Add configurable sandbox storage path

src/app_win/ui.c

@@ -892,6 +892,7 @@ static void on_webview2_message(const wchar_t *json)
         wchar_t name_buf[256] = {0}, os_buf[32] = {0}, img_buf[MAX_PATH] = {0};
         wchar_t tpl_buf[256] = {0}, user_buf[128] = {0}, pass_buf[128] = {0};
         wchar_t adapter_buf[256] = {0};
+        wchar_t storage_buf[MAX_PATH] = {0};
         int val;
         BOOL is_tpl = FALSE;
 
@@ -902,6 +903,7 @@ static void on_webview2_message(const wchar_t *json)
         json_get_string(json, L"adminUser", user_buf, 128);
         json_get_string(json, L"adminPass", pass_buf, 128);
         json_get_string(json, L"netAdapter", adapter_buf, 256);
+        json_get_string(json, L"storageFolder", storage_buf, MAX_PATH);
         json_get_bool(json, L"isTemplate", &is_tpl);
 
         ZeroMemory(&cfg, sizeof(cfg));
@@ -912,6 +914,7 @@ static void on_webview2_message(const wchar_t *json)
         cfg.username = user_buf;
         cfg.password = pass_buf;
         cfg.net_adapter = adapter_buf;
+        cfg.storage_folder = storage_buf;
         cfg.is_template = is_tpl;
 
         if (json_get_int(json, L"hddGb", &val)) cfg.hdd_gb = (DWORD)val;
@@ -1074,6 +1077,67 @@ static void on_webview2_message(const wchar_t *json)
             jb_object_end(&jb);
             webview2_post(json_buf);
         }
+    } else if (wcscmp(action, L"browseStorageFolder") == 0) {
+        IFileOpenDialog *dlg = NULL;
+        if (SUCCEEDED(CoCreateInstance(&CLSID_FileOpenDialog, NULL, CLSCTX_ALL,
+                                       &IID_IFileOpenDialog, (void **)&dlg))) {
+            DWORD opts = 0;
+            dlg->lpVtbl->GetOptions(dlg, &opts);
+            dlg->lpVtbl->SetOptions(dlg, opts | FOS_PICKFOLDERS | FOS_FORCEFILESYSTEM);
+            dlg->lpVtbl->SetTitle(dlg, L"Choose storage folder");
+            if (SUCCEEDED(dlg->lpVtbl->Show(dlg, g_hwnd_main))) {
+                IShellItem *item = NULL;
+                if (SUCCEEDED(dlg->lpVtbl->GetResult(dlg, &item))) {
+                    PWSTR path = NULL;
+                    if (SUCCEEDED(item->lpVtbl->GetDisplayName(item, SIGDN_FILESYSPATH, &path))) {
+                        wchar_t json_buf[MAX_PATH + 128];
+                        JsonBuilder jb;
+                        jb_init(&jb, json_buf, _countof(json_buf));
+                        jb_object_begin(&jb);
+                        jb_string(&jb, L"type", L"storageFolderPicked");
+                        jb_string(&jb, L"path", path);
+                        jb_object_end(&jb);
+                        webview2_post(json_buf);
+                        CoTaskMemFree(path);
+                    }
+                    item->lpVtbl->Release(item);
+                }
+            }
+            dlg->lpVtbl->Release(dlg);
+        }
+    } else if (wcscmp(action, L"getDriveFreeSpace") == 0) {
+        wchar_t path_buf[MAX_PATH] = {0};
+        ULARGE_INTEGER free_bytes = { 0 };
+        wchar_t root[4] = {0};
+        wchar_t json_buf[MAX_PATH + 128];
+        JsonBuilder jb;
+
+        json_get_string(json, L"path", path_buf, MAX_PATH);
+        if (path_buf[0] == 0) return;
+
+        /* Derive drive root: e.g. "R:\sandboxes" -> "R:\" */
+        if (wcslen(path_buf) >= 2 && path_buf[1] == L':') {
+            root[0] = path_buf[0]; root[1] = L':'; root[2] = L'\\'; root[3] = 0;
+        } else {
+            return; /* not an absolute path; JS will catch this */
+        }
+
+        if (!GetDiskFreeSpaceExW(root, &free_bytes, NULL, NULL)) return;
+
+        jb_init(&jb, json_buf, _countof(json_buf));
+        jb_object_begin(&jb);
+        jb_string(&jb, L"type", L"driveFreeSpace");
+        jb_string(&jb, L"path", path_buf);
+        /* JsonBuilder has only jb_int (32-bit). Serialize uint64 as a decimal
+           string so JS can Number() it without precision loss (Number handles
+           integers up to 2^53 safely). */
+        {
+            wchar_t num[32];
+            _snwprintf_s(num, _countof(num), _TRUNCATE, L"%llu", free_bytes.QuadPart);
+            jb_string(&jb, L"freeBytes", num);
+        }
+        jb_object_end(&jb);
+        webview2_post(json_buf);
     } else if (wcscmp(action, L"snapTake") == 0) {
         int vi;
         wchar_t sname[128] = {0};

