Camera: Add methods for read-only access to metadata.

- Define a read-only version of camera_metadata_entry_t
- Support finding with read-only output
- Add const to clone method input camera_metadata_t.

Bug: 6243944
Change-Id: I1bf37a4c8c8935711e803d7477393fe2c01f8216
diff --git a/camera/src/camera_metadata.c b/camera/src/camera_metadata.c
index afbaac5..7bca3f4 100644
--- a/camera/src/camera_metadata.c
+++ b/camera/src/camera_metadata.c
@@ -123,6 +123,8 @@
 
 camera_metadata_t *allocate_camera_metadata(size_t entry_capacity,
                                             size_t data_capacity) {
+    if (entry_capacity == 0) return NULL;
+
     size_t memory_needed = calculate_camera_metadata_size(entry_capacity,
                                                           data_capacity);
     void *buffer = malloc(memory_needed);
@@ -280,8 +282,9 @@
     return OK;
 }
 
-camera_metadata_t *clone_camera_metadata(camera_metadata_t *src) {
+camera_metadata_t *clone_camera_metadata(const camera_metadata_t *src) {
     int res;
+    if (src == NULL) return NULL;
     camera_metadata_t *clone = allocate_camera_metadata(
         get_camera_metadata_entry_count(src),
         get_camera_metadata_data_count(src));
@@ -425,6 +428,14 @@
             entry);
 }
 
+int find_camera_metadata_ro_entry(const camera_metadata_t *src,
+        uint32_t tag,
+        camera_metadata_ro_entry_t *entry) {
+    return find_camera_metadata_entry((camera_metadata_t*)src, tag,
+            (camera_metadata_entry_t*)entry);
+}
+
+
 int delete_camera_metadata_entry(camera_metadata_t *dst,
         size_t index) {
     if (dst == NULL) return ERROR;
@@ -611,12 +622,13 @@
         int verbosity,
         int indentation) {
     if (metadata == NULL) {
-        ALOGE("%s: Metadata is null.", __FUNCTION__);
+        fdprintf(fd, "%*sDumping camera metadata array: Not allocated",
+                indentation, "");
         return;
     }
     unsigned int i;
     fdprintf(fd,
-            "%*sDumping camera metadata array. %d / %d entries, "
+            "%*sDumping camera metadata array: %d / %d entries, "
             "%d / %d bytes of extra data.\n", indentation, "",
             metadata->entry_count, metadata->entry_capacity,
             metadata->data_count, metadata->data_capacity);