Add /compose/log/ API to retrieve the end of the build log

This allows the client to request the end of the anaconda.log during and
after a build. The amount of data returned can be set by adding
?size=<kbytes>

Output is raw bytes, starting on the next available line boundry.

src/pylorax/api/queue.py

@@ -408,3 +408,43 @@ def uuid_image(cfg, uuid):
     image_name = cfg_dict["image_name"]
 
     return (image_name, joinpaths(uuid_dir, image_name))
+
+def uuid_log(cfg, uuid, size=1024):
+    """Return `size` kbytes from the end of the anaconda.log
+
+    :param cfg: Configuration settings
+    :type cfg: ComposerConfig
+    :param uuid: The UUID of the build
+    :type uuid: str
+    :param size: Number of kbytes to read. Default is 1024
+    :type size: int
+    :returns: Up to `size` kbytes from the end of the log
+    :rtype: str
+
+    This function tries to return lines from the end of the log, it will
+    attempt to start on a line boundry, and may return less than `size` kbytes.
+    """
+    uuid_dir = joinpaths(cfg.get("composer", "lib_dir"), "results", uuid)
+    if not os.path.exists(uuid_dir):
+        raise RuntimeError("%s is not a valid build_id" % uuid)
+
+    # While a build is running the logs will be in /tmp/anaconda.log and when it
+    # has finished they will be in the results directory
+    status = uuid_status(cfg, uuid)
+    if status["queue_status"] == "RUNNING":
+        log_path = "/tmp/anaconda.log"
+    else:
+        log_path = joinpaths(uuid_dir, "logs", "anaconda", "anaconda.log")
+    if not os.path.exists(log_path):
+        raise RuntimeError("No anaconda.log available.")
+
+    with open(log_path, "r") as f:
+        f.seek(0, 2)
+        end = f.tell()
+        if end < 1024 * size:
+            f.seek(0, 0)
+        else:
+            f.seek(end - (1024 * size))
+        # Find the start of the next line and return the rest
+        f.readline()
+        return f.read()

src/pylorax/api/v0.py

@@ -833,6 +833,31 @@ DELETE `/api/v0/compose/delete/<uuids>`
   Returns the output image from the build. The filename is set to the filename
   from the build. eg. root.tar.xz or boot.iso.
 
+`/api/v0/compose/log/<uuid>[?size=kbytes]`
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+  Returns the end of the anaconda.log. The size parameter is optional and defaults to 1Mbytes
+  if it is not included. The returned data is raw text from the end of the logfile, starting on
+  a line boundry.
+
+  Example::
+
+      12:59:24,222 INFO anaconda: Running Thread: AnaConfigurationThread (140629395244800)
+      12:59:24,223 INFO anaconda: Configuring installed system
+      12:59:24,912 INFO anaconda: Configuring installed system
+      12:59:24,912 INFO anaconda: Creating users
+      12:59:24,913 INFO anaconda: Clearing libuser.conf at /tmp/libuser.Dyy8Gj
+      12:59:25,154 INFO anaconda: Creating users
+      12:59:25,155 INFO anaconda: Configuring addons
+      12:59:25,155 INFO anaconda: Configuring addons
+      12:59:25,155 INFO anaconda: Generating initramfs
+      12:59:49,467 INFO anaconda: Generating initramfs
+      12:59:49,467 INFO anaconda: Running post-installation scripts
+      12:59:49,467 INFO anaconda: Running kickstart %%post script(s)
+      12:59:50,782 INFO anaconda: All kickstart %%post script(s) have been run
+      12:59:50,782 INFO anaconda: Running post-installation scripts
+      12:59:50,784 INFO anaconda: Thread Done: AnaConfigurationThread (140629395244800)
+
 """
 
 import logging
@@ -845,7 +870,7 @@ from pylorax.api.crossdomain import crossdomain
 from pylorax.api.projects import projects_list, projects_info, projects_depsolve
 from pylorax.api.projects import modules_list, modules_info, ProjectsError
 from pylorax.api.queue import queue_status, build_status, uuid_delete, uuid_status, uuid_info
-from pylorax.api.queue import uuid_tar, uuid_image, uuid_cancel
+from pylorax.api.queue import uuid_tar, uuid_image, uuid_cancel, uuid_log
 from pylorax.api.recipes import list_branch_files, read_recipe_commit, recipe_filename, list_commits
 from pylorax.api.recipes import recipe_from_dict, recipe_from_toml, commit_recipe, delete_recipe, revert_recipe
 from pylorax.api.recipes import tag_recipe_commit, recipe_diff
@@ -1486,3 +1511,20 @@ def v0_api(api):
 
             # XXX - Will mime type guessing work for all our output?
             return send_file(image_path, as_attachment=True, attachment_filename=image_name, add_etags=False)
+
+    @api.route("/api/v0/compose/log/<uuid>")
+    @crossdomain(origin="*")
+    def v0_compose_log_tail(uuid):
+        """Return the end of the main anaconda.log, defaults to 1Mbytes"""
+        try:
+            size = int(request.args.get("size", "1024"))
+        except ValueError as e:
+            return jsonify(error={"msg":str(e)}), 400
+
+        status = uuid_status(api.config["COMPOSER_CFG"], uuid)
+        if status is None or status["queue_status"] == "WAITING":
+            return jsonify(status=False, uuid=uuid, msg="Build has not started yet. No logs to view")
+        try:
+            return Response(uuid_log(api.config["COMPOSER_CFG"], uuid, size), direct_passthrough=True)
+        except RuntimeError as e:
+            return jsonify(status=False, uuid=uuid, msg=str(e))