnCacheAcquireBegin(pContext->pUX, NULL, NULL, BOOTSTRAPPER_CACHE_OPERATION_COPY, sczBundlePath);
+            hr = UserExperienceOnCacheAcquireBegin(pContext->pUX, NULL, NULL, &sczBundlePath, &sczBundleDownloadUrl, NULL, &cacheOperation);
             ExitOnRootFailure(hr, "BA aborted cache acquire begin.");
 
             hr = CopyPayload(&progress, pContext->hSourceEngineFile, sczBundlePath, wzUnverifiedPath);
@@ -1142,6 +1138,7 @@ static HRESULT LayoutBundle(
 
 LExit:
     ReleaseStr(sczDestinationPath);
+    ReleaseStr(sczBundleDownloadUrl);
     ReleaseStr(sczBundlePath);
 
     return hr;
@@ -1160,11 +1157,16 @@ static HRESULT AcquireContainerOrPayload(
     int nEquivalentPaths = 0;
     LPCWSTR wzPackageOrContainerId = pContainer ? pContainer->sczId : pPackage ? pPackage->sczId : NULL;
     LPCWSTR wzPayloadId = pPayload ? pPayload->sczKey : NULL;
+    LPCWSTR wzPayloadContainerId = pPayload && pPayload->pContainer ? pPayload->pContainer->sczId : NULL;
     LPCWSTR wzDestinationPath = pContainer ? pContainer->sczUnverifiedPath: pPayload->sczUnverifiedPath;
     LPCWSTR wzRelativePath = pContainer ? pContainer->sczFilePath : pPayload->sczFilePath;
-    LPWSTR sczSourceFullPath = NULL;
     BURN_CACHE_ACQUIRE_PROGRESS_CONTEXT progress = { };
+    BOOL fBeginCalled = FALSE;
     BOOL fRetry = FALSE;
+    DWORD dwChosenSearchPath = 0;
+    BOOTSTRAPPER_CACHE_OPERATION cacheOperation = BOOTSTRAPPER_CACHE_OPERATION_NONE;
+    LPWSTR* pwzDownloadUrl = pContainer ? &pContainer->downloadSource.sczUrl : &pPayload->downloadSource.sczUrl;
+    LPWSTR* pwzSourcePath = pContainer ? &pContainer->sczSourcePath : &pPayload->sczSourcePath;
 
     progress.pCacheContext = pContext;
     progress.pContainer = pContainer;
@@ -1173,86 +1175,148 @@ static HRESULT AcquireContainerOrPayload(
 
     do
     {
-        LPCWSTR wzDownloadUrl = pContainer ? pContainer->downloadSource.sczUrl : pPayload->downloadSource.sczUrl;
-        LPCWSTR wzSourcePath = pContainer ? pContainer->sczSourcePath : pPayload->sczSourcePath;
-
         BOOL fFoundLocal = FALSE;
-        BOOL fCopy = FALSE;
-        BOOL fDownload = FALSE;
 
+        pContext->cSearchPaths = 0;
+        dwChosenSearchPath = 0;
         fRetry = FALSE;
         progress.fCancel = FALSE;
+        fBeginCalled = TRUE;
 
-        hr = CacheFindLocalSource(wzSourcePath, wzDestinationPath, pContext->pVariables, &fFoundLocal, &sczSourceFullPath);
-        ExitOnFailure(hr, "Failed to search local source.");
-        
-        if (fFoundLocal) // the file exists locally, so copy it.
-        {
-            // If the source path and destination path are different, do the copy (otherwise there's no point).
-            hr = PathCompare(sczSourceFullPath, wzDestinationPath, &nEquivalentPaths);
-            ExitOnFailure(hr, "Failed to determine if payload source path was equivalent to the destination path.");
+        hr = UserExperienceOnCacheAcquireBegin(pContext->pUX, wzPackageOrContainerId, wzPayloadId, pwzSourcePath, pwzDownloadUrl, wzPayloadContainerId, &cacheOperation);
+        ExitOnRootFailure(hr, "BA aborted cache acquire begin.");
 
-            fCopy = (CSTR_EQUAL != nEquivalentPaths);
-        }
-        else // can't find the file locally, so prompt for source.
+        // Skip the Resolving event and probing local paths if the BA already knew it wanted to download or extract.
+        if (BOOTSTRAPPER_CACHE_OPERATION_DOWNLOAD != cacheOperation &&
+            BOOTSTRAPPER_CACHE_OPERATION_EXTRACT != cacheOperation)
         {
-            DWORD dwLogId = pContainer ? (wzPayloadId ? MSG_PROMPT_CONTAINER_PAYLOAD_SOURCE : MSG_PROMPT_CONTAINER_SOURCE) : pPackage ? MSG_PROMPT_PACKAGE_PAYLOAD_SOURCE : MSG_PROMPT_BUNDLE_PAYLOAD_SOURCE;
-            LogId(REPORT_STANDARD, dwLogId, wzPackageOrContainerId ? wzPackageOrContainerId : L"", wzPayloadId ? wzPayloadId : L"", sczSourceFullPath);
+            hr = CacheGetLocalSourcePaths(wzRelativePath, *pwzSourcePath, wzDestinationPath, pContext->wzLayoutDirectory, pContext->pVariables, &pContext->rgSearchPaths, &pContext->cSearchPaths);
+            ExitOnFailure(hr, "Failed to search local source.");
 
-            hr = PromptForSource(pContext->pUX, wzPackageOrContainerId, wzPayloadId, sczSourceFullPath, wzDownloadUrl, &fRetry, &fDownload);
+            for (DWORD i = 0; i < pContext->cSearchPaths; ++i)
+            {
+                // If the file exists locally, choose it.
+                if (FileExistsEx(pContext->rgSearchPaths[i], NULL))
+                {
+                    dwChosenSearchPath = i;
+
+                    fFoundLocal = TRUE;
+                    break;
+                }
+            }
 