src/backend_win/asb_core.c

@@ -2599,6 +2599,79 @@ ASB_API void asb_detach(void)
     g_initialized = FALSE;
 }
 
+/* Validate a user-supplied storage folder, and (as a side effect) create
+   the target sandbox folder if it doesn't exist. Returns S_OK if OK or
+   empty; E_INVALIDARG with an asb_log explanation on failure. Empty folder
+   is OK (caller falls through to the default ProgramData path). Creates
+   parent directories recursively via SHCreateDirectoryExW so multi-level
+   paths like R:\new\nested\sandboxes work in one call. The later
+   single-level CreateDirectoryW in asb_vm_create still runs but is then
+   a harmless redundant call (returns ERROR_ALREADY_EXISTS, ignored). */
+static HRESULT validate_storage_folder(const wchar_t *folder, const wchar_t *vm_name)
+{
+    wchar_t root[4];
+    wchar_t target_disk[MAX_PATH];
+    UINT drive_type;
+    DWORD attrs;
+    int sh_rc;
+
+    if (!folder || !folder[0]) return S_OK;  /* empty = use default; nothing to validate */
+
+    /* 1. Absolute Windows path: <letter>:\... */
+    if (wcslen(folder) < 3 ||
+        !((folder[0] >= L'A' && folder[0] <= L'Z') || (folder[0] >= L'a' && folder[0] <= L'z')) ||
+        folder[1] != L':' || folder[2] != L'\\') {
+        asb_log(L"Error: Storage folder must be an absolute path like R:\\sandboxes (got: %s)", folder);
+        return E_INVALIDARG;
+    }
+
+    /* 2. Drive is a local fixed volume. */
+    root[0] = folder[0]; root[1] = L':'; root[2] = L'\\'; root[3] = L'\0';
+    drive_type = GetDriveTypeW(root);
+    if (drive_type != DRIVE_FIXED) {
+        asb_log(L"Error: Storage folder must be on a local fixed drive, not network/removable (%s, type=%u)",
+                root, drive_type);
+        return E_INVALIDARG;
+    }
+
+    /* 3. Combined path fits in MAX_PATH. The downstream construction is
+       <folder>\<name>\disk.vhdx — 11 fixed chars (separator + "\\disk.vhdx").
+       Reject early so swprintf_s never silently empties the buffer. */
+    if (wcslen(folder) + wcslen(vm_name) + 11 >= MAX_PATH) {
+        asb_log(L"Error: Storage folder path is too long; folder + sandbox name + \\disk.vhdx must fit in %d characters.",
+                MAX_PATH);
+        return E_INVALIDARG;
+    }
+
+    /* 4. The target sandbox folder is creatable (recursively). Use
+       SHCreateDirectoryExW so that something like R:\new\nested\path\<name>
+       gets all intermediate levels created in one call. Treat
+       ERROR_FILE_EXISTS / ERROR_ALREADY_EXISTS as success. */
+    {
+        wchar_t target_dir[MAX_PATH];
+        swprintf_s(target_dir, MAX_PATH, L"%s\\%s", folder, vm_name);
+        sh_rc = SHCreateDirectoryExW(NULL, target_dir, NULL);
+        if (sh_rc != ERROR_SUCCESS &&
+            sh_rc != ERROR_FILE_EXISTS &&
+            sh_rc != ERROR_ALREADY_EXISTS) {
+            asb_log(L"Error: Can't create storage folder %s (Win32 error %d)",
+                    target_dir, sh_rc);
+            return E_INVALIDARG;
+        }
+    }
+
+    /* 5. No existing disk.vhdx at the target sandbox folder. */
+    swprintf_s(target_disk, MAX_PATH, L"%s\\%s\\disk.vhdx", folder, vm_name);
+    attrs = GetFileAttributesW(target_disk);
+    if (attrs != INVALID_FILE_ATTRIBUTES) {
+        asb_log(L"Error: A sandbox already exists at %s. Pick a different folder or sandbox name.",
+                target_disk);
+        return E_INVALIDARG;
+    }
+
+    return S_OK;
+}
+
 /* ---- VM Create ---- */
 
