Proxy h2 (#402)

- add support for using proxy to setup http/2 connection
- right now only supports talking h1 with proxy and create the http/2 connection from the tunneling proxy. 
- Turns out google doesn't like `:authority` with `host`, I am totally okay with what ever the real world want. :)

### TODO:
The `AWS_TEST_HTTPS_H2_PROXY_URL` now has a proxy host that can talk http/2 with client. Used apache server with mod_proxy_http2. You can simply use that host for the proxy option and update the tls of proxy options to have h2 in the alpn string to create the h2 connection with proxy. However, I don't know what's the expected behavior for client to talk to a h2 proxy host. 

**`curl` doesn't seem supporting it.**

So, put it as TODO, but still have the host here incase we want to implement it in the future.

Author: TingDaoK

codebuild/linux-integration-tests.yml

@@ -16,7 +16,7 @@ phases:
   build:
     commands:
       - echo Build started on `date`
-      - aws s3 cp s3://aws-crt-test-stuff/setup_proxy_test_env.sh /tmp/setup_proxy_test_env.sh
+      - aws s3 cp s3://aws-crt-test-stuff/setup_proxy_test_env_h2.sh /tmp/setup_proxy_test_env.sh
       - chmod a+xr /tmp/setup_proxy_test_env.sh
       - python3 -c "from urllib.request import urlretrieve; urlretrieve('$BUILDER_HOST/$BUILDER_SOURCE/$BUILDER_VERSION/builder.pyz', 'builder.pyz')"
       - python3 builder.pyz build -p aws-c-http --cmake-extra=-DENABLE_PROXY_INTEGRATION_TESTS=ON

include/aws/http/private/proxy_impl.h

@@ -8,6 +8,7 @@
 
 #include <aws/http/http.h>
 
+#include <aws/common/hash_table.h>
 #include <aws/http/connection.h>
 #include <aws/http/proxy.h>
 #include <aws/http/status_code.h>
@@ -103,8 +104,11 @@ struct aws_http_proxy_user_data {
     struct aws_socket_options original_socket_options;
     bool original_manual_window_management;
     size_t original_initial_window_size;
+    bool prior_knowledge_http2;
     struct aws_http1_connection_options original_http1_options;
-
+    struct aws_http2_connection_options
+        original_http2_options; /* the resource within options are allocated with userdata */
+    struct aws_hash_table alpn_string_map;
     /*
      * setup/shutdown callbacks.  We enforce via fatal assert that either the http callbacks are supplied or
      * the channel callbacks are supplied but never both.

source/connection.c

@@ -887,7 +887,7 @@ static void s_client_bootstrap_on_channel_shutdown(
     aws_http_client_bootstrap_destroy(http_bootstrap);
 }
 
-static int s_validate_http_client_connection_options(const struct aws_http_client_connection_options *options) {
+int s_validate_http_client_connection_options(const struct aws_http_client_connection_options *options) {
     if (options->self_size == 0) {
         AWS_LOGF_ERROR(AWS_LS_HTTP_CONNECTION, "static: Invalid connection options, self size not initialized");
         return aws_raise_error(AWS_ERROR_INVALID_ARGUMENT);
@@ -926,6 +926,11 @@ static int s_validate_http_client_connection_options(const struct aws_http_clien
         return aws_raise_error(AWS_ERROR_INVALID_ARGUMENT);
     }
 
+    if (options->prior_knowledge_http2 && options->tls_options) {
+        AWS_LOGF_ERROR(AWS_LS_HTTP_CONNECTION, "static: HTTP/2 prior knowledge only works with cleartext TCP.");
+        return aws_raise_error(AWS_ERROR_INVALID_ARGUMENT);
+    }
+
     return AWS_OP_SUCCESS;
 }
 
@@ -964,6 +969,15 @@ int aws_http_alpn_map_init_copy(
     struct aws_allocator *allocator,
     struct aws_hash_table *dest,
     struct aws_hash_table *src) {
+    if (!src) {
+        AWS_ZERO_STRUCT(*dest);
+        return AWS_OP_SUCCESS;
+    }
+    if (!src->p_impl) {
+        AWS_ZERO_STRUCT(*dest);
+        return AWS_OP_SUCCESS;
+    }
+
     if (aws_http_alpn_map_init(allocator, dest)) {
         return AWS_OP_ERR;
     }
@@ -998,11 +1012,6 @@ int aws_http_client_connect_internal(
 
     /* make copy of options, and add defaults for missing optional structs */
     struct aws_http_client_connection_options options = *orig_options;
-    if (options.prior_knowledge_http2 && options.tls_options) {
-        AWS_LOGF_ERROR(AWS_LS_HTTP_CONNECTION, "static: HTTP/2 prior knowledge only works with cleartext TCP.");
-        return aws_raise_error(AWS_ERROR_INVALID_ARGUMENT);
-    }
-
     struct aws_http1_connection_options default_http1_options;
     AWS_ZERO_STRUCT(default_http1_options);
     if (options.http1_options == NULL) {
@@ -1030,17 +1039,15 @@ int aws_http_client_connect_internal(
 
     struct aws_http2_setting *setting_array = NULL;
     struct aws_hash_table *alpn_string_map = NULL;
-    if (!aws_mem_acquire_many(
-            options.allocator,
-            3,
-            &http_bootstrap,
-            sizeof(struct aws_http_client_bootstrap),
-            &setting_array,
-            options.http2_options->num_initial_settings * sizeof(struct aws_http2_setting),
-            &alpn_string_map,
-            sizeof(struct aws_hash_table))) {
-        goto error;
-    }
+    aws_mem_acquire_many(
+        options.allocator,
+        3,
+        &http_bootstrap,
+        sizeof(struct aws_http_client_bootstrap),
+        &setting_array,
+        options.http2_options->num_initial_settings * sizeof(struct aws_http2_setting),
+        &alpn_string_map,
+        sizeof(struct aws_hash_table));
 
     AWS_ZERO_STRUCT(*http_bootstrap);