Allow servers to select compression level via initial MD.

Setting the newly added compression_level field of
grpc_op::send_initial_metadata by a server now has the effect of
applying that compression level for the subsequent call messages leaving
the server. The ultimate meaning of the level depends on the client's
supported compression algorithms.

1 files changed, 137 insertions, 22 deletions

diff --git a/src/core/lib/surface/call.c b/src/core/lib/surface/call.c
index 9b2b94eedf..911b5b80bb 100644
--- a/src/core/lib/surface/call.c
+++ b/src/core/lib/surface/call.c
@@ -420,6 +420,65 @@ grpc_compression_algorithm grpc_call_test_only_get_compression_algorithm(
   return algorithm;
 }
 
+static grpc_compression_algorithm compression_algorithm_for_level_locked(
+    grpc_call *call, grpc_compression_level level) {
+  /* Establish a "ranking" or compression algorithms in increasing order of
+   * compression.
+   * This is simplistic and we will probably want to introduce other
+   * dimensions
+   * in the future (cpu/memory cost, etc). */
+  const grpc_compression_algorithm algos_ranking[] = {GRPC_COMPRESS_GZIP,
+                                                      GRPC_COMPRESS_DEFLATE};
+  const uint32_t accepted_encodings = call->encodings_accepted_by_peer;
+  if (level > GRPC_COMPRESS_LEVEL_HIGH) {
+    extern int grpc_compress_filter_trace;
+    if (grpc_compress_filter_trace) {
+      gpr_log(GPR_ERROR,
+              "Unknown compression level %d. Compression will be disabled.",
+              (int)level);
+    }
+    return GRPC_COMPRESS_NONE;
+  }
+
+  const size_t num_supported =
+      GPR_BITCOUNT(accepted_encodings) - 1; /* discard NONE */
+  if (level == GRPC_COMPRESS_LEVEL_NONE || num_supported == 0) {
+    return GRPC_COMPRESS_NONE;
+  }
+
+  GPR_ASSERT(level > 0);
+
+  /* intersect algos_ranking with the supported ones keeping the ranked order
+   */
+  grpc_compression_algorithm
+      sorted_supported_algos[GRPC_COMPRESS_ALGORITHMS_COUNT];
+  size_t algos_supported_idx = 0;
+  for (size_t i = 0; i < GPR_ARRAY_SIZE(algos_ranking); i++) {
+    const grpc_compression_algorithm alg = algos_ranking[i];
+    for (size_t j = 0; j < num_supported; j++) {
+      if (GPR_BITGET(accepted_encodings, alg) == 1) {
+        /* if \a alg in supported */
+        sorted_supported_algos[algos_supported_idx++] = alg;
+        break;
+      }
+    }
+    if (algos_supported_idx == num_supported) break;
+  }
+
+  switch (level) {
+    case GRPC_COMPRESS_LEVEL_NONE:
+      abort(); /* should have been handled already */
+    case GRPC_COMPRESS_LEVEL_LOW:
+      return sorted_supported_algos[0];
+    case GRPC_COMPRESS_LEVEL_MED:
+      return sorted_supported_algos[num_supported / 2];
+    case GRPC_COMPRESS_LEVEL_HIGH:
+      return sorted_supported_algos[num_supported - 1];
+    default:
+      abort();
+  };
+}
+
 uint32_t grpc_call_test_only_get_message_flags(grpc_call *call) {
   uint32_t flags;
   gpr_mu_lock(&call->mu);
@@ -545,15 +604,28 @@ static grpc_linked_mdelem *linked_from_md(grpc_metadata *md) {
   return (grpc_linked_mdelem *)&md->internal_data;
 }
 