-            // If the BA requested download then ensure a download url is available (it may have been set
-            // during PromptForSource so we need to check again).
-            if (fDownload)
+            if (BOOTSTRAPPER_CACHE_OPERATION_COPY == cacheOperation)
+            {
+                if (!fFoundLocal)
+                {
+                    cacheOperation = BOOTSTRAPPER_CACHE_OPERATION_NONE;
+                }
+            }
+            else
             {
-                wzDownloadUrl = pContainer ? pContainer->downloadSource.sczUrl : pPayload->downloadSource.sczUrl;
-                if (!wzDownloadUrl || !*wzDownloadUrl)
+                if (fFoundLocal) // the file exists locally, so copy it.
+                {
+                    cacheOperation = BOOTSTRAPPER_CACHE_OPERATION_COPY;
+                }
+                else if (wzPayloadContainerId)
+                {
+                    cacheOperation = BOOTSTRAPPER_CACHE_OPERATION_EXTRACT;
+                }
+                else if (*pwzDownloadUrl && **pwzDownloadUrl)
                 {
-                    hr = E_INVALIDARG;
+                    cacheOperation = BOOTSTRAPPER_CACHE_OPERATION_DOWNLOAD;
                 }
             }
 
-            // Log the error
-            LogExitOnFailure(hr, MSG_PAYLOAD_FILE_NOT_PRESENT, "Failed while prompting for source (original path '%ls').", sczSourceFullPath);
+            // Let the BA have a chance to override the action, but their chance to change the source is during begin or complete.
+            hr = UserExperienceOnCacheAcquireResolving(pContext->pUX, wzPackageOrContainerId, wzPayloadId, pContext->rgSearchPaths, pContext->cSearchPaths, fFoundLocal, &dwChosenSearchPath, *pwzDownloadUrl, wzPayloadContainerId, &cacheOperation);
+            ExitOnRootFailure(hr, "BA aborted cache acquire resolving.");
         }
 
-        if (fCopy)
+        switch (cacheOperation)
         {
-            hr = UserExperienceOnCacheAcquireBegin(pContext->pUX, wzPackageOrContainerId, wzPayloadId, BOOTSTRAPPER_CACHE_OPERATION_COPY, sczSourceFullPath);
-            ExitOnRootFailure(hr, "BA aborted cache acquire begin.");
+        case BOOTSTRAPPER_CACHE_OPERATION_COPY:
+            // If the source path and destination path are different, do the copy (otherwise there's no point).
+            hr = PathCompare(pContext->rgSearchPaths[dwChosenSearchPath], wzDestinationPath, &nEquivalentPaths);
+            ExitOnFailure(hr, "Failed to determine if payload paths were equivalent, source: %ls, destination: %ls.", pContext->rgSearchPaths[dwChosenSearchPath], wzDestinationPath);
 
-            hr = CopyPayload(&progress, INVALID_HANDLE_VALUE, sczSourceFullPath, wzDestinationPath);
-            // Error handling happens after sending complete message to BA.
+            if (CSTR_EQUAL != nEquivalentPaths)
+            {
+                hr = CopyPayload(&progress, INVALID_HANDLE_VALUE, pContext->rgSearchPaths[dwChosenSearchPath], wzDestinationPath);
+                // Error handling happens after sending complete message to BA.
+
+                // TODO: wait for verification?
+                // We successfully copied from a source location, set that as the last used source.
+                if (SUCCEEDED(hr))
+                {
+                    CacheSetLastUsedSource(pContext->pVariables, pContext->rgSearchPaths[dwChosenSearchPath], wzRelativePath);
+                }
+            }
 
-            // We successfully copied from a source location, set that as the last used source.
-            if (SUCCEEDED(hr))
+            fBeginCalled = FALSE;
+            UserExperienceOnCacheAcquireComplete(pContext->pUX, wzPackageOrContainerId, wzPayloadId, hr, &fRetry);
+            if (fRetry)
             {
-                CacheSetLastUsedSource(pContext->pVariables, sczSourceFullPath, wzRelativePath);
+                hr = S_OK;
             }
-        }
-        else if (fDownload)
-        {
-            hr = UserExperienceOnCacheAcquireBegin(pContext->pUX, wzPackageOrContainerId, wzPayloadId, BOOTSTRAPPER_CACHE_OPERATION_DOWNLOAD, wzDownloadUrl);
-            ExitOnRootFailure(hr, "BA aborted cache download payload begin.");
 
+            ExitOnFailure(hr, "Failed to acquire payload from: '%ls' to working path: '%ls'", pContext->rgSearchPaths[dwChosenSearchPath], wzDestinationPath);
+
+            break;
+        case BOOTSTRAPPER_CACHE_OPERATION_DOWNLOAD:
             hr = DownloadPayload(&progress, wzDestinationPath);
             // Error handling happens after sending complete message to BA.
-        }
 
-        if (fCopy || fDownload)
-        {
+            fBeginCalled = FALSE;
+            UserExperienceOnCacheAcquireComplete(pContext->pUX, wzPackageOrContainerId, wzPayloadId, hr, &fRetry);
+            if (fRetry)
+            {
+                hr = S_OK;
+            }
+
+            ExitOnFailure(hr, "Failed to acquire payload from: '%ls' to working path: '%ls'", *pwzDownloadUrl, wzDestinationPath);
+
+            break;
+        case BOOTSTRAPPER_CACHE_OPERATION_EXTRACT:
+            Assert(pPayload->pContainer);
+
+            hr = ApplyExtractContainer(pContext, pPayload->pContainer);
+            // Error handling happens after sending complete message to BA.
+
+            fBeginCalled = FALSE;
+            UserExperienceOnCacheAcquireComplete(pContext->pUX, wzPackageOrContainerId, wzPayloadId, hr, &fRetry);
+            if (fRetry)
+            {
+                hr = S_OK;
+            }
+
+            ExitOnFailure(hr, "Failed to extract container for payload: %ls", wzPayloadId);
+
+            break;
+        case BOOTSTRAPPER_CACHE_OPERATION_NONE:
+            hr = E_FILENOTFOUND;
+            LogErrorId(hr, MSG_RESOLVE_SOURCE_FAILED, wzPayloadId, pPackage ? pPackage->sczId : NULL, pContainer ? pContainer->sczId : NULL);
+
+            fBeginCalled = FALSE;
             UserExperienceOnCacheAcquireComplete(pContext->pUX, wzPackageOrContainerId, wzPayloadId, hr, &fRetry);
             if (fRetry)
             {
                 hr = S_OK;
             }
+
+            ExitOnFailure(hr, "Failed to resolve source, payload: %ls, package: %ls, container: %ls", wzPayloadId, pPackage ? pPackage->sczId : NULL, pContainer ? pContainer->sczId : NULL);
+
+            break;
         }
-        ExitOnFailure(hr, "Failed to acquire payload from: '%ls' to working path: '%ls'", fCopy ? sczSourceFullPath : wzDownloadUrl, wzDestinationPath);
     } while (fRetry);
-    ExitOnFailure(hr, "Failed to find external payload to cache.");
 
