Support the containers.conf container_name_as_hostname option

When containers.conf has the "container_name_as_hostname" option set,
use that value, with values that don't fit `[A-Za-z0-9][A-Za-z0-9._-]+`
stripped out.

Signed-off-by: Nalin Dahyabhai <[email protected]>

Author: nalind

run_common.go

@@ -2092,3 +2092,28 @@ func relabel(path, mountLabel string, shared bool) error {
 	}
 	return nil
 }
+
+// mapContainerNameToHostname returns the passed-in string with characters that
+// don't match the pattern "[A-Za-z0-9][A-Za-z0-9._-]+" stripped out.
+func mapContainerNameToHostname(containerName string) string {
+	const initialAllowedChars = "abcdefghijklmnopqrstuvwxyz" + "ABCDEFGHIJKLMNOPQRSTUVWXYZ" + "0123456789"
+	const allowedChars = initialAllowedChars + "._-"
+	var mapped string
+	if containerName != "" {
+		mapped += strings.Map(func(r rune) rune {
+			if !strings.Contains(initialAllowedChars, string(r)) {
+				return -1
+			}
+			return r
+		}, containerName[:1])
+	}
+	if len(containerName) > 1 {
+		mapped += strings.Map(func(r rune) rune {
+			if !strings.Contains(allowedChars, string(r)) {
+				return -1
+			}
+			return r
+		}, containerName[1:])
+	}
+	return mapped
+}

run_freebsd.go

@@ -586,7 +586,17 @@ func (b *Builder) configureNamespaces(g *generate.Generator, options *RunOptions
 		} else if b.Hostname() != "" {
 			g.SetHostname(b.Hostname())
 		} else {
-			g.SetHostname(stringid.TruncateID(b.ContainerID))
+			hostname := stringid.TruncateID(b.ContainerID)
+			defConfig, err := config.Default()
+			if err != nil {
+				return false, "", fmt.Errorf("failed to get container config: %w", err)
+			}
+			if defConfig.Containers.ContainerNameAsHostName {
+				if mapped := mapContainerNameToHostname(b.Container); mapped != "" {
+					hostname = mapped
+				}
+			}
+			g.SetHostname(hostname)
 		}
 	} else {
 		g.SetHostname("")

run_linux.go

@@ -991,7 +991,17 @@ func (b *Builder) configureNamespaces(g *generate.Generator, options *RunOptions
 		} else if b.Hostname() != "" {
 			g.SetHostname(b.Hostname())
 		} else {
-			g.SetHostname(stringid.TruncateID(b.ContainerID))
+			hostname := stringid.TruncateID(b.ContainerID)
+			defConfig, err := config.Default()
+			if err != nil {
+				return false, "", fmt.Errorf("failed to get container config: %w", err)
+			}
+			if defConfig.Containers.ContainerNameAsHostName {
+				if mapped := mapContainerNameToHostname(b.Container); mapped != "" {
+					hostname = mapped
+				}
+			}
+			g.SetHostname(hostname)
 		}
 	} else {
 		g.SetHostname("")

tests/containers.conf

@@ -63,3 +63,7 @@ default_capabilities = [
 default_sysctls = [
     "net.ipv4.ping_group_range=0 0",
 ]
+
+# Use the container's name as its hostname, in preference over its ID.
+#
+container_name_as_hostname = true

tests/run.bats

@@ -997,3 +997,18 @@ _EOF
 	run_buildah ? bud --pull=false --layers .
         expect_output --substring -- "-c requires an argument"
 }
+
+@test "container_name_as_hostname" {
+  skip_if_no_runtime
+
+  _prefetch alpine
+
+  name=alpine-working-container-for-test
+  run_buildah from --name :"$name": --cidfile ${TEST_SCRATCH_DIR}/cid alpine
+  cid="$output"
+  export CONTAINERS_CONF=${TEST_SOURCES}/containers.conf
+  run_buildah run $cid hostname
+  expect_output "$name"
+  run_buildah run $(cat ${TEST_SCRATCH_DIR}/cid) hostname
+  expect_output "$name"
+}