+static grpc_metadata *get_md_elem(grpc_metadata *metadata,
+                                  grpc_metadata *additional_metadata, int i,
+                                  int count) {
+  grpc_metadata *res =
+      i < count ? &metadata[i] : &additional_metadata[i - count];
+  GPR_ASSERT(res);
+  return res;
+}
+
 static int prepare_application_metadata(grpc_call *call, int count,
                                         grpc_metadata *metadata,
                                         int is_trailing,
-                                        int prepend_extra_metadata) {
+                                        int prepend_extra_metadata,
+                                        grpc_metadata *additional_metadata,
+                                        int additional_metadata_count) {
+  int total_count = count + additional_metadata_count;
   int i;
   grpc_metadata_batch *batch =
       &call->metadata_batch[0 /* is_receiving */][is_trailing];
-  for (i = 0; i < count; i++) {
-    grpc_metadata *md = &metadata[i];
+  for (i = 0; i < total_count; i++) {
+    const grpc_metadata *md =
+        get_md_elem(metadata, additional_metadata, i, count);
     grpc_linked_mdelem *l = (grpc_linked_mdelem *)&md->internal_data;
     GPR_ASSERT(sizeof(grpc_linked_mdelem) == sizeof(md->internal_data));
     l->md = grpc_mdelem_from_string_and_buffer(
@@ -572,9 +644,10 @@ static int prepare_application_metadata(grpc_call *call, int count,
       break;
     }
   }
-  if (i != count) {
+  if (i != total_count) {
     for (int j = 0; j <= i; j++) {
-      grpc_metadata *md = &metadata[j];
+      const grpc_metadata *md =
+          get_md_elem(metadata, additional_metadata, j, count);
       grpc_linked_mdelem *l = (grpc_linked_mdelem *)&md->internal_data;
       GRPC_MDELEM_UNREF(l->md);
     }
@@ -595,24 +668,36 @@ static int prepare_application_metadata(grpc_call *call, int count,
       }
     }
   }
-  for (i = 1; i < count; i++) {
-    linked_from_md(&metadata[i])->prev = linked_from_md(&metadata[i - 1]);
+  for (i = 1; i < total_count; i++) {
+    grpc_metadata *md = get_md_elem(metadata, additional_metadata, i, count);
+    grpc_metadata *prev_md =
+        get_md_elem(metadata, additional_metadata, i - 1, count);
+    linked_from_md(md)->prev = linked_from_md(prev_md);
   }
-  for (i = 0; i < count - 1; i++) {
-    linked_from_md(&metadata[i])->next = linked_from_md(&metadata[i + 1]);
+  for (i = 0; i < total_count - 1; i++) {
+    grpc_metadata *md = get_md_elem(metadata, additional_metadata, i, count);
+    grpc_metadata *next_md =
+        get_md_elem(metadata, additional_metadata, i + 1, count);
+    linked_from_md(md)->next = linked_from_md(next_md);
   }
-  switch (prepend_extra_metadata * 2 + (count != 0)) {
+
+  switch (prepend_extra_metadata * 2 + (total_count != 0)) {
     case 0:
       /* no prepend, no metadata => nothing to do */
       batch->list.head = batch->list.tail = NULL;
       break;
-    case 1:
+    case 1: {
       /* metadata, but no prepend */
-      batch->list.head = linked_from_md(&metadata[0]);
-      batch->list.tail = linked_from_md(&metadata[count - 1]);
+      grpc_metadata *first_md =
+          get_md_elem(metadata, additional_metadata, 0, count);
+      grpc_metadata *last_md =
+          get_md_elem(metadata, additional_metadata, total_count - 1, count);
+      batch->list.head = linked_from_md(first_md);
+      batch->list.tail = linked_from_md(last_md);
       batch->list.head->prev = NULL;
       batch->list.tail->next = NULL;
       break;
+    }
     case 2:
       /* prepend, but no md */
       batch->list.head = &call->send_extra_metadata[0];
@@ -621,17 +706,22 @@ static int prepare_application_metadata(grpc_call *call, int count,
       batch->list.head->prev = NULL;
       batch->list.tail->next = NULL;
       break;
-    case 3:
+    case 3: {
       /* prepend AND md */