 LExit:
-    ReleaseStr(sczSourceFullPath);
+    if (fBeginCalled)
+    {
+        UserExperienceOnCacheAcquireComplete(pContext->pUX, wzPackageOrContainerId, wzPayloadId, hr, &fRetry);
+    }
+
+    pContext->cSearchPathsMax = max(pContext->cSearchPaths, pContext->cSearchPathsMax);
 
     return hr;
 }
@@ -1355,48 +1419,6 @@ LExit:
     return hr;
 }
 
-static HRESULT PromptForSource(
-    __in BURN_USER_EXPERIENCE* pUX,
-    __in_z LPCWSTR wzPackageOrContainerId,
-    __in_z_opt LPCWSTR wzPayloadId,
-    __in_z LPCWSTR wzLocalSource,
-    __in_z_opt LPCWSTR wzDownloadSource,
-    __inout BOOL* pfRetry,
-    __inout BOOL* pfDownload
-    )
-{
-    HRESULT hr = S_OK;
-    BOOTSTRAPPER_RESOLVESOURCE_ACTION action = BOOTSTRAPPER_RESOLVESOURCE_ACTION_NONE;
-
-    hr = UserExperienceOnResolveSource(pUX, wzPackageOrContainerId, wzPayloadId, wzLocalSource, wzDownloadSource, &action);
-    if (FAILED(hr))
-    {
-        ExitFunction();
-    }
-
-    switch (action)
-    {
-    case BOOTSTRAPPER_RESOLVESOURCE_ACTION_NONE:
-        hr = E_FILENOTFOUND;
-        break;
-
-    case BOOTSTRAPPER_RESOLVESOURCE_ACTION_RETRY:
-        *pfRetry = TRUE;
-        break;
-
-    case BOOTSTRAPPER_RESOLVESOURCE_ACTION_DOWNLOAD:
-        *pfDownload = TRUE;
-        break;
-
-    default:
-        hr = E_INVALIDARG;
-        break;
-    }
-
-LExit:
-    return hr;
-}
-
 static HRESULT CopyPayload(
     __in BURN_CACHE_ACQUIRE_PROGRESS_CONTEXT* pProgress,
     __in HANDLE hSourceFile,
diff --git a/src/engine/cache.cpp b/src/engine/cache.cpp
index 6ac313e0..84b7f131 100644
--- a/src/engine/cache.cpp
+++ b/src/engine/cache.cpp
@@ -11,7 +11,7 @@ static const DWORD FILE_OPERATION_RETRY_WAIT = 2000;
 
 static BOOL vfInitializedCache = FALSE;
 static BOOL vfRunningFromCache = FALSE;
-static LPWSTR vsczSourceProcessPath = NULL;
+static LPWSTR vsczSourceProcessFolder = NULL;
 static LPWSTR vsczWorkingFolder = NULL;
 static LPWSTR vsczDefaultUserPackageCache = NULL;
 static LPWSTR vsczDefaultMachinePackageCache = NULL;
@@ -140,8 +140,8 @@ extern "C" HRESULT CacheInitialize(
             wzSourceProcessPath = sczCurrentPath;
         }
 
-        hr = StrAllocString(&vsczSourceProcessPath, wzSourceProcessPath, 0);
-        ExitOnFailure(hr, "Failed to initialize cache source path.");
+        hr = PathGetDirectory(wzSourceProcessPath, &vsczSourceProcessFolder);
+        ExitOnFailure(hr, "Failed to initialize cache source folder.");
 
         // If we're not running from the cache, ensure the original source is set.
         if (!vfRunningFromCache)
@@ -393,112 +393,166 @@ LExit:
     return hr;
 }
 
-extern "C" HRESULT CacheFindLocalSource(
+extern "C" HRESULT CacheGetLocalSourcePaths(
+    __in_z LPCWSTR wzRelativePath,
     __in_z LPCWSTR wzSourcePath,
     __in_z LPCWSTR wzDestinationPath,
+    __in_z_opt LPCWSTR wzLayoutDirectory,
     __in BURN_VARIABLES* pVariables,
-    __out BOOL* pfFound,
-    __out_z LPWSTR* psczSourceFullPath
+    __inout LPWSTR** prgSearchPaths,
+    __out DWORD* pcSearchPaths
     )
 {
     HRESULT hr = S_OK;
-    LPWSTR sczSourceProcessFolder = NULL;
     LPWSTR sczCurrentPath = NULL;
-    LPWSTR sczLastSourcePath = NULL;
     LPWSTR sczLastSourceFolder = NULL;
-    LPWSTR sczLayoutPath = NULL;
-    LPWSTR sczLayoutFolder = NULL;
-    LPCWSTR rgwzSearchPaths[4] = { };
+    LPWSTR* psczPath = NULL;
+    BOOL fPreferSourcePathLocation = FALSE;
+    BOOL fTryLastFolder = FALSE;
+    BOOL fTryRelativePath = FALSE;
+    BOOL fSourceIsAbsolute = FALSE;
     DWORD cSearchPaths = 0;
 