 ASB_API HRESULT asb_vm_create(const AsbVmConfig *config)
@@ -2627,6 +2700,7 @@ ASB_API HRESULT asb_vm_create(const AsbVmConfig *config)
     if (config->image_path) wcscpy_s(cfg.image_path, MAX_PATH, config->image_path);
     if (config->username) wcscpy_s(cfg.admin_user, 128, config->username);
     if (config->password) wcscpy_s(cfg.admin_pass, 128, config->password);
+    if (config->storage_folder) wcscpy_s(cfg.storage_folder, MAX_PATH, config->storage_folder);
     cfg.ram_mb = config->ram_mb;
     cfg.hdd_gb = config->hdd_gb;
     cfg.cpu_cores = config->cpu_cores;
@@ -2644,6 +2718,12 @@ ASB_API HRESULT asb_vm_create(const AsbVmConfig *config)
     is_template_create = config->is_template;
     cfg.is_template = is_template_create;
 
+    /* Validate user-supplied storage folder (if any). Empty folder is OK. */
+    if (!is_template_create) {
+        HRESULT vhr = validate_storage_folder(cfg.storage_folder, cfg.name);
+        if (FAILED(vhr)) return vhr;
+    }
+
     /* Defaults */
     if (cfg.hdd_gb == 0) cfg.hdd_gb = 64;
     if (cfg.ram_mb == 0) cfg.ram_mb = 4096;
@@ -2750,10 +2830,15 @@ ASB_API HRESULT asb_vm_create(const AsbVmConfig *config)
         CreateDirectoryW(vhdx_dir, NULL);
 
         if (is_template_create) {
+            /* Templates always live host-wide in ProgramData. */
             swprintf_s(vhdx_dir, MAX_PATH, L"%s\\AppSandbox\\templates", base_dir);
             CreateDirectoryW(vhdx_dir, NULL);
             swprintf_s(vhdx_dir, MAX_PATH, L"%s\\AppSandbox\\templates\\%s", base_dir, cfg.name);
+        } else if (cfg.storage_folder[0]) {
+            /* User-chosen folder: <storage_folder>\<name>. */
+            swprintf_s(vhdx_dir, MAX_PATH, L"%s\\%s", cfg.storage_folder, cfg.name);
         } else {
+            /* Default: %ProgramData%\AppSandbox\<name>. */
             swprintf_s(vhdx_dir, MAX_PATH, L"%s\\AppSandbox\\%s", base_dir, cfg.name);
         }
     }

src/backend_win/asb_core.h

@@ -62,6 +62,10 @@ typedef struct {
     BOOL   ssh_enabled;            /* TRUE = install OpenSSH Server in guest */
     BOOL   ssh_deploy_key;         /* TRUE = deploy the AppSandbox public key (needs ssh_enabled) */
     BOOL   is_template;            /* TRUE = create as template VM */
+    /* Optional: folder under which `<storage_folder>\<name>\disk.vhdx` will
+       live. NULL or empty = use default `%ProgramData%\AppSandbox\<name>\`.
+       Ignored for templates (which always live in ProgramData). Windows only. */
+    const wchar_t *storage_folder;
 } AsbVmConfig;
 
 /* ---- Snapshot/branch info (returned by query functions) ---- */

src/backend_win/hcs_vm.h

@@ -34,6 +34,7 @@ typedef struct {
     wchar_t os_type[32];          /* L"Windows" or L"Linux" */
     wchar_t image_path[MAX_PATH]; /* ISO path */
     wchar_t vhdx_path[MAX_PATH];  /* will be created if doesn't exist */
+    wchar_t storage_folder[MAX_PATH]; /* empty = default; transient, not persisted */
     DWORD   ram_mb;
     DWORD   hdd_gb;
     DWORD   cpu_cores;