Add new reading / parsing functions that take a Context object.

This will allow the caller to optionally cancel long-running parsing calls.

pkg/pdfcpu/model/parse.go

@@ -17,6 +17,7 @@ limitations under the License.
 package model
 
 import (
+	"context"
 	"encoding/hex"
 	"strconv"
 	"strings"
@@ -292,7 +293,7 @@ func ParseObjectAttributes(line *string) (objectNumber *int, generationNumber *i
 	return objectNumber, generationNumber, nil
 }
 
-func parseArray(line *string) (*types.Array, error) {
+func parseArray(c context.Context, line *string) (*types.Array, error) {
 	if log.ParseEnabled() {
 		log.Parse.Println("ParseObject: value = Array")
 	}
@@ -329,7 +330,7 @@ func parseArray(line *string) (*types.Array, error) {
 
 	for !strings.HasPrefix(l, "]") {
 
-		obj, err := ParseObject(&l)
+		obj, err := ParseObjectContext(c, &l)
 		if err != nil {
 			return nil, err
 		}
@@ -527,11 +528,15 @@ func parseName(line *string) (*types.Name, error) {
 	return &nameObj, nil
 }
 
-func processDictKeys(line *string, relaxed bool) (types.Dict, error) {
+func processDictKeys(c context.Context, line *string, relaxed bool) (types.Dict, error) {
 	l := *line
 	var eol bool
 	d := types.NewDict()
 	for !strings.HasPrefix(l, ">>") {
+		if err := c.Err(); err != nil {
+			return nil, err
+		}
+
 		key, err := parseName(&l)
 		if err != nil {
 			return nil, err
@@ -564,7 +569,7 @@ func processDictKeys(line *string, relaxed bool) (types.Dict, error) {
 			continue
 		}
 
-		obj, err := ParseObject(&l)
+		obj, err := ParseObjectContext(c, &l)
 		if err != nil {
 			return nil, err
 		}
@@ -597,7 +602,7 @@ func processDictKeys(line *string, relaxed bool) (types.Dict, error) {
 	return d, nil
 }
 
-func parseDict(line *string, relaxed bool) (types.Dict, error) {
+func parseDict(c context.Context, line *string, relaxed bool) (types.Dict, error) {
 	if line == nil || len(*line) == 0 {
 		return nil, errNoDictionary
 	}
@@ -623,7 +628,7 @@ func parseDict(line *string, relaxed bool) (types.Dict, error) {
 		return nil, errDictionaryNotTerminated
 	}
 
-	d, err := processDictKeys(&l, relaxed)
+	d, err := processDictKeys(c, &l, relaxed)
 	if err != nil {
 		return nil, err
 	}
@@ -829,7 +834,7 @@ func parseNumericOrIndRef(line *string) (types.Object, error) {
 	return parseIndRef(s, l, l1, line, i, i2, rangeErr)
 }
 
-func parseHexLiteralOrDict(l *string) (val types.Object, err error) {
+func parseHexLiteralOrDict(c context.Context, l *string) (val types.Object, err error) {
 	if len(*l) < 2 {
 		return nil, errBufNotAvailable
 	}
@@ -843,8 +848,8 @@ func parseHexLiteralOrDict(l *string) (val types.Object, err error) {
 			d   types.Dict
 			err error
 		)
-		if d, err = parseDict(l, false); err != nil {
-			if d, err = parseDict(l, true); err != nil {
+		if d, err = parseDict(c, l, false); err != nil {
+			if d, err = parseDict(c, l, true); err != nil {
 				return nil, err
 			}
 		}
@@ -892,6 +897,12 @@ func parseBooleanOrNull(l string) (val types.Object, s string, ok bool) {
 
 // ParseObject parses next Object from string buffer and returns the updated (left clipped) buffer.
 func ParseObject(line *string) (types.Object, error) {
+	return ParseObjectContext(context.Background(), line)
+}
+
+// ParseObjectContext parses next Object from string buffer and returns the updated (left clipped) buffer.
+// If the passed context is cancelled, parsing will be interrupted.
+func ParseObjectContext(c context.Context, line *string) (types.Object, error) {
 	if noBuf(line) {
 		return nil, errBufNotAvailable
 	}
@@ -915,7 +926,7 @@ func ParseObject(line *string) (types.Object, error) {
 	switch l[0] {
 
 	case '[': // array
-		a, err := parseArray(&l)
+		a, err := parseArray(c, &l)
 		if err != nil {
 			return nil, err
 		}
@@ -929,7 +940,7 @@ func ParseObject(line *string) (types.Object, error) {
 		value = *nameObj
 
 	case '<': // hex literal or dict
-		value, err = parseHexLiteralOrDict(&l)
+		value, err = parseHexLiteralOrDict(c, &l)
 		if err != nil {
 			return nil, err
 		}