-    // If the source path provided is a full path, obviously that is where we should be looking.
-    if (PathIsAbsolute(wzSourcePath))
+    AssertSz(vfInitializedCache, "Cache wasn't initialized");
+
+    hr = GetLastUsedSourceFolder(pVariables, &sczLastSourceFolder);
+    fPreferSourcePathLocation = !vfRunningFromCache || FAILED(hr);
+    fTryLastFolder = SUCCEEDED(hr) && sczLastSourceFolder && *sczLastSourceFolder && CSTR_EQUAL != ::CompareStringW(LOCALE_NEUTRAL, NORM_IGNORECASE, vsczSourceProcessFolder, -1, sczLastSourceFolder, -1);
+    fTryRelativePath = CSTR_EQUAL != ::CompareStringW(LOCALE_NEUTRAL, NORM_IGNORECASE, wzSourcePath, -1, wzRelativePath, -1);
+    fSourceIsAbsolute = PathIsAbsolute(wzSourcePath);
+
+    // If the source path provided is a full path, try that first.
+    if (fSourceIsAbsolute)
     {
-        rgwzSearchPaths[0] = wzSourcePath;
-        cSearchPaths = 1;
+        hr = MemEnsureArraySize(reinterpret_cast<LPVOID*>(prgSearchPaths), cSearchPaths + 1, sizeof(LPWSTR), BURN_CACHE_MAX_SEARCH_PATHS);
+        ExitOnFailure(hr, "Failed to ensure size for search paths array.");
+
+        psczPath = *prgSearchPaths + cSearchPaths;
+        ++cSearchPaths;
+
+        hr = StrAllocString(psczPath, wzSourcePath, 0);
+        ExitOnFailure(hr, "Failed to copy absolute source path.");
     }
-    else
+
+    // Try the destination path next.
+    hr = MemEnsureArraySize(reinterpret_cast<LPVOID*>(prgSearchPaths), cSearchPaths + 1, sizeof(LPWSTR), BURN_CACHE_MAX_SEARCH_PATHS);
+    ExitOnFailure(hr, "Failed to ensure size for search paths array.");
+
+    psczPath = *prgSearchPaths + cSearchPaths;
+    ++cSearchPaths;
+
+    hr = StrAllocString(psczPath, wzDestinationPath, 0);
+    ExitOnFailure(hr, "Failed to copy absolute source path.");
+
+    if (!fSourceIsAbsolute)
     {
-        // Use the destination path first.
-        rgwzSearchPaths[0] = wzDestinationPath;
-        cSearchPaths = 1;
-
-        // If we're not running from cache or we couldn't get the last source, use
-        // the source path location. In the case where we are in the bundle's
-        // package cache and couldn't find a last used source we unfortunately will
-        // be picking the package cache path which isn't likely to have what we are
-        // looking for.
-        hr = GetLastUsedSourceFolder(pVariables, &sczLastSourceFolder);
-        if (!vfRunningFromCache || FAILED(hr))
+        // Calculate the source path location.
+        // In the case where we are in the bundle's package cache and
+        // couldn't find a last used source that will be the package cache path
+        // which isn't likely to have what we are looking for.
+        hr = MemEnsureArraySize(reinterpret_cast<LPVOID*>(prgSearchPaths), cSearchPaths + 1, sizeof(LPWSTR), BURN_CACHE_MAX_SEARCH_PATHS);
+        ExitOnFailure(hr, "Failed to ensure size for search paths array.");
+
+        hr = PathConcat(vsczSourceProcessFolder, wzSourcePath, &sczCurrentPath);
+        ExitOnFailure(hr, "Failed to combine source process folder with source.");
+
+        // If we're not running from cache or we couldn't get the last source,
+        // try the source path location next.
+        if (fPreferSourcePathLocation)
         {
-            hr = PathGetDirectory(vsczSourceProcessPath, &sczSourceProcessFolder);
-            ExitOnFailure(hr, "Failed to get current process directory.");
+            (*prgSearchPaths)[cSearchPaths] = sczCurrentPath;
+            ++cSearchPaths;
+            sczCurrentPath = NULL;
+        }
 
-            hr = PathConcat(sczSourceProcessFolder, wzSourcePath, &sczCurrentPath);
+        // If we have a last used source and it is not the source path location,
+        // add the last used source to the search path next.
+        if (fTryLastFolder)
+        {
+            hr = MemEnsureArraySize(reinterpret_cast<LPVOID*>(prgSearchPaths), cSearchPaths + 1, sizeof(LPWSTR), BURN_CACHE_MAX_SEARCH_PATHS);
+            ExitOnFailure(hr, "Failed to ensure size for search paths array.");
+
+            psczPath = *prgSearchPaths + cSearchPaths;
+            ++cSearchPaths;
+
+            hr = PathConcat(sczLastSourceFolder, wzSourcePath, psczPath);
             ExitOnFailure(hr, "Failed to combine last source with source.");
+        }
 
-            rgwzSearchPaths[cSearchPaths] = sczCurrentPath;
+        if (!fPreferSourcePathLocation)
+        {
+            (*prgSearchPaths)[cSearchPaths] = sczCurrentPath;
             ++cSearchPaths;
+            sczCurrentPath = NULL;
         }
 
-        // If we have a last used source and it does not duplicate the existing search path,
-        // add the last used source to the search path second.
-        if (sczLastSourceFolder && *sczLastSourceFolder)
+        // Also consider the layout directory if doing Layout.
+        if (wzLayoutDirectory)
         {
-            hr = PathConcat(sczLastSourceFolder, wzSourcePath, &sczLastSourcePath);
-            ExitOnFailure(hr, "Failed to combine last source with source.");
+            hr = MemEnsureArraySize(reinterpret_cast<LPVOID*>(prgSearchPaths), cSearchPaths + 1, sizeof(LPWSTR), BURN_CACHE_MAX_SEARCH_PATHS);
+            ExitOnFailure(hr, "Failed to ensure size for search paths array.");
 
-            if (1 == cSearchPaths || CSTR_EQUAL != ::CompareStringW(LOCALE_NEUTRAL, NORM_IGNORECASE, rgwzSearchPaths[1], -1, sczLastSourcePath, -1))
-            {
-                rgwzSearchPaths[cSearchPaths] = sczLastSourcePath;
-                ++cSearchPaths;
-            }
+            psczPath = *prgSearchPaths + cSearchPaths;
+            ++cSearchPaths;
+
+            hr = PathConcat(wzLayoutDirectory, wzSourcePath, psczPath);
+            ExitOnFailure(hr, "Failed to combine layout source with source.");
         }
+    }
 
