Allow stopping the parser via a channel

... this adds a new function to the LineProcessor interface

go.mod

@@ -1,8 +1,8 @@
-module github.com/tomachalek/vertigo/v3
+module github.com/tomachalek/vertigo/v4
 
 go 1.12
 
 require (
-	github.com/stretchr/testify v1.3.0
+	github.com/stretchr/testify v1.5.1
 	golang.org/x/text v0.3.2
 )

go.sum

@@ -2,9 +2,14 @@ github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0 h1:4G4v2dO3VZwixGIRoQ5Lfboy6nUhCyYzaqnIAPPhYs4=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
-github.com/stretchr/testify v1.3.0 h1:TivCn/peBQ7UY8ooIcPgZFpTNSz0Q2U6UrFlUfqbe0Q=
-github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
+github.com/stretchr/testify v1.5.1 h1:nOGnQDM7FYENwehXlg/kFVnos3rEvtKTjRvOWSzb6H4=
+github.com/stretchr/testify v1.5.1/go.mod h1:5W2xD1RspED5o8YsWQXVCued0rvSQ+mT+I5cxcmMvtA=
 golang.org/x/text v0.3.2 h1:tW2bmiBqwgJj/UpqtC8EpXEZVYOwU0yG4iWbprSVAcs=
 golang.org/x/text v0.3.2/go.mod h1:bEr9sfX3Q8Zfm5fL9x+3itogRgK3+ptLWKqgva+5dAk=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
+gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=

parser.go

@@ -104,10 +104,13 @@ type structAttrAccumulator interface {
 
 // --------------------------------------------------------
 
+// LineProcessor describes an object able to handle
+// Vertigo's parsing events.
 type LineProcessor interface {
 	ProcToken(token *Token, line int, err error)
 	ProcStruct(strc *Structure, line int, err error)
 	ProcStructClose(strc *StructureClose, line int, err error)
+	StopChannel() chan struct{}
 }
 
 // ----
@@ -255,6 +258,8 @@ func ParseVerticalFile(conf *ParserConf, lproc LineProcessor) error {
 	ch := make(chan []procItem)
 	errCh := make(chan error, 1)
 	chunk := make([]procItem, channelChunkSize)
+	stop := lproc.StopChannel()
+
 	go func() {
 		i := 0
 		progress := 0
@@ -282,6 +287,14 @@ func ParseVerticalFile(conf *ParserConf, lproc LineProcessor) error {
 			if progress%logProgressEachNth == 0 {
 				log.Printf("...processed %d lines.\n", progress)
 			}
+			select {
+			case <-stop:
+				log.Print("WARNING: Vertigo parser received a stop command")
+				errCh <- nil
+				close(ch)
+				return
+			default:
+			}
 		}
 		if i > 0 {
 			ch <- chunk[:i]