From a1ce8e41033c69e6e32a465d5101177f7cd9cb50 Mon Sep 17 00:00:00 2001
From: Levin Alexander <levin.alexander@samedi.de>
Date: Thu, 11 Oct 2018 13:01:02 +0000
Subject: [PATCH 1/2] Forward unhandled escape sequences unchanged

Fixes parsing of HL7 Hex-Escape sequences (\X....\) and other variable-length escape sequences that are not handled by the parser code.

This will break with an array overflow in case escape sequences are not paired correctly.
---
 messageparser.go      |  7 +++++++
 messageparser_test.go | 19 ++++++++++++++++++-
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/messageparser.go b/messageparser.go
index c757a70..1d7ae4a 100644
--- a/messageparser.go
+++ b/messageparser.go
@@ -225,6 +225,13 @@ func unescape(b []byte, d *Delimiters) []byte {
 				r[j] = d.Escape
 				j++
 				r[j] = c
+				j++
+				i++
+				for ; b[i] != d.Escape; i++ {
+					r[j] = b[i]
+					j++
+				}
+				r[j] = d.Escape
 			}
 
 			j++
diff --git a/messageparser_test.go b/messageparser_test.go
index ec3bdc3..c4157d9 100644
--- a/messageparser_test.go
+++ b/messageparser_test.go
@@ -287,7 +287,7 @@ func TestParseSimpleContent(t *testing.T) {
 			Field{FieldItem{Component{"^~\\&"}}},
 			Field{FieldItem{Component{"field"}}},
 			Field{FieldItem{
-				Component{"\\|~^&\\X484559"},
+				Component{"\\|~^&\\X484559\\"},
 			}},
 			Field{FieldItem{
 				Component{"component1"},
@@ -321,6 +321,23 @@ func TestParseLiteralNewline(t *testing.T) {
 	}, m)
 }
 
+func TestParseTrailingHexEscapes(t *testing.T) {
+	a := assert.New(t)
+
+	m, d, err := ParseMessage([]byte(`MSH|^~\&|Foo\X41\|Bar\X42\Fred`))
+	a.NoError(err)
+	a.Equal(&Delimiters{'|', '^', '~', '\\', '&'}, d)
+	a.Equal(Message{
+		Segment{
+			Field{FieldItem{Component{`MSH`}}},
+			Field{FieldItem{Component{`|`}}},
+			Field{FieldItem{Component{`^~\&`}}},
+			Field{FieldItem{Component{`Foo\X41\`}}},
+			Field{FieldItem{Component{`Bar\X42\Fred`}}},
+		},
+	}, m)
+}
+
 func TestParseBad(t *testing.T) {
 	a := assert.New(t)
 

From 42a420207546ccda97498f4639f1c225a9f658c2 Mon Sep 17 00:00:00 2001
From: Levin Alexander <levin.alexander@samedi.de>
Date: Thu, 11 Oct 2018 15:28:08 +0200
Subject: [PATCH 2/2] Silently fix unpaired escape characters in parsing

---
 messageparser.go      |  4 ++--
 messageparser_test.go | 19 ++++++++++++++++++-
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/messageparser.go b/messageparser.go
index 1d7ae4a..7073860 100644
--- a/messageparser.go
+++ b/messageparser.go
@@ -197,7 +197,7 @@ func ParseMessage(buf []byte) (Message, *Delimiters, error) {
 }
 
 func unescape(b []byte, d *Delimiters) []byte {
-	r := make([]byte, len(b))
+	r := make([]byte, len(b)+1) // +1 to make room for possible unpaired escape character
 
 	j, e := 0, false
 	for i := 0; i < len(b); i++ {
@@ -227,7 +227,7 @@ func unescape(b []byte, d *Delimiters) []byte {
 				r[j] = c
 				j++
 				i++
-				for ; b[i] != d.Escape; i++ {
+				for ; i < len(b) && b[i] != d.Escape; i++ {
 					r[j] = b[i]
 					j++
 				}
diff --git a/messageparser_test.go b/messageparser_test.go
index c4157d9..7fd8992 100644
--- a/messageparser_test.go
+++ b/messageparser_test.go
@@ -321,7 +321,7 @@ func TestParseLiteralNewline(t *testing.T) {
 	}, m)
 }
 
-func TestParseTrailingHexEscapes(t *testing.T) {
+func TestParseHexEscapes(t *testing.T) {
 	a := assert.New(t)
 
 	m, d, err := ParseMessage([]byte(`MSH|^~\&|Foo\X41\|Bar\X42\Fred`))
@@ -338,6 +338,23 @@ func TestParseTrailingHexEscapes(t *testing.T) {
 	}, m)
 }
 
+func TestParseUnpairedInvalidHexEscapes(t *testing.T) {
+	a := assert.New(t)
+
+	m, d, err := ParseMessage([]byte(`MSH|^~\&|Foo\X41|Bar\X42\Fred`))
+	a.NoError(err)
+	a.Equal(&Delimiters{'|', '^', '~', '\\', '&'}, d)
+	a.Equal(Message{
+		Segment{
+			Field{FieldItem{Component{`MSH`}}},
+			Field{FieldItem{Component{`|`}}},
+			Field{FieldItem{Component{`^~\&`}}},
+			Field{FieldItem{Component{`Foo\X41\`}}},
+			Field{FieldItem{Component{`Bar\X42\Fred`}}},
+		},
+	}, m)
+}
+
 func TestParseBad(t *testing.T) {
 	a := assert.New(t)