Restrict top output to container's pids only

Due to the way ps arguments work, it was possible to display pids
that dont below to the container in top output. We now filter pids
that dont belong to the container out of the output.  This also means
the pid column must be present in the output or we throw an error.

This resolves issue #391
Signed-off-by: baude <bbaude@redhat.com>

Closes: #400
Approved by: rhatdan

1 files changed, 52 insertions, 2 deletions

diff --git a/libpod/container_top.go b/libpod/container_top.go
index 3eb484acd..241e3a3e7 100644
--- a/libpod/container_top.go
+++ b/libpod/container_top.go
@@ -38,7 +38,7 @@ func (c *Container) getContainerPids() ([]string, error) {
 }
 
 // GetContainerPidInformation calls ps with the appropriate options and returns
-// the results as a string
+// the results as a string and the container's PIDs as a []string
 func (c *Container) GetContainerPidInformation(args []string) ([]string, error) {
 	if !c.locked {
 		c.lock.Lock()
@@ -57,5 +57,55 @@ func (c *Container) GetContainerPidInformation(args []string) ([]string, error)
 	if err != nil {
 		return []string{}, errors.Wrapf(err, "unable to obtain information about pids")
 	}
-	return strings.Split(results, "\n"), nil
+
+	filteredOutput, err := filterPids(results, pids)
+	if err != nil {
+		return []string{}, err
+	}
+	return filteredOutput, nil
+}
+
+func filterPids(psOutput string, pids []string) ([]string, error) {
+	var output []string
+	results := strings.Split(psOutput, "\n")
+	// The headers are in the first line of the results
+	headers := fieldsASCII(results[0])
+	// We need to make sure PID in headers, so that we can filter
+	// Pids that don't belong.
+
+	// append the headers back in
+	output = append(output, results[0])
+
+	pidIndex := -1
+	for i, header := range headers {
+		if header == "PID" {
+			pidIndex = i
+		}
+	}
+	if pidIndex == -1 {
+		return []string{}, errors.Errorf("unable to find PID field in ps output. try a different set of ps arguments")
+	}
+	for _, l := range results[1:] {
+		if l == "" {
+			continue
+		}
+		cols := fieldsASCII(l)
+		pid := cols[pidIndex]
+		if StringInSlice(pid, pids) {
+			output = append(output, l)
+		}
+	}
+	return output, nil
+}
+
+// Detects ascii whitespaces
+func fieldsASCII(s string) []string {
+	fn := func(r rune) bool {
+		switch r {
+		case '\t', '\n', '\f', '\r', ' ':
+			return true
+		}
+		return false
+	}
+	return strings.FieldsFunc(s, fn)
 }