-        // Also consider the layout directory if set on the command line or by the BA.
-        hr = VariableGetString(pVariables, BURN_BUNDLE_LAYOUT_DIRECTORY, &sczLayoutFolder);
-        if (E_NOTFOUND != hr)
+    if (fTryRelativePath)
+    {
+        hr = MemEnsureArraySize(reinterpret_cast<LPVOID*>(prgSearchPaths), cSearchPaths + 1, sizeof(LPWSTR), BURN_CACHE_MAX_SEARCH_PATHS);
+        ExitOnFailure(hr, "Failed to ensure size for search paths array.");
+
+        hr = PathConcat(vsczSourceProcessFolder, wzRelativePath, &sczCurrentPath);
+        ExitOnFailure(hr, "Failed to combine source process folder with relative.");
+
+        if (fPreferSourcePathLocation)
         {
-            ExitOnFailure(hr, "Failed to get bundle layout directory property.");
+            (*prgSearchPaths)[cSearchPaths] = sczCurrentPath;
+            ++cSearchPaths;
+            sczCurrentPath = NULL;
+        }
 
-            hr = PathConcat(sczLayoutFolder, wzSourcePath, &sczLayoutPath);
-            ExitOnFailure(hr, "Failed to combine layout source with source.");
+        if (fTryLastFolder)
+        {
+            hr = MemEnsureArraySize(reinterpret_cast<LPVOID*>(prgSearchPaths), cSearchPaths + 1, sizeof(LPWSTR), BURN_CACHE_MAX_SEARCH_PATHS);
+            ExitOnFailure(hr, "Failed to ensure size for search paths array.");
 
-            rgwzSearchPaths[cSearchPaths] = sczLayoutPath;
+            psczPath = *prgSearchPaths + cSearchPaths;
             ++cSearchPaths;
+
+            hr = PathConcat(sczLastSourceFolder, wzRelativePath, psczPath);
+            ExitOnFailure(hr, "Failed to combine last source with relative.");
         }
-    }
 
-    *pfFound = FALSE; // assume we won't find the file locally.
+        if (!fPreferSourcePathLocation)
+        {
+            (*prgSearchPaths)[cSearchPaths] = sczCurrentPath;
+            ++cSearchPaths;
+            sczCurrentPath = NULL;
+        }
 
-    for (DWORD i = 0; i < cSearchPaths; ++i)
-    {
-        // If the file exists locally, copy its path.
-        if (FileExistsEx(rgwzSearchPaths[i], NULL))
+        if (wzLayoutDirectory)
         {
-            hr = StrAllocString(psczSourceFullPath, rgwzSearchPaths[i], 0);
-            ExitOnFailure(hr, "Failed to copy source path.");
+            hr = MemEnsureArraySize(reinterpret_cast<LPVOID*>(prgSearchPaths), cSearchPaths + 1, sizeof(LPWSTR), BURN_CACHE_MAX_SEARCH_PATHS);
+            ExitOnFailure(hr, "Failed to ensure size for search paths array.");
 
-            *pfFound = TRUE;
-            break;
-        }
-    }
+            psczPath = *prgSearchPaths + cSearchPaths;
+            ++cSearchPaths;
 
-    // If nothing was found, return the first thing in our search path as the
-    // best path where we thought we should have found the file.
-    if (!*pfFound)
-    {
-        hr = StrAllocString(psczSourceFullPath, rgwzSearchPaths[0], 0);
-        ExitOnFailure(hr, "Failed to copy source path.");
+            hr = PathConcat(wzLayoutDirectory, wzSourcePath, psczPath);
+            ExitOnFailure(hr, "Failed to combine layout source with relative.");
+        }
     }
 
 LExit:
     ReleaseStr(sczCurrentPath);
-    ReleaseStr(sczSourceProcessFolder);
     ReleaseStr(sczLastSourceFolder);
-    ReleaseStr(sczLastSourcePath);
-    ReleaseStr(sczLayoutFolder);
-    ReleaseStr(sczLayoutPath);
+
+    AssertSz(cSearchPaths <= BURN_CACHE_MAX_SEARCH_PATHS, "Got more than BURN_CACHE_MAX_SEARCH_PATHS search paths");
+    *pcSearchPaths = cSearchPaths;
 
     return hr;
 }
@@ -1079,7 +1133,7 @@ extern "C" void CacheUninitialize()
     ReleaseNullStr(vsczDefaultMachinePackageCache);
     ReleaseNullStr(vsczDefaultUserPackageCache);
     ReleaseNullStr(vsczWorkingFolder);
-    ReleaseNullStr(vsczSourceProcessPath);
+    ReleaseNullStr(vsczSourceProcessFolder);
 
     vfRunningFromCache = FALSE;
     vfInitializedCache = FALSE;
@@ -1224,17 +1278,12 @@ static HRESULT GetLastUsedSourceFolder(
     )
 {
     HRESULT hr = S_OK;
-    LPWSTR sczOriginalSource = NULL;
 
     hr = VariableGetString(pVariables, BURN_BUNDLE_LAST_USED_SOURCE, psczLastSource);
     if (E_NOTFOUND == hr)
     {
         // Try the original source folder.
-        hr = VariableGetString(pVariables, BURN_BUNDLE_ORIGINAL_SOURCE, &sczOriginalSource);
-        if (SUCCEEDED(hr))
-        {
-            hr = PathGetDirectory(sczOriginalSource, psczLastSource);
-        }
+        hr = VariableGetString(pVariables, BURN_BUNDLE_ORIGINAL_SOURCE_FOLDER, psczLastSource);
     }
 
     return hr;
diff --git a/src/engine/cache.h b/src/engine/cache.h
index acc7acb7..eb964f58 100644
--- a/src/engine/cache.h
+++ b/src/engine/cache.h
@@ -1,6 +1,7 @@
 #pragma once
 // Copyright (c) .NET Foundation and contributors. All rights reserved. Licensed under the Microsoft Reciprocal License. See LICENSE.TXT file in the project root for full license information.
 
