*: raven is archived, long live sentry-go

I don't have sentry set up to test this, but it looks like it is
migrated correctly.

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

vendor/github.com/getsentry/sentry-go/sourcereader.go

@@ -0,0 +1,69 @@
+package sentry
+
+import (
+	"bytes"
+	"io/ioutil"
+	"sync"
+)
+
+type sourceReader struct {
+	mu    sync.Mutex
+	cache map[string][][]byte
+}
+
+func newSourceReader() sourceReader {
+	return sourceReader{
+		cache: make(map[string][][]byte),
+	}
+}
+
+func (sr *sourceReader) readContextLines(filename string, line, context int) ([][]byte, int) {
+	sr.mu.Lock()
+	defer sr.mu.Unlock()
+
+	lines, ok := sr.cache[filename]
+
+	if !ok {
+		data, err := ioutil.ReadFile(filename)
+		if err != nil {
+			sr.cache[filename] = nil
+			return nil, 0
+		}
+		lines = bytes.Split(data, []byte{'\n'})
+		sr.cache[filename] = lines
+	}
+
+	return sr.calculateContextLines(lines, line, context)
+}
+
+// `contextLine` points to a line that caused an issue itself, in relation to returned slice
+func (sr *sourceReader) calculateContextLines(lines [][]byte, line, context int) ([][]byte, int) {
+	// Stacktrace lines are 1-indexed, slices are 0-indexed
+	line--
+
+	contextLine := context
+
+	if lines == nil || line >= len(lines) || line < 0 {
+		return nil, 0
+	}
+
+	if context < 0 {
+		context = 0
+		contextLine = 0
+	}
+
+	start := line - context
+
+	if start < 0 {
+		contextLine += start
+		start = 0
+	}
+
+	end := line + context + 1
+
+	if end > len(lines) {
+		end = len(lines)
+	}
+
+	return lines[start:end], contextLine
+}