[BUILD] Align ext headers with CMake install set

Narrow //ext:headers to the four headers installed by CMake and add
internal targets for the remaining curl, client detail, and server
headers. Update direct consumers so implementation-only dependencies do
not propagate transitively.

This brings the Bazel surface in line with the CMake package introduced
in #4327 and closes #4625.

Author: ParthibanRajasekaran

CHANGELOG.md

@@ -15,6 +15,22 @@ Increment the:
 
 ## [Unreleased]
 
+* [BUILD] Narrow the `//ext:headers` Bazel target to the four headers the
+  CMake package installs, and add internal targets for the rest
+  [#4634](https://github.com/open-telemetry/opentelemetry-cpp/pull/4634)
+  * `//ext:headers` now exposes only the four that `ext/CMakeLists.txt`
+    installs: `http/client/http_client.h`,
+    `http/client/http_client_factory.h`,
+    `http/client/curl/http_client_factory_curl.h` and
+    `http/common/url_parser.h`.
+  * Code that included any of the other six moves to an internal target:
+    `//ext:curl_implementation_headers` or `//ext:http_client_detail` in
+    `implementation_deps`, and `//ext:server_headers` for tests and examples.
+  * CMake narrowed to the same four in #4327, which first shipped in 1.29.0.
+    A CMake consumer of the other six lost them there, so this change brings
+    the Bazel surface in line rather than removing anything CMake still
+    installs.
+
 * [CODE HEALTH] Prevent `std::out_of_range` escaping `noexcept` substr callers.
   [#4562](https://github.com/open-telemetry/opentelemetry-cpp/pull/4562)
 

examples/http/BUILD

@@ -39,6 +39,7 @@ cc_binary(
         "//api",
         "//exporters/ostream:ostream_span_exporter",
         "//ext:headers",
+        "//ext:server_headers",
         "//sdk/src/trace",
     ],
 )

exporters/elasticsearch/BUILD

@@ -16,6 +16,9 @@ cc_library(
         "include/opentelemetry/exporters/elasticsearch/es_log_record_exporter.h",
         "include/opentelemetry/exporters/elasticsearch/es_log_recordable.h",
     ],
+    implementation_deps = [
+        "//ext:http_client_detail",
+    ],
     linkopts = select({
         "//bazel:windows": [
             "-DEFAULTLIB:advapi32.lib",

exporters/otlp/BUILD

@@ -212,6 +212,9 @@ cc_library(
     copts = [
         "-DCURL_STATICLIB",
     ],
+    implementation_deps = [
+        "//ext:http_client_detail",
+    ],
     linkopts = select({
         "//bazel:windows": [
             "-DEFAULTLIB:advapi32.lib",
@@ -804,6 +807,7 @@ cc_test(
     deps = [
         ":otlp_http_exporter",
         "//api",
+        "//ext:server_headers",
         "//sdk/src/metrics",
         "//test_common/src/http/client/nosend:http_client_nosend",
         "@com_google_googletest//:gtest_main",

exporters/zipkin/BUILD

@@ -37,6 +37,9 @@ cc_library(
     copts = [
         "-DCURL_STATICLIB",
     ],
+    implementation_deps = [
+        "//ext:http_client_detail",
+    ],
     strip_include_prefix = "include",
     tags = ["zipkin"],
     deps = [
@@ -68,6 +71,7 @@ cc_test(
     deps = [
         ":zipkin_exporter",
         ":zipkin_recordable",
+        "//ext:curl_implementation_headers",
         "//test_common/src/http/client/nosend:http_client_nosend",
         "@com_google_googletest//:gtest_main",
     ],

ext/BUILD

@@ -5,13 +5,83 @@ load("@rules_cc//cc:cc_library.bzl", "cc_library")
 
 package(default_visibility = ["//visibility:public"])
 
