apacheGH-36770: [C++] Use custom endpoint for s3 using environment va…

…riable AWS_ENDPOINT_URL (apache#36791)

### Rationale for this change
we need a way to read custom object storage (such as minio host or other s3-like storage).
use environment variable `AWS_ENDPOINT_URL `

### What changes are included in this PR?
set variable endpoint_override according the environment variable

### Are these changes tested?
unittest and tested on pyarrow

### Are there any user-facing changes?
No

* Closes: apache#36770

Authored-by: yiwei.wang <yiwei.wang@weride.ai>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>

cpp/src/arrow/filesystem/s3fs.cc

@@ -127,6 +127,7 @@ using internal::ToAwsString;
 using internal::ToURLEncodedAwsString;
 
 static const char kSep = '/';
+constexpr char kAwsEndpointUrlEnvVar[] = "AWS_ENDPOINT_URL";
 
 // -----------------------------------------------------------------------
 // S3ProxyOptions implementation
@@ -337,6 +338,10 @@ Result<S3Options> S3Options::FromUri(const Uri& uri, std::string* out_path) {
   } else {
     options.ConfigureDefaultCredentials();
   }
+  auto endpoint_env = arrow::internal::GetEnvVar(kAwsEndpointUrlEnvVar);
+  if (endpoint_env.ok()) {
+    options.endpoint_override = *endpoint_env;
+  }
 
   bool region_set = false;
   for (const auto& kv : options_map) {

cpp/src/arrow/filesystem/s3fs_test.cc

@@ -297,6 +297,13 @@ TEST_F(S3OptionsTest, FromUri) {
 
   // Invalid option
   ASSERT_RAISES(Invalid, S3Options::FromUri("s3://mybucket/?xxx=zzz", &path));
+
+  // Endpoint from environment variable
+  {
+    EnvVarGuard endpoint_guard("AWS_ENDPOINT_URL", "http://127.0.0.1:9000");
+    ASSERT_OK_AND_ASSIGN(options, S3Options::FromUri("s3://mybucket/", &path));
+    ASSERT_EQ(options.endpoint_override, "http://127.0.0.1:9000");
+  }
 }
 
 TEST_F(S3OptionsTest, FromAccessKey) {