convert erlfdb_error 2101 to transaction_too_large for main

[jiangphcn]

Overview

If transaction exceeds byte limit using the _bulk_docs endpoint, the {u'reason': u'2101', u'ref': 3853288219, u'error': u'erlfdb_error'} with 500 error code was returned. This is user-friendly. Using this PR is to provide meaningful error message to users.

Testing recommendations

The test python code:

import requests, json, random, string, os
print(requests.post(
    "https://127.0.0.1:15984/foo/_bulk_docs"
    , json={
        "docs":
            [
                {"foo": "".join(random.choice(string.ascii_lowercase) for x in range(16000000))}
            ]}
    , auth=('foo', 'bar')
).json())

Original response:

{u'reason': u'2101', u'ref': 3853288219, u'error': u'erlfdb_error'}

New response:

{u'reason': u'The request transaction is larger than 10MB', u'error': u'transaction_too_large'}

make elixir tests=test/elixir/test/bulk_docs_test.exs
make exunit tests=src/couchdb/test/elixir/test/bulk_docs_test.exs

BulkDocsTest
  * test bulk docs raises error for invlaid `docs` parameter (75.5ms)
  * test bulk docs supplies `id` if not provided in doc (38.9ms)
  * test bulk docs can detect conflicts (64.4ms)
  * test bulk docs raises error for invlaid `new_edits` parameter (13.3ms)
  * test bulk docs raises error for missing `docs` parameter (13.0ms)
  * test bulk docs raises transaction_too_large error for transaction larger than 10MB (1384.9ms)
  * test bulk docs raises error for `all_or_nothing` option (13.6ms)
  * test bulk docs raises conflict error for combined update & delete (40.6ms)
  * test bulk docs emits conflict error for duplicate doc `_id`s (23.2ms)
  * test bulk docs can create, update, & delete many docs per request (78.3ms)


Finished in 2.0 seconds
10 tests, 0 failures

Randomized with seed 913112

Related Issues or Pull Requests

#3215

Checklist

• Code is written and works correctly
• Changes are covered by tests
• Any new configurable parameters are documented in rel/overlay/etc/default.ini
• A PR for documentation changes has been made in https://github.com/apache/couchdb-documentation

[jiangphcn]

talked to @nickva before. He agrees that we can use +1 in #3215 (review) to merge this PR.

[nickva]

+1

Added just for completeness

[jiangphcn]

thanks @nickva