Fix snap_package bugs

First and foremost this fixes the bug in which #8827 where
`snap_package` hangs forever.

See the comment in the code for the nitty-gritty details, but snap never
returns an EOF so you have to jump through GREAT hoops not to hang
forever.

UNLESS you want to use nonblock+read, but it takes MUCH longer:

```
[phil@ldt-hardwired ~]$ time /tmp/test.rb char

real	0m0.252s
user	0m0.207s
sys	0m0.044s
[phil@ldt-hardwired ~]$ time /tmp/test.rb select

real	0m5.244s
user	0m0.183s
sys	0m0.056s
```

That's just for doing `GET /v2/snaps/black`

Second, if you try to install a snap that doesn't exist on the `stable`
channel then Chef crashes with a `undefined method [] on nil`, so let's
check for that explicitly.

And a bunch of other fixes that were required to even install anything:

* prevent get_current_versions from returning `[nil]`
* don't try to 'update' when something is not yet installed
* don't try to install versions, install packages
* don't try to push ruby hashes into HTTP without JSONing them first
* when installing, install one at a time, it's the only API that accepts a channel
* options is an array, not a hash

NOTE... there's a lot of janky here. A lot. It's the minimalist stuff
from #9106 I could pull in, while also making the socket stuff not
painfully slow. That PR aims to support versions and lots of other and
should be fixed up and [eventually] merged... but in the meantime this
provider doesn't even come close to working and this at least gets
packages installing.

After this, I never want to touch snap again.

Signed-off-by: Phil Dibowitz <phil@ipom.com>

1 files changed, 96 insertions, 28 deletions

diff --git a/lib/chef/provider/package/snap.rb b/lib/chef/provider/package/snap.rb
index 1e4d6102b9..7fdedd0078 100644
--- a/lib/chef/provider/package/snap.rb
+++ b/lib/chef/provider/package/snap.rb
@@ -59,15 +59,14 @@ class Chef
         def get_current_versions
           package_name_array.each_with_index.map do |pkg, i|
             installed_version(i)
-          end
+          end.compact
         end
 
         def install_package(names, versions)
           if new_resource.source
             install_snap_from_source(names, new_resource.source)
           else
-            resolved_names = names.each_with_index.map { |name, i| available_version(i).to_s unless name.nil? }
-            install_snaps(resolved_names)
+            install_snaps(names)
           end
         end
 
@@ -75,14 +74,16 @@ class Chef
           if new_resource.source
             install_snap_from_source(names, new_resource.source)
           else
-            resolved_names = names.each_with_index.map { |name, i| available_version(i).to_s unless name.nil? }
-            update_snaps(resolved_names)
+            if get_current_versions.empty?
+              install_snaps(names, versions)
+            else
+              update_snaps(names)
+            end
           end
         end
 
         def remove_package(names, versions)
-          resolved_names = names.each_with_index.map { |name, i| installed_version(i).to_s unless name.nil? }
-          uninstall_snaps(resolved_names)
+          uninstall_snaps(names)
         end
 
