ARROW-7934 : [C++] Fix UriEscape for empty string

[projjal]

No description provided.

[projjal]

@ursabot crossbow submit -g gandiva

[ursabot]

AMD64 Conda Crossbow Submit (#92476) builder has been succeeded.

Revision: b094c92

Submitted crossbow builds: ursa-labs/crossbow @ ursabot-538

Task	Status
gandiva-jar-osx
gandiva-jar-trusty

[github-actions]

https://issues.apache.org/jira/browse/ARROW-7934

[projjal]

This should fix the nightly gandiva-linux failure where arrow-uri test for UriEscape with empty string is failing. When s is empty, the local variable escaped and s both point to the same address, for the library implementation that is being used in the docker image in the build, thereby creating problems.

[bkietz]

Please add a test which fails without this change, or at least link to documentation indicating uriEscapeExA cannot accept an empty string.

[projjal]

Please add a test which fails without this change, or at least link to documentation indicating uriEscapeExA cannot accept an empty string.

There is already a test with empty string (

arrow/cpp/src/arrow/util/uri_test.cc

Line 33 in f3ac832

ASSERT_EQ(UriEscape(""), "");

). But it passes generally but fails only in the gandiva-trusty nightly build (https://travis-ci.org/ursa-labs/crossbow/builds/654801307) which runs inside a centos image with devtoolset 2

uriEscapeExA return NULL if both input and output pointers are same

arrow/cpp/src/arrow/vendored/uriparser/UriEscape.c

Line 84 in f3ac832

if ((out == NULL) || (inFirst == out)) {

In the next line in uri.cc, string.resize is called with the null argument which causes the error.

[pitrou]

Thanks for the explanation @projjal .

[pitrou]

+1