+# Headers installed by CMake and exposed to Bazel consumers
 cc_library(
     name = "headers",
-    hdrs = glob(["include/**/*.h"]),
+    hdrs = [
+        "include/opentelemetry/ext/http/client/curl/http_client_factory_curl.h",
+        "include/opentelemetry/ext/http/client/http_client.h",
+        "include/opentelemetry/ext/http/client/http_client_factory.h",
+        "include/opentelemetry/ext/http/common/url_parser.h",
+    ],
+    strip_include_prefix = "include",
+    deps = [
+        "//api",
+    ],
+)
+
+# Internal: curl implementation headers
+# Used by: the curl client itself, its tests, and the w3c test server
+# These are implementation details and are not installed by CMake
+cc_library(
+    name = "curl_implementation_headers",
+    hdrs = [
+        "include/opentelemetry/ext/http/client/curl/http_client_curl.h",
+        "include/opentelemetry/ext/http/client/curl/http_operation_curl.h",
+        "include/opentelemetry/ext/http/client/curl/http_time_util.h",
+    ],
+    strip_include_prefix = "include",
+    visibility = [
+        "//exporters/zipkin:__pkg__",
+        "//ext/src/http/client/curl:__pkg__",
+        "//ext/test/http:__pkg__",
+        "//ext/test/w3c_tracecontext_http_test_server:__pkg__",
+    ],
+    deps = [
+        ":headers",
+        "@curl",
+    ],
+)
+
+# Internal: Detail headers for factory implementations
+# Used by: exporters/otlp, exporters/elasticsearch, exporters/zipkin
+cc_library(
+    name = "http_client_detail",
+    hdrs = [
+        "include/opentelemetry/ext/http/client/detail/default_factory.h",
+    ],
+    strip_include_prefix = "include",
+    visibility = [
+        "//exporters/elasticsearch:__pkg__",
+        "//exporters/otlp:__pkg__",
+        "//exporters/zipkin:__pkg__",
+    ],
+    deps = [
+        ":headers",
+    ],
+)
+
+# Internal: Embedded HTTP server headers (test and example use only)
+# TODO: Move to test_common per issue #4332
+# These are test infrastructure, not part of the public API
+cc_library(
+    name = "server_headers",
+    hdrs = [
+        "include/opentelemetry/ext/http/server/http_server.h",
+        "include/opentelemetry/ext/http/server/socket_tools.h",
+    ],
     linkopts = select({
-        # socket_tools.h calls Winsock; declare it on the interface so consumers link it too.
         "//bazel:windows": ["-DEFAULTLIB:Ws2_32.lib"],
         "//conditions:default": [],
     }),
     strip_include_prefix = "include",
+    visibility = [
+        "//examples/http:__pkg__",
+        "//exporters/otlp:__pkg__",
+        "//ext/test/http:__pkg__",
+        "//ext/test/w3c_tracecontext_http_test_server:__pkg__",
+    ],
+    deps = [
+        "//api",
+    ],
 )

ext/src/http/client/curl/BUILD

@@ -16,6 +16,9 @@ cc_library(
     defines = [
         "ENABLE_HTTP_CLIENT_CURL",
     ],
+    implementation_deps = [
+        "//ext:curl_implementation_headers",
+    ],
     include_prefix = "src/http/client/curl",
     linkopts = select({
         "//bazel:windows": [

ext/test/http/BUILD

@@ -8,11 +8,10 @@ cc_test(
     srcs = [
         "socket_tools_test.cc",
     ],
-    # ws2_32 is an interface linkopt of //ext:headers, so it is inherited here rather than
-    # relinked, which also lets the test verify the public target's usage requirements.
     tags = ["test"],
     deps = [
         "//ext:headers",
+        "//ext:server_headers",
         "@com_google_googletest//:gtest_main",
     ],
 )
@@ -24,7 +23,9 @@ cc_test(
     ],
     tags = ["test"],
     deps = [
+        "//ext:curl_implementation_headers",
         "//ext:headers",
+        "//ext:server_headers",
         "//ext/src/http/client/curl:http_client_curl",
         "//sdk/src/trace",
         "@com_google_googletest//:gtest_main",

ext/test/w3c_tracecontext_http_test_server/BUILD

@@ -19,7 +19,9 @@ cc_binary(
     deps = [
         "//api",
         "//exporters/ostream:ostream_span_exporter",
+        "//ext:curl_implementation_headers",
         "//ext:headers",
+        "//ext:server_headers",
         "//ext/src/http/client/curl:http_client_curl",
         "//sdk/src/trace",
         "@curl",