+      grpc_metadata *first_md =
+          get_md_elem(metadata, additional_metadata, 0, count);
+      grpc_metadata *last_md =
+          get_md_elem(metadata, additional_metadata, total_count - 1, count);
       batch->list.head = &call->send_extra_metadata[0];
       call->send_extra_metadata[call->send_extra_metadata_count - 1].next =
-          linked_from_md(&metadata[0]);
-      linked_from_md(&metadata[0])->prev =
+          linked_from_md(first_md);
+      linked_from_md(first_md)->prev =
           &call->send_extra_metadata[call->send_extra_metadata_count - 1];
-      batch->list.tail = linked_from_md(&metadata[count - 1]);
+      batch->list.tail = linked_from_md(last_md);
       batch->list.head->prev = NULL;
       batch->list.tail->next = NULL;
       break;
+    }
     default:
       GPR_UNREACHABLE_CODE(return 0);
   }
@@ -1229,7 +1319,29 @@ static grpc_call_error call_start_batch(grpc_exec_ctx *exec_ctx,
           error = GRPC_CALL_ERROR_TOO_MANY_OPERATIONS;
           goto done_with_error;
         }
-        if (op->data.send_initial_metadata.count > INT_MAX) {
+        /* process compression level */
+        grpc_metadata compression_md;
+        memset(&compression_md, 0, sizeof(grpc_metadata));
+        size_t additional_metadata_count = 0;
+        if (op->data.send_initial_metadata.compression_level >
+            GRPC_COMPRESS_LEVEL_NONE) {
+          if (call->is_client) {
+            error = GRPC_CALL_ERROR_NOT_ON_CLIENT;
+            goto done_with_error;
+          }
+          const grpc_compression_algorithm calgo =
+              compression_algorithm_for_level_locked(
+                  call, op->data.send_initial_metadata.compression_level);
+          char *calgo_name;
+          grpc_compression_algorithm_name(calgo, &calgo_name);
+          compression_md.key = "grpc-internal-encoding-request";
+          compression_md.value = calgo_name;
+          compression_md.value_length = strlen(calgo_name);
+          additional_metadata_count++;
+        }
+
+        if (op->data.send_initial_metadata.count + additional_metadata_count >
+            INT_MAX) {
           error = GRPC_CALL_ERROR_INVALID_METADATA;
           goto done_with_error;
         }
@@ -1237,7 +1349,8 @@ static grpc_call_error call_start_batch(grpc_exec_ctx *exec_ctx,
         call->sent_initial_metadata = 1;
         if (!prepare_application_metadata(
                 call, (int)op->data.send_initial_metadata.count,
-                op->data.send_initial_metadata.metadata, 0, call->is_client)) {
+                op->data.send_initial_metadata.metadata, 0, call->is_client,
+                &compression_md, (int)additional_metadata_count)) {
           error = GRPC_CALL_ERROR_INVALID_METADATA;
           goto done_with_error;
         }
@@ -1325,7 +1438,8 @@ static grpc_call_error call_start_batch(grpc_exec_ctx *exec_ctx,
         if (!prepare_application_metadata(
                 call,
                 (int)op->data.send_status_from_server.trailing_metadata_count,
-                op->data.send_status_from_server.trailing_metadata, 1, 1)) {
+                op->data.send_status_from_server.trailing_metadata, 1, 1, NULL,
+                0)) {
           error = GRPC_CALL_ERROR_INVALID_METADATA;
           goto done_with_error;
         }
@@ -1513,9 +1627,10 @@ uint8_t grpc_call_is_client(grpc_call *call) { return call->is_client; }
 grpc_compression_algorithm grpc_call_compression_for_level(
     grpc_call *call, grpc_compression_level level) {
   gpr_mu_lock(&call->mu);
-  const uint32_t accepted_encodings = call->encodings_accepted_by_peer;
+  grpc_compression_algorithm algo =
+      compression_algorithm_for_level_locked(call, level);
   gpr_mu_unlock(&call->mu);
-  return grpc_compression_algorithm_for_level(level, accepted_encodings);
+  return algo;
 }
 
 const char *grpc_call_error_to_string(grpc_call_error error) {