+#define BURN_CACHE_MAX_SEARCH_PATHS 7
 
 #ifdef __cplusplus
 extern "C" {
@@ -52,12 +53,14 @@ HRESULT CacheGetResumePath(
     __in_z LPCWSTR wzPayloadWorkingPath,
     __deref_out_z LPWSTR* psczResumePath
     );
-HRESULT CacheFindLocalSource(
+HRESULT CacheGetLocalSourcePaths(
+    __in_z LPCWSTR wzRelativePath,
     __in_z LPCWSTR wzSourcePath,
     __in_z LPCWSTR wzDestinationPath,
+    __in_z_opt LPCWSTR wzLayoutDirectory,
     __in BURN_VARIABLES* pVariables,
-    __out BOOL* pfFound,
-    __out_z LPWSTR* psczSourceFullPath
+    __inout LPWSTR** prgSearchPaths,
+    __out DWORD* pcSearchPaths
     );
 HRESULT CacheSetLastUsedSource(
     __in BURN_VARIABLES* pVariables,
diff --git a/src/engine/engine.mc b/src/engine/engine.mc
index c8b46806..f03bc1ea 100644
--- a/src/engine/engine.mc
+++ b/src/engine/engine.mc
@@ -151,9 +151,9 @@ Bundle global condition check didn't succeed - aborting without loading applicat
 
 MessageId=54
 Severity=Error
-SymbolicName=MSG_PAYLOAD_FILE_NOT_PRESENT
+SymbolicName=MSG_RESOLVE_SOURCE_FAILED
 Language=English
-Failed to resolve source for file: %2!ls!, error: %1!ls!.
+Failed to resolve source for payload: %2!ls!, package: %3!ls!, container: %4!ls!, error: %1!ls!.
 .
 
 MessageId=55
@@ -724,34 +724,6 @@ Language=English
 Acquiring package: %1!ls!, payload: %2!ls!, %3!hs! from: %4!ls!
 .
 
-MessageId=340
-Severity=Warning
-SymbolicName=MSG_PROMPT_BUNDLE_PAYLOAD_SOURCE
-Language=English
-Prompt for source of bundle payload: %2!ls!, path: %3!ls!
-.
-
-MessageId=341
-Severity=Warning
-SymbolicName=MSG_PROMPT_CONTAINER_SOURCE
-Language=English
-Prompt for source of container: %1!ls!, path: %3!ls!
-.
-
-MessageId=342
-Severity=Warning
-SymbolicName=MSG_PROMPT_CONTAINER_PAYLOAD_SOURCE
-Language=English
-Prompt for source of container: %1!ls!, payload: %2!ls!, path: %3!ls!
-.
-
-MessageId=343
-Severity=Warning
-SymbolicName=MSG_PROMPT_PACKAGE_PAYLOAD_SOURCE
-Language=English
-Prompt for source of package: %1!ls!, payload: %2!ls!, path: %3!ls!
-.
-
 MessageId=348
 Severity=Warning
 SymbolicName=MSG_APPLY_RETRYING_PACKAGE
diff --git a/src/engine/externalengine.cpp b/src/engine/externalengine.cpp
index 7e9bb25c..d6c44736 100644
--- a/src/engine/externalengine.cpp
+++ b/src/engine/externalengine.cpp
@@ -269,8 +269,7 @@ HRESULT ExternalEngineSetUpdate(
     )
 {
     HRESULT hr = S_OK;
-    LPCWSTR sczId = NULL;
-    LPWSTR sczLocalSource = NULL;
+    LPWSTR sczFilePath = NULL;
     LPWSTR sczCommandline = NULL;
     UUID guid = { };
     WCHAR wzGuid[39];
@@ -296,38 +295,30 @@ HRESULT ExternalEngineSetUpdate(
     {
         UpdateUninitialize(&pEngineState->update);
 
-        if (!wzLocalSource || !*wzLocalSource)
-        {
-            hr = StrAllocFormatted(&sczLocalSource, L"update\\%ls", pEngineState->registration.sczExecutableName);
-            ExitOnFailure(hr, "Failed to default local update source");
-        }
-
         hr = CoreRecreateCommandLine(&sczCommandline, BOOTSTRAPPER_ACTION_INSTALL, pEngineState->command.display, pEngineState->command.restart, BOOTSTRAPPER_RELATION_NONE, FALSE, pEngineState->registration.sczActiveParent, pEngineState->registration.sczAncestors, NULL, pEngineState->command.wzCommandLine);
         ExitOnFailure(hr, "Failed to recreate command-line for update bundle.");
 
-        // Per-user bundles would fail to use the downloaded update bundle, as the existing install would already be cached 
-        // at the registration id's location.  Here I am generating a random guid, but in the future it would be nice if the
-        // feed would provide the ID of the update.
-        if (!pEngineState->registration.fPerMachine)
+        // Bundles would fail to use the downloaded update bundle, as the running bundle would be one of the search paths.
+        // Here I am generating a random guid, but in the future it would be nice if the feed would provide the ID of the update.
+        rs = ::UuidCreate(&guid);
+        hr = HRESULT_FROM_RPC(rs);
+        ExitOnFailure(hr, "Failed to create bundle update guid.");
+
+        if (!::StringFromGUID2(guid, wzGuid, countof(wzGuid)))
         {
-            rs = ::UuidCreate(&guid);
-            hr = HRESULT_FROM_RPC(rs);
-            ExitOnFailure(hr, "Failed to create bundle update guid.");
+            hr = E_OUTOFMEMORY;
+            ExitOnRootFailure(hr, "Failed to convert bundle update guid into string.");
+        }
 
-            if (!::StringFromGUID2(guid, wzGuid, countof(wzGuid)))
-            {
-                hr = E_OUTOFMEMORY;
-                ExitOnRootFailure(hr, "Failed to convert bundle update guid into string.");
-            }
+        hr = StrAllocFormatted(&sczFilePath, L"%ls\\%ls", wzGuid, pEngineState->registration.sczExecutableName);
+        ExitOnFailure(hr, "Failed to build bundle update file path.");
 
-            sczId = wzGuid;
-        }
-        else
+        if (!wzLocalSource || !*wzLocalSource)
         {
-            sczId = pEngineState->registration.sczId;
+            wzLocalSource = sczFilePath;
         }
 
