Harvest should handle HTTP 414 responses from REST endpoints

With the recent change (#2740) to send the exact list of counters, there is the possibility that a template with a large number of counters could hit ONTAP's request URI limit.

When that happens, the Harvest REST collector should revert to the fields=* logic.

Here's a Python script that makes a request that is the maximum request URI length - 1, followed by a request that is too large. This script will cause the following error to be printed.

<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>414 Request-URI Too Long</title>
</head><body>
<h1>Request-URI Too Long</h1>
<p>The requested URL's length exceeds the capacity
limit for this server.<br />
</p>
</body></html>

import base64
import http.client

host = "10.193.48.154"
user = "admin"
password = "password"

apache_max = 8 * 1024 # 8,192

conn = http.client.HTTPConnection(host)

# Create basic auth token
auth = user + ":" + password
auth = auth.encode("utf-8")
auth = base64.b64encode(auth).decode("utf-8")

headers = {
    "Authorization": f"Basic {auth}",
}

big = "a" * apache_max
url = "/api/cluster?fields=" + big

# The host + url can be at most apache_max characters
too_big = apache_max - len(host)
just_right = apache_max - len(host) - 1

# Send the just_right request.
# This will return a 400 since it is a bogus request, but that's OK
conn.request("GET", url[:just_right], headers=headers)
response = conn.getresponse()
data = response.read()

print("Status:", response.status)
print("Reason:", response.reason)
print("Data:", data.decode("utf-8"))

# Send the too_big request.
# This will fail with a 414
conn.request("GET", url[:too_big], headers=headers)
response = conn.getresponse()
data = response.read()

print("Status:", response.status)
print("Reason:", response.reason)
print("Data:", data.decode("utf-8"))

conn.close()

NetApp / harvest

Harvest should handle HTTP 414 responses from REST endpoints #3029