Add JSON output to check command

changelog/unreleased/issue-1378

@@ -0,0 +1,7 @@
+Enhancement: Add JSON support to check
+
+Restic `check` now also supports the `--json` option and gives all
+statistics in JSON format.
+
+https://github.com/restic/restic/issues/1378
+https://github.com/restic/restic/pull/5194

cmd/restic/cmd_check.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"context"
+	"fmt"
 	"math/rand"
 	"os"
 	"strconv"
@@ -215,7 +216,12 @@ func runCheck(ctx context.Context, opts CheckOptions, gopts GlobalOptions, args
 		return errors.Fatal("the check command expects no arguments, only options - please see `restic help check` for usage and flags")
 	}
 
-	printer := newTerminalProgressPrinter(gopts.verbosity, term)
+	var printer progress.Printer
+	if !gopts.JSON {
+		printer = newTerminalProgressPrinter(gopts.verbosity, term)
+	} else {
+		printer = newJSONErrorPrinter(term)
+	}
 
 	cleanup := prepareCheckCache(opts, &gopts, printer)
 	defer cleanup()
@@ -431,6 +437,13 @@ func runCheck(ctx context.Context, opts CheckOptions, gopts GlobalOptions, args
 		return errors.Fatal("repository contains errors")
 	}
 	printer.P("no errors were found\n")
+	if gopts.JSON {
+		status := checkSuccess{
+			MessageType: "checked",
+			Message:     "no errors were found",
+		}
+		term.Print(ui.ToJSONString(status))
+	}
 
 	return nil
 }
@@ -478,3 +491,38 @@ func selectRandomPacksByFileSize(allPacks map[restic.ID]int64, subsetSize int64,
 	packs := selectRandomPacksByPercentage(allPacks, subsetPercentage)
 	return packs
 }
+
+type checkSuccess struct {
+	MessageType string `json:"message_type"` // "checked"
+	Message     string `json:"message"`
+}
+
+type checkError struct {
+	MessageType string `json:"message_type"` // "error"
+	Message     string `json:"message"`
+}
+
+type jsonErrorPrinter struct {
+	term ui.Terminal
+}
+
+func newJSONErrorPrinter(term ui.Terminal) *jsonErrorPrinter {
+	return &jsonErrorPrinter{
+		term: term,
+	}
+}
+
+func (*jsonErrorPrinter) NewCounter(_ string) *progress.Counter {
+	return nil
+}
+
+func (p *jsonErrorPrinter) E(msg string, args ...interface{}) {
+	status := checkError{
+		MessageType: "error",
+		Message:     fmt.Sprintf(msg, args...),
+	}
+	p.term.Print(ui.ToJSONString(status))
+}
+func (*jsonErrorPrinter) P(_ string, _ ...interface{})  {}
+func (*jsonErrorPrinter) V(_ string, _ ...interface{})  {}
+func (*jsonErrorPrinter) VV(_ string, _ ...interface{}) {}

doc/075_scripting.rst

@@ -245,6 +245,18 @@ are stored in JSON form. Specifying ``--json``  or ``--quiet`` will suppress any
 non-JSON messages the command generates.
 
 
+check
+-----
+
+The ``check`` command outputs JSON messages with the following format:
+
++------------------+--------------------------------+
+| ``message_type`` | Either "checked" or "error"    |
++------------------+--------------------------------+
+| ``message``      | Descriptive message            |
++------------------+--------------------------------+
+
+
 diff
 ----