From a3bede25fcbb5d39c070828ea2b4872d3c3f6792 Mon Sep 17 00:00:00 2001
From: Matthew Perry <perrygeo@gmail.com>
Date: Tue, 20 Sep 2016 11:31:34 -0400
Subject: [PATCH] rio overview branch logic, --ls opens readonly

---
 rasterio/rio/overview.py   | 16 ++++++++++------
 tests/test_rio_overview.py |  8 ++++++++
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/rasterio/rio/overview.py b/rasterio/rio/overview.py
index 32c5d210..656387bb 100644
--- a/rasterio/rio/overview.py
+++ b/rasterio/rio/overview.py
@@ -67,9 +67,8 @@ def overview(ctx, input, build, ls, rebuild, resampling):
 
     """
     with ctx.obj['env']:
-        with rasterio.open(input, 'r+') as dst:
-
-            if ls:
+        if ls:
+            with rasterio.open(input, 'r') as dst:
                 resampling_method = dst.tags(
                     ns='rio_overview').get('resampling') or 'unknown'
 
@@ -77,8 +76,8 @@ def overview(ctx, input, build, ls, rebuild, resampling):
                 for idx in dst.indexes:
                     click.echo("  Band %d: %s (method: '%s')" % (
                         idx, dst.overviews(idx) or 'None', resampling_method))
-
-            elif rebuild:
+        elif rebuild:
+            with rasterio.open(input, 'r+') as dst:
                 # Build the same overviews for all bands.
                 factors = reduce(
                     operator.or_,
@@ -91,8 +90,13 @@ def overview(ctx, input, build, ls, rebuild, resampling):
                 dst.build_overviews(
                     list(factors), Resampling[resampling_method])
 
-            elif build:
+        elif build:
+            with rasterio.open(input, 'r+') as dst:
                 dst.build_overviews(build, Resampling[resampling])
 
                 # Save the resampling method to a tag.
                 dst.update_tags(ns='rio_overview', resampling=resampling)
+
+        else:
+            raise click.UsageError(
+                "Please specify --ls, --rebuild, or --build ...")
diff --git a/tests/test_rio_overview.py b/tests/test_rio_overview.py
index 60efd731..9cee732f 100644
--- a/tests/test_rio_overview.py
+++ b/tests/test_rio_overview.py
@@ -66,3 +66,11 @@ def test_rebuild_ls(data):
 
     expected = "  Band 1: [2, 4, 8] (method: 'cubic')\n  Band 2: [2, 4, 8] (method: 'cubic')\n  Band 3: [2, 4, 8] (method: 'cubic')\n"
     assert result.output.endswith(expected)
+
+
+def test_no_args(data):
+    runner = CliRunner()
+    inputfile = str(data.join('RGB.byte.tif'))
+    result = runner.invoke(cli, ['overview', inputfile])
+    assert result.exit_code == 2
+    assert "Please specify --ls, --rebuild, or --build ..." in result.output