cashew: support additional usage API error result strings

cashew: support additional usage API error result strings

BUG=chromium-os:7728
TEST=Manual

Change-Id: I0cbf2f95605dff132ecb7f776b1d40e1925fbe4f

Committed: http://chrome-svn/viewvc/chromeos?view=rev&revision=fbf2e43

[Vince Laviano, 2010-10-15 00:36:05]

This CL enhances cashew to support a wider range of error result strings. I put
in a hook, OnCrosUsageErrorResult, where we can take action based on which error
string was returned. For now all errors are treated the same, and we take no
action other than generating a log message.

[Jason Glasgow, 2010-10-15 17:39:09]

LGTM

[Eric Shienbrood, 2010-10-15 18:43:18]

LGTM

http://codereview.chromium.org/3797006/diff/1/2
File src/service.cc (right):

http://codereview.chromium.org/3797006/diff/1/2#newcode60
src/service.cc:60: static const char *kCrosUsageStatusUnknownDevice = "UNKNOWN
DEVICE";
If you add a new status, you have to modify IsValidCrosUsageStatus() below. It
might be a bit less error prone to define an array of these strings, and have
IsValid search the array for the presence of the supplied string. Something to
keep in mind if you're working in this code in the future.

[Vince Laviano, 2010-10-15 20:25:12]

http://codereview.chromium.org/3797006/diff/1/2
File src/service.cc (right):

http://codereview.chromium.org/3797006/diff/1/2#newcode60
src/service.cc:60: static const char *kCrosUsageStatusUnknownDevice = "UNKNOWN
DEVICE";
On 2010/10/15 18:43:18, Eric Shienbrood wrote:
> If you add a new status, you have to modify IsValidCrosUsageStatus() below. It
> might be a bit less error prone to define an array of these strings, and have
> IsValid search the array for the presence of the supplied string. Something to
> keep in mind if you're working in this code in the future.

This is a good point.

Composing a rambling reply to your comment that I've since discarded (the gist
of which was "there would still be some duplication, so we should instead
generate code automatically from a single representation of the status codes")
led me to http://json-schema.org/ (xml-style schema validation for json). 

With a parser that supported this, we could get rid of most of the validation
code in Service::OnRequestComplete and in DataPlan::FromDictionaryValue,
including the code that needs IsValidCrosUsageStatus to exist.