Add PreValidate hook (#359)

Fix #332.

This adds a new "PreValidate" hook that is executed before checking
the backup location. This allows, for example, mounting a remote
source to make the directories of the location available.

"PreValidate" is added as a new hook to avoid any breakage that might
have been caused by changing the behaviour of the "before" hook.

Documentataion updates included.

README.md

@@ -34,7 +34,7 @@ Autorestic is a wrapper around the amazing [restic](https://restic.net/). While
 - Backup locations to multiple backends
 - Snapshot policies and pruning
 - Fully encrypted
-- Pre/After hooks
+- Before/after backup hooks
 - Exclude pattern/files
 - Cron jobs for automatic backup
 - Backup & Restore docker volume

docs/pages/config.md

@@ -56,6 +56,8 @@ version: 2
 
 extras:
   hooks: &foo
+    prevalidate:
+      - echo "Wake up!"
     before:
       - echo "Hello"
     after:

docs/pages/index.md

@@ -13,7 +13,7 @@ Autorestic is a wrapper around the amazing [restic](https://restic.net/). While
 - Backup locations to multiple backends
 - Snapshot policies and pruning
 - Fully encrypted
-- Pre/After hooks
+- Before/after backup hooks
 - Exclude pattern/files
 - Cron jobs for automatic backup
 - Backup & Restore docker volumes

docs/pages/location/hooks.md

@@ -6,23 +6,28 @@ They consist of a list of commands that will be executed in the same directory a
 
 The following hooks groups are supported, none are required:
 
+- `prevalidate`
 - `before`
 - `after`
 - `failure`
 - `success`
 
+The difference between `prevalidate` and `before` hooks are that `prevalidate` is run before checking the backup location is valid, including checking that the `from` directories exist. This can be useful, for example, to mount the source filesystem that contains the directories listed in `from`.
+
 ```yml | .autorestic.yml
 locations:
   my-location:
     from: /data
     to: my-backend
     hooks:
+      prevalidate:
+        - echo "Checks"
       before:
         - echo "One"
         - echo "Two"
         - echo "Three"
       after:
-        - echo "Byte"
+        - echo "Bye"
       failure:
         - echo "Something went wrong"
       success:
@@ -31,13 +36,15 @@ locations:
 
 ## Flowchart
 
-1. `before` hook
-2. Run backup
-3. `after` hook
-4. - `success` hook if no errors were found
+1. `prevalidate` hook
+2. Check backup location
+3. `before` hook
+4. Run backup
+5. `after` hook
+6. - `success` hook if no errors were found
    - `failure` hook if at least one error was encountered
 
-If the `before` hook encounters errors the backup and `after` hooks will be skipped and only the `failed` hooks will run.
+If either the `prevalidate` or `before` hook encounters errors then the backup and `after` hooks will be skipped and only the `failed` hooks will run.
 
 ## Environment variables
 

internal/config.go

@@ -132,6 +132,7 @@ func (c *Config) Describe() {
 
 		tmp = ""
 		hooks := map[string][]string{
+			"PreValidate": l.Hooks.PreValidate,
 			"Before":      l.Hooks.Before,
 			"After":       l.Hooks.After,
 			"Failure":     l.Hooks.Failure,

internal/location.go

@@ -34,6 +34,7 @@ const (
 
 type Hooks struct {
 	Dir         string    `mapstructure:"dir"`
+	PreValidate HookArray `mapstructure:"prevalidate,omitempty"`
 	Before      HookArray `mapstructure:"before,omitempty"`
 	After       HookArray `mapstructure:"after,omitempty"`
 	Success     HookArray `mapstructure:"success,omitempty"`
@@ -184,12 +185,18 @@ func (l Location) Backup(cron bool, specificBackend string) []error {
 		},
 	}
 
+	// Hooks before location validation
+	if err := l.ExecuteHooks(l.Hooks.PreValidate, options); err != nil {
+		errors = append(errors, err)
+		goto after
+	}
+
 	if err := l.validate(); err != nil {
 		errors = append(errors, err)
 		goto after
 	}
 
-	// Hooks
+	// Hooks after location validation
 	if err := l.ExecuteHooks(l.Hooks.Before, options); err != nil {
 		errors = append(errors, err)
 		goto after
@@ -289,12 +296,13 @@ func (l Location) Backup(cron bool, specificBackend string) []error {
 		}
 	}
 
-	// After hooks
+	// After backup hooks
 	if err := l.ExecuteHooks(l.Hooks.After, options); err != nil {
 		errors = append(errors, err)
 	}
 
 after:
+	// Success/failure hooks
 	var commands []string
 	var isSuccess = len(errors) == 0
 	if isSuccess {