-        hr = PseudoBundleInitialize(FILEMAKEVERSION(rmj, rmm, rup, rpr), &pEngineState->update.package, FALSE, sczId, BOOTSTRAPPER_RELATION_UPDATE, BOOTSTRAPPER_PACKAGE_STATE_ABSENT, FALSE, pEngineState->registration.sczExecutableName, sczLocalSource ? sczLocalSource : wzLocalSource, wzDownloadSource, qwSize, TRUE, sczCommandline, NULL, NULL, NULL, rgbHash, cbHash);
+        hr = PseudoBundleInitialize(FILEMAKEVERSION(rmj, rmm, rup, rpr), &pEngineState->update.package, FALSE, pEngineState->registration.sczId, BOOTSTRAPPER_RELATION_UPDATE, BOOTSTRAPPER_PACKAGE_STATE_ABSENT, FALSE, sczFilePath, wzLocalSource, wzDownloadSource, qwSize, TRUE, sczCommandline, NULL, NULL, NULL, rgbHash, cbHash);
         ExitOnFailure(hr, "Failed to set update bundle.");
 
         pEngineState->update.fUpdateAvailable = TRUE;
@@ -337,7 +328,7 @@ LExit:
     ::LeaveCriticalSection(&pEngineState->userExperience.csEngineActive);
 
     ReleaseStr(sczCommandline);
-    ReleaseStr(sczLocalSource);
+    ReleaseStr(sczFilePath);
 
     return hr;
 }
diff --git a/src/engine/userexperience.cpp b/src/engine/userexperience.cpp
index b6bd65dc..f6ae1491 100644
--- a/src/engine/userexperience.cpp
+++ b/src/engine/userexperience.cpp
@@ -395,29 +395,46 @@ EXTERN_C BAAPI UserExperienceOnCacheAcquireBegin(
     __in BURN_USER_EXPERIENCE* pUserExperience,
     __in_z_opt LPCWSTR wzPackageOrContainerId,
     __in_z_opt LPCWSTR wzPayloadId,
-    __in BOOTSTRAPPER_CACHE_OPERATION operation,
-    __in_z LPCWSTR wzSource
+    __in_z LPWSTR* pwzSource,
+    __in_z LPWSTR* pwzDownloadUrl,
+    __in_z_opt LPCWSTR wzPayloadContainerId,
+    __out BOOTSTRAPPER_CACHE_OPERATION* pCacheOperation
     )
 {
     HRESULT hr = S_OK;
     BA_ONCACHEACQUIREBEGIN_ARGS args = { };
     BA_ONCACHEACQUIREBEGIN_RESULTS results = { };
+    *pCacheOperation = BOOTSTRAPPER_CACHE_OPERATION_NONE;
 
     args.cbSize = sizeof(args);
     args.wzPackageOrContainerId = wzPackageOrContainerId;
     args.wzPayloadId = wzPayloadId;
-    args.operation = operation;
-    args.wzSource = wzSource;
+    args.wzSource = *pwzSource;
+    args.wzDownloadUrl = *pwzDownloadUrl;
+    args.wzPayloadContainerId = wzPayloadContainerId;
+    args.recommendation = *pCacheOperation;
 
     results.cbSize = sizeof(results);
+    results.action = *pCacheOperation;
 
-    hr = SendBAMessage(pUserExperience, BOOTSTRAPPER_APPLICATION_MESSAGE_ONCACHEACQUIREBEGIN, &args, &results);
+    hr = SendBAMessageFromInactiveEngine(pUserExperience, BOOTSTRAPPER_APPLICATION_MESSAGE_ONCACHEACQUIREBEGIN, &args, &results);
     ExitOnFailure(hr, "BA OnCacheAcquireBegin failed.");
 
     if (results.fCancel)
     {
         hr = HRESULT_FROM_WIN32(ERROR_INSTALL_USEREXIT);
     }
+    else
+    {
+        // Verify the BA requested an action that is possible.
+        if (BOOTSTRAPPER_CACHE_OPERATION_DOWNLOAD == results.action && *pwzDownloadUrl && **pwzDownloadUrl ||
+            BOOTSTRAPPER_CACHE_OPERATION_EXTRACT == results.action && wzPayloadContainerId ||
+            BOOTSTRAPPER_CACHE_OPERATION_COPY == results.action ||
+            BOOTSTRAPPER_CACHE_OPERATION_NONE == results.action)
+        {
+            *pCacheOperation = results.action;
+        }
+    }
 
 LExit:
     return hr;
@@ -444,7 +461,7 @@ EXTERN_C BAAPI UserExperienceOnCacheAcquireComplete(
     results.cbSize = sizeof(results);
     results.action = args.recommendation;
 
-    hr = SendBAMessage(pUserExperience, BOOTSTRAPPER_APPLICATION_MESSAGE_ONCACHEACQUIRECOMPLETE, &args, &results);
+    hr = SendBAMessageFromInactiveEngine(pUserExperience, BOOTSTRAPPER_APPLICATION_MESSAGE_ONCACHEACQUIRECOMPLETE, &args, &results);
     ExitOnFailure(hr, "BA OnCacheAcquireComplete failed.");
 
     if (FAILED(hrStatus))
@@ -490,6 +507,64 @@ LExit:
     return hr;
 }
 
+EXTERN_C BAAPI UserExperienceOnCacheAcquireResolving(
+    __in BURN_USER_EXPERIENCE* pUserExperience,
+    __in_z_opt LPCWSTR wzPackageOrContainerId,
+    __in_z_opt LPCWSTR wzPayloadId,
+    __in_z LPWSTR* rgSearchPaths,
+    __in DWORD cSearchPaths,
+    __in BOOL fFoundLocal,
+    __in DWORD* pdwChosenSearchPath,
+    __in_z_opt LPCWSTR wzDownloadUrl,
+    __in_z_opt LPCWSTR wzPayloadContainerId,
+    __inout BOOTSTRAPPER_CACHE_OPERATION* pCacheOperation
+    )
+{
+    HRESULT hr = S_OK;
+    BA_ONCACHEACQUIRERESOLVING_ARGS args = { };
+    BA_ONCACHEACQUIRERESOLVING_RESULTS results = { };
+
+    args.cbSize = sizeof(args);
+    args.wzPackageOrContainerId = wzPackageOrContainerId;
+    args.wzPayloadId = wzPayloadId;
+    args.rgSearchPaths = const_cast<LPCWSTR*>(rgSearchPaths);
+    args.cSearchPaths = cSearchPaths;
+    args.fFoundLocal = fFoundLocal;
+    args.dwRecommendedSearchPath = *pdwChosenSearchPath;
+    args.wzDownloadUrl = wzDownloadUrl;
+    args.recommendation = *pCacheOperation;
+
+    results.cbSize = sizeof(results);
+    results.dwChosenSearchPath = *pdwChosenSearchPath;
+    results.action = *pCacheOperation;
+
+    hr = SendBAMessage(pUserExperience, BOOTSTRAPPER_APPLICATION_MESSAGE_ONCACHEACQUIRERESOLVING, &args, &results);
+    ExitOnFailure(hr, "BA OnCacheAcquireResolving failed.");
+
+    if (results.fCancel)
+    {
+        hr = HRESULT_FROM_WIN32(ERROR_INSTALL_USEREXIT);
+    }
+    else
+    {
+        // Verify the BA requested an action that is possible.
+        if (BOOTSTRAPPER_CACHE_OPERATION_DOWNLOAD == results.action && wzDownloadUrl && *wzDownloadUrl ||
+            BOOTSTRAPPER_CACHE_OPERATION_EXTRACT == results.action && wzPayloadContainerId ||
+            BOOTSTRAPPER_CACHE_OPERATION_NONE == results.action)
+        {
+            *pCacheOperation = results.action;
+        }
+        else if (BOOTSTRAPPER_CACHE_OPERATION_COPY == results.action && results.dwChosenSearchPath < cSearchPaths)
+        {
+            *pdwChosenSearchPath = results.dwChosenSearchPath;
+            *pCacheOperation = results.action;
+        }
+    }
+
+LExit:
+    return hr;
+}
+
 EXTERN_C BAAPI UserExperienceOnCacheBegin(
     __in BURN_USER_EXPERIENCE* pUserExperience
     )
@@ -1861,45 +1936,6 @@ LExit:
     return hr;
 }
 