         alias purge_package remove_package
@@ -129,19 +130,72 @@ class Chef
             "Accept: application/json\r\n" +
             "Content-Type: application/json\r\n"
           if method == "POST"
-            request.concat("Content-Length: #{post_data.bytesize}\r\n\r\n#{post_data}")
+            pdata = post_data.to_json.to_s
+            request.concat("Content-Length: #{pdata.bytesize}\r\n\r\n#{pdata}")
           end
           request.concat("\r\n")
-          # While it is expected to allow clients to connect using HTTPS over a TCP socket,
-          # at this point only a UNIX socket is supported. The socket is /run/snapd.socket
-          # Note - UNIXSocket is not defined on windows systems
+
+          # while it is expected to allow clients to connect using https over
+          # a tcp socket, at this point only a unix socket is supported. the
+          # socket is /run/snapd.socket note - unixsocket is not defined on
+          # windows systems
           if defined?(::UNIXSocket)
-            UNIXSocket.open("/run/snapd.socket") do |socket|
-              # Send request, read the response, split the response and parse the body
-              socket.print(request)
-              response = socket.read
-              headers, body = response.split("\r\n\r\n", 2)
-              JSON.parse(body)
+            UNIXSocket.open('/run/snapd.socket') do |socket|
+              # send request, read the response, split the response and parse
+              # the body
+              socket.write(request)
+
+              # WARNING!!! HERE BE DRAGONs
+              #
+              # So snapd doesn't return an EOF at the end of its body, so
+              # doing a normal read will just hang forever.
+              #
+              # Well, sort of. if, after it writes everything, you then send
+              # yet-another newline, it'll then send its EOF and promptly
+              # disconnect closing the pipe and preventing reading. so, you
+              # have to read first, and therein lies the EOF problem.
+              #
+              # So you can do non-blocking reads with selects, but it
+              # makes every read take about 5 seconds. If, instead, we
+              # read the last line char-by-char, it's about half a second.
+              #
+              # Reading a character at a time isn't efficient, and since we
+              # know that http headers always have a blank line after them,
+              # we can read lines until we find a blank line and *then* read
+              # a character at a time. snap returns all the json on a single
+              # line, so once you pass headers you must read a character a
+              # time.
+              #
+              # - jaymzh
+
+              Chef::Log.trace(
+                "snap_package[#{new_resource.package_name}]: reading headers",
+              )
+              loop do
+                response = socket.readline
+                break if response.strip.empty? # finished headers
+              end
+              Chef::Log.trace(
+                "snap_package[#{new_resource.package_name}]: past headers, " +
+                'onto the body...',
+              )
+              result = nil
+              body = ''
+              socket.each_char do |c|
+                body << c
+                # we know we're not done if we don't have a char that
+                # can end JSON
+                next unless ['}', ']'].include?(c)
+                begin
+                  result = JSON.parse(body)
+                  # if we get here, we were able to parse the json so we
+                  # are done reading
+                  break
+                rescue JSON::ParserError
+                  next
+                end
+              end
+              result
             end
           end
         end
@@ -211,20 +265,22 @@ class Chef
           response.error!
         end
 
-        def install_snaps(snap_names)
-          response = post_snaps(snap_names, "install", new_resource.channel, new_resource.options)
-          id = get_id_from_async_response(response)
-          wait_for_completion(id)
+        def install_snaps(snap_names, versions)
+          snap_names.each do |snap|
+            response = post_snap(snap, "install", new_resource.channel, new_resource.options)
+            id = get_id_from_async_response(response)
+            wait_for_completion(id)
+          end
         end
 
         def update_snaps(snap_names)
-          response = post_snaps(snap_names, "refresh", new_resource.channel, new_resource.options)
+          response = post_snaps(snap_names, "refresh", nil, new_resource.options)
           id = get_id_from_async_response(response)
           wait_for_completion(id)
         end
 
         def uninstall_snaps(snap_names)
-          response = post_snaps(snap_names, "remove", new_resource.channel, new_resource.options)
+          response = post_snaps(snap_names, "remove", nil, new_resource.options)
           id = get_id_from_async_response(response)
           wait_for_completion(id)
         end
@@ -278,18 +334,20 @@ class Chef
               "action" => action,
               "snaps" => snap_names,
           }
-          if %w{install refresh switch}.include?(action)
+          if %w{install refresh switch}.include?(action) && channel
             request["channel"] = channel
           end
 
           # No defensive handling of params
           # Snap will throw the proper exception if called improperly
           # And we can provide that exception to the end user
-          request["classic"] = true if options["classic"]
-          request["devmode"] = true if options["devmode"]
-          request["jailmode"] = true if options["jailmode"]
+          if options
+            request["classic"] = true if options.include?("classic")
+            request["devmode"] = true if options.include?("devmode")
+            request["jailmode"] = true if options.include?("jailmode")
+            request["ignore_validation"] = true if options.include?("ignore-validation")
+          end
           request["revision"] = revision unless revision.nil?
-          request["ignore_validation"] = true if options["ignore-validation"]
           request
         end
 
@@ -305,12 +363,22 @@ class Chef
           call_snap_api("POST", "/v2/snaps", json)
         end
 
+        def post_snap(snap_name, action, channel, options, revision = nil)
+          json = generate_snap_json(snap_name, action, channel, options, revision = nil)
+          json.delete("snaps")
+          call_snap_api("POST", "/v2/snaps/#{snap_name}", json)
+        end
+
         def get_latest_package_version(name, channel)
           json = call_snap_api("GET", "/v2/find?name=#{name}")
           if json["status-code"] != 200
             raise Chef::Exceptions::Package, json["result"], caller
           end
 
+          unless json["result"][0]["channels"]["latest/#{channel}"]
+            raise Chef::Exceptions::Package, "No version of #{name} in channel #{channel}", caller
+          end
+
           # Return the version matching the channel
           json["result"][0]["channels"]["latest/#{channel}"]["version"]
         end