-EXTERN_C BAAPI UserExperienceOnResolveSource(
-    __in BURN_USER_EXPERIENCE* pUserExperience,
-    __in_z LPCWSTR wzPackageOrContainerId,
-    __in_z_opt LPCWSTR wzPayloadId,
-    __in_z LPCWSTR wzLocalSource,
-    __in_z_opt LPCWSTR wzDownloadSource,
-    __inout BOOTSTRAPPER_RESOLVESOURCE_ACTION* pAction
-    )
-{
-    HRESULT hr = S_OK;
-    BA_ONRESOLVESOURCE_ARGS args = { };
-    BA_ONRESOLVESOURCE_RESULTS results = { };
-
-    args.cbSize = sizeof(args);
-    args.wzPackageOrContainerId = wzPackageOrContainerId;
-    args.wzPayloadId = wzPayloadId;
-    args.wzLocalSource = wzLocalSource;
-    args.wzDownloadSource = wzDownloadSource;
-    args.recommendation = *pAction;
-
-    results.cbSize = sizeof(results);
-    results.action = *pAction;
-
-    hr = SendBAMessageFromInactiveEngine(pUserExperience, BOOTSTRAPPER_APPLICATION_MESSAGE_ONRESOLVESOURCE, &args, &results);
-    ExitOnFailure(hr, "BA OnResolveSource failed.");
-
-    if (results.fCancel)
-    {
-        hr = HRESULT_FROM_WIN32(ERROR_INSTALL_USEREXIT);
-    }
-    else
-    {
-        *pAction = results.action;
-    }
-
-LExit:
-    return hr;
-}
-
 EXTERN_C BAAPI UserExperienceOnRollbackMsiTransactionBegin(
     __in BURN_USER_EXPERIENCE* pUserExperience,
     __in LPCWSTR wzTransactionId
diff --git a/src/engine/userexperience.h b/src/engine/userexperience.h
index a1fb67a0..dd1fb086 100644
--- a/src/engine/userexperience.h
+++ b/src/engine/userexperience.h
@@ -126,8 +126,10 @@ BAAPI UserExperienceOnCacheAcquireBegin(
     __in BURN_USER_EXPERIENCE* pUserExperience,
     __in_z_opt LPCWSTR wzPackageOrContainerId,
     __in_z_opt LPCWSTR wzPayloadId,
-    __in BOOTSTRAPPER_CACHE_OPERATION operation,
-    __in_z LPCWSTR wzSource
+    __in_z LPWSTR* pwzSource,
+    __in_z LPWSTR* pwzDownloadUrl,
+    __in_z_opt LPCWSTR wzPayloadContainerId,
+    __out BOOTSTRAPPER_CACHE_OPERATION* pCacheOperation
     );
 BAAPI UserExperienceOnCacheAcquireComplete(
     __in BURN_USER_EXPERIENCE* pUserExperience,
@@ -144,6 +146,18 @@ BAAPI UserExperienceOnCacheAcquireProgress(
     __in DWORD64 dw64Total,
     __in DWORD dwOverallPercentage
     );
+BAAPI UserExperienceOnCacheAcquireResolving(
+    __in BURN_USER_EXPERIENCE* pUserExperience,
+    __in_z_opt LPCWSTR wzPackageOrContainerId,
+    __in_z_opt LPCWSTR wzPayloadId,
+    __in_z LPWSTR* rgSearchPaths,
+    __in DWORD cSearchPaths,
+    __in BOOL fFoundLocal,
+    __in DWORD* pdwChosenSearchPath,
+    __in_z_opt LPCWSTR wzDownloadUrl,
+    __in_z_opt LPCWSTR wzPayloadContainerId,
+    __inout BOOTSTRAPPER_CACHE_OPERATION* pCacheOperation
+    );
 BAAPI UserExperienceOnCacheBegin(
     __in BURN_USER_EXPERIENCE* pUserExperience
     );
@@ -426,14 +440,6 @@ BAAPI UserExperienceOnRegisterComplete(
     __in BURN_USER_EXPERIENCE* pUserExperience,
     __in HRESULT hrStatus
     );
-BAAPI UserExperienceOnResolveSource(
-    __in BURN_USER_EXPERIENCE* pUserExperience,
-    __in_z LPCWSTR wzPackageOrContainerId,
-    __in_z_opt LPCWSTR wzPayloadId,
-    __in_z LPCWSTR wzLocalSource,
-    __in_z_opt LPCWSTR wzDownloadSource,
-    __inout BOOTSTRAPPER_RESOLVESOURCE_ACTION* pAction
-    );
 BAAPI UserExperienceOnRollbackMsiTransactionBegin(
     __in BURN_USER_EXPERIENCE* pUserExperience,
     __in LPCWSTR wzTransactionId